2-cyanopyrrolidides as potent, stable inhibitors of dipeptidyl peptidase IV

Proline Analogues

Within the canonical repertoire of the amino acid involved in protein biogenesis, proline plays a unique role as an amino acid presenting a modified backbone rather than a side-chain. Chemical structures that mimic proline but introduce changes into its specific molecular features are defined as proline analogues. This review article summarizes the existing chemical, physicochemical, and biochemical knowledge about this peculiar family of structures. We group proline analogues from the following compounds: substituted prolines, unsaturated and fused structures, ring size homologues, heterocyclic, e.g., pseudoproline, and bridged proline-resembling structures. We overview (1) the occurrence of proline analogues in nature and their chemical synthesis, (2) physicochemical properties including ring conformation and cis/trans amide isomerization, (3) use in commercial drugs such as nirmatrelvir recently approved against COVID-19, (4) peptide and protein synthesis involving proline analogues, (5) specific opportunities created in peptide engineering, and (6) cases of protein engineering with the analogues. The review aims to provide a summary to anyone interested in using proline analogues in systems ranging from specific biochemical setups to complex biological systems.

Development of Long-Acting Dipeptidyl Peptidase-4 Inhibitors: Structural Evolution and Long-Acting Determinants

Considerable effort has been made to achieve less frequent dosing in the development of DPP-4 inhibitors. Enthusiasm for long-acting DPP-4 inhibitors is based on the promise that such agents with less frequent dosing regimens are associated with improved patient adherence, but the rational design of long-acting DPP-4 inhibitors remains a major challenge. In this Perspective, the development of long-acting DPP-4 inhibitors is comprehensively summarized to highlight the evolution of initial lead compounds on the path toward developing long-acting DPP-4 inhibitors over nearly three decades. The determinants for long duration of action are then examined, including the nature of the target, potency, binding kinetics, crystal structures, selectivity, and preclinical and clinical pharmacokinetic and pharmacodynamic profiles. More importantly, several possible approaches for the rational design of long-acting drugs are discussed. We hope that this information will facilitate the design and development of safer and more effective long-acting DPP-4 inhibitors and other oral drugs.

A review upon medicinal perspective and designing rationale of DPP-4 inhibitors

Type 2 Diabetes Mellitus (T2DM) is one of the highly prevalence disorder and increasing day by day worldwidely. T2DM is a metabolic disorder, which is characterized by deficiency in insulin or resistance to insulin and thus increases the glucose levels in the blood. Various approaches are there to treat diabetes but still there is no cure for this disease. DPP-4 inhibitor is a privileged target in the field of drug discovery and provides various opportunities in exploring this target for development of molecules as antidiabetic agents. DPP-4 acts by inhibiting the incretin action and thus decreases the level of blood glucose by imparting minimal side effects. Sitagliptin, vildagliptin, linagliptin etc. are the different DPP-4 based drugs approved throughout the world for the treatment of diabetes mellitus. Cyanopyrrolidines, triazolopiperazine amide, pyrrolidines are basic core nucleus present in various DPP-4 inhibitors and has potential effects. In the past few years, researchers had applied various approaches to synthesize potent DPP-4 inhibitors as antidiabetic agent without side effects like weight gain, cardiovascular risks, retinopathy etc. This review will also emphasize the recent strategies and rationale utilized by researchers for the development of DPP-4 inhibitors. This review also reveals about the various other approaches like molecular modelling, ligand based drug designing, high throughput screening etc. are used by the various research group for the development of potential DPP-4 inhibitors.

Discovery of the Orally Effective Thyrotropin-Releasing Hormone Mimetic: 1-{N-[(4S,5S)-(5-Methyl-2-oxooxazolidine-4-yl)carbonyl]-3-(thiazol-4-yl)-l-alanyl}-(2R)-2-methylpyrrolidine Trihydrate (Rovatirelin Hydrate)

We have explored orally effective thyrotropin-releasing hormone (TRH) mimetics, showing oral bioavailability and brain penetration by structure-activity relationship (SAR) study on the basis of in vivo antagonistic activity on reserpine-induced hypothermia in mice. By primary screening of the synthesized TRH mimetics, we found a novel TRH mimetic: l-pyroglutamyl-[3-(thiazol-4-yl)-l-alanyl]-l-prolinamide with a high central nervous system effect compared with TRH as a lead compound. Further SAR optimization studies of this lead compound led to discovery of a novel orally effective TRH mimetic: 1-{N-[(4S,5S)-(5-methyl-2-oxooxazolidine-4-yl)carbonyl]-3-(thiazol-4-yl)-l-alanyl}-(2R)-2-methylpyrrolidine trihydrate (rovatirelin hydrate), which was selected as a candidate for clinical trials.

