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Progenics Pharmaceuticals, Inc. (Nasdaq: PGNX) today reported positive preliminary data from an ongoing phase 1 study of PSMA ADC, an antibody-drug conjugate (ADC) designed to selectively deliver chemotherapy to cells that express prostate-specific membrane antigen (PSMA). Antitumor activity, as reflected by clinical and/or laboratory measures, was observed in four of nine patients treated at the highest tested dose of 1.8 mg/kg. PSMA ADC was generally well tolerated in patients treated to date, and patient enrollment continues at a higher dose. Findings were presented at the 2011 Genitourinary Cancers Symposium, a meeting co-sponsored by the American Society of Clinical Oncology (ASCO), the American Society for Radiation Oncology (ASTRO) and the Society of Urologic Oncology (SUO).
Data were reported for 21 patients who have been administered PSMA ADC at five dose levels between 0.4 mg/kg and 1.8 mg/kg. Of the nine patients treated at 1.8 mg/kg, four (44%) exhibited a decline in PSA (prostate-specific antigen), CTC (circulating tumor cells) and/or bone pain. In addition, one patient of three (33%) treated at 1.6 mg/kg showed a decline in CTC and bone pain.
The most common clinical adverse event was fatigue, while the most common laboratory adverse events were reversible neutropenia and elevations in liver enzymes. One patient experienced an acute, fatal case of pancreatitis that was deemed by the investigator to be possibly related to treatment. No evidence of pancreatic toxicity has been observed with PSMA ADC in other treated patients, consistent with results of preclinical studies. PSMA ADC exhibited dose-proportional pharmacokinetics, and no antibodies to PSMA ADC were observed in any subject. A maximum tolerated dose has not been determined, and enrollment of patients at a dose of 2.0 mg/kg has commenced.
“Treatment with PSMA ADC in this ongoing study resulted in meaningful reductions in two commonly used biomarkers of prostate cancer progression as well as in cancer-related bone pain, a common complication of prostate cancer,” said Robert J. Israel, M.D., Progenics’ Senior Vice President, Medical Affairs and Clinical Research. “These findings were observed in patients with tumors that had progressed despite standard chemotherapy. Based on these encouraging data, we look forward to further exploring the potential utility of this novel agent.”