Synthesis, characterization, and cellular investigations of porphyrin- And chlorin-indomethacin conjugates for photodynamic therapy of cancer

Abstract

Indomethacin is a potent non-steroidal anti-inflammatory drug (NSAID) with a strong selective inhibitor activity towards cyclooxygenase-2 (COX-2), an enzyme that is highly overexpressed in various tumour cells, being involved in tumourigenesis. Concomitantly, porphyrins have gained much attention as promising photosensitizers (PSs) for the non-invasive photodynamic therapy (PDT) of cancer. Herein, we report the design, and determine the singlet oxygen generation capacity andin vitrocellular toxicity of porphyrin- and chlorin-indomethacin conjugates (P2-IndandC2-Ind). Both the conjugates were obtained in high yields and were characterized by1H,19F and13C NMR as well as by high resolution mass spectrometry. The singlet oxygen generation properties were assessed by the 1,3-diphenylisobenzofuran singlet oxygen trap method, which showed thatC2andC2-Indare the best singlet oxygen photosensitizers. In addition, it was found that the presence of indomethacin did not influence the singlet oxygen generation of porphyrin or chlorin. Cytotoxicity studies of the conjugate in human HEp2 cells revealed that the porphyrin- and chlorin-indomethacin conjugates have similar dark cytotoxicities, while chlorinC2was shown to be the most phototoxic. Despite having lower cellular uptake thanC2-Indafter 24 hours, chlorinC2had a broad localization in HEp2 cells while the chlorin-indomethacin conjugateC2-Indcould be detected in the form of small aggregates. DFT calculations were performed to shed light on the reaction energy involved in the formation of the indomethacin conjugates and to compare the relative stability of selected isomers in solution. Moreover, the calculated energy of their first excited triplet state structures confirmed their use as suitable photosensitizers to generate singlet oxygen for PDT.