The discovery of potent nonstructural protein 5A (NS5A) inhibitors with a unique resistance profile-Part†1.

Nonstructural protein 5A (NS5A) represents a novel target for the treatment of hepatitis C virus (HCV). Daclatasvir, recently reported by Bristol-Myers-Squibb, is a potent NS5A inhibitor currently under investigation in phase 3 clinical trials. While the performance of daclatasvir has been impressive, the emergence of resistance could prove problematic and as such, improved analogues are being sought. By varying the biphenyl-imidazole unit of daclatasvir, novel inhibitors of HCV NS5A were identified with an improved resistance profile against mutant strains of the virus while retaining the picomolar potency of daclatasvir. One compound in particular, methyl ((S)-1-((S)-2-(4-(4-(6-(2-((S)-1-((methoxycarbonyl)-L-valyl)pyrrolidin-2-yl)-1H-imidazol-5-yl)quinoxalin-2-yl)phenyl)-1H-imidazol-2-yl)pyrrolidin-1-yl)-3-methyl-1-oxobutan-2-yl)carbamate (17), exhibited very promising activity and showed good absorption and a long predicted human pharmacokinetic half-life. This compound represents a promising lead that warrants further evaluation.

The discovery of potent nonstructural protein 5A (NS5A) inhibitors with a unique resistance profile-Part†2.

In ongoing studies towards novel hepatitis C virus (HCV) therapeutics, inhibitors of nonstructural protein 5A (NS5A) were evaluated. Specifically, starting from previously reported lead compounds, peripheral substitution patterns of a series of biaryl-linked pyrrolidine NS5A replication complex inhibitors were probed and structure-activity relationships were elucidated. Using molecular modelling and a supercritical fluid chromatographic (SFC) technique, intramolecular H-bonding and peripheral functional group topology were evaluated as key determinants of activity and membrane permeability. The novel compounds exhibited retained potency as compared with the lead compounds, and also showed promising results against a panel of resistance viruses. Together, the results of the study take us a step closer towards understanding the potency of daclatasvir, a clinical candidate upon which the compounds were based, and to designing improved analogues as second-generation antiviral agents targeting NS5A.

Discovery of a highly potent series of TLR7 agonists.

The discovery of a series of highly potent and novel TLR7 agonist interferon inducers is described. Structure-activity relationships are presented, along with pharmacokinetic studies of a lead molecule from this series of N9-pyridylmethyl-8-oxo-3-deazapurine analogues. A rationale for the very high potency observed is offered. An investigation of the clearance mechanism of this class of compounds in rat was carried out, resulting in aldehyde oxidase mediated oxidation being identified as a key component of the high clearance observed. A possible solution to this problem is discussed.

Trypanosoma brucei glycogen synthase kinase-3, a target for anti-trypanosomal drug development: a public-private partnership to identify novel leads.

BACKGROUND: Trypanosoma brucei, the causative agent of Human African Trypanosomiasis (HAT), expresses two proteins with homology to human glycogen synthase kinase 3ß (HsGSK-3) designated TbruGSK-3 short and TbruGSK-3 long. TbruGSK-3 short has previously been validated as a potential drug target and since this enzyme has also been pursued as a human drug target, a large number of inhibitors are available for screening against the parasite enzyme. A collaborative industrial/academic partnership facilitated by the World Health Organisation Tropical Diseases Research division (WHO TDR) was initiated to stimulate research aimed at identifying new drugs for treating HAT. METHODOLOGY/PRINCIPAL FINDINGS: A subset of over 16,000 inhibitors of HsGSK-3 ß from the Pfizer compound collection was screened against the shorter of two orthologues of TbruGSK-3. The resulting active compounds were tested for selectivity versus HsGSK-3ß and a panel of human kinases, as well as in vitro anti-trypanosomal activity. Structural analysis of the human and trypanosomal enzymes was also performed. CONCLUSIONS/SIGNIFICANCE: We identified potent and selective compounds representing potential attractive starting points for a drug discovery program. Structural analysis of the human and trypanosomal enzymes also revealed hypotheses for further improving selectivity of the compounds.