Section Review: Oncologic, Endocrine & Metabolic: Topoisomerase I inhibitors in gynaecologic cancers

Alternative administration of camptothecin analogues

In order to improve the therapeutic index of camptothecin (CPT) analogues, alternative administration of CPT analogues is being evaluated. Topotecan, irinotecan, rubitecan, lurtotecan and 9-aminocamptothecin have been administered orally with response rates equivalent to that seen after intravenous administration, where applicable. Oral availability and administration of some of the newer CPT analogues, including diflomotecan (BN80915) and grimatecan (ST1481), have also shown promising results. Aerosolisation of liposomal 9-nitrocamptothecin has been studied in patients with advanced malignancies involving the lung, demonstrating systemic antitumour activity. Intrathecal administration of topotecan has been studied in children with refractory neoplastic meningitis. It is well tolerated and associated with some antitumour activity. Intraperitoneal administration of topotecan as consolidation therapy in patients with ovarian cancer has shown promising results. Transdermal administration of rubitecan has been studied in mice. So far, no CPT has been approved for an alternative route of administration.

Cisplatin and Irinotecan (CPT-11) for Peritoneal Mesothelioma

Peritoneal mesothelioma is a rare malignancy that is seen in patients exposed to asbestos or in young women with no known exposure to asbestos. The clinical features of the disease are similar in these two groups, and include peritoneal carcinomatosis, ascites, thrombocytemia, systemic symptoms (fever and night sweats), and hypercoagulability. There is no known curative therapy for this disease. Cisplatin has activity in 25% of patients. Mesothelial cells are known to contain high levels of carboxylesterase, a key enzyme in the activation of Irinotecan (CPT-11) to SN-38. This retrospective review of our experience in combining cisplatin 50 or 60 mg/m2 i.v. or i.p. on day 1 with CPT-11 50 or 60 mg/m2 i.v. on day 1, 8, and 15. Courses were repeated every 4 weeks x 6. If i.p. administration of cisplatin were feasible, it was the preferred route. Response to treatment was based on RECIST criteria. Fourteen men and 3 women, median age 62 years (35-76 years) and median PS 1 (0-2) were treated. Median number of courses was two for nonresponders and six for responders. The overall response rate was 24%, but 76% of patients improved on treatment. Median survival is not reached. Grade > or = 2 side effects included anemia (n = 6), neutropenia (n = 3), nausea/vomiting (n = 4), and constipation (n = 2). Grade 1 side effects were fatigue, anorexia, weight loss, alopecia, diarrhea, neuropathy, and gastric reflux. There were no grade > or = 3 hematologic toxicities. The combination of cisplatin and CPT-11 is well tolerated and has clinical benefits in patients with peritoneal mesothelioma.

Alternative administration of camptothecin analogues

The binding of camptothecin (CPT) to the DNA-topoisomerase complex is reversible, but it needs to be maintained for maximal inhibitory activity. It is also dependent on the chemical structure of CPT. The lactone form is thought to be necessary for the activity. In human serum, the equilibrium between lactone and carboxylate is in favor of the latter. For these reasons, alternative administration of CPT analogues is being evaluated. The ideal compound would remain in lactone form and would expose the host for long periods of time to its effects. Oral administration of irinotecan (CPT-11) and topotecan (TPT) is discussed by other investigators. We studied oral rubitecan and reported a low lactone to total drug area under the plasma concentration-time curve (AUCP) ratio (14.7%), with low plasma concentration over time despite repeated administrations and the presence of an enterohepatic cycle. Aerosolization of a liposomal formulation of rubitecan is currently under study. Six patients have been treated once a day for 5 days every 3 weeks. The dose was 6.7 micrograms/kg/day. Plasma levels are dose for dose higher than those after oral administration, but the ratio of lactone versus total drug is low. No toxicity was observed. The study will continue with increasing doses and lengths of administration. Intrathecal administration of topotecan has been studied in a phase I trial in children. Doses of 0.4 mg are tolerated without toxicity, and clinical responses have been seen in patients with refractory meningial carcinomatosis. Phase II studies are planned. Intraperitoneal (i.p.) administration of topotecan has been studied in a phase I trial as a 24-hour infusion in 5% dextrose at pH 3.5 every 21 days. Dose-limiting toxicity is 4 mg/m2. Toxic effects are neutropenia, anemia, emesis, fever, and pain. Five of 10 patients with ascites had symptomatic relief. Pharmacokinetic analysis demonstrates a second-order kinetics with elimination half-lives of 0.49 and 2.7 hours. The peritoneal to plasma AUC ratio was 31.2. Intramuscular, transdermal, and subcutaneous administrations have been extensively studied in the mouse.

Topoisomerase-I inhibitors in gynecologic tumors

The first section of this article reviews recent studies that have clarified both the cellular role of topoisomerase I and the mechanisms of cytotoxicity of the topoisomerase inhibitors, the camptothecins. Different analogs of this new class of antitumor drug have been studied using various dose schedules in the treatment of refractory or recurrent gynecologic cancer. Response rates are between 13% and 25%. The main toxic effects are hematologic and gastrointestinal, the latter remains problematic. Radiotherapy, alkylate, platinum analogues, and topoisomerase II inhibitors are currently being studied in combination with camptothecins.