Bivalent Ligand Aiming Putative Mu Opioid Receptor and Chemokine Receptor CXCR4 Dimers in Opioid Enhanced HIV-1 Entry

Abstract

A bivalent compound 1a featuring both a mu opioid receptor (MOR) and a CXCR4 antagonist pharmacophore (naltrexone and IT1t) was designed and synthesized. Further binding and functional studies demonstrated 1a acting as a MOR and a CXCR4 dual antagonist with reasonable binding affinities at both receptors. Furthermore, compound 1a seemed more effective than a combination of IT1t and naltrexone in inhibiting HIV entry at the presence of morphine. Additional molecular modeling results suggested that 1a may bind with the putative MOR-CXCR4 heterodimer to induce its anti-HIV activity. Collectively, bivalent ligand 1a may serve as a promising lead to develop chemical probes targeting the putative MOR-CXCR4 heterodimer in comprehending opioid exacerbated HIV-1 invasion.

Figure 1

Chemical structures of naltrexone, IT1t, designed bivalent ligand 1a, and monovalent controls 2a and 3a.

Figure 2

Designing components of the bivalent ligand 1a: (a) Docking pose of naltrexone within the MOR from docking study (PDB ID: 4DKL(28)); (b) binding mode of IT1t within the CXCR4 from its crystal structure (PDB ID: 3ODU(23)); (c) attachment points.

Scheme 1. Synthetic Route of Bivalent Ligand 1a

Reagents and conditions: (a) CbzCl, CH₂Cl₂, MeOH; (b) diglycolic anhydride, THF; (c) 6β-naltrexamine, EDCI, HOBt, TEA, DMF; (d) H₂, MeOH, Pd/C, 60 psi; (e) diglycolic anhydride, DMF; (f) aminomethyl-substituted IT1t, EDCI, HOBt, TEA, DMF.

Figure 3

Viral inhibition effects of bivalent compound 1a with coexposure to morphine. HIV-1_IIIB infectivity in TZM-bl was determined based on the relative amount of Tat protein expressed by the virus using a luciferase-based assay. Morphine, 500 nM; IT1t, 60 nM (see Figure S5 for dose–response curve); Bivalent compound 1a,1000 nM; Naltrexone, 1500 nM. Values are from one experiment run at 3 days postinfection. All compounds or their combinations applied have been studied for their dose responses. Data are presented as mean% inhibition values ± SD [*p = > 0.05 X4 virus vs morphine; $p < 0.05 X4 virus vs IT1t; #p < 0.05 morphine vs morphine + IT1t; ¥p > 0.05 morphine + IT1t vs IT1t; p̂ < 0.05 M + I vs M + I + NTX; ¶p < 0.05 M + I + NTX vs Bivalent 1a + M; §p < 0.05 M + I + NTX vs Bivalent 1a].

Figure 4

Binding mode of MOR-CXCR4_1a complex after 100 ns MD simulation. Heterodimer MOR-CXCR4 is shown as a cartoon model in light-blue. Compound 1a is shown as stick and sphere models in magentas. Key residues of the CXCR4 and MOR are shown as stick models in cyan and orange, respectively.