Insulinoma-Associated Protein 1 Use in SCLC: History
View Latest Version
Please note this is an old version of this entry, which may differ significantly from the current revision.
Subjects: Oncology
Contributor:
Renato Rocha
,
Rui Henrique

Small cell lung carcinoma (SCLC) is an aggressive and difficult to treat cancer. Although immunohistochemistry is not mandatory for a SCLC diagnosis, it might be required, especially in small samples. Insulinoma-associated protein 1 (INSM1) is expressed in endocrine and nervous tissues during embryogenesis, generally absent in adults and re-expressed in SCLC and other neuroendocrine neoplasms. Its high specificity propelled its use as diagnostic biomarker and an attractive therapeutic target.  INSM1 is a highly sensitive (75–100%) and specific (82–100%) neuroendocrine immunohistochemical marker for SCLC diagnosis. It can be used in histological and cytological samples. Although advantageous, its standalone use is currently not recommended. Studies correlating INSM1 expression and prognosis have disclosed contrasting results, although the expression seemed to entail a worse survival. Targeting INSM1 effectively suppressed SCLC growth either as a suicide gene therapy regulator or as an indirect target of molecular-targeted therapy. INSM1 represents a valuable biomarker for SCLC diagnosis that additionally offers vast opportunities for the development of new prognostic and therapeutic strategies.

  • INSM1
  • biomarker
  • immunohistochemistry
  • small cell lung carcinoma
  • diagnosis
  • prognosis
  • therapy

1. Introduction

Lung cancer is the second-most prevalent and the deadliest cancer worldwide, having caused an estimated 1,796,144 deaths in 2020 [1]. Small cell lung carcinoma (SCLC) accounts for approximately 14% of lung cancer diagnoses in the US [1], characterized by highly aggressive behavior, frequent metastasis to multiple sites, and a high recurrence rate after the initial response to chemotherapy, with only 7% of patients, on average, surviving at least 5 years [1][2][3][4]. Typically, SCLC has a central perihilar location, with frequent mediastinal lymph node involvement at the time of diagnosis [5]. Its central location hampers surgical and cytological sample acquisition, which are, nonetheless, required for a definitive diagnosis [5].
The histopathologic evaluation of biopsy specimens is essential, required for appropriate tumor classification and staging. Morphologically, SCLC is composed of small cells with scant cytoplasm, finely granular (“salt and pepper”) chromatin, absent or inconspicuous nucleoli, a high mitotic count (in resection specimens, > 10 mitoses/2 mm2), and abundant necrosis. In small biopsies, a high proliferation index (Ki67) is a useful finding to support the diagnosis. Two subtypes are listed: “pure” SCLC and combined SCLC, the latter having, in addition to the main SCLC component, a non-small cell carcinoma (NSCLC) component [5]. SCLC is included in the group of lung neuroendocrine neoplasms (NEN), a set of neuroendocrine tumors that also comprises the low-grade typical carcinoid (TC), the intermediate-grade atypical carcinoid (AC), and neuroendocrine carcinomas (NEC), formerly high-grade neuroendocrine carcinomas, encompassing large cell neuroendocrine carcinoma (LCNEC) and SCLC itself. Although included in this group, a SCLC diagnosis exempts the expression of neuroendocrine (NE) immunohistochemical (IHC) markers in opposition to LCNEC, which mandatorily requires the expression of one or more markers [5]. Moreover, the different subtypes have markedly diverse clinical and pathological characteristics [6]. The SCLC treatment strategy differs from other pulmonary NEN and NSCLC, entailing the use of more aggressive chemotherapy regimens [6][7]. Hence, reliable diagnostic biomarkers are the key to facilitate a SCLC diagnosis, considering the frequent challenge in obtaining histological or cytological materials [8], given the location and advanced stage at diagnosis. Furthermore, if this marker would also prove useful for prognostic and predictive therapeutic effects, it would be a substantial asset to clinical practice and to prolonging the survival of these patients.
Insulinoma-associated protein 1 (INSM1) is a 510 amino acid transcription factor with a C-terminal containing five zinc-finger DNA-binding motifs and an N-terminal exhibiting repressor activity [9][10] that performs a key role in the physiologic development of neuroendocrine tissues across the body [11][12][13][14][15][16][17]. It is encoded by an intronless gene localized in the short arm of chromosome 20, INSM transcriptional repressor 1 (INSM1), originally IA-1, first discovered in 1992 in human pancreatic insulinoma tissue and murine insulinoma cell lines by Goto et al. [9][18]. Although present in the embryonic organogenesis stage of endocrine and nervous tissues, its expression virtually disappears in normal adult tissue [10][19][20], with a few exceptions, which include Kulchitsky cells of respiratory and gastrointestinal epithelium, NE cells of the adrenal medulla, pancreatic islets, and non-neoplastic prostate gland cells [10][21][22][23][24][25]. As a result, INSM1 shows an aberrant expression in adult tissues in a great variety of neuroendocrine and neuroepithelial neoplasms, including those of the lungs [4][6][13][19][21][22][23][24][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], pancreas [41], gastrointestinal tract [21][42], appendix [43], bladder [44][45], prostate [46], uterine cervix [47], head and neck [48], larynx [49], skin [50][51][52], pituitary gland [4], thyroid [53], parathyroid [21], and adrenal gland [4]. Other types of neoplasms with neuroendocrine differentiation also disclose INSM1 expression, such as paraganglioma [35][37], extra-skeletal myxoid chondrosarcoma [54], primitive neuroectodermal tumors [21], and peripheral neuroblastic tumors [55].

