Recent Patents on Cardiovascular Drug Discovery (Discontinued) - Volume 1, Issue 2, 2006

Tissue hypoxia occurs when local metabolism is disturbed by an imbalance between oxygen supply and consumption. This condition can lead to a variety of serious ischemic disorders, including a number of important cardiovascular diseases. In the search for therapeutic approaches, focused modalities which specifically target hypoxia have been particularly sought. These efforts would profit from the ability to utilize the mechanisms by which cells adjust to hypoxic conditions. At the center of the cellular response to hypoxia is hypoxia-inducible factor, HIF. This factor is composed of two subunits, an oxygen-sensitive HIF-α subunit and a constitutively expressed HIF-β subunit. Intracellular accumulation of HIF induces the coordinated expression of a number of adaptive genes against hypoxic insult. Because activation of HIF is a promising therapeutic modality for ischemic cardiovascular disease, recent studies have focused on the development of HIF stimulators. HIF levels are regulated by prolyl hydroxylation and asparaginyl hydroxylation of the HIF-α subunit. To date, a single HIF asparaginyl hydroxylase has been identified, factor inhibiting HIF (FIH), whereas the mammalian genome encodes three closely related proteins that have HIF prolyl hydroxylase activity, PHD1, PHD2 and PHD3. Recent patents have disclosed methods for identifying modulators of HIF or PHD as well as novel compounds with properties of HIF modulation or prolyl hydroxylase inhibition. This review highlights the identification of novel HIF stabilizers as specific molecularly targeted therapies against cardiovascular disease.

RNA interference (RNAi) in eukaryotes is a recently identified phenomenon in which small double stranded RNA molecules called short interfering RNA (siRNA) interact with messenger RNA (mRNA) containing homologous sequences in a sequence-specific manner. Ultimately, this interaction results in degradation of the target mRNA. Because of the high sequence specificity of the RNAi process, and the apparently ubiquitous expression of the endogenous protein components necessary for RNAi, there appears to be little limitation to the genes that can be targeted for silencing by RNAi. Thus, RNAi has enormous potential, both as a research tool and as a mode of therapy. Several recent patents have described advances in RNAi technology that are likely to lead to new treatments for cardiovascular disease. These patents have described methods for increased delivery of siRNA to cardiovascular target tissues, chemical modifications of siRNA that improve their pharmacokinetic characteristics, and expression vectors capable of expressing RNAi effectors in situ. Though RNAi has only recently been demonstrated to occur in mammalian tissues, work has advanced rapidly in the development of RNAi-based therapeutics. Recently, therapeutic silencing of apoliporotein B, the ligand for the low density lipoprotein receptor, has been demonstrated in adult mice by systemic administration of chemically modified siRNA. This demonstrates the potential for RNAi-based therapeutics, and suggests that the future for RNAi in the treatment of cardiovascular disease is bright.

Oxidative stress is a common denominator in many aspects of the pathogenesis of atherosclerosis and cardiovascular diseases. Some drugs, such as vitamin C, vitamin E, and a free radical scavenger, edaravone, are prescribed with oxidative stress as their main target. Furthermore, of the drugs in current clinical use, such as anti-hypertension reagents including angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARB), and antihyperlipidemic reagents like statins, protect various organs, e.g., vessel, brain, heart, and kidney, via anti-oxidative stress effects in addition to their original pharmacological properties. While results of clinical trials of anti-oxidative stress reagents in patients with cardiovascular disease are contradictory to date, this may be explained by a variety of reasons such as an inadequate study design. More competent anti-oxidative reagents are awaited, and superoxide dismutase mimetics, thiols, xanthine oxidase and NAD(P)H oxidase inhibitors, which regulate intracellular redox reaction and subsequently inhibit oxidative stress, are among promising candidates of future drug developments currently receiving much interest. In this review, the current advances will be highlighted in development of novel anti-oxidative therapeutic approaches against cardiovascular diseases.

In myocardial SPECT imaging with the popularly used 99mTc-sestamibi and 99mTc-tetrofosmin, intense liver uptake leads to a paradoxical decrease of counts in the absence of perfusion abnormalities, making it difficult to assess myocardial perfusion, particularly in the inferior or inferoapical left ventricular wall. 99mTc-N-DBODC5, which is a new lipophilic, mono-cationic nitride myocardial perfusion imaging agent, exhibits high myocardial uptake and excellent biodistribution kinetics with rapid liver clearance in rats and dogs. 99mTc-N-DBODC5 myocardial imaging during vasodilator stress can determine the severity of stenosis, though underestimates occur with mild coronary stenosis compared to 201Tl, in a similar way to what occurs with 99mTc-sestamibi and 99mTc-tetrofosmin. In particular, 99mTc-N-DBODC5's rapid liver clearance, which may significantly reduce the photon scatter from the liver, allows for the reduction of artifactual decreased myocardial perfusion and the improvement of the diagnostic accuracy of coronary artery disease.

In an ever-increasing population of patients with diabetes, morbidity and mortality due to the secondary complications require prompt identification of the underlying mechanisms. Aberration in the vascular endothelial cell function may be a key element in the development and progression of the chronic diabetic complications. We present the hypothesis that preservation and restoration of the endothelial cell function may potentially be the most efficient means of targeting the adverse effects of hyperglycemia.

