Phase I dose volume escalation of rectally administered PC-1005 to assess safety, pharmacokinetics, and antiviral pharmacodynamics as a multipurpose prevention technology (MTN-037)

Abstract

Background.

On demand, topical PrEP is desired by those preferring episodic, non-systemic PrEP. PC-1005 gel (MIV-150, zinc, and carrageenan) exhibits in vitro antiviral HIV-1, HPV, and HSV-2 activity, attractive for a multipurpose prevention technology (MPT) candidate. We evaluated the safety, pharmacokinetics, and antiviral effect of rectally-applied PC-1005.

Methods.

HIV-uninfected adults received a series of three rectal PC-1005 doses - 4, 16, and 32 mL separated by 2-week washout periods. Following each dose, plasma, rectal fluid and tissue, and vaginal fluid were collected over 48 h.

Results.

Thirteen adults enrolled; 12 completed all 3 doses. All 13 adverse events reported were Grade 1 or 2; five were judged study drug-related. Plasma MIV-150 peaked 1–2 h after dosing with a median peak concentrations range of 0.07–0.23 ng/mL and median half-life range of 4.9–7.4 hours across dose volumes; median concentrations were below assay quantitation limits (BLQ) 24 h after dosing. Rectal Tissue MIV-150 peaked 0.5–1 hours after dosing at 1.4 ng/g (ng/mL) (0.8, 1.9), 46.0 (30.7, 831.0), and 79.7 (11.9, 116.0), respectively, after each dose volume; median tissue concentrations were BLQ beyond 5 hours for all doses. All vaginal fluid samples were BLQ. Ex vivo antiviral assays showed 5 h of antiviral HPV and HSV effect, but no anti-HIV activity.

Conclusions.

MIV-150 rectal tissue concentrations were below the 100 ng/g target concentration and transient. Ex vivo assays demonstrated antiviral HSV and HPV effects, but not against HIV. PC-1005 requires a more potent antiviral and longer-lasting formulation for further consideration as an MPT candidate.

Introduction

Daily oral tenofovir and emtricitabine tablets, monthly vaginal microbicide ring-eluting dapivirine (DPV), and bi-monthly intramuscular injections of cabotegravir (CAB) provide safe and highly effective HIV pre-exposure prophylaxis (PrEP) for populations at risk of HIV acquisition ^1–6. Numerous long-acting strategies are currently under clinical development to provide options that enhance patient acceptance. PrEP choices provide options to meet unique desires and needs of each person at risk of HIV acquisition; many population level health benefits of choice have been amply demonstrated with contraceptive product choice ^7,8.

On demand, rectally-applied PrEP – providing protection only when (prior to sex) and where (rectally) one needs it – is commonly desired in a substantial portion of persons whose primary HIV acquisition risk is receptive anal sex ^9–15. Such a product minimizes the need for continuous and systemic presence of active drug. Given microbicide action at their site of application, the versatility of one product suitable for both rectal and vaginal application may provide added adherence benefits^16,17. Protection against other sexually transmitted viral infections (STIs) acquired through receptive anal sex is desirable. Human papillomavirus (HPV) and herpes simplex virus type 2 (HSV-2) infections have their own morbidities and each increase susceptibility to HIV infection^18–20. Therefore, a multipurpose prevention technology (MPT) could protect against all three viruses and have a synergistic protective effect against HIV^16,17. Neither the oral 2–1-1 IPERGAY regimen (on demand, but systemic) nor the vaginal DPV ring (topical, but not rectal) meet all the desired characteristics described; though they prove the effectiveness of on demand and topical PrEP products, respectively.

PC-1005 is a candidate MPT gel for the prevention of sexually transmitted viral infections (STIs), HIV, HSV, and HPV. Formulated for rectal and vaginal use, PC-1005 contains MIV-150 (phenethylthiazolylthiourea non-nucleoside reverse transcriptase inhibitor) and zinc acetate (selective antiviral agent [HIV and HSV]) formulated with carrageenan (a gelling agent with anti-HPV activity). Preclinical studies have shown PC-1005 and its components to be effective against HIV, HPV, and HSV-2^21–28. PC-1005 was safe and well tolerated in a phase 1 trial when applied vaginally once daily²⁹. These data suggest a potential role for PC-1005 as an on-demand, topical microbicide MPT to reduce HIV, HSV, and HPV acquisition risk. Our study objective was to evaluate the safety, acceptability, pharmacokinetics (PK), and pharmacodynamics (PD) of rectally-applied PC-1005.

