16th International HIV Drug Resistance Workshop 12-16 June 2007, Barbados

RESISTANCE TO PYRIMIDINEDIONE HIV INHIBITORS REQUIRES MULTIPLE MUTATIONS IN BOTH REVERSE TRANSCRIPTASE AND ENVELOPE

Antivir Ther. 2007; 12:S24 (abstract no. 22)

RW Buckheit Jr and KM Watson
ImQuest BioSciences, Inc. and ImQuest Pharmaceuticals, Inc., Frederick, MD, USA

BACKGROUND: The pyrimidinediones are unique small molecule inhibitors of HIV with two distinct mechanisms of action. The compounds inhibit RT at sub-nanomolar concentration levels and inhibit viral entry by binding to a novel conformational cell surface epitope at low nanomolar concentrations.

METHODS: Serial dose escalation, fixed dose serial passage and rapid resistance selection methods were employed to define resistance engendering mutations which arise upon treatment. PCR-based sequencing was performed to identify RT and Env mutations and site-directed mutagenesis employed to confirm the role of the changes in resistance. Competitive virus growth assays were performed to evaluate the effects of the mutations on viral fitness. Virus transmission and sterilization assays were performed to evaluate the ability of the pyrimidinediones to inhibit the transmission of wild-type and resistant viruses.

RESULTS: With serial passage in increasing concentrations of compound, selection for resistance engendering mutations follows a defined path consisting of the initial appearance of RT mutations (resulting in approximately 100-fold loss in sensitivity) followed by heterogeneous mutations in Env which allow the virus to escape entry inhibition (1000–10,000-fold resistance). Following the loss of entry inhibition, multiple additional changes occur in RT, several of which have no resistance-engendering effects alone but synergize with primary mutations. Passage of virus in the presence of fixed concentrations of compound yields the initial RT mutations but without loss of entry inhibition. The pyrimidinediones prevent the transmission of all mutant viruses bearing RT or Env mutations alone (albeit with 100-fold loss of sensitivity) and remain active against MDR strains. The ability of the pyrimidinediones to sterilize a culture is dependent on the particular analogue employed, suggesting minor differences in molecular structure provides differing inhibitory potential.

CONCLUSIONS: The pyrimidinediones represent excellent therapeutic and microbicide development candidates based on their dual mechanism of action, high level of potency, lack of toxicity, and the inability of viruses resistant to one of the mechanisms of action to abrogate the activity of the second mechanism. The pyrimidinediones might be expected to provide the same level of protection in patients as the combination of Sustiva and Fuzeon, but in one small molecule.

2007-06-12
22

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