Novel DPP-4 inhibitors against diabetes

DPP-4 specifically degrades the incretin hormone GLP-1 and GIP, both of which are vital modulators of blood glucose homeostasis. Attributed to its potential biological function, DPP-4 inhibition has presently represented an attractive therapeutic strategy for treating diabetes and aroused a significant interest in the pharmaceutical industry. Chemical stability, selectivity and pharmacokinetic properties have been continuously emphasized during the long journey of R&D centered on DPP-4 inhibitors. The current landscape of the development of DPP-4 inhibitors is outlined in this review, with a focus on rational drug design and structural optimization to pursue chemical stability, selectivity and favorable pharmacokinetic properties. In addition, the structure-activity relationships, based on reported DPP-4 inhibitors, will be discussed.

Selective Inhibitors of Fibroblast Activation Protein (FAP) with a (4-Quinolinoyl)-glycyl-2-cyanopyrrolidine Scaffold

Fibroblast activation protein (FAP) is a serine protease that is generally accepted to play an important role in tumor growth and other diseases involving tissue remodeling. Currently there are no FAP inhibitors with reported selectivity toward both the closely related dipeptidyl peptidases (DPPs) and prolyl oligopeptidase (PREP). We present the discovery of a new class of FAP inhibitors with a N-(4-quinolinoyl)-Gly-(2-cyanopyrrolidine) scaffold. We have explored the effects of substituting the quinoline ring and varying the position of its sp(2) hybridized nitrogen atom. The most promising inhibitors combined low nanomolar FAP inhibition and high selectivity indices (>10(3)) with respect to both the DPPs and PREP. Preliminary experiments on a representative inhibitor demonstrate that plasma stability, kinetic solubility, and log D of this class of compounds can be expected to be satisfactory.

Synthesis and structure-activity relationships of potent 1-(2-substituted-aminoacetyl)-4-fluoro-2-cyanopyrrolidine dipeptidyl peptidase IV inhibitors

Dipeptidyl peptidase IV (DPP-IV) inhibitors have attracted attention as potential drugs for use in the treatment of type 2 diabetes because they prevent the degradation of glucagon-like peptide-1 (GLP-1) and extend its duration of action. We previously reported that 2-cyano-4-fluoropyrrolidines act as potent DPP-IV inhibitors and have been modifying the 1-position of pyrrolidine to obtain more useful inhibitors. An L-tert-butylglycine derivative was found to be a stable and potent DPP-IV inhibitor that exhibits a glucose lowering effect in vivo. Here, we report the synthesis of and biological data on the aforementioned derivatives.

A three-dimensional pharmacophore model for dipeptidyl peptidase IV inhibitors

Dipeptidyl peptidase IV (DPP-IV) is a valid drug target for type-2 diabetes and DPP-IV inhibitors have been proven to efficiently improve glucose tolerance. In our study, 3D pharmacophore models were generated using a training set of 22 DPP-IV inhibitors. The best model consisted of important chemical features and mapped well into the active site of DPP-IV. The model gave high correlation coefficients of 0.97 and 0.84 for the training set and the test set, respectively, showing its good predictive ability for biological activity. Furthermore, the pharmacophore model demonstrated the capability to retrieve inhibitors from database with a high enrichment factor of 42.58. All results suggest that the model provides a useful tool for designing novel DPP-IV inhibitors.