2. INSM1 and SCLC Oncogenesis

INSM1 is a key player in various biological functions and interacts with a wide range of molecules. It has an essential role in embryogenesis and differentiation of the pancreas, sympathoadrenal system, and nervous system [10][11][56][57]. It partakes in distinct signaling pathways, including the Sonic Hedgehog (Shh), Phosphatidylinositol-4,5-Bisphosphate 3-Kinase (PI3K)/AKT serine/threonine kinase (AKT), Mitogen-Activated Protein Kinase Kinase (MAP2K)/ Extracellular Signal-Regulated Protein Kinase (ERK)1/2, adenosine kinase (ADK), Tumor Protein 53 (TP53), Wingless-Type (Wnt), histone acetylation, Lysine-Specific Demethylase 1 (LSD1), cyclin D1, achaete-scute family BHLH transcription factor 1 (ASCL1), and MYCN proto-oncogene bHLH transcription factor (MYCN) pathways [58][59]. These signaling pathways are not uniformly present throughout the body, and INSM1 interactions with various molecules in neuroendocrine cells of different locations are due to multiple tissue-specific regulatory elements in the upstream region of the gene [18]. Since it is not the focus of this review and has been already covered elsewhere [10][58][59], the overall function of INSM1 is described here in a simplistic manner.
INSM1 exhibits activity as a transcriptional repressor, binding to genes such as NeuroD/β2 and insulin gene (INS), fundamental to pancreatic development, while simultaneously exhibiting extranuclear activity through binding to cellular regulator proteins such as receptor for activated C kinase 1 (RACK1) and cyclin D1, promoting differentiation and cell cycle arrest [60]. Via interactions with Neurogenin-3 and neuronal differentiation 1 (NEUROD1), INSM1 participates in pancreatic β-cell differentiation, which illustrates one of its functions as a crucial regulator of neuroendocrine differentiation [10]. INSM1 binding to Phox2b and ASCL1 promotes sympathoadrenal cell differentiation, and, in a study with mice, a homozygous mutation of the gene was shown to cause fetal death due to catecholamine deficiency [57]. In the brain, INSM1 plays a pan-neurogenic role and fosters basal progenitor cell formations, supporting cortex development and expansion [56][61]. One of its most compelling functions is its autoregulation capacity, through binding of the INSM1 protein to the promoter region of its own gene [16], with studies showing that this region is a possible target for cancer gene therapy [62][63][64][65][66][67][68]. Furthermore, it contributes to the differentiation of anterior pituitary and enteric endocrine cells, the transformation of neuroblastoma cells, and, possibly, when decreased, to the development of diabetes mellitus [11][58][69][70][71].
INSM1 activity is also apparent in the lungs, as pulmonary neuroendocrine cell differentiation is dependent on complex interactions between INSM1, ASCL1, and Hes Family BHLH Transcription Factor 1 (Hes1) [4][12]. During lung organogenesis, epithelial cells may take two routes: neuroendocrine differentiation or non-neuroendocrine differentiation [72]. Hes1, a Notch-signaling gene responsible for inhibiting the formation of neuroendocrine cells, is expressed in non-neuroendocrine cells, while ASCL1, a master regulator of neuroendocrine differentiation, is expressed in neuroendocrine cells [12]. Thus, ASCL1 expression is negatively correlated with Hes1 activity [12]. A murine model showed that INSM1 mutants depicted ASCL1 downregulation and Hes1 upregulation, compromising the terminal neuroendocrine differentiation, and that INSM1 could bind to the Hes1 gene in different sequences, including a promoter region, repressing its transcriptional activity and consequently allowing for neuroendocrine cells differentiation [12]. Epigenetic mechanisms such as the recruitment of histone-modifying factors via a Snail/Gfi-1 (SNAG) domain contained in the INSM1 N-terminus may also play a part in repressing Hes1 expression [12][69]. On the other hand, ASCL1 seems to directly or indirectly control INSM1 expression, suggesting a possible interdependence [12]. Subsequently, a study with a conditional lung-specific INSM1 transgenic mouse model illuminated the INSM1 effects on lung alveologenesis, revealing that, when ectopically expressed on bronchiolar epithelial cells, alveolarization is compromised in the terminal stages of lung maturation, leading to septation defects and, ultimately, alveolar space enlargement [25]. This process resulted from the inhibition of cyclin D1 expression in club cells, with the consecutive blockage of bronchiolar epithelial cell cycle progression [25]. Club cells do not normally express INSM1 but have been found to be closely connected with pulmonary neuroendocrine cells, with the latter acting as stem cells and a means of regeneration for club cells in the event of injury. Thus, INSM1 might be involved in lung injury repair pathways [25][73]. Interestingly, in this study, INSM1 ectopic expression in non-NE cells did not induce NE precursor differentiation, implying the existence of alternative molecular pathways [25]. In short, pulmonary neuroendocrine cell differentiation is partly dependent on INSM1 expression, whereas, in other types of respiratory cells, it may harm lung alveologenesis.
Regardless of decades of study, SCLC oncogenesis remains poorly understood. Other than the inactivation of the tumor suppressor genes TP53 and RB1, no major biomolecular events are widely recognized in the genesis of this neoplasm, in addition to being vastly heterogeneous, owing to the multitude of genes potentially involved [40][74][75]. SCLC and NSCLC are clearly distinct on every level, from the clinical to histopathologic features and, accordingly, on a molecular basis [40][74]. Identifying genes with a discordant expression between these two subtypes of cancer is of great importance, as it may be useful for diagnostic, prognostic, and therapeutic purposes and to increase the knowledge about causative molecular mechanisms. Naturally, as a neuroendocrine neoplasm, the profiling of genes with a neuroendocrine function has been carried out, with many showing upregulation, including chromogranin A (CGA), ASCL1, and INSM1. [40][74]. ASCL1 is reportedly associated with SCLC carcinogenesis, with studies showing a close relation between ASCL1 and INSM1, since both show similar expression patterns in fetal lung neuroendocrine cells and cancer cells, exhibiting neuroendocrine differentiation [4][40][76]. Therefore, INSM1 may be directly or indirectly implicated in SCLC oncogenesis. INSM1 has been shown to regulate neural cell-specific transcription factor POU Class 3 Homeobox 2 (POU3F2), alongside ASCL1, in SCLC cell lines, which sequentially promote the expression of NE molecules such as CGA, synaptophysin (SYN), and neural cell adhesion molecule 1 (NCAM1) [4][38]. Previously, it was shown that INSM1 could bind to Hes1 in normal pulmonary neuroendocrine cells, promoting neuroendocrine differentiation [12]. Inversely, Fujino et al. showed that the forced expression of Hes1 or Notch receptor 1 (NOTCH1) resulted in the inhibition of INSM1 expression and, consequently, of the downstream molecules [4]. On another note, in that same study, ASCL1 expression did not control INSM1 expression, as opposed to the findings of a contemporary study by Jia et al. in normal pulmonary neuroendocrine cells, as discussed beforehand, but also contrarily to a more recent study using SCLC cell lines, where INSM1 was upregulated by ASCL1 [4][12][77]. Thus, the exact location of INSM1 in ASCL1-related molecular pathways is not yet fully understood, and further studies are required. Fujino et al. also reported that INSM1 expression had opposite effects in SCLC and NSCLC, with INSM1 knockdown inducing apoptosis and decreased cell growth in the former and forced expression causing inhibited cell growth in the latter, suggesting that INSM1-related oncogenicity mechanisms may be dependent on other molecules exclusive to a cancer subtype, as may be the case for other neuroendocrine factors [4]. More recently, Chen et al. found that INSM1 was involved in the complex Shh-PI3K/AKT-MYCN/ASCL1-MEK/ERK1/2 transcriptional network in NE lung cancers, including SCLC [77]. Shh and MYCN are both important for normal embryogenic development but were also associated with neuroendocrine lung tumors and other types of cancer, including neuroblastoma, in which INSM1 may also play an active role [70][77]. Essentially, Shh activates INSM1 through the activation of MYCN via PI3K/AKT and alternative pathways, which, in turn, phosphorylates MEK/ERK1/2, ultimately resulting in the stabilization of MYCN, which causes further INSM1 activation, leading to a positive feedback loop that promotes tumor growth [77]. The upregulation of INSM1 is caused by the binding of MYCN and ASCL1 to an E2-box sequence in its promoter region [77]. In summary, INSM1 is crucial for the NE differentiation of SCLC, associated with various master NE genes, such as ASCL1 and Shh, in pathways most likely connected to oncogenesis. The INSM1 intervention in SCLC oncogenic molecular pathways is displayed in Figure 1.
Jmp 03 00013 g001 550
Figure 1. Intervention of INSM1 in SCLC oncogenic molecular pathways. INSM1 participates in different molecular pathways that may promote SCLC oncogenesis. INSM1 regulates POU3F2 alongside ASCL1 in SCLC cell lines, which sequentially promote the expression of NE molecules such as CGA, SYN, and NCAM1/CD56, which have been shown to promote SCLC tumor growth through unknown mechanisms [4][38]. Notch1 and Hes1 inhibit both INSM1 and ASCL1 [4]. MYCN and ASCL1 can bind to the INSM1 promoter E2-box, upregulating INSM1. Additionally, MYCN has been shown to promote SCLC tumor growth [77]. INSM1 can activate MYCN via the MEK/ERK1/2 pathway, which then binds to the INSM1 promoter E2-box, causing further MYCN activation and forming a positive feedback loop (in green) that promotes tumor growth. MYCN is also activated by Shh either by the PI3K/AKT pathway or Shh pathway [77]. The inhibition of SCLC tumor growth was achieved by the blockage of the Shh pathway using different inhibitors [77].

3. INSM1 Diagnostic Use

3.1. Immunohistochemistry

The diagnosis of SCLC does not absolutely require immunohistochemistry, as it may be achieved by histomorphological observation alone [5], but it improves the diagnostic accuracy [8], particularly in cases with limited materials, such as small biopsies, a frequent type of sample in this scenario, and consequently, a reliable immunohistochemical marker is very important. Classic neuroendocrine markers such as CGA, SYN, and CD56 are widely used by pathologists, but all of them have limitations, with CGA typically disclosing the lowest median sensitivity, ranging from 46–100% [4][6][13][23][24][26][28][32][35][36][37][38], SYN depicting an intermediate sensitivity ranging from 55–100% [4][6][13][23][24][26][28][32][35][36][37][38], and CD56 typically showing the highest sensitivity, ranging from 68–100% [13][23][24][26][28][31][32][35][36][37][38]. On the other hand, CGA discloses the highest specificity, and all of them are prone to showing nonspecific cytoplasmatic and membranous background staining, particularly in areas with necrosis, which are common in small biopsies, making a diagnosis difficult, especially in cases with weak or focal expression. Additionally, 10–25% of lung NEC, similar to SCLC, might not stain with the typical triple-marker panel [5][30][78][79]. Indeed, searching for a marker that might be highly sensitive and specific is a priority, as replacing multiple marker panels with a single one should not only save tissue, which is frequently scarce in the context of SCLC and lung pathology in general with the advent of molecular studies [27], but also reduce costs [23][37]. In recent years, interest in INSM1 as a diagnostic NE biomarker for IHC has grown after the initial studies by Rosenbaum et al. and Fujino et al. [4][21]. 
INSM1 is a reliable immunohistochemical marker of NE differentiation for use in SCLC diagnosis, with high sensitivity and specificity, as demonstrated by most studies [4][6][23][24][32][37][38], with the great advantage over other markers of showing exclusive nuclear expression [13][21][35][37]. Furthermore, staining apparently represents true NE differentiation, as studies reported its expression only on the SCLC component of mixed SCLC/non-neuroendocrine tumors [4][23]. Nonetheless, INSM1 also shows expression in other neuroendocrine tumors, including carcinoid tumors of the lungs and LCNEC [6][13][19][23][24][26][28][35][37][38], and thus cannot be used to differentiate SCLC from those tumors, a task that still mostly relies on histomorphological interpretation [19]. Importantly, INSM1 expression is retained in metastases [23][31], which is of special importance for SCLC, as metastatic deposits are commonly more accessible for biopsy than the primary tumor. Some studies have found that INSM1 may be expressed in NE tumors in the absence of other NE markers [13][24][26][37][38], whereas others disclosed a superior sensitivity of INSM1 IHC, even compared to the combined panel of classic NE markers, supporting the standalone use of INSM1 [24][37]. Nonetheless, other studies showed inferior sensitivity compared to the combined panel [23][28][31][35], no cases of isolated INSM1 expression [23][28], or depicted the diagnostic pitfall of INSM1 expression in rare cases of NSCLC, favoring a more conservative use of INSM1 only as a complementary NE marker [19][23][27][31][35]. Two common problems are reported in the literature: (1) the use of TMA as the type of tested sample [13][27][28], as SCLC samples are difficult to obtain and there was a need to preserve tissue, causing a possible underrepresentation of tumor heterogeneity, and (2) the lack of a standard cutoff for INSM1 IHC positivity [24][27][28], making it difficult to ascertain and compare biomarker sensitivity and specificity across studies. There is no doubt, however, of INSM1’s importance as an immunohistochemical marker for SCLC, although more studies might be required to illuminate the uncertainties that remain.

3.2. Immunocytochemistry

As previously stated, SCLC is a tumor mainly localized in the central area of the lungs, making access to a biopsy particularly difficult. Hence, cytological samples (through FNA—fine needle aspiration) and small biopsies are, frequently, the only sources of tumors available. The former discloses a better morphological preservation of cells compared with the latter, which frequently has crush artifacts, likely making cytology samples preferable for the primary morphological diagnosis [5][29][32][34][80]. FNA also has the advantage of being minimally invasive and more cost-effective [29]. Often, FNA is the first step in the diagnostic workup of a lung mass [30][81]. With limited materials available, the immunocytochemical confirmation of SCLC through a combined panel of classic neuroendocrine markers, such as those used in IHC, can be difficult, and thus, finding a single marker constitutes a priority [4][30][32][37][38]. Recently, several studies on INSM1 immunocytochemical application were published, mostly evaluating cell blocks (CB) and direct smears [22][29][31][32][33][34][36]. Cell blocks, although preferable to direct smears, owing to their similarity to paraffin-embedded sections of biopsies, are not available in many cases, because FNA may only harvest a small number of cells [29]. Furthermore, markers with nuclear staining, such as INSM1, are preferable for direct smears [29][82][83]
INSM1 is a useful marker for SCLC diagnosis in a variety of cytology samples, disclosing both a high sensitivity and specificity for the differential diagnosis with NSCLC, with the drawback also of showing expression in other types of NE tumors and even, to a lesser degree, in some types of NE cells. In general, studies have reported superior sensitivity to CGA and SYN, similar to that of CD56. In comparison to histology, the sensitivity was mostly similar or slightly inferior, with a good, although imperfect, matching between the cytology and histology samples, with sometimes slightly inferior intensity and extension, suggesting the superiority of INSM1 in histology over cytology. Although no consensus was reached regarding combined or single-marker use, the possibility of a marker that can save material and reduce costs is especially important for immunocytochemistry, and in the context of SCLC, further studies with larger casuistics, comparisons with other markers and tumor types and direct comparisons between histology and cytology use, should be encouraged.

