Received for publication November 9, 2005.
Revised December 17, 2005.
Accepted for publication January 6, 2006.

S-2-pentyl-4-pentynoic hydroxamic acid and its metabolite S-2-pentyl-4-pentynoic acid in the NMRI-exencephaly-mice model: pharmacokinetic profiles, teratogenic effects, and histone deacetylase inhibition abilities of further VPA hydroxamates and amides

Abstract

Structure-activity relationship (SAR) studies of valproic acid (VPA) derivatives have revealed a quantitative correlation between histone deacetylase (HDAC) inhibition and induction of neural tube defects (NTDs) in the NMRI-exencephaly-mouse model, but this correlation was so far limited to congeners with a carboxylic acid function. Whereas the classical HDAC inhibitor Trichostatin A is active only as a hydroxamate but not as a carboxylic acid, we found that neither VPA amides nor hydroxamates inhibit HDACs, but can cause NTDs; e.g. 2-Pentyl-4-pentynoic hydroxamic acid with its S-enantiomer being the potent teratogen. We therefore investigated the hypothesis that hydroxamic acid derivatives of VPA might be metabolized in vivo and possibly pro-teratogenic as had been shown for valpromide but not valproic hydroxamic acid. We developed two stereoselective quantification methods based on chiral derivatization of VPA hydroxamates with (1R,2S,5R)-(-)-menthylchloroformate and carboxylic acid derivatives with (S)-(-)-1-naphthylethylamin followed by GC-NPD analysis of biological samples. We then determined the pharmacokinetic profiles of S-2-pentyl-4-pentynoic hydroxamic acid and of S-2-pentyl-4-pentynoic acid in mice. S-2-pentyl-4-pentynoic hydroxamic acid was found to be extensively metabolized to the corresponding carboxylic acid without affecting the stereochemistry at position C2. Furthermore the metabolite S-2-pentyl-4-pentynoic acid was found to be very stable in vivo with an extended half life of 4.2 h compared to that of VPA with 1.4 h. Comparison of the individual HDAC inhibition abilities of further VPA amides and hydroxamates, as measured by cellular and enzymatic assays, led us to the conclusion that both classes of VPA derivatives can be pro-teratogenic.

Key words: acetylation, anticancer agents, nuclear receptors, pharmacokinetics, reproductive toxicology, structure-activity relationships