Structure‐Activity Studies of Novel Amidine Analogues of Chlorambucil: Correlation of Cytotoxic Activity with DNA‐Binding Affinity and Topoisomerase II Inhibition

Abstract

A series of amidine analogues of chlorambucil (9-12), where 5-[4-(N-alkylamidino)phenyl]-2-furancarboxamide and the chlorambucil moiety are linked by a NH(CH(2))(2)NH chain, was synthesized and their cytotoxicity has been tested against the growth of human breast cancer MCF-7 cells. Evaluation of the cytotoxicity of compounds 9-12 employing a MTT assay and inhibition of [(3)H]thymidine incorporation into DNA demonstrated that these conjugates were more active than chlorambucil. Data from the ethidium displacement assay indicated that these compounds bind in the minor groove of DNA and show moderate specificity for AT base pairs. Compounds 9-12 were potent topoisomerase II inhibitors, with 50% inhibitory concentrations (IC(50))ranging from 10 to 40 microM. The cytotoxicity of the compounds 9-12 correlates with their DNA-binding affinities and their relative potency as topoisomerase II inhibitors. Altogether, these data suggest (i) that the cytotoxic activity of compounds 9-12 may be due to the combined effects of alkylation, DNA-minor groove binding, and (ii) that N-(2-aminoethyl)-5-(4-N-alkylamidinophenyl)-2-furancarboxamides (5-8) ligands are suitable linkers that favors DNA targeting by chlorambucil derivatives.

Synthesis and Cytotoxic Activity of Novel Amidine Analogues of Bis(2‐chloroethyl)amine

“…The compounds 7 -12 exhibited a smooth trend of decreasing cytotoxic potency as the size of N-terminal amidine group increases. A similar correlation was observed in our previous work for other amidine analogues of 4-[bis(2-chloroethyl)amino]benzenebutanoic acid [10,11]. The concentrations of 7 and 9 needed to inhibit [ 3 H]thymidine incorporation into DNA by 50% (IC 50 ) in MDA-MB-231 was found to be 5 l 2 lM and 12 l 2 lM, respectively, suggesting higher cytotoxic potency compared to chlorambucil (IC 50 = 49 l 2 lM).…”

Investigation of DNA‐Binding Properties of Organic Molecules Using Quantitative Structure‐Activity Relationship (QSAR) Models

“…A series of amidine analogs of chlorambucil was synthesized by Bielawska et al,33 where 5‐[4‐(N‐alkylamidino)phenyl]‐2‐furancarboxamide and chlorambucil moiety are linked by a NH(CH 2 ) 2 NH linkage. The data from ethidium displacement assay indicated that these compounds bind in the minor groove of DNA and show moderate specificity for AT base pair.…”

Amidine Analogues of Melphalan: Synthesis, Cytotoxic Activity, and DNA Binding Properties

“…The DNA binding of these compounds could result in their effective inhibition of regulatory protein binding in the minor groove, as has been shown for other amidines [8,9,11,17]. It is well known that sites of topoisomerase mediated DNA cleavage are not randomly distributed in DNA fragments, hence, this enzyme seem to recognize specific sequences in a given substrate.…”