Mechanism of Action: Histone deacetylase inhibitor (HDACi). Vorinostat, a hydroxamic acid, is a pan-HDACi of class I and II HDACis.3 In HIV-1 latency, histone deacetylases (HDACs) are recruited to the proviral 5' long terminal repeat (LTR) where they catalyze deacetylation of lysine residues on histones, resulting in chromatin condensation on nucleosome 1 (nuc-1) and preventing HIV transcription. Inhibition of HDAC activity promotes histone acetylation (hyperacetylation) of lysine residues by histone acetyltransferases (HATs), leading to chromatin relaxation and transcriptional activation.3,4 Some research suggests that the activity of HDACis in inducing HIV transcription may not be caused by direct effects on histone acetylation, but may be caused by effects on other proteins, such as release of free positive transcription elongation factor b (P-TEFb) from the inhibitory 7SK small nuclear ribonucleoprotein (snRNP).5,6
Half-life (T½): As an FDA-approved treatment for cutaneous T-cell lymphoma, vorinostat half-life properties have been previously described. After oral administration of vorinostat in patients with advanced cancer, the mean terminal half-life of vorinostat was approximately 2 hours, and the mean terminal half-lives of vorinostat’s two inactive metabolites, O-glucuronide and 4-anilino-4-oxobutanoic acid, were approximately 2 hours and 11 hours, respectively.7
Metabolism/Elimination: Vorinostat is eliminated primarily through metabolism via glucuronidation and hydrolysis (major pathways), followed by β-oxidation. Cytochrome P450 (CYP) enzymes have a negligible role in vorinostat metabolism. Less than 1% of a total vorinostat dose is recovered as unchanged drug in urine, indicating that vorinostat is not excreted renally. Urinary recovery of a vorinostat dose at steady state was approximately 16% as the inactive metabolite O-glucuronide and approximately 36% as the inactive metabolite 4-anilino-4-oxobutanoic acid.7
Resistance: Resistance to vorinostat in the context of HIV infection has not been described.
Dosing in Clinical Trials
Study Identifier: NCT01319383
Study Purpose: Study to determine the efficacy of vorinostat in inducing HIV RNA expression within resting CD4 T cells after single and multiple short-interval vorinostat doses
Study Population: HIV-infected adults receiving stable ART, with plasma HIV-1 RNA <50 copies/mL and CD4 cell count >300 cells/µL for at least 6 months before study entry
Dosing: Initially, vorinostat 400 mg was administered as single oral doses at two different times. Thereafter, five participants in whom resting CD4 T cell-associated HIV RNA was shown to increase after the single vorinostat dose then received multiple, repeated short-interval dosing with vorinostat 400 mg once daily for 3 consecutive days a week (total of 8 weekly dosing cycles for a total of 22 vorinostat doses), in combination with ART. (Between each dosing cycle, there were 4-day rest periods. A 4- to 8-week interval followed the fourth dosing cycle.)8-10
(See references cited above for information on study results.)
Study Identifier: NCT01365065
Study Purpose: Study to determine the ability of vorinostat to induce HIV RNA expression within resting CD4 T cells after 14 days of daily vorinostat dosing
Study Population: HIV-infected adults receiving suppressive ART, with HIV-1 plasma RNA <50 copies/mL for at least 3 years and CD4 count >500 cells/µL
Dosing: Vorinostat 400 mg once daily for 14 days, in combination with ART. 5,11-13
(See references cited above for information on study results.)
