Raman spectroscopic profiling of cell death induced by cytotoxic copper(II), manganese(II), and silver(I) complexes containing dicarboxylate and 1,10-phenanthroline ligands: novel insights into in vitro mechanisms

Raman spectroscopy is a label-free, chemically selective technique increasingly employed to probe intracellular biochemical changes associated with drug exposure. Herein, Raman microspectroscopy was applied to evaluate the in vitro responses of MCF-7 (cancerous) and MCF-12A (noncancerous) breast cells to a series of cytotoxic copper(II) (Cu(II)), manganese(II) (Mn(II)), and silver(I) (Ag(I)) complexes containing dicarboxylate and 1,10-phenathroline ligands. Their spectral responses were analysed using principal component analysis (PCA), establishing distinct molecular fingerprints for each metal complex, reflecting divergent mechanisms of action (MOAs). The Cu(II) complexes produced signatures consistent with canonical apoptosis, including reduced DNA backbone vibrations at ∼785 cm⁻¹ and protein conformational changes at ∼1660 cm⁻¹. The Mn(II) complexes demonstrated features of oxidative stress (∼1450 and 1180 cm⁻¹) and spectral features associated with autophagy (∼718 cm⁻¹), in addition to signatures of an apoptotic response like those observed by the Cu(II) analogues, supporting a multimodal mechanism. In contrast, Ag(I) complexes elicited distinct biochemical alterations suggestive of non-canonical pathways, including markers linked to cholesterol metabolism at ∼703 cm⁻¹ and steroid-related activity indicated by multiple features > 1600 cm⁻¹. These spectral distinctions shed light on the role of different types of metal centres in modulating downstream cellular responses and underscore Raman spectroscopy's utility in resolving subtle yet functionally relevant biochemical differences across this series of complexes. Collectively, these findings provide novel insights into the MOAs of this class of complex and support the broader application of Raman spectroscopy to inform future design and evaluation of metal-based cytotoxic agents.