Reaction of Geldanamycin and C17-Substituted Analogues with Glutathione:  Product Identifications and Pharmacological Implications

Abstract

17-Dimethylaminoethylamino-17-demethoxygeldanamycin (DMAG) and 17-allylamino-17-demethoxygeldanamycin (17-AAG) are two derivatives of geldanamycin (GA) that are currently undergoing clinical evaluation as anticancer agents. These agents bind to heat shock protein 90 (hsp90), resulting in the destabilization of client proteins and inhibition of tumor growth. In a search for the mechanism of hepatotoxicity, which is a dose-limiting toxicity for these agents, we found that GA and its derivatives, 17-AAG and 17-DMAG, react chemically (i.e., nonenzymatically) with glutathione (GSH). A combination of liquid chromatography/electrospray ionization/mass spectrometry and nuclear magnetic resonance analyses were used to identify the product of this reaction as a GSH adduct in which the thiol group of GSH is substituted in the 19-position of the benzoquinone ring. The reaction proceeds rapidly with GA and 17-DMAG (half-lives of approximately 1.5 and 36 min, respectively) and less rapidly with 17-AAG and its major metabolite, 17-AG (half-lives of approximately 9.8 and 16.7 h). The reaction occurs at pH 7.0, 37 degrees C, and a physiological concentration of GSH, indicating that cellular GSH could play a role in modulating the cellular toxicity of these agents and therefore be a factor in their mechanism of differential toxicity. Moreover, reactions with thiol groups of critical cellular proteins could be important to the mechanism of toxicity with this class of anticancer agents.

Up-regulation of Heat Shock Protein 27 Induces Resistance to 17-Allylamino-Demethoxygeldanamycin through a Glutathione-Mediated Mechanism

“…First, GA and 17-AAG were recently shown to bind GSH in a nonenzymatic reaction in vitro (42). Direct binding of 17-AAG to GSH may reduce binding to Hsp90 in vivo and could therefore explain protection of tumor cells by increased GSH levels.…”

New non-quinone geldanamycin analogs from genetically engineered Streptomyces hygroscopicus

“…This conjugation with sulfur-containing nucleophiles may contribute to the dose-limiting hepatotoxicity of these quinone-containing compounds. 13,14 For these reasons, new non-quinone 1 analogs with improved pharmacological profiles are needed. 15,16 Recently, we reported the development of non-quinone 1 analogs by a mutasynthetic approach and directed biosynthetic method.…”

“…16 13 C NMR and HMQC spectra revealed the presence of 28 carbon signals comprising two carbonyl, six aromatic or olefinic quaternary, six aromatic or olefinic methine, four oxymethine, two aliphatic methine, two aliphatic methylene, two O-methyl, and four C-methyl carbons. Additionally, four exchangeable proton signals were observed in DMSO-d 6 : two hydroxyl protons (d 5.10 and 4.76), one phenolic hydroxyl proton (d 9.13) and one amide proton (d 9.33).…”

A New Post-PKS Modification Process in the Carbamoyltransferase Gene Inactivation Strain of Streptomyces hygroscopicus 17997

“…It has been reported that an Nglycyltransferase is discovered in S. sannanensis IFO 14239 (sannamycin-producer), and the gene sequences of similar glycyltransferase have been detected in other aminoglycoside antibiotic producers by DNA hybridization [30]. Up to now, there has been no report that the biological modification of GDM analogues at C-19, although this position can be nonenzymatically modified by glutathione [31]. GDMCT-1-1 was not observed in the wild-type S. hygroscopicus 17997 strain, because its intermediate product (GDMCT-1-7, a possible substrate of the putative glycyltransferase) is rapidly carbamoylated by GdmN, and therefore is not available for latter glycylation reaction.…”