Background
Nontuberculous mycobacteria (NTM) belong to the same family that includes pathogens causing tuberculosis and leprosy. These emerging, opportunistic pathogens cause a wide spectrum of diseases in individuals with compromised immune systems such as TB-like lung disease along with localised and systemic infections. Treatment of NTM infections is complex, prolonged and can be associated with high failure rates due to its innate resistance to several classes of commonly used antimicrobials.
NTM are mostly intracellular pathogens, and some species are resistant to potent anti-TB drugs. Our team has developed an innovative drug screening model for the most resistant NTM species (Mycobacteroides abscessus), located within human stem cell derived macrophages.
Hypothesis: A fluorescent reporter-based infection model comprising of M. abscessus internalised within stem cell derived macrophages1 provides a powerful platform for high-throughput screening (HTS) of broad-spectrum drug libraries to identify novel bactericidal agents that can kill bacteria inside host cells.
Methods: Our fluorescent reporter-based infection assay for drug screening was automated for integration within the HTS platform. The assay was designed to compare drug screening candidates against azithromycin and clarithromycin, clinically used anti-mycobacterial antibiotics. We have further optimised critical downstream validation assays (in vitro infection testing, biofilm assays and in vivo testing in a mouse infection model) that will verify the bactericidal activity of identified drug candidates post-HTS.
Results: We have successfully adapted our physiologically relevant M. abscessus infection model in human stem cell derived macrophages and are now screening a compound library of >6000 FDA approved, off-patent drugs that include a diverse array of different compound classes. An M. abscessus infection assay within stem cell derived lung alveolar and airway epithelial cells has been developed to complement the macrophage infection assay. Furthermore, a TNF-alpha knockout mouse model was modified to mimic a natural route of infection (via inhalation) to enable the testing of different drug efficacies.
Conclusions: Our unique screening/validation pipeline with a broad-spectrum drug library has the potential to not only identify compounds with direct antimicrobial activity against M. abscessus but also those that are non-cytotoxic and can potentiate the action of host cells for bacterial clearance.