Degradation of antineoplastic drug etoposide in aqueous environment by photolysis and photocatalysis. Identification of photocatalytic transformation products and toxicity assessment

Abstract

This study presents the photolytic and photocatalytic degradation of antineoplastic drug etoposide (ETO) in aqueous solutions under UV irradiation. Photolytic degradation of ETO was slow with insufficient mineralization. The quantum yield of ETO’s photolytic degradation was calculated and ranged from 0.00029 to 0.00273 mol Einstein−1. Photocatalytic degradation was proven effective, especially at pH 4, where kobs reached 0.963 min−1. Overall, 29 TPs of photocatalysis were detected at pH 4 and 7. Structures were proposed for 23 of them, based on complementary use of low-/high- resolution MS and Quantitative Structure-Retention Relationship (QSRR) prediction models. The main proposed transformations were: addition and/or demethylation of hydroxyl groups, cyclization, dehydrogenation, full or partial deprotection of diols and the loss of sugar or 2,6-dimethoxyphenol moiety. Mineralization did not follow ETO’s degradation. Toxicity assessment using Vibrio fischeri bioassay and in silico prediction model revealed the formation of partially recalcitrant and possibly toxic TPs.