Farnesyl protein transferase inhibitors as targeted therapies for hematologic malignancies

Farnesyl protein transferase inhibitors (FTIs) represent a new class of anticancer agents specifically targeting aberrant biologic processes involved with cellular transformation and malignancy. Originally developed to inhibit tumors by preventing activation of oncogenic ras genes via suppression of their posttranslational farnesylation, their anticancer activity appears to stem from their ability to inhibit farnesylation of various proteins that mediate signal transduction, growth, apoptosis, and angiogenesis. The safety, biologic activity, clinical response, and pharmacokinetics of R115777, a potent, orally active FTI, were recently investigated in a phase I dose-ranging study in patients with acute leukemias. Patients with acute myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), or chronic myelogenous leukemia (CML) in blast crisis received R115777 100 mg, 300 mg, 600 mg, 900 mg, or 1,200 mg twice daily for 21 days. Cycles were repeated every 28 to 31 days for up to four cycles. An overall response rate of 29% (10/34 evaluable patients) was observed across all R115777 doses. R115777 was well tolerated; common adverse events included fatigue, increased creatinine, nausea, and neutropenia. Dose-limiting toxicity occurred at 1,200 mg twice daily. Farnesylation of lamin A and HDJ-2, examined as biologic end points, was inhibited by R115777 doses ≥ 600 mg twice daily. Pharmacokinetic evaluation suggests that R115777 is concentrated in bone marrow at steady state. The biologic and antitumor activity and favorable tolerability of R115777 support further clinical evaluation alone and in combination therapy in hematologic malignancies.