Dostarlimab in Cancer Treatment: Comparison
Please note this is a comparison between Version 2 by Jason Zhu and Version 1 by Prashant Kesharwani.

Immunotherapy is one of the four pillars of cancer treatment that has emerged as a beacon of hope for cancer patients. Certain immunotherapies, for example, immune checkpoint inhibitor therapy, monoclonal antibody therapy and chimeric antigen T-cell therapy have garnered extensive interest in response to their exceptional properties that activate the immune system to respond to cancer cells, inhibiting their progression. In the era of rapid development, dostarlimab, an anti-programmed cell death protein (PD-1) monoclonal antibody has mesmerized the medical profession by showing complete (100%) cure of patients with colorectal cancer. Not only this, the results obtained from clinical trials revealed no major side effects in any of the participants in the study. Dostarlimab has also shown promising results in endometrial cancer, ovarian cancer, melanoma, head and neck cancer, and breast cancer therapy. 

  • immunotherapy
  • clinical trial
  • dostarlimab

1. Dostarilimab and Mechanism of Action

Dostarlimab (Jemperli™) or dostarlimab-gxly is a humanized mAB which acts as an antagonist for programmed death-1 (PD-1) receptors. It is being developed by GlaxoSmithKline (GSK) under a license from AnaptysBio Inc for the treatment of several forms of cancer including endometrial cancer, colorectal cancer, ovarian cancer, cancer of the head and neck, small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), squamous cell cancer (SCC), fallopian tube cancer, pancreatic cancer, and many more. According to preliminary findings from the GARNET trial, dostarlimab has recently been approved (22 April 2021) for adults with advanced or recurrent advanced mismatch repair-deficient endometrial cancer (dMMR) in the EU and USA. The dose of dostarlimab that is generally recommended is 500 mg every 3 weeks (for the first four doses), after the fourth dose, 1000 mg every 6 weeks is administered until disease progression or any unacceptable toxicity is noticed [26,27,28][1][2][3].
PD1 is an immune checkpoint receptor found in T-cells that suppresses cancer-specific immune responses. The humanized IgG4 mAB, dostarlimab, is derived from a Chinese hamster ovary cell and has a molecular weight of approx 144 kDa. A binding between the PD-1 ligands (PD-L1 and PD-L2) and the PD-1 receptor on T-cells inhibits cytokine and T-cell proliferation. In some tumors, PD-1 ligands are upregulated, and signaling through this pathway may contribute to the suppression of active T-cell immunity. This is where the drug dostarlimab comes into the picture. It inhibits programmed cell death receptor-1 (PD-1) and blocks the interaction of receptors with PD-L1 and PD-L2, which in turn activates T-cells and enhances overall immunity. Studies have depicted that dostarlimab binds with PD-1 receptors of both humans and cynomolgus monkeys with high affinity, as seen from the results obtained in flow cytometry and plasmon resonance. Moreover, a human CD4+ mixed lymphocyte reaction assay showed that dostarlimab worked as a functional antagonist, resulting in increased IL-2 production. This assay also showed the enhanced activity of dostarlimab when TIM3 antibodies or LAG3 antibodies were present. In the presence of antibodies, dostarlimab exhibited increased activity, but no significant cytokine release was observed from human PBMCs (peripheral blood mononuclear cells) [29][4].
A pharmacokinetic study for dostarlimab-gxly was performed on patients with solid tumors which included 150 endometrial cancer patients. It was noted that there was a proportionate increase in mean Cmax, AUC0−inf and AUC0−τ over the dose range of 1.0–10 mg/kg. Moreover, the mean cycles of Cmax and AUC0−τ after the administration of 500 mg dostarlimab once every 3 weeks was reported to be in the range of 171 µg/mL and 35,730 µg∙h/mL, respectively, and 309 µg/mL and 95,820 µg∙h/mL, respectively, at a dose of 1000 mg administered once every 6 weeks. Similarly, the study also evidenced the mean steady-state volume of the distribution of dostarlimab to be around 5.3 L, and the mean steady-state clearance to be in the range of 0.007 L/h. There were no clinically significant differences observed in the pharmacokinetics characteristics of dostarlimab based on gender, age, ethnicity, tumor type, or renal or hepatic impairment. Although, there are no studies conducted to determine whether dostarlimab-gxly is carcinogenic or genotoxic. Fertility studies have been performed for this drug on monkeys which, after repeating doses for one and three months, found no significant effects on male or female reproductive organs, although most animals in these studies were not sexually mature by the time of study [30][5].
The first-in-human study, 4010-01-001, otherwise known as the GARNET trial (NCT02715284), evaluated dostarlimab pharmacokinetics (PK), pharmacodynamics (PD), tolerability, clinical activity and safety across multiple solid cancer types, which included endometrial, NSCL and cancer of the ovaries and fallopian tubes. A modified 3 + 3 design was used to evaluate three weight-based doses (1, 3 and 10 mg/kg) administered every 2 weeks intravenously in Part 1. Part 2A used two fixed-dose regimens, 500 mg every 3 weeks intravenously, and 1000 mg every 6 weeks intravenously was administered in in Part 2B. Data from Part 1 demonstrated a maximum receptor occupancy at 2.4 g/mL dostarlimab serum concentrations. Furthermore, a PK model was constructed using the PK data from Part 1 to predict dostarlimab concentrations that would exceed those leading to maximal receptor occupancy at fixed doses. Similarly, Part 2A demonstrated dose-proportional PK and the median serum trough concentrations to be approximately 40 and 50 ng/mL after a single dose of 500 mg and 1000 mg, respectively [31][6].

