Hybrid molecules of protoflavones and spirooxindole derivatives with selective cytotoxicity against triple-negative breast cancer cells

The combination of compounds with complementary bioactivities into hybrid molecules is an emerging concept in drug discovery. In this study, we aimed to synthesize new hybrid compounds based on p53-MDM2/X protein–protein interaction spiropyrazoline oxindole-based inhibitors and ataxia telangiectasia and Rad3-related (ATR) protoflavone-based inhibitors through copper(i) catalysed azide–alkyne cycloaddition. Five new hybrids were prepared along with three representative reference fragments. The compounds were tested against human breast cancer cell lines MCF-7 (hormone-dependent, wild-type p53) and MDA-MB-231 (triple-negative, mutant p53). Most of the new hybrids were more cytotoxic than their reference fragments and several showed 2–4 times selective toxicity against MDA-MB-231 cells. Relevant pharmacological benefit gained from the hybrid coupling was further confirmed by virtual combination index calculations using the Chou method. Compound 13 modulated doxorubicin-induced DNA damage response through inhibiting the ATR-dependent activation of Chk-1, while increasing the activation of Chk-2. Our results suggest that the new hybrids may serve as new leads against triple negative breast cancer.