Caratterizzazione in vitro della biotrasformazione di nuovi potenziali farmaci per la terapia dei tumori

Drug metabolism studies play an important role in drug discovery and development [Foti and Dalvie, Drug Metab Dispos, 44: 1229, 2016]. A first aim of this work was to evaluate the reactivity of some nitrobenzoxadiazole (NBD) derivatives, namely the experimental antitumor agent 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) and its analogues MC3181 and MC2753, towards the tripeptide glutathione (GSH). The obtained results showed that, differently from NBDHEX and MC3181, the benzoic acid ester of NBDHEX (MC2753), was stable in the presence of a physiological concentration of GSH [Fulci et al., J Enzyme Inhib Med Chem, 32: 240, 2017]. Subsequent experiments, aimed at assessing the stability of MC2753 to esterases, demonstrated its high susceptibility to hydrolysis catalyzed by a human liver microsomal carboxylesterase(s). Substitution of the ester group of MC2753 with an amide group gave compound MC4351, which was stable in the presence of human liver microsomes (HLMs), and quite less reactive than NBDHEX and MC3181 towards GSH. In the perspective of a possible repositioning of the antiprotozoal drug pyrimethamine (PYR) in the oncological field [Fang, Cancers (Basel), 6:494, 2014], a study was undertaken to improve the knowledge on its metabolic fate. In vitro studies were therefore conducted to investigate the possible oxidation and/or glucuronidation of PYR by HLMs or rat liver microsomes (RLMs). PYR was found to be stable in the presence of uridine 5'-diphospho-glucuronic acid (UDPGA)-supplemented HLMs or RLMs. On the other hand, PYR underwent NADPH-dependent metabolism by phenobarbital-induced RLMs, as well as by HLMs from a subject receiving phenobarbital; liquid chromatograpy coupled to diode array detection and mass spectrometry (LC-DAD-MS) analysis indicated formation of at least three monoxygenated metabolites. In vitro microsomal stability experiments were also conducted on a small panel of derivatives of the experimental tubulin polymerization inhibitor 7-phenylpyrroloquinolinone (7-PPyQ). Among the studied compounds, the N-benzoyl derivatives of 7-PPyQ named MG2718 and MG2854 are of considerable interest, due to their stability in HLMs both in the absence (hydrolytic metabolism) and in the presence of NADPH (oxidative metabolism). Both compounds are currently being screened for antineoplastic activity. Further trials analyzed the liver cytosolic stability of a small panel of aromatic aldehydes including o-vanillin, an inhibitor of NFkB with significant antitumor activity [Marton et al., Anticancer Res, 36: 5743, 2016], and some of its structural analogues. The same compounds are currently being screened for antitumor activity at the Biological Research Center (BRC) of the Hungarian Academy of Sciences (Szeged), and at the Department of Pharmaceutical Sciences (DSF) of Padua University. The aim of the project is to identify o-vanillin analogues endowed with a better pharmacological profile, in terms of both anticancer efficacy and metabolic stability. The results obtained indicate a significant involvement of a murine aldehyde oxidase(s) (AOX) in the metabolism of all the studied aldehydes, and the existence of remarkable differences between human and mouse in the rate of liver cytosolic metabolism of these compounds. Finally, a collaborative project has been recently established with the Aptuit Research Center in Verona and the Molecular Modeling Section of the DSF of Padua University, to identify form-selective inhibitors of the main human sulfotransferases (SULTs) involved in drug metabolism. The studies have led to the identification of two potent inhibitors of two major hepatic SULTs, namely SULT1A1 and SULT1B1.