In vitro antiviral activity of SCH446211 (SCH6), a novel inhibitor of the hepatitis C virus NS3 serine protease.

BACKGROUND: Current hepatitis C virus (HCV) therapies may cure approximately 60% of infections. They are often contraindicated or poorly tolerated, underscoring the need for safer and more effective drugs. A novel, alpha-ketoamide-derived, substrate-based inhibitor of the HCV serine protease (SCH446211) was developed. Compared with earlier reported inhibitors of similar chemical class, it has a P1'-P2' extension which provides extended interaction with the protease active site. The aim of this study was to evaluate the in vitro antiviral activity of SCH446211. METHODS: Binding constant of SCH446211 to HCV NS3 protease was measured with the chromogenic substrate in vitro cleavage assay. Cell-based activity of SCH446211 was evaluated in replicon cells, which are Huh-7 hepatoma cells stably transfected with a subgenomic HCV RNA as reported previously. After 72 h of incubation with SCH446211, viral transcription and protein expression were measured by real-time RT-PCR (TaqMan), quantitative in situ hybridization, immunoblot and indirect immunofluorescence. RESULTS: The binding constant of SCH446211 to HCV NS3 protease was 3.8 +/- 0.4 nM. HCV replication and protein expression were inhibited by SCH446211 in replicon cells as consistently shown by four techniques. In particular, based on quantitative real-time RT-PCR measurements, the IC50 and IC90 of SCH446211 were estimated to be 40 +/- 20 and 100 +/- 20 nM (n = 17), respectively. Long-term culture of replicon cells with SCH446211 reduced replicon RNA to <0.1 copy per cell. SCH446211 did not show cellular toxicity at concentrations up to 50 microM. CONCLUSIONS: SCH446211 is a potent inhibitor of HCV protease in vitro. Its extended interaction with the HCV NS3 protease active site is associated with potent in vitro antiviral activity. This observation is potentially a useful guide for development of future potent inhibitors against HCV NS3 protease.

Interaction of small molecule inhibitors of HIV-1 entry with CCR5.

The CC-chemokine receptor 5 (CCR5) is the major coreceptor for macrophage-tropic (R5) HIV-1 strains. Several small molecule inhibitors of CCR5 that block chemokine binding and HIV-1 entry are being evaluated as drug candidates. Here we define how CCR5 antagonists TAK-779, AD101 (SCH-350581) and SCH-C (SCH-351125), which inhibit HIV-1 entry, interact with CCR5. Using a mutagenesis approach in combination with a viral entry assay to provide a direct functional read out, we tested predictions based on a homology model of CCR5 and analyzed the functions of more than 30 amino acid residues. We find that a key set of aromatic and aliphatic residues serves as a hydrophobic core for the ligand binding pocket, while E283 is critical for high affinity interaction, most likely by acting as the counterion for a positively charged nitrogen atom common to all three inhibitors. These results provide a structural basis for understanding how specific antagonists interact with CCR5, and may be useful for the rational design of new, improved CCR5 ligands.

Antiviral activity of transiently expressed IFN-kappa is cell-associated.

Most type I interferons (IFNs) are expressed by the majority of cell types in response to viral infection. In contrast, IFN-kappa has been reported to have a cellular distribution limited to keratinocytes and certain lymphoid cell populations. Recombinant expressed IFN-kappa has been shown previously to possess weak antiviral activity when directly compared with IFN-beta. In order to expand on the antiviral potential of IFN-kappa, we transiently transfected human cell lines to circumvent the need to purify recombinant proteins and to avoid the possible loss of biologic activity by the purification process. We evaluated the transcriptional signaling and antiviral activity of IFN-kappa in parallel with IFN-alpha2b with mammalian expression vectors to express each protein transiently. Both IFN-kappa and IFN-alpha2b exhibited comparable transcriptional and antiviral activities. However, in contrast to IFN-alpha2b transcriptional signaling and antiviral activity, IFN-kappa activity was not detectable in conditioned cell culture medium. Subsequent experiments revealed there was a direct relationship between IFN-kappa-expressing cells and antiviral activity. These results were confirmed in immunocytochemical studies. Furthermore, IFN-kappa exhibited cell-associated antiviral activity against a hepatitis C virus (HCV) replicon cell line. This novel IFN signaling strategy may represent an important distinct and divergent mechanism for limiting viral infections.

Discovery and characterization of vicriviroc (SCH 417690), a CCR5 antagonist with potent activity against human immunodeficiency virus type 1.

