Background:  The aim of this study was to examine the potential for 3 quinolone derivatives with proven ARV activity (naphthyridone 3 [HM13N], WM5, WM21) to suppress HIV-induced plasmacytoid dendritic cell (pDC)-mediated immunopathogenesis. Activated pDC produce large quantities of interferon-α (IFN-α), which limits viral replication and primes adaptive immune responses. While IFN-α may be beneficial during the initial stages of infection we have recently shown that pDC overactivation contributes to HIV-induced immune dysregulation and suppresses memory T cell responses. Quinolone derivatives were shown to inhibit tat-mediated HIV-1 transcription. Chloroquine (CQ) shares some structural homology with quinolones and is being tested in clinical trials to reduce HIV-induced immune activation.

Methods:  Peripheral blood mononuclear cells (PBMC) from healthy donors were cultured overnight with AT-2 HIV-1_MN in the presence of HM13N, WM5, WM21, or CQ at varying concentrations. All compounds were solubilized in DMSO, and 0.1% DMSO with or without HIV was used as controls. IFN-α was measured in culture supernatants by ELISA. Expression of co-stimulatory markers, apoptosis, and uptake of fluorescently labeled HIV were examined by flow cytometry. Friedman test with Dunn’s correction was used for multiple comparisons. Wilcoxon signed rank test was used for pairwise analysis. P values of less than 0.05 were considered significant.

Results:  All compounds induced a significant dose-dependent reduction of HIV-induced IFN-α production by PBMC. Interestingly, HM13N, but none of the other compounds, significantly increased CD80 expression on HIV-activated pDC compared to control. Conversely, CD80 expression was significantly reduced on monocytes after treatment with HM13N and CQ. Overnight stimulation with HM13N uniquely induced a morphological change in monocytes, which resembled the increase in granularity seen during differentiation into macrophages. This change was independent of HIV, and not associated with increased apoptosis, as measured by Annexin V staining. HM13N but not CQ significantly reduced uptake of fluorescently labeled HIV by monocytes and myeloid DC. No significant change was observed in HIV uptake by pDC or CD4⁺ T cells.

Conclusions:  In addition to its inhibitory effects on HIV-1 replication, HM13N suppresses HIV-induced IFN-α secretion while promoting an antigen presenting phenotype. These unique immunomodulatory properties distinguish HM13N from CQ and other quinolones and render it a potential candidate for immune therapy.