Novel hepatitis C virus protease inhibitors: thiazolidine derivatives

Design, Synthesis, Computational Investigations, and Antitumor Evaluation of N-Rhodanine Glycosides Derivatives as Potent DNA Intercalation and Topo II Inhibition against Cancer Cells

Nitrogen and sulfur glycosylation was carried out via the reaction of rhodanine (1) with α-acetobromoglucose 3 under basic conditions. Deacetylation of the protected nitrogen nucleoside 4 was performed with CH₃ONa in CH₃OH without cleavage of the rhodanine ring to afford the deprotected nitrogen nucleoside 6. Further, deacetylation of the protected sulfur nucleoside 5 was performed with CH₃ONa in CH₃OH with the cleavage of the rhodanine ring to give the hydrolysis product 7. The protected nitrogen nucleosides 11a-f were produced by condensing the protected nitrogen nucleoside 4 with the aromatic aldehydes 10a-f in C₂H₅OH while using morpholine as a secondary amine catalyst. Deacetylation of the protected nitrogen nucleosides 11a-f was performed with NaOCH₃/CH₃OH without cleavage of the rhodanine ring to afford the deprotected nitrogen nucleosides 12a-f. NMR spectroscopy was used to designate the anomers' configurations. To examine the electrical and geometric properties derived from the stable structure of the examined compounds, molecular modeling and DFT calculations using the B3LYP/6-31+G (d,p) level were carried out. The quantum chemical descriptors and experimental findings showed a strong connection. The IC₅₀ values for most compounds were very encouraging when evaluated against MCF-7, HepG2, and A549 cancer cells. Interestingly, IC₅₀ values for 11a, 12b, and 12f were much lower than those for Doxorubicin (7.67, 8.28, 6.62 μM): (3.7, 8.2, 9.8 μM), (3.1, 13.7, 21.8 μM), and (7.17, 2.2, 4.5 μM), respectively. Against Topo II inhibition and DNA intercalation, when compared to Dox (IC₅₀ = 9.65 and 31.27 μM), compound 12f showed IC₅₀ values of 7.3 and 18.2 μM, respectively. In addition, compound 12f induced a 65.6-fold increase in the rate of apoptotic cell death in HepG2 cells, with the cell cycle being arrested in the G2/M phase as a result. Additionally, it upregulated the apoptosis-mediated genes of P53, Bax, and caspase-3,8,9 by 9.53, 8.9, 4.16, 1.13, and 8.4-fold change, while it downregulated the Bcl-2 expression by 0.13-fold. Therefore, glucosylated Rhodanines may be useful as potential therapeutic candidates against cancer because of their topoisomerase II and DNA intercalation activity.

New N-ribosides and N-mannosides of rhodanine derivatives with anticancer activity on leukemia cell line: Design, synthesis, DFT and molecular modelling studies

N-ribosylation and N-mannosylation compounds have a great role in compounds activity as anticancer. The reaction of 2-thioxo-4-thiazolidinone (rhodanine) derivatives, as aglycon part, was done with ribofuranose and mannopyranose sugars (glycone part) followed by deacetylation without cleavage of the rhodanine under acidic medium. Conformational analysis has been studied using NMR methods (2D, DQF-COSY, HMQC and HMBC). All final the new deprotected nucleosides were screened against leukemia 1210, and were found to be considerably less potent (Ic50% 1.4-10.6 μM) than doxorubicin (Ic50% 0.02 μM). Compounds 10d and 10e which contain ribose moiety have better activity than those with mannose sugar. DFT calculations with B3LYP/6-31 + G (d) level were used to analyze the electronic and geometric characteristics deduced from the stable structure of the compounds. The principal quantum chemical descriptors showed a good correlation with the experimental observations. Rapid Overlay Comparison Similarity (ROCS) study was operated to explain the compounds similarity and to figure out the most important pharmacophoric features.

