Benzinga | Oct 18, 2021 07:04AM EDT

BioXcel Therapeutics Announces Expansion of Phase 2 Trial of BXCL701 in De Novo and Treatment-Emergent Small-Cell Neuroendocrine Prostate Cancer

BioXcel Therapeutics, Inc. (NASDAQ:BTAI), a clinical-stage biopharmaceutical company utilizing artificial intelligence approaches to develop potentially transformative medicines in neuroscience and immuno-oncology, today announced that it has expanded its ongoing Phase 1b/2 trial of BXCL701, the Company's investigational, orally administered innate immune activator, in heavily pre-treated metastatic castration-resistant prostate cancer (mCRPC) patients with either de novo or treatment-emergent small-cell neuroendocrine carcinoma (SCNC). The Company's decision to advance BXCL701 into the second stage of the Phase 2a efficacy portion of the study follows the achievement of the protocol-specified efficacy threshold for cohort expansion, meaning observation of three composite responses.

"There is currently no standard of care for mCRPC patients presenting with the SCNC phenotype," said Vincent J. O'Neill, M.D., Senior Vice President and Chief Medical Officer of BioXcel. "SCNC is a particularly rare and difficult to treat variation of mCRPC. The decision to expand the SCNC cohort builds upon positive interim safety and efficacy data from the adenocarcinoma cohort presented last month at ESMO and moves us into the next stage of the evaluation lifecycle. With three composite responses observed among ten evaluable patients, and what we believe is a manageable side effect profile, we continue to be encouraged by BCXL701's potential to generate an immune response in 'cold' tumor types. We intend to continue recruitment of additional patients for our SCNC cohort, and we look forward to the further evaluation of BXCL701 in this mCRPC patient population, as well as in our adenocarcinoma cohort, which also continues enrollment."

The Phase 1b/2 trial is an open-label, multicenter study to evaluate the safety and efficacy of BXCL701 in combination with pembrolizumab for men with mCRPC presenting with either SCNC or adenocarcinoma phenotypes. Eligibility criteria include progression as defined by PCWG3* criteria and at least one prior line of cytotoxic chemotherapy for inclusion in the SCNC cohort, or one or two androgen signaling inhibitors and at least one line of taxane chemotherapy for inclusion in the adenocarcinoma cohort. mCRPC patients with SCNC received 0.3 mg of BXCL701 twice daily (BID) on days 1 through 14 of a 21-day cycle (0.2 mg BID the first week of Cycle 1) plus 200 mg of pembrolizumab administered intravenously on day 1 and every subsequent 21 days. The primary trial endpoint is a composite response rate, defined as either RECIST 1.1 objective response or PSA50 or CTC count conversion, with a target of achieving >15% response rate. Provided there are at least three composite responses observed in any patient cohort in the first stage of the Phase 2a portion of the study, additional patients may be accrued within that cohort during the second stage, for a total of up to 28 patients. Secondary endpoints include duration of response, progression-free survival, and overall survival. As of October 18, three of ten SCNC evaluable patients achieved composite response, satisfying the protocol-specified threshold for continued expansion.

*Prostate Cancer Working Group 3 (PCWG3) is an international working group of clinical and translational experts in prostate cancer who issued Consensus Guidelines on key principles of trial conduct for trials in castration-resistant prostate cancer