PRINCIPAL DRUG-METABOLIZING ENZYME-SYSTEMS IN L1210 LEUKEMIA SENSITIVE OR RESISTANT TO BCNU IN-VIVO

1, 3-Bis(2-chloroethyl)-1-nitrosourea (BCNU) resistance has been mostl y studied in vitro. In an attempt to better understand BCNU resistance in the in vivo situation, we compared the principal drug-metabolizing enzyme systems in two L1210 leukemia lines, one sensitive and one res istant to BCNU (L1210/BCNU), passaged in vivo in mice. The following e nzymes were assayed by immunoblotting: cytochromes P-450 (1A1/1A2, 2B1 /2B2, 2C8-10, 2E1, 3A), epoxide hydrolase (EH) and glutathione S-trans ferases (GST-alpha, -mu and -pi). The following enzymes and cofactors were assayed fluorometrically or spectrophotometrically: 1-chloro-2-4 dinitrobenzene-GST (CDNB-GST), total glutathione (GSH), UDP-glucuronos yltransferase, beta-glucuronidase, sulfatase and sulfotransferase. Res ults showed that cytochrome P-450 1A1/1A2 was the only isoenzyme detec ted in both L1210 and L1210/BCNU. CDNB-GST activity was significantly higher in L1210/BCNU compared with L1210. The isoenzyme GST-alpha was more abundant in L1210/BCNU compared with L1210, whereas GST-pi was ex pressed less in the BCNU-resistant leukemia line. GST-mu was not detec ted in either L1210 leukemia lines. GSH levels were similar in the two L1210 lines. No significant difference was observed between the two l eukemia lines for the conjugative enzymes UDP-glucuronosyltransferase and sulfotransferase, whereas their corresponding hydrolytic enzymes b eta-glucuronidase and sulfatase were about two-fold lower in the BCNU- resistant leukemia line. Epoxide hydrolase was 1.3-fold higher in L121 0/BCNU compared with L1210 and this level was about three-fold higher than in mouse liver. In conclusion, these studies showed the presence of cytochrome P-450 1A1/1A2 in the two L1210 leukemia lines studied, a nd indicated noteworthy differences between the two leukemia lines for many enzyme systems such as GST, beta-glucuronidase, sulfatase and ep oxide hydrolase. These data are of importance to better understand the mechanisms of drug resistance to nitrosoureas in vivo.