Macrocarpal C isolated from Eucalyptus globulus inhibits dipeptidyl peptidase 4 in an aggregated form

Dipeptidyl peptidase 4 (DPP-4) inhibitors are used for the treatment of type-2 diabetes mellitus. Various synthetic inhibitors have been developed to date, and plants containing natural DPP-4 inhibitors have also been identified. Here, 13 plant samples were tested for their DPP-4 inhibitory activity. Macrocarpals A–C were isolated from Eucalyptus globulus through activity-guided fractionation and shown to be DPP-4 inhibitors. Of these, macrocarpal C showed the highest inhibitory activity, demonstrating an inhibition curve characterised by a pronounced increase in activity within a narrow concentration range. Evaluation of macrocarpal C solution by turbidity, nuclear magnetic resonance spectroscopy and mass spectrometry indicated its aggregation, which may explain the characteristics of the inhibition curve. These findings will be valuable for further study of potential small molecule DPP-4 inhibitors.     

The Placement of DPP-4 Inhibitors in Clinical Practice Recommendations for the Treatment of Types 2 Diabetes

ObjectiveTo review the most recent clinical data on the safety and efficacy of dipeptidyl peptidase-4 (DPP-4) inhibitors and to evaluate their position in current treatment guidelines and algorithms.MethodsPubMed searches were performed to identify published data regarding both the safety and efficacy of DPP-4 inhibitors approved for use in the United States and clinical guidelines describing recommendations for their use.ResultsIn the past 2 years, more than 100 publications have added clinical trial data on DPP-4 inhibitors to the medical literature. Since becoming available in 2006, these agents have demonstrated an excellent safety/tolerability profile, and as add-on to metformin, DPP-4 inhibitors may have comparable glycemic efficacy as other oral agents. As a result, DPP-4 inhibitors have assumed roles in clinical practice guidelines and treatment algorithms that are comparable to the sulfonylurea class. Advantages of DPP-4 inhibitors include an oral route of administration, a mechanism of action based on glucose-stimulated insulin secretion, and a low risk of hypoglycemia. The main disadvantage associated with this class is a relatively high cost. There is also less clinical experience with DPP-4 agents than classes of agents that have been in use for decades; however, long-term data on the safety and efficacy of DPP-4 agents will be available in the near future to refine their place in therapy. From 2 large clinical trials recently reported, EXAMINE and SAVOR, this class of agents does not increase overall adverse cardiovascular outcomes nor the risk of pancreatitis or pancreatic cancer.ConclusionBased on comparisons of nonglycemic effects such as risk of hypoglycemia, weight gain, and durability, DPP-4 inhibitors may be considered as an alternative to sulfonylureas. However, direct cost may be a determining factor in the choice of therapy. (Endocr Pract. 2013;19:1050-1061)     

Medicinal chemistry approaches to the inhibition of dipeptidyl peptidase-4 for the treatment of type 2 diabetes

Emerging as an epidemic of the 21st century type 2 diabetes has become a major health problem throughout the globe. The number of deaths attributable to diabetes reflects the insufficient glycemic control achieved with the treatments used in recent past. DPP-4 inhibitors have been investigated as a new therapy with novel mechanisms of action and improved tolerability. DPP-4, a protease that specifically cleaves dipeptides from proteins and oligopeptides after a penultimate N-terminal proline or alanine, is involved in the degradation of a number of neuropeptides, peptide hormones and cytokines, including the incretins GLP-1 and GIP. As soon as released from the gut in response to food intake, GLP-1 and GIP exert a potent glucose-dependent insulinotropic action, thereby playing a key role in the maintenance of post-meal glycemic control. Consequently, inhibiting DPP-4 prolongs the action of GLP-1 and GIP, which in turn improves glucose homeostasis with a low risk of hypoglycemia and potential for disease modification. Indeed, clinical trials involving diabetic patients have shown improved glucose control by administering DPP-4 inhibitors, thus demonstrating the benefit of this promising new class of antidiabetics. Intense research activities in this area have resulted in the launch of sitagliptin and vildagliptin (in Europe only) and the advancement of a few others into preregistration/phase 3, for example, saxagliptin, alogliptin and ABT-279. Achieving desired selectivity for DPP-4 over other related peptidases such as DPP-8 and DPP-9 (inhibition of which was linked to toxicity in animal studies) and long-acting potential for maximal efficacy (particularly in more severe diabetic patients) were the major challenges. Whether these goals are achieved with the present series of inhibitors in the advanced stages of clinical development is yet to be confirmed. Nevertheless, treatment of this metabolic disorder especially in the early stages of the disease via DPP-4 inhibition has been recognized as a validated principle and a large number of inhibitors are presently in various stage of pre-clinical/clinical development. Sitagliptin is a new weapon in the arsenal of oral antihyperglycemic agents. This review will focus on the journey of drug discovery of DPP-4 inhibitors for oral delivery covering a brief scientific background and medicinal chemistry approaches along with the status of advanced clinical candidates.     

