Novel 7-Alkyl Methylenedioxy-Camptothecin Derivatives Exhibit Increased Cytotoxicity and Induce Persistent Cleavable Complexes Both with Purified Mammalian Topoisomerase I and in Human Colon Carcinoma SW620 Cells

Abstract

An alkylating camptothecin (CPT) derivative, 7-chloromethyl-10,11-methylenedioxy-camptothecin (7-CM-MDO-CPT) was recently shown to produce irreversible topoisomerase I (top1) cleavage complexes by binding to the +1 base of the scissile strand of a top1 cleavage site. We demonstrate that 7-CM-EDO-CPT (7-chloromethyl-10,11-ethylenedioxy-camptothecin) also induces irreversible top1-DNA complexes. 7-CM-MDO-CPT, 7-CM-EDO-CPT, and the nonalkylating derivative 7-ethyl-10,11-methylenedioxy-camptothecin (7-E-MDO-CPT) also induced reversible top1 cleavable complexes, which were markedly more stable to salt-induced reversal than those induced by 7-ethyl-10-hyroxy-CPT, the active metabolite of CPT-11. This greater stability of the top1 cleavable complexes was contributed by the 7-alkyl and the 10,11-methylene- (or ethylene-) dioxy substitutions. Studies in SW620 cells showed that 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT are more potent inducers of cleavable complexes and more cytotoxic than CPT. The reversal of the cleavable complexes induced by 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT was markedly slower after drug removal than that for CPT, which is consistent with the data with purified top1. By contrast to CPT, 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT were cytotoxic irrespective of the presence of 10 microM aphidicolin. These results suggest that 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT are more potent top1 poisons than CPT and produce long lasting top1 cleavable complexes and greater cytotoxicity than CPT in cells.

Induction of Topoisomerase I Cleavage Complexes by the Vinyl Chloride Adduct 1,N 6-Ethenoadenine

“…For this purpose, we used the alkylating CPT, 7-ClMe-MDO-CPT. This drug alkylates the N3 position of the ϩ1 guanine or adenine in the presence of top1 (29,34). As reported previously, in the control oligonucleotide, 7-ClMe-MDO-CPT stimulated top1 cleavage complexes (Fig.…”

Molecular and Biological Determinants of the Cytotoxic Actions of Camptothecins: Perspective for the Development of New Topoisomerase I Inhibitors

“…Both the 7-substitution and the 10,11-methylenedioxy or ethylenedioxy substitutions increase the potency of the drugs against topo I. 14,15,23,24 They also confer enhanced stabilization of the topo I-DNA cleavage complexes, which become less reversible. The 7-substitutions can be used to increase solubility.…”

Hydrophilic Camptothecin Analogs That Form Extremely Stable Cleavable Complexes with DNA and Topoisomerase I

“…The activity of camptothecin (CPT) and its analogs may be improved on through development of analogs that form more stable cleavable complexes with topoisomerase (topo) I and DNA (1,2). The topo I-DNA-CPT ternary complex is in an equilibrium state and, as such, is readily reversible (3).…”