The Centre for the AIDS Programme of Research in South Africa (CAPRISA) 004 trial [1▪▪] was a turning point for the biomedical prevention of HIV among women. After years of research — in which various vaginally applied products showed no effect or an undesirable effect on HIV acquisition — CAPRISA 004 served as a proof of concept that a topical gel can protect women. The gel's active agent, 1% tenofovir, is an antiretroviral (ARV) drug that interferes with a key stage in the replication cycle of HIV. Almost all current trials of topical products for HIV prevention involve ARV drugs, which are now considered to be among the most promising agents for topical (and oral) preexposure prophylaxis (PrEP).
In the wake of the CAPRISA 004 trial, clinical trials and preclinical studies are actively exploring the relative merits of ARV drugs, the acceptability of different delivery strategies and the biological and behavioral factors that may alter the effectiveness of topical HIV-prevention products. This article reviews some of the recent clinical research on the use of vaginal products for HIV prevention.
ANTIRETROVIRAL CANDIDATES FOR TOPICAL CHEMOPROPHYLAXIS
Current candidates for topical PrEP include ARV drugs that target different stages of the HIV life cycle, notably host cell entry and reverse transcription. Although the reverse transcriptase inhibitor tenofovir has received the most attention for ARV-based topical PrEP [2▪,3,4,5▪,6], several other ARVs are also under consideration, including four other reverse transcriptase inhibitors, emtricitabine, dapivirine (TMC-120), UC781 and MIV-150 [7,8,9▪,10,11]. Maraviroc, a CCR5 coreceptor antagonist that prevents the entry of HIV into host cells, is also being explored for topical PrEP [12,13].
Researchers are also looking at the prospects of combining more than one ARV drug in a vaginal delivery system, an approach that may offer an efficacy advantage by targeting more than one event in the viral replication cycle . This tactic should also present a greater barrier to the development of resistant viruses . Various combinations are being considered for gels (tenofovir and emtricitabine , and tenofovir and dapivirine ), rings (dapivirine and maraviroc ) and films (tenofovir and maraviroc ). Most ARV drugs (alone or in combination) for topical use are in phase I and II trials or in preclinical development except dapivirine, which is now being investigated in phase III trials (see below).
Compared with oral formulations, topical products should be able to deliver higher concentrations of a drug in the female genital tract — which is often the initial site of male-to-female HIV acquisition. Recent studies of oral and vaginal tenofovir formulations found that the levels of tenofovir diphosphate (the active form of tenofovir) were 1000 times greater in vaginal fluids and vaginal tissue samples when the drug was delivered vaginally [19▪,20]. Nevertheless, the minimum concentration of a drug needed to prevent HIV acquisition has yet to be determined [21▪].
Various dosing strategies — coitally dependent and independent — are being explored. Any dosing schedule must consider the pharmacokinetics of the active ingredient and its tolerance for incomplete adherence by the user [22▪]. Early trials with gels typically used a coitally dependent application, which has the advantage of providing a high dose of the product at the time of potential exposure to HIV. The disadvantage is that the user will need to anticipate her sexual encounters and seek privacy to apply the product if she does not want to disclose her use of an HIV-prevention gel. The CAPRISA 004 team provided some flexibility to this strategy by instituting a ‘BAT-24’ regimen — one dose up to 12 h Before sex and one dose within 12 h After sex, but no more than Two doses in 24 h [1▪▪].
A coitally independent approach, involving the daily administration of a gel is another dosing option. The Microbicide Trials Network (MTN) used this approach in the MTN 003 trial (see below). A coitally independent approach can also involve sustained drug delivery, such as by the use of a vaginal ring that is replaced once every few weeks.
Delivery systems must allow the active drug to remain on the surfaces of the vaginal walls and cervix for an adequate (yet currently undetermined) amount of time. It is critical that neither the active drug nor the delivery system cause mucosal toxicity, which may increase the risk of HIV [23,24]. The original formulation of tenofovir gel (used in the MTN 003 and CAPRISA 004 trials) is hyperosmolar, which is associated with mucosal irritation and tissue damage. For this reason, the gel was reformulated for rectal use with a reduced glycerine content, which improved epithelial integrity in vitro[25▪▪]. The newly formulated tenofovir gel can be used as a dual compartment (vaginal and rectal) product.