Discovery of potent, selective, and orally bioavailable oxadiazole-based dipeptidyl peptidase IV inhibitors

A novel series of oxadiazole based amides have been shown to be potent DPP-4 inhibitors. The optimized compound 43 exhibited excellent selectivity over a variety of DPP-4 homologs.     

Natural compounds with DPP-4 inhibitory effects: Implications for the treatment of diabetes

Dipeptidyl peptidase-4 (DPP-4) inhibitors are antidiabetes agents that decrease blood glucose by preventing the degradation of endogenous glucagon-like peptide-1. The first DPP-4 was sitagliptin followed by several other agents in the class introduced to manage diabetes. Recent studies have suggested that naturally occurring compounds can exert an antidiabetes effect through DPP-4 inhibition. Such compounds may have a place in the treatment of diabetes within the diet; however, while DPP-4 inhibition alone is not associated with hypoglycemia, in combinations with other medication hypoglycemia can result, therefore, it is critical to know what herbal or food-based compounds may have these activities in the management of diabetes patients. In this review, we have outlined the compounds that have DPP-4 inhibition that may have utility in the treatment of diabetes.     

Discovery of 3-aminopiperidines as potent, selective, and orally bioavailable dipeptidyl peptidase IV inhibitors

Substituted 3-aminopiperidines 3 were evaluated as DPP-4 inhibitors. The inhibitors showed good DPP-4 potency with superb selectivity over other peptidases (QPP, DPP8, and DPP9). Selected DPP-4 inhibitors were further evaluated for their hERG potassium channel, calcium channel, Cyp2D6, and pharmacokinetic profiles.     

Discovery of new binding elements in DPP-4 inhibition and their applications in novel DPP-4 inhibitor design

Probing with tool molecules, and by modeling and X-ray crystallography the binding modes of two structurally distinct series of DPP-4 inhibitors led to the discovery of a rare aromatic fluorine H-bond and the spatial requirement for better biaryl binding in the DPP-4 enzyme active site. These newly found binding elements were successfully incorporated into novel DPP-4 inhibitors.     

Design of potent dipeptidyl peptidase IV (DPP-4) inhibitors by employing a strategy to form a salt bridge with Lys554

We report a design strategy to obtain potent DPP-4 inhibitors by incorporating salt bridge formation with Lys554 in the S1′ pocket. By applying the strategy to the previously identified templates, quinoline 4 and pyridines 16a, 16b, and 17 have been identified as subnanomolar or nanomolar inhibitors of human DPP-4. Docking studies suggested that a hydrophobic interaction with Tyr547 as well as the salt bridge interaction is important for the extremely high potency. The design strategy would be useful to explore a novel design for DPP-4 inhibitors having a distinct structure with a unique binding mode.     

A DPP-4 Inhibitor Suppresses Fibrosis and Inflammation on Experimental Autoimmune Myocarditis in Mice

Myocarditis is a critical inflammatory disorder which causes life-threatening conditions. No specific or effective treatment has been established. DPP-4 inhibitors have salutary effects not only on type 2 diabetes but also on certain cardiovascular diseases. However, the role of a DPP-4 inhibitor on myocarditis has not been investigated. To clarify the effects of a DPP-4 inhibitor on myocarditis, we used an experimental autoimmune myocarditis (EAM) model in Balb/c mice. EAM mice were assigned to the following groups: EAM mice group treated with a DPP-4 inhibitor (linagliptin) (n = 19) and those untreated (n = 22). Pathological analysis revealed that the myocardial fibrosis area ratio in the treated group was significantly lower than in the untreated group. RT-PCR analysis demonstrated that the levels of mRNA expression of IL-2, TNF-α, IL-1β and IL-6 were significantly lower in the treated group than in the untreated group. Lymphocyte proliferation assay showed that treatment with the DPP-4 inhibitor had no effect on antigen-induced spleen cell proliferation. Administration of the DPP-4 inhibitor remarkably suppressed cardiac fibrosis and reduced inflammatory cytokine gene expression in EAM mice. Thus, the agents present in DPP-4 inhibitors may be useful to treat and/or prevent clinical myocarditis.     