Synthesis, in-Vitro Cytotoxicity and Antimicrobial Evaluations of Some Novel Thiazole Based Heterocycles

Condensation of rhodanine (1) with pyrazol-3(2H)-one derivatives (2a-f) gave 5-substituted-2-thioxo-1,3-thiazolidin-4-one derivatives (3a-f). Reaction of compound (1) with 2-arylmethylidene-malononitrile (4a-d) yielded the unexpected derivatives (5a-d). The latter compounds were subjected to cyclization reactions with malononitrile under different basic conditions, hydroxylamine hydrochloride and/or thiourea to furnish the fused thiazole derivatives (6a-d) and (8-10a-d). Coupling of (1) with diazotized aromatic amines (11a-c) in pyridine afforded the arylhydrazones (12a-c). Fusion of latter compounds with malononitrile afforded the thiazolopyridazine derivatives (13a-c). The structures of the newly synthesized compounds were elucidated via spectral data and elemental analyses. The in-vitro cytotoxic activity of compounds (3a-f) against the cell line MCF-7 was evaluated. Also, the synthesized products were investigated for their antibacterial and antifungal activities against six standard organisms including the G⁺ bacteria, Staphylococcus aureus and Bacillus subtilis, G^- bacteria, Escherichia coli and Proteus vulgaris in addition to fungi, Candida albicans and Aspergillus flavus.

Green Synthesis, Biological Activity Evaluation, and Molecular Docking Studies of Aryl Alkylidene 2, 4-thiazolidinedione and Rhodanine Derivatives as Antimicrobial Agents

AIMS AND OBJECTIVE

The magic scaffolds rhodanine and thiazolidine are very important heterocyclic compounds in drug design and discovery. Those are important heterocyclic compounds that have attracted a great deal of attention due to the fact that they exhibit a variety of bioactivities including antibacterial, antifungal, antiviral, antimalarial, and anti-inflammatory activities. These agents often exhibit selective toxicity. The goal of this study was molecular docking, green and solvent-free efficient synthesis of a new series of hetero/aromatic substituted rhodanine and thiazolidine analogues and then investigation of their antimicrobial activity.

MATERIALS AND METHODS

To a mixture of TZD or rhodanine (1 mmol) in the presence of ionic liquid ChCl/urea, various aldehyde (1 mmol) was added. After completion of the reaction, obtained crude compound was collected by filtration and products were recrystallized from ethanol. The binding-free energy between all synthesized compounds with 3EEJ protein (C. glabrata enzyme) were obtained by molecular docking studies. These compounds were evaluated using microdilution method against (ATCC 6538) and (ATCC 12228) Gram-negative, (ATCC 8739) and (ATCC 9027) as Gram-positive and (ATCC 1012), (ATCC 339), C. (ATCC 1057), (ATCC 503), (ATCC 340) and (ATCC 194) as fungi.

RESULTS

All of the acceptable products were determined by 1H NMR, 13C NMR, Mas and FT-IR spectroscopy. The binding-free energy between compounds 10a and 10b with 3EEJ protein were found to be -8.08 kcal/mol and -8.15 kcal/mol, respectively. These compounds having a heteroaromatic ring attached to the TZD or rhodanine core showed excellent antimicrobial activity with MIC values of 0.25-8 μg/mL (compound 10a) and 0.5-16 μg/mL (compound 10b) against the most tested fungi strains, Gram-positive and Gram-negative bacteria.

CONCLUSION

A convenient and rapid method has been developed for the synthesis of rhodanine and thiazolidine-2,4-dione (TZD) derivatives as efficient antimicrobial agents using a Deep Eutectic Ionic Liquids (DEILs) choline chloride urea under solvent-free condition. Among the newly synthesized compounds, (Z)-5-((quinoxalin-3-yl) methylene) thiazolidine-2, 4-dione (10a) and (Z)- 5- ((quinoxalin-3-yl) methylene)-2-thioxothiazolidin-one (10b) exerted the promising effect and these compounds can be considered to be further probed as inhibitors of cgDHFR enzyme.

Organic Reactions in Ionic Liquids: Ionic Liquid-accelerated Facile Synthesis of 3-alkyl-2,4-thiazolidinediones

The room temperature ionic liquid [bmim]PF6 is a new green solvent for the N-alkylation of 2,4-thiazolidinones. Significant rate enhancement and improved yields have been observed.

Novel Rhodanine Derivative, 5-[4-(4-Fluorophenoxy) phenyl]methylene-3-{4-[3-(4-methylpiperazin-1-yl) propoxy]phenyl}-2-thioxo-4-thiazolidinone dihydrochloride, Induces Apoptosis via Mitochondria Dysfunction and Endoplasmic Reticulum Stress in Human Colon Cancer Cells

