What is an investigational drug?
An investigational drug is one that is under study and is not approved by the U.S. Food and Drug Administration (FDA) for sale in the United States. Medical research studies are conducted to evaluate the safety and effectiveness of an investigational drug. These research studies are also called clinical trials. Once an investigational drug has been proven safe and effective in clinical trials, FDA may approve the drug for sale in the United States.
What is cenicriviroc?
Cenicriviroc is an investigational drug that is being studied for the treatment of HIV infection.
Cenicriviroc belongs to a class (group) of HIV drugs called entry and fusion inhibitors.2
Entry and fusion inhibitors block HIV from getting into and infecting certain cells of the immune system. This prevents HIV from multiplying and can reduce the amount of HIV in the body.
Cenicriviroc works by attaching to one of two proteins on the surface of the immune cells. These proteins are called the CCR5 and CXCR4 coreceptors. Cenicriviroc attaches to the CCR5 coreceptor. When cenicriviroc attaches to the CCR5 coreceptor, certain strains of HIV—called R5-tropic virus—cannot attach to, enter, or infect the cell.3
Cenicriviroc also appears to block another receptor known as CCR2. The CCR2 receptor is associated with inflammatory diseases. The potential benefits of blocking the CCR2 receptor in people with HIV are being studied.4,5
How are clinical trials of investigational drugs conducted?
Clinical trials are conducted in “phases.” Each phase has a different purpose and helps researchers answer different questions.6
Phase I trials: Researchers test an investigational drug in a small group of people (20–80) for the first time. The purpose is to evaluate its safety and identify side effects.
Phase II trials: The investigational drug is administered to a larger group of people (100–300) to determine its effectiveness and to further evaluate its safety.
Phase III trials: The investigational drug is administered to large groups of people (1,000–3,000) to confirm its effectiveness, monitor side effects, compare it with standard or equivalent treatments, and collect information that will allow the investigational drug to be used safely.6
In most cases, an investigational drug must be proven safe and effective in a Phase III clinical trial to be considered for approval by the FDA for sale in the United States. Some drugs go through the FDA’s accelerated approval process and are approved before a Phase III clinical trial is complete. After a drug is approved by the FDA and made available to the public, researchers track its safety in Phase IV trials to seek more information about the drug’s risks, benefits, and optimal use.6
In what phase of testing is cenicriviroc?
Cenicriviroc is currently being studied in Phase II clinical trials.2
What have recent studies shown about cenicriviroc?
In a 10-day Phase I/II study, several different strengths of cenicriviroc taken once daily were compared to placebo in HIV-infected participants who had been taking HIV medicines before entering the study (treatment-experienced). (A placebo is an inactive drug that is identical in appearance to the active drug being studied.) Study participants did not receive additional HIV medicines as part of a background regimen. (A background regimen is a combination of drugs that are not being studied as the investigational drug[s] in the clinical trial, but are given to help control a participant’s HIV infection.)4,7,8
In the adults who had been taking HIV medicines before entering the study and who had not been previously treated with a CCR5 antagonist, cenicriviroc at all strengths was effective in reducing HIV viral load (the amount of HIV in the blood). Cenicriviroc was also shown to have anti-inflammatory activity. In terms of safety, no serious side effects occurred. The most common side effects were headache, nausea, constipation, diarrhea, and sinus infection/inflammation (sinusitis).4,7,8
Additional Phase II studies of cenicriviroc in HIV-infected adults who have not taken HIV medicines before are under way.9
What side effects might cenicriviroc cause?
In the 10-day Phase I/II study discussed under the previous question, the most common side effects reported were the following: headache, nausea, constipation, diarrhea, and sinus infection/inflammation (sinusitis). Overall, side effects occurring in this study were considered mild.4,7
Because cenicriviroc is still being studied, information on possible side effects of the drug is not complete. As testing of cenicriviroc continues, additional information on possible side effects will be gathered.
Where can I get more information about clinical trials studying cenicriviroc?
More information about cenicriviroc-related research studies
is available from the AIDSinfo
database of ClinicalTrials.gov
study summaries. Click on the title of any trial in the list to see the ClinicalTrials.gov
trial summary and more information about the study.
I am interested in participating in a clinical trial of cenicriviroc. How can I find more information about participating in a clinical trial?
Participating in a clinical trial can provide benefits. For example, a volunteer participant can benefit from new research treatments before they are widely available. Participants also receive regular and careful medical attention from a research team that includes doctors and other health professionals. However, clinical trials may also involve risks of varying degrees, such as unpleasant, serious, or even life-threatening side effects from the treatment being studied.6
Your health care provider can help you decide whether participating in a clinical trial is right for you. For more information, visit NIH Clinical Research Trials and You
. United States National Library of Medicine. ChemIDplus Advanced
. National Institute of Allergy and Infectious Diseases (NIAID). NIAID ChemDB, HIV Drugs in Development
. Briz V, Poveda E, Soriano V. HIV entry inhibitors: mechanisms of action and resistance pathways
. J Antimicrob Chemother. 2006 Apr;57(4):619-27.
. Marier JF, Trinh M, Pheng LH, Palleja SM, Martin DE. Pharmacokinetics and pharmacodynamics of TBR-652, a novel CCR5 antagonist, in HIV-1-infected, antiretroviral treatment-experienced, CCR5 antagonist-naïve patients
. Antimicrob Agents Chemother. 2011 Jun;55(6):2768-74.
. Klibanov OM, Williams SH, Iler CA. Cenicriviroc, an orally active CCR5 antagonist for the potential treatment of HIV infection
. Curr Opin Investig Drugs. 2010 Aug;11(8):940-50.
. National Institutes of Health (NIH). NIH Clinical Research Trials and You
. Tobira Therapeutics, Inc. A Proof of Concept, Multiple Dose-Escalating Study to Evaluate the Antiviral Activity, Safety, and Pharmacokinetics of the CCR5 Antagonist TBR 652 in HIV 1-Infected, Antiretroviral Treatment-Experienced, CCR5 Antagonist-Naïve Patients
. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on March 22, 2010. NLM Identifier: NCT01092104. Last accessed May 13, 2013.
. Martin DE, Palleja S, Gathe J, et al. TBR-652, a potent dual chemokine receptor 5/chemokine receptor 2 (CCR5/CCR2) antagonist in phase 2 development for treatment of HIV infection
. Abstract presented at: 18th International AIDS Conference; July 18-23, 2010; Vienna, Austria. Abstract MOAB0104.
. Tobira Therapeutics, Inc. A Phase 2b Randomized, Double-Blind, Double-Dummy Trial of 100 or 200 mg Once-Daily Doses of Cenicriviroc (CVC, TBR 652) or Once-Daily EFV, Each With Open-Label FTC/TDF, in HIV 1-Infected, Antiretroviral Treatment-Naïve, Adult Patients With Only CCR5-Tropic Virus
. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on April 18, 2011. NLM Identifier: NCT01338883. Last accessed April 4, 2013.
Last Reviewed: May 29, 2013
Last Updated: May 29, 2013