Current Medicinal Chemistry - Volume 20, Issue 30, 2013

Reactive oxygen species (ROS) are a group of highly reactive chemicals under tight control of intracellular antioxidants. The balance in oxidation-antioxidation is essential for maintaining normal cell functions, and any imbalance could lead to a wide range of diseases including cancer. The intracellular level of ROS is generally elevated in cancer cells, revealing a critical role of ROS in the process of carcinogenesis and cancer progression. Conversely, there is also evidence showing that ROS can act as cancer suppressors. This may be due to the varying antioxidant capacities of different cancers. These findings indicate a complex redox state in cancer cells. In this review we summarize the main features of ROS and their functions with respect to cancer initiation, hallmarks of cancer, and signaling in cancer cells. ROSelevating and ROS-depleting anticancer strategies and their mechanisms are thoroughly discussed. We argue that the rationale for therapy choice depends on a complete understanding of cancer cell redox state, namely, the “redox signaling signature” of cancer.

In the panorama of HIV protease inhibitors (HIV PIs), many efforts have been devoted to the development of new compounds with reduced peptidic nature in order to improve pharmacokinetics and pharmacodynamics features. The introduction of cyclic scaffolds in the design of new chemical entities reduces flexibility and affords more rigid inhibitors. Specifically, common dipeptide isosteres are replaced by a central cyclic scaffold designed to address the key interactions with catalytic aspartic acids and residues belonging to the flap region of the active site. The current interest in cyclic chemotypes addressing key interactions of HIV protease is motivated by the different nature of interactions formed with the enzyme, although maintaining key structural resemblance to a peptide substrate, hopefully giving rise to novel HIV-1 PIs displaying an improved profile towards multidrug resistant strains. This approach has been demonstrated for Tipranavir, which is a potent FDA approved HIV-1 PI representing the most famous example of heterocyclic aspartic protease inhibitors.

The aim of this review is to highlight the advances in the field of heme oxygenase-1 (HO-1) inhibitors over the past years, particularly from a medicinal chemistry point of view; progresses made in the field strongly helped to clarify physiological roles of the heme oxygenase (HO) system. HO is a family of ubiquitously expressed enzymes which regulate the regiospecific catabolism of heme leading to the formation of equimolar amounts of carbon monoxide (CO), ferrous iron (Fe++), and biliverdin. HO exists in two distinct, catalytically active isoforms: HO-1 and HO-2. HO-1 is an inducible 32-kDa protein, while HO-2 is a constitutively synthesized 36-kDa protein and generally is unresponsive to any of the inducers of HO-1. A third isoform, HO-3, is still an elusive protein. The HO system, along with its catabolism products, is involved in a variety of crucial physiological functions, including cytoprotection, inflammation, anti-oxidative effects, apoptosis, neuro-modulation, immune-modulation, angiogenesis, and vascular regulation. The use of selective HO inhibitors is a very important tool to clarify the role of the HO system and the mechanisms underlying its physiological effects and pathological involvement; due to the inducible nature of HO-1, selective inhibition of HO-1 isoform is generally preferable. Notably, HO-1 inhibitors may be also beneficial in therapeutic applications and have been mainly studied for treatment of hyperbilirubinemia and certain types of cancer. Historically, the first molecules used as non selective HO-1 inhibitors were metalloporphyrins (Mps). The subsequent development of the imidazole-dioxolane derivatives afforded the first generation of non-porphyrin based, isozyme selective HO-1 inhibitors.

Hepatitis C virus (HCV) infection is one of the main causes of liver disease worldwide. Its treatment is currently based on the combination of peg-interferon, ribavirin, and, for patients with genotype 1, a protease inhibitor (telaprevir or boceprevir). However, interferon-based combinations are not effective in all patients. Moreover, they are contraindicated in patients who cannot receive interferon (e.g. those with decompensated cirrhosis), and are frequently associated with adverse events. Consequently, there is a need to develop new drugs to treat HCV infection. This review focuses on preclinical and clinical data regarding sofosbuvir (GS-7977), a uridine nucleotide analogue inhibitor of HCV NS5 B polymerase that is effective against HCV genotypes 1,2, 3,4 and 6. Thanks to its excellent pharmacokinetic profile, sofosbuvir can be administered in an oral single daily dose. In vitro it exerts a potent antiviral effect against HCV. Clinical data show that combined with peg-interferon and ribavirin for 12 weeks it yields SVR of about 90% in subjects with HCV genotype 1 and about 100% in patients with HCV genotype 2 or 3. Moreover, sofosbuvir and ribavirin administered for 12 weeks yield similar high SVR rate (84% for genotype 1 and 100% for genotype 2/3 patients) as well as sofosbuvir and daclatasvir (an inhibitor of NS5A) which produce SVR rate of about 100% regardless of genotype or of ribavirin employment. Safety and tolerability of sofosbuvir appear to be excellent. In conclusion, sofosbuvir especially in interferon-free combinations represents a very promising option in the treatment of chronic hepatitis C.

