Assessing the cytotoxic effects of Group IX metal N-heterocyclic carbene complexes of iridium and rhodium on B16-F10 melanoma and non-cancerous RAW 264.7 cells

Abstract

The development of highly effective and selective anticancer agents remains a central challenge in oncological research. Herein, we report a systematic evaluation of the anticancer activity of a series of rhodium- and iridium-based NHC (N-heterocyclic carbene) complexes (complexes 1, 3, 5–7), including the novel complex 3, as well as two imidazole-containing complexes (2 and 4). Their cytotoxic profiles were investigated against B16-F10 melanoma cells and benchmarked against non-cancerous RAW 264.7 macrophage cells to assess cancer selectivity. Cytotoxicity of complexes 1–7 was quantified using the crystal violet assay following exposure to 0.01 mM and 0.1 mM concentrations over 24, 48, and 72 h. Half-maximal inhibitory concentrations (IC50) were determined to establish comparative selectivity and potency indices. Mechanistic insight was further obtained through morphological assessment of treated cells at IC50 values using polarised light optical differential interference contrast (PlasDIC) microscopy. At 0.1 mM, all complexes induced a pronounced reduction in B16-F10 cell viability, with complexes 2 and 3 emerging as the most potent, achieving >90% inhibition after 72 h. Notably, early time-point IC50 values (24 h) revealed marked cytotoxicity in melanoma cells (complex 2: 0.04 mM; complex 3: 0.05 mM), while eliciting minimal effects in RAW 264.7 macrophages, indicating selective anti-cancer activity. Morphological analysis of B16-F10 cells demonstrated features consistent with both apoptosis (membrane blebbing, apoptotic bodies, nuclear fragmentation) and necrosis (cell swelling, debris). Cell cycle analysis demonstrated a general increase in the S phase in B16-F10 cells, indicative of replication stress or cell cycle arrest, whereas no significant changes were observed in RAW 264.7 cells. Collectively, complexes 2, 3, and 5, display a compelling combination of potency and selectivity towards B16-F10 melanoma cells, with reduced cytotoxicity towards non-cancerous RAW 264.7 cells. These results support the continued development of NHC-based metal complexes as promising selective anticancer agents and warrant further mechanistic and in vivo investigation.

HIGHLIGHTS • Range of Rh and Ir metal complexes tested against B16F10 melanoma cells and non-cancerous RAW 264.7 macrophage cells with moderate activity (0.04–0.09 mM IC50) and high selectivity. • Morphological analysis of B16-F10 cells revealed both apoptotic (membrane blebbing, apoptotic bodies, nuclear fragmentation) and necrotic (cell swelling, debris) features. • Cell cycle analysis showed a general increase in S phase in B16-F10 cells and showed no significant changes in RAW 264.7 cells.