A phase 1, open-label, dose-escalation study of pralatrexate incombination with bortezomib in patients with relapsed/refractory multiple myeloma

Pralatrexate inhibits folic acid metabolism, and preclinical studies have shown that it is cytotoxic to multiple myeloma cells. This phase 1 study investigated the safety and efficacy of pralatrexate in combination with bortezomib in adults with relapsed or refractory multiple myeloma. A standard 3 + 3 design was used. Patients received intravenous pralatrexate at doses ranging from 10 to 30 mg/m(2) and intravenous bortezomib at a dose of 13 mg/m(2) on days 1, 8 and 15 of each 4-week cycle. Eleven patients were enrolled and completed a median of two cycles. The maximum tolerated dose was 20 mg/m(2). Two patients experienced dose-limiting toxicity of mucositis. The most frequent non-haematological toxicities were fatigue (55%) and mucositis (45%). There were three serious adverse events in three patients: rash, sepsis and hypotension. One patient (9%) had a very good partial response, 1 (9%) had a partial response, 1 (9%) had minimal response and two (18%) had progressive disease. The median duration of response was 4months, the median time to next treatment was 34 months and the median time to progression was 4months. Pralatrexate, in combination with bortezomib, was generally safe and demonstrated modest activity in relapsed or refractory multiple myeloma.