Abstract LBA009: Orally available ENPP1 inhibitor, TXN10128, restores STING activation in tumor microenvironment and confers anti-tumor responses in combination with immune checkpoint blockade
Authors: Kim Sungjoon , Ali Imran , Yu Ahran , Lee Sun woo , Park Sung young , Choi Jung hwan , Park Yong-yea , Park Chan sun 
Published: December 2021

Abstract
Background Recently, there are growing needs of immune modulators that can convert cold tumors into hot tumors, which can be utilized for combination treatment with existing immune related therapies. An orally available small molecule that is capable of activating innate immune response can be an ideal candidate to meet those needs. Upon binding to 2’3’-cGAMP, STING activates TBK1-IRF3 signaling cascade in cancer cells as well as host cells and promotes innate immune responses against cancer cells, leading to T cell mediated anti-tumor immunity by facilitating T cell priming and infiltration. Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), a transmembrane protein highly expressed in subset of cancer cells, has been known to hydrolyze 2’3’-cGAMP and negatively regulates the STING activation. Inhibition of ENPP1 can prevent 2’3’-cGAMP degradation in tumor microenvironment (TME) and restore STING activation, leading to innate immune responses. It has been shown that ENPP1 inhibitor can enhance anti-tumor immunity by restoring 2’3’-cGAMP level in TME and can prevent tumor growth when co-treated with immune checkpoint blockade (ICB) as well as with radiation therapy. Methods The activity of ENPP1 inhibitors were measured in enzymatic assay using 2’3’-cGAMP as substrate and in cellular STING activation assay using IRF3-responsive reporter. Also, the effects on innate immune response were estimated in LIN (Lymphocyte INfiltration) assay measuring lymphocyte infiltration and TMED (TME in Dish) assay measuring tumor spheroid growth and immune cell activation. In vivo efficacy of TXN10128 (PO dosing) was evaluated in MC38 syngeneic model in combination with and anti-PD-L1 (IV dosing). Tumor growth was monitored and immune cells in tumor were analyzed. Results TXN10128 inhibited ENPP1 activity with single digit nanomolar potency in enzyme assay and further induced STING activation in cellular assay. In 3D spheroid co-culture condition, TXN10128 enhances lymphocyte infiltration and inhibits the spheroid growth. TXN10128 has a drug-like properties desirable for oral administration in terms of physicochemical properties and pharmacokinetics parameters. Systemic exposure of TXN10128 by PO dosing resulted in synergistic tumor growth inhibition with anti-PD-L1 antibody and improved tumor-infiltrating lymphocytes (TIL) profile as expected in MC38 syngeneic model. Additional in vivo studies are on-going to expand applicable cancer types to TXN10128 treatment. Conclusions TXN10128 is a potent and selective ENPP1 inhibitor that can exert immune response in 3D co-culture condition, which is consistent with tumor growth inhibition and favorable TIL profile in animal model. Together with promising drug-likeness, these studies demonstrate that TXN10128 is a suitable candidate for clinical investigation as a combination partner with existing immunotherapies.
Citation Format: Sungjoon Kim, Imran Ali, Ahran Yu, Sun woo Lee, Sung young Park, Jung hwan Choi, Yong-yea Park, Chan sun Park. Orally available ENPP1 inhibitor, TXN10128, restores STING activation in tumor microenvironment and confers anti-tumor responses in combination with immune checkpoint blockade [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA009.