A phase I dose escalation study of PCUR-101 in men with metastatic castration-resistant prostate cancer (mCRPC)

e16517 Background: The combination of PCUR-101 (a synthetic form of the plant-derived medicinal agent, plumbagin) and surgical castration caused regression of androgen dependent tumors in mice. These promising pre-clinical results led to this first-in-human study of PCUR-101 in combination with androgen deprivation therapy (ADT) in men with metastatic, castrate resistant PCa (mCRPC). Methods: The goal of this phase I multicenter trial was to determine the safety profile, maximum tolerated dose (MTD), recommended phase II dose, clinical activity, and pharmacokinetic (PK) parameters of PCUR-101. A 3 + 3 dose escalation design was employed. Patients (pts) in cohorts of 3 were treated with escalating doses of PCUR-101 (50 mg – 200 mg) orally once daily continuously. Cycles were 28 days. Exploratory correlates of IL-6 and urine polyamines were also included. Results: 12 pts (median age 75 [range 63-86]) with mCRPC on ADT were treated in the dose escalation cohorts. No DLTs were observed during treatment and the MTD was not reached. The most frequent adverse events (AEs) included diarrhea (11 pts; all grade 1 or 2), nausea (7 pts; all grade 1 or 2), vomiting (4 pts; all grade 1 or 2) and constipation (3 pts; all grade 1 or 2). No objective responses were observed but 1 pt had PSA decrease by > 50%. Pts remained on study treatment for a median of 10 weeks (range 3-32 weeks). 5 pts, with stable disease, remain on active treatment. PK data could not be fully evaluated due to issues with the PK assay. Analyses of IL-6 and putrescine levels in pt samples indicate that, as compared to no treatment, PCUR-101 treatment in each cycle was associated with decreases in their levels. Reasons for treatment discontinuation included disease progression (n = 4), adverse event (n = 1; nausea and vomiting), subject withdrawal (n = 1), and investigator or sponsor decision (n = 1). After treating 12 pts, the sponsor decided to stop the trial in order to reformulate the study drug to allow for higher dosing and to redevelop the PK assay. Conclusions: At the doses evaluated, PCUR-101 combined with ADT was seen to be safe and may prolong disease stability in men with mCRPC. A second phase I study is planned using a new drug formulation and PK assay. Clinical trial information: NCT03137758.