Voltammetric Behaviour of the Anticancer Drug Irinotecan and its Metabolites in Acetonitrile. Implications for Electrochemical Therapeutic Drug Monitoring

In this paper the voltammetric behaviour of the anticancer drug irinotecan (CPT-11), its injectable form in the clinical treatment regimen, irinotecan hydrochloride (CPT-11HCl), and its main metabolites (namely SN-38, SN-38G, APC, and NPC), and the natural chemical analogous camptothecin (CPT) were investigated in acetonitrile using a glassy carbon electrode (GCE), in view of developing an analytical protocol for the therapeutic drug monitoring (TDM) of CPT-11 in patients under chemotherapy regimens. Our results showed that all compounds provided rather complex cyclic voltammetric (CV) patterns in both the negative and positive potential regions. The overall results indicated that the processes recorded in the negative potential region at both GCE and Pt electrodes could be hardly exploited for TDM applications, because of the overlapping of the peaks. Instead, in the positive potential region, the oxidation of the piperidine moiety of CPT-11, which was obtained in CPT-11HCl acetonitrile solutions basified with Na2B4O7 (synthetic solutions), proved to be useful for irinotecan quantification, as its process at the GCE took place over a potential region essentially free from interference. Preliminary differential pulse voltammetry (DPV) measurements performed in synthetic solutions of CPT-11HCl, over the concentration range 0.2 – 9 µM, showed a linear dependence between peak current and concentration with a satisfactory correlation coefficient of 0.992. The reproducibility was within 5% from three replicates.