Vorinostat will be studied in a Phase II trial as part of a combined approach to reducing the latent HIV reservoir. This proof-of-concept study will examine the use of 4-drug ART (which will always include raltegravir) plus two anti-HIV vaccines (ChAdV63.HIVconsv [ChAd] prime and MVA.HIVconsv [MVA] boost vaccines), followed by 10 doses of the HDACi vorinostat over 28 days. This combination approach will be compared to ART given alone.14
In addition, a Phase IIa eradication study in patients on ART will examine the use of AGS-004, an investigational HIV immunotherapy, plus the HDACi vorinostat to eliminate the latent HIV reservoir.15
In the Phase I/II study (NCT01319383), no vorinostat-associated adverse events (AEs) were reported during single limited exposures to vorinostat in eight HIV-infected participants on suppressive ART. No AEs greater than grade I severity occurred.8
During multiple short-interval vorinostat dosing in five participants, some mild, transient gastrointestinal symptoms and headache occurred (all below grade I severity). Transient thrombocytopenia occurred in all participants, with only one participant on a single study visit developing thrombocytopenia reaching grade I toxicity.9
A neurocognitive assessment performed on all five participants at baseline and study end found no significant change in neurocognitive functioning.16
In the Phase II study of 20 HIV-infected adults on suppressive ART, where oral vorinostat 400 mg was administered once daily for 14 days (NCT01365065), 90% of study participants experienced a grade 1 or 2 AE, with nausea, diarrhea, fatigue, and thrombocytopenia being the most common AEs. There was no occurrence of AEs of a higher grade, dose modifications, or drug discontinuations. Significant and prolonged changes in host gene expression were observed at Day 84, which investigators said warranted long-term follow-up.5,12
As an FDA-approved treatment for cutaneous T-cell lymphoma, vorinostat drug interactions have been previously described. In this context, previous studies have indicated that vorinostat at the 400-mg dose level does not inhibit CYP-drug-metabolizing enzymes. Because vorinostat is not eliminated via CYP pathways, drug-drug interactions between vorinostat and agents that are known CYP inhibitors or inducers are not anticipated. Vorinostat is not a substrate of human P-glycoprotein (P-gp) and is not likely to inhibit P-gp at a serum concentration of 2 µM (Cmax
) in humans.7
An in vitro
study investigating the interaction of CYP modulators (nevirapine, cobicistat, rifampin, and ketoconazole) on vorinostat in human hepatocytes found that vorinostat metabolism was affected by CYP modulators; however, there was no meaningful change in the clearance of vorinostat.17
During the Phase II study involving 20 participants who received at least three antiretroviral agents and once-daily vorinostat over 14 days (NCT01365065), there were no significant interactions between vorinostat and ART.5
- United States National Library of Medicine. ChemIDplus Advanced. Available at: http://chem.sis.nlm.nih.gov/chemidplus/rn/149647-78-9. Last accessed on July 5, 2015.
- National Institute of Allergy and Infectious Diseases (NIAID). NIAID ChemDB, HIV Drugs in Development. Available at: http://chemdb.niaid.nih.gov/DrugDevelopmentHIV.aspx. Last accessed on July 5, 2015.
- Rasmussen TA, Tolstrup M, Winckelmann A, Ostergaard L, Søgaard OS. Eliminating the latent HIV reservoir by reactivation strategies. Hum Vaccin Immunother. 2013 Apr 1;9(4):790-799. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3903897/. Last accessed on July 5, 2015.
- Matalon S, Rasmussen TA, Dinarello CA. Histone Deacetylase Inhibitors for Purging HIV-1 from the Latent Reservoir. Mol Med. 2011 May-Jun;17(5-6):466-72. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3105138/. Last accessed on July 5, 2015.
- Elliott JH, Wightman F, Solomon A, et al. Activation of HIV Transcription with Short-Course Vorinostat in HIV-Infected Patients on Suppressive Antiretroviral Therapy. PLoS Pathog. 2014 Nov 13;10(11):e1004473. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4231123/. Last accessed on July 5, 2015.
- Bartholomeeusen K, Fujinaga K, Xiang Y, Peterlin BM. Histone deacetylase inhibitors (HDACis) that release the positive transcription elongation factor b (P-TEFb) from its inhibitory complex also activate HIV transcription. J Biol Chem. 2013 May 17;288(20):14400-7. Available at: http://www.ncbi.nlm.nih.gov/pubmed/23539624. Last accessed on July 5, 2015.
- Merck Sharp & Dohme Corp. Zolinza: Full Prescribing Information, April 2013. DailyMed. Available at: http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cd86ee78-2781-468b-930c-3c4677bcc092. Last accessed on July 5, 2015.
