Resistance analysis and characterization of a thiazole analogue, BP008, as a potent hepatitis C virus NS5A inhibitor

Novel xylenyl-spaced bis-thiazoles/thiazines: synthesis, biological profile as herpes simplex virus type 1 inhibitors and in silico simulations

Aims: Development of some potent bis-thiazole and bis-thiazine derivatives that could be used as antiviral prototypes. Materials & methods: Xylenyl-spaced bis-carbazone scaffold 3 was used as a versatile building block for bis-thiazole derivatives 6a-e and 9a-d and bis-thiazine derivatives 12a-f. These bis-heterocycles were screened as herpes simplex virus type 1 (HSV-1) inhibitors. Results: The new bis-heterocyclic compounds showed remarkable antiviral activity (e.g., compound 6d cytotoxicity concentration CC50 >500 μg/ml). The antiviral capacity of the synthesized bis-compounds was supported by a molecular docking study against the glycoprotein D receptor of HSV-1. Compounds 6b, 9b, and 12c displayed the best binding coefficients. Conclusion: A new series of xylenyl-spaced bis-carbazone scaffolds were used as a building scaffold to construct a host of bis-thiazole/thiazine derivatives that could be used as antiviral prototypes.

Thiazole: A Versatile Standalone Moiety Contributing to the Development of Various Drugs and Biologically Active Agents

For many decades, the thiazole moiety has been an important heterocycle in the world of chemistry. The thiazole ring consists of sulfur and nitrogen in such a fashion that the pi (π) electrons are free to move from one bond to other bonds rendering aromatic ring properties. On account of its aromaticity, the ring has many reactive positions where donor–acceptor, nucleophilic, oxidation reactions, etc., may take place. Molecules containing a thiazole ring, when entering physiological systems, behave unpredictably and reset the system differently. These molecules may activate/stop the biochemical pathways and enzymes or stimulate/block the receptors in the biological systems. Therefore, medicinal chemists have been focusing their efforts on thiazole-bearing compounds in order to develop novel therapeutic agents for a variety of pathological conditions. This review attempts to inform the readers on three major classes of thiazole-bearing molecules: Thiazoles as treatment drugs, thiazoles in clinical trials, and thiazoles in preclinical and developmental stages. A compilation of preclinical and developmental thiazole-bearing molecules is presented, focusing on their brief synthetic description and preclinical studies relating to structure-based activity analysis. The authors expect that the current review may succeed in drawing the attention of medicinal chemists to finding new leads, which may later be translated into new drugs.

High throughput screening identifies inhibitors for parvovirus B19 infection of human erythroid progenitor cells

Parvovirus B19 (B19V) infection can cause hematological disorders and fetal hydrops during pregnancy. Currently, no antivirals or vaccines are available for the treatment or the prevention of B19V infection. To identify novel small-molecule antivirals against B19V replication, we developed a high throughput screening assay, which is based on an in vitro nicking assay using recombinant N-terminal 1-176 amino acids of the viral large nonstructural protein (NS1N) and a fluorescently labeled DNA probe (OriQ) that spans the nicking site of the viral DNA replication origin. We collectively screened 17,040 compounds and identified 2,178 (12.78%) hits that possess >10% inhibition of the NS1 nicking activity, among which 84 hits were confirmed to inhibit nicking in a dose-dependent manner. Using ex vivo expanded primary human erythroid progenitor cells (EPCs) infected by B19V, we validated 24 compounds demonstrated >50% in vivo inhibition of B19V infection at 10 μM, which can be categorized into 7 structure scaffolds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, the top 4 compounds were chosen to examine their inhibitions of B19V infection in EPCs at two times of the 90% maximal effective concentration (EC₉₀). A purine derivative (P7), demonstrated an antiviral effect (EC₅₀=1.46 μM) without prominent cytotoxicity (CC₅₀=71.8 μM) in EPCs, exhibited 92% inhibition of B19V infection in EPCs at 3.32 μM, which can be used as the lead compound in future studies for the treatment of B19V infection caused hematological disorders. Importance B19V encodes a large non-structural protein NS1. Its N-terminal domain (NS1N) consisting of 1-176 amino acids binds to viral DNA and serves as an endonuclease to nick the viral DNA replication origins, which is a pivotal step in rolling hairpin-dependent B19V DNA replication. For high throughput screening (HTS) of anti-B19V antivirals, we miniaturized a fluorescence-based in vitro nicking assay, which employs a fluorophore-labeled probe spanning the trs and the NS1N protein, into a 384-well plate format. The HTS assay showed a high reliability and capability in screening 17,040 compounds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, a purine derivative demonstrated an antiviral effect of 92% inhibition of B19V infection in EPCs at 3.32 μM (two times EC₉₀). Our study demonstrated a robust HTS assay for screening antivirals against B19V infection.