We previously reported that 5-[4-(4-fluorophenoxy) phenyl] methylene-3-{4-[3-(4-methylpiperazin-1-yl)propoxy]phenyl}-2-thioxo-4-thiazolidinone dihydrochloride (KSK05104) has potent, selective and metabolically stable IKKβ inhibitory activities. However, the apoptosis-inducing of KSK05104 and its underlying mechanism have not yet been elucidated in human colon cancer cells. We show that KSK05104 triggered apoptosis, as indicated by externalization of Annexin V-targeted phosphatidylserine residues in HT-29 and HCT-116 cells. KSK05104 induced the activation of caspase-8, -9, and -3, and the cleavage of poly (ADP ribose) polymerase-1 (PARP-1). KSK05104-induced apoptosis was significantly suppressed by pretreatment with z-VAD-fmk (a broad caspase inhibitor). KSK05104 also induced release of cytochrome c (Cyt c), apoptosis inducing factor (AIF), and endonuclease G (Endo G) by damaging mitochondria, resulting in caspase-dependent and -independent apoptotic cell death. KSK05104 triggered endoplasmic reticulum (ER) stress and changed the intracellular calcium level ([Ca²⁺]_i). Interestingly, treatment with KSK05104 activated not only ER stress marker proteins including inositol-requiring enzyme 1-alpha (IRE-1α) and protein kinase RNA-like endoplasmic reticulum kinase (PERK), but also μ-calpain, and caspase-12 in a time-dependent manner. KSK05104-induced apoptosis substantially decreased in the presence of BAPTA/AM (an intracellular calcium chelator). Taken together, these results suggest that mitochondrial dysfunction and ER stress contribute to KSK05104-induced apoptosis in human colon cancer cells.

Simultaneous Improvement of Antimicrobial, Antifouling, and Transport Properties of Forward Osmosis Membranes with Immobilized Highly-Compatible Polyrhodanine Nanoparticles

This work shows that incorporating highly compatible polyrhodanine nanoparticles (PRh-NPs) into a polyamide (PA) active layer allows for fabricating forward osmosis (FO) thin-film composite (TFC)-PRh membranes that have simultaneously improved antimicrobial, antifouling, and transport properties. To the best of our knowledge, this is the first reported study of its kind to this date. The presence of the PRh-NPs on the surface of the TFC-PRh membranes active layers is evaluated using FT-IR spectroscopy, SEM, and XPS. The microscopic interactions and their impact on the compatibility of the PRh-NPs with the PA chains were studied using molecular dynamics simulations. When tested in forward osmosis, the TFC-PRh-0.01 membrane (with 0.01 wt % PRh) shows significantly improved permeability and selectivity because of the small size and the high compatibility of the PRh-NPs with PA chains. For example, the TFC-PRh-0.01 membrane exhibits a FO water flux of 41 l/(m²·h), higher than a water flux of 34 l/(m²·h) for the pristine TFC membrane, when 1.5 molar NaCl was used as draw solution in the active-layer feed-solution mode. Moreover, the reverse solute flux of the TFC-PRh-0.01 membrane decreases to about 115 mmol/(m²·h) representing a 52% improvement in the reverse solute flux of this membrane in comparison to the pristine TFC membrane. The surfaces of the TFC-PRh membranes were found to be smoother and more hydrophilic than those of the pristine TFC membrane, providing improved antifouling properties confirmed by a flux decline of about 38% for the TFC-PRh-0.01 membranes against a flux decline of about 50% for the pristine TFC membrane when evaluated with a sodium alginate solution. The antimicrobial traits of the TFC-PRh-0.01 membrane evaluated using colony-forming units and fluorescence imaging indicate that the PRh-NPs hinder cell deposition on the TFC-PRh-0.01 membrane surface effectively, limiting biofilm formation.

Analysis of Kunitz inhibitors from plants for comprehensive structural and functional insights

Legume Kunitz type trypsin inhibitor (KTI) family is one of the most versatile families of proteins. A typical KTI features a single peptide folded in β-trefoil manner, with the molecular weight about 20-22kDa and two disulphide bonds. The members are known to inhibit a wide range of serpins proteases at the same time many of them possess unique features. Copaifera langsdorffii Trypsin inhibitor (CTI) has a β-trefoil fold made up of two non-covalently bound polypeptide chains with only a single disulfide bridge. Delonix regia Trypsin inhibitor (DrTI) has one amino acid insertion between P1 and P2 of the reactive site distorting its conformation. Bauhinia bauhinioides Cruzipain inhibitor (BbCI) has a conservative β-trefoil fold but lacks disulfide bonds. Such subtle differences in structures make Kunitz inhibitors different from other inhibitor families. Most of the studies on these inhibitors are focused towards their proposed role in defense from insect pests and wounding but their exact physiological role in nature is still uncharted. Thus, it would be very interesting to closely analyze the structural details of these inhibitors in order to ascertain their biological role and other fascinating applications.