Inhibiting human immunodeficiency virus type 1 (HIV-1) infection by blocking the host cell coreceptors CCR5 and CXCR4 is an emerging strategy for antiretroviral therapy. Currently, several novel coreceptor inhibitors are being developed in the clinic, and early results have proven promising. In this report, we describe a novel CCR5 antagonist, vicriviroc (formerly SCH-D or SCH 417690), with improved antiviral activity and pharmacokinetic properties compared to those of SCH-C, a previously described CCR5 antagonist. Like SCH-C, vicriviroc binds specifically to the CCR5 receptor and prevents infection of target cells by CCR5-tropic HIV-1 isolates. In antiviral assays, vicriviroc showed potent, broad-spectrum activity against genetically diverse and drug-resistant HIV-1 isolates and was consistently more active than SCH-C in inhibiting viral replication. This compound demonstrated synergistic anti-HIV activity in combination with drugs from all other classes of approved antiretrovirals. Competition binding assays revealed that vicriviroc binds with higher affinity to CCR5 than SCH-C. Functional assays, including inhibition of calcium flux, guanosine 5'-[35S]triphosphate exchange, and chemotaxis, confirmed that vicriviroc acts as a receptor antagonist by inhibiting signaling of CCR5 by chemokines. Finally, vicriviroc demonstrated diminished affinity for the human ether a-go-go related gene transcript ion channel compared to SCH-C, suggesting a reduced potential for cardiac effects. Vicriviroc represents a promising new candidate for the treatment of HIV-1 infection.

Generation and properties of a human immunodeficiency virus type 1 isolate resistant to the small molecule CCR5 inhibitor, SCH-417690 (SCH-D).

We describe the generation of two genetically related human immunodeficiency virus type 1 (HIV-1) isolates highly (>20,000-fold) resistant to the small molecule CCR5 inhibitor, SCH-417690 (formerly SCH-D). Both viruses were cross-resistant to other small molecules targeting entry via CCR5, but they were inhibited by some MAbs against the same coreceptor on primary CD4+ T-cells. The resistant isolates remained sensitive to inhibitors of other stages of virus entry, and to replication inhibitors acting post-entry. Neither escape mutant could replicate detectably in peripheral blood mononuclear cells (PBMC) from two donors homozygous for the CCR5-Delta32 allele and both were insensitive to the CXCR4-specific inhibitor, AMD3100. Hence, the SCH-D escape mutants retained the R5 phenotype. One of the resistant isolates was, however, capable of replication in U87.CD4.CXCR4 cells and, after expansion in those cells, was sensitive to AMD3100 in primary CD4+ T-cells. Hence, some X4 variants may be present in this escape mutant swarm. A notable observation was that the SCH-D escape mutants were also cross-resistant to PSC-RANTES and AOP-RANTES, chemokine derivatives that are reported to down-regulate cell surface CCR5 almost completely. However, the extent to which CCR5 is down-regulated was dependent upon the detection MAb. Hence, the escape mutants may be using a CCR5 configuration that is only detected by some anti-CCR5 MAbs. Finally, two SCH-D-resistant clonal viruses revealed no amino acid changes in the gp120 V3 region relative to the parental viruses, in marked contrast to clones resistant to the AD101 small molecule CCR5 inhibitor that possess 4 such sequence changes. Several sequence changes elsewhere in gp120 (V2, C3 and V4) were present in the SCH-D-resistant clones. Their influence on the resistant phenotype remains to be determined.

Piperazine-based CCR5 antagonists as HIV-1 inhibitors. IV. Discovery of 1-[(4,6-dimethyl-5-pyrimidinyl)carbonyl]- 4-[4-[2-methoxy-1(R)-4-(trifluoromethyl)phenyl]ethyl-3(S)-methyl-1-piperazinyl]- 4-methylpiperidine (Sch-417690/Sch-D), a potent, highly selective, and orally bioavailable CCR5 antagonist.

The nature and the size of the benzylic substituent are shown to be the key to controlling receptor selectivity (CCR5 vs M1, M2) and potency in the title compounds. Optimization of the lead benzylic methyl compound 3 led to the methoxymethyl analogue 30, which had excellent receptor selectivity and oral bioavailability in rats and monkeys. Compound 30 (Sch-417690/Sch-D), a potent inhibitor of HIV-1 entry into target cells, is currently in clinical trials.

The differential sensitivity of human and rhesus macaque CCR5 to small-molecule inhibitors of human immunodeficiency virus type 1 entry is explained by a single amino acid difference and suggests a mechanism of action for these inhibitors.

