Antiviral treatment of chronic hepatitis B virus infections: the past, the present and the future

Understanding the molecular basis of HBV drug resistance by molecular modeling

Despite the significant successes in the area of anti-HBV agents, resistance and cross-resistance against available therapeutics are the major hurdles in drug discovery. The present investigation is to understand the molecular basis of drug resistance conferred by the B and C domain mutations of HBV-polymerase on the binding affinity of five anti-HBV agents [lamivudine (3TC, 1), adefovir (ADV, 2), entecavir (ETV, 3), telbivudine (LdT, 4) and clevudine (l-FMAU, 5)]. In this regard, homology modeled structure of HBV-polymerase was used for minimization, conformational search and induced fit docking followed by binding energy calculation on wild-type as well as on mutant HBV-polymerases (L180M, M204V, M204I, L180M+M204V, L180M-M204I). Our studies suggest a significant correlation between the fold resistances and the binding affinity of anti-HBV nucleosides. The binding mode studies reveals that the domain C residue M204 is closely associated with sugar/pseudosugar ring positioning in the active site. The positioning of oxathiolane ring of 3TC (1) is plausible due the induced fit orientation of the M204 residue in wild-type, and further mutation of M204 to V204 or I204 reduces the final binding affinity which leads to the drug resistance. The domain B residue L180 is not directly close ( approximately 6A) to the nucleoside/nucleoside analogs, but indirectly associated with other active-site hydrophobic residues such as A87, F88, P177 and M204. These five hydrophobic residues can directly affect on the incoming nucleoside analogs in terms of its association and interaction that can alter the final binding affinity. There was no sugar ring shifting observed in the case of adefovir (2) and entecavir (3), and the position of sugar ring of 2 and 3 is found similar to the sugar position of natural substrate dATP and dGTP, respectively. The exocyclic double bond of entecavir (3) occupied in the backside hydrophobic pocket (made by residues A87, F88, P177, L180 and M204), which enhances the overall binding affinity. The active site binding of LdT (4) and l-FMAU (5) showed backward shifting along with upward movement without enforcing M204 residue and this significant different binding mode makes these molecules as polymerase inhibitors, without being incorporated into the growing HBV-DNA chain. Structural results conferred by these l- and d-nucleosides, explored the molecular basis of drug resistance which can be utilized for future anti-HBV drug discovery.

Recombinant interferon-alpha2b poly(lactic-co-glycolic acid) microspheres: pharmacokinetics-pharmacodynamics study in rhesus monkeys following intramuscular administration

AIM

Investigation into pharmacokinetic-pharmacodynamic properties of interferon- alpha (IFN-alpha)2b-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres (MS) in rhesus monkey primates.

METHOD

IFN-alpha2b was loaded with biodegradable PLGA with 3 inherent viscosities using a double emulsion and solvent evaporation method. The particle size, surface morphology, and in vitro release profiles were investigated. Two groups of rhesus monkeys (n=3) were injected intramuscularly with either 3 MIU/kg commercial IFN-alpha2b lyophilized powder or IFN-alpha2b-loaded PLGA microspheres (inherent viscosity of 0.89 dL/g). In vitro release was determined by Lowry protein assay. The serum IFN and neopterin levels were determined by the enzyme-linked immunosorbent assay (ELISA) method to evaluate biological activity of the microspheres in rhesus monkeys.

RESULTS

The IFN-alpha2b microspheres with 3 inherent viscosities (0.39, 0.89, and 1.13 dL/g) were entirely spherical and had a smooth surface. The average diameter of each type was 45.55, 81.23, and 110.25 microm, respectively. The in vitro release was 30 d. The pharmacokinetic-pharmacodynamic properties between the IFN-alpha2b microspheres and IFN-alpha2b lyophilized powder were significantly different (P<0.05).

CONCLUSION

The drug residence time for the IFN-alpha2b of the PLGA microsphere with an inherent viscosity of 0.89 dL/g in plasma significantly increased and had a longer time of biological effects in rhesus monkeys following intramuscular administration.

Antivirals: current state of the art

Most of the antiviral agents that have been approved, and are currently used in the treatment of virus infections, are targeted at HIV, HBV, herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV) and HCV or influenza virus. Additional compounds for HIV, HBV, HSV, VZV, CMV, HCV, influenza virus and several other viral infections, for example poxvirus (e.g., variola, vaccinia and monkeypox), respiratory syncytial virus, hemorrhagic fever virus (e.g., Lassa, Rift Valley and Ebola) and enterovirus (e.g., polio, Coxsackie and echo), are still in the experimental stage, that is, under clinical or preclinical development.