Insights into the genetic basis for natural phenotypic resistance of human rhinoviruses to pleconaril

Recent phylogenetic analyses of the deduced amino acid sequence of the major viral capsid protein (VP1) of all human rhinovirus (HRV) serotypes revealed two distinct species within the genus: species A (75 serotypes) and species B (25 serotypes). Pleconaril is a novel capsid inhibitor of HRVs. All 75 species A serotypes and 18 of the 25 species B serotypes are susceptible to inhibition by pleconaril in cell culture. The seven resistant serotypes are HRV-4, -5, -42, -84, -93, -97 and -99. We were interested in understanding the genetic basis for phenotypic resistance to pleconaril among these naturally occurring viruses. We compared the 25 amino acids of VP1 that comprise the drug-binding pocket of susceptible and resistant species B viruses. A consistent difference was observed at two positions: the vast majority of susceptible viruses had tyrosine and valine at VP1 residues 152 and 191, respectively (Y152 and V191); all resistant viruses had phenylalanine and leucine at these positions (F152 and L191). HRV-14, a pleconaril susceptible virus, has a drug-binding pocket amino acid composition that differs from the naturally resistant HRV-5 and HRV-42 only at these two positions. To gain further insight into the role of these specific residues in natural resistance to pleconaril, we substituted the amino acids at these two positions individually and in combination in an infectious clone of HRV-14 and tested the rescued virus for susceptibility to pleconaril and virion stability. The results indicate that substitution of V191 to Leu in HRV-14 has a profound negative impact on drug susceptibility but that full resistance to pleconaril is only seen when combined with Phe at position 152 in a HRV-14 double variant (F152, L191). These data identify L191 in species B HRV as a potentially key residue in conferring significantly reduced susceptibility to pleconaril. These results may be useful in distinguishing naturally occurring viral resistance to pleconaril from treatment-emergent resistance.