3.3. INSM1 Gene Expression and Diagnostic Use

Few studies have reported on INSM1 gene expression as a means for SCLC diagnosis. These have shown that INSM1 gene expression correlates with neuroendocrine differentiation, being expressed in a variety of tumors, including insulinoma, glucagonoma, pituitary tumor, pheochromocytoma, medullary thyroid carcinoma, and, most importantly, SCLC, whereas the expression was not disclosed in non-neuroendocrine tumors or normal cells [9].
INSM1 gene expression is associated with NE differentiation, directly correlates with INSM1 IHC (protein) expression, and may have prognostic implications, being closely associated with the SCLC molecular profile. The sensitivity of genetic methods remains to be determined, since only one study disclosed any results in this regard [39]. With the advent of INSM1 IHC, the potential of using alternative genetic sequencing techniques for this biomarker has moved into the background.

3.4. INSM1 Diagnostic Use—Conclusions

Unequivocally, INSM1 is an important diagnostic biomarker of NE differentiation for SCLC, both in histology and cytology samples, depicting a high sensitivity, specificity, and reproducibility among studies. Its main advantage over other currently used marker is the exclusive nuclear staining and minimal background staining. Furthermore, INSM1 is expressed both in primary SCLC and its metastases. The fact that INSM1 staining represents true NE differentiation is a double-edged sword, because expression means that stained cells have some level of neuroendocrine differentiation, which may potentially have future prognostic or therapeutic implications in cases of mixed SCLC tumors, but it also signifies that expression is found in other NE tumors, not only in the lungs but also in other locations. Thus, INSM1 expression alone does not allow for a reliable diagnosis of SCLC. Furthermore, INSM1 may also be expressed, albeit rarely, in NSCLC. The fact that no consensus in the positivity cutoff exists, either for histology or cytology, is also a limitation to its use and precludes a more accurate estimation of the sensitivity and specificity. Despite the high sensitivity, not all studies conclude the superiority of INSM1 over the commonly used classic NE combined panel (SYN, CGA, and CD56), and thus, some authors do not endorse its use as a replacement. Nevertheless, the possibility of saving materials and reducing costs may justify INSM1 use as a standalone marker if differences in the sensitivity and specificity do not significantly differ following the definition of a universal cutoff value.
Comparing techniques, IHC for INSM1 seems to be slightly superior to ICC, both in sensitivity and specificity, but the differences are not marked enough to justify abandoning a commonly used method of SCLC diagnosis, considering the good histology–cytology correlation. As for INSM1 gene expression, there is concordance with IHC but no studies available comparing with INSM1 ICC. Nonetheless, one may extrapolate that if cytology and histology marker expression are correlated, and the primary antibodies used are the same, it seems likely that the gene expression will also correlate with the ICC results. Importantly, INSM1 mRNA expression was shown, similar to IHC expression, to correspond to bona fide NE differentiation. Unfortunately, very few studies report on the use of INSM1 gene profiling techniques, limiting comparisons.
We conclude that both INSM1 IHC and ICC are reliable ancillary methods for SCLC diagnosis and that standalone usage of the marker should be postponed until further studies are made and a standard cutoff for staining positivity is agreed on. Table 1 shows detailed results from a variety of studies on INSM1 immunochemical use for the diagnosis of SCLC, summarizing the above comments and showing results on the various sensitivities in INSM1 and classic NE markers, specificity for differential diagnosis with NSCLC, and INSM1 expression in other types of NE tumors of the lungs.
 
Table 1. INSM1 immunochemistry for small cell lung cancer diagnosis—retrospective analysis since 2015.
INSM1 specificity (SCLC vs. NSCLC),% calculation: 100× (1—NSCLC INSM1-positive cases/total NSCLC cases); * Only adenocarcinoma and squamous cell carcinoma; ** 3 cases of LCNEC, and 2 carcinoids were thymic; *** pleural effusion samples were also evaluated, the results not included due to the small sample size (5 cases).

4. INSM1 as a Prognostic Marker

SCLC is characterized by its highly aggressive clinical behavior, frequent metastasis, and high recurrence rate after the initial response to first-line chemotherapy [2][3][4]. Given its dismal prognosis, there is a high demand for biomarkers that may predict patient outcomes, but no consensus has been reached concerning the prognostic biomarkers for lung NEC, including SCLC [6]. It was shown that classic NE markers such as CGA, SYN, and CD56, typically used as ancillary immunohistochemical markers for NE tumors diagnosis, may also have prognostic value [4][78][84][85]. Naturally, with the discovery of new NE markers, alternative uses to diagnoses were investigated. In 2015, Fujino et al. [4][38] reported that INSM1 knockdown in SCLC cell lines resulted in the suppression of cell proliferation and increased apoptosis, suggesting that INSM1 may have an oncogenic role in SCLC progression. Following this observation, subsequent studies have attempted to demonstrate the prognostic value of INSM1 [24][86][87][88][89].
McColl et al. aimed to better understand the mechanisms underlying chemorefractory SCLC. Using gene profiling techniques, two subgroups of SCLC were identified: one predominantly expressing INSM1 mRNA and the other expressing mostly Yes1-associated transcriptional regulator (YAP1), a key mediator of the Hippo pathway [89]. Most SCLC cases analyzed disclosed high INSM1 expression and low YAP1 expression. Western blotting showed that, at the protein level, differences were maintained, and there were even 15 SCLC cell lines disclosing mutually exclusive expression of the markers. The IHC staining of both markers also corroborated these findings, with the majority of tumors showing strong INSM1 staining, whereas YAP1 was positive in only a few. Then, INSM1 IHC staining in 55 additional specimens of SCLC (in a TMA) disclosed that a higher INSM1 expression was associated with an increased overall survival (OS), progression-free survival (PFS), and chemo-responsiveness [89], indicating that a higher INSM1 expression may be associated with a better outcome, contrarily to Fujino et al.’s hypothesis [4][38]. McColl et al. proceeded to investigate subgroups’ responses to commonly used chemotherapy agents for the treatment of SCLC, and all three agents (cisplatin, etoposide, and irinotecan) were more effective against cells from the INSM1-expressing group. They also demonstrated that BCL2 apoptosis regulator (BCL2), a gene associated with a better prognosis expressed in the majority of SCLC [90], was expressed at both the transcript and protein levels in cells from the aforementioned group [89], suggesting a connection between both genes. The authors proposed that SCLC might be prognostically divided into two groups: the most prevalent “classic” SCLC, which is INSM1+ and shows a relatively better prognosis, and a variant group, INSM1-, in which YAP1+ tumors are included, disclosing a worse prognosis [89]. Despite that the BCL2 expression was increased in the first group, the precise mechanisms associated with chemosensitivity and a better outcome remain elusive. This study shows that INSM1 may be useful for stratifying patients into groups susceptible or resistant to chemotherapy, with potential therapeutic implications in the future.
Conversely, Minami et al., in a study comprising 75 patients with SCLC and LCNEC, aimed to determine the relationship between INSM1 expression (through IHC) and prognosis. They found that the OS and recurrence-free survival (RFS) were significantly worse not only in the INSM1+ group but also in INSM1+ SCLC patients [87]. Moreover, patients with clinical stage I and INSM1+ SCLC endured significantly poorer RFS than the INSM1- patients with the same disease stage. Thus, these authors proposed that the first group of patients should be managed more aggressively, with preoperative chemotherapy, whereas the second would benefit from surgery alone. Other NE markers depicted no differences in the OS or RFS, except for SYN positivity, which was associated with a significantly poorer RFS. After a multivariable analysis, taking into account multiple factors associated with the OS and RFS, INSM1 was shown to be the strongest predictor of a poor prognosis for the OS and RFS [87]. These results support the use of INSM1 as a prognostic biomarker and emphasize its superiority over other NE markers. The findings of this study are, however, limited by the relatively small number of subjects and by the retrospective nature of the study. Furthermore, a prognosis might have been underestimated owing to the inclusion of patients that did not go through postoperative chemotherapy due to poor respiratory or overall function [87].
Sakakibara et al. conducted a study aiming to determine the prognostic role of INSM1 in SCLC [24]. The SCLC subgroup with absent IHC NE marker expression disclosed a statistically significant better prognosis, in accordance with their previous study, compared to the group with NE marker expression, and within that group, inferior expression levels correlated with a better outcome. As for INSM1 IHC expression, a subgroup with low INSM1 expression had a statistically better prognosis than the subgroup with high expression; therefore, low INSM1 and low NE markers expression are possibly associated with a good prognosis [24]. Although, in the univariable analysis, INSM1 and NE expression was statistically associated with lower survival, the multivariable analysis disclosed only marginal significance. This study further alerts to the possibility of using INSM1 to guide the therapy and follow-up of SCLC patients, although limited through the inclusion of some cases that had pre-op chemotherapy [24][87].
In a different way, Baine et al. aimed to identify different SCLC subtypes based on ASCL1, NEUROD1, POU2F3, and YAP1 IHC expression, providing a histopathologic and immunohistochemical characterization, in which the expression of NE markers was included [88]. Regardless of this study not directly focusing on INSM1, it is important because these subtypes may be correlated with previously INSM1-defined SCLC subtypes [89]. The NE expression, including INSM1, was markedly reduced in the ASCL1/NEUROD1 double-negative group and was inversely associated with the YAP1 expression. The YAP1 expression seemed to be associated with combined SCLC histology, and a higher expression was observed in the NSCLC component. Most SCLC were found to express ASCL1 and/or NEUROD1, which were associated with a high NE program [88]. In line with McColl et al., this study shows that SCLC may be divided into two distinct groups: one with high ASCL1 and/or NEUROD1 levels, with concomitant high INSM1 expression, and another with a low expression of those two markers, which, in turn, shows low INSM1 expression [88][89]. Contrarily to McColl et al., this study considered YAP1 expression in SCLC to be mostly irrelevant, and thus, no subtype was defined with that marker [88][89]. One important finding of this study is that even the ASCL1/NEUROD1 double-negative group showed NE expression to a lesser extent, raising doubts about the “non-NE subtype of SCLC” [91], as the availability of more sensitive markers such as INSM1 make this classification obsolete [23][37][88]. Despite no analysis of the patient prognostic factors being performed, this study was useful to corroborate previous findings that further confirmed the INSM1 prognostic value of INSM1 [88][89]. Some studies have already depicted a possible relation between INSM1 and ASCL1 in SCLC [4][12], but more are needed concerning the other markers, as new molecular pathways may help find new treatment strategies and improve the overall knowledge of this particular type of cancer.
In a recent study from Xu et al., researchers examined INSM1 IHC expression in 73 SCLC samples from surgical resections and reported that a high INSM1 expression was positively correlated with lymph node metastasis (LNM) and advanced TNM stage [86]. In a univariable analysis of the patient prognosis, the high INSM1 group showed worse overall survival, and the multivariable analysis deemed INSM1 as an independent prognosticator for SCLC. In the group of patients undergoing chemotherapy with LNM, INSM1 positivity was significantly associated with reduced OS and chemoresistance, but this was not disclosed in the group of patients undergoing chemotherapy without LNM. Interestingly, the INSM1 status did not seem to affect the prognosis in patients who did not undergo chemotherapy. The researchers went further and investigated INSM1’s non-neuroendocrine role in SCLC using in vitro experiments to illuminate the possible mechanisms underlying those findings. They found that INSM1 overexpression downregulated protein kinase AMP-activated catalytic subunit alpha 2 (PRKAA2) expression, reduced glucose intake activity, augmented tumor migration capacity, and induced cisplatin resistance [86]. These effects, both in vitro and in vivo, were reversed by metformin, an antidiabetic drug that currently is under study as an adjuvant for chemotherapy in lung cancer patients [92][93][94][95][96]. Thus, INSM1 might be useful beyond diagnostic and prognostic use to help select cancer patients for trials with metformin [86]. An advantage of this study is that all selected patients had not received any prior treatment, a factor that may have contributed to bias in other studies [24][86]. Nevertheless, the study had some limitations: (1) a modest sample size; (2) a failure to confirm the increased tumor growth with INSM1 overexpression in vitro, which should be expected based on the in vivo results; and (3) the use of a single SCLC cell line. In short, this study showed that INSM1 may predict the poor prognosis in SCLC, given its contribution to tumor metastasis and chemoresistance, and these effects might be explained by PRKAA2 downregulation [86]
In summary, INSM1, an undisputedly useful diagnostic marker, is still in its infancy concerning a prognostic role in SCLC. At this point, it is quite difficult to claim whether it will be used to predict aggressive or indolent behavior, since, despite most studies affirming that INSM1 high expression associates with the overall worse prognosis, there was one study with opposed results [89], making meaningful conclusions impossible with so few studies on this matter. Efforts to define SCLC subtypes should be continued, as there is no current consensus about their definition and might simplify the search for prognostic factors. Focus on molecular pathways involving INSM1, and known oncogenes or tumor suppressor genes should also be useful and could serve as an entry point for the discovery of novel therapeutic targets.

