Phase II Trial of Single Agent Val-boroPro (Talabostat) Inhibiting Fibroblast Activation Protein in Patients with Metastatic Colorectal Cancer

Kalyani Narra, Stefanie R. Mullins, Hyung-Ok Lee, Brenda Strzemkowski-Brun, Kimberly Magalong, Victoria J. Christiansen, Patrick A. McKee, Brian Egleston, Steven J. Cohen, Louis M. Weiner, Neal J. Meropol and Jonathan D. Cheng

volume 6 | issue 11

November 2007
Pages: 1691 - 1699

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Purpose: Fibroblast Activation Protein (FAP) is a tumor fibroblast protease that has been shown to potentiate colorectal cancer growth. The clinical impact of FAP inhibition was tested using Val-boroPro (Talabostat), the first clinical inhibitor of FAP enzymatic activity, in a phase II study of patients with metastatic colorectal cancer. Methods: Patients with metastatic colorectal cancer who had previously received systemic chemotherapies were treated with single agent Val-boroPro 200 μg p.o. BID continuously. Eligibility included measurable disease, performance status of 0 to 2, and adequate organ function. Laboratory correlates evaluated the pharmacodynamic effects of Val-boroPro on FAP enzymatic function in the peripheral blood. Results: Twenty-eight patients (median age 62; 12 males, 16 females) were enrolled in this study. There were no objective responses. Six of 28 (21%) patients had stable disease for a median of 25 weeks (range 11-38 weeks). Laboratory analysis demonstrated significant, although incomplete inhibition of FAP enzymatic activity in the peripheral blood. Conclusion: This phase II trial of Val-boroPro demonstrated minimal clinical activity in patients with previously treated metastatic colorectal cancer. However it provides the initial proof-of-concept that physiologic inhibition of FAP activity can be accomplished in patients with colorectal cancer, and lays the groundwork for future studies targeting the tumor stroma.