Essa Pharma presents updated Phase 1 Masofaniten clinical data

Essa Pharma announced the presentation of updated dose escalation data from its Phase 1/2 study evaluating masofaniten in combination with enzalutamide at the European Society of Medical Oncology 2023 Congress, taking place October 20-24, 2023, in Madrid, Spain. Masofaniten is a first-in-class N-terminal domain androgen receptor inhibitor that suppresses androgen activity through a novel mechanism of action and is being developed for the treatment of prostate cancer. This Phase 1/2 multicenter, open-label clinical trial is enrolling patients with mCRPC who have received androgen deprivation therapy and who are naive to second-generation antiandrogens but may have been treated previously with one line of prior chemotherapy in the metastatic hormone-sensitive prostate cancer setting. The data presented today are from the first four cohorts of patients in the Phase 1 dose escalation portion of the study. Masofaniten has no effect on enzalutamide exposure, thus allowing the use of full dose per label of enzalutamide in combination. Enzalutamide reduces masofaniten exposure but twice daily dosing of masofaniten appears to mitigate the reduction and maintains clinically relevant drug exposures. In patients evaluable for safety, masofaniten combined with enzalutamide, continues to be well-tolerated at the doses tested through 21 cycles of dosing in some patients. Most frequent adverse events were Grade 1 and 2, related to either AR inhibition or gastrointestinal tract irritation. In Cohort 4, one patient experienced a Grade 3 rash, which was observed immediately following administration of masofaniten combined with enzalutamide and deemed probably related. In the patients evaluable for efficacy, rapid, deep and durable reductions in PSA were observed, regardless of previous chemotherapy status, including in patients who received lower than the full dose of enzalutamide. In the first three cohorts, 90% of patients achieved PSA50 and PSA90, 80% of patients achieved PSA90 in less than 90 days, and 70% of patients achieved PSA less than0.2mg/mL. Across all dose cohorts including patients in the recently enrolled cohort four, 88% of patients achieved PSA50, 69% of patients achieved PSA90, 63% of patients achieved PSA90 in less than 90 days, and 56% of patients achieved PSA less than0.2mg/mL. The randomized Phase 2 dose expansion portion of the study is currently enrolling.