Farnesyltransferase inhibitors--a novel approach in the treatment of advanced pancreatic carcinomas.

Ras oncogenes (K-, H- and N-ras) are known to be involved in signal transduction pathways regulating cell growth and differentiation in many human cancers. These proteins are synthesized as a cytosolic precursor that ultimately localizes to the inner plasma membrane. This process is initiated by the attachment of a farnesyl moiety to the protein and is catalysed by the farnesyl transferase. Since activated (mutated) ras oncogenes have been shown to be essential for the malignant phenotype in many tumors, farnesyl transferase inhibitors (FTIs) have emerged as a novel class of antineoplastic agents. Four FTIs are currently in clinical trials. Two of these agents, R-115777 and SCH-66336, are orally active heterocyclic compounds and already in phase II/III studies. Preliminary results of R-115777 or SCH-66336 in combination with gemcitabine or 5-FU/FA in patients with advanced pancreatic carcinomas have been reported. The dose-limiting toxicity was neutropenia, nausea, diarrhea and fatigue. The recommended doses for phase II studies were 200 mg R-115777 or 2 x 200 mg SCH-66336. Durable objective partial responses were noted in several patients. Furthermore, the FTIs were found to be well tolerated. Ongoing phase III studies in patients with advanced pancreatic cancers will determine the extent of clinical activity and whether these agents can be used as single agents for the treatment of pancreatic carcinomas or have to be used in combination with other cytostatic drugs. In addition, it remains to be clarified whether FTIs may sensitize drug-resistant cancers following conventional chemotherapy.