Cyclosporin A Enhance the Cytotoxicity of Immunotoxin to the HER-2-Overexpressing SK-OV-3 Cells: A Prospective Study

This study explores the synergistic effect of T-CUS 245C combined with cyclosporin A, and its possible mechanism. T-CUS 245C is an immunotoxin conjugated with tastuzumab and recombinant cucurmosin 245C (CUS 245C ). Cyclosporin A is a calcium antagonist mainly used as an immune-suppressive agent, which enhances the cytotoxicity of immunotoxins through an unknown mechanism. The sulforhodamine B assay, flow cytometry, DNA fragmentation apoptosis assay, and western blot analysis were used to evaluate the synergistic effects of cyclosporin A combined with T-CUS 245C on proliferation inhibition and apoptosis induction in SK-OV-3 ovarian cancer cells with HER-2-overexpressing. Meanwhile, using confocal microscopy and flow cytometry, the effect of cyclosporin A on the intracellular distribution of T-CUS 245C was observed and quantified. The results of this study showed that the combination index of cyclosporin A combined with T-CUS 245C is less than 0.7, indicating that cyclosporin A significantly enhances the proliferation inhibition and apoptosis induction induced by T-CUS 245C in SK-OV-3 cells. The confocal microscopy and flow cytometry results show that cyclosporin A effectively increases the dispersion of T-CUS 245C in the cytoplasm by promoting the endolysosomal escape. This study demonstrates that cyclosporin A combined with T-CUS 245C has a synergistic anticancer effect, by facilitating the release of T-CUS 245C in the intracellular space. Graphical Abstract