5. Gene Therapy and Other Treatment Options Targeting INSM1 or Related Molecules

Compared to NSCLC, SCLC always had a more limited range of therapeutic options [75]. Cisplatin and etoposide are used as a first-line chemotherapy for many years, with initial chemosensitivity but later developing resistance, and only recently, immunotherapy in the form of nivolumab, a PD-1 antagonist, was approved for third-line use by the FDA in recurrent SCLC, unfortunately with less than 20% of patients benefiting from this strategy [86][91][97][98].
INSM1’s very low expression in adult tissues and re-expression in neuroendocrine tumors, disclosing a high specificity, has made it an attractive target for novel therapies. No studies directly targeting INSM1 have been carried out, as the transcription factors are especially difficult to target using small molecules [99][100]. Instead, the focus has been placed on targeting INSM1-expressing tumors using INSM1 promoter-specific suicide gene therapy [62][63][64][65][66][67][68] or the molecules involved in INSM1-related signaling pathways [77][99][100][101].
In transcriptionally targeted suicide gene therapy, a suicide gene contained in a vector, usually of a viral nature, is incorporated into cancer cells, and through a cancer-specific promoter, its activity is regulated, allowing the conversion of a nontoxic prodrug—for example, ganciclovir—to a cell toxic agent, with the goal of avoiding the side effects produced by chemotherapy agents in noncancer cells [64]. It is long-known that INSM1 contains a promoter region with the genes responsible for regulating its own expression [102]. Published in 2006, a study by Pedersen et al. was the first to report INSM1 usefulness in targeted suicide gene therapy in SCLC [62]. The authors found that a 1.7-kb region in the INSM1 promoter showed a high expression in SCLC cell lines but was absent in non-neuroendocrine cell lines, with sufficient activity and specificity for inclusion in gene therapy and superiority vs. other contemporarily available promoters. When regulated by this promoter region, the suicide gene herpes simplex virus thymidine kinase (HSV-TK) in combination with ganciclovir significantly augmented the sensitivity for the prodrug in SCLC cell lines. Considering these discoveries, the INSM1 promoter has been suggested as an exciting new promoter for gene therapy given the very high activity and tumor specificity, propelling further studies [62]. These findings were replicated both in vitro and in vivo in primitive neuroectodermal tumors that show neuroendocrine features similar to SCLC [63]. In another study, INSM1 promotor-driven adenoviral HSV-TK gene therapy was tested in the treatment of various neuroendocrine tumors, and it was found that the adenoviral genome interfered with the promoter specificity, resulting in in vivo off-target activity in mouse pancreas, kidneys, and lungs [66]. An interesting feature of suicide gene therapy is the possibility of multiple modifications, and in their studies, Akerstrom et al. demonstrated that, by adding a chicken β-globin HS4 insulator sequence and two copies of mouse neuronal-restrictive silencer element (NRSE), not only nonspecific INSM1 promoter activation was reduced, but also, the activity of the new construct was increased compared to the original, both in vitro and in vivo, although only in vitro for SCLC [66][67]. Subsequently, the modified INSM1 promoter-driven adenoviral HSV-TK construct in combination with ganciclovir was tested in insulinoma in vitro and in vivo, with results analogous to those of previous studies [68]. Studies in other types of tumors also proved useful, since the underlying basis of the therapeutic method extends to the various INSM1-expressing neuroendocrine tumors. Moreover, the same research team conducted a study aimed at detecting neuroendocrine tumors, including SCLC, using a modified INSM1 promoter in an adenoviral construct combined with the Gaussia luciferase gene. They found that, after the infection of an INSM1-positive NE lung tumor in a xenograft mouse model, luciferase activity was detectable, demonstrating a less conventional method of diagnosing these tumors and an alternative use for adenoviral constructs [103]. Christensen et al. demonstrated the efficacy of INSM1 promoter-based suicide gene therapy both in vitro and in vivo in SCLC cell lines and xenografted mice, using a YCD/5-FC and a YCD-YUPRT/5-FC model. The therapy proved to be highly cytotoxic to SCLC but not to other cell lines and significantly delayed the tumor growth in SCLC xenografts compared to the controls, with better results than the previous HSV-TK/ganciclovir model, mainly due to YCD-YUPRT-produced toxins having an important bystander cytotoxic effect [64]. Later, the INSM1 promoter-driven YCD-YUPRT/5-FC suicide gene therapy model was proven efficient in SCLC chemoresistant cell lines and xenografts, even in cases displaying higher INSM1 promoter activity compared to chemosensitive SCLC, notwithstanding the high levels of cytotoxicity in both. In the same study, another INSM1 promoter-driven construct was tested—NTR with the SN27686 prodrug—also with positive results. Interestingly, INSM1 promoter-driven YCD-YUPRT/5-FC gene therapy combined with chemotherapy, as well as double suicide gene therapy, disclosed superior results to single gene therapy in chemoresistant SCLC cells [65].
In more recent years, the focus of INSM1-related therapeutic strategies has shifted away from gene therapy and has moved towards targeting molecules being involved in signaling pathways in which it plays a role. In the anterior pituitary gland, INSM1 interacts with LSD1 through its SNAG domain at the N-terminus, contributing to neuroendocrine cell differentiation [69]. LSD1 inhibitor T-3775440 has been shown to efficiently suppress SCLC proliferation in vitro and delay tumor growth in vivo, possibly by interfering with the INSM1-LSD1 interaction and preventing the expression of NE genes, such as ASCL1. Through INSM1 knockdown, comparable results in gene expression and cell proliferation were obtained, sustaining those findings [99]. This study supports the hypothesis that SCLC carcinogenesis is, in part, led by neuroendocrine differentiation, as LSD1 interactions with INSM1 and the consequent effects are similar to those observed in the anterior pituitary gland, opening the way to new therapeutic targets. As previously discussed in the introduction section, INSM1 is involved in the Shh and MYCN common pathways [77]. Shh can upregulate MYCN via activation of the PI3K/AKT pathway or via Smoothened activation. Different Shh or related molecules inhibitors were used to treat SCLC cells, and it was found that 5E1, a Shh direct inhibitor, and GANT-61, an inhibitor of Gli1, a transcription factor induced by Smoothened that directly upregulates MYCN, downregulated the INSM1 expression and suppressed SCLC proliferation in single uses, with GANT-61 exhibiting a superior effect but requiring an above threshold dosage. Although Smoothened inhibitors such as cyclopamine or vismodegib did not affect cancer growth when used alone, they amplified the inhibitory effects when combined with 5E1 or GANT-61, increasing the sensitivity of the latter and enabling its use within a safe therapeutic range (10 µM). Indeed, GANT-61 plus vismodegib was the most efficient combination. These findings support the role of INSM1 as a crucial SCLC oncogenic factor, since INSM1 knockdown inhibited the tumor growth and enhanced the effects of Shh pathway inhibitors. Apoptosis via caspase-3 activation was depicted in both INSM1 knockdown and Shh pathway inhibitors [77]. Shh signaling pathway inhibitors represent an exciting new opportunity for SCLC treatment, albeit further studies with different inhibitor combinations are required to corroborate these findings. The same authors reported that 5′-Iodotubercidin repressed INSM1 expression, restricting the growth of human neuroblastoma cell lines. The main mechanism involved was ADK blockage, but the suppression of the ERK1/2 and AKT signaling pathways was also present, suggesting a hypothetical use in SCLC, since these are shared pathways [101]. A recent study by Norton et al. found through genome-scale CRISPR/Cas9 inactivation screening to murine SCLC cell lines that protein neddylation inhibition was effective in suppressing those cells [100]. MLN4924 effectively caused cell death in vitro and in vivo and suppressed the expression of master neuroendocrine regulators such as ASCL1 and INSM1. The authors could not identify the molecular mechanism underlying these results but hypothesized that treatment stabilized a putative INSM1 transcriptional repressor regulated by ubiquitin-mediated proteolysis, either directly or through neddylation of an upstream regulator of that repressor [100]. Thus, SCLC treatment strategies directed to neuroendocrine differentiation controllers maintain their relevance.
In conclusion, suicide gene therapy and targeting related molecules are both effective strategies of exploiting INSM1 for SCLC treatment. Over the years, modifications have been made to INSM1 promoter-driven gene therapy that increased its sensitivity toward cancer cells and decreased the collateral damage to normal cells. INSM1 promoter was used to regulate gene therapy in three models: (adenoviral) HSV-TK/ganciclovir, YCD or YCD-YUPRT/5-FC, and NTR/SN27686. Further studies with direct comparisons are required. More recently, research has focused on targeting INSM1-related molecules, namely LSD1, Shh, and MYCN signaling pathway molecules, and protein neddylation. INSM1 and many of these molecules are related to the induction of NE differentiation in SCLC, which is increasingly recognized as a key factor in oncogenicity. Finding new ways to control neuroendocrine cell states will be crucial for developing new tools against this and other types of neuroendocrine neoplasms. Lastly, targeting INSM1 directly is a difficult challenge but may prove largely beneficial. A summary of the different treatment options in SCLC involving INSM1 is displayed in Figure 2.
Figure 2. INSM1 treatment options in SCLC. Summary of the researched therapeutic approaches for SCLC using INSM1. Currently, there are no studies available on INSM1 as a direct target, due to the difficult nature of targeting transcription factors [99][100]; therefore, preclinical trials would be of high interest. INSM1 has been used as a regulator of suicide gene therapy in HSV-TK/ganciclovir, YCD or YCD-YUPRT/5-FU, and NTR/SN27686 models [62][63][64][65][66][67][68]. Alternatively, targeting multiple molecules in INSM1-related pathways has also been an effective approach for SCLC treatment. LSD1 inhibitors, Shh pathway inhibitors, and protein neddylation inhibitors successfully reduced the SCLC tumor growth, and 5’-Iodotubercidin was efficient in neuroblastoma treatment (not shown in the figure) [77][99][100][101]. These studies were conducted in in vitro and in vivo in mouse models; thus, clinical trials may be the next step to establishing their effectiveness.

