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A phase 2 study of prostate specific membrane antigen antibody drug conjugate (PSMA ADC) in patients (pts) with progressive metastatic castration-resistant prostate cancer (mCRPC) following abiraterone and/or enzalutamide (abi/enz).

2015; Lippincott Williams & Wilkins; Volume: 33; Issue: 7_suppl Linguagem: Inglês

10.1200/jco.2015.33.7_suppl.144

1527-7755

Daniel P. Petrylak, Nicholas J. Vogelzang, Gurkamal Chatta, Mark T. Fleming, David C. Smith, Leonard J. Appleman, Arif Hussain, Manuel Modiano, Parminder Singh, Scott T. Tagawa, Ira Gore, Edward F. McClay, Anthony Mega, Oliver Sartor, Bradley G. Somer, Raymond Wadlow, Neal D. Shore, Nancy Stambler, Vincent A. DiPippo, Robert J. Israel,

Radiopharmaceutical Chemistry and Applications

144 Background: PSMA is a validated target that is overexpressed selectively on prostate cancer cells. PSMA ADC is a fully human IgG1 antibody conjugated to the microtubule disrupting agent MMAE which binds to PSMA-positive cells, inducing cytotoxicity. A phase 1 study showed activity and tolerability at doses from 1.8-2.5 mg/kg. We have enrolled 119 mCRPC pts who progressed following abi/enz in a phase 2 trial of PSMA ADC. Methods: mCRPC pts (83 taxane experienced (TE) and 36 chemo-naïve (CN)) were administered PSMA ADC 2.5 or 2.3 mg/kg IV Q3 wk for up to 8 cycles. 95% of pts received prior abi and/or enz treatment. Safety, antitumor activity (including PSA, CTCs, and tumor imaging) and exploratory biomarkers were assessed. Results: In all treated pts, PSA declines of ≥30% and ≥50% were 30% and 14%, respectively (n=113); CTC counts showed a decline of ≥50% in 78% of pts and conversion from ≥5 to <5 cells/7.5 ml blood in 47% (n=77) at any time during the study. For 2.3 mg/kg pts (n=82), corresponding PSA declines were 35% and 17%; CTC declines of ≥50% were seen in 81% and conversions in 46% (n=54). For CN pts, PSA declines of ≥30% and ≥50% were 31% and 20% (n=35); CTC declines of ≥50% were seen in 89% and conversion in 53% (n=19). Radiologic response by RECIST in 31 pts with measurable target lesions: PR in 4 pts, SD in 19 pts, and PD in 8 pts. Efficacy responses were associated with: low neuroendocrine serum markers (low CgA, low NSE, and high PSA), high PSMA expression (CTCs or tumor tissue). The most common treatment-related AEs ≥CTCAE grade 3 were neutropenia (TE: 25%; CN: 22%), fatigue (20%; 8%), electrolyte imbalance (16%; 11%), anemia (10%; 8%), and neuropathy (8%; 8%). Grade 1-2 neuropathy occurred in 40% (TE) and 50% (CN) of pts. Two 2.5 mg/kg pts (n=34) and one 2.3 mg/kg pt (n=85) died of sepsis. 2.3 mg/kg was better tolerated than 2.5 mg/kg. Conclusions: PSMA ADC was active in abi/enz refractory mCRPC pts. Clinically significant AEs included neutropenia and neuropathy. CTC conversions/reductions, PSA declines, and radiologic evidence of antitumor activity were seen in CN as well as heavily pretreated pts. Clinical trial information: NCT01695044.