In Vivo Enhanced Antitumor Activity of Carmustine [N,N′-Bis(2-chloroethyl)-N-nitrosourea] by Simvastatin

Abstract

The effects of a combination of simvastatin, a cholesterol-lowering agent, and carmustine (BCNU; N,N′-bis(2-chloroethyl)-N-nitrosourea) on experimental C₆ glioma were studied in vitro and in vivo. In vitro simvastatin and BCNU alone inhibited cell proliferation in a dose-dependent fashion. A subliminal concentration of simvastatin (0.1 µm) markedly and synergistically increased the BCNU toxicity to C₆ glioma cells. The cytofluorimetric analysis of DNA from simvastatin-treated C₆ glioma cells showed, besides the already described arrest in G₁, an arrest/retardation in G₂-M. Mitotic index from C₆ cells incubated with simvastatin (10 µm) decreased by about 90%, indicating a specific C₆ arrest/retardation in G₂. The drug effects could be completely reversed by simvastatin withdrawal or mevalonate addition to the cultured cells. The combination of simvastatin and BCNU resulted predominantly from the profound retardation of cells in the G₂-M compartment of the cell cycle. In vivo simvastatin (administered daily mixed with food) and BCNU (single i.p. injection), when given separately, caused a dose-dependent inhibition of labeling index in C₆ glioma homografts (ID₅₀, 61 mg/kg/day and 8.7 mg/kg, respectively). The combination of the lowest doses tested (simvastatin, 25 mg/kg/day and BCNU 0.3 mg/kg) resulted in a significant growth delay (compared to either drug alone) in C₆ glioma (P < 0.05). There was no significant increase in toxicity as assessed by myelosuppression (WBC counts and bone marrow labeling index) and body weight. The results provide in vivo support for the combined use of simvastatin, a cholesterollowering agent, and BCNU in brain tumor treatment.