Preclinical Development of PNT6555, a Boronic Acid-Based, Fibroblast Activation Protein-α (FAP)-Targeted Radiotheranostic for Imaging and Treatment of FAP-Positive Tumors.

The overexpression of fibroblast activation protein-α (FAP) in solid cancers relative to levels in normal tissues has led to its recognition as a target for delivering agents directly to tumors. Radiolabeled quinoline-based FAP ligands have established clinical feasibility for tumor imaging, but their therapeutic potential is limited due to suboptimal tumor retention, which has prompted the search for alternative pharmacophores. One such pharmacophore is the boronic acid derivative N-(pyridine-4-carbonyl)-d-Ala-boroPro, a potent and selective FAP inhibitor (FAPI). In this study, the diagnostic and therapeutic (theranostic) potential of N-(pyridine-4-carbonyl)-d-Ala-boroPro-based metal-chelating DOTA-FAPIs was evaluated. Methods: Three DOTA-FAPIs, PNT6555, PNT6952, and PNT6522, were synthesized and characterized with respect to potency and selectivity toward soluble and cell membrane FAP; cellular uptake of the Lu-chelated analogs; biodistribution and pharmacokinetics in mice xenografted with human embryonic kidney cell-derived tumors expressing mouse FAP; the diagnostic potential of 68Ga-chelated DOTA-FAPIs by direct organ assay and small-animal PET; the antitumor activity of 177Lu-, 225Ac-, or 161Tb-chelated analogs using human embryonic kidney cell-derived tumors expressing mouse FAP; and the tumor-selective delivery of 177Lu-chelated DOTA-FAPIs via direct organ assay and SPECT. Results: DOTA-FAPIs and their natGa and natLu chelates exhibited potent inhibition of human and mouse sources of FAP and greatly reduced activity toward closely related prolyl endopeptidase and dipeptidyl peptidase 4. 68Ga-PNT6555 and 68Ga-PNT6952 showed rapid renal clearance and continuous accumulation in tumors, resulting in tumor-selective exposure at 60 min after administration. 177Lu-PNT6555 was distinguished from 177Lu-PNT6952 and 177Lu-PNT6522 by significantly higher tumor accumulation over 168 h. In therapeutic studies, all 3 177Lu-DOTA-FAPIs exhibited significant antitumor activity at well-tolerated doses, with 177Lu-PNT6555 producing the greatest tumor growth delay and animal survival. 225Ac-PNT6555 and 161Tb-PNT6555 were similarly efficacious, producing 80% and 100% survival at optimal doses, respectively. Conclusion: PNT6555 has potential for clinical translation as a theranostic agent in FAP-positive cancer.

Dipeptidyl Peptidase Inhibition Enhances CD8 T Cell Recruitment and Activates Intrahepatic Inflammasome in a Murine Model of Hepatocellular Carcinoma.

The mRNA expression of the dipeptidyl peptidase 4 (DPP4) gene family is highly upregulated in human hepatocellular carcinoma (HCC) and is associated with poor survival in HCC patients. Compounds that inhibit the DPP4 enzyme family, such as talabostat and ARI-4175, can mediate tumour regression by immune-mediated mechanisms that are believed to include NLRP1 activation. This study investigated the expression and activity of the DPP4 family during the development of HCC and evaluated the efficacy of ARI-4175 in the treatment of early HCC in mice. This first report on this enzyme family in HCC-bearing mice showed DPP9 upregulation in HCC, whereas intrahepatic DPP8/9 and DPP4 enzyme activity levels decreased with age. We demonstrated that ARI-4175 significantly lowered the total number of macroscopic liver nodules in these mice. In addition, ARI-4175 increased intrahepatic inflammatory cell infiltration, including CD8+ T cell numbers, into the HCC-bearing livers. Furthermore, ARI-4175 activated a critical component of the inflammasome pathway, caspase-1, in these HCC-bearing livers. This is the first evidence of caspase-1 activation by a pan-DPP inhibitor in the liver. Our data suggest that targeting the DPP4 enzyme family may be a novel and effective approach to promote anti-tumour immunity in HCC via caspase-1 activation.

Fibroblast activation protein is dispensable for control of glucose homeostasis and body weight in mice.

