Antiretroviral drug exposure is directly linked to individual host factors which include age, weight, diet, and genetics. However, the main factor impacting long-term drug exposure is drug adherence. Adherence is a strong predictor of HIV treatment outcomes, but measuring adherence is difficult due to the inaccuracy of self-reporting and other commonly used monitoring methods. Furthermore, individual pharmacokinetic (PK) variations can also have a direct impact in treatment outcomes, even in cases of optimal adherence. This indicates the need for objective measures of antiretroviral exposure that can integrate adherence and pharmacokinetics into one single test. To date, no gold standard measure to monitor antiretroviral exposure and adherence has been applied in clinical practice. Tenofovir (TFV) and its active metabolite, tenofovir diphosphate (TFV-DP), have distinctive pharmacological characteristics that make them ideal candidates for drug adherence and exposure monitoring. The long half-life (~14-17 days) and low coefficient of variation of TFV-DP in red blood cells (RBC) are properties well suited for monitoring average dose exposure over time. Based on these, we propose the novel hypothesis that RBC levels of TFV-DP are an accurate and precise measure of long-term drug exposure in HIV-infected and HIV-negative individuals. In addition, we aim to quantify TFV and TFV-DP in dried blood spots (DBS) as a simple method to measure drug exposure. To test our hypotheses, we propose the following Aims: 1) to elucidate the PK profile of TFV and TFV-DP in HI infected and HIV-negative individuals using plasma, peripheral blood mononuclear cells (PBMC), RBC and DBS;2) to determine the relationships between age, gender, race, weight and pharmacogenetics (PG) on the metabolism of TFV and TFV-DP, and;3) to characterize the association of TFV-DP levels in DBS with viral suppression in HIV-infected patients.
Aims 1 and 2 will be investigated in an intensive, 30-day pharmacokinetic study of treatment-naive HIV-infected individuals who are initiating TFV-based therapy (as ordered by their primary care provider). The PK parameters from HIV-infected individuals will be compared to HIV-negative subjects and host factors such as age, gender, race, weight and genetic variations in drug transporters will be assessed through non-linear mixed effects modeling.
Aim 3 will be investigated by prospectively comparing DBS levels of TFV-DP in HIV-infected patients on long-standing TFV-based therapy who have incomplete viral suppression vs. individuals with an undetectable viral load. Complimentary to this research proposal, a five-year mentored career development program is proposed by the applicant. This incorporates intensive mentoring guided by an internationally recognized, well established investigator with expertise in clinical pharmacology of HIV infection and intracellular metabolism of antiretrovirals. The primary mentor will be supported by a mentoring team composed by key faculty members with expertise in HIV clinical research, biostatistics, treatment adherence and pharmacogenetics. In addition, the candidate has developed a detailed didactic plan that includes formal training in biostatistics, clinical pharmacology, epidemiology, grant writing and design of clinical trials. The candidate's overarching career goal is to become a successful clinical investigator in HIV treatment and care. The current K23 proposal will provide the foundation for a strong research program on antiretroviral drug exposure and drug adherence, while facilitating Dr. Castillo-Mancilla's development into an independently-funded investigator.

Public Health Relevance

Drug exposure to antiretrovirals is mainly driven by drug adherence, which is a strong predictor of HIV treatment efficacy. Measuring adherence has proven to be difficult and there is no gold standard measure of drug exposure and drug adherence in clinical practice. The proposed research will develop a new pharmacologic approach to quantify drug exposure and adherence, which could lead to more efficacious HIV treatment and prevention strategies.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Mentored Patient-Oriented Research Career Development Award (K23)
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Acquired Immunodeficiency Syndrome Research Review Committee (AIDS)
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Sharp, Gerald B
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University of Colorado Denver
Internal Medicine/Medicine
Schools of Medicine
United States
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Seifert, Sharon M; Castillo-Mancilla, Jose R; Erlandson, Kristine et al. (2017) Adherence biomarker measurements in older and younger HIV-infected adults receiving tenofovir-based therapy. J Acquir Immune Defic Syndr :
Seifert, Sharon M; Chen, Xinhui; Meditz, Amie L et al. (2016) Intracellular Tenofovir and Emtricitabine Anabolites in Genital, Rectal, and Blood Compartments from First Dose to Steady State. AIDS Res Hum Retroviruses 32:981-991
Chen, Xinhui; Seifert, Sharon M; Castillo-Mancilla, Jose R et al. (2016) Model Linking Plasma and Intracellular Tenofovir/Emtricitabine with Deoxynucleoside Triphosphates. PLoS One 11:e0165505
Zheng, Jia-Hua; Rower, Caitlin; McAllister, Kevin et al. (2016) Application of an intracellular assay for determination of tenofovir-diphosphate and emtricitabine-triphosphate from erythrocytes using dried blood spots. J Pharm Biomed Anal 122:16-20
Castillo-Mancilla, Jose R; Brown, Todd T; Erlandson, Kristine M et al. (2016) Suboptimal Adherence to Combination Antiretroviral Therapy Is Associated With Higher Levels of Inflammation Despite HIV Suppression. Clin Infect Dis 63:1661-1667
Castillo-Mancilla, Jose; Seifert, Sharon; Campbell, Kayla et al. (2016) Emtricitabine-Triphosphate in Dried Blood Spots as a Marker of Recent Dosing. Antimicrob Agents Chemother 60:6692-6697
Chen, Xinhui; Castillo-Mancilla, Jose R; Seifert, Sharon M et al. (2016) Analysis of the Endogenous Deoxynucleoside Triphosphate Pool in HIV-Positive and -Negative Individuals Receiving Tenofovir-Emtricitabine. Antimicrob Agents Chemother 60:5387-92
Anderson, Peter L; Reirden, Daniel; Castillo-Mancilla, Jose (2016) Pharmacologic Considerations for Preexposure Prophylaxis in Transgender Women. J Acquir Immune Defic Syndr 72 Suppl 3:S230-4
Castillo-Mancilla, Jose R; Aquilante, Christina L; Wempe, Michael F et al. (2016) Pharmacogenetics of unboosted atazanavir in HIV-infected individuals in resource-limited settings: a sub-study of the AIDS Clinical Trials Group (ACTG) PEARLS study (NWCS 342). J Antimicrob Chemother 71:1609-18
Chai, Peter R; Castillo-Mancilla, Jose; Buffkin, Eric et al. (2015) Utilizing an Ingestible Biosensor to Assess Real-Time Medication Adherence. J Med Toxicol 11:439-44

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