DPP IV inhibitor blocks mescaline-induced scratching and amphetamine-induced hyperactivity in mice.

Dipeptidyl peptidase IV (DPP IV) is a ubiquitous membrane-bound enzyme that cleaves the two N-terminal amino acids from peptides with a proline or alanine residue in the second position from the amino end. Potential substrates for DPP IV include several neuropeptides, suggesting a role for DPP IV in neurological processes. We have developed a potent DPP IV inhibitor (IC50 = 30 nM), 1-(2-amino-3-methyl-butyryl)-azetidine-2-carbonitrile (AMAC), which has shown efficacy in two established models of psychosis: mescaline-induced scratching and amphetamine-induced hyperactivity. In the mescaline-induced scratching model, AMAC treatment before mescaline administration reduced the number of scratching paroxysms by 68% (P < 0.01). The compound showed a dose-dependent effect, inhibiting significantly at 6, 20 and 60 mg/kg (37%, 39% and 68%, respectively). In the amphetamine-induced hyperactivity model, 50 and 60 mg/kg AMAC, given before injection of amphetamine, significantly reduced hyper-locomotion by 65% and 76%, respectively. Additionally, AMAC showed no significant activity in binding assays for 20 receptors thought to be involved in the pathology of schizophrenia, including dopamine, serotonin and glutamate. A structurally similar analog, 1-(2-dimethylamino-3-methyl-butyryl)-azetidine-2-carbonitrile (DAMAC), that does not inhibit DPP IV, was inactive in both models. Taken together, these data suggest that the antipsychotic effects of AMAC are the result of DPP IV inhibition.

Dipeptidyl peptidase IV: development, design, synthesis and biological evaluation of inhibitors.

Dipeptidyl peptidase IV (DPP IV, EC 3.4.14.5) is a highly specific serine protease which cleaves off N-terminal dipeptides from peptides with a penultimate proline or alanine. The enzyme is widely distributed in mammalian cells and tissues, but specific activities differ greatly. In the hematopoietic system it is found almost exclusively on T cells, where it is identified as CD26, a T cell activation molecule. DPP IV may be involved in the metabolism of peptides, intestinal assimilation and cell adhesion and it plays an integral role in T cell activation. DPP IV inhibitors may provide help during the further elucidation of the biological function(s) of this enzyme. Moreover, because of the integral role the enzyme plays in T cell activation, specific inhibition of DPP IV may constitute a new way of immune modulation. N-Peptidyl-O-acylhydroxylamines and boronic acid analogues of proline and alanine are two known DPP IV inhibitors. The major drawbacks for their therapeutic use are for the hydroxylamines, the toxicity and for the boronic acid derivatives, the chemical liability. A low toxicity, acceptable stability and a high specificity are essential criteria for the design of inhibitors that are suitable, not only for experimental, but also for therapeutic use. Therefore we proposed 5 types of potential DPP IV inhibitors: azapeptides, azetidines, Michael substrates, reduced peptides and phosphonic acids. All the synthesized compounds possess a substrate-like structure, which is a pre-requisite for recognition by the enzyme. We choose for a modified proline or alanine at the penultimate position, substituted with glycine, alanine, valine, isoleucine or phenylalanine at the N-terminus. The prepared compounds were screened biologically at a 5 mM concentration with a fluorometric method using Gly-Pro-4-Me-2NA as substrate.