Protein-Linked DNA Strand Breaks Induced by NSC 314622, a Novel Noncamptothecin Topoisomerase I Poison

Abstract

NSC 314622 was found to have a cytotoxicity profile comparable to the topoisomerase I (top1) inhibitors camptothecin (CPT) and saintopin in the National Cancer Institute In Vitro Anticancer Drug Discovery Screen using the COMPARE analysis. In vitro data showed that NSC 314622 induced DNA cleavage in the presence of top1 at micromolar concentrations. Cleavage specificity was different from CPT in that NSC 314622 did not cleave all sites induced by CPT whereas some sites were unique to the NSC 314622 treatment. Top1-induced DNA cleavage was also more stable than cleavage induced by CPT. NSC 314622 did not induce DNA cleavage in the presence of human topoisomerase II. High concentrations of NSC 314622 did not produce detectable DNA unwinding, which suggests that NSC 314622 is not a DNA intercalator. DNA damage analyzed in human breast carcinoma MCF7 cells by alkaline elution showed that NSC 314622 induced protein-linked DNA single-strand breaks that reversed more slowly than CPT-induced strand breaks. CEM/C2, a CPT-resistant cell line because of a top1 point mutation [Cancer Res 55:1339-1346 (1995)], was cross-resistant to NSC 314622. These results demonstrate that NSC 314622 is a novel top1-targeted drug with a unique chemical structure.

Synthesis and Evaluation of Indenoisoquinoline Topoisomerase I Inhibitors Substituted with Nitrogen Heterocycles

“…2 Subsequent in vitro testing confirmed this prediction and more potent derivatives (such as 2) have been developed. [2][3][4][5][6][7][8][9] Irinotecan (3) and topotecan (4) are the only current Top1 inhibitors approved by the Food and Drug Administration (FDA) for the treatment of cancer and they validate Top1 as a therapeutic target for anticancer drug development. However, these camptothecin derivatives are not ideal drug molecules.…”

Inhibition of Flp Recombinase by the Topoisomerase I-targeting Drugs, Camptothecin and NSC-314622

“…Rather, the active site of Flp may share sufficient structural similarities to that of eukaryotic topo I to be able to bind the two drugs specifically, although Flp differs from topo I regarding drug affinity. Flp is less sensitive than topo I toward CPT (26), but the effect of NSC-314622 on the two enzymes appears comparable (17). Drug interaction with topo I is very specific as revealed by several single amino acid mutations conferring drug resistance to the enzyme (32)(33)(34)(35)(36) and by topo I from vaccinia virus being drug-resistant because of a single amino acid difference compared with the cellular forms of topo I (37,38).…”

“…An ϳ50% reduction of activity was observed in the presence of 0.05 mM NSC-314622 (open circles) or 1 mM CPT (filled circles), respectively. In comparison, topo I-mediated ligation is reduced by 50% in the presence of 1 M CPT (26), whereas the inhibition efficiencies of NSC-31422 on topo I and Flp appear comparable (17).…”

“…CPT and its derivatives are among the most promising anticancer drugs available today and have long been known specifically to target topo I in human cells. Although NSC-314622 is structurally unrelated to the camptothecins, its mode of action appears to be similar to that of CPT (17). Both drugs inhibit the religation step of topo I catalysis, whereas they have no effect on the cleavage reaction (16 -19).…”

“…3, 15, and 16) and the newly synthesized CPT-like agent NSC-314622 (17). CPT and its derivatives are among the most promising anticancer drugs available today and have long been known specifically to target topo I in human cells.…”