Bromines on N-allyl position of cationic porphyrins affect both radio- and photosensitizing properties

With the aim to develop improved dual-action sensitizers suitable for both photodynamic therapy (PDT) and radiotherapy, we prepared a series of metal and metal-free cationic porphyrins, brominated either on beta-or N-allyl positions. Photo-and radiosensitizing efficacy was evaluated in MDA-MB-231 breast cancer cells incubated with 1 mM porphyrin and treated with graded doses of visible light or 0-6 Gy of Co-60 gamma irradiation. Metabolic activity after PDT or cell survival after gamma irradiation were estimated by a colorimetric (MTT) or clonogenicity assay, respectively. The highest photo-and radiosensitizing activities were observed with the porphyrins substituted with bromines on N-allyl positions. The non-metalated N-allyl bromoporphyrin exhibited the highest photocytotoxicity (LD50 = 4.1 +/- 0.6 J cm(-2), compared to 15.3 +/- 2.2 J cm(-2) for the non-brominated analog). The radiosensitizing capacity of the cationic porphyrins was also affected by these substitutions with the non-metalated N-allyl bromo analog showing the best improvement (LD50 = 1.2 +/- 0.4 Gy vs. 3.6 +/- 0.9 Gy for the non-brominated analog). The increased photodynamic and radiosensitizing potencies due to bromine addition hold potential for the development of new, improved drugs for cancer treatment in combination with photodynamic and radiation therapy.