Abstract LB221: Development of PD-L1-targeted sialidase as a novel cancer immunotherapeutic approach

Abstract Sialoglycans have emerged as a critical glyco-immune checkpoint that impairs antitumor response by inhibiting innate and adaptive immunity. We have previously reported that Bi-Sialidase - an engineered human sialidase-Fc fusion - potentiates antitumor immune response by cleaving terminal sialic acids from sialoglycans (desialylating) on tumor cells and immune cells. Furthermore, we have shown that a tumor-targeted sialidase, a heterodimeric molecule consisting of one chain of sialidase-Fc and a second chain of a HER2-targeting antibody (trastuzumab), leads to more efficient desialylation of tumor cells than the non-targeted Bi-Sialidase and demonstrates antitumor activity in trastuzumab-resistant and low HER2-expressing tumor models. To evaluate the potential of targeted desialylation of both tumor cells and immune cells, we designed and characterized a PD-L1-targeted sialidase in preclinical models, since PD-L1 is expressed on both tumor cells and immune cells. Furthermore, the design of the PD-L1-targeted sialidase enables the combinatorial blockade of two orthogonal immune checkpoint pathways, inhibiting both the PD-1/PD-L1 axis and immunosuppressive sialoglycans. We generated a humanized anti-human PD-L1 antibody with comparable PD-1/PD-L1 blockade potency to the existing anti-PD-L1 drugs, atezolizumab and avelumab. Subsequently, we constructed a bifunctional heterodimeric molecule, consisting of one chain of sialidase-Fc of a third generation of engineered human sialidase (Neu 2) and a second chain of the in-house generated anti-PD-L1 antibody. The PD-L1-targeted sialidase maintained its potency for inhibiting the PD-1/PD-L1 axis as compared to its parental anti-PD-L1 antibody, and demonstrated improved desialylation of PD-L1-expressing tumor cells and immune cells in vitro. We tested the PD-L1-targeted sialidase in transgenic mouse tumor models that express human PD-1 and PD-L1 replacing their murine counterparts, since the parental PD-L1 antibody doesn’t cross-react with the mouse antigen. In the transgenic human PD-L1-expressing mouse colon carcinoma CT26 subcutaneous tumor model, the PD-L1-targeted sialidase exhibited enhanced efficacy compared to the Bi-Sialidase or the anti-PD-L1 antibody. Furthermore, the PD-L1-targeted sialidase demonstrated a dose-dependent tumor growth inhibition and modulation of immune cell infiltration. In conclusion, these results suggested that PD-L1-targeted sialidase offers a promising cancer immunotherapeutic approach, which simultaneously inhibits immunosuppressive sialoglycans and the PD-1/PD-L1 axis through targeted delivery of engineered human sialidase to PD-L1-expressing tumor cells and immune cells. Citation Format: Jenny Che, Lihui Xu, Wayne Gatlin, Robert LeBlanc, Lizhi Cao, James Broderick, Li Peng. Development of PD-L1-targeted sialidase as a novel cancer immunotherapeutic approach [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 LB221.