RU.521 (RU3205217) is a selective cyclic GMP-AMP synthetase (cGAS) inhibitor (mouse: IC50=0.11 μM), (human: IC50=2.94 μM). RU.521 is an inhibitor of the receptor activated by dsDNA (IC50=700 nM). RU.521 inhibits cGAS-mediated interferon upregulation. RU.521 reduces constitutive interferon expression in macrophages derived from a mouse model of Aicardi-Goutieres syndrome.

dsDNA:700 nM, THP-1-Dual cells:38.4 μM (CC50), H69AR cells:32.9 μM

METHODS: Human THP1-Dual cells were treated with RU.521 for 24 hours, and the cytotoxicity was determined using the CCK-8 assay.
RESULTS: RU.521 inhibited cell growth (CC50=38.4 μM). [1]

METHODS: To study the effect of RU.521 on sepsis, mice were intraperitoneally injected with RU.521 (5 mg/kg) (injected with LPS) in a single dose.
RESULTS: RU.521 enhanced cardiac function, reduced cardiac inflammation, oxidative stress and apoptosis, and alleviated the symptoms of sepsis in mice. [2]

Small-molecule compounds were serially diluted to concentrations spanning the range tested in the response curves were added to 6.7?×?10^5 RAW-Blue macrophages plated 16?h prior in 96-well dishes, then harvested 72?h after compound addition. ATP was measured using CellTiter Glo Viability Assay using 50?μM Tamoxifen as a positive control for cytotoxicity. Viability values were generated using vehicle (DMSO) or the first dose as 100% and Tamoxifen as 0%. Outliers were removed.

the chronically elevated levels of cytokines observed in Trex1 null mice are a consequence of constitutively activated cGAS, due to the inability to eliminate aberrantly localized self-DNA. We harvested BMDMs from 6–8-week old Trex1 ?/? mice, treated them with each compound, and measured expression levels of IFNB1 by quantitative reverse transcription PCR (qRT-PCR). Treatment of primary BMDMs with RU.521 or its analogs reduced IFNB1 expression, indicating their effectiveness in suppressing intrinsic DNA-dependent, constitutively-activated type I interferon expression in cells deficient of a cytoplasmic DNA exonuclease.