In Vivo Half-Life Extension of BMP1/TLL Metalloproteinase Inhibitors Using Small-Molecule Human Serum Albumin Binders.

Reducing the required frequence of drug dosing can improve the adherence of patients to chronic treatments. Hence, drugs with longer in vivo half-lives are highly desirable. One of the most promising approaches to extend the in vivo half-life of drugs is conjugation to human serum albumin (HSA). In this work, we describe the use of AlbuBinder 1, a small-molecule noncovalent HSA binder, to extend the in vivo half-life and pharmacology of small-molecule BMP1/TLL inhibitors in humanized mice (HSA KI/KI). A series of conjugates of AlbuBinder 1 with BMP1/TLL inhibitors were prepared. In particular, conjugate c showed good solubility and a half-life extension of >20-fold versus the parent molecule in the HSA KI/KI mice, reaching half-lives of >48 h with maintained maximal inhibition of plasma BMP1/TLL. The same conjugate showed a half-life of only 3 h in the wild-type mice, suggesting that the half-life extension was principally due to specific interactions with HSA. It is envisioned that conjugation to AlbuBinder 1 should be applicable to a wide range of small molecule or peptide drugs with short half-lives. In this context, AlbuBinders represent a viable alternative to existing half-life extension technologies.

Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells.

A splice form of IGF-1, IGF-1Eb, is upregulated after exercise or injury. Physiological responses have been ascribed to the 24-amino acid COOH-terminal peptide that is cleaved from the NH3-terminal 70-amino acid mature IGF-1 protein. This COOH-terminal peptide was termed "mechano-growth factor" (MGF). Activities claimed for the MGF peptide included enhancing muscle satellite cell proliferation and delaying myoblast fusion. As such, MGF could represent a promising strategy to improve muscle regeneration. Thus, at our two pharmaceutical companies, we attempted to reproduce the claimed effect of MGF peptides on human and mouse muscle myoblast proliferation and differentiation in vitro. Concentrations of peptide up to 500 ng/ml failed to increase the proliferation of C2C12 cells or primary human skeletal muscle myoblasts. In contrast, all cell types exhibited a proliferative response to mature IGF-1 or full-length IGF-1Eb. MGF also failed to inhibit the differentiation of myoblasts into myotubes. To address whether the response to MGF was lost in these tissue culture lines, we measured proliferation and differentiation of primary mouse skeletal muscle stem cells exposed to MGF. This, too, failed to demonstrate a significant effect. Finally, we tested whether MGF could alter a separate documented in vitro effect of the peptide, activation of p-ERK, but not p-Akt, in cardiac myocytes. Although a robust response to IGF-1 was observed, there were no demonstrated activating responses from the native or a stabilized MGF peptide. These results call in to question whether there is a physiological role for MGF.

Human-induced pluripotent stem cell-derived cardiomyocytes exhibit temporal changes in phenotype.

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) have been recently derived and are used for basic research, cardiotoxicity assessment, and phenotypic screening. However, the hiPS-CM phenotype is dependent on their derivation, age, and culture conditions, and there is disagreement as to what constitutes a functional hiPS-CM. The aim of the present study is to characterize the temporal changes in hiPS-CM phenotype by examining five determinants of cardiomyocyte function: gene expression, ion channel functionality, calcium cycling, metabolic activity, and responsiveness to cardioactive compounds. Based on both gene expression and electrophysiological properties, at day 30 of differentiation, hiPS-CMs are immature cells that, with time in culture, progressively develop a more mature phenotype without signs of dedifferentiation. This phenotype is characterized by adult-like gene expression patterns, action potentials exhibiting ventricular atrial and nodal properties, coordinated calcium cycling and beating, suggesting the formation of a functional syncytium. Pharmacological responses to pathological (endothelin-1), physiological (IGF-1), and autonomic (isoproterenol) stimuli similar to those characteristic of isolated adult cardiac myocytes are present in maturing hiPS-CMs. In addition, thyroid hormone treatment of hiPS-CMs attenuated the fetal gene expression in favor of a more adult-like pattern. Overall, hiPS-CMs progressively acquire functionality when maintained in culture for a prolonged period of time. The description of this evolving phenotype helps to identify optimal use of hiPS-CMs for a range of research applications.

Chronic inhibition of hypoxia-inducible factor prolyl 4-hydroxylase improves ventricular performance, remodeling, and vascularity after myocardial infarction in the rat.

