Inhibition of respiratory syncytial virus fusion by the small molecule VP-14637 via specific interactions with F protein.
Human respiratory syncytial virus (RSV) is a major cause of respiratory tract infections worldwide. Several novel small-molecule inhibitors of RSV have been identified, but they are still in preclinical or early clinical evaluation. One such inhibitor is a recently discovered triphenol-based molecule, VP-14637 (ViroPharma). Initial experiments suggested that VP-14637 acted early and might be an RSV fusion inhibitor. Here we present studies demonstrating that VP-14637 does not block RSV adsorption but inhibits RSV-induced cell-cell fusion and binds specifically to RSV-infected cells with an affinity corresponding to its inhibitory potency. VP-14637 is capable of specifically interacting with the RSV fusion protein expressed by a T7 vaccinia virus system. RSV variants resistant to VP-14637 were selected; they had mutations localized to two distinct regions of the RSV F protein, heptad repeat 2 (HR2) and the intervening domain between heptad repeat 1 (HR1) and HR2. No mutations arose in HR1, suggesting a mechanism other than direct disruption of the heptad repeat interaction. The F proteins containing the resistance mutations exhibited greatly reduced binding of VP-14637. Despite segregating with the membrane fraction following incubation with intact RSV-infected cells, the compound did not bind to membranes isolated from RSV-infected cells. In addition, binding of VP-14637 was substantially compromised at temperatures of < or =22 degrees C. Therefore, we propose that VP-14637 inhibits RSV through a novel mechanism involving an interaction between the compound and a transient conformation of the RSV F protein.
Douglas
Janet L
JL
Gilead, Foster City, California 94404, USA. Janet_douglas@gilead.com
Panis
Marites L
ML
Ho
Edmund
E
Lin
Kuei-Ying
KY
Krawczyk
Steve H
SH
Grant
Deborah M
DM
Cai
Ruby
R
Swaminathan
Swami
S
Cihlar
Tomas
T
D000818:Animals; D002459:Cell Fusion; D002460:Cell Line; D024882:Drug Resistance, Viral / Q000235:genetics; D006801:Humans; D006835:Hydrazones; D008561:Membrane Fusion / Q000187:drug effects*; D009154:Mutation; D010636:Phenols / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D012136:Respiratory Syncytial Viruses / Q000187:drug effects* / Q000378:metabolism / Q000472:pathogenicity; D013777:Tetrazoles / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D006835:Hydrazones; D010636:Phenols; D013777:Tetrazoles; D014764:Viral Proteins; C423511:VP-14637