Phase II Trial of Opaganib Addition in Metastatic Castration‐Resistant Prostate Cancer After Disease Progression on Abiraterone or Enzalutamide

INTRODUCTION: Opaganib is a first-in-class oral sphingolipid metabolism inhibitor that inhibits sphingosinekinase 2 (SphK2) and dihydroceramide desaturase (DES) and that has a demonstrated safety and preliminary anti-cancer activity signal in a Phase I study. METHODS: In this phase II trial, patients with metastatic castration-resistant prostate cancer who had disease progression on novel hormonal agents (NHAs) abiraterone or enzalutamide were enrolled and treated with opaganib while continuing their NHA. After safety lead-in cohorts, the trial enrolled cohort 2 (abiraterone + opaganib 500 mg Q 12 h) and cohort 3 (enzalutamide + opaganib 500 mg Q 12 h). The primary efficacy endpoint was the proportion of patients with disease control at Day 113. The postulated disease control rate was 10%. Secondary efficacy endpoints include prostate-specific antigen (PSA) progression-free survival (PSA-PFS) and PSA response rates. The primary safety endpoint was the incidence of adverse events (AEs). RESULTS: The disease control rates were 15% (95% CI = 4%-35%, 4 of 26 patients) in cohort 2 and 9% (95% CI = 2%-24%, 3 of 34 patients) in cohort 3. The median PSA-PFS was 56 days (95% CI = 35-112 days) in cohort 2 and 55 days (95% CI = 35-56 days) in cohort 3. The most common AEs of grade 3 or higher were hypertension (8%) and musculoskeletal AEs (8%) in cohort 2 and grade 3 anemia (18%) in cohort 3. CONCLUSION: The trial did not meet its primary objective of demonstrating 30% disease control at 113 days. However, subjects who experienced a PSA response or stabilization warrant further exploration for biomarkers of response. TRIAL REGISTRATION: ClinicalTrials.gov number: NCT04207255.