A. Haemers

Inhibition of CD26/dipeptidyl peptidase IV activity in vivo prolongs cardiac allograft survival in rat recipients

The CD26 antigen, one of the major costimulatory molecules in T cell activation, was shown to possess dipeptidyl peptidase IV (DPP IV) activity. Previously, we demonstrated that immunosuppressed kidney transplant patients exhibit lower DPP IV serum activity as compared with healthy individuals. In the present study, we analyzed the role of CD26/DPP IV in the immune cascade triggered by organ transplantation and leading to acute rejection of cardiac allografts in rat recipients. Transplantation of hearts from (Lewis x Brown Norway)F1 donors into Lewis hosts resulted in an early (24 hr) increase in cellular CD26 expression, followed by a rise in DPP IV serum activity, which peaked at day 6, i.e., before the time of actual graft loss. Specific targeting of DPP IV activity with a novel, low-molecular-weight inhibitor of the diphenyl-phosphonate group (prodipine) abrogated acute rejection and prolonged cardiac allograft survival to 14.0+/-0.9 days (P<0.0001). Prodipine treatment prevented the early peak of cellular CD26 expression and thoroughly suppressed systemic DPP IV activity. The inhibition of DPP IV was associated with severely impaired host cytotoxic T lymphocyte responses in vitro. These results demonstrate the role of CD26/DPP IV in alloantigen-mediated immune regulation in vivo and provide the first direct evidence that CD26/DPP IV plays an important role in the mechanism of allograft rejection. The model of targeting CD26/DPP IV may reveal essential interactions on the level of costimulatory alternate T cell activation pathways, allowing a more subtle approach for more selective immunosuppression in transplant recipients.

The Therapeutic Potential of Inhibitors of Dipeptidyl Peptidase IV (DPP IV) and Related Proline-Specific Dipeptidyl Aminopeptidases

In this review the structural and functional aspects of dipeptidyl peptidase IV (DPP IV) will be described, and the therapeutic potential of DPP IV inhibitors will be highlighted. DPP IV will be situated in clan SC, a group of serine proteases that contains several proline specific peptidases. Structural aspects of DPP IV and its interaction with different types of inhibitors are recently revealed by the publication of several crystal structures. Especially the design and development of new DPP IV inhibitors based on the three-dimensional structure, substrate specificity and catalytic mechanism will be discussed. In the last years there was an important development of new pyrrolidine-2-nitriles with very promising therapeutic properties for the treatment of type 2 diabetes. The role of DPP IV in peptide metabolism of members of the PACAP/glucagon peptide family, neuropeptides and chemokines has been thoroughly investigated during recent years. This is directly related to the promising therapeutic potential of DPP IV inhibitors in the treatment of type 2 diabetes and in the treatment of immunological disorders. Several inhibitors are currently under investigation in clinical trials for the treatment of type 2 diabetes and represent a new class of drugs for the treatment of this disease.

Pyrrolidides: synthesis and structure-activity relationship as inhibitors of dipeptidyl peptidase IV

Summary Dipeptidyl peptidase IV cleaves specifically the peptide bond at the carboxyl side of a proline at the penultimate N-terminal position of a peptide. It is thought to be important for the regulation of biologically active peptides. Moreover, it has been identified as an activation marker of T-lymphocytes (CD26). Pyrrolidides and thiazolidides are known as reversible inhibitors of DPP IV. Several homologues, unsaturated, open and 3-substituted analogues were synthesized in order to determine the structure-activity relationship of the P-1 site. l -Isoleucine was taken as P-2 amino acid. 1-( l -Isoleucyl)-3( S )-fluoropyrrolidine is about as active as the non-fluorinated compound and behaves as a competitive inhibitor. Other changes decrease or abolish the activity.

Dipeptide-derived diphenyl phosphonate esters: mechanism-based inhibitors of dipeptidyl peptidase IV

A number of dipeptide diphenyl phosphonate esters were studied as inhibitors of dipeptidyl peptidase IV, focusing on the role of the P2 residue in the inactivation process. The active compounds were slow irreversible inhibitors of the catalytic activity of the enzyme. With proline (or alanine) in the P1 position, the rate constants of inactivation correlated with the acylation rate constants reported for homologous dipeptide derived substrates. The kinetic data indicate that the mechanism of inhibition consists of the formation of a fairly weak initial complex, followed by a slow irreversible inactivation step. This indicates that, as in the case of trypsin-like proteinases, dipeptide diphenyl phosphonate esters form a covalent adduct with the catalytic site of DPP IV, even though this enzyme belongs to a completely distinct class of serine peptidases. Enantioselectivity and secondary specificity further support the evidence that diphenyl phosphonate esters are mechanism-based inhibitors. The dipeptide diphenyl phosphonate esters had a half-life of 3-10 h at 37 degrees C in Tris buffer. The inhibitors were degraded in human plasma, depending on the type of amino-terminal amino acid. The compound with proline in the P2 position was the most resistant to degradation in plasma. Due to their stability and the irreversible nature of the inhibition, the diphenyl phosphonate esters promise to be useful tools in the continuing investigation of the physiological function of dipeptidyl peptidase IV.

Inhibitors of the purine salvage pathway: a valuable approach for antiprotozoal chemotherapy?

