Synthesis, cytotoxicity, apoptosis-inducing activity and molecular docking studies of novel isatin–podophyllotoxin hybrids†

Podophyllotoxin, along with its numerous derivatives and related compounds, is well known for its broad-spectrum pharmacological activity, especially for anticancer potential. In this study, several isatin–podophyllotoxin hybrid compounds were successfully synthesized with good yields through microwave-prompted three-component reactions of 2-amino-1,4-naphthoquinone, various substituted isatins, and tetronic acid. Their cytotoxicity was assessed against four types of human cancer cell lines, HepG2 (hepatoma carcinoma), MCF7 (breast cancer), A549 (non-small lung cancer), and KB (epidermoid carcinoma), alongside nontumorigenic HEK-293 human embryonic kidney cells. Among 14 compounds screened, 7f possessed the strongest cytotoxicity to KB and A549 cell lines, with IC₅₀ values of 1.99 ± 0.22 and 0.90 ± 0.09 μM, respectively. Further studies revealed that product 7f could arrest the cell cycle of A549 cells at S phase and induce apoptosis of A549 cells. This compound was examined for its binding ability against cyclin-dependent kinases (CDKs) and procaspase/caspase systems. The results indicated that 7f exhibited significant interactions with the residues of the ATP binding sites of CDK2/cyclin A and CDK5/p25 and also activated procaspase 6 through stable zinc chelation. Additionally, physicochemical and pharmacokinetic properties related to drug-likeness, in parallel with toxicity, were computationally assessed to identify the main issues that need to be addressed in structural optimization. Taken together, compound 7f was identified as a potent cytotoxic agent that could be considered for anticancer drug discovery and development.