6. Conclusions

SCLC represents one of the most aggressive and difficult forms of cancer to treat. Furthermore, its diagnosis is made more complex owing to the difficulty in obtaining representative and high-quality samples, given its usual central perihilar location. It is included in the extensive group of neuroendocrine neoplasms, which share the hallmark expression of neuroendocrine markers. Although not essential for SCLC diagnosis (as typical morphological features may suffice), diagnostic biomarkers can prove very beneficial to aid in diagnosis, especially in dubious cases, such as in the not-uncommon presence of tissue necrosis. In this review, we characterized a molecule—INSM1—that may positively respond to the challenges in SCLC, disclosing diagnostic, as well as possible prognostic and therapeutic, applications. INSM1 has emerged as a diagnostic NE biomarker for SCLC since 2015, primarily as an IHC or ICC marker. Although CGA, SYN, and CD56 are widely used immunochemical markers but all of them have limitations and often have to be used simultaneously in a triple marker panel, leading to the extensive use of limited tissue. INSM1 is a reliable IHC and ICC marker with high sensitivity, specificity, and a distinctive exclusively nuclear expression. INSM1 sensitivity was disclosed in the majority of the studies as superior to CGA and SYN, as well as similar to CD56 and combined triple marker use, with a universally high specificity for the differential diagnosis with NSCLC. Staining represents true NE differentiation, which is an advantage in the differential diagnosis with NSCLC, despite some studies reporting a rare expression in that type of tumor [27], but a disadvantage in comparisons with other NE neoplasms. Importantly, the expression is retained in metastasis, facilitating a diagnosis in some cases. Nonetheless, no consensus has been reached concerning INSM1 standalone use and a standard cutoff for immunohistochemistry. Larger-scale studies to address these issues are a priority. Controversy persists regarding INSM1 and SCLC prognosis, and further studies are necessary to clarify this matter. Suicide gene therapy using the INSM1 promoter as a regulator in different models and targeting molecules in INSM1-related signaling pathways, such as LSD1, Shh, and protein neddylation, disclosed successful results in vitro and in vivo in SCLC cell lines and xenografted mouse models. The next steps are to find new ways to alter the neuroendocrine differentiation of SCLC and to conduct clinical trials with these therapeutics. Direct targeting of INSM1 or transcription factors in general is a difficult challenge but may result in substantial survival improvement in SCLC patients. INSM1 represents a valuable biomarker for SCLC diagnosis that also provides ample opportunities for the development of new prognostic and therapeutic strategies.
 