Quantum molecular modeling of hepatitis C virus inhibition through non-structural protein 5B polymerase receptor binding of C5-arylidene rhodanines

We have carried out high-level quantum chemical computations followed by molecular docking studies on a set of 17C₅-arylidene rhodanine isomers to provide insights into the binding modes with different reported binding pockets of the nonstructural protein 5B (NS5B) polymerase that contribute to the hepatitis C virus (HCV) inhibition. We optimized the multi-target profile of the selected rhodanine analogs to investigate potential non-nucleotide inhibitors (NNIs) by quantum chemical optimization of the 18 isomers followed by docking with quantum chemically optimized structures of each isomer with NS5B polymerase at multiple binding pockets. The binding affinities of the PP-I, PP-II and TP-II pockets of NS5B polymerase were analyzed for all the 17 isomers of 2-[(5Z)-5-(2,4-dichlorobenzylidene)-4-oxo-2-thioxo-1,3-thiazolidin-3-yl]-3-phenylpropanoic acid. On the basis of binding propensity at the different pockets and inhibitor constants, we ranked these isomers as potential candidates for the HCV inhibition. We have identified four isomers as promising NNIs of NS5B polymerase with comparable binding and inhibition to the standard (1,3) dichloro substituted isomer that exhibits in vitro activity and several other isomers as candidates in a "multi-targeted drug" approach.

5-Ene-4-thiazolidinones - An efficient tool in medicinal chemistry

The presented review is an attempt to summarize a huge volume of data on 5-ene-4-thiazolidinones being a widely studied class of small molecules used in modern organic and medicinal chemistry. The manuscript covers approaches to the synthesis of 5-ene-4-thiazolidinone derivatives: modification of the C5 position of the basic core; synthesis of the target compounds in the one-pot or multistage reactions or transformation of other related heterocycles. The most prominent pharmacological profiles of 5-ene derivatives of different 4-thiazolidinone subtypes belonging to hit-, lead-compounds, drug-candidates and drugs as well as the most studied targets have been discussed. Currently target compounds (especially 5-en-rhodanines) are assigned as frequent hitters or pan-assay interference compounds (PAINS) within high-throughput screening campaigns. Nevertheless, the crucial impact of the presence/nature of C5 substituent (namely 5-ene) on the pharmacological effects of 5-ene-4-thiazolidinones was confirmed by the numerous listed findings from the original articles. The main directions for active 5-ene-4-thiazolidinones optimization have been shown: i) complication of the fragment in the C5 position; ii) introduction of the substituents in the N3 position (especially fragments with carboxylic group or its derivatives); iii) annealing in complex heterocyclic systems; iv) combination with other pharmacologically attractive fragments within hybrid pharmacophore approach. Moreover, the utilization of 5-ene-4-thiazolidinones in the synthesis of complex compounds with potent pharmacological application is described. The chemical transformations cover mainly the reactions which involve the exocyclic double bond in C5 position of the main core and correspond to the abovementioned direction of the 5-ene-4-thiazolidinone modification.

An updated evolutionary study of Flaviviridae NS3 helicase and NS5 RNA-dependent RNA polymerase reveals novel invariable motifs as potential pharmacological targets

The rate of Flaviviridae family virus infections worldwide has increased dramatically in the last few years. In addition, infections caused by arthropod vector viruses including Hepatitis C, West Nile, Dengue fever, Yellow fever and Japanese encephalitis are emerging throughout the world. Based on a recent taxon update, the Flaviviridae family comprises four main genera; Flavivirus, Hepacivirus, Pestivirus and a recent genus Pegivirus. Although the new scientific classification plays a key role in providing useful information about the relationships between viruses, many new documented viruses remain unclassified. Furthermore, based on the different results of several studies the classification is unclear. In an effort to provide more insights into the classification of viruses, a holistic evolutionary study of the two viral enzymes NS3 helicase and NS5 RNA-dependent RNA polymerase (RdRp) has been conducted in this study. These two viral enzymes are very crucial for the inhibition of viruses due to the fact that they are involved in the survival, proliferation and transmission of viruses. The main goal of this study is the presentation of two novel updated phylogenetic trees of the enzymes NS3 helicase and NS5 RdRp as a reliable phylogeny "map" to correlate the information of the closely related viruses and identify new possible targets for the Flaviviridae family virus inhibition. Despite the earliest trials for drugs against Flaviviridae related viruses, no antiviral drug vaccine has been available to date. Therefore there is an urgent need for research towards the development of efficient antiviral agents.

