Farnesyltransferase Inhibitor Tipifarnib (Zarnestra) in Refractory Mantle Cell Lymphoma (MCL): A Therapeutic Target Only for Specific Patients Categorized by the 2-Gene Classifier for Predictive Response to Tipifarnib.

Background. Mantle cell lymphoma is one of the most refractory B-cell lymphomas. Despite the recent improvement of novel therapeutic strategies including high dose therapy and the introduction of immunotherapy, MCL patients are not cured by conventional therapeutic strategies. The increasing understanding of the MCL cell biology leads to the development of new drugs targeting to molecular mechanisms of the disease. Among the specific genes found to be overexpressed in MCL by gene expression profiling analysis, farnesyltransferase (FTase) encodes for an enzyme essential in the post- translational modifications of proteins that require prenylation for conversion to mature forms, allowing their participation in various signaling pathways regulating growth and survival. We recently demonstrated that inhibition of FTase by tipifarnib (Zarnestra) is associated in vitro with growth inhibition and apoptosis of MCL cell lines and in vivo with tumor xenograft stability. To determine the efficacy, the safety profile and the toxicity of tipifarnib in MCL, we conducted a phase II trial in patients with refractory MCL, and we evaluated the response considering published molecular predictors.

Methods. Primary endpoint was the efficacy measured by the evaluation of the overall response rate (ORR) at 4 cycles, and, in case of response, at 6 cycles. Planned sample size of the study was 27 evaluable patients enrolled for an analysis based on an optimal two-stage design comprising 11 patients for the first stage and 16 for the second stage, under the hypothesis of an ORR of 35% to conclude for an effective drug and an ORR of 10% to conclude for an ineffective drug. Tipifarnib was administered at 300 mg orally twice daily for the first 21 days of each 28-days cycle for 4 to 6 cycles. Prediction of response was retrospectively evaluated in the initial tumor biopsy by the analysis of the 2-gene classifier, the RASGRP1/APTX gene expression ratio, and the AKAP13 expression level.

Results. Eleven patients with refractory MCL were included in the analysis. Median number of lines of therapy before tipifarnib was 2.5 (range 1–7). Median age was 71 (range 66–79). All patients presented with stage IV disease and with good performance status. At 4 cycles of tipifarnib, 1 patient presented a complete response and 10 patients were in progressive disease. Two patients progressed during or after the first cycle, three patients after 3 cycles, and five patients after 4 cycles. No grade III-IV hematological toxicities were recorded. One patient presented an unrelated neurological symptom after the first dose administered. Evaluation of the molecular prediction of response to tipifarnib was realized for 3 patients: one responder patient and two non-responder patients. Results showed an increase in the RASGRP1/APTX gene expression ratio and a decrease in AKAP13 expression in the responder patient, and a decrease in the RASGRP1/APTX gene expression ratio and an increase in AKAP13 expression in the non-responder patients. This corresponds to the expected results of the response prediction to tipifarnib.

Conclusion. Tipifarnib in refractory MCL was beneficial for only one patient. Response could be exactly predicted by specific molecular predictors of response evaluated in the initial tumor biopsy. These results demonstrate the necessity of categorizing molecularly the patients when targeted therapies are proposed to select those patients that might respond to.