Topoisomerase-I inhibitors in gynecologic tumors

Camptothecin nanocolloids based on N,N,N-trimethyl chitosan: efficient suppression of growth of multiple myeloma in a murine model

Camptothecin (CPT) exhibits very strong antitumor effects by inhibiting the activity of DNA topoisomerase I, but its application is greatly limited due to its low solubility and the instability of the active lactone form. To overcome these shortcomings, in the present study, we prepared novel camptothecin nanocolloids based on N,N,N-trimethyl chitosan (CPT-TMC) to efficiently and safely administer CPT systemically. Herein, we investigated the antitumor activity of CPT-TMC against a murine Balb/c myeloma model. Our results showed that CPT-TMC more effectively inhibited tumor growth and prolonged survival time than CPT in vivo, but no statistical difference was observed in vitro between CPT-TMC and CPT. These findings suggest that N,N,N-trimethyl chitosan could increase the stability and the antitumor effect of CPT and CPT-TMC is a potential approach for the effective treatment of multiple myeloma.

In vivo antitumor and antimetastatic activities of camptothecin encapsulated with N-trimethyl chitosan in a preclinical mouse model of liver cancer

Application of camptothecin (CPT) is hampered due to its extreme water insolubility and unpredictable side effects. Therefore, it is essential to establish an efficient and safe protocol for the administration of camptothecin against tumor growth and metastasis. Here, we encapsulated camptothecin with N-trimethyl chitosan (CPT-TMC) and tested it on BALB/c mice subcutaneously injected with murine hepatocellular carcinoma cells at the hindlimb feet pad. CPT-TMC effectively inhibited tumor growth and lymphatic metastasis, prolonged survival time, yet without apparent toxic effects. Thus, CPT-TMC may provide a novel and effective therapeutic strategy against human advanced hepatic cancer without conspicuous systemic toxic effects.

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.

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.