The role of alpha-cell dysregulation in fasting and postprandial hyperglycemia in type 2 diabetes and therapeutic implications

The hyperglycemic activity of pancreatic extracts was encountered some 80 yr ago during efforts to optimize methods for the purification of insulin. The hyperglycemic substance was named "glucagon," and it was subsequently determined that glucagon is a 29-amino acid peptide synthesized and released from pancreatic alpha-cells. This article begins with a brief overview of the discovery of glucagon and the contributions that somatostatin and a sensitive and selective assay for pancreatic (vs. gut) glucagon made to understanding the physiological and pathophysiological roles of glucagon. Studies utilizing these tools to establish the function of glucagon in normal nutrient homeostasis and to document a relative glucagon excess in type 2 diabetes mellitus (T2DM) and precursors thereof are then discussed. The evidence that glucagon excess contributes to the development and maintenance of fasting hyperglycemia and that failure to suppress glucagon secretion contributes to postprandial hyperglycemia is then reviewed. Although key human studies are emphasized, salient animal studies highlighting the importance of glucagon in normal and defective glucoregulation are also described. The past eight decades of research in this area have led to development of new therapeutic approaches to treating T2DM that have been shown to, or are expected to, improve glycemic control in patients with T2DM in part by improving alpha-cell function or by blocking glucagon action. Accordingly, this review ends with a discussion of the status and therapeutic potential of glucagon receptor antagonists, alpha-cell selective somatostatin agonists, glucagon-like peptide-1 agonists, and dipeptidyl peptidase-IV inhibitors. Our overall conclusions are that there is considerable evidence that relative hyperglucagonemia contributes to fasting and postprandial hyperglycemia in patients with T2DM, and there are several new and emerging pharmacotherapies that may improve glycemic control in part by ameliorating the hyperglycemic effects of this relative glucagon excess.

Design and synthesis of long-acting inhibitors of dipeptidyl peptidase IV

A series of (4-substituted prolyl)prolinenitriles were synthesized and evaluated as inhibitors of dipeptidylpeptidase IV (DPP-IV). Among those tested, the 4beta-[4-(hydroxyphenyl)prolyl]prolinenitriles showed a potent inhibitory activity with a long duration of action. Metabolic formation of the corresponding phenol glucuronates was found to contribute to their long duration of action. The activity profiles of the synthesized compounds are reported and structure-activity relationships are also presented.

Lead optimization of [(S)-γ-(arylamino)prolyl]thiazolidine focused on γ-substituent: Indoline compounds as potent DPP-IV inhibitors

Dipeptidyl peptidase IV (DPP-IV) inhibitors are looked to as a potential new antidiabetic agent class. A series of [(S)-gamma-(arylamino)prolyl]thiazolidine compounds in which the electrophilic nitrile is removed are chemically stable DPP-IV inhibitors. To discover a structure for the gamma-substituent of the proline moiety more suitable for interacting with the S(2) pocket of DPP-IV, optimization focused on the gamma-substituent was carried out. The indoline compound 22e showed a DPP-IV-inhibitory activity 100-fold more potent than that of the prolylthiazolidine 10 and comparable to that of NVP-DPP728. It also displayed improved inhibitory selectivity for DPP-IV over DPP8 and DPP9 compared to compound 10. Indoline compounds such as 22e have a rigid conformation with double restriction of the aromatic moiety by proline and indoline structures to promote interaction with the binding site in the S(2) pocket of DPP-IV. The double restriction effect provides a potent inhibitory activity which compensates for the decrease in activity caused by removing the electrophilic nitrile.

Synthesis, kinetic evaluation, and utilization of a biotinylated dipeptide proline diphenyl phosphonate for the disclosure of dipeptidyl peptidase IV-like serine proteases

In this study, we report on the synthesis, kinetic characterisation, and application of a novel biotinylated and active site-directed inactivator of dipeptidyl peptidase IV (DPP-IV). Thus, the dipeptide-derived proline diphenyl phosphonate NH(2)-Glu(biotinyl-PEG)-Pro(P)(OPh)(2) has been prepared by a combination of classical solution- and solid-phase methodologies and has been shown to be an irreversible inhibitor of porcine DPP-IV, exhibiting an over all second-order rate constant (k(i)/K(i)) for inhibition of 1.57 x 10(3) M(-1) min(-1). This value compares favourably with previously reported rates of inactivation of DPP-IV by dipeptides containing a P(1) proline diphenyl phosphonate grouping [B. Boduszek, J. Oleksyszyn, C.M. Kam, J. Selzler, R.E. Smith, J.C. Powers, Dipeptide phophonates as inhibitors of dipeptidyl peptidase IV, J. Med. Chem. 37 (1994) 3969-3976; B.F. Gilmore, J.F. Lynas, C.J. Scott, C. McGoohan, L. Martin, B. Walker, Dipeptide proline diphenyl phosphonates are potent, irreversible inhibitors of seprase (FAPalpha), Biochem, Biophys. Res. Commun. 346 (2006) 436-446.], thus demonstrating that the incorporation of the side-chain modified (N-biotinyl-3-(2-(2-(3-aminopropyloxy)-ethoxy)-ethoxy)-propyl) glutamic acid residue at the P(2) position is compatible with inhibitor efficacy. The utilisation of this probe for the detection of both purified dipeptidyl peptidase IV and the disclosure of a dipeptidyl peptidase IV-like activity from a clinical isolate of Porphyromonas gingivalis, using established electrophoretic and Western blotting techniques previously developed by our group, is also demonstrated.