Synthesis and biological evaluation of new rhodanine analogues bearing 2-chloroquinoline and benzo[h]quinoline scaffolds as anticancer agents

Several rhodanine derivatives (9-39) were synthesized for evaluation of their potential as anticancer agents. Villsmeier cyclization to synthesize aza-aromatic aldehydes, rhodanine derivatives preparation and Knoevenagel type of condensation between the rhodanines and aza-aromatic aldehydes are key steps used for the synthesis of 31 compounds. In vitro antiproliferative activity of the synthesized rhodanine derivatives (9-39) was studied on a panel of six human tumor cell lines viz. HGC, MNK-74, MCF-7, MDAMB-231, DU-145 and PC-3 cell lines. Some of the compounds were capable of inhibiting the proliferation of cancer cell lines at a micromolar concentration. Six compounds are found to be potent against HGC cell lines; compound 15 is found to be active against HGC - Gastric, MCF7 - Breast Cancer and DU145 - Prostate Cancer cell lines; compound 39 is potent against MNK-74; four compounds are found to be potent against MCF-7 cell lines; three compounds are active against MDAMB-231; nine compounds are found to be potent against DU-145; three compounds are active against PC-3 cell lines. These compounds constitute a promising starting point for the development of novel and more potent anticancer agents in future.

A solvent-free protocol for the green synthesis of arylalkylidene rhodanines in a task-specific ionic liquid

2-Hydroxyethylammonium formate acts as a task-specific ionic liquid (TSIL) for the Knoevenagel condensation of carbonyl compounds with rhodanine to afford arylalkylidene rhodanines under solvent-free conditions and in good-to-excellent yields. Additionally, compared with those in organic solvents, the yields obtained in the presence of our ionic liquid (IL) were significantly increased. The detailed mechanism of the catalytic effect of TSIL is also reported for the first time.

5-Isopropylidene-3-ethyl rhodanine induce growth inhibition followed by apoptosis in leukemia cells

5-Isopropylidene-3-ethyl rhodanine II was prepared by conventional and Microwave assisted synthesis. For the first time, we found that rhodanine II treatment led to cytotoxicity in leukemic cell line, CEM by inducing apoptosis.

An efficient one-pot, three-component synthesis of 5-hydrazinoalkylidene rhodanines from 1,2-diaza-1,3-dienes

A novel three-component synthesis of 5-hydrazinoalkylidene rhodanine derivatives starting from aliphatic primary amines, carbon disulfide, and 1,2-diaza-1,3-dienes is described. The reaction proceeds successfully under both solution and solid-phase conditions.

3-Phenyl-2-thioxo-1,3-thia-zolidin-4-one

In the mol­ecule of the title compound, C₉H₇NOS₂, the heterocycle and the phenyl ring are oriented at a dihedral angle of 72.3 (1)°. Adjacent mol­ecules are connected through C—H⋯O inter­actions.

Chemical probes of UDP-galactopyranose mutase

Many pathogenic prokaryotes and eukaryotes possess the machinery required to assemble galactofuranose (Galf)-containing glycoconjugates; these glycoconjugates can be critical for virulence or viability. Accordingly, compounds that block Galf incorporation may serve as therapeutic leads or as probes of the function of Galf-containing glycoconjugates. The enzyme UDP-galactopyranose mutase (UGM) is the only known generator of UDP-galactofuranose, the precursor to Galf residues. We previously employed a high-throughput fluorescence polarization assay to investigate the Klebsiella pneumoniae UGM. We demonstrate the generality of this assay by extending it to UGM from Mycobacterium tuberculosis. To identify factors influencing binding, we synthesized a directed library containing a 5-arylidene-2-thioxo-4-thiazolidinone core, a structure possessing features common to ligands for both homologs. Our studies offer a blueprint for identifying inhibitors of the growing family of UGM homologs and provide insight into UGM inhibition.

