Novel BODIPY-Loaded Liposomes Enhance Cellular Uptake and PDT Efficacy in 2D and 3D Models

Background: Photodynamic therapy (PDT) is a cancer treatment that combines a photosensitizer (PS), light, and oxygen to generate reactive oxygen species (ROS), leading to tumor cell death. PDT efficacy depends largely on PS accumulation within tumors, prompting the development of third-generation PSs and nanotechnology-based delivery systems. Among these, BODIPYs (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) are promising PSs due to their favorable photophysical properties, while liposomes improve drug delivery, cellular uptake, and sustained release profiles. This study describes the synthesis of two novel BODIPY derivatives differing in the position of a methyl ester group on the meso-phenyl ring, their incorporation into liposomes, and evaluation of PDT efficacy. Methods: Cellular uptake of BODIPY-loaded liposomes, intracellular ROS generation, apoptosis, necrosis, and lipid peroxidation were assessed by flow cytometry in colorectal and ovarian cancer cell lines. The antitumor activity of the liposomal formulations was further evaluated in both 2D and 3D models using MTT and clonogenic assays. The involvement of ferroptosis and necroptosis in PDT-induced cell death was also investigated. Results: Liposomal formulations significantly enhanced cellular uptake compared with free compounds. Following light activation, both formulations induced potent antitumor effects through multiple cell death mechanisms, including canonical and non-canonical pathways, and maintained strong efficacy in 3D tumor spheroids. Conclusions: Liposome-encapsulated BODIPYs represent promising PDT agents by improving cellular uptake and eliciting robust antitumor activity through complementary cell death mechanisms. Furthermore, the methyl ester substituent on the meso-phenyl ring provides a versatile platform for future conjugation with targeting ligands, supporting the development of third-generation, tumor-targeted photosensitizers and warranting further preclinical investigation.