Spectrophotometric Investigations of Charge Transfer Complexes of Tyrosine Kinase Inhibitors with Iodine as a σ-Electron Acceptor: Application to Development of Universal High-Throughput Microwell Assay for Their Determination in Pharmaceutical Formulations

Background and Objective: Tyrosine kinase inhibitors (TKIs) are used for the treatment of different types of cancers. The current study describes, for the first time, the ultraviolet-visible spectrophotometric investigation of charge transfer complexes (CTCs) of seven TKIs, as electron donors, and iodine, as σ-electron. Materials and Methods: The formation of CTCs was promoted in dichloromethane, among the other solvents used in the investigation. The molar absorptivity values, association constants, and free energy changes of the CTCs were determined. Stoichiometric ratio of TKI: iodine as well as TKIs site(s) of interaction were addressed. Reaction was the basis for constructing a novel simple and accurate 96-microwell spectrophotometric assay (MW-SPA) with high-throughput property for the quantitative determination of TKIs in their pharmaceutical formulations. Results: Beer's law, which relates CTC absorbances to TKI concentrations, was followed within the optimal range of 2 to 100 µg/well (r ranged from 0.9991 to 0.9998). Detection and quantification limits ranged from 0.91 to 3.60 and 2.76 to 10.92 g µmL^-1, respectively. Relative standard deviations values for the intra- and inter-assay precisions of the proposed MW-SPA did not exceed 2.13 and 2.34%, respectively. Studies of recovery demonstrated MW-SPA accuracy, with results ranging from 98.9% to 102.4%. All TKIs, both in bulk form and in pharmaceutical formulations (tablets), were effectively determined using the suggested MW-SPA. Conclusions: The current MW-SPA involved a simple procedure and it was convenient as it could analyse all proposed TKIs utilizing a single assay system at once measuring wavelengths for all TKIs. In addition, the proposed MW-SPA has high throughput which enables the processing of a batch of huge samples' number in very short reasonable time period. In conclusion, TKIs can be routinely analysed in their dosage forms in quality control laboratories, and the assay can be highly valuable and helpful in this regard.