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.

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

Hepatitis C virus (HCV) is a global health problem, affecting approximately 3% of the world's population. The standard treatment for HCV infection is often poorly tolerated and ineffective. Therefore, the development of novel or more effective treatment strategies to treat chronic HCV infection is urgently needed. In this report, BP008, a potent small-molecule inhibitor of HCV replication, was developed from a class of compounds with thiazol core structures by means of utilizing a cell-based HCV replicon system. The compound reduced the reporter expression of the HCV1b replicon with a 50% effective concentration (EC(50)) and selective index value of 4.1 ± 0.7 nM and >12,195, respectively. Sequencing analyses of several individual clones derived from BP008-resistant RNAs purified from cells harboring HCV1b replicon revealed that amino acid substitutions mainly within the N-terminal region (domain I) of NS5A were associated with decreased inhibitor susceptibility. Q24L, P58S, and Y93H are the key substitutions for resistance selection; F149L and V153M play the compensatory role in the replication and drug resistance processes. Moreover, BP008 displayed synergistic effects with alpha interferon (IFN-α), NS3 protease inhibitor, and NS5B polymerase inhibitor, as well as good oral bioavailability in SD rats and favorable exposure in rat liver. In summary, our results pointed to an effective small-molecule inhibitor, BP008, that potentially targets HCV NS5A. BP008 can be considered a part of a more effective therapeutic strategy for HCV in the future.

Successful propagation of flavivirus infectious cDNAs by a novel method to reduce the cryptic bacterial promoter activity of virus genomes.

Reverse genetics is a powerful tool to study single-stranded RNA viruses. Despite tremendous efforts having been made to improve the methodology for constructing flavivirus cDNAs, the cause of toxicity of flavivirus cDNAs in bacteria remains unknown. Here we performed mutational analysis studies to identify Escherichia coli promoter (ECP) sequences within nucleotides (nt) 1 to 3000 of the dengue virus type 2 (DENV2) and Japanese encephalitis virus (JEV) genomes. Eight and four active ECPs were demonstrated within nt 1 to 3000 of the DENV2 and JEV genomes, respectively, using fusion constructs containing DENV2 or JEV segments and empty vector reporter gene Renilla luciferase. Full-length DENV2 and JEV cDNAs were obtained by inserting mutations reducing their ECP activity in bacteria without altering amino acid sequences. A severe cytopathic effect occurred when BHK21 cells were transfected with in vitro-transcribed RNAs from either a DENV2 cDNA clone with multiple silent mutations within the prM-E-NS1 region of dengue genome or a JEV cDNA clone with an A-to-C mutation at nt 90 of the JEV genome. The virions derived from the DENV2 or JEV cDNA clone exhibited infectivities similar to those of their parental viruses in C6/36 and BHK21 cells. A cis-acting element essential for virus replication was revealed by introducing silent mutations into the central portion (nt 160 to 243) of the core gene of DENV2 infectious cDNA or a subgenomic DENV2 replicon clone. This novel strategy of constructing DENV2 and JEV infectious clones could be applied to other flaviviruses or pathogenic RNA viruses to facilitate research in virology, viral pathogenesis, and vaccine development.

Synthesis, activity, and pharmacokinetic properties of a series of conformationally-restricted thiourea analogs as novel hepatitis C virus inhibitors.

A series of novel conformationally-restricted thiourea analogs were designed, synthesized, and evaluated for their anti-HCV activity. Herein we report the synthesis, structure-activity relationships (SARs), and pharmacokinetic properties of this new class of thiourea compounds that showed potent inhibitory activities against HCV in the cell-based subgenomic HCV replicon assay. Among compounds tested, the fluorene compound 4b was found to possess the most potent activity (EC(50)=0.3 microM), lower cytotoxicity (CC(50)>50 microM), and significantly better pharmacokinetic properties compared to its corresponding fluorenone compound 4c.

Design and efficient synthesis of novel arylthiourea derivatives as potent hepatitis C virus inhibitors.

A novel class of arylthiourea HCV inhibitors bearing various functionalities, such as cyclic urea, cyclic thiourea, urea, and thiourea, on the alkyl linker were designed and synthesized. Herein we report the synthesis and structure-activity relationships (SARs) of this novel class of arylthiourea derivatives that showed potent inhibitory activities against HCV in the cell-based subgenomic HCV replicon assay. Among compounds tested, the new carbazole derivative 64, which has an eight-carbon linkage between the phenyl and carbazole rings and a tolyl group at the N-9 position of carbazole, was found to possess strong anti-HCV activity (EC50=0.031 microM), lower cytotoxicity (CC50 >50 microM), and higher selectivity index (SI >1612) compared to its derivatives.

Functional characterization of hepatitis B virus X protein based on the inhibition of tumorigenesis in nude mice injected with CCL13-HBx cells.

