title: Verapamil, and its metabolite norverapamil, inhibit macrophage-induced, bacterial efflux pump-mediated tolerance to multiple anti-tubercular drugs.
abstract: Drug tolerance likely represents an important barrier to tuberculosis treatment shortening. We previously implicated the Mycobacterium tuberculosis efflux pump Rv1258c as mediating macrophage-induced tolerance to rifampicin and intracellular growth. In this study, we infected the human macrophage-like cell line THP-1 with drug-sensitive and drug-resistant M. tuberculosis strains and found that tolerance developed to most antituberculosis drugs, including the newer agents moxifloxacin, PA-824, linezolid, and bedaquiline. Multiple efflux pump inhibitors in clinical use for other indications reversed tolerance to isoniazid and rifampicin and slowed intracellular growth. Moreover, verapamil reduced tolerance to bedaquiline and moxifloxacin. Verapamil's R isomer and its metabolite norverapamil have substantially less calcium channel blocking activity yet were similarly active as verapamil at inhibiting macrophage-induced drug tolerance. Our finding that verapamil inhibits intracellular M. tuberculosis growth and tolerance suggests its potential for treatment shortening. Norverapamil, R-verapamil, and potentially other derivatives present attractive alternatives that may have improved tolerability.
authors.affiliation: Department of Microbiology.
authors.forename: Kristin N
authors.initials: KN
authors.lastname: Adams
authors.affiliation: Department of Medicine, Division of Infectious Diseases.
authors.forename: John D
authors.initials: JD
authors.lastname: Szumowski
authors.affiliation: Department of Microbiology Department of Medicine, Division of Infectious Diseases Department of Immunology, University of Washington, Seattle, Washington.
authors.forename: Lalita
authors.initials: L
authors.lastname: Ramakrishnan
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors; D002460:Cell Line; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D006801:Humans; D008264:Macrophages / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D014700:Verapamil / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D002121:Calcium Channel Blockers; D002352:Carrier Proteins; C016904:norverapamil; D014700:Verapamil
keywords: R-verapamil; efflux; efflux pump inhibitor; norverapamil; persistence; tolerance; tuberculosis; verapamil