Investigations on the electrochemical behavior of sunitinib and metabolites N-desethyl-sunitinib and sunitinib-N-oxide and its selective determination using molecularly imprinted polymer-based sensor

Sunitinib (SUN) is an orally administered tyrosine kinase inhibitor and is mainly metabolized via N-deethylation to form the primary active metabolite N-desethyl-sunitinib (M1) and via oxidation to sunitinib-N-oxide (M2). In this study, we first investigated the electrochemical behavior of sunitinib and its N-desethyl and N-oxide metabolites on a bare glassy carbon electrode (GCE) by cyclic voltammetry (CV) technique. Based on the results, a plausible electrooxidation mechanism is proposed, yielding the oxo-desfluoro-sunitinib (quinoneimine metabolite) via oxidative defluorination of sunitinib. After this phase of the study, due to the low sensitivity and selectivity results obtained from the bare GCE, we aimed to develop the first molecularly imprinted polymer (MIP)-based electrochemical sensor for the sensitive and selective determination of SUN. The MA@SDS/MIPGCE sensor was prepared by thermal polymerization of methacrylic acid (MA) as a functional monomer in the presence of SUN on a GCE surface under the optimized parameters such as template/monomer ratio, drop amount, polymerization temperature and time, removal solution and time, and rebinding time, which affect the structure and response of the sensor. The surface characterization of the developed sensor was performed by scanning electron microscopy (SEM), and the electrochemical characterization was performed by CV and electrochemical impedance spectroscopy (EIS). The electroanalytical performance of the MA@SDS/MIP-GCE sensor was tested by differential pulse voltammetry (DPV) under the optimized conditions in comparison with the NIPbased sensor. The linearity of the developed sensor for the determination of SUN was investigated in the concentration range of 0.5 - 5.0 nM for standard and serum solutions with low LOD and LOQ values. The application of the MIP sensor for the determination of SUN in pharmaceutical dosage form (capsule) and serum samples was demonstrated with excellent recoveries. The results showed that the MA@SDS/MIP-GCE sensor is a sensitive, specific, selective, rapid, and economical option for the quantitative determination of SUN.