A Phase I trial of the novel proteasome inhibitor PS341 in advanced solid tumor malignancies

Purpose: The purpose of this study was to evaluate the toxicity and pharmacodynamic behavior of the novel proteasome inhibitor PS341 administered as a twice weekly i.v. bolus for 2 weeks, followed by a 1-week recovery period in patients with advanced solid tumor malignancies. Experimental Design: In this Phase I trial, 43 patients were treated with PS341 in doses ranging from 0.13 to 1.56 mg/m(2)/dose. A standard Phase I design was used. Pharmacodynamic studies were performed to access 20S proteasome activity. Results: Forty-three patients were treated with 89 cycles of PS341. Patients were heavily pretreated. Dose-limiting toxicities on this schedule were diarrhea and sensory neurotoxicity. Other side effects seen were fatigue, fever, anorexia, nausea, vomiting, rash, pruritus, and headache. There was no dose-limiting hematological toxicity. A dose-related inhibition of 20S proteasome activity with increasing dose of PS341 was seen. There was one major response in a patient with refractory non-small cell lung carcinoma. Conclusions: Given the results of this trial, it is safe and reasonable to recommend treatment with PS341 on the schedule used in this trial at 1.56 mg/m2/dose in Phase 11 trials. Particular care should be taken with patients with preexisting neuropathy. Further testing in Phase 11 trials is warranted.