- Archin NM, Liberty AL, Kashuba AD, et al. Administration of vorinostat disrupts HIV-1 latency in patients on antiretroviral therapy. Nature. 2012 Jul 25;487(7408):482-5. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3704185/. Last accessed on July 5, 2015.
- Archin NM, Bateson R, Tripathy M, et al. HIV-1 Expression Within Resting CD4+ T Cells After Multiple Doses of Vorinostat. J Infect Dis. 2014 Sep 1;210(5):728-35. Available from National AIDS Treatment Advocacy Project (NATAP): http://www.natap.org/2014/HIV/JInfectDis.2014Archin-728-35.pdf. Last accessed on July 5, 2015.
- University of North Carolina, Chapel Hill. A Phase I/II Investigation of the Effect of Vorinostat (VOR) on HIV RNA Expression in the Resting CD4+ T Cells of HIV-Infected Patients Receiving Stable Antiretroviral Therapy. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on March 17, 2011. NLM Identifier: NCT01319383. Available at: https://www.clinicaltrials.gov/ct2/show/study/NCT01319383. Last accessed on July 5, 2015.
- Wightman F, Elliot JH, Solomon AE, et al. Multidose vorinostat in HIV-infected individuals on effective ART leads to an increase in regulatory T cells but no change in inducible virus or HIV-specific T cells. Abstract presented at: 20th International AIDS Conference; July 20-25, 2014; Melbourne, Australia. Abstract LBPE07. Available at: http://pag.aids2014.org/abstracts.aspx?aid=11368. Last accessed on July 5, 2015.
- Elliott J, Solomon A, Wightman F, et al. The Safety and Effect of Multiple Doses of Vorinostat on HIV Transcription in HIV-Infected Patients Receiving Combination Antiretroviral Therapy. Abstract presented at: 20th Conference on Retroviruses and Opportunistic Infections (CROI); March 3-6, 2013; Atlanta, GA. Abstract 50LB. Available from National Association of People with HIV Australia (NAPWHA):http://napwha.org.au/sites/default/files/CROI%202013%20vorinostat%20final%202.pdf. Last accessed on July 5, 2015.
- Bayside Health. A Pilot Study to Assess the Safety and Effect on HIV Transcription of Vorinostat in Patients Receiving Suppressive Combination Anti-retroviral Therapy. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on June 1, 2011. NLM Identifier: NCT01365065. Available at: https://www.clinicaltrials.gov/ct2/show/NCT01365065. Last accessed on July 5, 2015.
- Imperial College London. Research In Viral Eradication of HIV Reservoirs. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on October 23, 2014. NLM Identifier: NCT02336074. Available at: https://www.clinicaltrials.gov/ct2/show/NCT02336074. Last accessed on July 5, 2015.
- Argos Therapeutics: Press Release, dated April 1, 2015. NIH Funds Study of Fully Personalized Immunotherapy AGS-004 Combined With a Latency Reversing Therapy for the Treatment of HIV. Available at: http://ir.argostherapeutics.com/releasedetail.cfm?ReleaseID=904466. Last accessed on July 5, 2015.
- Robertson K, Kuruc J, Gay C, Archin N, Eron J, Margolis D. Preliminary assessment of the neurocognitive effects of vorinostat administration in HIV eradication. Abstract presented at 20th International AIDS Conference; July 20-25, 2014; Melbourne, Australia. Abstract WEPE018. Available at: http://pag.aids2014.org/Abstracts.aspx?AID=8679. Last accessed on July 5, 2015.
- Shaik H, Pillai VC, Parise RA, et al. Metabolism of Vorinostat in Primary Human Hepatocytes Is Not Affected by HAART Drugs, Nevirapine and Cobicistat. Poster presented at: 2014 American Association of Pharmaceutical Scientists (AAPS) Annual Meeting and Exposition; November 2-6, 2014; San Diego, CA. Poster T2293. Available at: http://abstracts.aaps.org/Verify/AAPS2014/PosterSubmissions/T2293.pdf. Last accessed on July 5, 2015.
Last Reviewed: July 5, 2015
Last Updated: July 5, 2015