Future directions for clinical research with CPT-11 (irinotecan).

CPT-11 is a new agent with a unique mechanism of action, namely the inhibition of topoisomerase I. An examination of data from the laboratory reveals several leads which should be pursued in the clinic. A dose-response effect for CPT-11 activity has been noted in the human tumour cloning assay. CPT-11 has activity against breast and mesothelioma colony-forming units in a human tumour cloning assay, and has in vivo activity against a number of paediatric malignancies. Promising combinations in preclinical in vivo models include CPT-11/mitomycin C and CPT-11/cytosine arabinoside. There is incomplete cross-resistance among topoisomerase I inhibitors, suggesting that combinations of topoisomerase I inhibitors should be investigated. Several natural products have been identified which have potential to decrease CPT-11-induced diarrhoea. The level of carboxylesterase in a patient's tumour appears to be related to the in vitro activity of CPT-11, suggesting that measurement of carboxylesterase in a patient's tumour could be used to identify patients who are most likely to respond to treatment with CPT-11. These preclinical findings suggest substantial further clinical potential for CPT-11 in terms of decreased CPT-11-induced diarrhoea as well as increased antitumour activity, which should be explored in phase I and II studies.