Abstract

NOVEL STING PLATFORM FOR
NEW COMPOUNDS DISCOVERY

The innate immune system mediates the
presentation of tumor antigens, priming and activating tumor-specific immune
cells that enable the optimal induction of adaptive antitumor immunity.
Targeting the STING pathway involved in the innate immune response is believed
to activate dendritic cells and priming tumor-targeted T cells. This response opens
new avenues for the development of anti-cancer
therapies. STING is a cytoplasmic protein which plays an essential role in
innate immunity. Upon infection, pathogen dsDNAs activate a DNA sensor, the
cyclic GMP-AMP synthase (cGAS). Activated cGas leads to the production of
2’-3’cGAMP, a cyclic dinucleotide, which then binds to STING proteins. In turn
phosphorylated STING interacts with TBK1 leading to the recruitment and
activation of IRF3 dimer. Nuclear translocation of IRF3 dimer leads to the transcription
of genes encoding IFN-α/β. The STING pathway controls NF-κB dependent
inflammatory cytokines expression. With the emergence of STING- targeting
strategies, Cisbio provides a versatile panel of biochemical and cell-based
HTRF assays enabling further investigations of the STING pathway.

Here we provide a
detailed pharmacological evaluation of the well-known STING binders 2’3’cGAMP,
dicGMP, dicAMP and DMXAA, using the new HTRF human STING biochemical assay.
Using this HTRF kit, inhibitory constants (Ki) similar to previously reported
values were obtained (ref) with Ki 2’3’cGAMP= 2.5nM, Ki dicGMP= 1.2µM, Ki
dicAMP ≥10µM (Zhang, et al 2013).
The newly released HTRF in-vitro STING assay represents a rapid and accurate
method enabling screening and pharmacological characterization of STING
compounds. Evidence proves that the new HTRF phospho and total STING assays
along with phospho-TBK1 and phospho-IRF3 enable an in depth understanding of Sting
signaling. Finally, we show a dose-dependent IFNb secretion upon cGAMP
induced-STING activation by HTRF IFN-beta assay.

Cisbio is providing a comprehensive
understanding of the STING pathway by offering a series of HTRF assays leading
to new agonists discovery.