Loss of the Protease Dimerization Inhibition Activity of Tipranavir (TPV) and Its Association with the Acquisition of Resistance to TPV by HIV-1

Abstract

Tipranavir (TPV), a protease inhibitor (PI) inhibiting the enzymatic activity and dimerization of HIV-1 protease, exerts potent activity against multi-PI-resistant HIV-1 isolates. When a mixture of 11 multi-PI-resistant (but TPV-sensitive) clinical isolates (HIV 11MIX ), which included HIV B and HIV C , was selected against TPV, HIV 11MIX rapidly (by 10 passages [HIV 11MIX P10 ]) acquired high-level TPV resistance and replicated at high concentrations of TPV. HIV 11MIX P10 contained various amino acid substitutions, including I54V and V82T. The intermolecular FRET-based HIV-1 expression assay revealed that TPV's dimerization inhibition activity against cloned HIV B (cHIV B ) was substantially compromised. The introduction of I54V/V82T into wild-type cHIV NL4-3 (cHIV NL4-3 I54V/V82T ) did not block TPV's dimerization inhibition or confer TPV resistance. However, the introduction of I54V/V82T into cHIV B (cHIV B I54V/V82T ) compromised TPV's dimerization inhibition and cHIV B I54V/V82T proved to be significantly TPV resistant. L24M was responsible for TPV resistance with the cHIV C genetic background. The introduction of L24M into cHIV NL4-3 (cHIV NL4-3 L24M ) interfered with TPV's dimerization inhibition, while L24M increased HIV-1's susceptibility to TPV with the HIV NL4-3 genetic background. When selected with TPV, cHIV NL4-3 I54V/V82T most readily developed TPV resistance and acquired E34D, which compromised TPV's dimerization inhibition with the HIV NL4-3 genetic background. The present data demonstrate that certain amino acid substitutions compromise TPV's dimerization inhibition and confer TPV resistance, although the loss of TPV's dimerization inhibition is not always associated with significantly increased TPV resistance. The findings that TPV's dimerization inhibition is compromised with one or two amino acid substitutions may explain at least in part why the genetic barrier of TPV against HIV-1's development of TPV resistance is relatively low compared to that of darunavir.