A Potent, Selective, and Orally Bioavailable HCV NS5A Inhibitor for Treatment of Hepatitis C Virus: (S)-1-((R)-2-(Cyclopropanecarboxamido)-2-phenylacetyl)-N-(4-phenylthiazol-2-yl)pyrrolidine-2-carboxamide

Starting from the initial lead 4-phenylthiazole 18, a modest HCV inhibitor (EC₅₀ = 9440 nM), a series of structurally related thiazole derivatives has been identified as a novel chemical class of potent and selective HCV NS5A inhibitors. The introduction of a carboxamide group between the thiazole and pyrrolidine ring (42) of compound 18 resulted in a dramatic increase in activity (EC₅₀ = 0.92 nM). However, 42 showed only moderate pharmacokinetic properties and limited oral bioavalability of 18.7% in rats. Further optimization of the substituents at the 4-position of the thiazole ring and pyrrolidine nitrogen of the lead compound 42 led to the identification of compound 57, a highly potent and selective NS5A inhibitor of HCV (EC₅₀ = 4.6 nM), with greater therapeutic index (CC₅₀/EC₅₀ > 10000). Pharmacokinetic studies revealed that compound 57 had a superior oral exposure and desired bioavailability of 45% after oral administration in rats.

Synthesis and antiviral activity of some new bis-1,3-thiazole derivatives

Treatment of 3-phenyl-1,3-thiazolidin-4-one derivative 1 with phenylisothiocyanate in DMF, in the presence of potassium hydroxide, at room temperature gave the non-isolable potassium salt 2. The in-situ reaction of 2 with differently substituted N-aryl hydrazonoyl chlorides 3, 7a-d and 14a-d afforded the corresponding 2-(pyrazolyl)thiazolylimino-5-(thiadiazolylidene)thiazolidin-4-one derivatives 6, 10a-d and 17a-d, respectively. Reaction of 2 with further α-haloketones yielded the 4-(pyrazolyl)thiazolylimino-bis-thiazolidine derivatives 22, 25 and 26. Single crystal X-ray analysis was used in structure elucidation of the products. The in-vitro antiviral screening against four viruses (Poliovirus, Influenza A (H1N1) virus, Hepatitis B virus and Hepatitis C virus) for the obtained compounds was examined. Structure activity relationship (SAR) was also studied. The goal of the work was achieved in discovering a very active compound 10a as anti HCV agent (EC50 0.56 μM).

In vitro activity and resistance profile of samatasvir, a novel NS5A replication inhibitor of hepatitis C virus

The hepatitis C virus (HCV) nonstructural 5A (NS5A) protein is a clinically validated target for drugs designed to treat chronic HCV infection. This study evaluated the in vitro activity, selectivity, and resistance profile of a novel anti-HCV compound, samatasvir (IDX719), alone and in combination with other antiviral agents. Samatasvir was effective and selective against infectious HCV and replicons, with 50% effective concentrations (EC50s) falling within a tight range of 2 to 24 pM in genotype 1 through 5 replicons and with a 10-fold EC50 shift in the presence of 40% human serum in the genotype 1b replicon. The EC90/EC50 ratio was low (2.6). A 50% cytotoxic concentration (CC50) of >100 μM provided a selectivity index of >5 × 10(7). Resistance selection experiments (with genotype 1a replicons) and testing against replicons bearing site-directed mutations (with genotype 1a and 1b replicons) identified NS5A amino acids 28, 30, 31, 32, and 93 as potential resistance loci, suggesting that samatasvir affects NS5A function. Samatasvir demonstrated an overall additive effect when combined with interferon alfa (IFN-α), ribavirin, representative HCV protease, and nonnucleoside polymerase inhibitors or the nucleotide prodrug IDX184. Samatasvir retained full activity in the presence of HIV and hepatitis B virus (HBV) antivirals and was not cross-resistant with HCV protease, nucleotide, and nonnucleoside polymerase inhibitor classes. Thus, samatasvir is a selective low-picomolar inhibitor of HCV replication in vitro and is a promising candidate for future combination therapies with other direct-acting antiviral drugs in HCV-infected patients.