This entry is adapted from the peer-reviewed paper 10.3390/jmp3030013

References

  1. Cancer.Net—Lung Cancer—Small Cell: Statistics. Available online: https://www.cancer.net/cancer-types/lung-cancer-small-cell/statistics (accessed on 18 April 2022).
  2. Rodriguez, E.; Lilenbaum, R.C. Small cell lung cancer: Past, present, and future. Curr. Oncol. Rep. 2010, 12, 327–334.
  3. Kris, M.G.; Benowitz, S.I.; Adams, S.; Diller, L.; Ganz, P.; Kahlenberg, M.S.; Le, Q.-T.; Markman, M.; Masters, G.A.; Newman, L.; et al. Clinical Cancer Advances 2010: Annual Report on Progress Against Cancer From the American Society of Clinical Oncology. J. Clin. Oncol. 2010, 28, 5327–5347.
  4. Fujino, K.; Motooka, Y.; Hassan, W.A.; Ali Abdalla, M.O.; Sato, Y.; Kudoh, S.; Hasegawa, K.; Niimori-Kita, K.; Kobayashi, H.; Kubota, I.; et al. Insulinoma-Associated Protein 1 Is a Crucial Regulator of Neuroendocrine Differentiation in Lung Cancer. Am. J. Pathol. 2015, 185, 3164–3177.
  5. WHO Classification of Tumours Editorial Board. Thoracic Tumours, 5th ed.; International Agency for Research on Cancer Publications: Lyon, France, 2021; Volume 5.
  6. Narayanan, D.; Mandal, R.; Hardin, H.; Chanana, V.; Schwalbe, M.; Rosenbaum, J.; Buehler, D.; Lloyd, R.V. Long Non-coding RNAs in Pulmonary Neuroendocrine Neoplasms. Endocr. Pathol. 2020, 31, 254–263.
  7. Dingemans, A.M.C.; Früh, M.; Ardizzoni, A.; Besse, B.; Faivre-Finn, C.; Hendriks, L.E.; Lantuejoul, S.; Peters, S.; Reguart, N.; Rudin, C.M.; et al. Small-cell lung cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up☆. Ann. Oncol. 2021, 32, 839–853.
  8. Thunnissen, E.; Borczuk, A.C.; Flieder, D.B.; Witte, B.; Beasley, M.B.; Chung, J.H.; Dacic, S.; Lantuejoul, S.; Russell, P.A.; den Bakker, M.; et al. The Use of Immunohistochemistry Improves the Diagnosis of Small Cell Lung Cancer and Its Differential Diagnosis. An International Reproducibility Study in a Demanding Set of Cases. J. Thorac. Oncol. 2017, 12, 334–346.
  9. Goto, Y.; De Silva, M.G.; Toscani, A.; Prabhakar, B.S.; Notkins, A.L.; Lan, M.S. A novel human insulinoma-associated cDNA, IA-1, encodes a protein with "zinc-finger" DNA-binding motifs. J. Biol. Chem. 1992, 267, 15252–15257.
  10. Lan, M.S.; Breslin, M.B. Structure, expression, and biological function of INSM1 transcription factor in neuroendocrine differentiation. FASEB J. 2009, 23, 2024–2033.
  11. Gierl, M.S.; Karoulias, N.; Wende, H.; Strehle, M.; Birchmeier, C. The zinc-finger factor Insm1 (IA-1) is essential for the development of pancreatic beta cells and intestinal endocrine cells. Genes Dev. 2006, 20, 2465–2478.
  12. Jia, S.; Wildner, H.; Birchmeier, C. Insm1 controls the differentiation of pulmonary neuroendocrine cells by repressing Hes1. Dev. Biol. 2015, 408, 90–98.
  13. Zombori, T.; Turkevi-Nagy, S.; Sejben, A.; Juhász-Nagy, G.; Cserni, G.; Furák, J.; Tiszlavicz, L.; Krenács, L.; Kővári, B. The panel of syntaxin 1 and insulinoma-associated protein 1 outperforms classic neuroendocrine markers in pulmonary neuroendocrine neoplasms. APMIS 2021, 129, 186–194.
  14. Zhu, J.; Wang, H.; Ramelot, T.A.; Kennedy, M.A.; Hu, R.; Yue, X.; Liu, M.; Yang, Y. Solution NMR structure of zinc finger 4 and 5 from human INSM1, an essential regulator of neuroendocrine differentiation. Proteins 2017, 85, 957–962.
  15. Osipovich, A.B.; Long, Q.; Manduchi, E.; Gangula, R.; Hipkens, S.B.; Schneider, J.; Okubo, T.; Stoeckert, C.J., Jr.; Takada, S.; Magnuson, M.A. Insm1 promotes endocrine cell differentiation by modulating the expression of a network of genes that includes Neurog3 and Ripply3. Development 2014, 141, 2939–2949.
  16. Breslin, M.B.; Zhu, M.; Notkins, A.L.; Lan, M.S. Neuroendocrine differentiation factor, IA-1, is a transcriptional repressor and contains a specific DNA-binding domain: Identification of consensus IA-1 binding sequence. Nucleic Acids Res. 2002, 30, 1038–1045.
  17. Xie, J.; Cai, T.; Zhang, H.; Lan, M.S.; Notkins, A.L. The zinc-finger transcription factor INSM1 is expressed during embryo development and interacts with the Cbl-associated protein. Genomics 2002, 80, 54–61.
  18. Lan, M.S.; Li, Q.; Lu, J.; Modi, W.S.; Notkins, A.L. Genomic organization, 5′-upstream sequence, and chromosomal localization of an insulinoma-associated intronless gene, IA-1. J. Biol. Chem. 1994, 269, 14170–14174.
  19. Tsai, H.K.; Hornick, J.L.; Vivero, M. INSM1 expression in a subset of thoracic malignancies and small round cell tumors: Rare potential pitfalls for small cell carcinoma. Mod. Pathol. 2020, 33, 1571–1580.
  20. Liu, W.D.; Wang, H.W.; Muguira, M.; Breslin, M.B.; Lan, M.S. INSM1 functions as a transcriptional repressor of the neuroD/beta2 gene through the recruitment of cyclin D1 and histone deacetylases. Biochem. J. 2006, 397, 169–177.
  21. Rosenbaum, J.N.; Guo, Z.; Baus, R.M.; Werner, H.; Rehrauer, W.M.; Lloyd, R.V. INSM1: A Novel Immunohistochemical and Molecular Marker for Neuroendocrine and Neuroepithelial Neoplasms. Am. J. Clin. Pathol. 2015, 144, 579–591.
  22. Rodriguez, E.F.; Fite, J.J.; Chowsilpa, S.; Maleki, Z. Insulinoma-associated protein 1 immunostaining on cytology specimens: An institutional experience. Hum. Pathol. 2019, 85, 128–135.
  23. Mukhopadhyay, S.; Dermawan, J.K.; Lanigan, C.P.; Farver, C.F. Insulinoma-associated protein 1 (INSM1) is a sensitive and highly specific marker of neuroendocrine differentiation in primary lung neoplasms: An immunohistochemical study of 345 cases, including 292 whole-tissue sections. Mod. Pathol. 2019, 32, 100–109.
  24. Sakakibara, R.; Kobayashi, M.; Takahashi, N.; Inamura, K.; Ninomiya, H.; Wakejima, R.; Kitazono, S.; Yanagitani, N.; Horiike, A.; Ichinose, J.; et al. Insulinoma-associated Protein 1 (INSM1) Is a Better Marker for the Diagnosis and Prognosis Estimation of Small Cell Lung Carcinoma Than Neuroendocrine Phenotype Markers Such as Chromogranin A, Synaptophysin, and CD56. Am. J. Surg. Pathol. 2020, 44, 757–764.
  25. Chen, C.; Breslin, M.B.; Lan, M.S. Ectopic expression of a small cell lung cancer transcription factor, INSM1 impairs alveologenesis in lung development. BMC Pulm. Med. 2016, 16, 49.
  26. Yu, L.; Dong, Y.; Xue, J.; Xu, S.; Wang, G.; Kuang, D.; Duan, Y. SOX11 is a sensitive and specific marker for pulmonary high-grade neuroendocrine tumors. Diagn. Pathol. 2022, 17, 2.
  27. Wang, M.; Abi-Raad, R.; Baldassarri, R.; Adeniran, A.J.; Cai, G. Expression of insulinoma-associated protein 1 in non-small cell lung cancers: A diagnostic pitfall for neuroendocrine tumors. Hum. Pathol. 2021, 115, 104–111.
  28. Staaf, J.; Tran, L.; Söderlund, L.; Nodin, B.; Jirström, K.; Vidarsdottir, H.; Planck, M.; Mattsson, J.S.M.; Botling, J.; Micke, P.; et al. Diagnostic Value of Insulinoma-Associated Protein 1 (INSM1) and Comparison With Established Neuroendocrine Markers in Pulmonary Cancers. Arch. Pathol. Lab. Med. 2020, 144, 1075–1085.
  29. Hou, T.; Gan, Q.; Joseph, C.T.; Sun, X.; Gong, Y. Insulinoma-associated protein 1 immunostaining for various types of neuroendocrine tumors on FNA smears. Cancer Cytopathol. 2020, 128, 725–732.
  30. Viswanathan, K.; Siddiqui, M.T.; Borczuk, A.C. Insulinoma-associated protein 1 is a sensitive and specific marker for lung neuroendocrine tumors in cytologic and surgical specimens. J. Am. Soc. Cytopathol. 2019, 8, 299–308.
  31. Švajdler, M.; Mezencev, R.; Šašková, B.; Ondič, O.; Mukenšnábl, P.; Michal, M. Triple marker composed of p16, CD56, and TTF1 shows higher sensitivity than INSM1 for diagnosis of pulmonary small cell carcinoma: Proposal for a rational immunohistochemical algorithm for diagnosis of small cell carcinoma in small biopsy and cytology specimens. Hum. Pathol. 2019, 85, 58–64.
  32. Nakra, T.; Nambirajan, A.; Guleria, P.; Phulware, R.H.; Jain, D. Insulinoma-associated protein 1 is a robust nuclear immunostain for the diagnosis of small cell lung carcinoma in cytology smears. Cancer Cytopathol. 2019, 127, 539–548.
  33. Abe, H.; Takase, Y.; Sadashima, E.; Fukumitsu, C.; Murata, K.; Ito, T.; Kawahara, A.; Naito, Y.; Akiba, J. Insulinoma-associated protein 1 is a novel diagnostic marker of small cell lung cancer in bronchial brushing and cell block cytology from pleural effusions: Validity and reliability with cutoff value. Cancer Cytopathol. 2019, 127, 598–605.
  34. Rodriguez, E.F.; Chowsilpa, S.; Maleki, Z. Insulinoma-Associated Protein 1 Immunostain: A Diagnostic Tool for Pulmonary Small Cell Carcinoma in Cytology. Acta Cytol. 2018, 62, 333–338.