Vasopressin receptor antagonists are a new class of drugs that address the problems of fluid retention, hyponatremia, and renal dysfunction in heart failure. Elevated vasopressin levels in heart failure cause myocardial fibrosis, hypertrophy and vasoconstriction by activating the V1a receptors, as well as water retention and hyponatremia by activating V2 receptors. Antagonism of V1a receptors alone is of little benefit. In contrast, antagonism of V2 receptors results in increased free water excretion and increased sodium concentration. Vasopressin receptor antagonists may be viewed as the first new class of agents with predominantly aquaretic effects, in contrast to the natriuretic effects of loop diuretics. The predominant action of vasopressin receptor antagonists is water excretion, without depletion of other electrolytes, and less neurohormonal stimulation compared with loop diuretics. Classified as neurohormonal antagonists, vasopressin receptor antagonists acutely may improve congestion and hyponatremia, while chronically preventing progression of left ventricular dysfunction. Several compounds have been evaluated in late-stage clinical trial programs, and at least one may be used as an adjunct to standard medical therapy, combining aquaresis for congestion with neurohormonal antagonism for morbidity and mortality. We reviewed recent patents dealing with heart failure, hyponatremia, anti-diuretic hormone, and vasopressin antagonists.

Heart failure is characterised by decreased cardiac output, which results in the development of both peripheral hypoperfusion and pulmonary congestion and can lead to the development of acute pulmonary edema. The primary objective in treating a patient with decompensated heart failure is hemodynamic stabilization, which is usually achieved by inotropic support. Classic inotropic agents provide short-term hemodynamic improvement, but their use has been correlated with poor prognosis. Levosimendan, a new calcium sensitizer, offers hemodynamic and symptomatic improvement without increasing cAMP and intracellular calcium concentrations. This agent improves contractility without increasing the risk of cardiac events such as arrhythmias. By combining a positive inotropic action mediated via calcium sensitization and a vasodilatory effect via ATP-dependent potassium channels, it appears to be superior than classic positive inotropic agents. Furthermore, it seems to have prolonged benefit in heart failure patients, and it also has antiinflammatory and antiapoptotic properties. In conclusion, levosimendan seems to be a particularly promising agent for the treatment of decompensated heart failure, as in addition to improving cardiac output, it has a more favorable side-effect profile than classic inotropic agents, and it affects multiple pathways with key role in the pathophysiology of heart failure.

Cardiovascular disease (CVD) is the most critical global health threat, which contributes more than one third of global morbidity. CVD includes heart disease, vascular disease, atherosclerosis, stroke and hypertension. The most important independent risk factors for CVD include dyslipidemia along with hypertension, obesity, sedentary lifestyle, diabetes and chronic inflammation. These factors are directly regulated by diet, metabolism and physical activity. Diets rich in fat and carbohydrate coupled to sedentary lifestyles have contributed to the increase in dyslipidemia, type 2 diabetes, obesity and CVD in the world. Discovery of Peroxisome Proliferator Activated Receptors (PPARs) as a key regulator of metabolic pathways has led to significant insight into the mechanisms regulating these processes. Three PPAR subtypes, encoded by distinct genes, are designated as PPAR-α, PPAR-δ (also know as β) and PPAR-γ. PPARs act as nutritional sensors that regulate a variety of homeostatic functions including metabolism, inflammation and development. PPAR-α is the main metabolic regulator for catabolism whereas PPAR-γ regulates anabolism or storage. PPARs are expressed in the cardiovascular system such as endothelial cells, vascular smooth muscle cells and monocytes /macrophages. It has been shown that they play an important role in the modulation of inflammatory, fibrotic and hypertrophic responses. In 1997, a Glaxo patent described that Troglitazone (first PPAR-g ligand to reach market) reduced TNF-induced VCAM1 expression in HUVECs indicating the potential benefit in atherosclerosis. A series of patents from Eli Lilly and Dr. Reddy's Laboratories Ltd. between 1999 and 2005 described a variety of PPAR-α and -α,γ dual ligands in a number of patents having glucose, triglyceride, cholesterol lowering, HDL elevating and body weight reducing activity. Patents from Metabolex and Tularik in 2001 and 2002 described the beneficial effects of SPPARM molecules for insulin resistance and diabetes, without showing concern on PPAR-g related side effects such as edema and body weight. GSK and Takeda described the potential effects of PPAR- δ modulators during 2001 to 2004 in few patents. Several clinical and preclinical studies have demonstrated the beneficial effects of PPAR ligands on various cardiovascular risk factors. This review intends to capture some of the key studies in this area as is described in some recent patents and literature.

Maintenance of endothelial cells (ECs), the building blocks of the vascular tree, is a presumed function of fibroblast growth factors (FGFs). In particular, the two prototypic members of FGF family, namely FGF1 and FGF2, due to their potent mitogenic and pro-migratory activities, have the ability to induce metabolic and phenotypic changes in ECs that are required to stimulate angiogenesis. In addition to FGF1 and FGF2, 23 other members of the FGF family have since been identified and characterized and they are reviewed in relation to their disease pathology. Particular emphasis is given to the biology of the FGFs and FGFRs on how they mediate the onset of angiogenesis. The focus of the present review is to survey what is known about the role of the currently identified FGFs and their four high affinity tyrosine kinase receptors in diseases and the angiogenesis-targeted drugs currently in clinical trials. Some new and promising patented drugs that target the angiogenic pathway are discussed. Examination of the currently patented drugs may identify more potent and specific regulators of FGF/FGFR signaling system for treatment of tumor angiogenesis in clinical settings. Additionally, novel drug development strategies are highlighted and reviewed.