Materials and Methods

Overall Design

MTN-037 was a phase 1, open label, sequential dose/volume escalation trial designed to characterize the safety, PK, PD, and acceptability of a single rectal PC-1005 dose administered at three sequential gel volumes (4 mL, 16 mL, and 32 mL). Eligible research participants were administered each of three PC-1005 volumes, followed by endpoint assessment over 48-hours; a two-week washout period separated the dosing assessment periods (Figure 1).

Figure 1.

Study schema. Each participant was to receive 3 rectal doses of PC-1005 gel at increasing volumes of 4, 16, and 32 mL with a washout period between doses. *PK sampling 48 h after application – participants were randomized to only one 48 h post-dose sampling visit (4a, 6a, or 8a).

Institutional review boards at the two clinical research sites – Birmingham, AL, and Pittsburgh, PA – approved the study. NIH/NIAID holds the Investigational New Drug application on file with the US Food and Drug Administration. Potential research participants provided written informed consent prior to full screening activities. The study was conducted between August 2018 and January 2019.

Study Product

PC-1005 gel is a translucent gel, moderately hyperosmolar in the colorectum (447mOsmol/kg), and contains three primary constituents: MIV-150 (50 μM, 18.4 ug, 0.002% w/w), zinc acetate dihydrate (13.7 mM, 0.894 mg, 0.3% w/w), and carrageenan.

Study Population

Eligible study participants were HIV-negative cis- or transgender men and women in good health, conveyed a history of receptive anal intercourse (RAI), and were 18 years or older. Research participants agreed to remain abstinent for the 5-month study, and participants of childbearing potential agreed to use effective contraception throughout the study. Eligible participants had no current or recent (past 3 months) diagnoses or treatment of anogenital STIs or current STI requiring treatment, no recent gynecologic, genital, or rectal procedures (≤2 months) or rectal biopsies (≤one week), had not received HIV PrEP (one month) or post exposure prophylaxis (≤3 months), and agreed to abstain from using anticoagulants or rectally-administered products. The sample size of 12 research participants provides preliminary safety and PK/PD data in an early Phase I study.

Procedures

All doses were administered in the clinic by study personnel followed by endpoint assessments (safety, acceptability, PK, PD) over 48 h with at least a two-week washout between doses. Blood plasma was collected from each participant before each dose and at 1, 2, 3, 4, 5–6, and 24 h after dosing. Participants were randomized 1:1:1:1 to one sampling time window: 0.5–1 hour, 1.5–3 hours, 3.5–5 hours, or 24 hours after dosing. Within each sampling window, matrices were collected sequentially as follows: rectal fluid (swab and sponge), rectal lavage effluent (following enema administration), rectal tissue (biopsy forceps during flexible sigmoidoscopy), and vaginal fluid (swab, as applicable). During flexible sigmoidoscopy, six biopsies were taken at pre-dose (baseline) and approximately nine biopsies were taken at post-dose times as assigned, all at 10–15 cm above the anal verge. Participants were randomly assigned (1:1:1) to provide a 48-hour sample of blood plasma, rectal fluid, rectal lavage effluent, rectal tissue, and vaginal fluid (if applicable) after only one of the three doses. Randomization was stratified to incorporate 1–2 participants of each sex assigned at birth at each of the four sampling windows and to incorporate two participants of each sex at 48 h for each dose/volume.

Safety Assessments

Safety was assessed at each visit using medical history, directed physical examination, and laboratory testing. Adverse events (AEs) were graded and assessed for attribution to study drug using the Division of AIDS Table for Grading the Severity of Adult and Pediatric Adverse Events, Corrected Version 2.1, July 2017, and Addenda 2 and 3 (Male Genital [Dated November 2007] and Rectal [Clarification Dated May 2012] Grading Tables for Use in Microbicide Studies) (http://rsc.tech-res.com/clinical-research-sites/safety-reporting/daidsgrading-tables). An exploratory objective, rectal biopsy specimens were stained with hematoxylin and eosin, and evaluated using a qualitative injury and inflammation score previously described³⁰.