  35. Kriegsmann, K.; Zgorzelski, C.; Kazdal, D.; Cremer, M.; Muley, T.; Winter, H.; Longuespée, R.; Kriegsmann, J.; Warth, A.; Kriegsmann, M. Insulinoma-associated Protein 1 (INSM1) in Thoracic Tumors is Less Sensitive but More Specific Compared With Synaptophysin, Chromogranin A, and CD56. Appl. Immunohistochem. Mol. Morphol. 2018, 28, 237–242.
  36. Doxtader, E.E.; Mukhopadhyay, S. Insulinoma-associated protein 1 is a sensitive and specific marker of neuroendocrine lung neoplasms in cytology specimens. Cancer Cytopathol. 2018, 126, 243–252.
  37. Rooper, L.M.; Sharma, R.; Li, Q.K.; Illei, P.B.; Westra, W.H. INSM1 Demonstrates Superior Performance to the Individual and Combined Use of Synaptophysin, Chromogranin and CD56 for Diagnosing Neuroendocrine Tumors of the Thoracic Cavity. Am. J. Surg. Pathol. 2017, 41, 1561–1569.
  38. Fujino, K.; Yasufuku, K.; Kudoh, S.; Motooka, Y.; Sato, Y.; Wakimoto, J.; Kubota, I.; Suzuki, M.; Ito, T. INSM1 is the best marker for the diagnosis of neuroendocrine tumors: Comparison with CGA, SYP and CD56. Int. J. Clin. Exp. Pathol. 2017, 10, 5393–5405.
  39. Lan, M.S.; Russell, E.K.; Lu, J.; Johnson, B.E.; Notkins, A.L. IA-1, a new marker for neuroendocrine differentiation in human lung cancer cell lines. Cancer Res. 1993, 53, 4169–4171.
  40. Amelung, J.T.; Bührens, R.; Beshay, M.; Reymond, M.A. Key genes in lung cancer translational research: A meta-analysis. Pathobiology 2010, 77, 53–63.
  41. Tanigawa, M.; Nakayama, M.; Taira, T.; Hattori, S.; Mihara, Y.; Kondo, R.; Kusano, H.; Nakamura, K.; Abe, Y.; Ishida, Y.; et al. Insulinoma-associated protein 1 (INSM1) is a useful marker for pancreatic neuroendocrine tumor. Med. Mol. Morphol. 2018, 51, 32–40.
  42. González, I.; Lu, H.C.; Sninsky, J.; Yang, C.; Bishnupuri, K.; Dieckgraefe, B.; Cao, D.; Chatterjee, D. Insulinoma-associated protein 1 expression in primary and metastatic neuroendocrine neoplasms of the gastrointestinal and pancreaticobiliary tracts. Histopathology 2019, 75, 568–577.
  43. McHugh, K.E.; Mukhopadhyay, S.; Doxtader, E.E.; Lanigan, C.; Allende, D.S. INSM1 Is a Highly Specific Marker of Neuroendocrine Differentiation in Primary Neoplasms of the Gastrointestinal Tract, Appendix, and Pancreas. Am. J. Clin. Pathol. 2020, 153, 811–820.
  44. Chen, J.F.; Yang, C.; Sun, Y.; Cao, D. Expression of novel neuroendocrine marker insulinoma-associated protein 1 (INSM1) in genitourinary high-grade neuroendocrine carcinomas: An immunohistochemical study with specificity analysis and comparison to chromogranin, synaptophysin, and CD56. Pathol.-Res. Pract. 2020, 216, 152993.
  45. Kim, I.E., Jr.; Amin, A.; Wang, L.J.; Cheng, L.; Perrino, C.M. Insulinoma-associated Protein 1 (INSM1) Expression in Small Cell Neuroendocrine Carcinoma of the Urinary Tract. Appl. Immunohistochem. Mol. Morphol. 2020, 28, 687–693.
  46. Xin, Z.; Zhang, Y.; Jiang, Z.; Zhao, L.; Fan, L.; Wang, Y.; Xie, S.; Shangguan, X.; Zhu, Y.; Pan, J.; et al. Insulinoma-associated protein 1 is a novel sensitive and specific marker for small cell carcinoma of the prostate. Hum. Pathol. 2018, 79, 151–159.
  47. Kuji, S.; Watanabe, R.; Sato, Y.; Iwata, T.; Hirashima, Y.; Takekuma, M.; Ito, I.; Abe, M.; Nagashio, R.; Omae, K.; et al. A new marker, insulinoma-associated protein 1 (INSM1), for high-grade neuroendocrine carcinoma of the uterine cervix: Analysis of 37 cases. Gynecol. Oncol. 2017, 144, 384–390.
  48. Rooper, L.M.; Bishop, J.A.; Westra, W.H. INSM1 Is a Sensitive and Specific Marker of Neuroendocrine Differentiation in Head and Neck Tumors. Am. J. Surg. Pathol. 2018, 42, 665–671.
  49. Yuan, C.; Jiao, F.; Zhai, C.; Zhang, J.; Wang, S.; Zhu, L. Application of INSM1 in Diagnosis and Grading of Laryngeal Neuroendocrine Carcinoma. Laryngoscope 2021, 131, E2662–E2668.
  50. Parra, O.; Linos, K.; Yan, S.; Lilo, M.; LeBlanc, R.E. Comparative performance of insulinoma-associated protein 1 (INSM1) and routine immunohistochemical markers of neuroendocrine differentiation in the diagnosis of endocrine mucin-producing sweat gland carcinoma. J. Cutan. Pathol. 2021, 48, 41–46.
  51. Rush, P.S.; Rosenbaum, J.N.; Roy, M.; Baus, R.M.; Bennett, D.D.; Lloyd, R.V. Insulinoma-associated 1: A novel nuclear marker in Merkel cell carcinoma (cutaneous neuroendocrine carcinoma). J. Cutan. Pathol. 2018, 45, 129–135.
  52. Lilo, M.T.; Chen, Y.; LeBlanc, R.E. INSM1 Is More Sensitive and Interpretable than Conventional Immunohistochemical Stains Used to Diagnose Merkel Cell Carcinoma. Am. J. Surg. Pathol. 2018, 42, 1541–1548.
  53. Maleki, Z.; Abram, M.; Dell’Aquila, M.; Kilic, I.; Lu, R.; Musarra, T.; Barkan, G.; Rajakorpi, E.; Rossi, E.D.; Kholová, I. Insulinoma-associated protein 1 (INSM-1) expression in medullary thyroid carcinoma FNA: A multi-institutional study. J. Am. Soc. Cytopathol. 2020, 9, 185–190.
  54. Yoshida, A.; Makise, N.; Wakai, S.; Kawai, A.; Hiraoka, N. INSM1 expression and its diagnostic significance in extraskeletal myxoid chondrosarcoma. Mod. Pathol. 2018, 31, 744–752.
  55. Wang, H.; Krishnan, C.; Charville, G.W. INSM1 Expression in Peripheral Neuroblastic Tumors and Other Embryonal Neoplasms. Pediatr. Dev. Pathol. 2019, 22, 440–448.
  56. Farkas, L.M.; Haffner, C.; Giger, T.; Khaitovich, P.; Nowick, K.; Birchmeier, C.; Pääbo, S.; Huttner, W.B. Insulinoma-associated 1 has a panneurogenic role and promotes the generation and expansion of basal progenitors in the developing mouse neocortex. Neuron 2008, 60, 40–55.
  57. Wildner, H.; Gierl, M.S.; Strehle, M.; Pla, P.; Birchmeier, C. Insm1 (IA-1) is a crucial component of the transcriptional network that controls differentiation of the sympatho-adrenal lineage. Development 2008, 135, 473–481.
  58. Mahalakshmi, B.; Baskaran, R.; Shanmugavadivu, M.; Nguyen, N.T.; Velmurugan, B.K. Insulinoma-associated protein 1 (INSM1): A potential biomarker and therapeutic target for neuroendocrine tumors. Cell. Oncol. 2020, 43, 367–376.
  59. Chen, C.; Notkins, A.L.; Lan, M.S. Insulinoma-Associated-1: From Neuroendocrine Tumor Marker to Cancer Therapeutics. Mol. Cancer Res. 2019, 17, 1597–1604.
  60. Zhang, T.; Chen, C.; Breslin, M.B.; Song, K.; Lan, M.S. Extra-nuclear activity of INSM1 transcription factor enhances insulin receptor signaling pathway and Nkx6.1 expression through RACK1 interaction. Cell. Signal. 2014, 26, 740–747.
  61. Duggan, A.; Madathany, T.; de Castro, S.C.; Gerrelli, D.; Guddati, K.; García-Añoveros, J. Transient expression of the conserved zinc finger gene INSM1 in progenitors and nascent neurons throughout embryonic and adult neurogenesis. J. Comp. Neurol. 2008, 507, 1497–1520.
  62. Pedersen, N.; Pedersen, M.W.; Lan, M.S.; Breslin, M.B.; Poulsen, H.S. The insulinoma-associated 1: A novel promoter for targeted cancer gene therapy for small-cell lung cancer. Cancer Gene Ther. 2006, 13, 375–384.
  63. Wang, H.W.; Breslin, M.B.; Chen, C.; Akerstrom, V.; Zhong, Q.; Lan, M.S. INSM1 promoter-driven adenoviral herpes simplex virus thymidine kinase cancer gene therapy for the treatment of primitive neuroectodermal tumors. Hum. Gene Ther. 2009, 20, 1308–1318.
  64. Christensen, C.L.; Gjetting, T.; Poulsen, T.T.; Cramer, F.; Roth, J.A.; Poulsen, H.S. Targeted cytosine deaminase-uracil phosphoribosyl transferase suicide gene therapy induces small cell lung cancer-specific cytotoxicity and tumor growth delay. Clin. Cancer Res. 2010, 16, 2308–2319.
  65. Michaelsen, S.R.; Christensen, C.L.; Sehested, M.; Cramer, F.; Poulsen, T.T.; Patterson, A.V.; Poulsen, H.S. Single agent- and combination treatment with two targeted suicide gene therapy systems is effective in chemoresistant small cell lung cancer cells. J. Gene Med. 2012, 14, 445–458.
  66. Akerstrom, V.; Chen, C.; Lan, M.S.; Breslin, M.B. Modifications to the INSM1 promoter to preserve specificity and activity for use in adenoviral gene therapy of neuroendocrine carcinomas. Cancer Gene Ther. 2012, 19, 828–838.
  67. Akerstrom, V.; Chen, C.; Lan, M.S.; Breslin, M.B. Adenoviral insulinoma-associated protein 1 promoter-driven suicide gene therapy with enhanced selectivity for treatment of neuroendocrine cancers. Ochsner J. 2013, 13, 91–99.
  68. Tseng, A.W.; Chen, C.; Breslin, M.B.; Lan, M.S. Tumor-specific promoter-driven adenoviral therapy for insulinoma. Cell. Oncol. 2016, 39, 279–286.
  69. Welcker, J.E.; Hernandez-Miranda, L.R.; Paul, F.E.; Jia, S.; Ivanov, A.; Selbach, M.; Birchmeier, C. Insm1 controls development of pituitary endocrine cells and requires a SNAG domain for function and for recruitment of histone-modifying factors. Development 2013, 140, 4947–4958.