Protease inhibitors and their peptidomimetic derivatives as potential drugs

Precise spatial and temporal regulation of proteolytic activity is essential to human physiology. Modulation of protease activity with synthetic peptidomimetic inhibitors has proven to be clinically useful for treating human immunodeficiency virus (HIV) and hypertension and shows potential for medicinal application in cancer, obesity, cardiovascular, inflammatory, neurodegenerative diseases, and various infectious and parasitic diseases. Exploration of natural inhibitors and synthesis of peptidomimetic molecules has provided many promising compounds performing successfully in animal studies. Several protease inhibitors are undergoing further evaluation in human clinical trials. New research strategies are now focusing on the need for improved comprehension of protease-regulated cascades, along with precise selection of targets and improved inhibitor specificity. It remains to be seen which second generation agents will evolve into approved drugs or complementary therapies.

High-throughput screening of low molecular weight NS3-NS4A protease inhibitors using a fluorescence resonance energy transfer substrate

Hepatitis C virus (HCV) NS3-NS4A protease is an attractive target for anti-HCV agents because of its important role in replication. An optimized fluorescence resonance energy transfer (FRET) substrate for NS3-NS4A protease, based on the sequence of the NS5A-5B cleavage site, was designed and synthesized. High-throughput screening of in-house compound libraries was performed using a FRET substrate FS10 (MOCAcDKIVPC-SMSYK-Dnp) and MBP-NS3-NS4A fusion protein. Several hit compounds were found, including YZ-9577 (2-oxido-1,2,5-oxadiazole-3,4-diyl) bis (phenylmethanone) with potent inhibitory activity (IC50=1.6 microM) and good selectivity against other human serine proteases.

SAR and 3D-QSAR studies on thiadiazolidinone derivatives: exploration of structural requirements for glycogen synthase kinase 3 inhibitors

The 2,4-disubstituted thiadiazolidinones (TDZD) are described as the first ATP-noncompetitive GSK-3 inhibitors. Following an SAR study about TDZD, different structural modifications in the heterocyclic ring aimed to test the influence of each heteroatom on the biological study are here reported here. Various compounds such as hydantoins, dithiazolidindiones, rhodanines, maleimides, and triazoles were synthesized and screened as GSK-3 inhibitors. After an extensive SAR study among these different heterocyclic families, TDZDs have been revealed as a privileged scaffold for the selective inhibition of GSK-3. A CoMFA analysis was also performed highlighting the molecular electrostatic field interaction in the interaction of TDZDs with GSK-3. Moreover, first mapping studies indicate two binding modes which in turn might imply relevant differences in the mechanism that underly the inhibitory activity of TDZDs.

Antiviral compounds from traditional Chinese medicines Galla Chinese as inhibitors of HCV NS3 protease

Under the guidance of bioassay, the EtOAc extract fraction of the Traditional Chinese Medicine (TCM) Galla Chinese was found to be efficient in inhibiting the NS3 protease of HCV and purified the fraction to get three polyphenol compounds 1,2,6-tri-O-galloyl-beta-D-glucose (1), 1,2,3,6-tetra-O-galloyl-beta-D-glucose (2), and 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (3), which were identified as inhibitors of Hepatitis C Virus (HCV) NS3 protease. Compounds 1, 2, and 3 inhibited HCV NS3 protease with IC50 of 1.89, 0.75, and 1.60 microM, respectively.

Emerging therapies for hepatitis C virus infection

Hepatitis C virus (HCV) has infected millions of people worldwide and has emerged as a global health crisis. The currently available therapy is interferon (IFN) either alone or in combination with ribavirin. However, the disappointing efficacy of IFN has led to the considerable need for improved treatments and a number of new therapies are under evaluation in clinical trials. These include pegylated IFNs, which have altered physiochemical characteristics allowing once-weekly dosing. Combination of pegylated IFN with ribavirin should further improve sustained response rates. However, not all patients are successfully treated with IFNs, particularly those infected with genotype 1 of the virus, and it is likely that potent, specific drugs will be required. The majority of new approaches currently trying to combat this viral disease are aimed at inhibition of viral targets. Most effort has been directed towards inhibition of the NS3 serine protease, and potent inhibitors have now been described. However, a clinical candidate is yet to emerge against this difficult target. Considerable work by leading researchers has provided crystal structures of the key replicative enzymes, NS3 protease, NS3 helicase, NS5B polymerase and full-length NS3 protease-helicase, and there is much hope that such structural information will bear fruit. More recently, inhibition of host targets, particularly inosine monophosphate dehydrogenase (IMPDH), has become of interest and there are on-going clinical trials with such inhibitors. Research aimed at novel treatments for HCV disease is gathering pace and very recent developments in cell-based assay systems can only hasten the discovery of improved therapies.