FDA Fast Tracks Novel Treatment for Metastatic Small Cell Neuroendocrine Prostate Cancer

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The FDA has granted Fast Track designation to BioXcel Therapeutics, Inc’s investigational therapy combined with an immune checkpoint inhibitor to treat patients with metastatic small cell neuroendocrine prostate cancer (SCNC) whose disease progressed on chemotherapy and who show no evidence of microsatellite instability. The novel agent, BXCL701, is an oral innate immune activator that was developed to produce inflammation within the tumor microenvironment. Doing so increases the detectability of tumors by the adaptive immune system, which leads to a strong anticancer immune response, according to investigators.¹

“SCNC is characterized by poor prognosis and a low survival rate, and current treatment options are suboptimal,” said Vincent J. O’Neill, MD, BioXcel Therapeutics executive vice president and chief of Product Development and Medical Officer, in a press release. “We are encouraged by the potential of BXCL701, which has demonstrated clinical proof of concept in both SCNC and adenocarcinoma. Following the positive survival results from our Phase II trial that we reported at the end of last year, we look forward to further discussing the registration path at an upcoming meeting with the FDA.”¹

An open-label, single-arm, multicenter, Phase II trial (NCT03910660) is currently analyzing BXCL701 combined with Keytruda (pembrolizumab) to treat patients with metastatic castration-resistant prostate cancer (mCRPC) with SCNC and adenocarcinoma phenotypes.

Patients with the SCNC phenotype were administered BXCL701 twice daily at a dose of 0.2 mg from days one to seven, then 0.3 mg from days seven to 14 for the first 21-day cycle, followed by 0.3 mg afterwards, with 200 mg of intravenous Keytruda administered with BXCL701 on the first day of each cycle.²

The trial’s primary endpoint is composite response rate quantified by objective response per RECIST v1.1 criteria and/or a decrease in prostate-specific antigen of at least 50% (PSA50) and/or circulating tumor count conversion. The trial’s secondary endpoints included overall survival (OS), progression-free survival, duration of response, and biomarker assessment defined by changes in circulating cytokines and the correlation of outcomes with baseline tumor characteristics.²

Among patients with SCNC (n = 28), median OS was 13.6 months and the 12-month OS rate was 56.5%. As of the data cutoff of September 6, 2023, patients with the adenocarcinoma phenotypes who were administered the combination achieved a median OS of 15.5 months with a 12-month OS rate of 59% among 29 evaluable patients.^2,3

In terms of safety, the most commonly reported adverse effects (AEs) included fatigue (32%), hypotension (21%), pruritus (21%), dizziness (18%), and nausea (12%), with 41% of patients reporting any-grade immune-related AEs, of whom 7% reported grade three or higher AEs.

Eighteen percent of patients were forced to discontinue treatment because of an AE, of which 18% were associated with BXCL701 and 15% were associated with Keytruda, according to the investigators.

“The FDA’s fast track designation for the investigation of BXCL701 in SCNC is an important recognition of our most advanced immuno-oncology asset and an acknowledgment of its potential to address the considerable unmet medical need in these patients,” said BioXcel Therapeutics CEO Vimal Mehta, PhD, said in a press release. “At the same time, it further validates the unique AI-based drug re-innovation approach that we used to discover this asset. BXCL701 has already demonstrated considerable potential in our clinical trials to date, and we plan to further define its development path while exploring strategic options for our OnkosXcel Therapeutics subsidiary.”¹

References

1. BioXcel Therapeutics receives FDA fast track designation for BXCL701 for treatment of small cell neuroendocrine prostate cancer (SCNC). News release. BioXcel Therapeutics. February 12, 2024. Accessed February 13, 2024. https://www.biospace.com/article/releases/bioxcel-therapeutics-receives-fda-fast-track-designation-for-bxcl701-for-treatment-of-small-cell-neuroendocrine-prostate-cancer-scnc-/?keywords=cancer

2. BioXcel Therapeutics reports positive overall survival results from single-arm, open-label phase 2 trial of BXCL701 in patients with small cell neuroendocrine prostate cancer. News release. BioXcel Therapeutics. October 10, 2023. Accessed February 13, 2024. https://ir.bioxceltherapeutics.com/news-releases/news-release-details/bioxcel-therapeutics-reports-positive-overall-survival-results

3. BioXcel Therapeutics reports positive overall survival results from single-arm, open-label phase 2 trial of BXCL701 in patients with metastatic castration-resistant prostate cancer (mCRPC) of adenocarcinoma phenotype. BioXcel Therapeutics, Inc. News release. November 8, 2023. Accessed February 13, 2024. https://www.globenewswire.com/news-release/2023/11/08/2776064/0/en/BioXcel-Therapeutics-Reports-Positive-Overall-Survival-Results-from-Single-Arm-Open-Label-Phase-2-Trial-of-BXCL701-in-Patients-with-Metastatic-Castration-Resistant-Prostate-Cancer-.html