Phase I Study of the Farnesyltransferase Inhibitor Lonafarnib with Paclitaxel in Solid Tumors

Purpose: To establish the maximum tolerated dose of lonafarnib, a novel farnesyltransferase inhibitor, in combination with paclitaxel in patients with solid tumors and to characterize the safety, tolerability, dose-limiting toxicity, and pharmacokinetics of this combination regimen. Experimental Design: In a Phase I trial, lonafarnib was administered p.o., twice daily (b.i.d.) on continuously scheduled doses of 100 mg, 125 mg, and 150 mg in combination with i.v. paclitaxel at doses of 135 mg/m² or 175 mg/m² administered over 3 h on day 8 of every 21-day cycle. Plasma paclitaxel and lonafarnib concentrations were collected at selected time points from each patient. Results: Twenty-four patients were enrolled; 21 patients were evaluable. The principal grade 3/4 toxicity was diarrhea (5 of 21 patients), which was most likely due to lonafarnib. dose-limiting toxicities included grade 3 hyperbilirubinemia at dose level 3 (100 mg b.i.d. lonafarnib and 175 mg/m² paclitaxel); grade 4 diarrhea and grade 3 peripheral neuropathy at dose level 3A (125 mg b.i.d. lonafarnib and 175 mg/m² paclitaxel); and grade 4 neutropenia with fever and grade 4 diarrhea at level 4 (150 mg b.i.d. lonafarnib and 175 mg/m² paclitaxel). The maximum tolerated dose established by the continual reassessment method was lonafarnib 100 mg b.i.d. and paclitaxel 175 mg/m². Paclitaxel appeared to have no effect on the pharmacokinetics of lonafarnib. The median duration of therapy was eight cycles, including seven cycles with paclitaxel. Six of 15 previously treated patients had a durable partial response, including 3 patients who had previous taxane therapy. Notably, two of five patients with taxane-resistant metastatic non-small cell lung cancer had partial responses. Conclusions: When combined with paclitaxel, the recommended dose of lonafarnib for Phase II trials is 100 mg p.o. twice daily with 175 mg/m² of paclitaxel i.v. every 3 weeks. Additional studies of lonafarnib in combination regimens appear warranted, particularly in patients with non-small cell lung cancer.