AD101 and SCH-C are two chemically related small molecules that inhibit the entry of human immunodeficiency virus type 1 (HIV-1) via human CCR5. AD101 also inhibits HIV-1 entry via rhesus macaque CCR5, but SCH-C does not. Among the eight residues that differ between the human and macaque versions of the coreceptor, only one, methionine-198, accounts for the insensitivity of macaque CCR5 to inhibition by SCH-C. Thus, the macaque coreceptor engineered to contain the natural human CCR5 residue (isoleucine) at position 198 is sensitive to HIV-1 entry inhibition by SCH-C, whereas a human CCR5 mutant containing the corresponding macaque residue (methionine) is resistant. Position 198 is in CCR5 transmembrane (TM) helix 5 and is not located within the previously defined binding site for AD101 and SCH-C, which involves residues in TM helices 1, 2, 3, and 7. SCH-C binds to human CCR5 whether residue 198 is isoleucine or methionine, and it also binds to macaque CCR5. However, the binding of a conformation-dependent monoclonal antibody to human CCR5 is inhibited by SCH-C only when residue 198 is isoleucine. These observations, taken together, suggest that the antiviral effects of SCH-C and AD101 involve stabilization, or induction, of a CCR5 conformation that is not compatible with HIV-1 infection. However, SCH-C is unable to exert this effect on CCR5 conformation when residue 198 is methionine. The region of CCR5 near residue 198 has, therefore, an important influence on the conformational state of this receptor.

Genetic and phenotypic analyses of human immunodeficiency virus type 1 escape from a small-molecule CCR5 inhibitor.

We have described previously the generation of an escape variant of human immunodeficiency virus type 1 (HIV-1), under the selection pressure of AD101, a small molecule inhibitor that binds the CCR5 coreceptor (A. Trkola, S. E. Kuhmann, J. M. Strizki, E. Maxwell, T. Ketas, T. Morgan, P. Pugach, S. X. L. Wojcik, J. Tagat, A. Palani, S. Shapiro, J. W. Clader, S. McCombie, G. R. Reyes, B. M. Baroudy, and J. P. Moore, Proc. Natl. Acad. Sci. USA 99:395-400, 2002). The escape mutant, CC101.19, continued to use CCR5 for entry, but it was at least 20,000-fold more resistant to AD101 than the parental virus, CC1/85. We have now cloned the env genes from the the parental and escape mutant isolates and made chimeric infectious molecular clones that fully recapitulate the phenotypes of the corresponding isolates. Sequence analysis of the evolution of the escape mutants suggested that the most relevant changes were likely to be in the V3 loop of the gp120 glycoprotein. We therefore made a series of mutant viruses and found that full AD101 resistance was conferred by four amino acid changes in V3. Each change individually caused partial resistance when they were introduced into the V3 loop of a CC1/85 clone, but their impact was dependent on the gp120 context in which they were made. We assume that these amino acid changes alter how the HIV-1 Env complex interacts with CCR5. Perhaps unexpectedly, given the complete dependence of the escape mutant on CCR5 for entry, monomeric gp120 proteins expressed from clones of the fully resistant isolate failed to bind to CCR5 on the surface of L1.2-CCR5 cells under conditions where gp120 proteins from the parental virus and a partially AD101-resistant virus bound strongly. Hence, the full impact of the V3 substitutions may only be apparent at the level of the native Env complex.

The effect of ribavirin and IMPDH inhibitors on hepatitis C virus subgenomic replicon RNA.