Pharmacokinetics

An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for determination of plasma MIV-150 and MIV-160 (internal standard) was developed and validated on a Waters H-Class UPLC coupled with a Waters Xevo TQS Micro (performed at University of Colorado). Analyte extraction from the plasma matrix used liquid-liquid extraction with methyl tert-butyl ether. Chromatographic separation used a Waters Acquity UPLC BEH C18 1.7 μm, 2.1×50 mm column with analyte elution under isocratic conditions with a high organic wash over a 4.5-minute run time at 0.500 mL/min flow rate with two mobile phases: 43% (95:5 acetonitrile: water + 0.1% formic acid) and 57% (H2O + 0.1% formic acid). A separate mobile phase (99:1 acetonitrile: water + 0.1% formic acid) helped clean the system to prevent carryover. Analyte detection and quantitation used protonated electrospray ionization (ESI+) and MS/MS detection. Precursor/product transitions (m/z) in the positive ion mode were 369.1/224.1 and 343.1/198.1 ions for MIV-150 and MIV-160, respectively. The assay analytical range was 0.010 ng/mL to 500ng/mL when 200 μL human plasma was extracted.

Development and validation of assays for non-plasma samples were performed for analysis using the validated plasma assay. Rectal tissue samples were weighed and homogenized in plasma: collagenase solution. Rectal sponges and vaginal swabs were weighed before and after collection to obtain the collected fluid weight. Sponges and swabs were extracted with blank human plasma (absent study drug). The non-plasma matrices required further dilution with human plasma to fall within the assay’s analytical range, which resulted in a plasma matrix (>99%) for which the validated MIV-150 plasma assay was used. The MIV-150 median sample lower limit of quantitation (LLOQ) was 0.709 ng/g (ng/mL) in rectal tissue, 1.02 ng/mL in rectal fluid, and 0.204 ng/mL in vaginal fluid.

PK data analysis involved concentration-time plots for all matrices. Non-compartmental PK parameters (peak concentration [C_max], time to C_max [T_max], concentration 24 h after dosing [C₂₄], area under the concentration-time curve to last concentration [AUC_last], and half-life) for plasma MIV-150 were estimated using Phoenix WinNonlin software (v 8.3 Certara, Cary, NC). For sparsely sampled rectal tissue and fluid, C_max and C₂₄ were conservatively estimated using the median concentration within each matrix-sample time window identified for T_max and the 24-hour sampling time, respectively. Crude estimates of the time after dosing until passing below the EC₅₀ (50% of maximal effective [inhibitory] concentration) were calculated using the terminal half-life and rectal tissue MIV-150 concentration during the first 5 h, accounting for time elapsed prior to each available concentration for this estimate. We have previously shown that MIV-150 has an IC₅₀ and IC₉₀ of 0.9 nM and 1.9 nM, respectively, against SHIV-RT in PBMCs³¹.

Anti-HIV Pharmacodynamics

For each participant’s scheduled biopsy time, three freshly collected colorectal biopsies were placed in tissue culture media and challenged with 10⁴ TCID₅₀ HIV for 2 hours; then, 0.5 mL supernatant was collected (then media replaced) on day 3, 7, 10, and 14 (completed at each clinical site lab)^32,33. The unit of analysis was the median (of three) log₁₀ cumulative 14-day supernatant HIV p24 antigen concentrations using well-plate volume-correction and biopsy-weight adjustment (performed at University of Pittsburgh). p24 assay LLOQ was 30 pg/mL with LLOQ/2 (15 pg/mL) imputed for calculations. For inclusion in the analysis, each biopsy required all four supernatant samples and each sample time required at least two biopsy results. Data were plotted and summarized using descriptive statistics with assessment of change from the pre-dose baseline over time, and the log₁₀ MIV-150 (concentration) vs. antiviral p24 (response) relationship was estimated using inhibitory E_max modeling using SAS (version 9.4, Cary, NC) and WinNonlin (Phoenix v. 8.3, Certara, Cary, NC).

Anti-HPV Pharmacodynamics

The anti-HPV activity of enema effluents from six participants (Pittsburgh site only) was evaluated using the HPV16 PsV luciferase assay³⁴ to estimate EC₅₀ based on rectal enema effluent dilutions (performed at Population Council’s Center for Biomedical Research). Different dilutions of enema effluents were challenged with HPV16 PsV (5×105 copies) on HeLa cell monolayers and incubated for 72 h at 37°C, 5% CO₂ and 98% humidity before performing the luciferase assay as previously described. EC₅₀ values were estimated using curve-fitting analysis with GraphPad Prism (version 9.0.0, La Jolla, CA). The Mann Whitney test (p < 0.05) was used to compare the antiviral activity of baseline and different rectal enema effluent collection times.

