Cytotoxicity of PP(Arg)2- and PP(Ala)2(Arg)2-based photodynamic therapy and early stage of apoptosis induction in human breast cancers in vitro

Mitochondria are cell energetic centers where ATP is produced. They also play a very important role in the PDT as intracellular sites of photosensitizer localization. Photosensitizers gathering in mitochondria (like porphyrin derivatives used in this work) are more effective in tumor cell destruction. Moreover, it was assumed that di-amino acid substituents attached to porphyrin ring will strengthen the effectivity of interaction with membrane receptors of examined cells. MTT assay was performed to investigate the influence of PP(Arg)2 and PP(Ala)2(Arg)2-based PDT on breast cancer cell viability for 24 h, 48 h and 120 h after cell irradiation. Then the influence of PP(Ala)2(Arg)2- and PP(Arg)2-mediated PDT on early mitochondrial apoptosis induction via measurements of the transmembrane mitochondrial potential changes was examined. Results showed that lower energy doses and maximal nontoxic photosensitizer doses of PP(Ala)2(Arg)2 and PP(Arg)2 applied in PDT can imply apoptotic cell death. It was confirmed that modification of the protoporphyrin IX by attaching two alanine substituents raised the efficiency of photodynamic therapy.