Structure activity relationship of L-Ir(III)Cl-cp complexes interfering CDK4-cyclin D1 and AKT-mTOR pathways to suppress colorectal cancer tumorigenesis and induce cell death via PARP and caspase-3 pathways.

Naphthyl-functionalized half-sandwich Ir(III) complexes were designed as non‑platinum metal candidates for colorectal cancer cell growth inhibition, the naphthyl group was purposefully introduced in the ligands in order to facilitate DNA intercalation and enhancing biomolecular interactions. In this work, eight naphthyl-functionalized half-sandwich Ir(III) complexes (L-Ir(cp)Cl) [cp = pentamethylcyclopentadienyl] (C1a-C4a, C1b-C4b) were designed and synthesized bearing central pyridine- or pyrimidine-based N, N-chelating ligands. The target complexes were obtained in high yields via simple single step reaction and characterized by 1H NMR, 13C NMR, UV-vis, IR spectroscopy and high-resolution mass spectrometry (HR-MS). The structures of six complexes (C3a-C4a, C1b-C4b) were determined by single-crystal X-ray analysis, showing a typical half-sandwich "three-legged piano-stool" geometry with a chloride ancillary ligand (Ir-Cl), which may be relevant to their biological activity.

In vitro antiproliferative activity was assessed in colorectal cancer RPMI 4788 and LOVO cells via MTT assays. In both these series C1b and C2b exhibited potent proliferation-inhibitory effects, with stronger activity in RPMI 4788 cells, and C2b outperforming C1b. Cancer cell imaging, flow cytometry, and clonogenic assays confirmed strong inhibition of cell proliferation. Concentration- and time-dependent migration assays showed significantly reduced cancer cell migration.

Cell-cycle analysis suggested S-phase accumulation in RPMI 4788 cells, and C2b treatment decreased the expression of Cyclin D1 and CDK4. Western blot analysis revealed changes in the representative proteins associated with apoptosis and cell growth, including PARP, Caspase-3, Bcl-2, AKT, and mTOR.

This study provided experimental evidence supporting these novel Ir(III) complexes, especially C2b as potential in vitro antiproliferative agents in colorectal cancer cells that need to be further explored in other cancers by detailed in vitro and in vivo mechanistic investigations.