Anti-HSV Pharmacodynamics

The anti-HSV activity of enema effluent was evaluated using an HSV-2 plaque reduction assay (performed at Population Council’s Center for Biomedical Research)³⁴. For this purpose, rectal enema effluents were incubated with HSV-2 (106 PFU/mL) for 30 min at 37°C °C, 5% CO₂ and 98% humidity, and the virus in each sample was titrated using the plaque assay. All rectal enema dilutions and assay virus and cell controls were tested in triplicate and processed side-by-side under the same conditions as the rectal enema samples. HSV EC₅₀ values and antiviral activity compared to baseline were estimated as for HPV. Spearman’s rank correlation was used to correlate anti-HPV and anti-HSV activity (GraphPad Prism v9.0.0).

Results

Participant characteristics

Across both study sites, 16 people were screened and 13 participants were enrolled, including 7 men and 6 women (sex assigned at birth). Twelve participants (92%) completed the study, receiving all three doses. One participant received only the 4 mL dose before being lost to follow-up but was included in all analyses. The median age at baseline was 34 years (range 20 – 50). Six participants identified as white, five as black, and two as mixed-race. One participant identified as of Hispanic ethnicity. The median baseline body mass index was 30.6 kg/m² (range: 22.9 – 46.3).

Safety

Six participants reported 13 AEs, all were Grade 1 (10 AEs) or 2 (3 AEs). Of these, five grade 1 AEs in three participants were deemed related to study product: diarrhea (4 mL), abdominal distension (4 mL), abdominal pain (4 mL and 32 mL), and constipation (4 mL). Three Grade 1 AEs occurring before dosing were deemed not related to study product. Five post-dose AEs were judged not related: hemorrhoids (grade 1), elevated AST (grade 2), vertigo (grade 2), and elevated blood creatinine (occurring twice in the same participant: Grade 2, then Grade 1). There were no AE-related product holds or discontinuations.

Histology

Of the 49 biopsies assessed after product dosing, 8 biopsies showed a worsening in scoring when compared to the pre-dose baseline. These were observed at nearly all doses and sample times without pattern.

Pharmacokinetics

Rectal application of PC-1005 gel yielded quantifiable concentrations of MIV-150 in plasma in all participants at all dose volume levels, peaking one or two hours after dosing; all dose-volume group medians fell below the LLOQ by 24 h (Figure 2). The 4 mL dose volume plasma concentrations were consistently below the 16mL and 32 mL dose volumes, which overlapped with each other. When progressing from dose volumes of 4 mL to 16 mL (4X increase) and 16 mL to 32 mL (2x increase), the median plasma MIV-150 peak concentration (C_max) increased only 2.6-fold and 1.2-fold, respectively, while area-under-the-curve (AUC_last) increased 2.6-fold and 1.1-fold, respectively, indicating non-dose proportionality (Supplemental Table 1). Plasma MIV-150 terminal half-life ranged from 4.9 to 7.4 hours across dose volumes.

Figure 2. Median (IQR).

Plasma MIV-150 concentration (pg/mL) over time by PC-1005 gel volume administered rectally. Samples with concentration below the LLOQ (BLQ) are imputed with the value of LLOQ/2 for display purposes.

Rectal tissue homogenate MIV-150 concentrations were quantifiable by the earliest, 0.5–1-hour, sampling window in all participants and all dose volumes (Figure 3, Supplemental Table 1). In the next sampling period, 1.5 to 3-hours, rectal tissue MIV-150 concentrations begin falling below the LLOQ and, in the 3.5 to 5-hour period, a majority of samples (6 of 10) are below the LLOQ. By the 24-hour sampling window, none of the samples are quantifiable. As a convenient reference, the median assay LLOQ, 0.7 ng/g is narrowly above the MIV-150 EC₅₀, 0.3 ng/g (equivalent to 0.3 ng/mL based on in vitro cell-based anti-HIV assays³⁵).

Figure 3.

MIV-150 rectal tissue homogenate concentration (ng/g) by hours after dosing. LLOQ indicated is the study median LLOQ (0.7 ng/g; each individual LLOQ varies with biopsy weight); BLQ samples are imputed as LLOQ/2 for display purposes. Two values in the 3.5 to 5-hour sample window are below the median LLOQ by virtue of having a large biopsy mass, but are, in fact, quantifiable in the tissue MIV-150 assay.

Rectal fluid MIV-150 concentrations remained far above the LLOQ through the first 5 hours after dosing and ranged very widely within each dose volume group from ~100-fold (16 mL and 32 mL) to 800-fold (4 mL) (Supplemental Figure 1). Rectal fluid MIV-150 remained quantifiable in 44% (4/9) of participants sampled at 24 h and 8% (1/12) at 48 h (Supplemental Table 1).

