Pyridoxal hydrochloride thiosemicarbazones with copper ions inhibit cell division via Topo-I and Topo-IIɑ.

Topoisomerase (Topo) accelerates cell growth and division, and has been a theoretical target for anti-cancer drugs for decades. A series of pyridoxal thiosemicarbazone (PLT) ligands were designed and synthesized, and the dependence of their antiproliferative activity on copper was investigated. The insertion of N-cyclohexyl-2-((3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl)methylene)-N-methylhydrazinecarbothioamide hydrochloride (compound 9) and Chlorido(N-cyclohexyl-2-((3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl)methylene)-N-methylhydrazinecarbothioamide hydrochloride-O,N,S)‑copper(II) nitrate (9-Cu complex) into Topo-I and Topo-II prevented uncoiling of DNA through hydrogen bonds and intermolecular forces. The combination of PLT derivatives and copper gluconate (CuGlu) improved their anti-tumour activity against a cell line with high expression of topoisomerase (SK-BR-3). The non-linear regression equations of the inhibitory activity and anti-tumour activity of Topo-I and Topo-IIɑ in SK-BR-3 cells had R2 values of 0.93 and 0.94, respectively. In addition to lipophilicity, inhibition of topoisomerase also affected the activity of PLT ligands by coordinating with copper ions. At the cellular level, PLTs and CuGlu penetrate the cell membrane to form metabolites in the cell, thus selectively inhibiting the activity of Topo-I and Topo-IIɑ, and ultimately inhibiting cell division. These findings will inform the design of future anti-cancer thiosemicarbazone drugs.