For many years, the purine salvage pathway of parasitic protozoa has been regarded as an attractive chemotherapeutic target. Parasitic protozoa lack de novo synthesis and rely entirely on the purine salvage pathway to meet their purine demands. Because of the great phylogenetic difference between parasite and host, there are often sufficient distinctions that can be exploited to design specific inhibitors for the parasitic enzymes. As a result, this pathway has been thoroughly investigated over the last twenty years. It is only quite recently that the genome studies of Trypanosoma, Leishmania and Plasmodium have been published. Based on these genomic data however, the existence of by-pass mechanisms by other enzymes and transporter systems could be suggested. Taking into account such proposition, the question might arise as to whether inhibition of a single salvage enzyme will be able or not to cause parasite death or growth arrest. In this paper, the key enzymes in the purine salvage pathways of relevant pathogenic species from the genera Trypanosoma, Leishmania and Plasmodium are reviewed. Their potential as drug targets is critically evaluated and where possible, correlated to literature data on antiparasitic activity of their inhibitors. While many studies over the past ten years have yielded contradictory results, this review attempts to clarify these findings by discussing the latest elements of progress in the field. Additionally, as part of a broader discussion on substrate analogue types of inhibitors, special attention is paid to iminoribitol derivatives, serving as transition state analogues of nucleoside-processing enzymes and comprising the most potent inhibitors reported for purine salvage enzymes. More specifically, the development of three generations of immucillins and a newer series of N-(arylmethyl-) substituted iminoribitol derivatives will be discussed. Finally, this review also covers subversive substrates of salvage enzymes: compounds that are transformed by enzymatic activity into cytotoxic agents. Although not by directly intervening in the process of purine recovery, the subversive substrate approach might deliver antiprotozoal compounds that rely on salvage enzymes for their activity.

Synthesis and antibacterial evaluation of phosphonic acid analogues of diaminopimelic acid

Abstract Diaminopimelic acid is an essential amino acid in the peptidoglycan of Gram-negative bacteria, mycobacteria and some Gram-positive bacteria. It can be used as a target for the development of antibacterial agents. In this article the synthesis of a series of phosphonic acid analogues of this diamino-dicarboxylic acid is described: mono- and diphosphonic acid derivatives as well as their homologues, N -alkyl analogues and some peptidyl derivatives. A phenylphosphinic derivative was also prepared. All the prepared compounds were tested for their antibacterial activity against a series of Gram-positive, Gram-negative and mycobacteria. They were also tested as possible inhibitors of the UDP-MurNAc- l -Ala-γ- d -Glu: meso -DAP synthetase. No significant biological activity was found.

Study of the enzymatic degradation of vasostatin I and II and their precursor chromogranin a by dipeptidyl peptidase IV using high-performance liquid chromatography/electrospray mass spectrometry

The interaction of dipeptidyl peptidase IV with structurally related proteins differing in chain length, namely vasostatin I and II and their precursor protein chromogranin A, was examined using high-performance liquid chromatography in combination with electrospray mass spectrometry. Suitable analytical procedures were developed involving the use of reversed-phase high-performance liquid chromatography for purification of the enzymatic degradation products and a peptide mapping procedure for evaluating the enzymatic degradation of the large precursor protein chromogranin A. While vasostatin I was found to be a substrate for dipeptidyl peptidase IV, no N-terminal cleavage of Leu-Pro could be noted for chromogranin A. With respect to vasostatin II, N-terminal degradation was only observed after degradation in the C-terminal domain to proteins containing < or = 78 amino acids. The specificity of the N-terminal release of Leu-Pro was proved by addition of a DPP IV specific inhibitor.

Synthesis and evaluation of azaproline peptides as potential inhibitors of dipeptidylpeptidase IV and prolyl oligopeptidase

A series of azaproline dipeptides with various N-substituents were synthesized as possible active-site-directed inhibitors of two proline-specific serine proteases, dipeptidyl peptidase IV and prolyl oligopeptidase. Compounds with semicarbazide, carbazate, acylhydrazine and sulphonylhydrazine structures were tested. Some compounds show moderate activity, i.e., in the millimolar range.

Synthesis and antibacterial evaluation of 1-(4-thiazolylmethyl)- and 7-(4-thiazolylmethyl)amino-substituted quinolones

Abstract A group of 6-fluoro-1,4-dihydro-4-oxo-7-piperazinyl-1-(4-thiazolylmethyl)quinoline-3-carboxylic acids and 1-ethyl-6-fluoro-1,4-dihydro-7-(2-methyl-4-thiazolyl) methylamino-4-oxoquinoline-3-carboxylic acid were synthesized. All compounds were tested in vitro against a series of Gram-positive and Gram-negative bacteria. No important antibacterial activity was found among the compounds tested.

AN EFFICIENT SYNTHESIS OF ORTHOGONALLY PROTECTED SPERMIDINE

ABSTRACT A major problem in the use of spermidine for the synthesis of biologically interesting compounds is the selective orthogonal protection of the three different amino groups. Our approach is based on the Fukuyama reaction, starting from putrescine and 3-amino-1-propanol and affording N 8-benzyloxycarbonyl-N 1-tert-butyloxycarbonyl-N 4-(2-nitrobenzenesulfonyl)spermidine (5) in 5 steps in high yield.