Sulfur (S), as the second element in the main group 6A just below oxygen (O), has been often used as an isosteric replacement for O in enzymatic mechanistic studies. In addition, S has also been used as an isosteric replacement for CH2. These S-based mechanistic probes have been used in the studies with protein enzyme systems such as the sirtuin family of the protein Nε-acyl-lysine deacylases, phosphotransferases, and fatty acid desaturase, as well as various RNA enzymes (ribozymes). These probes are basically the O→S mutants of the corresponding O(or CH2)-containing substrates for the enzymatic reactions under study. This article will review the significant contributions that the S-based probes have been able to make toward an enhanced mechanistic understanding of different types of the enzyme-catalyzed reactions.

Polymyxins are polypeptide antibiotics, with a primary effect of membrane damaging due to their selective binding to the lipopolysaccharide of Gram-negative bacteria. Their nephro- and neurotoxic side effects limited their use, however, in the last decade the emergence of multidrug-resistant Gram-negative bacteria led to the reintroduction of polymyxins into clinical practice. This review provides an overview about the history and the latest developments of polymyxins. We describe the antimicrobial effects, pharmacodynamics, pharmacokinetics and different routes of administration. We highlight natural classic polymyxins, namely polymyxin B and E, the non-classic agents polymyxin M, S and T. Novel polymyxin chemical structure derivatives will be listed including NAB739, NAB740, NAB741 and NAB7061, that can have important therapeutical role in the future.

Diabetic nephropathy (DN) is a major complication of diabetes and the leading cause of end-stage renal disease (ESRD). Approximately, one third of diabetic patients develop diabetic nephropathy. As diabetes and its associated metabolic diseases are becoming epidemic, DN is emerging as a major health threat to humans. Currently, there are no effective therapeutic treatments for the disease. As a result, most DN cases progress to ESRD; patients with ESRD will need to undergo renal replacement through either dialysis or kidney transplantation. Therefore, developing new and effective means to control DN has been a major focus in the diabetes research. DN is a complex disease with pathological changes occurred in the glomerulus and renal tubules. It is, nonetheless, widely believed that the primary defects lie in the glomeruli, which lead to disrupting the integrity of the glomerular filtration barrier. While a variety of factors contribute to the impairment of glomerular filtration function, a large body of evidence demonstrates that damage in podocytes is the leading cause. Renal fibrosis plays critical roles in promoting DN progression. The primary mechanism responsible for renal fibrosis is abnormal activation of the transforming growth factor (TGF)-β pathway. Based on this understanding of DN pathogenesis, one strategy to control DN is to specifically protect podocytes from diabetes-induced injuries and to inhibit TGF-β signaling using gene therapy methodology. In this review, we will discuss the current research effort in developing gene therapy for DN.

Tuberculosis (TB), an ongoing public health threat, is worsened by the emergence of drug resistance. With an estimated 630000 cases per year of multidrug resistant (MDR)-TB, and 9% of those being extensively drug resistant (XDR)-TB, there is an urgent need for new and more effective anti-TB drugs. New TB treatment regimens should be able to shorten the duration of therapy that currently takes at least six months. The non-compliance with this long treatment duration is one of the reasons for the development of drug resistance. In spite of the difficulties and alleged lack of interest from the pharmaceutical industry for the discovery and development of new antibiotics, several new or repurposed drugs are being evaluated in clinical trials. This review article summarizes the information available and presents an update on the drugs currently in clinical trials for TB and briefly introduces some new compounds in pre-clinical development.

A methodology is described for the highly efficient and divergent synthesis of pseudosugars which allows the stereoselective introduction of polar groups at either the α or the β pseudoanomeric positions. Using this method, a series of 3-deoxycarbasugar analogues of mannose bearing a pyridyl group are rationally designed, prepared and tested for inhibition of Golgi α-mannosidase II.