OBJECTIVE: Fibroblast Activation Protein (FAP), an enzyme structurally related to dipeptidyl peptidase-4 (DPP-4), has garnered interest as a potential metabolic drug target due to its ability to cleave and inactivate FGF-21 as well as other peptide substrates. Here we investigated the metabolic importance of FAP for control of body weight and glucose homeostasis in regular chow-fed and high fat diet-fed mice. METHODS: FAP enzyme activity was transiently attenuated using a highly-specific inhibitor CPD60 and permanently ablated by genetic inactivation of the mouse Fap gene. We also assessed the FAP-dependence of CPD60 and talabostat (Val-boroPro), a chemical inhibitor reportedly targeting both FAP and dipeptidyl peptidase-4 RESULTS: CPD60 robustly inhibited plasma FAP activity with no effect on DPP-4 activity. Fap gene disruption was confirmed by assessment of genomic DNA, and loss of FAP enzyme activity in plasma and tissues. CPD60 did not improve lipid tolerance but modestly improved acute oral and intraperitoneal glucose tolerance in a FAP-dependent manner. Genetic inactivation of Fap did not improve glucose or lipid tolerance nor confer resistance to weight gain in male or female Fap-/- mice fed regular chow or high-fat diets. Moreover, talabostat markedly improved glucose homeostasis in a FAP- and FGF-21-independent, DPP-4 dependent manner. CONCLUSION: Although pharmacological FAP inhibition improves glucose tolerance, the absence of a metabolic phenotype in Fap-/-mice suggest that endogenous FAP is dispensable for the regulation of murine glucose homeostasis and body weight. These findings highlight the importance of characterizing the specificity and actions of FAP inhibitors in different species and raise important questions about the feasibility of mouse models for targeting FAP as a treatment for diabetes and related metabolic disorders.

An Atypical Parvovirus Drives Chronic Tubulointerstitial Nephropathy and Kidney Fibrosis.

The occurrence of a spontaneous nephropathy with intranuclear inclusions in laboratory mice has puzzled pathologists for over 4 decades, because its etiology remains elusive. The condition is more severe in immunodeficient animals, suggesting an infectious cause. Using metagenomics, we identify the causative agent as an atypical virus, termed "mouse kidney parvovirus" (MKPV), belonging to a divergent genus of Parvoviridae. MKPV was identified in animal facilities in Australia and North America, is transmitted via a fecal-oral or urinary-oral route, and is controlled by the adaptive immune system. Detailed analysis of the clinical course and histopathological features demonstrated a stepwise progression of pathology ranging from sporadic tubular inclusions to tubular degeneration and interstitial fibrosis and culminating in renal failure. In summary, we identify a widely distributed pathogen in laboratory mice and establish MKPV-induced nephropathy as a new tool for elucidating mechanisms of tubulointerstitial fibrosis that shares molecular features with chronic kidney disease in humans.

Circulating fibroblast activation protein and dipeptidyl peptidase 4 in rheumatoid arthritis and systemic sclerosis.

AIM: To quantify circulating fibroblast activation protein (cFAP) and dipeptidyl peptidase 4 (cDPP4) protease activities in patients with rheumatoid arthritis (RA), systemic sclerosis (SSc), and a control group with mechanical back pain and to correlate plasma levels with disease characteristics. METHODS: Plasma was collected from patients with RA (n = 73), SSc (n = 37) and control subjects (n = 26). DPP4 and FAP were quantified using specific enzyme activity assays. RESULTS: Median cDPP4 was significantly lower in the RA group (P = 0.02), and SSc group (P = 0.002) compared with controls. There were no significant differences in median cFAP between the three groups. DPP4 and FAP demonstrated a negative correlation with inflammatory markers and duration of disease. There were no associations with disease subtypes in RA, including seropositive and erosive disease. Decreased cDPP4 was found in SSc patients with myositis. Plasma FAP was lower in RA patients receiving prednisone (P = 0.001) or leflunomide (P = 0.04), but higher with biologic agents (P = 0.01). RA patients receiving leflunomide also had decreased cDPP4 (P = 0.014). SSc patients receiving prednisone (P = 0.02) had lower cDPP4 but there was no association with cFAP. CONCLUSIONS: No association was found between cFAP and RA or SSc. Plasma DPP4 was decreased in RA and SSc when compared with controls. cDPP4 and cFAP correlated negatively with inflammatory markers and there were no significant correlations with disease characteristics in this RA cohort.

