Correlation Between Compartmental Tenofovir Concentrations And An Ex Vivo Rectal Biopsy Model Of Tissue Infectibility In The Rmp-02/Mtn-006 Phase 1 Study

Objectives: This study was designed to assess the dose-response relationship between tissue, blood, vaginal and rectal compartment concentrations of tenofovir (TFV) and tenofovir diphosphate (TFVdp) and ex vivo rectal HIV suppression following oral tenofovir disoproxil fumarate (TDF) and rectal administration of TFV 1% vaginally-formulated gel. Design: Phase 1, randomized, two-site (US), double-blind, placebo-controlled study of sexually-abstinent males and females.Methods: Eighteen participants received a single 300 mg exposure of oral TDF and were then randomized 2: 1 to receive a single then seven-daily rectal exposures of TFV 1% gel (40 mg TFV per 4 ml gel application) or hydroxyethyl-cellulose (HEC) placebo gel. Blood and rectal biopsies were collected for pharmacokinetic TDF and TFVdp analyses and ex vivo HIV-1 challenge.Results: There was a significant fit for the TFVdp dose-response model for rectal tissue (p = 0.0004), CD4(MMC)(+) (p<0.0001), CD4(MMC)(-) (p<0.0001), and Total(MMC) (p<0.0001) compartments with r(2) ranging 0.36-0.64. Higher concentrations of TFVdp corresponded with lower p24, consistent with drug-mediated virus suppression. The single oral treatment failed to provide adequate compartment drug exposure to reach the EC50 of rectal tissue TFVdp predicted to be necessary to suppress HIV in rectal tissue. The EC50 for CD4(MMC)(+) was within the single topical treatment range, providing evidence that a 1% topical, vaginally-formulated TFV gel provided in-vivo doses predicted to provide for 50% efficacy in the ex vivo assay. The 7-daily topical TFV gel treatment provided TFVdp concentrations that reached EC90 biopsy efficacy for CD4(MMC)(-), CD4(MMC)(+) and TotalMMC compartments.Conclusion: The TFVdp MMC compartment (CD4+, CD4- and Total) provided the best surrogate for biopsy infectibility and the 7-daily topical TFV gel treatment provided the strongest PK profile for HIV suppression.