Specific mutations in the ras gene impair the
guanosine triphophatase (
GTPase) activity of
Ras proteins, which play a fundamental role in the signaling cascade, leading to uninterrupted growth signals and to the transformation of normal cells into malignant phenotypes. It has been shown that normal cells transfected with mutant ras gene become cancerous and that unfarnesylated, cytosolic mutant
Ras protein does not anchor onto cell membranes and cannot induce this transformation. Posttranslational modification and plasma membrane association of mutant Ras is necessary for this transforming activity. Since its identification, the
enzyme protein farnesyltransferase (FTase) that catalyzes the first and essential step of the three Ras-processing steps has emerged as the most promising target for therapeutic intervention. FTase has been implicated as a potential target in inhibiting the prenylation of a variety of
proteins, thus in controlling varied disease states (e.g.
cancer,
neurofibromatosis, restenosis, viral
hepatitis,
bone resorption,
parasitic infections, corneal
inflammations, and diabetes) associated with
prenyl modifications of Ras and other
proteins. Furthermore, it has been suggested that FTase inhibitors indirectly help in inhibiting
tumors via suppression of angiogenesis and induction of apoptosis. Major milestones have been achieved with small-molecule FTase inhibitors that show efficacy without toxicity in vitro, as well as in mouse models bearing ras-dependent
tumors. With the determination of the crystal structure of mammalian FTase, existent leads have been fine-tuned and new potent molecules of diverse structural classes have been designed. A few of these molecules are currently in the clinic, with at least three
drug candidates in Phase II studies and one in Phase III. This article will review the progress that has been reported with FTase inhibitors in
drug discovery and in the clinic.