Apigenin improves cytotoxicity of antiretroviral drugs against HTLV-1 infected cells through the modulation of AhR signaling.

Objectives: HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neuroinflammatory autoimmune disease characterized by high levels of infected immortalized T cells in circulation, which makes it difficult for antiretroviral (ART) drugs to work effectively. In previous studies, we established that Apigenin, a flavonoid, can exert immunomodulatory effects to reduce neuroinflammation. Flavonoids are natural ligands for the aryl hydrocarbon receptor (AhR), which is a ligand activated endogenous receptor involved in the xenobiotic response. Consequently, we tested Apigenin's synergy in combination with ART against the survival of HTLV-1-infected cells.

Methods: First, we established a direct protein-protein interaction between Apigenin and AhR. We then demonstrated that Apigenin and its derivative VY-3-68 enter activated T cells, drive nuclear shuttling of AhR, and modulate its signaling both at RNA and protein level.

Results: In HTLV-1 producing cells with high AhR expression, Apigenin cooperates with ARTs such as Lopinavir (LPN) and Zidovudine (AZT), to impart cytotoxicity by exhibiting a major shift in IC₅₀ that was reversed upon AhR knockdown. Mechanistically, Apigenin treatment led to an overall downregulation of NF-κB and several other pro-cancer genes involved in survival.

Conclusions: This study suggest the potential combinatorial use of Apigenin with current first-line antiretrovirals for the benefit of patients affected by HTLV-1 associated pathologies.