Building a Molecular Trap for a Serine Protease from Aptamer and Peptide Modules.

In drug development, molecular intervention strategies are usually based on interference with a single protein function, such as enzyme activity or receptor binding. However, in many cases, protein drug targets are multifunctional, with several molecular functions contributing to their pathophysiological actions. Aptamers and peptides are interesting synthetic building blocks for the design of multivalent molecules capable of modulating multiple functions of a target protein. Here, we report a molecular trap with the ability to interfere with the activation, catalytic activity, receptor binding, etc. of the serine protease urokinase-type plasminogen activator (uPA) by a rational combination of two RNA aptamers and a peptide with different inhibitory properties. The assembly of these artificial inhibitors into one molecule enhanced the inhibitory activity between 10- and 10,000-fold toward several functions of uPA. The study highlights the potential of multivalent designs and illustrates how they can easily be constructed from aptamers and peptides using nucleic acid engineering, chemical synthesis, and bioconjugation chemistry. By aptamer to aptamer and aptamer to peptide conjugation, we created, to the best of our knowledge, the first trivalent molecule which combines three artificial inhibitors binding to three different sites in a protein target. We hypothesize that by simultaneously preventing all of the functional interactions and activities of the target protein, this approach may represent an alternative to siRNA technology for a functional knockout.

Understanding the molecular mechanism of host-based statin resistance in hepatitis C virus replicon containing cells.

A number of statins, the cholesterol-lowering drugs, inhibit the in vitro replication of hepatitis C virus (HCV). In HCV-infected patients, addition of statins to the earlier standard of care therapy (pegIFN-α and ribavirin) resulted in increased sustained virological response rates. The mechanism by which statins inhibit HCV replication has not yet been elucidated. In an attempt to gain insight in the underlying mechanism, hepatoma cells carrying an HCV replicon were passaged in the presence of increasing concentrations of fluvastatin. Fluvastatin-resistant replicon containing cells could be generated and proved ∼8-fold less susceptible to fluvastatin than wild-type cultures. The growth efficiency of the resistant replicon containing cells was comparable to that of wild-type replicon cells. The fluvastatin-resistant phenotype was not conferred by mutations in the viral genome but is caused by cellular changes. The resistant cell line had a markedly increased HMG-CoA reductase expression upon statin treatment. Furthermore, the expression of the efflux transporter P-gp was increased in fluvastatin-resistant replicon cells (determined by qRT-PCR and flow cytometry). This increased expression resulted also in an increased functional transport activity as measured by the P-gp mediated efflux of calcein AM. In conclusion, we demonstrate that statin resistance in HCV replicon containing hepatoma cells is conferred by changes in the cellular environment.

Are statins a viable option for the treatment of infections with the hepatitis C virus?

Statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors that are widely used for the treatment of hypercholesterolemia. Besides their cholesterol-lowering effect, statins have been reported to have antiviral activity against a variety of viruses, including hepatitis C virus (HCV). Several statins inhibit the in vitro replication of subgenomic HCV replicons and also suppress in vitro RNA replication of infectious HCV. The precise mechanism of the anti-HCV activity of statins has not yet been defined. Recent studies suggest that the antiviral effect may result from the inhibition of geranylgeranylation of cellular proteins, rather than the inhibition of cholesterol synthesis. Despite the antiviral effect observed in vitro, statin monotherapy seems to be insufficient for the treatment of chronic HCV infection. However, several prospective and retrospective studies have demonstrated that the addition of statins to IFN-α and ribavirin therapy increases SVR, RVR, and EVR rates without the occurrence of additional adverse events. These clinical data, together with the excellent safety profile and low cost, suggest that statins may play a role in HCV therapy until more potent and safe direct-acting antivirals become available. This article forms part of a symposium in Antiviral Research on "Hepatitis C: next steps toward global eradication."