INVITRO AND INVIVO LIGHT DOSE-RATE EFFECTS RELATED TO HEMATOPORPHYRIN DERIVATIVE PHOTODYNAMIC THERAPY

Abstract

In vitro and in vivo experiments were performed to evaluate the parameter of light dose rate as it relates to the efficiency of hematoporphyrin derivative (HPD)-induced photosensitization. Exponentially growing Chinese hamster ovary cells were incubated with HPD (25 .mu.g/ml) and were then exposed to red light (630 nm) delivered at different dose rates. A total of 5 dose rates (0.5, 5.0, 15, 23 and 60 milliwats/cm2) were examined following a 1-h HPD incubation, 2 dose rates (1 and 20 mW/cm2) were examined after a 12-h HPD incubation and 3 dose rates (0.4, 4 and 40 mW/cm2) were examined following a 16-h incubaton and a 30-min serum wash protocol. The effect of light dose rate was determined from cell survival curves obtained by standard clonigenic colony formation assays. Similar levels of cellular toxicity were obtained when cells from each HPD incubation group were treated with equal doses of red light delivered at different dose rates. For in vivo experiments, albino mice were given injections of HPD (7.5 mg/kg) and 24 h later the right hind leg of each mouse was treated with localized red light (630 nm). A total dose of 270 j/cm2 was delivered to the right hind leg at dose rates of 5, 25, or 125 mW/cm2. The resulting acute skin damage induced by HPD photosensitization was scored over a 30-day period and skin response curves for the 1st dose rates were obtained. Comparable levels of damage were induced in each of the 3 experimental groups. The photosensitizing efficiency of HPD photodynamic therapy evidently is not affected by nonthermal variations in clinically relevant dose rates of delivered light.