Cervical cancer has become a major health concern due to the rise in mortality and morbidity around the world [2,3]. This rise, particularly in developing countries, is attributed to poor screening and vaccination programmes against HPV [3,5,6]. This disease is considered more aggressive and has a relatively worse prognosis [3,4]. Owing to the lack of targeted therapies, the clinical management of cervical cancer is challenging and remains difficult. As a result, there is an important need to find novel biomarkers and drug targets that can improve cervical cancer clinical management. While considered an interesting area of study, new and existing research opportunities emerge to unveil novel aspects of CYP4Z1 in cancer development and therapy. Our recent initial screening has identified overexpression of CYP4Z1 in a small number of tumour samples for each type of human tumour including cervical cancer [11]. Therefore, the implications of this observation have been taken to fully characterise the CYP4Z1 expression in a large cohort of cervical cancers.

As the current study was the first investigating the CYP4Z1 expression in cervical cancers, we found that 55% of the tumours expressed CYP4Z1, where the expression in each tumour sample was specifically confined to tumour cells. Normal cervix tissues showed no CYP4Z1 expression at all. The high frequency of CYP4Z1 expression in cervical cancer is consistent with the findings of our earlier initial screening [11]. Moreover, our results agree with CYP4Z1 transcription profiling in cervical cancers shown by the Human Protein Atlas. Low to high CYP4Z1 mRNA levels were identified in cervical cancers compared to normal cervix tissues [24]. Importantly, this CYP4Z1 differential expression between normal tissues and tumour tissues was significantly observed in many studies. In these studies, CYP4Z1 was expressed at much higher levels in cancers of the breast, ovary, and prostate than in their corresponding normal tissues [8,10,11]. Moreover, we recently identified a similar fashion of CYP4Z1 differential expression in bladder [14] and colon cancers (data not published).

The role of the CYP4Z1 enzyme as a prognostic marker in cervical cancer was assessed in this study. This was the first study indicating a significant correlation between CYP4Z1 expression and cervical cancer patients’ survival. CYP4Z1 expression was associated with poor survival rate and identified as an independent factor for poor prognosis in cervical cancer patients, along with tumour stage. These findings are in agreement with previous studies identifying CYP4Z1 as a prognostic marker for ovarian and prostate cancers [12,13]. Further significant associations were found between CYP4Z1 expression and tumour invasion and lymph node metastasis. These findings demonstrate the possible role of the CYP4Z1 enzyme in the progression and malignancy of cervical cancer.

As few functional studies have interrogated the role of CYP4Z1 in cancer development particularly breast cancer [16,19,20,25], mechanisms behind functions of CYP4Z1 in cervical cancer progression are still unknown. By using in vitro and in vivo models, CYP4Z1 overexpression was found to promote breast cancer-cell invasion, migration, proliferation, and tumour angiogenesis [16,19,20]. This was particularly triggered by activation of ERK1/2 and PI3K/Akt signalling pathways through increased expression of vascular endothelial growth factor-A (VEGF-A) and decreased production of the tissue inhibitor of metalloproteinase-2. It is important to note that all of these changes were biochemically associated with increased production of 20-HETE and 14,15-EET [19,22]. Such CYP4Z1 enzymatic activity of metabolising arachidonic acid to either 20-HETE or 14,15-EET was reported by many studies [21,22]. Importantly, the 20-HETE was shown in many studies to work in conjugation with VEGF, enhancing tumour angiogenesis, growth, and metastasis [26,27]. Beside VEGF, 20-HETE was shown to be involved in activation of the PI3K/Akt- and mitogen-activated protein kinase (MAPK) pathways necessary for proliferation and survival of cancer cells [28]. Regarding 14,15-EET, it was reported that 14,15-EET promoted tumour angiogenesis by stimulating tyrosine-protein kinase (Src) and activated transcription-3 (STAT-3)-dependent production of VEGF [29]. Moreover, 14,15-EET was found to partly regulate the pro-tumourigenic pathways of PI3K/Akt, MAPK, and VEGF [22,30,31]. The activation of these signalling pathways in HPV-induced cervical cancers wwas reported by numerous studies [32,33,34]. Further analysis of the mechanistic role of CYP4Z1 in the tumourigenesis process showed that synergic expression of pseudogene CYP4Z2P and CYP4Z1-3’UTRs enhanced tumour neovascularization in breast cancer partly through activating pathways of PI3K/Akt and ERK1/2 [20]. Moreover, overexpression of CYP4Z1 and/or CYP4Z2P in breast cancer cells may promote transcriptional activity of oestrogen receptors, stemness, and tamoxifen resistance [25]. Taken as a whole, these findings may provide a plausible mechanism for CYP4Z1-driven tumour development. However, the link between the CYP4Z1 enzyme and cervical cancer development remains elusive.

Knowledge in the field of the CYP4Z1 enzyme’s substrate recognition and catalytic properties is now quite valuable in the design and development of more selective cancer therapies. A limited number of reports explored the substrate-binding mode of CYP4Z1 [35,36,37,38]. Several key amino acid residues have been identified for substrate binding of CYP4Z1 including Arg487, Asn381, Ser383, Ser222, Ser113, and Asn381 [35,36]. Recently, luciferin benzyl ether was identified as the best luminogenic substrate for CYP4Z1 using the permeabilised cells of fission yeast expressing CYP4Z1 [36]. These recent advances in determining the CYP4Z1 enzyme’s substrate recognition have led to the development of selective inhibitors for CYP4Z1. The first inhibitor identified was 1-benzylimidazole, which showed efficient blocking ability for production of 14, 15-EET in CYP4Z1 positive tumour cells relative to a poor inhibitory profile against other CYPs [38]. Interestingly, a new highly potent inhibitor (Compound 9) for CYP4Z1 was developed using systematic virtual screening. This novel inhibitor showed selective binding and high nanomolar affinity to CYP4Z1 [37]. These latest advances may accelerate the development of CYP4Z1 targeted therapies.

The future of cancer therapy relies mainly on the use of biomarkers that guide clinicians in each step of cancer management. For this purpose, there is an increasing interest in discovery and development of novel biomarkers that help in cancer diagnosis, prognosis, and monitoring treatment response [39]. For cancer diagnosis, biomarkers can be used for cancer risk assessment, early detection of cancer, and accurate staging of disease. For instance, analysis of differentially expressed protein in discrimination between normal and cancer tissues [40]. Regarding cancer prognosis, biomarkers help in estimating the course of cancer disease and therefore the most suitable management strategy. Moreover, biomarkers can also be used for predicting the response of patients to various treatment strategies [41]. In this case, for example, the biomarker expression levels generally reflected the extent of cancer burden, therefore, high levels of biomarker mostly indicated poor prognosis and sometimes the opposite. As it reflected the cancer burden, biomarkers could also be used in the cancer staging system [40]. Overall, the discovery of novel biomarkers probably CYP4Z1 may hold promise for cervical cancer management.