BACKGROUND: Hypoxia inducible factors (HIFs) are transcription factors that are regulated by HIF-prolyl 4-hydroxylases (PHDs) in response to changes in oxygen tension. Once activated, HIFs play an important role in angiogenesis, erythropoiesis, proliferation, cell survival, inflammation, and energy metabolism. We hypothesized that GSK360A, a novel orally active HIF-PHD inhibitor, could facilitate local and systemic HIF-1 alpha signaling and protect the failing heart after myocardial infarction (MI). METHODS AND RESULTS: GSK360A is a potent (nanomolar) inhibitor of HIF-PHDs (PHD1>PHD2 = PHD3) capable of activating the HIF-1 alpha pathway in a variety of cell types including neonatal rat ventricular myocytes and H9C2 cells. Male rats treated orally with GSK360A (30 mg x kg x d) had a sustained elevation in circulating levels of erythropoietin and hemoglobin and increased hemoxygenase-1 expression in the heart and skeletal muscle. In a rat model of established heart failure with systolic dysfunction induced by ligation of left anterior descending coronary artery, chronic treatment with GSK360A for 28 days prevented the progressive reduction in ejection fraction, ventricular dilation, and increased lung weight, which were observed in the vehicle-treated animals, for up to 3 months. In addition, the microvascular density in the periinfarct region was increased (>2-fold) in GSK360A-treated animals. Treatment was well tolerated (survival was 89% in the GSK360A group vs. 82% in the placebo group). CONCLUSIONS: Chronic post-myocardial infarction treatment with a selective HIF PHD inhibitor (GSK360A) exerts systemic and local effects by stabilizing HIF-1 alpha signaling and improves long-term ventricular function, remodeling, and vascularity in a model of established ventricular dysfunction. These results suggest that HIF-PHD inhibitors may be suitable for the treatment of post-MI remodeling and heart failure.

Antithrombotic potential of GW813893: a novel, orally active, active-site directed factor Xa inhibitor.

BACKGROUND: Factor Xa (FXa) has been a target of considerable interest for drug development efforts aimed at suppressing thrombosis. In this report, a new orally active, small molecule, active-site directed FXa inhibitor, GW813893, has been profiled in a succession of in vitro and in vivo assays involved in its preclinical characterization as a potential antithrombotic therapeutic. METHODS: In vitro profiling of GW813893 consisted of assessing its inhibitory potential against FXa and a broad panel of related and unrelated enzymes and receptors. Additionally, the FXa inhibition potential of GW813893 was assessed in prothrombinase and plasma-based clotting assays. In vivo characterization of GW813893 consisted of thrombosis studies in a rat inferior vena cava model, a rat carotid artery thrombosis model, and a rabbit jugular thrombosis model. Bleeding studies were conducted in a rat tail transection model. Ex vivo determinations of compound effects on FX and clotting activity were also undertaken. RESULTS: GW813893 was more than 90-fold selective over all enzymes tested, and it inhibited FXa and prothrombinase activity with a Ki of 4.0 nM and 9.7 nM, respectively. In vivo, GW813893 concentration-dependently suppressed thrombotic activity in all models tested. The antithrombotic activity correlated with the suppression of plasma-based clotting activity and the inhibition of plasma FX activity (P < 0.02). Over the antithrombotic dose-range, an increased bleeding diathesis was not observed. CONCLUSION: These experiments demonstrate that GW813893 is a potent, selective, orally active inhibitor of FXa. The data suggest that GW813893 has robust antithrombotic potential at doses that have no detectable hemostasis liability. Collectively, the profile suggests that GW813893 has the preclinical pharmacology underpinnings of an oral antithrombotic therapeutic.

Cathepsin S expression is up-regulated following balloon angioplasty in the hypercholesterolemic rabbit.

OBJECTIVE: Neointimal development following balloon angioplasty involves many factors including smooth muscle cell (SMC) migration and proliferation and extracellular matrix (ECM) remodeling. Further, in hypercholesterolemic (HC) conditions, there is an influx of macrophage foam cells (FCs) into the restenotic lesion, which also involves degradation of the basement membrane and surrounding ECM. The ECM remodeling that occurs during restenosis has been shown to be mediated by various proteases. Here we have investigated the role of cathepsin S (CatS), a cysteine protease, in this process. METHODS AND RESULTS: We have demonstrated by Taqman quantitative PCR, Western blot, and immunohistochemistry that CatS is up-regulated in restenotic lesions of HC rabbits following balloon injury of the iliofemoral artery. CatS mRNA expression was elevated 28-fold in balloon-injured vessels relative to uninjured contralateral vessels in HC rabbits 8 weeks post-angioplasty (p<0.05). CatS protein expression was detected within 1 day post-injury, persisted throughout the entire time course evaluated (60 days post-injury), and was co-localized with SMCs, macrophages, and FCs. In contrast, cystatin C (CysC), the endogenous inhibitor of cathepsins, was only minimally up-regulated following injury. CysC mRNA expression was elevated 3.5-fold in balloon-injured vessels relative to uninjured contralateral vessels in HC rabbits 8 weeks post-angioplasty (p<0.005), and up-regulation of protein expression was not detected until days 28 and 60 post-injury. Additional biochemical studies using recombinant rabbit CatS revealed that rabbit CatS digests laminin, fibronectin, and type I collagen. Further, CatS expression was evaluated in SMCs that were induced to migrate through a matrix-coated Boyden chamber upon platelet-derived growth factor (PDGF) stimulation. The addition of a selective CatS inhibitor reduced SMC migration dose-dependently with an 80% reduction in migration at 30 nM (p<0.005). Additionally, we have shown that CatS protein expression by human macrophages was increased upon stimulation with oxidized low density lipoprotein (ox-LDL), implying augmentation of CatS production during foam cell formation. CONCLUSION: Taken together, our results indicate an enhanced expression of CatS during neointima formation and it is associated with invading SMCs, macrophages, and FCs, highlighting the importance of CatS in the pathogenesis of restenosis.

Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury.

Thymosin beta 4 (Tß4) was previously shown to reduce infarct size and improve contractile performance in chronic myocardial ischemic injury via two phases of action: an acute phase, just after injury, when Tß4 preserves ischemic myocardium via antiapoptotic or anti-inflammatory mechanisms; and a chronic phase, when Tß4 activates the growth of vascular or cardiac progenitor cells. In order to differentiate between the effects of Tß4 during the acute and during the chronic phases, and also in order to obtain detailed hemodynamic and biomarker data on the effects of Tß4 treatment suitable for use in clinical studies, we tested Tß4 in a rat model of chronic myocardial ischemia using two dosing regimens: short term dosing (Tß4 administered only during the first 3 days following injury), and long term dosing (Tß4 administered during the first 3 days following injury and also every third day until the end of the study). Tß4 administered throughout the study reduced infarct size and resulted in significant improvements in hemodynamic performance; however, chamber volumes and ejection fractions were not significantly improved. Tß4 administered only during the first 3 days following injury tended to reduce infarct size, chamber volumes and improve hemodynamic performance. Plasma biomarkers of myocyte injury were significantly reduced by Tß4 treatment during the acute injury period, and plasma ANP levels were significantly reduced in both dosing groups. Surprisingly, neither acute nor chronic Tß4 treatment significantly increased blood vessel density in peri-infarct regions. These results suggest the following: repeated dosing may be required to achieve clinically measureable improvements in cardiac function post-myocardial infarction (MI); improvement in cardiac function may be observed in the absence of a high degree of angiogenesis; and that plasma biomarkers of cardiac function and myocardial injury are sensitive pharmacodynamic biomarkers of the effects of Tß4.

Potent quinoxaline-based inhibitors of PDGF receptor tyrosine kinase activity. Part 1: SAR exploration and effective bioisosteric replacement of a phenyl substituent.

Novel substituted 2-anilino- and 2-cycloalkylaminoquinoxalines have been found to be useful and selective inhibitors of PDGF-R autophosphorylation. Replacement of an anilino-substituent with substituted cyclohexylamino- or norbornylamino substituents led to significant improvements in the pharmacokinetic profile of these analogues.

Potent quinoxaline-based inhibitors of PDGF receptor tyrosine kinase activity. Part 2: the synthesis and biological activities of RPR127963 an orally bioavailable inhibitor.

RPR127963 demonstrates an excellent pharmacokinetic profile in several species and was found to be efficacious in the prevention of restenosis in a Yucatan mini-pig model upon oral administration of 1-5 mg/kg. The in vitro selectivity profile and SAR of the highly optimized PDGF-R tyrosine kinase inhibitor are highlighted.

Stent-induced restenosis in the swine coronary artery is inhibited by a platelet-derived growth factor receptor tyrosine kinase inhibitor, TKI963.

Activities of vascular smooth muscle cells (SMCs) such as proliferation, migration, and matrix production contribute to restenosis following clinical interventions of angioplasty and stent placement. Because activation of platelet-derived growth factor (PDGF)-receptor tyrosine kinase (PDGFr-TK) influences these processes and promotes restenosis, TKI963, an inhibitor of the PDGFr-TK was discovered, and its efficacy was evaluated in blocking stent-induced restenosis as analyzed by intravascular ultrasound (IVUS). TKI963, a low-molecular-weight compound, inhibited the cell-free PDGFbetar-TK with a K(i) value of 56 +/- 14 nM. TKI963 also inhibited PDGF-dependent events in human aortic SMCs (e.g., in situ PDGFr autophosphorylation, mitogenesis, chemotaxis, and collagen production with median inhibitory concentration values of approximately 300 nM) without affecting the activity of a series of membrane receptor tyrosine kinases and intracellular serine/threonine kinases. In vivo, stent-induced restenosis in the swine coronary artery was reduced by oral administration of TKI963 (1.25, 2.5, and 5 mg/kg BID, for 28 days). Late lumen cross-sectional area (CSA) loss, plaque CSA growth, and plaque volume in the stent determined by IVUS were dose-relatedly decreased (33-62% at 1.25 mg/kg BID to 66-92% at 5 mg/kg BID, depending on the parameter) compared with controls. TKI963 treatment of