Final results of phase I/II study of decitabine (DAC) combined with temozolomide (TMZ) in metastatic melanoma (MM).

Abstract

8530 Background: TMZ is widely used in MM despite low response rates (7-13%) and no improvement in median overall survival (OS) 7.7 months (m) when compared to dacarbazine in Phase III trials. The DNA repair protein, O6-methylguanine-DNA-methyltransferase (MGMT), is implicated in melanoma resistance to TMZ and can be depleted with extended schedule TMZ. DNA mismatch repair (MMR) deficiency is another mechanism of resistance that can be reversed with DNA hypomethylators such as DAC. We sought to determine the recommended phase II Dose (RP2D), safety, and efficacy of DAC in combination with extended schedule TMZ in MM. Methods: In the Phase I portion, pts were treated with 2 dose levels (DL) of DAC: 0.075 mg/kg IV QD and 0.15 mg/kg IV QD. DAC was administered qd x 5 d/wk for 2 wks, and TMZ was administered PO at 75 mg/m2 qd for 4 wks, starting on wk 2 of each 6-wk cycle. A Simon 2-stage Phase II design with success defined as ≥5 Objective Responses (OR) in 34 evaluable patients gave µ=0.10 and 85% power. PK sampling was performed on Days 1 and 8; PBMC and tumor tissues were studied on Days 1, 8, 15 and 29 of cycle 1. Results: The RP2D is DAC 0.15 mg/kg and TMZ 75 mg/m2. 35 patients were accrued to the Phase II portion of the study, the majority with M1c disease (88%); brain metastases were present in 42%. 2/35 were not evaluable (NE) for efficacy. For the remaining 33 patients, the best RECIST responses were 1CR, 4 PR, 13 SD, and 15 PD, for an OR rate of 15% and a clinical benefit rate (CR+PR+SD) of 54%. The median PFS was 2.8 m, median OS was 15.2 m (compared to 7.7 m), and 1-year OS rate was 62% (compared to 25%). Grade 3/4 neutropenia was observed in 68% of pts but reversible, lasting >7 d in only 5 pts (DLT rate 15%). Only 2 patients discontinued therapy for hematologic toxicity. PK studies revealed no effect of DAC on the PK profile of TMZ. Conclusions: The combination of DAC and TMZ is safe and results in improved median OS from historic reference of 7.7 m to 15.2 m, and 1-year OS rate from 25% to 62%. The addition of DAC appears to improve the clinical activity of TMZ, possibly through dual modulation of DNA repair (depletion of MGMT and re-expression of MMR), and warrants further evaluation in a randomized setting.