The recent development of in vitro hepatitis C virus (HCV) RNA replication systems has provided useful tools for studying the intracellular anti-HCV activity of ribavirin. Ribavirin has been shown to: (1) induce "error catastrophe" in poliovirus, Proc. Natl. Acad. Sci. USA 98, 6895-6900), (2) be a pseudo-substrate of the HCV RNA-dependent RNA polymerase (RdRp) in vitro, J. Biol. Chem. 276, 46094-46098), and (3) increase mutations in HCV RNA in the binary T7 polymerase/HCV cDNA replication system, J. Virol. 76, 8505-8517). These findings have led to the hypothesis that ribavirin may also induce error catastrophe in HCV. However, the functional relevance of ribavirin-induced HCV RNA mutagenesis is unclear. By use of a colony formation assay, in which RNA is isolated from the HCV subgenomic replicon system following treatment, the impact of ribavirin, inosine-5'-monophosphate dehydrogenase (IMPDH) inhibitors, and the combination was assessed. Ribavirin reduced HCV replicon colony-forming efficiency (CFE) in a dose-dependent fashion, suggesting that ribavirin may be misincorporated into replicon RNA and result in an anti-replicon effect analogous to error catastrophe. This effect was markedly suppressed by addition of exogenous guanosine. Combination treatment with ribavirin and mycophenolic acid (MPA) or VX-497, both potent, nonnucleoside IMPDH inhibitors, led to a greatly enhanced anti-replicon effect. This enhancement was reversed by inclusion of guanosine with the treatment. In contrast, MPA or VX-497 alone had only marginal effects on both the quantity and quality (CFE) of replicon RNA, suggesting that although IMPDH inhibition is an important contributing factor to the overall ribavirin anti-HCV replicon activity, IMPDH inhibition by itself is not sufficient to exert an anti-HCV effect. Sequencing data targeting the neo gene segment of the HCV replicon indicated that ribavirin together with MPA or VX-497 increased the replicon error rate by about two-fold. Taken together these results further suggest that lethal mutagenesis may be an effective anti-HCV strategy. The colony formation assay provides a useful tool for evaluating mutagenic nucleoside analogs for HCV therapy. Finally, the data from combination treatment indicate potential therapeutic value for an enhanced anti-HCV effect when using ribavirin in combination with IMPDH inhibition.

Expression of a novel murine type I IFN in the pancreatic islets induces diabetes in mice.

IFN-kappa belongs to a recently identified subclass of type I IFNs. In this study, we report the cloning and preliminary characterization of the murine homologue of IFN-kappa. The gene encodes a 200-aa protein which is 38.5% homologous to human IFN-kappa. Murine IFN-kappa contains four cysteines in analogous positions to those observed in the IFN-alpha and an additional fifth unique cysteine, C174. The murine gene is located on chromosome 4, where other type I murine IFN genes, IFN-alpha and IFN-beta, are clustered. This region is syntenic with human chromosome 9 where the gene encoding IFN-kappa and the type I IFN gene cluster are found. Mouse IFN-kappa is expressed at low levels in peritoneal macrophages and its expression is up-regulated by dsRNA and IFN-gamma. Similar to previously reported transgenic mice carrying type I and type II IFNs, transgenic mice overexpressing murine IFN-kappa in the beta cells of the pancreas develop overt diabetes with hyperglycemia. Histological characterization of pancreatic islets from these transgenic mice showed inflammatory infiltrates with corresponding destruction of beta cells.

Entry inhibitors SCH-C, RANTES, and T-20 block HIV type 1 replication in multiple cell types.

The small-molecule CCR5 antagonist SCH-C (SCH 351125) was tested for its ability to inhibit HIV-1 replication in peripheral blood mononuclear cells (PBMCs), cord blood mononuclear cells, immature dendritic cells (DCs), and macrophages. Inhibition of infection of PBMCs by virus associated with mature DC in trans was also studied. For comparison, the peptide-based fusion inhibitor T-20 and the CC-chemokine RANTES were also evaluated. Although some cell type-dependent differences in potency were observed, each of the three entry inhibitors was active against the replication of three different CCR5-using primary isolates in each cell type. CCR5-dependent HIV-1 infectivity, whether DC associated or not, is thus vulnerable to inhibitors that block the virus-cell fusion process by different mechanisms. Together, these results suggest that SCH-C and other entry inhibitors should be evaluated for their clinical potential as inhibitors of HIV-1 replication in several settings, including the prevention of maternal-infant transmission and the prevention of sexual transmission by topical application as a microbicide.

Oximino-piperidino-piperidine-based CCR5 antagonists. Part 2: synthesis, SAR and biological evaluation of symmetrical heteroaryl carboxamides.

The synthesis, SAR and biological evaluation of symmetrical amide analogues of our clinical candidate SCH 351125 are described. A series of potent and orally bioavailable CCR5 antagonists containing symmetrical 2,6-dimethyl isonicotinamides and 2, 6-dimethyl pyrimidines amides were generated with enhanced affinity for the CCR5 receptor.

Biological evaluation and interconversion studies of rotamers of SCH 351125, an orally bioavailable CCR5 antagonist.

The separation and biological evaluation of rotamers as well as interconversion studies on rotamers of our clinical candidate SCH 351125 are described.

Piperazine-based CCR5 antagonists as HIV-1 inhibitors. III: synthesis, antiviral and pharmacokinetic profiles of symmetrical heteroaryl carboxamides.