The design of gel applicators is also under consideration. Participants in a phase III trial typically apply the gel by way of a single-dose, plastic applicator. These applicators are expensive and may not be a good option for widespread use. A low-cost, paper applicator may be an alternative. Participants in a recent study preferred a user-filled, paper applicator and were able to give themselves a proper dose of the gel .
Vaginal rings, which are currently being used in contraceptive formulations and hormonal therapy , allow the slow delivery of one or more drugs within the vagina over a period of several weeks. Rings offer an important alternative to gels because they can be inserted for a month or more; and the user is not required to remember a daily regimen or anticipate sexual activity.
Although some researchers have expressed concerns about the formation of microbial biofilms on vaginal rings , previous trials have not given any indication that the potential formation of a biofilm on a ring has any safety implications or significant impact on performance (Microbicides Trial Network-ASPIRE (A Study to Prevent Infection with a Ring for Extended Use) protocol team; 10 July 2012, personal communication). Even so, some investigations of biofilm formation are planned in a forthcoming phase III trial (MTN 020, described below).
Other delivery methods — vaginal tablets, soft-gel capsules, diaphragms and thin films — are also being considered as drug carriers for topical PrEP [22▪,29–33]. These methods show promise, but they are still in preclinical investigations or early-phase clinical trials.
Only a single clinical trial, MTN 003, has reported any effectiveness results for an ARV-based, topical PrEP product since the completion of the CAPRISA 004 trial. The MTN 003 trial — also known as Vaginal and Oral Interventions to Control the Epidemic — was designed to evaluate the safety and effectiveness of daily 1% tenofovir gel, two oral ARV tablets (tenofovir disoproxyl fumarate (TDF) and a fixed-dose combination tablet of TDF and emtricitabine (Truvada). The oral TDF and the tenofovir gel arms were dropped in 2011 following interim reviews, which determined that neither product was effective in the study population [34▪]. Truvada continues to be evaluated and the final results are to be reported in early 2013 .
The ineffectiveness of tenofovir gel in the MTN 003 trial is disappointing and not yet fully understood. Several possibilities are being explored. Low adherence to a daily gel regimen might have been a factor. It was assumed that a once-daily gel application would have greater compliance than a coitally dependent application because it could be linked to a daily routine and does not require a woman to anticipate her sexual activity. However, participants might have abandoned gel use altogether if they found the product unacceptable (e.g. because of leakage).
The daily dosing might also have been high enough to cause mucosal toxicity, which outweighed the benefits of tenofovir's ARV activity. Another possibility involves the role of cell-associated viruses in the transmission of HIV. Although most HIV transmission probably occurs in the form of cell-free viruses, transmission by cell-associated viruses is not prevented by tenofovir gel in humanized BLT (bone marrow, liver, thymus) mice [36▪].
Several phase II or III safety and effectiveness trials of topical products are planned or under way [37▪▪]. Earlier this year, the International Partnership for Microbicides (IPM) launched The Ring Study (IPM027), a long-term safety and efficacy trial of a vaginal ring containing 25 mg of dapivirine [38▪]. The dapivirine ring is designed to be used and replaced every 4 weeks. The trial, involving 1650 women in several African countries, will be conducted over a 24-month period. Results are expected in 2015.
The MTN will also test the dapivirine ring in a parallel trial, called MTN020 or ASPIRE. This phase III trial will enroll about 3476 women at several sites in Africa. The trial is slated to begin recruitment in the latter half of 2012; results are expected late in 2014 or early 2015 . ASPIRE and The Ring Study are the first large-scale trials that will test an ARV-based, HIV-prevention product that does not involve the use of tenofovir and uses a sustained drug delivery system.
The Follow-on African Consortium for Tenofovir Studies (FACTS) is conducting FACTS 001, a phase III trial that began in October 2011, and will enroll more than 2200 women at nine sites in Africa [40▪]. The trial uses the same dosing schedule as CAPRISA 004 (BAT-24), and the results are expected in May 2014.
