(UroToday.com) The 2024 American Society of Clinical Oncology Genitourinary (ASCO GU) cancers symposium held in San Francisco, CA between January 25th and 27th was host to a prostate cancer poster session. Dr. Christos Kyriakopoulos presented the phase 1 results and phase 2 study design of a phase 1/2 trial evaluating the combination of oral EPI-7386 (masofaniten) plus enzalutamide versus enzalutamide alone in patients with metastatic castration-resistant prostate cancer (mCRPC).
EPI-7386 is an aniten, a class of compounds that inhibit androgen receptor activity by binding to the N-terminal domain, irrespective of resistance abrogation in the ligand binding domain that render androgen receptor pathway inhibitors (ARPIs) ineffective. Preclinical data supports disruption of androgen receptor regulated gene transcription even in the presence of resistance mechanisms, including ligand-binding domain point mutations and truncated splice variants. Preclinical RNAseq and CHIPseq data suggest that the combination of EPI-7386 plus enzalutamide results in a deep blockade of the androgen receptor pathway with greater antitumor activity compared to enzalutamide alone.
This is a phase 1/2 multicenter clinical trial (NCT05075577) evaluating the combination of EPI-7386 plus enzalutamide in mCRPC patients on ADT, but naïve to prior ARPIs (one line of prior chemotherapy in the metastatic hormone-sensitive setting was allowed). The phase 1 portion examined escalating doses of masofaniten + enzalutamide at 120 or 160 mg once daily doses. The primary and secondary endpoints of the phase 1 portion are to evaluate the safety and pharmacokinetics of masofaniten + enzalutamide when co-administered, and to establish the recommended phase 2 combination dose (RP2D). The phase 2 portion was designed as a two arm, 2:1 randomized, open-label trial evaluating the anti-tumor activity of masofaniten in combination with enzalutamide versus enzalutamide alone. Approximately 120 patients were planned for randomization to masofaniten 600 mg twice daily + enzalutamide 160 mg once daily (n=80) versus single agent enzalutamide at 160 mg once daily (n = 40).
Phase 1 completed enrollment with 18 patients in four cohorts, with 16 patients evaluable for efficacy, as per protocol. The combination regimen was well-tolerated with a safety profile consistent with enzalutamide monotherapy. One grade 3 rash was observed in cohort 4 evaluating masofaniten 600 mg twice daily + enzalutamide 160 mg once daily.
Pharmacokinetics results demonstrated enzalutamide exposure was not impacted by concomitant administration of masofaniten, allowing testing of the full dose of enzalutamide (160 mg). In contrast, masofaniten exposure was consistently reduced by concomitant administration of enzalutamide, which is a known CYP3A4 inducer that metabolizes masofaniten; however, the masofaniten levels remained within the clinically relevant range with the highest exposures and Cmin observed using masofaniten twice daily dosing.
While efficacy data remain immature, the following outcomes have been observed:
- PSA50: 14/16 (88%)
- PSA90: 13/16 (81%)
- PSA <0.2: 9/16 (56%)
Based on the available results, Dr. Kyriakopoulos concluded that the recommended phase 2 combination dose for the phase 2 portion was established at masofaniten 600 mg twice daily plus enzalutamide 160 mg once daily. Updated results, including long term follow-up of the dose escalation patients, and phase 2 study design, will be presented.
Presented by: Christos Kyriakopoulos, MD, Associate Professor, Division of Hematology, Medical Oncology, and Palliative Care, University of Wisconsin-Madison Carbone Cancer Center, Seattle, WA
Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2024 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, San Francisco, CA, January 25th – January 27th, 2024
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