A novel orally bioavailable small molecular ENPP1 inhibitor (OC-1) for cancer immunotherapy.

Abstract

e15136 Background: Ectonucleotide pyrophosphatase/phosphodiesterase I (ENPP1) is a type II transmembrane glycoprotein with nucleotide pyrophosphatase and phosphodiesterase enzymatic activities. Inhibiting ENPP1 activity has emerged as an attractive approach in cancer immunotherapy, based on two distinct mechanisms. One mechanism is the stabilization of cyclic GMP–AMP (2’3’-cGAMP), which binds to stimulator of IFN genes (STING) and functions as an endogenous second messenger to activate the innate immune system; the other is the lowering of adenosine concentrations in the tumor microenvironment. ENPP1 inhibitors have shown promising monotherapy activity and synergy with various targeted therapies in preclinical models. Methods: OC-1 was characterized, for activity and selectivity, in the following in vitro assays: a luminescence-based enzymatic assay; cell proliferation assays; selectivity assays against 15 phosphodiesterases (PDE) based on inhibition of enzymatic activity; and a cytokine release assay in human THP cells and mouse splenocytes looking at changes in IFN-β/CXCL10. Oral bioavailability of OC-1 in mice and rats was studied following oral gavage. Plasma exposures were quantified using standard LC/MS/MS methods. In vivo tumor growth inhibition (TGI) of OC-1 was evaluated in syngeneic mouse tumor models (CT26 and MC38), as monotherapy and in combination with an anti-PD1 antibody. OC-1 was dosed orally in all in-vivo models. Results: We have discovered a novel small molecule inhibitor of ENPP1, OC-1, with a Ki value less than 10 nM in an ENPP1 enzymatic assay. Increase in gene expression of IFN-β and CXCL10/IP10 was observed in OC-1-treated THP1 cells. No inhibition in cell proliferation in various cancer lines was seen up to the highest concentration tested (30 µM). OC-1 was also selective against 15 PDEs with IC50 > 30 µM. The mean oral bioavailability of OC-1 was 72% and 63% in mice and rats, respectively. OC-1 showed single agent activity (20 – 40% TGI) and combination activity of approximately 75% TGI when it was combined with an anti-PD-1 antibody in in vivo efficacy studies with no impact on body weight. Conclusions: In summary, OC-1 is an orally bioavailable ENPP1 inhibitor with promising anti-tumor activity in preclinical models. Its physicochemical properties make it a suitable candidate for clinical investigation.