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A phase I study of the safety and pharmacokinetics of DSTP3086S, an anti-STEAP1 antibody-drug conjugate (ADC), in patients (pts) with metastatic castration-resistant prostate cancer (CRPC).
Abstracts that were granted an exception in accordance with ASCO's Conflict of Interest Policy are designated with a caret symbol (^).
Background: Six-transmembrane epithelial antigen of the prostate-1 (STEAP1) protein is a cell-surface antigen overexpressed in human epithelial prostate cancers. The ADC DSTP3086S contains the humanized IgG1 anti-STEAP1 monoclonal antibody linked to the potent anti-mitotic agent MMAE. Methods: This study evaluated safety, pharmacokinetics, and pharmacodynamic activity of intravenous DSTP3086S (0.3-2.8 mg/kg) given every 3 weeks (q3w) to pts with CRPC. A traditional 3+3 design was used to determine maximum-tolerated dose, followed by cohort expansion at the recommended Phase II dose (RP2D). Clinical activity was evaluated per PCWG criteria. Dose escalation results are presented. Results: Twenty-eight pts were enrolled with a median age of 67 (43-76), all ECOG PS 0-1, and with a median of 7 prior systemic regimens (including a median of 4 hormonal and 3 non-hormonal regimens). Pts received a median of 3 doses (range 1-10) of DSTP3086S. Reversible Grade 3 transaminitis DLTs occurred in one pt each in the 2.25 mg/kg and 2.8 mg/kg cohorts. Serious AEs (SAE) related to study drug (3 total) included one DVT (Grade 3) in the 1.5 mg/kg cohort, as well as one GI hemorrhage (Grade 3) and one sepsis event (Grade 5) in the 2.25 mg/kg cohort. The most common related AEs across all doses were fatigue (36%), nausea (32%), constipation (25%), decreased appetite and diarrhea (each 21%), and musculoskeletal pain and vomiting (each 18%). Exposure for total antibody, free MMAE, and conjugated MMAE was dose proportional. Approximately 60% of the tumor samples assessed showed high STEAP1 expression. CTC reductions were most robust at 2.8 mg/kg; 4/4 patients with unfavorable CTCs at baseline (median of 99, range: 21-205) exhibited CTC conversions from unfavorable to favorable (<5) after a single dose of DSTP3086S. CTC conversions were also observed at lower doses. PSA decreases of ≥ 50% were observed in 1 pt at 2.25 mg/kg, and 2 pts at 2.8 mg/kg who also had PCWG2 radiologic responses. Conclusions: DSTP3086S at the RP2D of 2.8 mg/kg q3w has a tolerable safety profile and shows evidence of anti-tumor activity. Enrollment in the expansion cohort is ongoing.
Abstracts by D. C. Danila:
A first-in-human, open-label, phase I/II safety, pharmacokinetic, and proof-of-concept study of ARN-509 in patients with progressive advanced castration-resistant prostate cancer (CRPC).Meeting: 2011 ASCO Annual Meeting | Abstract No: TPS190Category: Genitourinary Cancer - Prostate Cancer
A noncomparative randomized phase II study of two dose levels of itraconazole in men with metastatic castration-resistant prostate cancer (mCRPC): A DOD/PCCTC trial.Meeting: 2011 ASCO Annual Meeting | Abstract No: 4532Category: Genitourinary Cancer - Prostate Cancer