Prevention of vaginal and rectal HIV transmission by antiretroviral combinations in humanized mice

<div><p>With more than 7,000 new HIV infections daily worldwide, there is an urgent need for non-vaccine biomedical prevention (nBP) strategies that are safe, effective, and acceptable. Clinical trials have demonstrated that pre-exposure prophylaxis (PrEP) with antiretrovirals (ARVs) can be effective at preventing HIV infection. In contrast, other trials using the same ARVs failed to show consistent efficacy. Topical (vaginal and rectal) dosing is a promising regimen for HIV PrEP as it leads to low systematic drug exposure. A series of titration studies were carried out in bone marrow/liver/thymus (BLT) mice aimed at determining the adequate drug concentrations applied vaginally or rectally that offer protection against rectal or vaginal HIV challenge. The dose-response relationship of these agents was measured and showed that topical tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) can offer 100% protection against rectal or vaginal HIV challenges. From the challenge data, EC₅₀ values of 4.6 μM for TDF and 0.6 μM for FTC for HIV vaginal administration and 6.1 μM TDF and 0.18 μM for FTC for rectal administration were obtained. These findings suggest that the BLT mouse model is highly suitable for studying the dose-response relationship in single and combination ARV studies of vaginal or rectal HIV exposure. Application of this sensitive HIV infection model to more complex binary and ternary ARV combinations, particularly where agents have different mechanisms of action, should allow selection of optimal ARV combinations to be advanced into pre-clinical and clinical development as nBP products.</p></div

Dose-response relationships analyzed using the median effect model.

<p>Horizontal lines represent group medians; every circular datum represents an individual sample from one of the animals (n = 3); triangles depict samples that were below the lower limit of quantitation (BLQ) of the analytical method, and values were calculated as follows: [(assay BLQ)/2]/(median tissue mass). TFV tissue concentrations following vaginal (A, blue) and rectal (B, red) dosing; TFV-DP tissue concentrations following vaginal (C, blue) and rectal (D, red) dosing.</p

Results of TDF + FTC combination (Round 3) dose ranging infection study.

<p>Results of TDF + FTC combination (Round 3) dose ranging infection study.</p

Results of broad-range (Round 1) dose ranging infection study.

<p>Results of broad-range (Round 1) dose ranging infection study.</p

Results of narrow-range (Round 2) dose ranging infection study for EC₅₀ determination.

<p>Results of narrow-range (Round 2) dose ranging infection study for EC₅₀ determination.</p

Experimental design.

<p>Humanized BLT mice were used to determine the efficacy of topically applied TDF and FTC to prevent both vaginal and rectal HIV transmission. Vaginal and rectal HIV exposures (yellow arrow) were conducted within 30 min (typically 10–15 min) following TDF and FTC application. Peripheral blood samples were collected at the indicated times (upward orange arrows) and viral load quantified by real-time PCR.</p

Dose-response curves for TDF and FTC single-drug infection studies.

<p>Plots of efficacy versus concentration of TDF or FTC dose applied prior to HIV challenge for Round 1 (broad concentration range, open circles) and Round 2 (narrow concentration range, filled circles). Dashed lines are fits to a sigmoidal dose-response (variable slope) model used to calculate EC₅₀ of TDF and FTC providing protection against vaginal and rectal HIV challenges in humanized BLT mice.</p

TFV and TFV-DP tissue concentration-time profiles following either vaginal or rectal dosing using 32 μM TDF.

<p>Median effect plots for (A) vaginal and (B) rectal drug dosing. <i>F</i>_<i>a</i>, fraction affected; <i>F</i>_<i>u</i>, fraction unaffected; <i>D</i>, dose (nM); blue circles, TDF; red circles, FTC; green circles, TDF-FTC combination. Dose response index (DRI) plots for (C) vaginal and (D) rectal dosing of both drugs in the TDF-FTC combination. <i>F</i>_<i>a</i>, fraction affected; blue circles, TDF; red circles, FTC. The DRI of 1 shown in as a broken line represents no dose reduction relative to the drugs evaluated individually. Predicted EC₅₀-EC₉₇ values for the TDF-FTC combination for (E) vaginal and (F) rectal drug dosing.</p

Novel multipurpose pod-intravaginal ring for the prevention of HIV, HSV, and unintended pregnancy: Pharmacokinetic evaluation in a macaque model

<div><p>Globally, women bear an uneven burden for sexual HIV acquisition. Results from two clinical trials evaluating intravaginal rings (IVRs) delivering the antiretroviral agent dapivirine have shown that protection from HIV infection can be achieved with this modality, but high adherence is essential. Multipurpose prevention technologies (MPTs) can potentially increase product adherence by offering protection against multiple vaginally transmitted infections and unintended pregnancy. Here we describe a coitally independent, long-acting pod-IVR MPT that could potentially prevent HIV and HSV infection as well as unintended pregnancy. The pharmacokinetics of MPT pod-IVRs delivering tenofovir alafenamide hemifumarate (TAF₂) to prevent HIV, acyclovir (ACV) to prevent HSV, and etonogestrel (ENG) in combination with ethinyl estradiol (EE), FDA-approved hormonal contraceptives, were evaluated in pigtailed macaques (<i>N</i> = 6) over 35 days. Pod IVRs were exchanged at 14 days with the only modification being lower ENG release rates in the second IVR. Plasma progesterone was monitored weekly to determine the effect of ENG/EE on menstrual cycle. The mean <i>in vivo</i> release rates (mg d^-1) for the two formulations over 30 days ranged as follows: TAF₂ 0.35–0.40; ACV 0.56–0.70; EE 0.03–0.08; ENG (high releasing) 0.63; and ENG (low releasing) 0.05. Mean peak progesterone levels were 4.4 ± 1.8 ng mL^-1 prior to IVR insertion and 0.075 ± 0.064 ng mL^-1 for 5 weeks after insertion, suggesting that systemic EE/ENG levels were sufficient to suppress menstruation. The TAF₂ and ACV release rates and resulting vaginal tissue drug concentrations (medians: TFV, 2.4 ng mg^-1; ACV, 0.2 ng mg^-1) may be sufficient to protect against HIV and HSV infection, respectively. This proof of principle study demonstrates that MPT-pod IVRs could serve as a potent biomedical prevention tool to protect women’s sexual and reproductive health and may increase adherence to HIV PrEP even among younger high-risk populations.</p></div

Pigtailed macaque TAF2-ACV-ENG-EE pod-IVR study timelines and biological sample collection points (<i>N</i> = 6).

<p>Configuration A pod-IVRs (rapid-releasing ENG) were inserted on Day 0 and replaced on Day 14 with Configuration B pod-IVRs (slow-releasing ENG). The Configuration B IVRs were removed on Day 30 and animals were euthanized on Day 34 (animal ID BB495 and DC42), Day 35 (animal ID PHz1 and PPk2), and Day 36 (animal ID PEc2 and BB0539). Blue arrows, in order of collection, blood, pH, and vaginal fluid (two Weck-Cel samples per time point—two proximal and two distal to the IVR). Green arrows, colposcopy examination (right after blood collection). Red arrows, vaginal tissues (six pinch biopsies per time point—three proximal and three distal to the IVR). Complete vaginal tracks were collected at necropsy. Pale blue and pale red arrows correspond to sample collection points with the IVR removed.</p