Doctor of Philosophy
Human immunodeficiency virus (HIV) and opioid abuse have been described as synergistic epidemics. Pharmacologically, it has been found that opioids have the capacity to enhance HIV infection and replication. Research has shown that activation of the mu-opioid receptor (MOR) elevates the expression of the HIV-1 entry co-receptor CXCR4 on T-lymphocytes in the peripheral nervous system, thus allowing for enhanced viral entry and invasion. Although the exact mechanism for opioid modulation of CXCR4 expression and subsequent exacerbation of HIV is unknown, several hypotheses exist. One hypothesis is that MOR and CXCR4 are functionally interacting through the formation of a heterodimer. This hypothesis is supported by studies substantiating the ability for MOR and CXCR4 to form heterodimers with other GPCRs, and the finding that MOR and CXCR4 were co-expressed in several central and peripheral regions including immune cells. To test this hypothesis, a series of bivalent ligands containing both a mu opioid receptor (MOR) antagonist and a CXCR4 antagonist pharmacophore was designed and synthesized to understand the pharmacological role of the putative CXCR4-MOR heterodimer in opioid exacerbated HIV progression.
These bivalent ligands were evaluated for their binding and functional activities in radioligand binding, antibody binding, [35S]GTPγS, and calcium mobilization assays. In these assays, the bivalent ligands were shown to maintain binding and functional activities in both MOR and CXCR4 monoclonal cell lines. In addition, these bivalent ligands were evaluated for their ability to block HIV entry in a reverse transcriptase assay, and for their ability to inhibit morphine exacerbated HIV invasion in an LTR-luciferase assay. In these assays, the bivalent ligands were shown to inhibit HIV entry in a dose dependent manner. However, due to experimental limitations in our morphine exacerbated reporter system, the ability for the bivalent ligands to inhibit viral entry upon morphine co-exposure was not fully validated. Finally, molecular modeling approaches were utilized to visualize the putative binding modes of the bivalent ligands in a constructed MOR-CXCR4 heterodimer model.
Overall, these studies have provided a solid basis for the utility of bivalent ligands in studying MOR-CXCR4 interactions and their involvement in opioid potentiated HIV progression. Further studies are ongoing to optimize the bivalent ligands construct and explore new analyses to evaluate their ability to block opioid modulation of the virus.
© Bethany A. Reinecke
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VCU University Archives
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VCU Theses and Dissertations
Date of Submission
Available for download on Monday, April 29, 2024