DPP8 and DPP9 inhibition induces pro-caspase-1-dependent monocyte and macrophage pyroptosis.

Val-boroPro (Talabostat, PT-100), a nonselective inhibitor of post-proline cleaving serine proteases, stimulates mammalian immune systems through an unknown mechanism of action. Despite this lack of mechanistic understanding, Val-boroPro has attracted substantial interest as a potential anticancer agent, reaching phase 3 trials in humans. Here we show that Val-boroPro stimulates the immune system by triggering a proinflammatory form of cell death in monocytes and macrophages known as pyroptosis. We demonstrate that the inhibition of two serine proteases, DPP8 and DPP9, activates the pro-protein form of caspase-1 independent of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1ß but does cleave and activate gasdermin D to induce pyroptosis. Mice lacking caspase-1 do not show immune stimulation after treatment with Val-boroPro. Our data identify what is to our knowledge the first small molecule that induces pyroptosis and reveals a new checkpoint that controls the activation of the innate immune system.

Human FGF-21 Is a Substrate of Fibroblast Activation Protein.

FGF-21 is a key regulator of metabolism and potential drug candidate for the treatment of type II diabetes and other metabolic disorders. However, the half-life of active, circulating, human FGF-21 has recently been shown to be limited in mice and monkeys by a proteolytic cleavage between P171 and S172. Here, we show that fibroblast activation protein is the enzyme responsible for this proteolysis by demonstrating that purified FAP cleaves human FGF-21 at this site in vitro, and that an FAP-specific inhibitor, ARI-3099, blocks the activity in mouse, monkey and human plasma and prolongs the half-life of circulating human FGF-21 in mice. Mouse FGF-21, however, lacks the FAP cleavage site and is not cleaved by FAP. These findings indicate FAP may function in the regulation of metabolism and that FAP inhibitors may prove useful in the treatment of diabetes and metabolic disorders in humans, but pre-clinical proof of concept studies in rodents will be problematic.

Neuropeptide Y is a physiological substrate of fibroblast activation protein: Enzyme kinetics in blood plasma and expression of Y2R and Y5R in human liver cirrhosis and hepatocellular carcinoma.

Fibroblast activation protein (FAP) is a dipeptidyl peptidase (DPP) and endopeptidase that is weakly expressed in normal adult human tissues but is greatly up-regulated in activated mesenchymal cells of tumors and chronically injured tissue. The identities and locations of target substrates of FAP are poorly defined, in contrast to the related protease DPP4. This study is the first to characterize the physiological substrate repertoire of the DPP activity of endogenous FAP present in plasma. Four substrates, neuropeptide Y (NPY), peptide YY, B-type natriuretic peptide and substance P, were analyzed by mass spectrometry following proteolysis in human or mouse plasma, and by in vivo localization in human liver tissues with cirrhosis and hepatocellular carcinoma (HCC). NPY was the most efficiently cleaved substrate of both human and mouse FAP, whereas all four peptides were efficiently cleaved by endogenous DPP4, indicating that the in vivo degradomes of FAP and DPP4 differ. All detectable DPP-specific proteolysis and C-terminal processing of these neuropeptides was attributable to FAP and DPP4, and plasma kallikrein, respectively, highlighting their combined physiological significance in the regulation of these neuropeptides. In cirrhotic liver and HCC, NPY and its receptor Y2R, but not Y5R, were increased in hepatocytes near the parenchymal-stromal interface where there is an opportunity to interact with FAP expressed on nearby activated mesenchymal cells in the stroma. These novel findings provide insights into the substrate specificity of FAP, which differs greatly from DPP4, and reveal a potential function for FAP in neuropeptide regulation within liver and cancer biology.

Fibroblast Activation Protein (FAP) Accelerates Collagen Degradation and Clearance from Lungs in Mice.

