Chemical Probes for Drug-Resistance Assessment by Binding Competition (RABC): Oseltamivir Susceptibility Evaluation

摘要

For the treatment of influenza infections, neuraminidase (NA) inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza) are the most useful therapies. Oseltamivir is an oral prodrug that is converted by an endogenous esterase to oseltamivir carboxylate (OS, 1, Figure 1). Upon the binding of OS to NA, an induced fit of NA to reorient the Glu276 residue toward Arg224 creates a larger hydrophobic pocket for the side chain of OS. NAs can evolve resistance to OS with mutations such as H274Y to alter the hydrophobic pocket and thus, result in decreased binding with OS by several hundred fold. In contrast, zanamivir is effective for the H274Y mutant and most influenza viruses because it is structurally similar to the natural substrate and its binding does not require a conformational change of the enzyme. The worldwide surge of drug-resistant influenza viruses has prompted the need for the development of quick tests for OS susceptibility. We propose a new method, namely a resistance assessment by binding competition (RABC) assay, using labeled zanamivir as the chemical probe to identify the influenza subtypes that are resistant to OS but still sensitive to zanamivir. As illustrated in Figure 1, in the presence of OS, zanamivir-based probes can bind the OS-resistant viruses but not the OS-sensitive viruses because of competitive binding of OS.