As discussed above, it is not clear whether the modest level of effectiveness (39%) found in the CAPRISA 004 trial, and the lack of effectiveness found in the MTN-003 trial, resulted from the properties of the topical product or from low levels of product adherence or from a combination of factors. Analysis of the CAPRISA 004 results showed that higher tenofovir concentrations (>1000 ng/ml) were associated with a lower risk of HIV infection [41▪▪]. Such a finding hints that low adherence might have played some role in the results.
Identifying the characteristics of a product that are associated with greater adherence and with sustained adherence is critical. Women may be reluctant to use a vaginal gel for a variety of reasons. For example, an acceptability study of VivaGel (a non-ARV microbicide candidate) (Starpharma, Melbourne, Australia) and two placebo gels found that only 59% of the participants were likely to use VivaGel. The participants reported problems with all three gels, including leakage, interference with sexual behavior and decreased sexual satisfaction .
A better understanding of the relationship (if any) between adherence to an HIV-prevention method and contraceptive use may also provide some insights. The CAPRISA 004 team showed that women who became pregnant were less adherent to the study gel than women who did not become pregnant [43▪]. The team could not determine whether the women wanted to become pregnant and so were reluctant to use a gel (with unknown effects on a fetus) or whether the pregnant women were less adherent for some other reason. Most of the pregnancies occurred among women who were using oral contraception.
No product can work if it is not used, and so adherence, and thus, human behavior, will play a major role in the real-world use of a topical PrEP product. Determining what drives adherence to an HIV-prevention method will be critical. We need to understand why trial participants come to their follow-up visits, accept multiple blood draws and, at the same time, do not use their study product. Biomedical HIV prevention cannot be a stand-alone medical approach but must also involve sociobehavioral research.
One of the potential consequences of using ARV drugs for HIV prevention is the development of drug resistance. At the time of infection, when the viral load is usually high, HIV could be exposed to suboptimal levels of an ARV drug— a combination that would provide a suitable environment for the development of viral resistance. Drug resistance may have an impact on future therapy.
In the CAPRISA 004 trial, the investigators did not find K65R or K70E mutations (which confer resistance to tenofovir) in plasma virus among the participants who seroconverted [1▪▪]. Deep pyrosequencing did reveal TDF-related resistant mutants at very low levels in participants who seroconverted in both arms of the trial . The CAPRISA team also screened cervicovaginal swabs from seroconverters in the tenofovir arm for K65R and K70E mutations . Only one K65R mutation was detected near the assay detection limit (∼1%), and this could merely reflect background resistance levels. The apparent absence of resistance in these instances might be partly explained by trial procedures because seroconverters are removed from the study product as soon as their HIV infection is diagnosed, which could effectively prevent the emergence of resistance.
FUTURE RESEARCH AND ROLLOUT PROGRAMS
In July, the Food and Drug Administration approved a label change to include HIV prevention for Truvada oral tablets. This action suggests that the rollout of an ARV-based, HIV-prevention program may soon become a reality. Much operational research will need to be conducted to make such a program effective. Many of the same issues will also apply to the rollout of topical products — including an HIV-test requirement, repeated testing for hepatic and renal function and other potential side effects, testing for viral resistance among people who become infected with HIV, determining where to distribute these products and ensuring sustained adherence.
Rollout programs, demonstration projects or phase IV trials will need to assess these issues for individuals who want to start using an ARV drug for HIV prevention. For example, the CAPRISA 008 trial will assess a rollout of tenofovir gel among 700 South African women. One group will receive the gel in a public-sector family planning clinic, while another group will receive the gel at a CAPRISA research clinic. Both groups will return to their respective clinics for follow-up. The trial should provide some indication of the issues that might arise in a large-scale rollout.
Current research on topical PrEP is focused on the potential of antiretroviral drugs. The field is exploring a wide variety of delivery vehicles and dosing strategies through basic scientific research and clinical trials. We need a suite of tools for HIV prevention so that each individual at risk can use the method(s) she or he chooses. If topical PrEP is to become an effective biomedical ‘tool,’ it will be essential to make the product a fundamental part of people's lives, including their sex lives.
We would like to thank all the participants in the microbicide clinical trials and the funders of HIV-prevention research. We are also grateful to Allison Burns and Tamara Fasnacht of FHI 360 for providing a thorough compilation of the microbicide literature.
