Design, Synthesis, and Cytotoxicity Evaluation of Novel Indolin-2-One Based Molecules on Hepatocellular Carcinoma HepG2 Cells as Protein Kinase Inhibitors

A series of indolinone-based derivatives were designed and synthesized using the hybrid pharmacophoric design approach as cytotoxic kinase inhibitors. The cytotoxic effects of the designed molecules were tested against MCF-7 and HepG-2 cell lines. Compounds <b>9</b> and <b>20</b> were the most cytotoxic, with IC₅₀ values against HepG-2 and MCF-7 cells ranging from 2.53 to 7.54 µM. Additionally, compounds <b>9</b> and <b>20</b> were also found to be slightly more cytotoxic than indirubin with 2.2-2.7-fold higher cytotoxicity with HepG-2 cells. CDK-2 and CDK-4 kinase enzyme inhibition assay showed that compound <b>9</b> had a higher inhibitory effect (4.8-fold) than indirubin against CDK-2 and comparable inhibition against CDK-4. Moreover, compound <b>20</b> displayed nanomolar inhibitory action against both EGFR kinase and VFGFR-2 enzyme, which were around 8.8- and 5.4-fold higher than the IC₅₀ values of indirubin. Compounds <b>9</b> and <b>20</b> induced cell cycle arrest at the G₁ phase on HepG2 cells. The levels of the key apoptotic proteins assessed revealed elevated levels of the Bax/Bcl-2 ratio, which in turn initiated the caspase3/7 cascade that led to the activation of both intrinsic and extrinsic apoptotic pathways. The cell cycle inhibitory proteins p53 and p21 were significantly upregulated upon treatment with compounds <b>9</b> and <b>20</b>. The docking results revealed that compound <b>9</b> exhibits stronger binding affinity to CDK-2 than indirubin, and compound <b>20</b> showed a similar binding mode to sorafenib with VEGFR-2.