Off target effects of rectal tenofovir gel
The antiviral tenofovir is a widely used drug for HIV prevention and treatment as an oral pill. A vaginal gel formulation of 1% tenofovir has been tested in three large clinical trials to prevent sexual HIV transmission to women. In one of these trials, CAPRISA 004, an overall 39% reduction of HIV transmission by the gel was reported, whereas the other two trials, VOICE and FACTS 001, did not find protective efficacy. Adherence to the product was low in all three trials, compromising the power of the trials to measure efficacy and emphasizing an urgent need to find topical alternatives that are more acceptable to women.
In surveys, men having sex with men (MSM) indicate that they would likely use a rectal gel if it were efficacious to prevent HIV transmission during anal intercourse. Thus, the Microbicides Trial Network (MTN) has initiated testing of rectal microbicide formulations. Between 2010 and 2011, Dr. Ian McGowan, leader of the MTN’s rectal microbicide agenda, VIDD Associate Member Dr. James Dai and Affiliate Investigator Dr. Florian Hladik carried out a phase 1 safety and acceptability trial of a rectal 1% tenofovir gel formulation (MTN 007). Sixty-five subjects from 3 US sites were randomized into one of 4 study arms: 1% tenofovir gel, 2% nonoxynol-9 (N-9) gel (a detergent and mucosal irritant included as a positive toxicity control), placebo gel, and no treatment.
Decrease in cytokine IL-10 expression in the rectal mucosa following tenofovir treatment. Rectal biopsies are from a subject treated with 1% tenofovir gel daily. Top: day 0; bottom: after 7 days of tenofovir. IL-10 is stained red and nuclei blue. Black arrows: columnar epithelial cells.
Curtesy of Florian Hladik
MTN 007 was designed to comprehensively detect possible ‘off target’ effects from rectal tenofovir treatment. The current study carried out by Hladik, Dai, VIDD Members Dr. Raphael Gottardo and Dr. Julie McElrath, and collaborators from other institutions, used a systems biology approach to analyze in detail rectal biopsies for gene expression and protein abundance differences related to tenofovir gel use. They also analyzed vaginal epithelial cells treated with tenofovir in vitro.
In rectal biopsies, once daily dosing of rectal tenofovir gel for seven days resulted in the suppression of ~10 times more genes than that of N-9 (505 vs 56, respectively). The authors found strong inhibition of interleukin (IL-10), an important immunoregulatory cytokine (see figure). Genes indicating localized leukocyte infiltration and T-cell recruitment increased, including chemokines CXCL9, CCL2 and CCL21, and cell surface markers CD7 and CCR7. Immunohistological biopsy staining correlated with transcriptional findings; an increase in infiltrating lymphocytes was confirmed by higher densities of CD3 and CD7 expressing cells.
Additionally, evidence of mitochondrial dysfunction was found in biopsies from subjects who received tenofovir. Two genes involved in mitochondrial basic processes, cellular PNPT1 and mitochondrial ATP6, were significantly down-regulated. In addition to transcriptional changes, electron microscopy in two subjects revealed that the number of mitochondria per cell decreased by more than half after seven days of treatment.
While a microbicide may be efficacious in preventing infection, it is necessary to investigate potential adverse effects on the molecular level in order to fully understand how the drug affects users and systems biology can uncover previously unidentified ‘off target’ consequences that might go unnoticed using more traditional safety assays. Although 1% tenofovir gel appeared clinically safe in multiple studies, this paper demonstrates that its effects on the rectal mucosa are pronounced and manifold. The results of the three efficacy trials render licensure of vaginal tenofovir gel unlikely, and its broad effects on the rectal mucosa raise some safety concerns for that anatomic site. A number of other drugs are being tested as topical microbicides and better alternatives to tenofovir may arise from these studies.
Hladik F, Burgener A, Ballweber L, Gottardo R, Vojtech L, Fourati S, Dai JY, Cameron MJ, Strobl J, Hughes SM, Hoesley C, Andrew P, Johnson S, Piper J, Friend DR, Ball TB, Cranston RD, Mayer KH, McElrath MJ, McGowan I. Mucosal effects of tenofovir 1% gel. Elife. 2015;4:e04525.
Further reading on MTN 007:
McGowan I, Hoesley C, Cranston RD, Andrew P, Janocko L, Dai JY, Carballo-Dieguez A, Ayudhya RK, Piper J, Hladik F, Mayer K. A phase 1 randomized, double blind, placebo controlled rectal safety and acceptability study of tenofovir 1% gel (MTN-007). PLoS One. 2013;8(4):e60147.
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