Conflicts of interest
L.V.D. was Principal Investigator for FEM-PrEP, an oral preexposure prophylaxis trial, funded by the U.S. Agency for International Development and the Bill & Melinda Gates Foundation for community preparatory work in some sites. Gilead Sciences donated the study product.
There are no conflicts of interest.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
▪ of special interest
▪▪ of outstanding interest
Additional references related to this topic can also be found in the Current World Literature section in this issue (pp. 608–609).
1 Covered in detail elsewhere in this journal. Cited Here...
1▪▪. Abdool Karim Q, Abdool Karim SS, Frohlich JA, et al. Effectiveness and safety of tenofovir gel, an antiretroviral microbicide, for the prevention of HIV infection in women. Science 2010; 329:1168–1174.
This article describes the landmark CAPRISA 004 study; the first clinical trial to show that topical chemoprophylaxis with an ARV gel can effectively prevent HIV acquisition. It provided a vital boost to the field of topical HIV-prevention research.
2▪. Gengiah TN, Baxter C, Mansoor LE, et al. A drug evaluation of 1% tenofovir gel and tenofovir disoproxil fumarate tablets for the prevention of HIV infection. Expert Opin Investig Drugs 2012; 21:695–715.
This article provides an excellent overview of the research conducted on tenofovir gel and TDF tablets.
3. Mehendale S, Deshpande S, Kohli R, et al. Acceptability of coitally-associated versus daily use of 1% tenofovir vaginal gel among women in Pune, India. Int Health 2012; 4:63–69.
4. Moss JA, Baum MM, Malone AM, et al. Tenofovir and tenofovir disoproxil fumarate pharmacokinetics from intravaginal rings. AIDS 2012; 26:707–710.
5▪. Schwartz JL, Rountree RW, Kashuba ADM, et al. A multicompartment, single and multiple dose pharmacokinetic study of the vaginal candidate microbicide 1% tenofovir gel. PLoS One 2011; 6:e25974.
This study was the first to assess the pharmacokinetics of vaginally applied tenofovir gel.
6. Williams BG, Abdool Karim SS, Karim QA, Gouws E. Epidemiological impact of tenofovir gel on the HIV epidemic in South Africa. J Acquir Immune Defic Syndr 2011; 58:207–210.
7. Bunge K, Macio I, Meyn L, et al.
The safety, persistence, and acceptability of an antiretroviral microbicide candidate UC781. J Acquir Immune Defic Syndr 2012; 60:337–343.
8. Parikh UM, Dobard C, Sharma S, et al. Complete protection from repeated vaginal simian-human deficiency virus exposures in macaques by topical gel containing tenofovir alone or with emtricitabine. J Virol 2009; 83:10358–10365.
9▪. Lewi P, Heeres J, Arien K, et al. Reverse transcriptase inhibitors as microbicides. Curr HIV Res 2012; 10:27–35.
This article provides a detailed review of studies on the use of reverse transcriptase inhibitors as drugs for topical HIV prevention.
10. Singer R, Derby N, Mawson P, et al.
An EVA vaginal ring containing the NNRTI MIV-150 protects against SHIV-RT infection in vivo. In: Proceedings of the18th Conference on Retroviruses and Opportunistic Infections; February 27–March 2 2011; Boston, Massachusetts, USA. .
11. Singer R, Derby N, Rodriguez, et al.
The nonnucleoside reverse transcriptase inhibitor MIV-150 in carrageenan gel prevents rectal transmission of simian/human immunodeficiency virus infection in macaques. J Virol 2011; 85:5504–5512. doi: 10.1128/JVI.02422-10
12. Forbes CJ, Lowry D, Geer L, et al. Nonaqueous silicone elastomer gels as a vaginal microbicide delivery system for the HIV-1 entry inhibitor maraviroc. J Control Release 2011; 156:161–169.
13. Malcolm RK, Veazey RS, Geer L, et al. Sustained release of the CCR5 inhibitors CMPD167 and maraviroc from vaginal rings in rhesus macaques. Antimicrob Agents Chemother 2012; 56:2251–2258.
14. Pirrone V, Thakkar N, Jacobson JM, et al. Combinatorial approaches to the prevention and treatment of HIV-1 Infection. Antimicrob Agents Chemother 2011; 55:1831doi: 10.1128/AAC.00976-10.
