MECHLORETHAMINE-INDUCED ENHANCEMENT OF RADIATION SENSITIVITY OF GUANINE

This study describes and characterizes the interactions of nitrogen mu stard mechlorethamine (HN2) with guanine and the radiation sensitivity of guanine in the presence of HN2. Briefly, in an equimolar solution (0 . 5 mmoldm(-3)) the pH-dependence (pH 3 . 0-12 . 0) and time-depend ence (0-36 h) of alkylation of guanine at room temperature were determ ined using a reverse-phase highperformance liquid chromatography (hplc ) column. Based on the hplc peak areas of the product and intact guani ne, the optimal pH for alkylation was determined to be 8 . 0. Similarl y, the optimal time required for alkylation was 10 h. Two products, i. e. alkylated guanines, were detected (10:1, peak areas measured at 260 nm) and purified. Structural studies of the products were performed b y direct insertion probe-electron impact mass spectrometry. These prod ucts were identified as N-(2-chloroethyl)-N-[2-(7-guanyl)-ethyl] methy lamine (product 1) and (2-hydroxyethyl)-N-[2-(7-guanyl)ethyl]-methylam ine (product 2). At optimal conditions, samples of either guanine or a n equimolar solution of guanine and HN2 were Co-60 irradiated (gamma-r ay) at 25 Gy min(-1) at doses up to 400 Gy. Both sets of samples were analysed by hplc. In each case, the sole radiation product observed an d characterized was 8-hydroxy-guanine. Dose-yield plots were linear an d showed that HN2 enhanced the radiation sensitivity of guanine. This increase in radiation sensitivity is attributed to the differences in electrophilic properties between nitrogen mustard and guanine.