Preclinical efficacy evaluation of ixabepilone (BMS-247550) in combination with cetuximab or capecitabine in human colon and lung carcinoma xenografts

12017 Background: Ixabepilone belongs to a class of structurally novel, microtubule-stabilizing agents that exert their antimitotic action by binding to tubulin with a binding mode that is distinct from the taxanes. Preclinical findings that ixabepilone has antitumor activity in a broad spectrum of tumor types, including taxane-resistant tumors, is borne out by Phase II clinical trials where ixabepilone has demonstrated activities in multiple tumor types including breast, renal, pancreatic, prostate and lymphoma. The aim of this series of studies was to further characterize the therapeutic potential of ixabepilone in combination with currently approved chemotherapy agents. Methods: Antitumor activity was evaluated in the GEO human colon and L2987 human lung carcinoma xenografts. Therapeutic synergism of the combination was defined as the attainment of efficacy that was significantly better than the best response of the individual single agents administered at their maximum-tolerated dose (MTD) or optimal dose (OD). Results: In the GEO tumors, single-agent ixabepilone produced 1.1 log cell kill (LCK) at its MTD. Cetuximab at its OD yielded 0.8 LCK. The combination of ixabepilone and cetuximab produced 1.7 LCK which was significantly superior to ixabepilone alone (P=0.0173) and cetuximab alone (P=0.0002). Similar synergistic efficacy was observed in the L2987 tumors. The combined efficacy of capecitabine plus ixabepilone was evaluated in the GEO tumors. In this tumor, single-agent ixabepilone was modestly active (LCK = 0.8) at its MTD. Single-agent capecitabine was not effective (LCK = 0.4) at its MTD. However, the combination of the two agents produced therapeutic synergism, yielding antitumor efficacy (1.9 LCK) that was superior to either of the agents alone at their MTDs (P=0.035 and 0.0004, respectively). Conclusions: Ixabepilone demonstrates robust synergistic antitumor efficacy when used in combination with cetuximab or capecitabine in human xenografts providing a biologic rationale for these combinations in the treatment of cancer. [Table: see text]