Future therapies for chronic hepatitis C

Therapy for hepatitis C has been fairly stagnant for the past decade, but the past few years have seen major progress and evolution, beginning with the approval of two HCV protease inhibitors in 2011. In spite of considerable improvements in response rates with these agents, a need for additional agents with improved potency and tolerability remains. Toward this goal and over the course of just a few months, the HCV therapy pipeline has already become crowded with direct-acting antivirals, host-targeted agents and unique interferons, all of which are positioned to be part of the next wave of therapeutic options. The ultimate goal of this push for new agents is to achieve a safe and straight forward yet highly effective therapy for hepatitis C that is widely embraced and readily available. Particularly among the 'baby boomer' population, it is predicted that over the next few years, more patients with currently quiescent infections will be newly diagnosed, and those currently diagnosed will be at increased risk of long-term complications of infection, and thus in need of treatment. A simple and safe treatment paradigm will become a necessity. This Review chronicles the latest developments in hepatitis C therapy and the potential effect these new treatments could have on delivery of care to patients infected with HCV.

Resistance studies of a dithiazol analogue, DBPR110, as a potential hepatitis C virus NS5A inhibitor in replicon systems

Hepatitis C virus (HCV), a member of the Flaviviridae family, affects approximately 3% of the world's population and is becoming the leading cause of liver disease in the world. Therefore, the development of novel or more effective treatment strategies to treat chronic HCV infection is urgently needed. In our previous study, we identified a potential HCV NS5A inhibitor, BP008. After further systemic optimization, we discovered a more potent HCV inhibitor, DBPR110. DBPR110 reduced the reporter expression of the HCV1b replicon with a 50% effective concentration (EC(50)) and a selective index value of 3.9 ± 0.9 pM and >12,800,000, respectively. DBPR110 reduced HCV2a replicon activity with an EC(50) and a selective index value of 228.8 ± 98.4 pM and >173,130, respectively. Sequencing analyses of several individual clones derived from the DBPR110-resistant RNAs purified from cells harboring genotype 1b and 2a HCV replicons revealed that amino acid substitutions mainly within the N-terminal region (domain I) of NS5A were associated with decreased inhibitor susceptibility. P58L/T and Y93H/N in genotype 1b and T24A, P58L, and Y93H in the genotype 2a replicon were the key substitutions for resistance selection. In the 1b replicon, V153M, M202L, and M265V play a compensatory role in replication and drug resistance. Moreover, DBPR110 displayed synergistic effects with alpha interferon (IFN-α), an NS3 protease inhibitor, and an NS5B polymerase inhibitor. In summary, our results present an effective small-molecule inhibitor, DBPR110, that potentially targets HCV NS5A. DBPR110 could be part of a more effective therapeutic strategy for HCV in the future.

Small molecule inhibitors of the hepatitis C virus-encoded NS5A protein

Hepatitis C virus (HCV) is a modern-day pandemic; 2-3% of the world's population are thought to be infected with the virus and are subsequently at risk of developing end-stage liver diseases. The traditional standard of care (SOC) for HCV-infected patients has been limited to a regimen of pegylated-interferon alpha (pegIFN) and ribavirin; displaying low cure rates in a majority of patients and severe side effects. However, in 2011 the first direct-acting antivirals (DAA) were licensed to treat HCV-infected patients in combination with SOC, which served to elevate treatment response rates. The HCV drug development pipeline is currently populated with many additional and improved DAAs; primarily molecules that target the virus-encoded protease or polymerase enzymes. These molecules are being evaluated both in combination with the traditional SOC and together with other DAAs as all-oral pegIFN-free regimens with the ultimate goal of developing multiple DAA-containing HCV therapies that do not rely on an pegIFN backbone. A recent addition to the arsenal of HCV inhibitors in development is represented by an entirely new DAA class; molecules that target the HCV-encoded non-enzymatic NS5A protein. NS5A is essential for HCV propagation and, although its actual functions are largely unknown, it is likely a key regulator of viral genome replication and virion assembly. The protein is exquisitely sensitive to small molecule-mediated inhibition; NS5A-targeting molecules are probably the most potent antiviral molecules ever discovered and exhibit a number of other attractive drug-like properties, including activity against many HCV genotypes/subtypes and once-daily dosing potential. Although their mechanism of action is unclear, NS5A-targeting molecules are already proving their utility in clinical evaluation; particularly as components of pegIFN-sparring DAA combination regimens. This review will aim to amalgamate our current understanding and knowledge of NS5A-targeting molecules; their discovery, properties, applications, and insight into their future impact as components of all-oral pegIFN-free DAA combination therapies to combat HCV infection.