2. Ongoing Clinical Trials for Dostarlimab

June 2022 saw a revolutionary discovery in the field of cancer treatment. For the very first time in science, a drug under clinical trial showed the complete eradication of a tumor with no reoccurrence. The mAB-based drug dostarlimab was evaluated for safety under efficacy against locally advanced rectal cancer [32][7].
Primary locally advanced rectal cancer is also known as stage III rectal cancer and is also indicative of resectable tumors with the involvement of lymph nodes. These tumors are characterized for invading and extending close to the mesorectal fascia. These types of colorectal cancer are generally treated with aggressive chemoradiation, short course radiotherapy, and total mesorectal surgery (TME) surgery. The results from this collective therapy are positive, showing excellent survival rates and low reoccurrence. Moreover, in some cases with locally advanced tumors, a complete removal of the tumor is the most preferred and beneficial option for control and survival [33][8].
As stated above, the standard method of treatment of locally advanced rectal cancer is radiation and neo-adjuvant chemotherapy followed by the surgical removal of the rectum. Additionally, it has also been noted that the cause of some rectal cancers is a lack of mismatch repair. In the context of metastatic disease, mismatch repair-deficient colorectal cancer responds to the programmed death 1 (PD-1) blockade, thus suggesting that a checkpoint blockade may be effective in mismatch repair-deficient patients. Scientists in partnership with GSK initiated a prospective phase 2 study in patients with stage II or III rectal adenocarcinomas who were mismatch repair-deficient. They were administered with single-agent anti-PD-1 mAB dostarlimab every 3 weeks for 6 months. Although this treatment is supposed to be followed with standard surgery and chemoradiotherapy, the patients who depict a clinically complete response following dostarlimab therapy would not undergo chemotherapy, radiotherapy, or surgery. This is also the primary endpoint for the study. Interim results were obtained from the study completed on a total of 12 patients that had successfully completed treatment with dostarlimab and had also undergone a minimum of 6 months’ follow-up. It was evidenced that all 12 patients (100%; 95% confidence interval, 74 to 100) had a complete clinical response and no form of existing tumor, progression and recurrence was noticed in 18F-fluorodeoxyglucose–positron-emission tomography, magnetic resonance imaging, biopsy, digital rectal examination, or endoscopic evaluation. Moreover, no adverse events of grade 3 or higher were reported. The study clearly depicted that a single agent PD1 was highly sensitive to mismatch repair-deficient, locally advanced rectal cancer and could bring about positive results; however, a longer follow-up study still needs to be performed to validate this point [34,35][9][10].
Dostarlimab was evaluated in a phase 1 nonrandomized clinical trial for patients with deficient mismatch repair endometrial cancer to assess antitumor activity and safety. Part 1 of this ongoing open-label, multicenter single group study began on 7 March 2016, and enrollment for patients with deficient mismatch mutation repair endometrial cancer began on 8 May 2017. Around 104 women with deficient mismatch mutation repair endometrial cancer were enrolled and each patient received intravenous dostarlimab 500 mg every three weeks for four doses, then 1000 mg every six weeks until disease progression, treatment discontinuation or withdrawal occurred. Specifically, the objective of this study was to evaluate the antitumor activity of dostarlimab on recurrent or advanced dMMR (mismatch repair deficiency) endometrial cancer (EC) patients, using the objective response rate (ORR) which was defined by blinded independent central review (BICR) using Response Evaluation Criteria in Solid Tumors (RECIST) guidelines. A similar concept is the duration of response (DOR), defined as the time from the first documented evidence of complete or partial response to the first documented evidence of disease progression or death, whichever occurs first. Following the first dose of dostarlimab administration, radiographic evaluations were performed 12 weeks after the first dose, every 6 weeks (±10 days) until month 12, and then every 12 weeks thereafter.
The results obtained from this analysis on patients with recurrent or advanced dMMR EC who had progressed after platinum-based chemotherapy and dostarlimab monotherapy were associated with an ORR of 42.3% (95% CI, 30.6–54.6%) in almost 30 patients, 29.6% in around 21 patients, and around 12.7% in 9 patients. The responses were durable, and the median DOR was not reached at 11.2 months in the follow-up period. The safety profile depicted by dostarlimab was manageable and comparable to that of other anti-PD-1 antibodies. Additionally, treatment-related adverse events (TRAEs) accounted for less than 2% of patients discontinuing treatment, and there were no treatment-related deaths. To the best of ocurrent knowledge, these results are the largest set of data to date on dMMR EC treated with a PD-1 inhibitor [31,36][6][11].
