Morpholinoethoxy-Substituted Cationic Metal-Free and Metallo Phthalocyanines: In Vitro Photodynamic Therapy Activities, PDT-Induced ROS Level Measurements, and Cellular Death Mechanism

In this study, morpholinoethoxy-attached cationic tetra-substituted phthalocyanines (Pcs), including metal-free (HQH₂Pc), zinc (HQZnPc), and indium (HQInPc) derivatives, were synthesized following established protocols. Their structures were confirmed by using standard spectroscopic techniques. The photodynamic therapy (PDT) efficacy of these compounds was evaluated against head, neck, and colon cancer cell lines. Reactive oxygen species (ROS) levels induced by PDT with cationic Pcs were quantified by using dichlorodihydrofluorescein diacetate. To elucidate the mechanisms of action, ROS generation was assessed at two distinct time points: 30 min (immediate response) and 24 h (delayed response) post-PDT. The cellular death mechanisms induced by Pc-mediated PDT in cancer cell lines were investigated using fluorescence staining with Apopxin Green, CytoCalcein Violet 450, and 7-AAD to differentiate apoptotic and necrotic pathways and provide insights into the mode of cell death. The results indicated that the Pcs exhibited minimal cytotoxicity in the absence of light, confirming their safety as photosensitizers. Cationic Pcs, particularly HQZnPc, showed high PDT-induced cytotoxicity and ROS production, primarily inducing apoptosis in cancer cell lines, with FaDu cells exhibiting the highest sensitivity. These results highlight HQZnPc’s strong potential for cancer therapy and underscore the need for further research into its delivery and mechanisms in complex tumor models.