Potential of repurposing chloroquine as an adjunct therapy for melioidosis based on a murine model of Burkholderia pseudomallei infection

Burkholderia pseudomallei is the etiologic agent of melioidosis, a major cause of community-acquired pneumonia and sepsis in the endemic areas. The overall mortality of patients with severe melioidosis remains high due to severe sepsis attributed to overwhelming inflammatory cytokine response in spite of recommended antibiotic therapy. It is crucial that therapeutic approaches beyond just effective antibiotic treatment such as adjunct therapy be considered to mitigate the dysregulated inflammatory signaling and augment host defenses. In an acute B. pseudomallei infection model, we have previously demonstrated that treatment with anti-malarial drug, chloroquine, modulated inflammatory cytokine levels and increased animal survivability via Akt-mediated inhibition of glycogen synthase kinase-3β (GSK3β). GSK3β is a downstream effector molecule within the phosphatidylinositol 3-kinase (PI3K)/ Akt axis which plays a pivotal role in regulating the production of pro- and anti-inflammatory cytokines. Here we evaluate the effect of chloroquine treatment in combination with a subtherapeutic dose of the antibiotic doxycycline on animal survivability, cytokine levels and phosphorylation states of GSK3β (Ser9) in a murine model of acute melioidosis infection to investigate whether chloroquine could be used as an adjunct therapy along with doxycycline for the treatment of melioidosis. Our findings revealed that 50 mg/kg b.w. chloroquine treatment together with a dose of 20 mg/kg b.w. doxycycline improved survivability (100%) of mice infected with 3 X LD50 of B. pseudomallei and significantly (P<0.05) lowered the bacterial loads in spleen, liver and blood compared to controls. B. pseudomallei-infected mice subjected to adjunct treatment with chloroquine and doxycycline significantly (P<0.05) reduced serum levels of pro-inflammatory cytokines (TNF-α, IFN-γ and IL-6) but increased levels of antiinflammatory cytokines (IL-4 and IL-10). Western blot analysis demonstrated that the intensities of pGSK3β (Ser9) in liver samples from mice treated with chloroquine and doxycycline combination were significantly (P<0.05) higher suggesting that the adjunct treatment resulted in significant inhibition of GSK3β. Taken together the bacteriostatic action of doxycycline coupled with the cytokine-modulating effect of chloroquine gave full protection to B. pseudomallei-infected mice and involved inhibition of GSK3β. Findings from the present study using B. pseudomallei-infected BALB/c mice suggest that chloroquine is a plausible candidate for repurposing as adjunct therapy to treat acute B. pseudomallei infection.