Krzysztof Lemke

Induction of unique structural changes in guanine-rich DNA regions by the triazoloacridone C-1305, a topoisomerase II inhibitor with antitumor activities

We recently reported that the antitumor triazoloacridone, compound C-1305, is a topoisomerase II poison with unusual properties. In this study we characterize the DNA interactions of C-1305 in vitro, in comparison with other topoisomerase II inhibitors. Our results show that C-1305 binds to DNA by intercalation and possesses higher affinity for GC- than AT-DNA as revealed by surface plasmon resonance studies. Chemical probing with DEPC indicated that C-1305 induces structural perturbations in DNA regions with three adjacent guanine residues. Importantly, this effect was highly specific for C-1305 since none of the other 22 DNA interacting drugs tested was able to induce similar structural changes in DNA. Compound C-1305 induced stronger structural changes in guanine triplets at higher pH which suggested that protonation/deprotonation of the drug is important for this drug-specific effect. Molecular modeling analysis predicts that the zwitterionic form of C-1305 intercalates within the guanine triplet, resulting in widening of both DNA grooves and aligning of the triazole ring with the N7 atoms of guanines. Our results show that C-1305 binds to DNA and induces very specific and unusual structural changes in guanine triplets which likely plays an important role in the cytotoxic and antitumor activity of this unique compound.

Structural factors affecting affinity of cytotoxic oxathiole-fused chalcones toward tubulin

Synthesis, in vitro cytotoxic activity, and interaction with tubulin of (E)-1-(6-alkoxybenzo[d][1,3]oxathiol-5-yl)-3-phenylprop-2-en-1-one derivatives (2) are described. Some of the compounds demonstrated cytotoxic activity at submicromolar concentrations, and the activity could be related to interaction with tubulin at the colchicine binding site. Interaction of selected derivatives with tubulin was evaluated using molecular modeling, and two different modes of the interaction were identified. The proposed models demonstrate how particular structural fragments participate in binding to the tubulin and explain the importance of the fragments for cytotoxic activity. It was demonstrated that concerning binding to tubulin, the 6-alkoxybenzoxathiole ring can be considered as structural equivalent of trimethoxyphenyl motif of colchicine, podophyllotoxin or combretastatin A4. The observation opened new ways of rational modifications of several groups of tubulin binders.

Structural Factors Affecting Cytotoxic Activity of (E)-1-(Benzo[d ][1,3]oxathiol-6-yl)-3-phenylprop-2-en-1-one Derivatives

Derivatives of (E)‐1‐(5‐alkoxybenzo[d][1,3]oxathiol‐6‐yl)‐3‐phenylprop‐2‐en‐1‐one demonstrated exceptionally high in vitro cytotoxic activity, with IC50 values of the most active derivatives in the nanomolar range. To identify structural fragments necessary for the activity, several analogs deprived of selected fragments were prepared, and their cytotoxic activity was tested. It was found that the activity depends on combined effects of (i) the heterocyclic ring, (ii) the alkoxy group at position 5 of the benzoxathiole ring, and (iii) the substituents in the phenyl ring B. Replacement of the sulfur atom by oxygen does not influence the activity. None of the listed structural fragments alone assured high cytotoxic activity.

Influence of S-Oxidation on Cytotoxic Activity of Oxathiole-Fused Chalcones.

Synthesis, in vitro cytotoxic activity, and interaction with tubulin of oxidized, isomeric 1‐(5‐alkoxybenzo[d][1,3]oxathiol‐6‐yl)‐3‐phenylprop‐2‐en‐1‐ones and 1‐(6‐alkoxybenzo[d][1,3]oxathiol‐5‐yl)‐3‐phenylprop‐2‐en‐1‐ones are described. Most of the compounds demonstrated cytotoxic activity at submicromolar concentrations. It was found that oxidation of sulfur atom of the oxathiole‐fused chalcones strongly influenced activity of the parent compounds, and that depending on relative position of the sulfur atom in the molecule, the activity was either increased or diminished. For isomers with sulfur atom para to the chalcone carbonyl group, oxidation led to increase in activity, while for isomers with sulfur atom meta to the carbonyl the activity dropped down. It was demonstrated that the compounds interact with tubulin at the colchicine binding site, and the interaction was evaluated using molecular modeling. It was concluded that the observed profound influence of oxidation of the sulfur atom on cytotoxic activity cannot be solely related to interaction of the compounds with tubulin.