Study of CB2R agonist GP1a as adjunct to antibiotic therapy in Mycobacterium bovis BCG-infected macrophages

Tuberculosis (TB) is an infectious disease which causes millions of deaths annually, despite the established treatments. Indeed, there is growing concern regarding bacterial resistance to current antibiotic therapies, due to prolonged multidrug treatment durations combined with poor patient adherence to prescribed regimens. Host-directed therapy (HDT) has emerged as a promising approach for TB treatment. Cannabinoids and their immunomodulatory effects have shown potential for significant therapeutic applications. Our group recently demonstrated that cannabinoid receptor type 2 (CB2R) agonists attenuate inflammatory processes by reducing pro-inflammatory cytokine production and pro-inflammatory gene expression, as well as inhibiting NF-κB pathway. In the present study, we aim to investigate CB2R agonist, GP1a, as a synergistic agent for conventional TB antibiotics (isoniazid and rifampicin) in M. bovis BCG-infected macrophages. Although GP1a-treatment (2.5-40µM) inhibited TNF-a release (p<0.005) by BCG-infected macrophage, it did not significantly alter either the percentage of infected cells or the bacterial burden within 72h post infection. We determined the EC₅₀ values for rifampicin and isoniazid to be 2.4 µg/mL and 0.05 µg/mL, respectively. Preliminary data indicate that co-treatment with GP1a (20 µM) and either rifampicin (0.1 µg/mL) or isoniazid (0.01 µg/mL) did not provide beneficial effects under the conditions tested. Further studies are needed to clarify the effects of these combinations on BCG persistence, cell viability, cytokine production, and lipid metabolism. To this end, we will test a range of GP1a and antibiotic concentrations, assess additional parameters, and evaluate other CB2R agonists to confirm whether the observed effects are associated with CB2R activation.