A phase I study of temsirolimus and bryostatin-1 in patients with metastatic renal cell carcinoma and soft tissue sarcoma

Background. Temsirolimus, an inhibitor of mammalian target of rapamycin (mTOR) complex 1, is approved for the treatment of metastatic renal cell carcinoma (RCC). Bryostatin-1 inhibits protein kinase C, a downstreameffector ofmTOR complex 2. We observed antitumor effects with the combination of temsirolimus and bryostatin-1 in RCC cell lines. Methods. Four cohorts of patients received weekly bryostatin- 1 (20 μg/m²) with temsirolimus (10, 15, 25, or 37.5 mg) in 28-day cycles. Results. Thirty patients received a total of 138 cycles across four dose levels. Twenty-five patients had RCC (17 clear cell, 7 papillary, and 1 unclassified). Two sarcoma patients with prior cytotoxic therapy experienced dose-limiting toxicity at 15 mg of temsirolimus (grade 3 neutropenia and grade 3 hypophosphatemia). Subsequently, patients with prior cytotoxic therapy were excluded. Two additional dose-limiting toxicities were noted with 37.5 mg of temsirolimus (grade 3 neutropenia and grade 3 creatinine elevation). Consequently, the maximum tolerated dose was defined as temsirolimus at 25 mg and bryostatin-1 at 20 μg/m² every 28 days.Of the 25RCCpatients, 3 patients had partial responses that lasted for 14 months, 28 months, and ≥80 months, respectively.Partial responses were seen in both clear cell and papillary histology. Conclusion. This combination of 37.5 mg of temsirolimus with 20 μg/m² of bryostatin-1 was reasonably safe and well tolerated. Durable responses were observed in 3 of 25 patients with RCC.