The unsymmetrical nicotinamide-N-oxide moiety in compound 1 was replaced with symmetrical isonicotinamides as well as 4,6-dimethyl pyrimidine-5-carboxamides. Compound 16 from the latter set reduced the number of rotamers, improved potency of inhibiting UIV entry, slightly diminished the affinity for the muscarine receptors and showed very good oral absorption.

Synthesis, SAR, and biological evaluation of oximino-piperidino-piperidine amides. 1. Orally bioavailable CCR5 receptor antagonists with potent anti-HIV activity.

We previously reported the discovery of 4-[(Z)-(4-bromophenyl)(ethoxyimino)methyl]-1'-[(2,4-dimethyl-3-pyridinyl)carbonyl]-4'-methyl-1,4'-bipiperidine N-oxide 1 (SCH 351125) as an orally bioavailable human CCR5 antagonist for the treatment of HIV-1 infection. Herein, we describe in detail the discovery of 1 from our initial lead compound as well as the synthesis and SAR studies directed toward optimization of substitution at the phenyl, oxime, and right-hand side amide groups in the oximino-piperidino-piperidine series. Substitutions (4-Br, 4-CF(3), 4-OCF(3), 4-SO(2)Me, and 4-Cl) at the phenyl group are well-tolerated, and small alkyl substitutions (Me, Et, (n)()Pr, (i)()Pr, and cyclopropyl methyl) at the oxime moiety are preferred for CCR5 antagonism. The 2,6-dimethylnicotinamide N-oxide moiety is the optimal choice for the right-hand side. Several compounds in this series, including compound 1, exhibited excellent antiviral activity in vitro. Compound 1, which has a favorable pharmacokinetic profile in rodents and primates, excellent oral bioavailability, and potent antiviral activity against a wide range of primary HIV-1 isolates, is a potentially promising new candidate for treatment of HIV-1 infection.

Anti-human immunodeficiency virus interactions of SCH-C (SCH 351125), a CCR5 antagonist, with other antiretroviral agents in vitro.

SCH-C (SCH 351125) is a small-molecule antagonist of the human immunodeficiency virus type 1(HIV-1) coreceptor CCR5. It has in vitro activity against R5 viruses with 50% inhibitory concentrations ranging from 1.0 to 30.9 nM. We have studied anti-HIV-1 interactions of SCH-C with other antiretroviral agents in vitro. Synergistic interactions were seen with nucleoside reverse transcriptase inhibitors (zidovudine and lamivudine), nonnucleoside reverse transcriptase inhibitors (efavirenz), and protease inhibitors (indinavir) at all inhibitory concentrations evaluated. We have also studied antiviral interactions between the HIV-1 fusion inhibitor T-20 and SCH-C against a panel of R5 HIV-1 isolates. We found synergistic interactions against all the viruses tested, some of which harbored resistance mutations to reverse transcriptase and protease inhibitors. Anti-HIV-1 synergy was also observed between SCH-C and another R5 virus inhibitor, aminooxypentane-RANTES. These findings suggest that SCH-C may be a useful anti-HIV drug in combination regimens and that a combination of chemokine coreceptor/fusion inhibitors may be useful in the treatment of multidrug-resistant viruses.

HIV-1 escape from a small molecule, CCR5-specific entry inhibitor does not involve CXCR4 use.

To study HIV-1 escape from a coreceptor antagonist, the R5 primary isolate CC1/85 was passaged in peripheral blood mononuclear cells with increasing concentrations of the CCR5-specific small molecule inhibitor, AD101. By 19 passages, an escape mutant emerged with a >20,000-fold resistance to AD101. This virus was cross-resistant to a related inhibitor, SCH-C, and partially resistant to RANTES but still sensitive to CCR5-specific mAbs. The resistant phenotype was stable; the mutant virus retained AD101 resistance during nine additional passages of culture in the absence of inhibitor. Replication of the escape mutant in peripheral blood mononuclear cells completely depended on CCR5 expression and did not occur in cells from CCR5-Delta32 homozygous individuals. The escape mutant was unable to use CXCR4 or any other tested coreceptor to enter transfected cells. Acquisition of CXCR4 use is not the dominant in vitro escape pathway for a small molecule CCR5 entry inhibitor. Instead, HIV-1 acquires the ability to use CCR5 despite the inhibitor, first by requiring lower levels of CCR5 for entry and then probably by using the drug-bound form of the receptor.