Hypothesis: the antitumor activities of statins may be mediated by IL-18.

Statins, which inhibit 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase, are thought to reduce the risk of cancer through the inhibition of Ras farnesylation and serum lipid level. A pleiotropic proinflammatory cytokine, interleukin-18 (IL-18), is reported to exhibit significant antitumor activities through the activation of cytotoxic T lymphocytes and natural killer cells and the inhibition of angiogenesis. Previously, we found that pravastatin, fluvastatin, and simvastatin induced the production of IL-18 in human monocytes. The addition of mevalonate abolished the IL-18 production induced by pravastatin, fluvastatin, and simvastatin, indicating that the IL-18 production might be a result of the inhibition of HMG-CoA reductase. We present a new hypothesis that the production of IL-18 might play roles in the action of statins on cancer.