Idiopathic pulmonary fibrosis is a disease characterized by progressive, unrelenting lung scarring, with death from respiratory failure within 2-4 years unless lung transplantation is performed. New effective therapies are clearly needed. Fibroblast activation protein (FAP) is a cell surface-associated serine protease up-regulated in the lungs of patients with idiopathic pulmonary fibrosis as well as in wound healing and cancer. We postulate that FAP is not only a marker of disease but influences the development of pulmonary fibrosis after lung injury. In two different models of pulmonary fibrosis, intratracheal bleomycin instillation and thoracic irradiation, we find increased mortality and increased lung fibrosis in FAP-deficient mice compared with wild-type mice. Lung extracellular matrix analysis reveals accumulation of intermediate-sized collagen fragments in FAP-deficient mouse lungs, consistent within vitrostudies showing that FAP mediates ordered proteolytic processing of matrix metalloproteinase (MMP)-derived collagen cleavage products. FAP-mediated collagen processing leads to increased collagen internalization without altering expression of the endocytic collagen receptor, Endo180. Pharmacologic FAP inhibition decreases collagen internalization as expected. Conversely, restoration of FAP expression in the lungs of FAP-deficient mice decreases lung hydroxyproline content after intratracheal bleomycin to levels comparable with that of wild-type controls. Our findings indicate that FAP participates directly, in concert with MMPs, in collagen catabolism and clearance and is an important factor in resolving scar after injury and restoring lung homeostasis. Our study identifies FAP as a novel endogenous regulator of fibrosis and is the first to show FAP's protective effects in the lung.

GLP-1(32-36)amide Pentapeptide Increases Basal Energy Expenditure and Inhibits Weight Gain in Obese Mice.

The prevalence of obesity-related diabetes is increasing worldwide. Here we report the identification of a pentapeptide, GLP-1(32-36)amide (LVKGRamide), derived from the glucoincretin hormone GLP-1, that increases basal energy expenditure and curtails the development of obesity, insulin resistance, diabetes, and hepatic steatosis in diet-induced obese mice. The pentapeptide inhibited weight gain, reduced fat mass without change in energy intake, and increased basal energy expenditure independent of physical activity. Analyses of tissues from peptide-treated mice reveal increased expression of UCP-1 and UCP-3 in brown adipose tissue and increased UCP-3 and inhibition of acetyl-CoA carboxylase in skeletal muscle, findings consistent with increased fatty acid oxidation and thermogenesis. In palmitate-treated C2C12 skeletal myotubes, GLP-1(32-36)amide activated AMPK and inhibited acetyl-CoA carboxylase, suggesting activation of fat metabolism in response to energy depletion. By mass spectroscopy, the pentapeptide is rapidly formed from GLP-1(9-36)amide, the major form of GLP-1 in the circulation of mice. These findings suggest that the reported insulin-like actions of GLP-1 receptor agonists that occur independently of the GLP-1 receptor might be mediated by the pentapeptide, and the previously reported nonapeptide (FIAWLVKGRamide). We propose that by increasing basal energy expenditure, GLP-1(32-36)amide might be a useful treatment for human obesity and associated metabolic disorders.

A high-throughput, multiplexed assay for superfamily-wide profiling of enzyme activity.

The selectivity of an enzyme inhibitor is a key determinant of its usefulness as a tool compound or its safety as a drug. Yet selectivity is never assessed comprehensively in the early stages of the drug discovery process, and only rarely in the later stages, because technical limitations prohibit doing otherwise. Here, we report EnPlex, an efficient, high-throughput method for simultaneously assessing inhibitor potency and specificity, and pilot its application to 96 serine hydrolases. EnPlex analysis of widely used serine hydrolase inhibitors revealed numerous previously unrecognized off-target interactions, some of which may help to explain previously confounding adverse effects. In addition, EnPlex screening of a hydrolase-directed library of boronic acid- and nitrile-containing compounds provided structure-activity relationships in both potency and selectivity dimensions from which lead candidates could be more effectively prioritized. Follow-up of a series of dipeptidyl peptidase 4 inhibitors showed that EnPlex indeed predicted efficacy and safety in animal models. These results demonstrate the feasibility and value of high-throughput, superfamily-wide selectivity profiling and suggest that such profiling can be incorporated into the earliest stages of drug discovery.

A pan inhibitor of DASH family enzymes induces immunogenic modulation and sensitizes murine and human carcinoma cells to antigen-specific cytotoxic T lymphocyte killing: implications for combination therapy with cancer vaccines.

