Novel mechanism of action of Anti-malarial drugs in the inhibition of Type I interferon production

Anti-malarial drugs (AMD) such as Hydroxychloroquine (HCQ) and Quinacrine (QC) are effective in the treatment of skin rash and arthritis in systemic lupus erythematosus (SLE). However which mechanism(s) are responsible for their beneficial action is uncertain. Type I interferon, (IFN-I) is strongly implicated in the pathogenesis of SLE and ‘interferonopathies’ such as Aicardi-Goutieres Syndrome (AGS). A new DNA activated IFN-I pathway, cyclic GMP-AMP (cGAMP) synthase (cGAS), was recently discovered and linked to AGS and mouse models of Lupus. In silico screening of drug libraries identified several antimalarial drugs (AMD) which could potentially inhibit cGAS activity by interacting with cGAS/DNA dimer complex. Electrophoretic Mobility Shift Assay revealed that AMD disrupted the double stranded DNA-cGAS complex in a dose dependent manner. These AMD also inhibited IFN-I expression in THP1 cells transfected with dsDNA and in 293T cells transfected with cGAS/STING plasmids validating that cGAS is a target of AMD. We synthesized several new AMD. One of these compounds, X6, had excellent water solubility and cell penetration. X6 localized to the cytosol and had a lower toxicity profile compared to QC. Biochemical and cellular assay revealed that X6 was a more potent inhibitor of IFN-I production than HCQ. Our studies identify new DNA sensor cGAS as a target of AMD activity, which provide a novel mechanism of action of these AMD. We have synthesized new AMD like drugs that are also able to inhibit cGAS as well as Toll pathways. These drugs could be beneficial for the treatment of AGS and/or Lupus.