Abstract

The microtubule disrupting agent 2-fluoro-1-methoxy-4-pentafluorophenylsulfonamidobenzene (T138067) binds covalently and selectively to β-tubulin and has been shown to evade drug-efflux pumps that confer multidrug resistance to other antimitotic drugs that are used in cancer chemotherapy (Shan et al., 1999). In addition to these resistance mechanisms, eukaryotic cells have developed other protection mechanisms that involve enzymes that modify electrophilic xenobiotics. To determine whether T138067 is a substrate for such enzymatic detoxification pathways, a metabolism study was initiated. GSH conjugation was shown to play a major role in T138067 metabolism. T138067-GSH conjugates were isolated from the culture media of T138067-treated cells and the bile of mice treated i.v. with T138067. The major T138067-GSH degradation products were also isolated from these sources. ¹⁹F NMR studies of the metabolites showed that metabolic conversions occurred through substitution of the para fluorine atom in the pentafluorophenyl ring of T138067. The T138067-GSH conjugate was also isolated from T138067 incubation buffer that had been exposed to mouse, rat, dog, or human liver slices, suggesting that this mechanism is not species-specific. All three human glutathioneS-transferases (α, μ, and π), which are expressed in a wide variety of tissues including human tumors, were shown to metabolize T138067 effectively in vitro. The combined data show that T138067 is being metabolized, in vitro and in vivo, predominantly via a glutathione S-transferase-mediated metabolic pathway.