[(S)-γ-(Arylamino)prolyl]thiazolidine compounds as a novel series of potent and stable DPP-IV inhibitors

Dipeptidyl peptidase-IV (DPP-IV) inhibitors, or glucagon-like peptide-1 (GLP-1) enhancers, are looked to as a potential new class of antidiabetic agents. In particular, potent and long-acting inhibitors might offer advantages in exploiting DPP-IV inhibition. The series of [(S)-gamma-(arylamino)prolyl]-(S)-2-cyanopyrrolidine compounds on which we reported previously has a highly potent inhibitory activity but seemed to be unstable in neutral aqueous solution. Here, we describe [(S)-gamma-(arylamino)prolyl]thiazolidine compounds as a novel series of potent and stable DPP-IV inhibitors. They are the thiazolidine analogs of [(S)-gamma-(arylamino)prolyl]-(S)-2-cyanopyrrolidine but with the electrophilic nitrile removed to improve chemical stability in aqueous solution. Of the compounds investigated in the present study, the [((S)-gamma-3,4-dicyanophenylamino)prolyl]thiazolidine 12 m was the most potent. The structure-activity relationship (SAR) of the gamma-substituent in the proline moiety of the thiazolidide was similar to that obtained with the (S)-2-cyanopyrrolidide. The gamma-substituent in the proline moiety of both the (S)-2-cyanopyrrolidide and the thiazolidide may engage with the S(2) binding pocket of DPP-IV and thereby achieve hydrophobic interaction in the same manner. Based on pharmacokinetic experiments in rats, the representative compound 11, which displayed high oral bioavailability (BA=83.9%) and long half-life in plasma (t(1/2)=5.27 h), was found to have an excellent pharmacokinetic profile.

Seco-prolinenitrile inhibitors of dipeptidyl peptidase IV define minimal pharmacophore requirements at P1

A series of seco-prolinenitrile-containing dipeptides were synthesized and assayed as inhibitors of the N-terminal sequence-specific serine protease dipeptidyl peptidase IV, a promising new target for treatment of type 2 diabetes. The inhibitors described herein assess the minimum structural requirements at P1 for this enzyme, resulting in the identification of inhibitors with low nM potency.

Discovery, SAR, and X-ray structure of novel biaryl-based dipeptidyl peptidase IV inhibitors

The discovery, SAR, and X-ray crystal structure of novel biarylaminoacyl-(S)-2-cyano-pyrrolidines and biarylaminoacylthiazolidines as potent inhibitors of dipeptidyl peptidase IV (DPP IV) are reported.

2-Cyano-4-fluoro-1-thiovalylpyrrolidine analogues as potent inhibitors of DPP-IV

We report the synthesis and biological activity of a series of 2-cyano-4-fluoro-1-thiovalylpyrrolidine inhibitors of DPP-IV. Within this series, compound 19 provided a potent, selective, and orally active DPP-IV inhibitor which demonstrated a very long duration of action in both rat and dog.

Diprolyl nitriles as potent dipeptidyl peptidase IV inhibitors

Dipeptidyl peptidase IV (DPP4) is a multifunctional type II transmembrane serine peptidase which regulates various physiological processes, most notably plasma glucose homeostasis by cleaving peptide hormones glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide. Inhibition of DPP4 is a potentially valuable therapy for type 2 diabetes. Synthesis and structure-activity relationships of a series of substituted diprolyl nitriles are described, leading to the identification of compound 1 with a measured DPP4 K(i) of 3.6 nM.

