Valinomycin boosts TB drugs to kill dormant, drug-resistant bacteria

Tuberculosis remains difficult to cure because single drugs often fail and some bacteria enter a state called phenotypic drug tolerance, where they survive despite treatment. Researchers led by Nitin Pal Kalia focused on that survival strategy. They targeted the bacterial energy machinery — the electron transport chain (ETC) that powers oxidative phosphorylation and ATP production — because dormant Mycobacterium tuberculosis (Mtb) still needs bioenergetics to survive. Instead of testing new antibiotics alone, the team tested combinations: established bioenergetic inhibitors bedaquiline (BDQ), telacebec (Q203), and clofazimine (CFZ) together with the potassium ionophore valinomycin. Valinomycin disrupts the proton motive force (pmf), a key component of how cells generate ATP. The idea was to attack energy production on multiple fronts so that dormant and drug-tolerant Mtb could not maintain the low-level metabolism that lets them survive conventional drugs. The study asked whether combining these drugs could turn drugs that only stop growth into treatments that actually kill and sterilize bacterial populations, including nutrient-starved non-replicating Mtb.

The team used several laboratory tests to measure how the combinations worked. Checkerboard assays measured interaction between drugs and revealed synergistic activity with bedaquiline (BDQ) and additive effects with telacebec (Q203) and clofazimine (CFZ). Those interactions matched biochemical changes: the combinations correlated with a two to three-fold reduction in ATP IC 50 values, indicating greater disruption of cellular energy. Time-dependent killing assay results were striking: valinomycin turned the inhibitors’ bacteriostatic activity at sub-MIC concentrations into bactericidal killing, achieving sterilization in the tested cultures. The lethal synergy seen in test tubes also appeared in a THP-1 macrophage intracellular model for TB, which simulates infection inside immune cells. Respiration assays confirmed that the combinations collectively halted oxygen consumption, consistent with collapse of the ETC and failure of oxidative phosphorylation. The effects were observed against both actively replicating and nutrient-starved non-replicating Mtb, which models the hard-to-kill, dormant bacterial population.

These findings point to a strategy of exploiting metabolic vulnerabilities in Mtb by hitting its bioenergetics from several directions at once. In the experiments reported by Nitin Pal Kalia and colleagues, the BDQ/valinomycin pairing stood out as a particularly powerful combination, converting drugs that merely stopped growth into combinations that could sterilize cultures. Because dormant and drug-tolerant bacteria are a major reason TB treatment is long and difficult, combinations that produce lethal synergy could form the basis of new sterilizing regimens. The study suggests that targeting the electron transport chain and proton motive force together can overcome phenotypic drug tolerance and may help shorten therapy or improve outcomes for drug-resistant and dormant infections. While the results are preclinical laboratory work, they map a clear path for further research into combination regimens that deliberately dismantle the energy systems that sustain persistent Mtb.