RESISTANCE TO A DRUG BLOCKING HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ENTRY (RPR103611) IS CONFERRED BY MUTATIONS IN GP41

A triterpene derived from betulinic acid (RPR103611) blocks human immu nodeficiency virus type 1 (HIV-1) infection and fusion of CD4(+) cells with cells expressing HIV-1 envelope proteins (gp120 and gp41), sugge sting an effect on virus entry, This compound did not block infection by a subtype D HIV-1 strain (NDK) or cell-cell fusion mediated by the NDK envelope proteins, The genetic basis of drug resistance was theref ore addressed by testing envelope chimeras derived from NDK and a drug -sensitive HIV-1 strain (LAI, subtype B). A drug-resistant phenotype w as observed for all chimeras bearing the ectodomain of NDK gp41, while the origins of gp120 and of the membrane anchor and cytoplasmic domai ns of gp41 had no apparent role, The envelope gene of a LAI variant, f ully resistant to the antiviral effect of RPR103611, was cloned and se quenced, Its product differed from the parental sequence at two positi ons in gp41, with changes of arginine 22 to alanine (R22A) and isoleuc ine 84 to serine (I84S), the gp120 being identical, In the context of LAI gp41, the I84S substitution was sufficient for drug resistance, Th erefore, in two different systems, differences in gp41 were associated with sensitivity or resistance to RPR103611, Modifications of gp41 ca n affect the quaternary structure of gp120 and gp41 and the accessibil ity of gp120 to antiviral agents such as neutralizing antibodies. Howe ver, a direct effect of RPR103611 on a gp41 target must also be envisi oned, in agreement with the blocking of apparently late steps of HIV-1 entry. This compound could be a valuable tool for structure-function studies of gp41.