OBJECTIVE: This study aimed to determine the effects of HBx on the inhibition of tumorigenesis in nude mice injected with CCL13-HBx cells. Therefore, the characteristics of the induced tumors and the phenomenon of apoptosis were assessed. METHODS: The induced tumors were identified using the specific marker of hepatocellular carcinoma (HCC), anti-alpha-fetoprotein (AFP), and their characteristics were pathologically examined. Apoptosis was detected by DNA fragmentation, and the expression of the proapoptotic proteins p53, Bax, Bad, caspase-3, and caspase-8 and the anti-apoptotic protein Bcl-2 was detected by Western blotting. To identify possible molecules involved in the inhibition of tumorigenesis, extracts of the induced tumors were separated by 2D-PAGE, and the proteins were identified by MS. RESULTS: The tumors of the nude mice injected with CCL13 and CCL13-HBx cells were identified as HCCs. Moreover, HBx was found to suppress tumor growth via apoptosis in the nude mice injected with CCL13-HBx cells. The MS findings revealed that phosphorylated myosin light chain was a candidate molecule involved in the inhibition of tumorigenesis. CONCLUSION: HBx suppressed tumorigenesis in the nude mice injected with CCL13-HBx cells, which proved to be a good animal model for the in vivo study of the effects of HBx on tumorigenesis.

Effects of hepatitis B virus X protein (HBx) on cell-growth inhibition in a CCL13-HBx stable cell line.

OBJECTIVE: The known function of hepatitis B virus X protein (HBx) is to determine the fate of cells by modulating various signaling pathways. In our previous study, we demonstrated that HBx inhibits tumor formation in nude mice injected with CCL13-HBx stable cell lines; however, the mechanism underlying this inhibition is unclear. METHODS: To investigate the possible mechanisms underlying HBx involvement in CCL13-HBx cells, gene profiles were initially analyzed by DNA microarray technology and subsequently confirmed by performing semiquantitative RT-PCR and Western blotting. Furthermore, the phenomenon of cell death via apoptosis was detected via DNA fragmentation, TUNEL staining, caspase-3 activity assay, and propidium iodide (PI) staining. RESULTS: The results indicated that HBx induction downregulated Wnt-3 and beta-catenin that are involved in cell proliferation. Moreover, HBx induction repressed cell growth and downregulated the expressions of cyclin D1, CDK4, cyclin E, CDK2, and cyclin B1. Furthermore, HBx induction triggered cell death via apoptosis, as determined by DNA fragmentation, TUNEL staining, caspase-3 activity assay, and PI staining. CONCLUSION: Most importantly, our results indicated that HBx induction in the CCL13-HBx stable cell line downregulated Wnt-3/beta-catenin expression and suppressed cell growth by repressing cell proliferation or triggering cell apoptosis.

Inhibition of tumorigenicity of the hepatitis B virus X gene in Chang liver cell line.

The hepatitis B virus X gene, which encodes the HBx protein, has multiple functions and is involved in hepatocarcinogenesis. However, the exact role of HBx in hepatocarcinogenesis is still controversial. We have established an inducible (tet-off system) HBx-expressing cell line, Chang-HBx. Compared with the original of Chang liver cell line (ATCC CCL13), Chang-HBx grows faster in serum-containing medium but slower in serum-free medium. Chang-HBx colony formation in soft agar shows an anchorage-demanding character and its tumorigenicity potential in BALB/c nude mice were substantially inhibited. HBx also causes the induction of G1 phase arrest of cell growth in early infection of HBV and therefore plays a negative role in tumorigenicity. An excellent mice animal model for producing hepatoma was also provided in this study.

Detection of the hepatitis B virus X protein (HBx) antigen and anti-HBx antibodies in cases of human hepatocellular carcinoma.

Hepatitis B virus X protein (HBx) expressed in Escherichia coli DH5alpha by recombinant DNA technology was purified to homogeneity by use of glutathione-Sepharose beads. Immunological characterization of the recombinant HBx protein was performed. Specific binding between the anti-HBx monoclonal antibody and HBx protein showed the specificity of the recombinant HBx protein. The intact HBx protein of the factor Xa-digested glutathione S-transferase-HBx fusion protein was further purified and was used as an antigen for screening the titers of anti-HBx antibodies in sera. Titers of anti-HBx in sera from 20 patients with hepatocellular carcinoma (HCC), 20 patients with chronic hepatitis (CH), and 20 healthy individuals were evaluated by Western blotting and a quantitative enzyme-linked immunosorbent assay. The results indicated that 70% of sera from HCC patients and 5% of sera from CH patients contained antibodies with significant binding to the HBx protein. Western blotting of HBx protein in liver extracts from 20 HCC patients was also performed by using the anti-HBx monoclonal antibody. Results showed that 85% of HCC patients' liver tissues contained a specific HBx protein with the same molecular size as the purified intact HBx. Full correlation was found between anti-HBx antibody positivity in serum and HBx protein positivity in HCC tissues. The data demonstrated that the etiology of HCC is involved with hepatitis B virus (HBV) infection and that HBx in particular plays a role in the development of HBV-related HCC.