15. Cutler B, Justman J. Vaginal microbicides and the prevention of HIV transmission. Lancet Infect Dis 2008; 8:685–697.
16. Schader SM, Colby-Germinario SP, Schachter J, et al. Synergy against drug-resistant HIV-1 with the microbicide antiretrovirals, dapivirine and tenofovir, in combination. AIDS 2011; 25:1585–1594.
18. Akil A. Development and characterization of tenofovir-maraviroc combination film for vaginal application. In: proceedings of the International Microbicides Conference; April 15–18 2012; Sydney, Australia.
19▪. Hendrix C, Minnis A, Guddera V, et al.
MTN-001: A Phase 2 cross-over study of daily oral and vaginal TFV in healthy, sexually active women results in significantly different product acceptability and vaginal tissue drug concentrations. [abstract 35LB]. In: Abstracts of the 18th Conference on Retroviruses and Opportunistic Infections; February 27–March 2 2011; Boston, Massachusetts, USA. http://www.retroconference.org/2011/Abstracts/42418.htm
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This study reported that the concentration of tenofovir in vaginal tissues and fluid were significantly higher in vaginal dosing compared with oral dosing.
20. Karim SS, Kashuba AD, Werner L, Karim QA. Drug concentrations after topical and oral antiretroviral preexposure prophylaxis: implications for HIV prevention in women. Lancet 2011; 378:279–281.
21▪. Ferguson LM, Rohan LC. The importance of the vaginal delivery route for antiretrovirals in HIV prevention. Ther Deliv 2011; 2:1535–1550.
Good review of vaginal delivery mechanism, dosing strategies, research done so far and future opportunities.
22▪. Adams JL, Kashuba ADM. Formulation, pharmacokinetics and pharmacodynamics of topical microbicides. Best Pract Res Clin Obstet Gynaecol 2012; 26:451–462. doi: 10.1016/j.bpobgyn.2012.01.004.
This article provides a timely description of nearly all of the HIV-prevention products that have been evaluated.
23. Fuchs EJ, Lee LA, Torbenson MS, et al. Hyperosmolar sexual lubricant causes epithelial damage in the distal colon: potential implication for HIV transmission. J Infect Dis 2007; 195:703–710.
24. Rohan LC, Moncla BJ, Kunjara Na, Ayudhya RP, et al. In vitro and ex vivo testing of tenofovir shows it is effective as an HIV-1 microbicide. PloS ONE 2010; 5:e9310.
25▪▪. Dezzutti CS, Rohan LC, Wang L, et al.
Reformulated tenofovir gel for use as a dual compartment microbicide. Journal Antimicrob Chemother 2012. [Epub ahead of print] doi: 10.1093/jac/dks173.
This article introduces a reduced glycine version of tenofovir gel that has less epithelial toxicity, which may improve the efficacy of gels for HIV prevention.
26. Cohen J, Brache V, Cochon L, et al.
Comparative safety study of prefilled, plastic and user-filled, paper vaginal applicators with candidate microbicide, tenofovir 1% gel. In: Proceedings of the International Microbicides Conference; 15–18 April 2012; Sydney, Australia.
27. Yoo JW, Lee CH. Drug delivery systems for hormone therapy. J Control Release 2006; 112:1–14.
28. Gunawardana M, Moss JA, Smith TJ, et al. Microbial biofilms on the surface of intravaginal rings worn in nonhuman primates. J Med Microbiol 2011; 60:828–837.
29. Agashe H, Hu M, Rohan L. Formulation and delivery of microbicides. Curr HIV Res 2012; 10:88–96.
30. Ham AS, Rohan LC, Boczar A, et al.
Vaginal film drug delivery of the pyrimidinedione IQP-0528 for the prevention of HIV infection. Pharm Res 2012; 29:1897–1907.
31. Johnson TJ, Srinivasan P, Albright TH, et al. Safe and sustained vaginal delivery of pyrimidinedione HIV-1 inhibitors from polyurethane intravaginal rings. Antimicrob Agents Chemother 2012; 56:1291–1299.
