Preclinical activity of 17 beta-[N-[N '-(2-chloroethyl)-N '-nitrosocarbamoyl]-L-alanyl]-5 alpha-dihydrotesterone (E91) against tumour colony forming units and haematopoietic progenitor cells

E91 (17 beta-[N-[N'-(2-chloroethyl)-N'-nitrosocarbamoyl]-L-alanyl]-5 alpha- dihydrotestosterone) (CNC-ala-DHT) is a newly synthesised alkylating compou nd consisting of N-[N'-(2-chloroethyl)-N'-nitrosocarbamoyl]-L-alanine (CNC- ala) as the alkylating moiety and of 5 alpha-dihydrotestosterone (DHT) as a steroid carrier molecule. We studied the antitumour activity of E91 (final concentrations: 0.1, 1, 10 and 30 mu mol/l) against freshly explanted huma n tumours, using an in vitro soft agar cloning system. A total of 54 tumour samples was evaluated using 1 h-exposure and 51 tumour specimens were stud ied using a continuous exposure for 21-28 days. In addition, the compound's activity was compared with other clinically used anticancer agents. After short-term exposure, 49 of 53 evaluable specimens (92%) had adequate colony formation, as compared with 49 of 50 (98%) after long-term exposure. After short-term exposure, E91 exhibited only marginal antitumour activity. Howe ver, in long-term exposure experiments, E91 had marked and concentration-de pendent antitumour activity (P<0.001). At concentrations of > 10 mu mol/l, E91 was as active as the other clinically used antineoplastic agents and at 30 mu mol/l, E91 was significantly more active than 5-fluorouracil (P=0.04 1). E91 showed activity against a wide spectrum of tumour types. The highes t activity was observed against colorectal carcinomas (3/4 tumour specimens inhibited at 30 mu mol/l). Sensitivity was also high remarkable in breast cancer specimens with 3/6 specimens inhibited at 30 mu mol/l. In vitro myel otoxicity was less than that of doxorubicin. At 30 mu mol/l, E91 induced a reduction of colony forming units-granulocyte macrophage (CFU-GM) to only 5 3% of control and of CFU-GEMM to 20% of control. We conclude that because o f broad activity and reduced myelotoxicity further clinical development of E91 appears warranted. (C) 1999 Elsevier Science Ltd. All rights reserved.