Optimization of 1,4-diazepan-2-one containing dipeptidyl peptidase IV inhibitors for the treatment of type 2 diabetes

Following the discovery of N-acyl-1,4-diazepan-2-one as a novel pharmacophore for potent and selective DPP-4 inhibitors, optimization of this new lead with different substitution on the seven-membered ring resulted in several highly potent and selective, orally bioavailable, and efficacious DPP-4 inhibitors, such as 3R-methyl-1-cyclopropyl-1,4-diazepan-2-one derivative 9i (DPP-4 IC(50)=8.0 nM) and 3R,6R-dimethyl-1,4-diazepan-2-one derivative 14a (DPP-4 IC(50)=9.7 nM).     

Fluoroolefins as amide bond mimics in dipeptidyl peptidase IV inhibitors

The synthesis, selectivity, rat pharmacokinetic profile, and drug metabolism profiles of a series of potent fluoroolefin-derived DPP-4 inhibitors (4) are reported. A radiolabeled fluoroolefin 33 was shown to possess a high propensity to form reactive metabolites, thus revealing a potential liability for this class of DPP-4 inhibitors.     

Discovery of 3H-imidazo[4,5-c]quinolin-4(5H)-ones as potent and selective dipeptidyl peptidase IV (DPP-4) inhibitors

In recent years, dipeptidyl peptidase IV inhibitors have been noted as valuable agents for treatment of type 2 diabetes. Herein, we report the discovery of a novel potent DPP-4 inhibitor with 3H-imidazo[4,5-c]quinolin-4(5H)-one as skeleton. After efficient optimization of the lead compound 2a at the 7- and 8-positions using a docking study, we found 28 as a novel DPP-4 inhibitor with excellent selectivity against various DPP-4 homologues. Compound 28 showed strong DPP-4 inhibitory activity compared to marketed DPP-4 inhibitors. We also found that a carboxyl group at the 7-position could interact with the residue of Lys554 to form a salt bridge. Additionally, introduction of a carboxyl group to 7-position led to both activity enhancement and reduced risk for hERG channel inhibition and induced phospholipidosis. In our synthesis of compounds with 7-carboxyl group, we achieved efficient regioselective synthesis using bulky ester in the intramolecular palladium coupling reaction.     

Selective inhibition of fibroblast activation protein protease based on dipeptide substrate specificity

Fibroblast activation protein (FAP) is a transmembrane serine peptidase that belongs to the prolyl peptidase family. FAP has been implicated in cancer; however, its specific role remains elusive because inhibitors that distinguish FAP from other prolyl peptidases like dipeptidyl peptidase-4 (DPP-4) have not been developed. To identify peptide motifs for FAP-selective inhibitor design, we used P(2)-Pro(1) and acetyl (Ac)-P(2)-Pro(1) dipeptide substrate libraries, where P(2) was varied and substrate hydrolysis occurs between Pro(1) and a fluorescent leaving group. With the P(2)-Pro(1) library, FAP preferred Ile, Pro, or Arg at the P(2) residue; however, DPP-4 showed broad reactivity against this library, precluding selectivity. By contrast, with the Ac-P(2)-Pro(1) library, FAP cleaved only Ac-Gly-Pro, whereas DPP-4 showed little reactivity with all substrates. FAP also cleaved formyl-, benzyloxycarbonyl-, biotinyl-, and peptidyl-Gly-Pro substrates, which DPP-4 cleaved poorly, suggesting an N-acyl-Gly-Pro motif for inhibitor design. Therefore, we synthesized and tested the compound Ac-Gly-prolineboronic acid, which inhibited FAP with a K(i) of 23 +/- 3 nm. This was approximately 9- to approximately 5400-fold lower than the K(i) values for other prolyl peptidases, including DPP-4, DPP-7, DPP-8, DPP-9, prolyl oligopeptidase, and acylpeptide hydrolase. These results identify Ac-Gly-BoroPro as a FAP-selective inhibitor and suggest that N-acyl-Gly-Pro-based inhibitors will allow testing of FAP as a therapeutic target.     

Efficacy and Safety of Dipeptidyl Peptidase-4 Inhibitors in Type 2 Diabetes Mellitus Patients with Moderate to Severe Renal Impairment: A Systematic Review and Meta-Analysis

Objective

To perform a systematic review and meta-analysis regarding the efficacy and safety of dipeptidyl peptidase-4 (DDP-4) inhibitors (“gliptins”) for the treatment of type 2 diabetes mellitus (T2DM) patients with moderate to severe renal impairment.

Methods

All available randomized-controlled trials (RCTs) that assessed the efficacy and safety of DDP-4 inhibitors compared with placebo, no treatment, or active drugs were identified using PubMed, EMBASE, Cochrane CENTRAL, conference abstracts, clinical trials.gov, pharmaceutical company websites, the FDA, and the EMA (up to June 2014). Two independent reviewers extracted the data, and a random-effects model was applied to estimate summary effects.

