Abstract 6115: Development of functionally differentiating anti-CD73 antibodies for cancer therapy
Authors: Zhang Zhenqing , Jia Yunli , Miao Xiaoniu , Huang Weifeng , Wang Chao , Yuan Zhijun , Jiang Wenchao , Li Zhiyuan , Chen Liandi , Tsun Andy 
Published: June 2022

Background: Although the discovery and development of first-generation of immune checkpoint inhibitors (towards PD1 and CTLA-4) was a major milestone for cancer therapy, current clinical response rates are still considered very limited. Combination treatments are predicted to improve on these current immunotherapies including the targeting of the adenosine pathway (CD39, CD73 or A2AR), which has shown a lot of promise in preclinical and early clinical studies. CD73 is an ecto-5′-nucleotidase which transforms adenosine monophosphate (AMP) to adenosine. Adenosine is a soluble immunosuppressive metabolite that can suppress natural killer cells and cytotoxic CD8+ T cells. Blockade of CD73-mediated conversion of AMP to adenosine may therefore recover anti-tumor immunity through preventing the enrichment of adenosine in the tumor microenvironment.

Method: In this campaign, two humanized and Fc-silenced IgG antibodies were generated named 7002-01 and 7002-04. The target binding epitopes of these candidates were revealed by binning experiments through bio-layer interferometry. Cell binding experiments were tested on human and cynomolgus CD73 overexpression CHO cell lines by flow cytometry. Cellular CD73 enzyme inhibition experiments were tested using A375, MDA-MB-231, H2030 and BT549 tumor cell lines via the CellTiter-Glo method. Soluble CD73 enzymatic tests were carried out on patient sera or recombinant CD73 protein using a similar method. T cell proliferation assays were performed using PBMC. In vivo efficacy studies were tested in B-NDG B2M-KO mice that were injected subcutaneously with A375 tumor cells and human PBMC.

Results: Two candidates, 7002-01 and 7002-04, were selected based on their functional activity, that recognize different non-overlapping binding epitopes on CD73. Both candidates selectively bind to and can inhibit the activities of both membrane-bound and soluble human CD73 to high levels and seem to maintain inhibition at high dose-ranges without a hook effect. Both candidates can potently rescue adenosine-mediated T cell regulation. Additionally, 7002-01 and 7002-04 have combination synergy or additive effects for CD73 inhibition on soluble CD73, tumor cell lines that express CD73, and PBMC. 7002-01 and 7002-04 have single-agent anti-tumor efficacy and combination synergy with anti-PD1 antibodies in mice. 7002-01 has a typical antibody-like PK profile when rhesus monkeys were administered with a single intravenous dose at 25 or 50 mg/kg. No drug-related toxicities have been observed in GLP toxicity studies with dosages at 50, 250, and 500 mg/kg (QW, 4 weeks).

Conclusion: Highly differentiating anti-CD73 antibodies were discovered that show maximal inhibition of both membranous and soluble CD73 without hook effects at high concentrations. 7002-01 was chosen as the lead molecule for its better overall activity profile and should be entering clinical trials by early 2022.

Citation Format: Zhenqing Zhang, Yunli Jia, Xiaoniu Miao, Weifeng Huang, Chao Wang, Zhijun Yuan, Wenchao Jiang, Zhiyuan Li, Liandi Chen, Andy Tsun. Development of functionally differentiating anti-CD73 antibodies for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6115.