Molecular and cytotoxic effects of camptothecin, a topoisomerase I inhibitor, on trypanosomes and Leishmania.

Abstract

Parasites pose a threat to the health and lives of many millions of human beings. Among the pathogenic protozoa, Trypanosoma brucei, Trypanosoma cruzi, and Leishmania donovani are hemoflagellates that cause particularly serious diseases (sleeping sickness, Chagas disease, and leishmaniasis, respectively). The drugs currently available to treat these infections are limited by marginal efficacy, severe toxicity, and spreading drug resistance. Camptothecin is an established antitumor drug and a well-characterized inhibitor of eukaryotic DNA topoisomerase I. When trypanosomes or leishmania are treated with camptothecin and then lysed with SDS, both nuclear and mitochondrial DNA are cleaved and covalently linked to protein. This is consistent with the existence of drug-sensitive topoisomerase I activity in both compartments. Camptothecin also inhibits the incorporation of [3H]thymidine in these parasites. These molecular effects are cytotoxic to cells in vitro, with EC50 values for T. brucei, T. cruzi, and L. donovani, of 1.5, 1.6, and 3.2 ,uM, respectively. For

An unusual type IB topoisomerase from African trypanosomes

“…Camptothecin enhances the formation of covalent complexes (Fig. 3, lane 2), consistent with our previous studies of cleavable complex formation in trypanosomes (13). Under these conditions, enhancement of cleavable complex formation by camptothecin is comparable for T. brucei and human enzymes (1.7-fold and 2.1-fold, respectively).…”

“…When disrupted (e.g., by SDS or alkali) such complexes yield a denatured enzyme covalently linked, via the active site tyrosine, to the 3Ј end of the enzyme-induced break in substrate DNA. In previous work with African trypanosomes we found that camptothecin promotes the formation of covalent protein-DNA complexes with both nuclear and mitochondrial DNA, and inhibits DNA biosynthesis (13). Furthermore, it is cytotoxic to three pathogenic kinetoplastids: T. brucei, T. cruzi, and L. donovani.…”

Camptothecin induced mitochondrial dysfunction leading to programmed cell death in unicellular hemoflagellate Leishmania donovani

“…Previous studies have shown that CPT treatment promotes stabilization of the cleavable complex with both nuclear as well as kinetoplast DNA. 23 Very little is known about the signalling pathway downstream of the formation of cleavable complex, which ultimately leads to increase in the number of apoptotic cells. In the present study, CPT-induced cytotoxic lesion inside leishmanial cells appears to inhibit the mitochondrial respiration, which is followed by an increase in mitochondrial membrane potential.…”

“…22 CPT, like other potential antileishmanial agents, has been shown to inhibit type I DNA topoisomerase of Leishmania donovani. 23 However, it is still unclear how the stabilization of topo I-DNA covalent complex and subsequent induction of DNA strand breaks lead to cytotoxicity in leishmanial cells.…”

Natural Products Active Against African Trypanosomes: A Step Towards New Drugs

“…41 Camptothecin 47, a pentacyclic alkaloid from Camptotheca acuminata (Nyssaceae), is a well known antitumor agent and a specific inhibitor of human DNA topoisomerase I. Bodley et al have shown that 47 also inhibits the nuclear and mitochondrial topoisomerase I of T. b. brucei thus blocking DNA replication and inducing the death of bloodstream trypomastigotes (IC 50 = 1.6 µM). 42 In a study of a series of camptothecin analogs, the 9-substituted-10,11-methylenedioxy derivatives were significantly more active on T. b. brucei bloodstream trypomastigotes than the parent compound and retained as intracellular target the parasites' topoisomerase I. For example, 9-chloro-10,11-methylenedioxycamptothecin 48 was 40 times more trypanocidal than 47 (IC 50 = 0.041 µM).…”