TGF-beta inhibitors influence leishmania infection outcome in a susceptible host

Transforming growth factor-β (TGF-β) is a key immunoregulatory cytokine that promotes parasite persistence in macrophages, immunosuppression by deactivation of macrophages and regulatory T cell differentiation and Th17-mediated pathogenesis in leishmaniasis. Targeting TGF-β signaling therefore represents a promising host-directed therapeutic approach. Herein, we investigated the therapeutic potential of pharmacological inhibitors targeting the TGF-β receptor and signaling pathway in vitro and in susceptible BALB/c mice in an experimental model of visceral leishmaniasis. BALB/c-derived peritoneal macrophages were infected with L. donovani promastigotes and treated with salirasib- a Ras inhibitor, angoline- an IL-6 inhibitor, SIS3- a SMAD3 inhibitor, or galunisertib- a TGF-β receptor inhibitor. Parasite burden and nitric oxide (NO) production were quantified, and cytokine responses were analyzed. While salirasib elevated NO production without reducing parasite load, and angoline failed to show significant effects, galunisertib markedly reduced intracellular amastigotes and enhanced NO levels. SIS3 alone induced modest cytokine alterations without significantly reducing parasite burden. Infected BALB/c mice treated with galunisertib significantly reduced hepatic and splenic parasite burdens, measured as Leishman-Donovan Units (LDUs). Cytokine profiling revealed that Galunisertib enhanced pro-inflammatory cytokines (IL-12, TNF-α, IFN-γ, IL-17) and downregulated TGF-β, whereas SIS3 selectively increased IL-12 and TNF-α while reducing IL-10. Combined galunisertib and SIS3 treatment synergistically increased both pro-inflammatory and anti-inflammatory cytokines, notably IL-10, which may offset parasite clearance. These findings establish TGF-β receptor inhibition as a promising host-directed therapeutic approach against visceral leishmaniasis, while highlighting the immunoregulatory complexities of targeting TGF-β signaling.