High-Throughput Drug Screening on Borrelia garinii and Borrelia afzelii Identified Hypocrellin A as an Active Drug Candidate Against Borrelia Species

Abstract Lyme disease (LD) is a tick-transmitted infection caused by Borrelia burgdorferi sensu lato species, which include B. burgdorferi, Borrelia afzelii and Borrelia garinii. The majority of patients with early LD can be cured by the standard treatment, yet some still suffer from posttreatment LD syndrome. The presence of Borrelia persisters has been proposed as a contributing factor, because they cannot be completely eradicated by the currently used antibiotics for LD. Finding new pharmaceuticals targeting Borrelia persisters is crucial for developing more effective treatments. Here, we first confirmed the existence of persisters in B. garinii and B. afzelii cultures and then conducted a high-throughput screening of a custom drug library against persister-rich stationary-phase B. garinii and B. afzelii cultures. Among 2427 compounds screened, hypocrellin A (HA), anthracycline class of drugs and topical antibiotics along with some other natural compounds were identified to have strong potential for killing persisters of B. garinii and B. afzelii. HA was the most active anti-Borrelia compound, capable of eradicating stationary-phase Borrelia persisters, in particular when combined with doxycycline and/or ceftriaxone. Liposoluble antioxidant vitamin E was found to antagonize the activity of HA, indicating HA’s target is the cell membrane where HA triggers the generation of reactive oxygen species in the presence of light. HA was found to have distinct bactericidal activity against Borrelia species but had poor or no activity against gram-positive and gram-negative bacteria. Identification of the abovementioned drug candidates may help develop more effective therapies for LD.