Discovery of novel potent HCV NS5B polymerase non-nucleoside inhibitors bearing a fused benzofuran scaffold.

This letter describes the discovery of a fused benzofuran scaffold viable for preparing a series of novel potent HCV NS5B polymerase non-nucleoside inhibitors. Designed on the basis of the functionalized benzofuran derivative nesbuvir (HCV-796), these compounds presumably bind similarly to the allosteric binding site in the "palm" domain of HCV NS5B protein. SAR of each potential hydrogen-bonding interaction site of this novel scaffold is discussed along with some preliminary genotypic profile and PK data of several advanced compounds.

Discovery of ravidasvir (PPI-668) as a potent pan-genotypic HCV NS5A inhibitor.

This Letter describes the synthesis, representative structure activity relationship (SAR), activity and PK profiles of a series of functionalized benzimidazole-naphthylene-imidazole derivatives as HCV NS5A inhibitors. This effort successfully led to the discovery of ravidasvir (PPI-668), which has been well tolerated and shown high sustained viral response rates as a key component in all-oral combination regimens in multiple human clinical trials.

Discovery of functionalized bisimidazoles bearing cyclic aliphatic-phenyl motifs as HCV NS5A inhibitors.

This Letter describes the discovery of a number of functionalized bisimidazoles bearing a cyclohexylphenyl, piperidylphenyl, or bicyclo[2,2,2]octylphenyl motif as HCV NS5A inhibitors. Compounds 2c, 4b and 6 have demonstrated low single-digit nM potency in gt-1a replicon and double-digit pM potency in gt-1b replicon, respectively. Moreover, both 4b and 6 have, respectively, exhibited good oral bioavailability in rats with a favorable liver/plasma ratio of the drug concentration.

Potent bisimidazole-based HCV NS5A inhibitors bearing annulated tricyclic motifs.

This Letter describes the synthesis and biological evaluation of a number of functionalized bisimidazoles bearing annulated tricyclic motifs as potent inhibitors of HCV NS5A protein. Compound 4 h, which contains a substituted tricyclic 6-6-6 xanthene, demonstrated broad genotypic spectrum, compelling potency, and good oral bioavailability with dose-dependent drug exposure level in multiple animal species.

Cardiac troponin T is essential in sarcomere assembly and cardiac contractility.

Mutations of the gene (TNNT2) encoding the thin-filament contractile protein cardiac troponin T are responsible for 15% of all cases of familial hypertrophic cardiomyopathy, the leading cause of sudden death in young athletes. Mutant proteins are thought to act through a dominant-negative mode that impairs function of heart muscle. TNNT2 mutations can also lead to dilated cardiomyopathy, a leading cause of heart failure. Despite the importance of cardiac troponin T in human disease, its loss-of-function phenotype has not been described. We show that the zebrafish silent heart (sih) mutation affects the gene tnnt2. We characterize two mutated alleles of sih that severely reduce tnnt2 expression: one affects mRNA splicing, and the other affects gene transcription. Tnnt2, together with alpha-tropomyosin (Tpma) and cardiac troponins C and I (Tnni3), forms a calcium-sensitive regulatory complex within sarcomeres. Unexpectedly, in addition to loss of Tnnt2 expression in sih mutant hearts, we observed a significant reduction in Tpma and Tnni3, and consequently, severe sarcomere defects. This interdependence of thin-filament protein expression led us to postulate that some mutations in tnnt2 may trigger misregulation of thin-filament protein expression, resulting in sarcomere loss and myocyte disarray, the life-threatening hallmarks of TNNT2 mutations in mice and humans.

The metal-binding domain of IGFBP-3 selectively delivers therapeutic molecules into cancer cells.

Conventional chemotherapy for cancer has limited specificity for cancer cells. Here, we investigate the possibility of improving the selectivity of chemotherapy by coadministering targeted biological modifier peptides. We show that the 22-amino acid metal-binding transporter domain (MBD) derived from insulin-like growth factor-binding protein-3 selectively targets cancer cells. The rate of MBD uptake by cells was measured using a panel of 54 human cancer cell lines and correlated with MBD cross-linking to cell surface transferrin receptor, caveolin 1, and integrin beta. Gene array data show that MBD uptake correlates with the expression of genes associated with cellular stress-coping mechanisms commonly upregulated in cancer (nuclear factor-kappaB, Hsp-70B). MBD-tagged peptides designed to inhibit such mechanisms have cytotoxic effects on a broad range of human cancer cell lines. The discriminant validity of these peptides as potential cotherapeutic agents was investigated by comparing their cytotoxicity to cancer cell lines versus normal human cell counterparts. Synergies between these peptides and marginally cytotoxic levels of 5-fluorouracil were demonstrated. Biodistribution data from in-vivo experiments in mice and rats confirm that MBD-tagged peptides and proteins preferably localize to specific tissues, such as kidney and pancreas. Intracardial injection of CCRF-CEM T-cell leukemia or MDA-MB-435 cells into Rag-2 mice establishes disseminated disease within 7 days. Twenty-five-day subcutaneous administration of a three-peptide cocktail (3 mg/kg) in combination with 5-fluorouracil in Rag-2 mice with established CCRF-CEM leukemia significantly reduces splenomegaly and bone marrow cancer cell burden. In a similar experiment using MDA-MB-435 cells, MBD-tagged peptides reduced human cell burden in bone marrow. Taken together, these data suggest that MBD-tagged molecules can be used as highly selective chemosensitizers in the treatment of hematological and disseminated malignancies.

In vivo regulation of the chicken cardiac troponin T gene promoter in zebrafish embryos.

The chicken cardiac troponin T (cTnT) gene is representative of numerous cardiac and skeletal muscle-specific genes that contain muscle-CAT (MCAT) elements within their promoters. We examined the regulation of the chicken cTnT gene in vivo in zebrafish embryos, and in vitro in cardiomyocyte, myoblast, and fibroblast cultures. Defined regions of the cTnT promoter were linked to the green fluorescent protein (GFP) gene for in vivo analysis, and the luciferase gene for in vitro analysis. Injection of the cTnT promoter constructs into fertilized zebrafish eggs resulted in GFP expression in both heart and skeletal muscle cells reproducing the pattern of expression of the endogenous cTnT gene in the chicken embryo. Promoter deletion analysis revealed that the cis-regulatory regions responsible for cardiac and skeletal muscle-specific expression functioned in an equivalent manner in both in vitro and in vivo environments. In addition, we show that mutation of the poly-ADP ribose polymerase-I (PARP-I) binding site adjacent to the distal MCAT element in the chicken cTnT promoter produced a non-cell-specific promoter in vitro and in the zebrafish. Thus, the PARP-I transcriptional regulatory mechanism that governs muscle specificity of the chicken cTnT promoter is conserved across several chordate classes spanning at least 350 million years of evolution.