Recent studies have suggested that pan inhibitors of dipeptidyl peptidase-4 activity and/or structure homologs (DASH), including ARI-4175, can mediate tumor regression by immune-mediated mechanisms. This study assessed the potential of combining ARI-4175 with cancer vaccines. We evaluated ARI-4175's effect on immunogenic modulation, ability to sensitize tumor cells to antigen-specific CTL killing, effect on immune-cell subsets and function, and antitumor activity in 2 tumor models, both as a monotherapy and in combination with a recombinant viral or dendritic cell (DC)-based tumor-cell vaccine. ARI-4175's effects on the growth, surface phenotype, and antigen-specific CTL-mediated lysis of murine and human carcinoma cell lines were assessed in vitro. In vivo, C57BL-6 mice were treated orally with ARI-4175, after which splenocytes were assessed by flow cytometry and functional assays. Antitumor studies were performed in murine models of colon carcinoma (MC38-CEA(+) in CEA-transgenic C57BL-6 mice) and rhabdomyosarcoma (M3-9-M in C57BL-6 mice). Mice received oral ARI-4175 alone or in combination with a vaccine consisting of recombinant vaccinia/fowlpox CEA-TRICOM (colon model) or a DC-based tumor-cell vaccine (rhabdomyosarcoma model). Exposure to ARI-4175 had no effect on the proliferation or viability of carcinoma cells in vitro; however, it did alter tumor phenotype, making murine and human tumor cells more sensitive to antigen-specific CTL killing. Assessment of immune-cell subsets and function indicated that ARI-4175 increased levels of natural killer cells and DCs. Detrimental immune effects, including reduced T effector cells and increased immunosuppressive cells (Tregs, MDSCs), were normalized when treatment stopped, suggesting that scheduling is critical when combining this agent with vaccine. As a monotherapy, ARI-4175 had potent antitumor activity in both tumor models, and had even greater effects when combined with a vaccine (either DC-based or poxviral vector based). These findings provide the rationale for the combined use of cancer immunotherapy with DASH enzyme inhibitors such as ARI-4175.

Quantitation of fibroblast activation protein (FAP)-specific protease activity in mouse, baboon and human fluids and organs.

The protease fibroblast activation protein (FAP) is a specific marker of activated mesenchymal cells in tumour stroma and fibrotic liver. A specific, reliable FAP enzyme assay has been lacking. FAP's unique and restricted cleavage of the post proline bond was exploited to generate a new specific substrate to quantify FAP enzyme activity. This sensitive assay detected no FAP activity in any tissue or fluid of FAP gene knockout mice, thus confirming assay specificity. Circulating FAP activity was ∼20- and 1.3-fold less in baboon than in mouse and human plasma, respectively. Serum and plasma contained comparable FAP activity. In mice, the highest levels of FAP activity were in uterus, pancreas, submaxillary gland and skin, whereas the lowest levels were in brain, prostate, leukocytes and testis. Baboon organs high in FAP activity included skin, epididymis, bladder, colon, adipose tissue, nerve and tongue. FAP activity was greatly elevated in tumours and associated lymph nodes and in fungal-infected skin of unhealthy baboons. FAP activity was 14- to 18-fold greater in cirrhotic than in non-diseased human liver, and circulating FAP activity was almost doubled in alcoholic cirrhosis. Parallel DPP4 measurements concorded with the literature, except for the novel finding of high DPP4 activity in bile. The new FAP enzyme assay is the first to be thoroughly characterised and shows that FAP activity is measurable in most organs and at high levels in some. This new assay is a robust tool for specific quantitation of FAP enzyme activity in both preclinical and clinical samples, particularly liver fibrosis.

A pan-inhibitor of DASH family enzymes induces immune-mediated regression of murine sarcoma and is a potent adjuvant to dendritic cell vaccination and adoptive T-cell therapy.

