A peptidomimetic inhibitor of ras functionality markedly suppresses growth of human prostate tumor xenografts in mice. Prospects for long-term clinical utility

Abstract

Purpose: These studies sought to evaluate the antitumor properties of an inhibitor of ras functionality, L-744,832, which acts at the level of its associated protein farnesyltransferase. Methods: Studies were carried out to measure the effects of L-744,832 alone and in combination with paclitaxel (PTXL) against TSU-PR1, DU-145 and PC-3 human prostate tumors xenografted to NCR-nu1 (AT) mice. Tumor-bearing mice were treated on a schedule of daily for 5 days ×2 or 3 with the MTD of L-744,832 and every 3–4 days ×4 with the MTD of PTXL starting 3–5 days after tumor implantation. Tumor volume in millimeters (4/3πr³) was measured 3–5 days after cessation of treatment and the increase in tumor volume in treated and control groups compared. Statistical analysis was carried out by the Chi-squared test. Results: L-744,832 at its MTD markedly inhibited the growth of all three tumors (T/C for increase in tumor mass varied from 11% to 15% and inhibition of growth had a rapid onset (within 1–2 days) and was independent of ras gene status. Estimated tumor doubling times were 8–12-fold greater in treated animals than in control animals. Treatment with L-744,832 for as long as 3 weeks had no untoward effects on the mice as determined by gross examination or necropsy. Administration of L-744,832 with this same dose and schedule potentiated the growth-inhibitory effect of PTXL at its MTD and induced some regression of TSU-PR1 with no obvious deleterious effects on the mice. Conclusions: L-744,832 could be safely administered over a protracted period of time to mice at doses which were markedly inhibitory to the growth of three human prostate tumor xenografts and in combination with PTXL was also well tolerated and brought about some regression of the TSU-PR1 tumor. Overall, these results suggest that L-744,832 could be clinically useful for long-term treatment of early-stage prostate cancer in patients and as an adjunct to cytotoxic therapy for late stages of this disease.