Glutamic acid analogues as potent dipeptidyl peptidase IV and 8 inhibitors

To find potent and selective inhibitors of dipeptidyl peptidase IV (DPP-IV), we synthesized a series of 2-cyanopyrrolidine with P2-site 4-substituted glutamic acid derivatives and tested their activities against DPP-IV, DPP8, and DPP-II. Analogues that incorporated a bulky substituent at the first carbon position of benzylamine or isoquinoline showed over 30-fold selectivity for DPP-IV over both DPP8 and DPP-II. From structure-activity relationship studies, we speculate that the S2 site of DPP8 might be similar to that of DPP-IV, while DPP-IV inhibitor with N-substituted glycine in the P2 site and/or with a moiety involving in hydrophobic interaction with the side chain of Phe357 might provide a better selectivity for DPP-IV over DPP8.

1-((S)-γ-Substituted prolyl)-(S)-2-cyanopyrrolidine as a novel series of highly potent DPP-IV inhibitors

1-(Gamma-substituted prolyl)-(S)-2-cyanopyrrolidines were designed based on the predicted binding mode of the known DPP-IV inhibitor NVP-DPP728 and evaluated for their inhibitory activity. In structure-activity relationship study at the gamma-position of proline, it became clear that compounds bearing (S)-stereochemistry were 20-fold more potent than the antipode. Of these compounds, the (3,4-dicyanophenyl)amino- and (3-chloro-4-cyanophenyl)amino-derivatives showed the highest inhibitory activity.

Ketopyrrolidines and ketoazetidines as potent dipeptidyl peptidase IV (DPP IV) inhibitors

In this paper, the synthesis and structure-activity relationships (SAR) of two classes of electrophile-based dipeptidyl peptidase IV (DPP IV) inhibitors, the ketopyrrolidines and ketoazetidines, is discussed. The SAR of these series demonstrate that the 2-thiazole, 2-benzothiazole, and 2-pyridylketones are optimal S1' binding groups for potency against DPP IV. In addition, both cyclohexyl glycine (CHG) and octahydroindole carboxylate (OIC) serve as the most potent S2 binding groups within each series. Stereochemistry at the alpha-position of the central ring is relevant to potency within the ketopyrrolidines series, but not in the ketoazetidine series. Finally, the ketoazetidines display enhanced stability over the corresponding ketopyrrolidines, while maintaining their potency. In fact, certain stabilized ketoazetidines can maintain their in vitro potency and inhibit DPP IV in the plasma for up to 6h.

Novel isoindoline compounds for potent and selective inhibition of prolyl dipeptidase DPP8

DPP8 is a prolyl dipeptidase homologous to DPP-IV, which is a drug target for Type II diabetes. The biological function of DPP8 is not known. To identify potent and selective chemical compounds against DPP8, we have synthesized a series of isoquinoline and isoindoline derivatives and have tested their inhibitory activity against DPP8, DPP-IV and DPP-II. Isoindoline derivatives were found to be more potent DPP8 inhibitors than isoquinoline derivatives. Isoindoline with a 1-(4,4'-difluor-benzhydryl)-piperazine group at the P2 site was observed to be a very potent DPP8 inhibitor, having an IC(50) value of 14nM with at least a 2500-fold selectivity over either DPP-IV or DPP-II. From SAR results, we speculate that the S1 site of DPP8 may be larger than that of DPP-IV, which would allow the accommodation of larger C-terminal residues, such as isoquinoline or isoindoline.

Synthesis and structure–activity relationships of potent 3- or 4-substituted-2-cyanopyrrolidine dipeptidyl peptidase IV inhibitors

Dipeptidyl peptidase IV (DPP-IV) inhibitors have attracted attention as potential drugs for use in the treatment of type 2 diabetes because they prevent degradation of glucagon-like peptide-1 (GLP-1) and extend its duration of action. A series of 2-cyanopyrrolidines are among the most potent of DPP-IV inhibitors. We focused our attention on substitutions at the 3- or 4-position of 2-cyanopyrrolidines and synthesized and evaluated various derivatives. Among them, the 4-fluoro derivative was found to exhibit better DPP-IV inhibitory activity and higher plasma drug concentrations after oral administration to rats than the 4-unsubstituted derivative. We report here on the synthesis and biological data of the aforementioned derivatives.

