Fluorescent palladium(ii) and platinum(ii) NHC/1,2,3-triazole complexes: antiproliferative activity and selectivity against cancer cells

Abstract

Fluorescent Pd(II) and Pt(II) complexes bearing 4-methylene-7-methoxycoumarin (MMC) and 2,6-diispropylphenyl (Dipp) substituted NHC/1,2,3-triazole hybrid ligands are described. Depending on the reaction conditions two different ligand coordination modes are observed, i.e., bidentate solely coordinating via NHCs or tetradentate coordinating via NHCs and 1,2,3-triazoles. All Dipp substituted complexes show antiproliferative activity against cervix (HeLa) and breast (MCF-7) human carcinoma cells. The activity significantly depends on the coordination mode, with the tetradentate motif being notably more effective (HeLa: IC₅₀ = 3.9 μM to 4.7 μM; MCF-7: IC₅₀ = 2.07 μM to 2.35 μM). Amongst the MMC series, only the Pd(II) complex featuring the bidentate coordination mode is active against HeLa (IC₅₀ = 6.1 μM). In contrast to its structurally related Dipp derivative (SI = 0.6), it shows a high selectivity for HeLa (SI > 16) compared to healthy skin cells (HaCaT). According to fluorescence microscopy, this compound is presumably located in late endosomes or lysosomes.