CRC cell cycle arrest and early apoptosis induction by mononuclear octahedral cobalt(III) Schiff base through the inhibition of CDK4/6 and BCL2.

Synthetic cobalt Schiff bases have recently emerged as promising metal-based anticancer candidates. In this study, we investigated the biological effects of a mononuclear octahedral cobalt(III) Schiff base complex [CoL3] (L = 2-((allylimino) methyl) - 6-methoxyphenol)) on the cell cycle progression and apoptosis of the HT-29 cells, a human colorectal cancer cell line. Cytotoxic activity of [CoL3] was evaluated using the MTT assay. Then, its impact on apoptosis was assessed via annexin V-FITC/propidium iodide (PI) staining. To elucidate the underlying mechanisms, we employed flow cytometry, real-time PCR, and Western blotting to analyze cell cycle distribution and the expression of apoptotic and cell cycle-related genes. Our results revealed that [CoL3] exhibited potent cytotoxicity with an IC50 of 3.47 µM and induced cell cycle arrest in the G1/S and G2/M transition phases in colorectal cancer cells (p < 0.001, p < 0.01). Treatment of colorectal cancer cells with [CoL3] resulted in a significant decrease in CDK4 and CDK6 expression, with mean values of 0.62 (p < 0.05) and 0.33 (p < 0.01), respectively. Additionally, the protein expression of CDK4 and CDK6 was downregulated, with mean protein intensities of 0.48 and 0.79, respectively (p < 0.001), supporting its role in G1 phase blockade. Moreover, [CoL3] downregulated BCL2 (p < 0.01), which was associated with increased early and late apoptosis in treated cells. Docking analyses further demonstrated favorable spontaneous binding of [CoL3] to CDK4 and CDK6, reinforcing its mechanistic involvement in cell cycle inhibition. Collectively, these findings indicate that [CoL3] induces cell-cycle arrest and promotes apoptosis in HT-29 colorectal cancer cells, potentially through the downregulation of CDK4/6 and BCL2.