The Intermediate Enzymes of Isoprenoid Metabolism as Anticancer Targets

Inhibitors of isoprenoid biosynthesis are widely used to treat human disease including statins and nitrogenous bisphosphonates. Due to the importance of core human isoprenoid biosynthesis for diverse cellular processes related to cancer cell growth and metastasis, inhibition of this pathway may produce beneficial anticancer consequences. For example, ras oncogenes are well known; ras proteins are overexpressed in many human cancers, and these proteins must be isoprenylated to function. The rho proteins are important for regulating cell motility, and also must be isoprenylated. This has drawn significant attention to inhibitors of protein prenyl transferases. In addition to the reactions that are targeted in current clinical applications, there are other enzymes that have not been studied as extensively. Inhibition of these enzymes, from mevalonate kinase to geranylgeranyl diphosphate synthase, could be attractive as a single agent therapy or in combination with current agents for treatment of cancers in which isoprenylated proteins have been implicated. While detailed in vivo data for many of these putative targets is lacking, there have been several breakthroughs in recent years that could facilitate further studies. In particular, compounds that specifically inhibit some of the downstream isoprenoid biosynthesis enzymes have been developed and their effects in cancer models are emerging. This review will discuss current knowledge of these lesser known isoprenoid pathway enzymes, identify trends in the development of their small molecule inhibitors, and describe the applications and effects of these compounds in cancer models.