Thymidine Uptake, Incorporation and Dna Polymerase Activity in Murine Bladder Tumor Cell,mbt–2, Exposed to Uv Activated Dihematoporphyrin Ether

Abstract

Abstract— Photodynamic therapy (PDT) is a new modality for treatment of malignancy. In this paper, we reported the effect of UV activated dihematoporphyrin ether (DHE) on [3H] thymidine uptake and DNA synthesis in murine bladder tumor cells,MBT–2. Exponentially growing cells were pretreated with 0.05–5μg/ml of DHE for 30 min in complete darkness prior to irradiation with 0.15‐0.90 J/cm2 of UV light (265 nm). The rates of thymidine uptake and DNA synthesis were suppressed in a DHE concentration and photic energy dependent manner. Double reciprocal analysis on the kinetics of the thymidine uptake and DNA synthesis indicated that the inhibition was non‐competitive, i.e. decrease in both the apparent Km value and maximum velocity in DHE plus UV light treated cells. The activities of DNA polymerase a and (3 were determined by [*H] dATP incorporation into DNA of permeabilizedMBT–2 cells. DNA polymerase a activity was approximately 60% of the control after 0.45 J/cm2 of UV light exposure; a further inhibition of DNA polymerase a was observed when 0.5–5ng/W of DHE and UV photoradiation were combined. In contrast, a slight stimulation of DNA polymerase fJ was noted after a similar treatment. This study demonstrates that photodynamic therapy‐induced suppression of DNA synthesis inMBT–2 cells is a complex process involving in reduction of thymidine transport as well as the perturbation of the enzymes involved in DNA synthesis.