Abstract A144: Urease-mediated alkalization of tumor microenvironment and its effects on T cell proliferation, cytokine release, and PD-1/PD-L1 interactions
Authors: Wong Wah Yau , Tian Baomin , Kumar Praveen , Gaspar Kim , Demas Steve , Rohmann Sven , Chao Heman L. 
Published: November 2016

The acidic tumor microenvironment is key for cancer progression by promoting invasiveness and metastatic behaviors of cancer cells. In addition, it protects cancer cells from immunotherapy by suppressing proliferation and cytotoxic activities of local immune cells. It has been reported that treatment with bicarbonate or other bases to neutralize the tumor microenvironment could improve immunotherapy responses. In this study, the novel immunoconjugate L-DOS47, which is in Phase I/II testing for non-small cell lung cancer, was used to augment the extracellular pH of acidified culture media that mimics the tumor microenvironment in vitro and its effects on the human T lymphoblastoid cell line Jurkat Clone E6-1 were examined. L-DOS47 is prepared by conjugation of a camelid single domain antibody specific for the human CEACAM6 antigen to Jack bean urease. The immunoconjugate specifically targets and delivers the urease enzyme to CEACAM6-expressing cancer cells where it induces cytotoxicity by converting urea into ammonia, raising pH in situ.

Jurkat cells are susceptible to lactate-induced acidity. Cell growth inhibition was observed in media supplemented with ≥6mM lactate and a corresponding pH of ≤6.7. However, the growth inhibitory effects of lactate could be reversed in the presence of 1 μg/mL L-DOS47 and 2-4mM urea. In addition, cytokine release in phytohemagglutinin (PHA) and phorbol 12-myristate 13-acetate (PMA) stimulated Jurkat cells was also inhibited by the acidic medium, which again could be partially restored by inclusion of L-DOS47/urea. To study the interactions of programmed cell death protein 1 (PD-1) on Jurkat cells with its ligand PD-L1, the human cancer cell lines MDA-MB231 and BxPC-3 were stimulated with Interferon gamma (IFNγ) to express PD-L1 on the cell surface. The IFNγ-stimulated cell lines were found to inhibit IL-2 production in co-incubated Jurkat cells by as much as 40% compared to non-stimulated cells. Interestingly, addition of L-DOS47/urea to the culture medium could partially restore cytokine production in these cells, suggesting a potential role of L-DOS47 in the process of PD-1/PD-L1 interactions. Based on our studies, the results have demonstrated that L-DOS47 exerts its cytotoxic effects on targeted cancer cells in both direct and indirect ways. The immunoconjugate not only generates cytotoxic levels of ammonia in situ but also raises the pH of the tumor microenvironment to promote proliferation and cytotoxic activities of local immune cells.

Citation Format: Wah Yau Wong, Baomin Tian, Praveen Kumar, Kim Gaspar, Steve Demas, Sven Rohmann, Heman L. Chao. Urease-mediated alkalization of tumor microenvironment and its effects on T cell proliferation, cytokine release, and PD-1/PD-L1 interactions [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A144.