Porphyrins in Photodynamic Therapy - A Search for Ideal Photosensitizers

Abstract

The utility of light as a therapeutic agent can be traced back over thousands of years when it was used in Ancient Egypt, India and China to treat a variety of skin diseases like psoriasis, vitiligo, rickets, cancer and psychosis. The isolation of porphyrins and their inherent tumor localizing properties coupled with its ability to generate reactive singlet oxygen when activated by light of particular wavelength which in turn results in cytotoxicity led to the emergence of a new modality namely, photodynamic therapy (PDT) as a therapeutic tool. The higher degree of selectivity offered by this modality and fewer side effects when compared to chemotherapy and radiotherapy has prompted the researchers around the globe to generate new photosensitizers. Porphyrins and expanded porphyrins are one class of molecules under intense investigation due to their photosensitizing ability for PDT application. Expanded porphyrins result from the expansion of the phi electron conjugation by increasing the number of heterocyclic rings or bridging carbons of the existing porphyrin framework. These chromophores show strong absorptions in the red region (650-800 nm) compared to that of normal 18phi porphyrins. The strong absorption of light by a water soluble nontoxic photosensitizing molecule in the therapeutic window resulting in maximum penetration of light into the tissues coupled with high singlet oxygen production will conceptualize an ideal photosensitizer. This review highlights various porphyrinoid sensitizers reported till date and their photosensitizing ability both in vitro and in vivo studies. Furthermore, the urgent need for developing ideal photosensitizer for PDT will also be highlighted.

Porphyrin-based cationic amphiphilic photosensitisers as potential anticancer, antimicrobial and immunosuppressive agents

“…It also has to be prepared by a reliable and cost-effective synthesis and has to be a stable, pure compound that is not toxic in the absence of light, but is efficient in generating singlet oxygen or other ROS upon red light activation. The generally accepted requirements that one has to take into account at the beginning of a search for a new PS also include easy administration and distribution (Vicente 2001;Pushpan et al 2002;Ethirajan et al 2011;Yoon et al 2013;Mehraban and Freeman 2015). Porphyrin-type compounds (Fig.…”

Cellular stress induced by photodynamic reaction with CoTPPS and MnTMPyPCl5 in combination with electroporation in human colon adenocarcinoma cell lines (LoVo and LoVoDX)

“…These compounds belong to a large class of fluorescent crystalline pigments, which are of natural or synthetic origin, having in common a substituted aromatic macrocyclic ring consisting of four pyrrole-type residues, linked together by four methine bridging groups. Porphyrins are verified as ideal photosensitizers because they are non-toxic, selectively retained in tumor tissue in high concentrations, water-soluble to a certain level, and cleared in a reasonable time from the body and rapidly from the skin, which prevents photosensitive reaction (Pushpan et al 2002;.…”

Diagnóstico Fotodinâmico: Princípios E Aplicações

“…Um PS ideal deve apresentar as seguintes características: baixa toxicidade na ausência de luz, ser um composto puro, hidrossolúvel, biologicamente estável, fotoquimicamente seletivo, apresentar intensa absorção na região espectral entre 600 a 700 nm, baixos custos de produção e rápida excreção do organismo (PUSHPAN et al, 2002).…”