Targeting BCL-2 and PI3K signaling pathways enhances cytotoxicity of gemtuzumab ozogamicin against acute myeloid leukemia cells.

Gemtuzumab ozogamicin (GO) is a humanized IgG4 anti-CD33 monoclonal antibody conjugated to the cytotoxic derivative of calicheamicin. GO was the first antibody-drug conjugate (ADC) approved for the treatment of patients with CD33+ acute myeloid leukemia (AML). Although GO exhibits cytotoxic activity against AML cells, its effectiveness may be limited by resistance mechanisms, highlighting the need to develop strategies that increase cell sensitivity to this ADC. In this study, we investigated whether inhibition of the anti-apoptotic protein BCL-2 and/or phosphatidylinositol 3 kinase (PI3K) pathway enhances GO-mediated cytotoxicity in AML cells with distinct phenotypes. Expectedly, GO decreased cell viability, induced G2/M arrest and apoptosis in leukemic cells. However, the degree of cellular response to GO differed among the four AML cell lines studied, indicating existence of resistant and sensitive cells, and this effect did not correlate with CD33 expression. We report that selective inhibition of BCL-2 and/or PI3K enhanced the pro-apoptotic effect of GO, both in GO-sensitive and GO-resistant AML cell lines. Importantly, the most pronounced effects were observed with the triple combination treatment, which successfully overcame GO resistance. Such inhibition caused cell line-dependent changes in the expression of apoptotic regulators, including BCL-2, MCL-1 and p53 protein, suggesting that cellular context shapes responses to combined treatments. In conclusion, our findings identify BCL-2 and PI3K inhibition as a promising new approach to sensitize AML cells to GO therapy, and highlight the importance of these pathways in determining the cellular response to gemtuzumab ozogamicin.