Current Medicinal Chemistry - Volume 22, Issue 24, 2015

Among the class of nonsteroidal anti-inflammatory drugs (NSAIDs), COX-2 inhibitors or “coxibs” selectively inhibit the activity of the inducible isoform of cyclooxygenase. Moreover, there is emerging evidence that the sulfonamide-type coxibs, but not the methylsulfones, display an inhibitory activity also against several isoforms of human carbonic anhydrase (CA, EC 4.2.1.1). In this regard, celecoxib and valdecoxib, possessing a primary sulfonamide that binds to the zinc ion at the active site of the enzyme, are nanomolar inhibitors of the cancer-related hCA IX isoform. Also meloxicam and lornoxicam, NSAIDs belonging to the class of “oxicams”, that contain a cyclic tertiary sulfonamide moiety, inhibit this isoform at low micromolar concentrations. The multiple pharmacological effects of the sulfonamide anti-inflammatory agents could be ascribed to the dual inhibition of CA and COX enzymes, supporting the evidence that inflammation and hypoxia pathways are involved in cancer onset and progression and suggesting that the antitumoral activity of these compounds should be further explored for their possible use in the polypharmacology of cancer prevention and therapy.

Heterocyclic N-oxides have emerged as potent compounds with anticancer, antibacterial, antihypertensive, antiparasitic, anti-HIV, anti-inflammatory, herbicidal, neuroprotective, and procognitive activities. The N-oxide motif has been successfully employed in a number of recent drug development projects. This review surveys the emergence of this scaffold in the mainstream medicinal chemistry with a focus on the discovery of the heterocyclic N-oxide drugs, N-oxide-specific mechanisms of action, drug-receptor interactions and synthetic avenues to these compounds. As the first review on this subject that covers the developments since 1950s to date, it is expected that it will inspire wider implementation of the heterocyclic N-oxide motif in the rational design of new medicinal agents.

Diabetic Nephropathy (DN) is believed to be a major microvascular complication of diabetes. The hallmark of DN includes deposition of Extracellular Matrix (ECM) proteins, such as, collagen, laminin and fibronectin in the mesangium and renal tubulo-interstitium of the glomerulus and basement membranes. Such an increased expression of ECM leads to glomerular and tubular basement membranes thickening and increase of mesangial matrix, ultimately resulting in glomerulosclerosis and tubulointerstitial fibrosis. The characteristic morphologic glomerular mesangial lesion has been described as Kimmelstiel–Wilson nodule, and the process at times is referred to as diabetic nodular glomerulosclerosis. Thus, the accumulation of ECM proteins plays a critical role in the development of DN. The relevant mechanism(s) involved in the increased ECM expression and their regulation in the kidney in diabetic state has been extensively investigated and documented in the literature. Nevertheless, there are certain other mechanisms that may yet be conclusively defined. Recent studies demonstrated that some of the new signaling pathways or molecules including, Notch, Wnt, mTOR, TLRs and small GTPase may play a pivotal role in the modulation of ECM regulation and expression in DN. Such modulation could be operational for instance Notch through Notch1/Jagged1 signaling, Wnt by Wnt/β- catenin pathway and mTOR via PI3-K/Akt/mTOR signaling pathways. All these pathways may be critical in the modulation of ECM expression and tubulo-interstitial fibrosis. In addition, TLRs, mainly the TLR2 and TLR4, by TLR2- dependent and TGF-β-dependent conduits, may modulate ECM expression and generate a fibrogenic response. Small GTPase like Rho, Ras and Rab family by targeting relevant genes may also influence the accumulation of ECM proteins and renal fibrosis in hyperglycemic states. This review summarizes the recent information about the role and mechanisms by which these molecules and signaling pathways regulate ECM synthesis and its expression in high glucose ambience in vitro and in vivo states. The understanding of such signaling pathways and the molecules that influence expression, secretion and amassing of ECM may aid in developing strategies for the amelioration of diabetic nephropathy.

Asymmetric dimethylarginine (ADMA) is a competitive endogenous inhibitor of nitric oxide synthase with a key role in the pathophysiology of endothelial dysfunction, in the progression of atherosclerosis and in cardiovascular diseases. Statins, renin-angiotensin-aldosterone system inhibitors, blood glucose lowering agents, insulin sensitizers, beta-blockers, estrogen replacement therapy, antioxidants, complex B vitamins, L-arginine and acetylsalicylic acid have been evaluated for their ability to reduce ADMA levels or inhibit its actions. Despite the major beneficial effects of these agents in cardiovascular disease, research has shown that their favorable actions are only partially mediated by reducing ADMA levels or by bypassing its effect in nitric oxide synthesis. Novel therapeutic approaches targeting selectively ADMA are encouraging, but have only been tested in vitro or in animal studies and further research is needed in order to conclude on how therapeutic strategies modulating ADMA actions can affect atherosclerosis progression and cardiovascular diseases.

Schizophrenia is a complex neuropsychiatric disorder with limited treatment options and highly debilitating symptoms, leading to poor personal, social, and occupational outcomes for an afflicted individual. Our current understanding of schizophrenia suggests that dopaminergic and glutamatergic systems have a significant role in the pathogenesis of the disease. Kynurenic acid, an endogenous glutamate antagonist, is found in elevated concentrations in the prefrontal cortex and cerebrospinal fluid of patients with schizophrenia, and this affects neurotransmitter release in a similar manner to previously observed psychotomimetic agents, such as phencyclidine, underlining the molecular basis to its link in schizophrenia pathophysiology. Kynurenic acid is a breakdown product of tryptophan degradation, through a transamination process mediated by kynurenine aminotransferase (KAT) enzymes. There are four KAT homologues reported, all of which are pyridoxal 5’- phosphate-dependent enzymes. All four KAT isoforms have been analysed structurally and biochemically, however the most extensive research is on KAT-I and KAT-II. These two enzymes have been targeted in structure-based drug design as a means of normalising raised kynurenic acid levels. The most potent KAT-I inhibitors and KAT-II inhibitors include phenylhydrazone hexanoic acid derivatives and a pyrazole series of compounds, respectively. KAT inhibitors have been shown to be effective in reducing kynurenic acid production, with accompanying changes in neurotransmitter release and pro-cognitive effects seen in animal studies. This review will discuss the characteristics pertaining to the different KAT isoforms, and will highlight the development of significant KAT inhibitors. KAT inhibitors have great potential for therapeutic application and represent a novel way in treating schizophrenia.