High-Throughput Drug Screening on Borrelia Garinii and Borrelia Afzelii Identified Hypocrellin A as an Active Drug Candidate against Borrelia Species

Lyme disease (LD) is a tick-transmitted infection caused by Borrelia burgdorferi sensu lato species which includes B. burgdorferi, B. afzelii, and B. garinii. The majority of patients with early LD can be cured by standard treatment, yet some still suffer from post-treatment Lyme disease syndrome (PTLDS). The presence of Borrelia persisters has been proposed as a contributing factor, which cannnot be completely killed by the currently used antibiotics for Lyme disease. Finding new pharmaceuticals targeting Borrelia persisters is crucial in developing more effective treatment. Here, we first confirmed the existence of persisters in cultures of B. garinii and B. afzelii and then conducted high-throughput screening of a custom drug library against persister-rich stationary-phase cultures of B. garinii and B. afzelii. 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 in 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-triggered reactive oxygen species (ROS) generation took place 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 above-mentioned drug candidates may help to develop more effective therapies for LD.