Multimodality therapy consisting of surgery, chemotherapy, and radiation will fail in approximately 40% of patients with pediatric sarcomas and result in substantial long-term morbidity in those who are cured. Immunotherapeutic regimens for the treatment of solid tumors typically generate antigen-specific responses too weak to overcome considerable tumor burden and tumor suppressive mechanisms and are in need of adjuvant assistance. Previous work suggests that inhibitors of DASH (dipeptidyl peptidase IV activity and/or structural homologs) enzymes can mediate tumor regression by immune-mediated mechanisms. Herein, we demonstrate that the DASH inhibitor, ARI-4175, can induce regression and eradication of well-established solid tumors, both as a single agent and as an adjuvant to a dendritic cell (DC) vaccine and adoptive cell therapy (ACT) in mice implanted with the M3-9-M rhabdomyosarcoma cell line. Treatment with effective doses of ARI-4175 correlated with recruitment of myeloid (CD11b) cells, particularly myeloid DCs, to secondary lymphoid tissues and with reduced frequency of intratumoral monocytic (CD11bLy6-CLy6-G) myeloid-derived suppressor cells. In immunocompetent mice, combining ARI-4175 with a DC vaccine or ACT with tumor-primed T cells produced significant improvements in tumor responses against well-established M3-9-M tumors. In M3-9-M-bearing immunodeficient (Rag1) mice, ACT combined with ARI-4175 produced greater tumor responses and significantly improved survival compared with either treatment alone. These studies warrant the clinical investigation of ARI-4175 for treatment of sarcomas and other malignancies, particularly as an adjuvant to tumor vaccines and ACT.

A general method for making peptide therapeutics resistant to serine protease degradation: application to dipeptidyl peptidase IV substrates.

Bioactive peptides have evolved to optimally fulfill specific biological functions, a fact which has long attracted attention for their use as therapeutic agents. While there have been some recent commercial successes fostered in part by advances in large-scale peptide synthesis, development of peptides as therapeutic agents has been significantly impeded by their inherent susceptibility to protease degradation in the bloodstream. Here we report that incorporation of specially designed amino acid analogues at the P1' position, directly C-terminal of the enzyme cleavage site, renders peptides, including glucagon-like peptide-1 (7-36) amide (GLP-1) and six other examples, highly resistant to serine protease degradation without significant alteration of their biological activity. We demonstrate the applicability of the method to a variety of proteases, including dipeptidyl peptidase IV (DPP IV), dipeptidyl peptidase 8 (DPP8), fibroblast activation protein α (FAPα), α-lytic protease (αLP), trypsin, and chymotrypsin. In summary, the "P1' modification" represents a simple, general, and highly adaptable method of generating enzymatically stable peptide-based therapeutics.

The high-fat high-fructose hamster as an animal model for niacin's biological activities in humans.

OBJECTIVE: Niacin has been used for more than 50 years to treat dyslipidemia, yet the mechanisms underlying its lipid-modifying effects remain unknown, a situation stemming at least in part from a lack of validated animal models. The objective of this study was to determine if the dyslipidemic hamster could serve as such a model. MATERIALS/METHODS: Dyslipidemia was induced in Golden Syrian hamsters by feeding them a high-fat, high-cholesterol, and high-fructose (HF/HF) diet. The effect of high-dose niacin treatment for 18 days and 28 days on plasma lipid levels and gene expression was measured. RESULTS: Niacin treatment produced significant decreases in plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and free fatty acids (FFA), but had no measureable effect on high-density lipoprotein cholesterol (HDL-C) in the dyslipidemic hamster. Niacin treatment also produced significant increases in hepatic adenosine ATP-Binding Cassette A1 (ABCA1) mRNA, ABCA1 protein, apolipoprotein A-I (Apo A-I) mRNA, and adipose adiponectin mRNA in these animals. CONCLUSIONS: With the exception of HDL-C, the lipid effects of niacin treatment in the dyslipidemic hamster closely parallel those observed in humans. Moreover, the effects of niacin treatment on gene expression of hepatic proteins related to HDL metabolism are similar to those observed in human cells in culture. The HF/HF-fed hamster could therefore serve as an animal model for niacin's lowering of proatherogenic lipids and mechanisms of action relative to lipid metabolism.

Identification of selective and potent inhibitors of fibroblast activation protein and prolyl oligopeptidase.