Potent and selective proline derived dipeptidyl peptidase IV inhibitors

In-house screening of the Merck sample collection identified proline derived homophenylalanine 3 as a DPP-IV inhibitor with modest potency (DPP-IV IC50=1.9 microM). Optimization of 3 led to compound 37, which is among the most potent and selective DPP-IV inhibitors discovered to date.

Discovery of potent and selective β-homophenylalanine based dipeptidyl peptidase IV inhibitors

Modification of in-house screening lead beta-aminoacyl proline 8 gave an equipotent thiazolidide 9. Extensive SAR studies on the phenyl ring of 9 led to the discovery of a novel series of potent and selective DP-IV inhibitors. Introduction of a fluorine at the 2-position proved to be crucial for the potency of this series. The 2,5-difluoro (22q) and 2,4,5-trifluoro (22t) analogues were potent inhibitors of DP-IV (IC(50)=270, 119nM, respectively).

Fluoro-Olefins as Peptidomimetic Inhibitors of Dipeptidyl Peptidases

The feasibility of the fluoro-olefin function as a peptidomimetic group in inhibitors for dipeptidyl peptidase IV and II (DPP IV and DPP II) is investigated by evaluation of N-substituted Gly-Psi[CF=C]pyrrolidines, Gly-Psi[CF=C]piperidines, and Gly-Psi[CF=C](2-cyano)pyrrolidines. Of this later class, the (Z)- and (E)-fluoro-olefin analogues were prepared and chemical stability in comparison with the parent amide was checked. Most of these compounds exhibited a strong binding preference toward DPP II with IC(50) values in the low micromolar range, while only low DPP IV inhibitory potential is seen.

γ-Amino-Substituted Analogues of 1-[(S)-2,4-Diaminobutanoyl]piperidine as Highly Potent and Selective Dipeptidyl Peptidase II Inhibitors

Using 1-[(S)-2,4-diaminobutanoyl]piperidine as lead compound, we developed a large series of highly potent and selective dipeptidyl peptidase II (DPP II) inhibitors. gamma-Amino substitution with arylalkyl groups, for example, a 2-chlorobenzyl moiety, resulted in a DPP II inhibitor with an IC(50) = 0.23 nM and a high selectivity toward DPP IV (IC(50) = 345 microM). Furthermore, it was shown that the basicity of the gamma-amino is important and that alpha-amino substitution is not favorable. Piperidine-2-nitriles did not show an increase in potency but rather reduced the selectivity. Introduction of a 4-methyl or a 3-fluorine on piperidine improved selectivity and preserved the high potency.

Fluoropyrrolidine amides as dipeptidyl peptidase IV inhibitors

Amides derived from fluorinated pyrrolidines and 4-substituted cyclohexylglycine analogues have been prepared and evaluated as inhibitors of dipeptidyl dipeptidase IV (DP-IV). Analogues which incorporated (S)-3-fluoropyrrolidine showed good selectivity for DP-IV over quiescent cell proline dipeptidase (QPP). Compound 48 had good pharmacokinetic properties and was orally active in an oral glucose tolerance test in lean mice.

The crystal structure of human dipeptidyl peptidase IV (DPPIV) complex with diprotin A

Dipeptidyl peptidase IV (DPPIV) is a serine protease, a member of the prolyl oligopeptidase (POP) family, and has been implicated in several diseases. Therefore, it seems important to develop selective inhibitors for human DPPIV (hDPPIV) that are able to control the biological function of hDPPIV. In order to elucidate the binding mode and substrate specificity, we determined the crystal structure complex of hDPPIV and diprotin A (IIe-Pro-IIe), a slowly hydrolyzed substrate of hDPPIV, at 2.2 A resolution. In this paper, we discuss the molecular interaction mechanism of diprotin A with hDPPIV based on the X-ray crystal structure.

4-Amino cyclohexylglycine analogues as potent dipeptidyl peptidase IV inhibitors

Substituted 4-amino cyclohexylglycine analogues were evaluated for DP-IV inhibitory properties. Bis-sulfonamide 15e was an extremely potent 2.6 nM inhibitor of the enzyme with excellent selectivity over all counterscreens. 2,4-difluorobenzenesulfonamide 15b and 1-naphthyl amide 16b, however, combined an acceptable in vitro profile with good pharmacokinetic properties in the rat, and 15b was orally efficacious at 3 mpk in an OGTT in lean mice.

