Chemosensitization of CDDP-Resistant Multiple Myeloma Cell Lines Following Treatment with Anti-TfR IgG3-Av.

Multiple myeloma (MM) is an incurable proliferative disorder of monoclonal malignant plasma cells. Multiple agents conventional dose chemotherapy regimens have resulted in improved response rates, however, there have been no significant improvements in overall survival. Recently, Bortezomib has been introduced for the treatment of MM and has resulted in significant response rates. Nevertheless, additional strategies for direct treatment of MM patients are urgently needed. In general, cancer cells have been shown to express significantly higher levels of the transferrin receptor (TfR) and thus, this receptor is an attractive target for cancer therapy. We have generated an anti-TfR IgG3-avidin fusion protein (anti-TfR-IgG3-Av) that can deliver biotinylated molecules into cancer cells and exhibits intrinsic pro-apoptotic activity against hematopoietic malignant cells including myeloma (Ng P. et al., 2002, PNAS 99:10706–11). We have also reported that certain monoclonal antibodies (e.g., rituximab) can sensitize tumor cells to various chemotherapeutic drug-induced apoptosis (Jazirehi and Bonavida, 2005, Oncogene 65:264–76). Thus, this study investigated whether anti-TfR IgG3-Av sensitizes drug-resistant MM cell lines to drug-induced apoptosis. We initially examined the CDDP-resistant lymphoblastoid IM-9 and ARH-77 cell lines for chemosensitization using a suboptimal dose of anti-TfR IgG3-Av. Several methods were used to assess the cytotoxic activity, namely viable cell recovery and apoptosis by both PI and caspase-3 activation. The findings demonstrate that treatment of tumor cells with anti-TfR IgG3-Av for 18 h following treatment with CDDP for an additional 18 h resulted in significant cytotoxicity and apoptosis and synergy was achieved. The combined treatment also resulted in significant mitochondrial membrane depolarization, suggesting that apoptosis was achieved through a type-II pathway. In comparison with tumor cell treatment with anti-TfR-IgG3-Av, the anti-TfR IgG3 was a more potent chemosensitizer, based on both the concentration used and the extent of apoptosis achieved. These findings demonstrate that anti-TfRIgG3-Av is a potential therapeutic antibody that will reverse MM drug resistance when used in combination with chemotherapeutic drugs.