Effects of Light Exposure on the Uptake and Destruction of Hematoporphyrin Derivative in Ehrlich Carcinoma Cell Suspension

Abstract

A mixture of porphyrins derived from hematoporphyrin and termed hematoporphyrin derivative (HpD) has been used for localization and photodynamic therapy (PDT) of tumours. Our data showed that HpD photobleached more rapidly when incorporated into tumour cells than in simple aqueous solutions. At light doses that are usually used in PDT about 30-40% of the HpD added to the cell suspension can be destroyed. In addition to photochemical modification, which leaves the porphyrin ring intact, more "drastic" reactions destroying the ring took place. At least one photoproduct was detected. This photoproduct (presumably a reduced porphyrin) has an emission peak at 640-650 nm and is optimally excited at 400 nm. However, the identity of the reactive oxygen species mediating HpD photobleaching in the cells is not clear. In cells, HpD may produce hydrogen peroxide (as a result of photosensitized oxidation of some biomolecules) and very reactive hydroxyl (OH®) radicals. We established that HpD is very reactive towards OH* radicals.Therefore, besides singlet oxygen, H,O, and OH® radicals may be involved in photobleaching. It was found that light exposure (A, = 630 nm) accelerates the cellular uptake of HpD. This process was induced, however, by lethal light doses. It could be supposed that light exposure in the presence of HpD results in a membrane damage that allows HpD to penetrate faster into the cells or facilitates the binding of the sensitizer to the membrane itself. However, a longterm dark incubation of tumour cells, previously subjected to limited injury by means of HpD-PDT, did not induce similar levels of the sensitizer accumulation. Our data suggest that the lightinduced increase in the HpD uptake by the tumour cells may be the result of covalent binding of HpD with certain intracellular molecules, probably with protein.

Influence of Extracellular Magnesium on the Antitumour Efficiency of Photodynamic Therapy

“…5 min after the addition of a PS, the cells were irradiated at 665 or 630 nm for E 6 and HpD, respectively. Our prior studies [25,26] showed that after a short incubation time (5 min) approximately 20-25% of the initial content of HpD (1 ug ml™") or E 6 (2 uM) is bound to EAC cells. It was also found that the presence of non-bound PSs in a medium has a negligible effect on the rate of HpDor E6-photosensitized damage of the cells.…”