Electrochemistry Study of Antineoplastic Raltitrexed Oxidation Mechanism and its Interaction with DNA

Abstract

Raltitrexede (RTX) is a folate analogue that belongs to the antimetabolites family and has antineoplastic activity correlated to inhibition of the thymidylate synthase (TS) enzyme. This study addresses the electrochemical characterization of RTX at a glassy carbon electrode, on a wide interval of pH, using voltammetric techniques. The interaction between RTX and double helix DNA (dsDNA) in physiological medium is also addressed, using a DNA‐electrochemical biosensor. A mechanism for the electrochemical oxidation of RTX is proposed. RTX is irreversibly electroxidized under a predominantly diffusion controlled and pH‐dependent process. The oxidation process in acid and physiological media occurs in two consecutive steps. The first oxidation step is pH‐independent and associated with the transfer of one electron of the nitro group at N10 position by releasing a methyl cation. The second oxidation step is pH‐dependent and occurs with the transfer of one electron and one proton from the carbon at C9 position, followed by a direct attack by a water molecule leading to an irreversible dissociation of an oxidation product of RTX. A strong interaction between RTX and dsDNA was revealed by using a multilayer dsDNA electrochemical biosensor. The experiments demonstrated that RTX interacts and binds to the dsDNA helix by different interaction modes, suggesting an intercalation in between the DNA base pairs leading to defects in its secondary structure.

Voltammetric Studies of 3‐Nitro‐tyrosine Electro‐oxidation at Solid Electrodes and its Interaction with DNA

“…DP voltammograms were recorded in a 1 μmol L −1 guanine (Gua) solution and in a Gua+dsDNA mixture (1 μmol L −1 /200 μg mL −1 ), prepared in phosphate buffer, pH=7.0, and detected only a single anodic peak, at E pGua =+0.69 V, with currents close to 14 nA [7, 42, 43], Figure 9, thus demonstrating, as expected, that the dsDNA molecule does not interfere in the Gua electro‐oxidation process. These experiments are important to demonstrate and confirm that the disappearance of the anodic peak of 3‐NO 2 ‐Tyr in the presence of dsDNA occurs in fact and exclusively due to the interaction of these molecules, hindering the access of 3‐NO 2 ‐Tyr to the GCE surface and its electro‐oxidation.…”

“…All DP voltammograms of 3‐NO 2 ‐Tyr detected only the anodic peak 1a, at E p1a =+0.81 V, due to the oxidation of the phenolic group [1], with currents close to 16 nA, Figure 6A. The DP voltammograms of dsDNA detected, as expected, two consecutive oxidation peaks, Figure 6B, the first anodic peak corresponds to the oxidation of deoxyguanosine residues (dGuo), at E pdGuo =+0.91 V and the second is associated with the oxidation of deoxyadenosine (dAdo) residues at E pdAdo =+1.17 V [7, 42, 43].…”

“…The low affinity of the dsDNA molecule with the GCE surface is well known in the literature, with reports on the complexity of its structure and its high hydrophilicity [7, 42, 43]. However, the electro‐oxidation of guanine in the absence/presence of the dsDNA was investigated in the present study as a control/model experiment, to demonstrate that the dsDNA molecule does not cause the blocking of the GCE surface, which could hinder new charge transfer processes.…”

“…In this way, the effects of the 3‐NO 2 ‐Tyr‐dsDNA interaction were monitored by DPV, as described in Section 2.1 , comparing the variations of the 3‐NO 2 ‐Tyr oxidation peak 1a in the absence/presence of the dsDNA, the variations of the DNA anodic peaks in the absence/presence of the 3‐NO 2 ‐Tyr and monitoring the detection of the 8‐oxoguanine oxidation peak, as an indicator of dsDNA oxidative damage [7, 42, 43].…”

DNA Electrochemical Biosensors for In Situ Probing of Pharmaceutical Drug Oxidative DNA Damage

“…Raltitrexede is a folate analog antimetabolite, used to treat solid cancer tumors, such as malignant mesothelioma and gastric, head, neck, and pancreatic cancers, and is the main course of treatment for advanced colorectal cancer. In acid and physiological media, raltitrexede oxidation at a GCE takes place in two steps: the first step is pH independent and related to a one-electron transfer from the nitro group at the N10 position, by releasing a methyl cation, and the second step is pH dependent and related to a one-electron and one-proton transfer from the carbon at the C9 position, followed by a direct attack by a water molecule, leading to an irreversible dissociation of the oxidation product [ 91 ]. The raltitrexede–dsDNA interaction was studied with a DNA electrochemical biosensor, demonstrating raltitrexede intercalation into the double helix [ 91 ].…”