Lubricant Investigation in Men to Inhibit Transmission of HPV Infection (LIMIT-HPV): design and methods for a randomised controlled trial

Use of a carrageenan-based gel had no impact on anal HPVs 16 and 18 viral loads in gay, bisexual, and other men who have sex with men

The Lubricant Investigation in Men to Inhibit Transmission of human papillomavirus (HPV) Infection randomized control trial in gay, bisexual, and other men who have sex with men (gbMSM) found that carrageenan use neither reduced acquisition of anal HPV infections nor influenced infection clearance. To investigate carrageenan's lack of protective effect, we compared the change in anal HPV16 and HPV18 viral loads following carrageenan use against placebo. We restricted our analysis to participants who completed the first four study visits and had a valid baseline sample (n = 161, 54 HIV-positive). Samples were tested for HPV detection using the linear array PCR assay. HPV16- and/or HPV18-positive samples were tested for viral load using real-time PCR. For participants who tested HPV16- (n = 29) or HPV18-positive (n = 10) at least once across visits 1-4, we compared the change in type-specific viral load between study arms using the Mann-Whitney U test. Although the median net change in HPV16 and HPV18 viral loads across visits 1-4 was higher in the treatment than placebo arm (HPV16: 0.68 vs. 0.18 copies/cell, p = 0.60; HPV18: 18.32 vs. 10.12 copies/cell, p = 0.52), these differences were not statistically significant. Results were similar by HIV status. Carrageenan use did not impact anal HPV16 or HPV18 viral loads, which may further explain its lack of protective effect in gbMSM.

Efficacy of a Carrageenan Gel in Increasing Clearance of Anal Human Papillomavirus Infections in Men: Interim Analysis of a Double-Blind, Randomized Controlled Trial

Preclinical studies have demonstrated carrageenan's anti-human papillomavirus (HPV) activity. We assessed efficacy of a carrageenan-based gel compared to a placebo gel in increasing the clearance of anal HPV infections among gay, bisexual, and other men who have sex with men (gbMSM). Of 255 enrolled gbMSM, 134 were HPV positive at baseline and had valid HPV results for ≥2 visits. Carrageenan did not differ from placebo in clearing all baseline infections (hazard ratio, 0.84 [95% confidence interval, .31-2.27]), based on having 2 consecutive HPV-negative visits following at least 1 HPV-positive visit. There were no remarkable differences for analyses at the HPV type level or by human immunodeficiency virus status.

CLINICAL TRIALS REGISTRATION

NCT02354144.

Protamine Sulfate Is a Potent Inhibitor of Human Papillomavirus Infection In Vitro and In Vivo

Human papillomavirus (HPV) infections are transmitted through sexual or other close contact and are etiologically associated with epithelial warts, papillomas, and intraepithelial lesions that may progress to cancer. Indeed, 4.8% of the global cancer burden is linked to HPV infection. Highly effective vaccines protect against two to nine of the most medically important HPV genotypes, yet vaccine uptake is inadequate and/or cost prohibitive in many settings. With HPV-related cancer incidence expected to rise over the coming decades, there is a need for effective HPV microbicides. Herein, we demonstrate the strong inhibitory activity of the heparin-neutralizing drug protamine sulfate (PS) against HPV infection. Pretreatment of cells with PS greatly reduced infection, regardless of HPV genotype or virus source. Vaginal application of PS prevented infection of the murine genital tract by HPV pseudovirions. Time-of-addition assays where PS was added to cells before infection, during infection, or after viral attachment demonstrated strong inhibitory activities on early infection steps. No effect on virus infection was found for cell lines deficient in heparan sulfate expression, suggesting that PS binds to heparan sulfate on the cell surface. Consistent with this, prophylactic PS exposure prevented viral attachment, including under low-pH conditions akin to the human vaginal tract. Our findings suggest PS acts dually to prevent HPV infection: prophylactic treatment prevents HPV attachment to host cells, and postattachment administration alters viral entry. Clinical trials are warranted to determine whether protamine-based products are effective as topical microbicides against genital HPVs.

