ANTI-TUMOR ACTIVITY OF CPT-11 IN EXPERIMENTAL HUMAN OVARIAN CANCER AND HUMAN SOFT-TISSUE SARCOMA Willy J.M. JANSEN 1 , Geertruida M. KOLFSCHOTEN 1 , Caroline A.M. ERKELENS 2 , Jannette V AN ARK-OTTE 1 , Herbert M. PINEDO 1 and Epie BOVEN 1 * 1 Department of Medical Oncology, Academic Hospital, Vrije Universiteit, Amsterdam, The Netherlands 2 Central Laboratory of Experimental Medicine, Vrije Universiteit, Amsterdam, The Netherlands CPT-11, a semi-synthetic derivative of camptothecin, was investigated for its activity in panels of 15 human ovarian- cancer lines and 10 human soft-tissue sarcoma lines grown s.c. in nude mice. Various factors were analyzed that may be of influence on the extent of tumor-growth inhibition induced by CPT-11. At equitoxic doses, CPT-11 was more effective in the daily 5 schedule than the weekly 2 schedule, although a 2-fold higher dose was administered in the weekly 2 schedule. Since i.p. and i.v. injections were similarly effective, the selected treatment schedule was 20 mg/kg i.p. daily 5, starting when tumors measured approximately 150 mm 3 . Growth inhibition of H75% was obtained in 8/15 human ovarian-cancer lines and in 6/10 human soft-tissue sarcoma lines. A weak correlation wasfound between topoisomerase-I mRNA in xenograft tissues and sensitivity to CPT-11. Rela- tive topoisomerase-I expression was highest in MRI-H-207 and W LS-160 xenografts, in which CPT -11 was able to induce cures of all tumors. T he high efficacy in the 2 panels of human tumor lines suggests over-prediction of its potential clinical activity in these tumor types. The difference in efficacy of CPT -11 between speciesmay be related to the metabolism of the drug, since CPT-11 is converted more efficiently into SN-38 in mice. In addition, mice may be less sensitive to SN -38-induced side-effects. On the basis of the preclinical data, frequent administration of lower doses of CPT-11 should be considered in order to increase response rates in the clinic. Int. J. Cancer 73:891–896, 1997.  1997 Wiley-Liss, Inc. CPT-11 (irinotecan or 7-ethyl-10[4-(1-piperidino)-1-piperidino]- carbonyloxy camptothecin) is a water-soluble derivative of campto- thecin, an inhibitor of the nuclear enzyme topoisomerase I. CPT-11 is a drug with limited activity, since to exert its action it needs to be converted into SN-38 (7-ethyl-10-hydroxy-camptothecin) in vivo by a carboxylesterase (Dancey and Eisenhauer, 1996). The metabo- lite SN-38 is more potent in vitro when compared with CPT-11. In 5 unselected human colon-cancer cell lines, SN-38 was found to be 130- to 570-fold more active than the parent compound (Jansen et al., 1997). The anti-tumor activity of camptothecins both in vitro and in vivo is significantly greater for the lactone form than the carboxylate form. The closed lactone ring is important both for passive diffusion into the cell and for inhibition of the activity of topoisomerase I. Thus, factors of influence on the lactone- carboxylate equilibrium of camptothecins, such as the pH, will determine their biological activity (Dancey and Eisenhauer, 1996). At pH 7 or above, the lactone ring of the drug hydrolyses into the less active carboxylate form. CPT-11, when given by i.p., i.v. or oral route, has shown substantial activity in a broad spectrum of mouse tumors (Kuni- moto et al., 1987). Impressive activity of the compound adminis- tered i.v. was measured in human tumor xenografts, such as colon-cancer and childhood-rhabdomyosarcoma xenografts (Hough- ton et al., 1995). Growth inhibition was also obtained in pediatric and adult central-nervous-system xenografts when the drug was administered i.p. (Hare et al., 1997). Clinical evaluation of CPT-11 has confirmed the therapeutic potential in a number of malignan- cies, particularly colorectal cancer, non-small-cell lung cancer and cervical cancer (Dancey and Eisenhauer, 1996). Camptothecins are particularly toxic to cells in the S-phase of the cell cycle, although the cellular levels of topoisomerase I appear to be relatively constant during the phases of the cell cycle (Dancey and Eisenhauer, 1996). Therefore, increased activity may be expected by altering the treatment regimen. Houghton et al. (1995) have suggested that more potent topoisomerase-I inhibition may be achieved by using a low-dose protracted schedule, as demonstrated in human tumor xenografts. In other experimental tumor models, Bissery et al. (1996) have demonstrated that CPT-11 was not markedly schedule-dependent with respect to toxicity, as has been confirmed in humans. We have established a panel of 15 human ovarian-cancer lines and a panel of 10 human soft-tissue-sarcoma lines grown as (s.c.) tumors in nude mice. The retention of the histological and antigenic characteristics of the tumor tissue of origin has been described (Boven et al., 1989; Molthoff et al., 1991). In the present experiments, CPT-11 was investigated for its activity in these human tumor xenografts, and various factors of possible influence on efficacy were analyzed. In the experiments, we first compared the growth inhibition induced by CPT-11 when given in a weekly 2 or a daily 5 schedule and when given i.p. or i.v. Thereafter, the best effective schedule of CPT-11 was studied in the 2 panels of human tumor xenografts. Topoisomerase-I mRNA expression was measured in the xenograft tissues, to determine whether a possible relation was present between gene content and the growth inhibi- tion induced by CPT-11. MATERIAL AND METHODS Animals Female nude mice (Hsd: athymic nude-nu) were purchased from Harlan CPB (Zeist, The Netherlands) at the age of 6 weeks. The animals were maintained in cages with paper filter covers, in controlled atmospheric conditions. Cages, covers, bedding, food and water were changed and sterilized weekly. Animals were handled in a sterile manner in a laminar down-flow hood. Tumor lines Human ovarian-cancer xenografts (Table I) and soft-tissue sarcoma xenografts (Table II) had been established earlier from fresh tumor tissue of patients or from in vitro cell lines. Ovarian- cancer xenografts (6) were generated from patients during second- look laparotomy after treatment, and 5 soft-tissue sarcoma xeno- grafts were grown from progressive or recurrent disease during or after treatment. None of the patients had been given CPT-11. Other xenografts were established from untreated patients, except for 3 patients whose pre-treatment was unknown. Tumors were grown s.c. in both flanks. For transplantation, fragments with a diameter of 2 to 3 mm were implanted through a small skin incision which was closed with a metal clamp. The panels represent a variety of histological sub-types occurring in ovarian-cancer patients or soft-tissue sarcoma patients. In serial passages, the tumor lines retained their histological sub-type and a consistent growth rate. *Correspondence to: Academic Hospital Vrije Universiteit. Department of Medical Oncology, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands. Fax (31)20-4444355. E-mail: e.boven.oncol@med.vu.nl Received 20 May 1997; Revised 4 August 1997 Int. J. Cancer: 73, 891–896 (1997)  1997 Wiley-Liss, Inc. Publication of the International Union Against Cancer Publication de l’Union Internationale Contre le Cancer