Fibroblast activation protein (FAP) is a serine protease selectively expressed on reactive stromal fibroblasts of epithelial carcinomas. It is widely believed to play a role in tumor invasion and metastasis and therefore to represent a potential new drug target for cancer. Investigation into its biological function, however, has been hampered by the current unavailability of selective inhibitors. The challenge has been in identifying inhibitors that are selective for FAP over both the dipeptidyl peptidases (DPPs), with which it shares exopeptidase specificity, and prolyl oligopeptidase (PREP), with which it shares endopeptidase specificity. Here, we report the first potent FAP inhibitor with selectivity over both the DPPs and PREP, N-(pyridine-4-carbonyl)-d-Ala-boroPro (ARI-3099, 6). We also report a similarly potent and selective PREP inhibitor, N-(pyridine-3-carbonyl)-Val-boroPro (ARI-3531, 22). Both are boronic acid based inhibitors, demonstrating that high selectivity can be achieved using this electrophile. The inhibitors are stable, easy to synthesize, and should prove to be useful in helping to elucidate the biological functions of these two unique and interesting enzymes, as well as their potential as drug targets.

4-Substituted boro-proline dipeptides: synthesis, characterization, and dipeptidyl peptidase IV, 8, and 9 activities.

The boroProline-based dipeptidyl boronic acids were among the first DPP-IV inhibitors identified, and remain the most potent known. We introduced various substitutions at the 4-position of the boroProline ring regioselectively and stereoselectively, and incorporated these aminoboronic acids into a series of 4-substituted boroPro-based dipeptides. Among these dipeptidyl boronic acids, Arg-(4S)-boroHyp (4q) was the most potent inhibitor of DPP-IV, DPP8 and DPP9, while (4S)-Hyp-(4R)-boroHyp (4o) exhibited the most selectivity for DPP-IV over DPP8 and DPP9.

Reverse D4F, an apolipoprotein-AI mimetic peptide, inhibits atherosclerosis in ApoE-null mice.

OBJECTIVE: Synthetic class A amphipathic helical peptide analogs of apolipoprotein-AI (apoAI; with varied phenylalanine residues) are emerging therapeutic approaches under investigation for atherosclerosis. Utilizing retroinverso sequencing, we designed reverse-D4F (Rev-D4F) peptide with 18 d-amino acids containing 4 phenylalanine residues and reverse order that allows the side chain residues to be of exact alignment and superimposable to those of the parent l-amino acid peptide. This study examined the effect of Rev-D4F on atherosclerosis in apolipoprotein E (apoE)-null mice and the underlying mechanisms. MATERIALS/METHODS: ApoE-null mice were fed a chow diet and administered water (control), Rev-D4F, or L4F mimetic peptides (0.4 mg/mL, equivalent to 1.6 mg/d) orally in drinking water for 6 weeks. Aortic root atherosclerotic lesion area, lesion macrophage content, and the ability of plasma high-density lipoprotein (HDL) to influence monocyte chemotaxis were measured. RESULTS: Rev-D4F significantly decreased aortic sinus atherosclerotic lesion area and lesion macrophage content without affecting plasma total and HDL-cholesterol levels in apoE-null mice. The HDL from Rev-D4F-treated mice showed enhanced anti-inflammatory monocyte chemotactic activity, while low-density lipoprotein (LDL) exhibited reduced proinflammatory activity. In in vitro studies, Rev-D4F inhibited LDL oxidation, endothelial cell vascular cell adhesion molecule 1 (VCAM-1), and monocyte chemotactic factor 1 (MCP-1) expression, and monocyte adhesion to aortic endothelial cells. CONCLUSIONS: The Rev-D4F inhibits atherosclerosis by inhibiting endothelial inflammatory/oxidative events and improving HDL function. The data suggest that Rev-D4F may be an effective apoAI mimetic peptide for further development in preventing atherosclerosis.

Design and synthesis of boronic acid inhibitors of endothelial lipase.

Endothelial lipase (EL) and lipoprotein lipase (LPL) are homologous lipases that act on plasma lipoproteins. EL is predominantly a phospholipase and appears to be a key regulator of plasma HDL-C. LPL is mainly a triglyceride lipase regulating (V)LDL levels. The existing biological data indicate that inhibitors selective for EL over LPL should have anti-atherogenic activity, mainly through increasing plasma HDL-C levels. We report here the synthesis of alkyl, aryl, or acyl-substituted phenylboronic acids that inhibit EL. Many of the inhibitors evaluated proved to be nearly equally potent against both EL and LPL, but several exhibited moderate to good selectivity for EL.