TRAIL-receptor antibodies synergize with chemotherapy to enhance anti-tumor activity in cholangiocarcioma

B50 Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) death receptors, TRAIL-R1 and TRAIL-R2, are expressed on the cell surface of many human tumor cells. Activation of these receptors induces programmed cell death. Mapatumumab and lexatumumab are fully human agonistic monoclonal antibodies (mAbs) that target and activate cell death via TRAIL-R1 or TRAIL-R2, respectively. Both mAbs are currently being evaluated in clinical trials.
 We assessed the in vitro and in vivo efficacy of mapatumumab or lexatumumab alone and in combination with chemotherapeutic agents in several cholangiocarcinoma (CCA) cell lines in cytotoxicity assays and xenograft tumor models.
 Three CCA cell lines representing intra- (HuCCT1) or extra- (EGI, TFK-1) hepatic, biliary duct cancer expressed low to moderate levels of both TRAIL-R1 and TRAIL-R2 on the cell surface and were either resistant (HuCCT1), weakly (EGI) or moderately sensitive (TFK-1) to treatment with mapatumumab or lexatumumab.
 Co-treatment with cisplatin, gemcitabine or 5-fluorouracil increased the cytotoxicity of both mAbs in most cells lines; in some cases a synergistic enhancement was observed. Co-treatment with the triplet of cisplatin and gemcitabine and either mAb was more effective than either single agent alone in all cell lines with most treatment triplets inducing >90% cytotoxicity. We examined the effect of pre-treating CCA cell lines with a single chemotherapeutic agent 24 hours before treatment with either mapatumumab or lexatumumab. Interestingly, pre-treatment with a single chemotherapeutic agent followed by mapatumumab or lexatumumab increased cytotoxicity more than that observed in co-treatment with the same single agent and either mAb in most cell lines. In some cell lines, pre-treatment with cisplatin followed by mapatumumab was as effective as co-treatment with cisplatin, gemcitabine and mapatumumab. We conclude that pre-treatment with chemotherapeutic agents can alter the sensitivity of CCA cell lines to TRAIL-R mAbs.
 Similarly, in a xenograft model of CCA, mapatumumab and either co- or pre-treatment with cisplatin and gemcitabine were more effective than either chemotherapy or mapatumumab alone. In addition, pre-treatment with chemotherapy was as effective as co-treatment with the triplet in inhibiting tumor growth. This in vivo result confirms the conclusion that chemotherapy can enhance the anti-tumor activity of mapatumumab and shows that pre-treatment with chemotherapy is a potential strategy for enhancing this activity. We continue to investigate the mechanism of increased TRAIL-R mAb sensitivity to pre-treatment with chemotherapy in CCA.These results demonstrate the significant anti-tumor activity of the TRAIL-R mAbs mapatumumab and lexatumumab as therapeutic agonist monoclonal antibodies that can augment the activity of cytotoxic agents used in the treatment of human cancer. This preclinical data supports the evaluation of these chemotherapeutic agents in combination with TRAIL-R mAbs in future clinical studies, particularly in biliary cancer.