Blocked Pathways: FTIs Shut Down Oncogene Signals

Abstract Learning Objectives After completing this course, the reader will be able to: Describe how mutations in ras oncogenes affect cell signal transduction pathways and disrupt cell growth, differentiation, proliferation, and survival. Identify the mechanisms of action of two classes of prenylation inhibitors, the farnesyl transferase inhibitors (FTIs) and the geranylgeranyl transferase-I inhibitors (GGTIs). Explain the in vitro and in vivo antitumor activity of FTIs and GGTIs in multiple myeloma and myelodysplastic syndrome. Access and take the CME test online and receive one hour of AMA PRA category 1 credit at CME.TheOncologist.com Ras proteins play fundamental roles in cell signal transduction pathways that regulate cell growth, differentiation, proliferation, and survival. ras mutations are among the most frequently encountered genetic abnormalities in human cancers and play a key role in tumorigenesis. The enzymatic attachment of a 15- or 20-carbon moiety to the Ras protein through farnesylation or geranylgeranylation, respectively, is a required step in the proper localization and activation of Ras. Inhibition of the catalytic enzymes, farnesyl transferase and geranylgeranyl transferase, is a novel, mechanism-based, targeted approach to cancer therapy development. Geranylgeranyl transferase inhibitors suppress tumor growth by accumulating cells in the G1/S cell cycle phase. One mechanism by which farnesyl transferase inhibitors suppress tumor growth is by inhibiting bipolar spindle formation, thereby blocking progression from prophase to metaphase. Although the exact molecular target responsible for the antitumor activity of farnesyl transferase inhibitors is unclear, at least in some tumor cells, inhibition of phosphoinositide-3-OH kinase/Akt-mediated cell survival pathways may play a critical role. Identifying the farnesylated proteins that are targeted by farnesyl transferase inhibitors and the tumor molecular signatures that dictate which set of patients will respond to farnesyl transferase inhibitors are critical end points for future mechanistic studies.