Mitochondria-Targeted Benzoxazole-Based Platinum Photosensitizer Complexes: Photophysical Properties and Photocytotoxicity Evaluation Against Breast and Gastric Cancer Cells

This study explores platinum­(II) phototherapy using cycloplatinated compounds with bidentate 2-(4-substituted) benzoxazole ligands, [Pt­(L)­(R)­(X)] (C1–C5). The compounds were synthesized and fully characterized, and their photophysical, cytotoxic, and phototoxic properties were analyzed. Time-dependent Density Functional Theory (TD-DFT) calculations supported the analysis of the complexes absorption and photoluminescence, with high-energy absorption showing 1L′LCT/1MLCT [π­(Cl, Me) → π*­(C^N)] contributions. Among the complexes, C4 (L = C^N, R = κ1-N-C^N, X = Cl) exhibited the highest quantum yield (ΦF = 48%) and showed strong antiproliferative activity in breast carcinoma (MCF-7) and gastric adenocarcinoma (AGS) cell lines. C1–C5 (C1, L = N^N, R = Cl, X = Cl, C2, L = N^N, R = Me, X = Me; C3, L = C^N, R = DMSO, X = Cl; C4, L = C^N, R = C^N, X = Cl, and C5, L = C^N, X = Me, R = DMSO) also demonstrated potential as photoactivatable agents. Mechanistic studies indicated that the complexes triggered ROS generation, mitochondrial dysfunction, and lysosomal damage, with C4 showing promise for photochemotherapeutic treatment of gastric and breast cancer due to its selectivity and effectiveness in targeting mitochondria and lysosomes.