Apoptosis induction of human lung cancer cell line in multicellular heterospheroids with humanized antiganglioside GM2 monoclonal antibody

The chimeric antiganglioside GM2 monoclonal antibody (MAb) KM966, which sho wed high effector functions such as complement-dependent cytotoxicity and a ntibody-dependent cellular cytotoxicity (ADCC), potently suppressed growth and metastases of GM2-positive human cancer cells inoculated into mice. To further improve the therapeutic efficacy of the anti-GM2 MAb in humans, we constructed a humanized anti-GM2 MAb, KM8969, The humanized KMS969 was more efficient in supporting ADCC against GM2-positive human cancer cell Lines than the chimeric KM966, whereas complement-dependent cytotoxicity was slig htly reduced in the humanized KM8969. In addition, the humanized KM8969 was shown to exert potent ADCC mediated by both Lymphocytes and monocytes, To investigate the effect of the humanized KM8969 on the biological function o f GM2 in the condition physiologically mimicking formation and growth of ca ncer masses, the heterospheroids composed of normal human dermal fibroblast s and GM2-positive human lung cancer cells were developed. Interestingly, t he humanized KM8969 gave rise to growth inhibition of heterospheroids witho ut dependence of the effector functions. Morphological and immunocytochemic al analysis suggested that the inhibitory effect was due to the apoptosis o f GM2-positive cancer cells in the heterospheroids. The result indicates th at GM2 captured by the antibody on the cell surface loses its physiological function that plays a critical role in maintaining the three-dimensional g rowth of cancer cells in contact with its own cells or other type of cells in a microenvironment. The humanized KM8969, which can destroy the cancer c ells via blocking functional GM2 on the cell surface as well as the effecto r functions, would have extraordinary potential in human cancer therapy.