Although cross-trial comparisons cannot be performed, it is generally noted that the response rates with anti-PD-1 therapies appear to be more favorable, as evidenced from the ORR range offered by single-agent therapies that ranged from 13.5% (90% CI, 6.5–27.5%) for bevacizumab to 21–27.3% (95% CI, 15–42.8%) for paclitaxel before the introduction of anti-PD-1 therapies. Although the GARNET trial was a single-group study, the antitumor activity observed in patients with dMMR EC was promising, suggesting that dostarlimab might have a role to play in the treatment of patients with dMMR EC. Dostarlimab demonstrated high ORR and a longer duration of response, reflecting its high potential against cancer. Furthermore, one year after inclusion in the GARNET trial, 74% of patients in the dMMR EC population are still alive. In addition to these wide actions of dostarlimab, a unique characteristic of this drug is its dosing regimen. Patients and caregivers both benefit from this unique dosing schedule after 12 weeks of initial treatment with dostarlimab, which may result in less frequent clinic visits and possibly lower healthcare costs. Altogether, the data from the GARNET study has demonstrated durable anticancer action not in only patients with (MMR-proficient) MMRp and dMMR endometrial cancers, but also for non-EC dMMR solid tumors. According to the GARNET trial data, dostarlimab monotherapy was accelerated for approval in the US as a treatment for recurrent/advanced dMMR solid tumors, following the progressive results obtained from prior treatment. Additionally, it has been approved in both Europe (conditional) and the USA (accelerated) for dMMR/MSI-H and dMMR endometrial cancer, respectively, during and after platinum-based chemotherapy [37,38,39][12][13][14]. Another trial similar to it was conducted for evaluating anti-PD-1/PD-L1 axis therapy for patients suffering from inoperable endometrial cancer. This ongoing study is being performed to establish the safety and efficacy of the drug and its generated antitumor immune response [40][15].
In the past few years, scientists have also tried exploring the potential of dostarlimab against locally advanced cervical cancer (LACC). They hypothesize that the use of dostarlimab as a consolidation therapy following chemotherapy might enhance progression-free survival rate in patients. Based on this rationale, a randomized, phase II, open-label study was set as maintenance therapy for patients with a high risk of LACC. This ongoing study is a randomized study that began in 28 June 2019, and included around 132 participants. Interim data and hence the results for this study are yet to be reported [41,42][16][17].
Lung cancer is another cancer that is accountable for the most cancer-related deaths worldwide. Amongst the type of lung cancer, almost 85% belong to the category of non-small cell lung cancer (NSCLC), for which the primary option for treatment is chemotherapy. In recent years, the introduction of immune checkpoint inhibitors has revolutionized the process of cancer treatment.
In a recent trial, the safety and antitumor activity of dostarlimab were studied in a first-in-human, phase 1, multi-center, open-label, two-part study GARNET cohort of 67 patients with recurrent or advanced NSCLC who had previously been treated with platinum-based chemotherapy. While Part 1 of the study was a dose escalation study and involved the evaluation of pharmacodynamics and pharmacokinetic characteristics of the drug at different doses of 1,3 and 10 mg/kg, Part 2, on the other hand, was conducted in two different subparts: Part 2A evaluated the dose safety and Part 2B dealt with evaluating the clinical efficacy of the drug. Immuno-related objective response rate (irORR) and safety were used as the primary endpoint to determine dostarlimab’s antitumor activity in patients with recurrent or advanced NSCLC. An irORR was defined as the proportion of patients achieving immune-related complete response (irCR) or immune-related partial response (irPR) based on the investigators’ assessment per immune-related RECIST (irRECIST). Monotherapy with dostarlimab produced strong antitumor activity and durable responses across all PD-L1 Tumor Proportion Score (TPS) status subgroups. It was noted that, in NSCLC, the safety profile of dostarlimab was acceptable, with low to a manageable toxicity, and was consistent with that of the other agents that block PD-L1. In the entire study, four patients, i.e., almost 6%, discontinued the study due to treatment-related TEAEs (treatment-emergent adverse effects) (TRAEs), and two deaths were caused because of treatment-emergent adverse effects (TEAEs) which were not considered related to treatment with dostarlimab.