In plasma and rectal matrices, median C_max and AUC_last values consistently increased when progressing from 4 mL to 16 mL to 32 mL doses, although not proportionally, and across matrices from plasma (lowest) to rectal tissue (middle) to rectal fluid (highest) (Supplemental Table 1). Half-life estimates were not possible, except for plasma.

Vaginal fluid MIV-150 was undetectable in all 6 female participants at all time points and all dose volumes, limiting comparisons to other matrices. Conservatively, using the vaginal fluid LLOQ as the upper limit of MIV-150 concentrations in vaginal fluid, rectal fluid and tissue MIV-150 concentrations were at least 3.1-log₁₀ and 2.5-log₁₀ higher, respectively.

Pharmacodynamics

HIV p24 concentrations after PC-1005 dosing were not statistically different than pre-dose values for any sample window or dose volume (including sequential pooling of sampling windows, dose volumes, or both) (p<0.10 (Figure 4.A). MIV-150 concentration versus log₁₀ cumulative weight-adjusted p24 indicated neither linear nor multi-component model-based anti-HIV concentration-response (Figure 4.B).

Figure 4.

PC-1005 anti-HIV pharmacodynamics after ex vivo rectal biopsy explant HIV challenge. Antiviral measures are Log10 p24 antigen (median, cumulative, volume-corrected, biopsy weight-adjusted). Left Panel. Concentration-time relationship displayed as Log10 p24 change from baseline (dashed line, 0) over hours post dose. Right Panel. Concentration-response displayed as Log10 p24 versus rectal tissue MIV-150 concentration (log scale).

HPV 16 PsV assay in rectal fluid showed EC₅₀ values between 0.16 and 2.4×10–5 (dilution factor). EC₅₀ values of enema effluents collected at early (0.5–5 hours) time points post PC-1005 gel application were significantly lower than enema effluents collected at baseline (p<0.04; Figure 5.A).

Figure 5.

Rectal enema effluents were collected at baseline, early (0.5–5 hours) and late (24 hours) time points. The anti-HPV activity and anti-HSV-2 activity were tested using the luciferase assay (Panel A) and plaque reduction assay (Panel B), respectively. Panel A shows the anti-HPV half maximal effective doses versus the rectal enema effluent collection time. EC₅₀ values from enema effluents collected at early (0.5–5 hours) time points post PC-1005 gel application were significantly lower than enema effluents collected at baseline (p<0.04). Panel B shows the HSV titer after preincubation with rectal enema effluents versus the collection time. The anti-HSV-2 activity was significantly different between enema effluents collected at early time points (0.5–5 hours) post gel application and those collected at baseline (p<0.02). Panel C indicates correlation between anti-HPV and anti-HSV-2 activity (Spearman r=0.7409; p<0.0001).

The HSV-2 assay in rectal fluid resulted in 66–87% decrease in HSV-2 plaque-forming units. The anti-HSV-2 activity was significantly different between enema effluents collected at early time points (0.5–5 hours) and those collected pre-dose (p<0.02; Figure 5.B). Anti-HPV activity correlated with anti-HSV-2 activity (Spearman r=0.74; p<0.0001; Figure 5.C).

Acceptability

Participants rated overall gel acceptability 7.17 on a scale of 1–10 and a high percentage found all three dose volumes very comfortable or comfortable (dose 1 = 91.7%; dose 2 = 91.7%; dose 3 = 83.3%). Detailed acceptability results were previously reported³⁶.

Discussion

Male and female research participants receiving PC-1005 gel rectally in escalating gel volumes of 4, 16, and 32 mL reported a high degree of acceptability and dosing comfort³⁶, with only a few mild attributable adverse effects. The extremely low picomolar plasma MIV-150 C_max, 3–4 log₁₀ below the rectal tissue C_max helps explain the excellent safety profile. A prior study dosed 4mL of PC-1005 once daily for 14 days per vagina and also indicated a well-tolerated and acceptable gel product²⁹, though 41% of the women recommended reducing the gel volume. Acceptability of a larger gel volume applied rectally in our study may be due to the far greater capacity of the lower gastrointestinal tract to accommodate product volume when compared to the vagina. Carballo-Dieguez, et al., previously reported an upper limit to rectal gel volume, using a hypo-osmolar personal lubricant, FemGlide, in which half of study participants found 50 mL unacceptable and 17% found 35 mL unacceptable³⁷.