  70. Chen, C.; Breslin, M.B.; Lan, M.S. INSM1 increases N-myc stability and oncogenesis via a positive-feedback loop in neuroblastoma. Oncotarget 2015, 6, 36700–36712.
  71. Tao, W.; Zhang, Y.; Ma, L.; Deng, C.; Duan, H.; Liang, X.; Liao, R.; Lin, S.; Nie, T.; Chen, W.; et al. Haploinsufficiency of Insm1 Impairs Postnatal Baseline β-Cell Mass. Diabetes 2018, 67, 2615–2625.
  72. Morimoto, M.; Nishinakamura, R.; Saga, Y.; Kopan, R. Different assemblies of Notch receptors coordinate the distribution of the major bronchial Clara, ciliated and neuroendocrine cells. Development 2012, 139, 4365–4373.
  73. Peake, J.L.; Reynolds, S.D.; Stripp, B.R.; Stephens, K.E.; Pinkerton, K.E. Alteration of pulmonary neuroendocrine cells during epithelial repair of naphthalene-induced airway injury. Am. J. Pathol. 2000, 156, 279–286.
  74. Taniwaki, M.; Daigo, Y.; Ishikawa, N.; Takano, A.; Tsunoda, T.; Yasui, W.; Inai, K.; Kohno, N.; Nakamura, Y. Gene expression profiles of small-cell lung cancers: Molecular signatures of lung cancer. Int. J. Oncol. 2006, 29, 567–575.
  75. Rudin, C.M.; Brambilla, E.; Faivre-Finn, C.; Sage, J. Small-cell lung cancer. Nat. Rev. Dis. Primers 2021, 7, 3.
  76. Kudoh, S.; Tenjin, Y.; Kameyama, H.; Ichimura, T.; Yamada, T.; Matsuo, A.; Kudo, N.; Sato, Y.; Ito, T. Significance of achaete-scute complex homologue 1 (ASCL1) in pulmonary neuroendocrine carcinomas; RNA sequence analyses using small cell lung cancer cells and Ascl1-induced pulmonary neuroendocrine carcinoma cells. Histochem. Cell Biol. 2020, 153, 443–456.
  77. Chen, C.; Breslin, M.B.; Lan, M.S. Sonic hedgehog signaling pathway promotes INSM1 transcription factor in neuroendocrine lung cancer. Cell. Signal. 2018, 46, 83–91.
  78. Hamanaka, W.; Motoi, N.; Ishikawa, S.; Ushijima, M.; Inamura, K.; Hatano, S.; Uehara, H.; Okumura, S.; Nakagawa, K.; Nishio, M.; et al. A subset of small cell lung cancer with low neuroendocrine expression and good prognosis: A comparison study of surgical and inoperable cases with biopsy. Hum. Pathol. 2014, 45, 1045–1056.
  79. Nicholson, S.A.; Beasley, M.B.; Brambilla, E.; Hasleton, P.S.; Colby, T.V.; Sheppard, M.N.; Falk, R.; Travis, W.D. Small cell lung carcinoma (SCLC): A clinicopathologic study of 100 cases with surgical specimens. Am. J. Surg. Pathol. 2002, 26, 1184–1197.
  80. Nandeesh, B.; Crasta, J.; Tirumalae, R. Fine-needle aspiration cytology in the diagnosis and typing of lung carcinomas. Clin. Cancer Investig. J. 2015, 4, 637–644.
  81. Roy-Chowdhuri, S.; Aisner, D.L.; Allen, T.C.; Beasley, M.B.; Borczuk, A.; Cagle, P.T.; Capelozzi, V.; Dacic, S.; da Cunha Santos, G.; Hariri, L.P.; et al. Biomarker Testing in Lung Carcinoma Cytology Specimens: A Perspective From Members of the Pulmonary Pathology Society. Arch. Pathol. Lab. Med. 2016, 140, 1267–1272.
  82. Zhao, L.; Guo, M.; Sneige, N.; Gong, Y. Value of PAX8 and WT1 Immunostaining in Confirming the Ovarian Origin of Metastatic Carcinoma in Serous Effusion Specimens. Am. J. Clin. Pathol. 2012, 137, 304–309.
  83. Gong, Y.; Symmans, W.F.; Krishnamurthy, S.; Patel, S.; Sneige, N. Optimal fixation conditions for immunocytochemical analysis of estrogen receptor in cytologic specimens of breast carcinoma. Cancer 2004, 102, 34–40.
  84. Eichhorn, F.; Dienemann, H.; Muley, T.; Warth, A.; Hoffmann, H. Predictors of survival after operation among patients with large cell neuroendocrine carcinoma of the lung. Ann. Thorac. Surg. 2015, 99, 983–989.
  85. Tanaka, Y.; Ogawa, H.; Uchino, K.; Ohbayashi, C.; Maniwa, Y.; Nishio, W.; Nakao, A.; Yoshimura, M. Immunohistochemical studies of pulmonary large cell neuroendocrine carcinoma: A possible association between staining patterns with neuroendocrine markers and tumor response to chemotherapy. J. Thorac. Cardiovasc. Surg. 2013, 145, 839–846.
  86. Xu, X.; Wang, G.; Duan, Y.; Huo, Z. Prognostic value and non-neuroendocrine role of INSM1 in small cell lung cancer. Pathol.-Res. Pract. 2021, 229, 153693.
  87. Minami, K.; Jimbo, N.; Tanaka, Y.; Ogawa, H.; Hokka, D.; Nishio, W.; Yoshimura, M.; Itoh, T.; Maniwa, Y. Insulinoma-associated protein 1 is a prognostic biomarker in pulmonary high-grade neuroendocrine carcinoma. J. Surg. Oncol. 2020, 122, 243–253.
  88. Baine, M.K.; Hsieh, M.S.; Lai, W.V.; Egger, J.V.; Jungbluth, A.A.; Daneshbod, Y.; Beras, A.; Spencer, R.; Lopardo, J.; Bodd, F.; et al. SCLC Subtypes Defined by ASCL1, NEUROD1, POU2F3, and YAP1: A Comprehensive Immunohistochemical and Histopathologic Characterization. J. Thorac. Oncol. 2020, 15, 1823–1835.
  89. McColl, K.; Wildey, G.; Sakre, N.; Lipka, M.B.; Behtaj, M.; Kresak, A.; Chen, Y.; Yang, M.; Velcheti, V.; Fu, P.; et al. Reciprocal expression of INSM1 and YAP1 defines subgroups in small cell lung cancer. Oncotarget 2017, 8, 73745–73756.
  90. Byers, L.A.; Wang, J.; Nilsson, M.B.; Fujimoto, J.; Saintigny, P.; Yordy, J.; Giri, U.; Peyton, M.; Fan, Y.H.; Diao, L.; et al. Proteomic profiling identifies dysregulated pathways in small cell lung cancer and novel therapeutic targets including PARP1. Cancer Discov. 2012, 2, 798–811.
  91. Rudin, C.M.; Poirier, J.T.; Byers, L.A.; Dive, C.; Dowlati, A.; George, J.; Heymach, J.V.; Johnson, J.E.; Lehman, J.M.; MacPherson, D.; et al. Molecular subtypes of small cell lung cancer: A synthesis of human and mouse model data. Nat. Rev. Cancer 2019, 19, 289–297.
  92. Lee, Y.; Joo, J.; Lee, Y.J.; Lee, E.K.; Park, S.; Kim, T.S.; Lee, S.H.; Kim, S.Y.; Wie, G.A.; Park, M.; et al. Randomized phase II study of platinum-based chemotherapy plus controlled diet with or without metformin in patients with advanced non-small cell lung cancer. Lung Cancer 2021, 151, 8–15.
  93. Fan, H.; Bai, S.; Guan, X.; Ma, W.; Fu, Y.; Zhang, X.; Deng, L.; Tian, J. Metformin improves survival in patients with concurrent diabetes and small cell lung cancer: A meta-analysis. Minerva Endocrinol. 2021, in press.
  94. Chun, S.G.; Liao, Z.; Jeter, M.D.; Chang, J.Y.; Lin, S.H.; Komaki, R.U.; Guerrero, T.M.; Mayo, R.C.; Korah, B.M.; Koshy, S.M.; et al. Metabolic Responses to Metformin in Inoperable Early-stage Non-Small Cell Lung Cancer Treated With Stereotactic Radiotherapy: Results of a Randomized Phase II Clinical Trial. Am. J. Clin. Oncol. 2020, 43, 231–235.
  95. Zeng, S.; Gan, H.X.; Xu, J.X.; Liu, J.Y. Metformin improves survival in lung cancer patients with type 2 diabetes mellitus: A meta-analysis. Med. Clin. 2019, 152, 291–297.
  96. Lu, H.; Xie, F.; Huang, Z.; Qin, J.; Han, N.; Mao, W. Effect of metformin in the prognosis of patients with small-cell lung cancer combined with diabetes mellitus. Adv. Clin. Exp. Med. 2018, 27, 1195–1199.
  97. Owonikoko, T.K.; Park, K.; Govindan, R.; Ready, N.; Reck, M.; Peters, S.; Dakhil, S.R.; Navarro, A.; Rodríguez-Cid, J.; Schenker, M.; et al. Nivolumab and Ipilimumab as Maintenance Therapy in Extensive-Disease Small-Cell Lung Cancer: CheckMate 451. J. Clin. Oncol. 2021, 39, 1349–1359.
  98. Iams, W.T.; Porter, J.; Horn, L. Immunotherapeutic approaches for small-cell lung cancer. Nat. Rev. Clin. Oncol. 2020, 17, 300–312.
  99. Takagi, S.; Ishikawa, Y.; Mizutani, A.; Iwasaki, S.; Matsumoto, S.; Kamada, Y.; Nomura, T.; Nakamura, K. LSD1 Inhibitor T-3775440 Inhibits SCLC Cell Proliferation by Disrupting LSD1 Interactions with SNAG Domain Proteins INSM1 and GFI1B. Cancer Res. 2017, 77, 4652–4662.
  100. Norton, J.P.; Augert, A.; Eastwood, E.; Basom, R.; Rudin, C.M.; MacPherson, D. Protein neddylation as a therapeutic target in pulmonary and extrapulmonary small cell carcinomas. Genes Dev. 2021, 35, 870–887.
  101. Chen, C.; Breslin, M.B.; Guidry, J.J.; Lan, M.S. 5′-Iodotubercidin represses insulinoma-associated-1 expression, decreases cAMP levels, and suppresses human neuroblastoma cell growth. J. Biol. Chem. 2019, 294, 5456–5465.
  102. Breslin, M.B.; Zhu, M.; Lan, M.S. NeuroD1/E47 regulates the E-box element of a novel zinc finger transcription factor, IA-1, in developing nervous system. J. Biol. Chem. 2003, 278, 38991–38997.
  103. Tseng, A.W.; Akerstrom, V.; Chen, C.; Breslin, M.B.; Lan, M.S. Detection of neuroendocrine tumors using promoter-specific secreted Gaussia luciferase. Int. J. Oncol. 2016, 48, 173–180.
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license; additional terms may apply. By using this site, you agree to the Terms and Conditions and Privacy Policy.
This entry is offline, you can click here to edit this entry!
Video Production Service
Feedback