Tumor-Selective Anticancer Strategies: Towards the Synthesis of Bromoacetic acid 4-glutathionylcarbonyloxy-butyl ester (1).

Erik Strauss¹ and Don Creighton².

¹Department of Biological Sciences, University of Maryland, Baltimore County, 100 Hilltop Circle, Baltimore, MD 21250. ²Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250.

The glutathione dependent glyoxalase pathway is composed of glyoxalase I (GlxI) and glyoxalase II (GlxII), which convert cytotoxic methylglyoxal into nontoxic D-lactate. This pathway relies on the tripeptide glutathione to react with methylglyoxal forming diastereomeric thiohemiacetals, which are converted to S-D-lactoylglutathione by glyoxalase I. The thioester hydrolase, glyoxalase II, cleaves the thioester bond of S-D-lactoyl-glutathione to form D-lactate. Past research has shown that GlxII activity is lower in many different human tumor cell lines versus normal cells. The overall objective of this research is to synthesize 1, which we predict will irreversibly inactivate GlxI and, at the same time, serve as a substrate for GlxII. We predict that 1 will exhibit tumoricidal activity by inducing the build up of cytotoxic methylglyoxal, and will selectively inhibit tumor cells, because of the reduced ability of tumor cells to hydrolyze the inactivator.

The aims are 1) to synthesize a bromo-acetic acid 4-ethylsulfanylcarbonyloxy-butyl ester 2 (CH₃CH₂SC(O)O(CH₂)₄OC(O)CH₂Br), 2) to oxidize 2 with p-chloroperbenzoic acid to give the corresponding S-oxide of 2 as a powerful acylating agent, 3) to react the S-oxide of 2 with glutathione to form 1. We predict that the bromoacetic acid function of 1 will irreversibly inactivate Glx1 by covalently bonding to an essential active site residue.

A combination of mass spectrometry, NMR, and HPLC is being employed to confirm the presence of the desired products. Enzyme activity will be monitored spectrophotometrically after the addition of 1 to Glx1 and Glx2. Our results should demonstrate the potential ability of 2 to impede the growth of tumor cells.