Suppression of Murine Neuroblastoma Growth in Vivo by Mevinolin, a Competitive Inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A Reductase

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase catalyzes the formation of mevalonate, an essential precursor for isoprenoid compounds in mammalian cells. Recent studies have shown that mevinolin, a competitive inhibitor of the reductase, inhibits cell proliferation and induces differentiation in cultured C1300 (Neuro-2A) murine neuroblastoma cells. We now report that mevinolin can inhibit neuroblastoma growth in vivo. The specific activity of HMG-CoA reductase in subcutaneous neuroblastomas increased more than 20-fold between the fifth and eighth days after tumor inoculation, and remained elevated for the remainder of the tumor lifetime in mice. The increase in reductase activity was correlated with a marked increase in tumor DNA content and exponential increase in tumor weight. Using an in vitro assay to monitor the ability of mouse serum to suppress sterol synthesis, we determined that mevinolin was inactivated or cleared from the circulation within 3-6 h after a single subcutaneous injection. However, by using subcutaneous osmotic pumps to deliver a constant infusion of mevinolin, we were able to maintain adequate blood levels of the drug for 7 d. Mevinolin (5 mg/kg per h) suppressed tumor growth (wet weight) significantly when treatment was carried out between day 1 and day 8 or between day 5 and day 12 after tumor inoculation. Histopathological examination of tumors from mevinolin-treated mice revealed few or no mitotic figures and marked cellular degeneration. Measurements of incorporation of (3H)acetate into neuroblastoma sterols and ubiquinones 24 h after implantation of osmotic pumps showed that mevinolin produced a marked inhibition of isoprenoid synthesis in the tumors in vivo. The data suggest that, in addition to their demonstrated utility as cholesterol-lowering drugs, competitive inhibitors of HMG-CoA reductase may have considerable potential as novel antineoplastic agents.