Characterization of resistance to a recombinant hexameric Fas-ligand (APO010) in human cancer cell lines

Multiple myeloma remains a hard-to-treat cancer as all patients eventually progress because of drug resistance. Thus, there is a need for novel and non-cross-resistant treatment options, and we aimed to address this issue by introducing a new immuno-oncology drug (APO010) in multiple myeloma treatment. APO010 is a hexameric Fas-ligand that mimics cytotoxic T-lymphocyte signaling through the Fas-receptor to induce apoptosis. APO010 is currently in clinical trials with multiple myeloma patients. Thus, an understanding of the mechanisms contributing to resistance to APO010 will be essential for future clinical studies with APO010, and it might be possible to develop strategies to circumvent this resistance. We developed APO010-resistant variants of human multiple myeloma cell lines (LP1, MOLP-8, and KMS-12-BM) and a human Burkitt's lymphoma cell line (Raji) by exposing the cells to gradually increasing concentrations of APO010 over a period of 6-12 months. The resistant cell lines were characterized on the basis of immunocytochemistry, Fas-receptor protein expression, mRNA expression analysis, and pathway analysis. APO010-resistant cell lines exhibited a 4- to 520-fold increase in resistance to APO010 and still remained sensitive to other chemotherapeutics. Downregulation of the Fas-receptor protein expression was observed in all resistant cell lines. mRNA expression analysis of the resistant versus parental cell lines confirmed a significant alteration in FAS expression between sensitive and resistant cell lines (p = 0.03), while pathway analysis revealed alterations in mRNA signaling pathways of Fas. On the basis of the pre-clinical data obtained, it can be concluded that downregulation of Fas-receptor can mediate resistance to APO010.