Titanium(IV) targets phosphoesters on nucleotides: implications for the mechanism of action of the anticancer drug titanocene dichloride

Abstract

Reactions between the anticancer drug titanocene dichloride (Cp2TiCl2) and various nucleotides and their constituents in aqueous solution or N,N-dimethylformamide (DMF) have been investigated by 1H and 31P NMR spectroscopy and in the solid state by IR spectroscopy. In aqueous solution over the pH* (pH meter reading in D2O) range 2.3-6.5, CMP forms one new species with Ti(IV) bound only to the phosphate group. In acidic media at pH*<4.6, three species containing titanocene bound to the phosphate group of dGMP, AMP, dTMP and UMP are formed rapidly. The bases also appear to influence titanocene binding. Only one of these Ti(IV)-bound species can be detected in the pH* range of 4.6-6.5 in each case. The order of reactivity towards Cp2TiCl2(aq) at pH* ca. 3 is GMP>TMP approximately AMP > CMP. At pH* > 7.0, hydrolysis of Cp2TiCl2 predominated and little reaction with the nucleotides was observed. Binding of deoxyribose 5'-phosphate and 4-nitrophenyl phosphate to Cp2TiCl2(aq) via their phosphate groups was detected by 31P NMR spectroscopy, but no reaction between Cp2TiCl2(aq) and deoxyguanosine, 9-ethylguanine or deoxy-D-ribose was observed in aqueous solution. The nucleoside phosphodiesters 3',5'-cyclic GMP and 2',3'-cyclic CMP did not react with Cp2TiCl2(aq) in aqueous solution; however, in the less polar solvent DMF, 3',5'-cyclic GMP coordination to [Cp2Ti]2+ via its phosphodiester group was readily observed. Binding of titanocene to the phosphodiester group of the dinucleotide GpC was also observed in DMF by 31P NMR. The nucleoside triphosphates ATP and GTP reacted more extensively with Cp2TiCl2(aq) than their monophosphates; complexes with bound phosphate groups were formed in acidic media and to a lesser extent at neutral pH. Cleavage of phosphate bonds in ATP (and GTP) by Cp2TiCl2(aq) to form inorganic phosphate, AMP (or GMP) and ADP (or GDP) was observed in aqueous solutions. In addition, titanocene binding to ATP was not inhibited by Mg(II), but the ternary complex titanocene-ATP-Mg appeared to form. These reactions contrast markedly with those of the drug cisplatin, which binds predominantly to the base nitrogen atoms of nucleotides and only weakly to the phosphate groups. The high affinity of Ti(IV) for phosphate groups may be important for its biological activity.

Novel titanocene anti-cancer drugs and their effect on apoptosis and the apoptotic pathway in prostate cancer cells

“…To elucidate the specificity of titanium dichloride to DNA, several spectroscopic studies have also been performed using various nucleotides. The interaction between Cp 2 TiCl 2 and 5 -GMP, 5 -AMP, 5 -CMP and 5 -TMP have been investigated in aqueous solution and have shown that both phosphate (O) and nucleobase (N) are possible binding sites in the interaction Ti-DNA [26]. This raises the important issue as to how these compounds mediate their down stream cellular effects, which is currently under investigation.…”

Non Platinum Metal Complexes as Anti‐cancer Drugs

“…Most interestingly, the binding to the DNA occurred rather via the phosphate backbone than via the nucleobases [85,88]. Binding studies suggested that the cellular uptake of titanocene dichloride may be mediated by the iron transport protein transferrin [89].…”

Designing organometallic compounds for catalysis and therapy

“…Therefore, these systems are promising candidates for delivery of treatments using the enhanced permeability and retention (EPR) effect. O,O-ligands have been used to prevent arene-Ru complexes from hydrolysing in RAPTA analogs derivatised with a sugar-bearing phosphate ligand and a biscarboxylate as chelator (77). 170 The Ru-P bond appears to stabilise the O,Ocomplex by accepting electron density.…”