32. Nel AM, Mitchnick LB, Risha P, et al. Acceptability of vaginal film, soft-gel capsule, and tablet as potential microbicide delivery methods among African women. J Womens Health (Larchmt) 2011; 20:1207–1214.
33. Patton D, Cosgrove Sweeney Y, Anders N, et al.
Pharmacokinetics of vaginally applied tenofovir formulations: plasma uptake. In: Proceedings of the International Microbicides Conference; 15–18 April 2012; Sydney, Australia.
34▪. Microbicide Trials Network. MTN statement on decision to discontinue use of tenofovir gel in VOICE, a major HIV prevention study in women (Nov 25, 2011). http://www.mtnstopshiv.org/node/3909
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This press release announces the discontinuation of tenofovir gel because of ineffectiveness — a surprising and disappointing finding — in the Vaginal and Oral Interventions to Control the Epidemic trial. (MTN 003).
36▪. Swanson M, Garcia-Martinex V. Cell-associated vaginal HIV transmission is highly efficient and not prevented by topically applied 1% tenofovir [abstract 565].In: Abstracts of the 19th Conference on Retroviruses and Opportunistic Infections; 5–8 March, 2012; Seattle, Washington, USA. http://www.retroconference.org/2012b/Abstracts/43046.htm
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This study reports an interesting finding about cell-associated HIV that may have consequences for the real-world effectiveness of tenofovir gel for chemoprophylaxis.
This webpage offers a comprehensive list describing the status of ongoing, completed and planned microbicide clinical trials. It is a standard reference in the field.
In conjunction with the ASPIRE study, this study (IPM 027) will be the first phase III trial to test the effectiveness of a vaginal ring containing an ARV for chemoprophylaxis.
This website describes the FACTS 001 trial, which will attempt to replicate the findings of the CAPRISA 004 study. The results of the study will be critical for the future of 1% tenofovir gel.
41▪▪. Abdool Karim. CAPRISA 004 two years on: Ten key lessons & their implications. In: Proceedings of the Presentation at the Microbicides 2012 conferences; 15 April 2012; Sydney, Australia. http://http://www.microbicides2012.org
/images/pdfs/m2012%20-%20abdool%20karim%20-%20caprisa%20004%20lessons.pdf [Accessed 10 July 2012]
This presentation summarizes the results and implications of the CAPRISA 004 trial, including the critical role of adherence, drug dosage, and genital tract inflammation (as measured by cytokine levels). These issues will set the direction for future investigations of topical chemoprophylaxis.
42. Carballo-Dieguez A, Giguere R, Dolezal C, et al.
‘Tell juliana’: acceptability of the candidate microbicide Vivagel((r)) and two placebo gels among ethnically diverse, sexually active young women participating in a Phase 1 Microbicide Study. AIDS Behav 2011. doi: 10.1007/s10461-011-0028-6
43▪. Matthews L, Sibeko S, Mansoor L. Pregnant women have poorer adherence to study gel in CAPRISA 004, a Phase IIB randomized controlled trial of 1% tenofovir gel. In: Proceedings of the 19th Conference on Retroviruses and Opportunistic Infections; 5–8 March 2012. http://www.retroconference.org/2012b/Abstracts/43363.htm
[Accessed 10 July 2012]
This abstract reports that pregnant women in the CAPRISA 004 trial were less likely to adhere to the study gel than nonpregnant women — a finding that raises basic questions about the behavioral factors involved in adherence.
44. Fischer W, Hunt G, Sibeko S, et al.
Tenofovir resistance mutation frequencies assessed by deep pyrosequencing of plasma virus from breakthrough hiv infections: CAPRISA 004 Microbicide Trial. In: Proceedings of the 19th Conference on Retroviruses and Opportunistic Infections; 5–8 March 2012; Seattle. http://www.retroconference.org/2012b/Abstracts/43477.htm
[Accessed 10 July 2012]
45. Wei X, Morris L, Naranbhai V, et al.
Sensitive tenofovir resistance screening of HIV-1 from the genital tract of women with breakthrough infections: CAPRISA 004 tenofovir gel trial. In: Proceedings of the 19th Conference on Retroviruses and Opportunistic Infections; 5–8 March 2012; Seattle. http://www.retroconference.org/2012b/Abstracts/44025.htm
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