Abstract 4480: Preclinical characterization of potent and selective oral PD-L1 small-molecule antagonists
Authors: Wang Liang-Chuan S. , Koblish Holly , Zhang Yue , Kulkarni Ashwini , Covington Maryanne , Gallagher Karen , Yang Gengjie , Rios-Doria Jonathan , Stevens Christina , Hansbury Michael , O'Connor Sybil , Yang Yan-ou , Diamond Sharon , Burke Krista , Xiao Kaijiong , Li Jingwei , Yao Wenqing , Wu Liangxing , Scherle Peggy , Hollis Gregory , Huber Reid 
Published: August 2019

Abstract
Monoclonal antibodies against PD-L1 or PD-1 have been approved for the treatment of multiple tumor histologies by virtue of their ability to restore T cell effector function, increase T cell proliferation and enhance infiltration of tumor-reactive T cells. A small molecule approach to PD-(L)1 axis blockade may offer distinct benefits over the use of monoclonal antibodies including improved tissue penetration, titratability, absence of immunogenicity, ease of administration, and potential for fixed dose oral-oral therapeutic combinations. We have identified a novel class of small molecule PD-L1 antagonists that are capable of functional PD-(L)1 axis blockade by virtue of their ability to induce PD-L1 internalization. In vitro, select small molecules demonstrate high affinity to human PD-L1, potently disrupt the PD-L1:PD-1 interaction (&lt;4nM), and inhibit Src homology region 2 domain-containing phosphatase (SHP2) recruitment to PD-1 (&lt;10nM). As a result, PD-1-mediated suppression of nuclear factor of activated T cells (NFAT) activation is reduced and IFNγ production by T cells is restored. These bioactive small molecule PD-L1 antagonists are shown to reduce surface PD-L1 levels in tumor cells and peripheral blood monocytes with IC50s ranging from 1-250nM, providing an in vivopharmacodynamic biomarker for compound activity. Using humanized NSG mice bearing MDA-MB-231 tumors, oral administration of small molecule PD-L1 antagonists for 28 days demonstrated a dose-dependent reduction in tumor growth with a concomitant and dose-dependent increase in the number of tumor-infiltrating T cells. These data were concordant with the dose-dependent reduction of surface PD-L1 levels seen on both tumor cells and tumor associated macrophages at the end of the study. Similar data, including dose-dependent tumor growth inhibition, PD-L1 internalization and increase in tumor-infiltrating T cells, were also obtained using a murine MC38 xenograft system genetically engineered to over express human PD-L1. No in vivo activity was observed when tumors were treated in immunocompromised mice, confirming the pharmacologic dependency on a competent immune system. Finally, these oral PD-L1 small molecule antagonists demonstrated equivalent anti-tumor activity in preclinical tumor models when compared head-to-head to clinically approved PD-(L)1 axis targeting monoclonal antibodies. In conclusion, effective PD-(L)1 axis blockade and functional activation of the immune system can be achieved in vivo through this novel series of orally bioavailable small molecule PD-L1 antagonists, supporting the clinical evaluation of the mechanism as a novel approach to immune therapy.
Citation Format: Liang-Chuan S. Wang, Holly Koblish, Yue Zhang, Ashwini Kulkarni, Maryanne Covington, Karen Gallagher, Gengjie Yang, Jonathan Rios-Doria, Christina Stevens, Michael Hansbury, Sybil O'Connor, Yan-ou Yang, Sharon Diamond, Krista Burke, Kaijiong Xiao, Jingwei Li, Wenqing Yao, Liangxing Wu, Peggy Scherle, Gregory Hollis, Reid Huber. Preclinical characterization of potent and selective oral PD-L1 small-molecule antagonists [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4480.