The pharmacodynamic effect of PC-1005 varied among the three viruses assayed. The suppressive effects of rectal fluid on HPV were rapid, achieving a maximal two-log₁₀ suppression within one hour, though returning to within one-log₁₀ by 24-hours. The one-log₁₀ HSV suppression was similarly rapid and lasted less than 24 h. This significant antiviral activity at early time points corresponds to findings of HPV and HSV-2 protection in cell-based assays and mouse viral challenge models^26,27,34,35. Carrageenan inhibits HPV infection by interfering with viral entry into host cells ²⁸. Similarly, carrageenan and zinc salts exhibit virucidal activity against HSV and interfere with the early steps of viral replication ³⁵. Therefore, it is expected that the carrageenan and zinc found in the rectal fluid will play a key role in impeding both viruses from entering the target epithelial cells. The carrageenan EC₅₀ values against HPV and HSV were in the low ng/mL range^26,27,34,35. The cell-based assays that we used are widely accepted to test compounds that interfere with viral entry into target cells, and the use of rectal fluid may add native antiviral factors. However, these ex vivo assays of rectal fluid may not account for the biological factors present in more complex human tissue.

In contrast, no HIV suppression compared to baseline was evident. This may be because MIV-150 rectal tissue concentrations either failed to exceed or only transiently exceeded the in vitro EC₅₀. In addition, MIV-150 and Zn may also have been poor candidates for the ex vivo HIV explant challenge assay due to loss of MIV-150 and Zn from biopsies into culture media during a two-hour HIV incubation as has previously been reported for maraviroc ³⁸. Furthermore, ex vivo tissue challenge does not account for any carrageenan effect in the colonic lumen. Prior macaque rectal SHIV challenge studies indicated a protective effect of PC-1005, although not as robust as vaginal SHIV challenge studies³⁹.

The PK data also indicate limitations for PC-1005 as a candidate MPT. The rectal tissue absorption is poor with brief duration. Large PK variability and lack of dose-proportionality complicate dose selection for advanced studies. Increasing rectal gel volume to increase tissue concentration and antiviral effect duration may be more limited than with oral formulations. For example, as the dose volume increases, there is proximal luminal redistribution which may increase systemic absorption with increased colonic surface area of drug exposure, but no increase in colonic luminal or rectal tissue concentration. Volumes above a certain amount are poorly tolerated and, at some volume, luminal distention may induce reflex colonic contractions and expulsion of gel contents ³⁷.

MIV-150 concentrations were detected in rectal tissue soon after dosing, but remained above the HIV EC₅₀ in less than half of participants by the 3.5 to 5-hour sample window. This rectal tissue PK pattern is comparable to dapivirine gel applied rectally ^40,41. The antiviral effect in rectal fluid, which includes any potential carageenan effect, lasts longer for HSV (5 h) and HPV (24 h). In contrast, rectal tissue tenofovir (TFV) diphosphate concentrations and ex vivo anti-HIV effects persist for several days after a single dose of a TFV douche or TFV alafenamide-containing fast-dissolving rectal insert ^42,43. While the duration of antiviral effect sufficient to provide pre-exposure prophylaxis is uncertain for any of the three viruses and likely depends on the poorly understood viral particle clearance following an exposure, an antiviral effect of less than one day would require dosing more than once a day to provide a high level of protection, unsuitable for single dose on demand use. The highly effective oral on demand (2–1-1) F/TDF requires dosing for three consecutive days. Additionally, with no detectable drug in vaginal fluid – a consistent finding for MIV-150 (this study), dapivirine⁴⁰, and tenofovir⁴⁴ – it is unlikely that a rectal microbicide will provide protection against vaginal virus acquisition.

Conclusions

PC-1005 gel demonstrated safety and acceptability after a single rectal dose across three different gel volumes. Suppressive antiviral activity of one-two log₁₀ for both HPV and HSV in rectal fluid occurred rapidly and lasted for part or all of one day, although anti-HIV activity could not be shown. MIV-150 rectal tissue concentrations were highly variable, not dose-proportional, and lasted only a few hours with negligible plasma or vaginal fluid exposure. To advance PC-1005 as a viable on-demand rectal MPT, it will be necessary to modify the formulation to achieve more sustained antiviral effects to avoid repeated dosing for HSV and HPV protection and to achieve efficacy against HIV.

Data Availability Statement:

Data available on request from the authors