SR8541A: A Potent ENPP1 Inhibitor Driving Dendritic Cell-Mediated Antitumor Responses

Recent studies have focused on innate and adaptive immune pathways, with a significant emphasis on the STING pathway, which is crucial for activating type 1 interferons upon detecting cytosolic nucleic acids by cGAS. cGAS identifies cytosolic DNA and converts it into 2′3′ cGAMP, a key ligand for STING. While synthetic ligands have shown effectiveness in preclinical models but not in phase 1 trials, another approach involves inhibiting ENPP1, a negative regulator that degrades 2′3′-cGAMP. SR-8314, a selective ENPP1 inhibitor, has been shown to activate the STING pathway, and the research continues with the development of SR-8541A, a clinical candidate with enhanced properties and increased immune response.

The study evaluated SR-8541A's binding to ENPP1 using a thermal shift assay and its inhibition of ENPP1 enzymatic activity with TMP or ATP substrates in cell-free or cell-based assays. The impact of SR-8541A on the STING pathway was assessed through RT-PCR, western blots, immune infiltration with PBMCs, and MSD ELISA assays. ENPP1 CRISPR knockout cells were utilized to verify SR-8541A's on-target activity. Pharmacokinetics, stability, and selectivity were also examined.

SR-8541A demonstrated a strong binding affinity for ENPP1 with an IC50 of 1.4 nM and induced STING pathway activation, evidenced by increased gene expression of IFNβ, ISG15, and CXCL10. The treatment led to a rise in secreted type 1 interferon and cytokines. Immune infiltration assays revealed that SR-8541A promotes immune cell migration into cancer spheroids, with dendritic cells playing a critical role in this process. NK cells require dendritic cells to infiltrate treated cancer spheroids. The knockout cell models confirmed that SR-8541A's effects are dependent on ENPP1. The compound was stable in liver microsomes and S9 fractions and showed good oral bioavailability in rodents, with ongoing tumor efficacy studies.

In conclusion, SR-8541A is a potent ENPP1 inhibitor with a robust immune response in 3D spheroid models. The findings, along with its physiochemical properties and tumor model data, suggest that SR-8541A is a promising candidate for clinical investigation.