3. Dostarlimab and Other Combination Therapies under Trial

There are several other immune check point inhibitors such as nivolumab, pembrolizumab, atezolizumab, durvalumab, and avelumab that are utilized for cancer treatment. Since dostarlimab is a mAB and not a drug transporter substrate or a cytokine modulator, it is unlikely to show any interactions between other drugs. However, a comparison of dostarlimab based on its pharmacodynamic and pharmacokinetic properties must be conducted with other such immune checkpoint inhibitor-based therapies to obtain a clear and optimal understanding. Dostarlimab, similar to nivolumab and pembrolizumab, specifically targets anti-PD-1 receptors, while atezolizumab, durvalumab and avelumab not only act through anti-PD-1 receptors but also block interaction with the PD-1 and B7.1 receptors. Similarly, the mean peak occupancy for dostarlimab is approx. ~90% and around 85% (70–97%) for nivolumab. The cumulative dose has also been recorded for these drugs: approximately 2-fold for dostarlimab, 3.7-fold for nivolumab, 2.2-fold for pembrolizumab, around 1.91-fold for atezolizumab, and 4.3-fold and 1.25-fold for durvalumab and avelumab, respectively. The three-week dosing schedule is similar for pembrolizumab and nivolumab dose schedules, and ensures the closer monitoring of patients as they begin a new treatment. A dose of 500 mg IV every 3 weeks, then 1000 mg IV every 6 weeks is generally administered as a safety regimen for dostarlimab, while this is 240 mg IV every 2 weeks and 200 mg IV every 3 weeks for nivolumab and pembrolizumab, respectively. Similarly, atezolizumab’s administered dose is 1200 mg or 15 mg/kg IV every 3 weeks; for durvalumab, this is 1500 mg IV every 4 weeks and for ICI avelumab this is 10 mg/kg IV every 2 weeks.
Dostarlimab is also being studied for its activity with one or more chemotherapeutic drugs, including niraparib, pembrolizumab, bevacizumab, cobolimab, and many more. Most of these studies conducted for different cancer types are still under trial. The data below covers some of such ongoing studies.
A combination study investigated the PARPi drug niraparib and anti-PD-1 mAB dostarlimab administered in patients with advanced head and neck squamous cell carcinoma (HNSCC). Niraparib is a type of targeted therapy that inhibits poly adenosine diphosphate-ribose polymerase (PARP), which is an enzyme that repairs DNA in times when it gets damaged. Blocking these PARP might prevent DNA repair in cancerous cells, causing them to die. This phase II trial involving 49 patients was initiated on February 8, 2021 [48][18]. Researchers hypothesize that combinatory immunotherapy might lead to a reduction in loco-regional recurrence (LRR) and distant metastasis (DM) rates in patients under high risk of HNSCC [49][19]. Similarly, a phase III trial was designed to study the effect of dostarlimab and niraparib for studying their effects in treating small cell lung cancer and other high-risk neuroendocrine carcinomas. This single-group open-label trial began on February 1, 2021, with an estimated enrollment of 48 patients [50][20]. Different phase II trials for this combination therapy (dostarlimab and niraparib) are currently being performed for patients with germline or somatic BRCA1/2- and PALB2-mutated pancreatic cancer [51][21], for breast cancer in patients with BRCA mutations [52][22], pediatric solid tumors [53][23], mesothelium NSCLC [54[24][25],55], and pancreatic [56][26], endometrium [57,58][27][28] and ovarian cancer [59,60][29][30].


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