Application of robotics to steady state enzyme kinetics: analysis of tight-binding inhibitors of dipeptidyl peptidase IV

Using available commercial robotics and instrumentation, we developed a fully automated and rigorous steady state enzyme kinetic assay for dipeptidyl peptidase IV (DPP IV; E.C. 3.4.14.5). The automated assay was validated with isoleucyl thiazolidide, a potent inhibitor of DPP IV with K(is)=110nM. Signal window analysis indicated that the assay had a 98% probability of detecting an inhibitor yielding 15% inhibition, with a predicted false positive rate of 0.13%. A mechanistic inhibition version of the automated assay was validated with isoleucyl 4-cyanothiazolidide, a very potent inhibitor of DPP IV. Isoleucyl 4-cyanothiazolidide was a competitive inhibitor of purified porcine DPP IV with K(is)=1 nM. Similar K(is) values were obtained for purified rat DPP IV and for DPP IV activity in human plasma from normal and diabetic donors. The pH dependence of K(is) for isoleucyl 4-cyanothiazolidide yielded a bell-shaped profile, with pK(a)=5.0 and pK(b)=7.6. To date, over 100,000 data points have been generated in profiling targeted compound libraries and in the analysis of tight-binding inhibitors of DPP IV. The data also show that robotic analysis is capable of producing full mechanistic inhibition analysis in a timely fashion to support drug discovery.

Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Dipeptidyl-peptidase IV/CD26 (DPP IV) is a cell-surface protease belonging to the prolyloligopeptidase family. It selectively removes the N-terminal dipeptide from peptides with proline or alanine in the second position. Apart from its catalytic activity, it interacts with several proteins, for instance, adenosine deaminase, the HIV gp120 protein, fibronectin, collagen, the chemokine receptor CXCR4, and the tyrosine phosphatase CD45. DPP IV is expressed on a specific set of T lymphocytes, where it is up-regulated after activation. It is also expressed in a variety of tissues, primarily on endothelial and epithelial cells. A soluble form is present in plasma and other body fluids. DPP IV has been proposed as a diagnostic or prognostic marker for various tumors, hematological malignancies, immunological, inflammatory, psychoneuroendocrine disorders, and viral infections. DPP IV truncates many bioactive peptides of medical importance. It plays a role in glucose homeostasis through proteolytic inactivation of the incretins. DPP IV inhibitors improve glucose tolerance and pancreatic islet cell function in animal models of type 2 diabetes and in diabetic patients. The role of DPP IV/ CD26 within the immune system is a combination of its exopeptidase activity and its interactions with different molecules. This enables DPP IV/CD26 to serve as a co-stimulatory molecule to influence T cell activity and to modulate chemotaxis. DPP IV is also implicated in HIV-1 entry, malignant transformation, and tumor invasion.

The crystal structure of dipeptidyl peptidase IV (CD26) reveals its functional regulation and enzymatic mechanism

The membrane-bound glycoprotein dipeptidyl peptidase IV (DP IV, CD26) is a unique multifunctional protein, acting as receptor, binding and proteolytic molecule. We have determined the sequence and 1.8 A crystal structure of native DP IV prepared from porcine kidney. The crystal structure reveals a 2-2-2 symmetric tetrameric assembly which depends on the natively glycosylated beta-propeller blade IV. The crystal structure indicates that tetramerization of DP IV is a key mechanism to regulate its interaction with other components. Each subunit comprises two structural domains, the N-terminal eight-bladed beta-propeller with open Velcro topology and the C-terminal alpha/beta-hydrolase domain. Analogy with the structurally related POP and tricorn protease suggests that substrates access the buried active site through the beta-propeller tunnel while products leave the active site through a separate side exit. A dipeptide mimicking inhibitor complexed to the active site discloses key determinants for substrate recognition, including a Glu-Glu motif that distinguishes DP IV as an aminopeptidase and an oxyanion trap that binds and activates the P(2)-carbonyl oxygen necessary for efficient postproline cleavage. We discuss active and nonactive site-directed inhibition strategies of this pharmaceutical target protein.