Targeting drug efflux and DNA repair enhances inotuzumab ozogamicin activity in IO-resistant B-ALL cell lines.

Inotuzumab ozogamicin (IO), an anti-CD22 antibody conjugated with calicheamicin, is highly effective against relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). However, acquired resistance limits the long-term efficacy of IO. To elucidate the underlying mechanisms of IO resistance and explore strategies to overcome it, six IO-resistant B-ALL sublines were newly established. Although CD22 expression was preserved in all resistant sublines, more than 80-fold increases in 50% inhibitory concentration (IC50) were observed, accompanied by acquired resistance to IO-induced apoptosis. Microarray analysis revealed upregulation of ABCB1, which was further confirmed by overexpression of the encoded protein, the drug efflux pump P-glycoprotein (P-gp). P-gp inhibition restored IO sensitivity by inhibiting calicheamicin efflux, a key resistance mechanism. Concurrently, poly (ADP-ribose) polymerase (PARP) inhibition of DNA damage repair enhanced IO cytotoxicity. Notably, in the triplet combination of IO with P-gp and PARP inhibitors, PARP inhibition of the repair of DNA damage caused by calicheamicin accumulation following P-gp inhibition markedly enhanced the antitumor effects of IO. This approach may offer a novel and effective therapeutic strategy for IO-resistant B-ALL.