Results

Thirteen reports of ten studies with a total of 1,915 participants were included in the final analysis. Compared with placebo or no treatment, DPP-4 inhibitors reduced HbA1c significantly (−0.52%, 95%CI −0.64 to −0.39) and had no increased risk of hypoglycemia (RR 1.10, 95%CI 0.92 to 1.32) or weight gain. In contrast to glipizide monotherapy, DPP-4 inhibitors showed no difference in HbA1c lowering effect (−0.08%, 95% CI −0.40 to 0.25) but had a lower incidence of hypoglycemia (RR 0.40, 95%CI 0.23 to 0.69). Furthermore, DPP-4 inhibitors were well-tolerated, without any additional mortality and adverse events. However, the quality of evidence was mostly as low, as assessed using the GRADE system for each outcome.

Conclusions

DPP-4 inhibitors are effective at lowering HbA1c in T2DM patients with moderate to severe renal impairment. DPP-4 inhibitors also have a potential advantage in lowering the risk of adverse events. Regarding the low quality of the evidence according to GRADE, additional well-designed randomized trials that focus on the safety and efficacy of DPP-4 inhibitors in various CKD stages are needed urgently.     

Probing the electronic structures and properties of neutral and anionic ScSi n (0,−1) (n = 1–6) clusters using ccCA-TM and G4 theory

We apply molecular docking, molecular dynamics (MD) simulation, and binding free energy calculation to investigate and reveal the binding mechanism between five xanthine inhibitors and DPP-4. The electrostatic and van der Waals interactions of the five inhibitors with DPP-4 are analyzed and discussed. The computed binding free energies using MM-PBSA method are in qualitatively agreement with experimental inhibitory potency of five inhibitors. The hydrogen bonds of inhibitors with Ser630 and Asp663 can stabilize the inhibitors in binding sites. The van der Waals interactions, especially the key contacts with His740, Asn710, Trp629, and Tyr666 have larger contributions to the binding free energy and play important roles in distinguishing the variant bioactivity of five inhibitors.     

Discovery of potent, selective, and orally bioavailable quinoline-based dipeptidyl peptidase IV inhibitors targeting Lys554

Dipeptidyl peptidase IV (DPP-4) inhibition is a validated therapeutic option for type 2 diabetes, exhibiting multiple antidiabetic effects with little or no risk of hypoglycemia. In our studies involving non-covalent DPP-4 inhibitors, a novel series of quinoline-based inhibitors were designed based on the co-crystal structure of isoquinolone 2 in complex with DPP-4 to target the side chain of Lys554. Synthesis and evaluation of designed compounds revealed 1-[3-(aminomethyl)-4-(4-methylphenyl)-2-(2-methylpropyl)quinolin-6-yl]piperazine-2,5-dione (1) as a potent, selective, and orally active DPP-4 inhibitor (IC??=1.3 nM) with long-lasting ex vivo activity in dogs and excellent antihyperglycemic effects in rats. A docking study of compound 1 revealed a hydrogen-bonding interaction with the side chain of Lys554, suggesting this residue as a potential target site useful for enhancing DPP-4 inhibition.     

Modeling assisted rational design of novel, potent, and selective pyrrolopyrimidine DPP-4 inhibitors

Molecular modeling was used to improve potency of the cyclohexylamine series. In addition, a 3-D QSAR method was used to gain insight for reducing off-target DPP-8/9 activities. Compounds 3, 4, and 5 were synthesized and found to be potent DPP-4 inhibitors, in particular 4 and 5 are designed to be highly selective against off-target DASH enzymes while maintaining potency on DPP-4.     

4-arylcyclohexylalanine analogs as potent, selective, and orally active inhibitors of dipeptidyl peptidase IV

A novel series of 4-arylcyclohexylalanine DPP-4 inhibitors was synthesized and tested for inhibitory activity as well as selectivity over the related proline-specific enzymes DPP-8 and DPP-9. Optimization of this series led to 28 (DPP-4 IC(50)=4.8 nM), which showed an excellent pharmacokinetic profile across several preclinical species. Evaluation of 28 in an oral glucose tolerance test demonstrated that this compound effectively reduced glucose excursion in lean mice.     

Aminopiperidine-fused imidazoles as dipeptidyl peptidase-IV inhibitors

A new series of DPP-4 inhibitors derived from piperidine-fused benzimidazoles and imidazopyridines is described. Optimization of this class of DPP-4 inhibitors led to the discovery of imidazopyridine 34. The potency, selectivity, cross-species DMPK profiles, and in vivo efficacy of 34 is reported.