Carrageenan as a Preventive Agent Against Human Papillomavirus Infection: A Narrative Review

ABSTRACT

Carrageenan, an extract from red algae, was identified over a decade ago as a potent inhibitor of human papillomavirus (HPV) infection in vitro. After this discovery, several studies evaluated carrageenan's anti-HPV activity in cells, experimental animals, and humans. We reviewed the evidence for carrageenan's anti-HPV activity. Studies had to be in vitro, in vivo, or in humans and report on carrageenan's anti-HPV activity. Of the 39 records identified in PubMed and 29 records in Clinicaltrials.gov, 22 records were included after screening: 8 in vitro (including 2 ex vivo), 3 in vivo, 5 in vitro and in vivo, 3 clinical studies, and 3 trial protocols. A total of 12 studies evaluated carrageenan exclusively, whereas 7 considered carrageenan combined with additional antiviral or other agents. One study protocol will evaluate carrageenan exclusively, and 2 others will evaluate carrageenan-combination products. Most clinical studies evaluated carrageenan's ability to prevent HPV acquisition (n = 4), whereas one study explored its ability to promote clearance of existing infection (defined as the absence of HPV DNA detection). Carrageenan's anti-HPV activity was observed consistently across study designs, except in 2 studies: 1 in vitro study where 2 of the HPV types tested were not significantly inhibited by carrageenan and 1 phase IIB trial in gay, bisexual, and other men who have sex with men. This review supports the premise that carrageenan, alone or in combination with other antiviral agents, might be a potential prevention strategy complementary to HPV vaccination for women.

Efficacy of a carrageenan gel in preventing anal human papillomavirus (HPV) infection: interim analysis of the Lubricant Investigation in Men to Inhibit Transmission of HPV Infection (LIMIT-HPV) randomised controlled trial

BACKGROUND

Carrageenan, a non-toxic gelling agent derived from red algae, has potent anti-human papillomavirus (HPV) activity in in vitro and animal studies. We assessed, in an interim analysis, the efficacy of a carrageenan-based gel in reducing the risk of new detections of anal HPV among gay, bisexual and other men who have sex with men (gbMSM).

METHODS

The LIMIT-HPV study (Lubricant Investigation in Men to Inhibit Transmission of HPV Infection) is a phase IIb, double-blind, placebo-controlled randomised controlled trial conducted in Montreal, Canada. gbMSM were randomly assigned (1:1) to receive a carrageenan-based or placebo gel. Participants were instructed to apply the gel to the anus, condom and/or partners' penis before and-as required-during receptive anal intercourse. Questionnaire data and anal samples were collected at 0, 1, 2, 3, 6, 9 and 12 months. We estimated new detections of anal HPV infection(s) detected via Linear Array using Cox proportional hazards models.

RESULTS

Participants recruited from February 2016 to December 2019 were randomly assigned to the carrageenan (n=127) or placebo (n=128) arm. The efficacy and safety analyses included 201 and 210 participants. The median follow-up time was 7.6 months (range: 0-28.5) in the carrageenan group and 9.3 months (range: 0-40.7) in the placebo group. The HR for new detections was 1.21 (95% CI 0.86 to 1.70): 69.4% and 65.1% new detections of HPV in the carrageenan and placebo arms, respectively. More adverse events were reported in the carrageenan (59.8%) compared with the placebo (39.8%) arm.

CONCLUSIONS

The interim analysis did not demonstrate a protective effect of carrageenan on the risk of new detections of anal HPV infection among gbMSM. Carrageenan gel use was associated with a higher proportion of adverse events. Given these findings and the (assumed) low probability that a beneficial effect would be found by the study's end, the trial was terminated as recommended by the Data Safety and Monitoring Board.

TRIAL REGISTRATION NUMBER

NCT02354144.

Assessment of the possible inhibitory effect of carrageenan in human papillomavirus DNA testing by polymerase chain reaction amplification

We assessed carrageenan's potential to inhibit human papillomavirus (HPV) DNA extraction and amplification in vaginal swab samples collected in a trial, assessing the efficacy of a carrageenan-based gel against HPV infections. Experiment #1 consisted of adding gel (carrageenan-containing or placebo) to swabs and comparing HPV DNA detection by polymerase chain reaction (PCR) to unmanipulated samples collected from the same participants. For Experiments #2 and #3, we tested vaginal samples for inhibition by addition of an internal control and amplification by real-time PCR. Experiment #4 investigated carrageenan's interference with the extraction process by assessing HPV45 detectability in undiluted and diluted HPV45 positive samples (n = 3) with carrageenan versus no gel. In Experiment #1, there was a loss of HPV positivity with the addition of carrageenan (n = 9), but none with placebo gel (n = 5). In Experiments #2 and #3, the absence of the amplified product was observed in samples from the carrageenan arm: 3.3% (1/30) and 0.5% (1/199) of samples. In Experiment #4, HPV45 was not detected in undiluted carrageenan-containing samples, but after 1/50 dilution, the same HPV45 copy number was detected. Carrageenan does not affect the DNA extraction process, and inhibition of HPV DNA amplification by carrageenan occurs infrequently.