Abstract PR02: Lyn kinase regulates myeloid-cell responses to mammary tumors

Abstract

Abstract Myeloid-cell enrichment in tumors is correlated with increased metastasis, reduced survival times, and poor treatment outcomes in multiple cancers, including breast cancer. Many signals (CSF, Il-6, chemokine) to myeloid cells in the tumor microenvironment are transduced through the Src-family kinase Lyn. Expression of both isoforms of Lyn (LynA and LynB) is regulated by cytokine signaling and cell type, and total Lyn expression is negatively correlated with breast cancer patient survival. Lyn expression in macrophages contributes to leukemogenesis, but the functional contributions of LynA and LynB in solid tumors have not been studied. We are examining the contributions of Lyn in trafficking of myeloid cells to mammary tumors, pro-tumor polarization of tumor-associated macrophages, and growth and metastasis of mammary tumors. In an E0771 orthotopic transplant model in hosts expressing or lacking LynA or LynB expression, we have discovered that Lyn expression in the mammary tumor microenvironment promotes the early recruitment of monocytes, macrophages, neutrophils, and dendritic cells, as determined by flow cytometry analysis of tumors early in development. Furthermore, Lyn promotes pro-tumor polarization of tumor-associated macrophages. Tumors from Lyn knockout animals contained populations of inflammatory, anti-tumor macrophages that were not significantly different in size from WT, but the CD206+, anti-inflammatory population was reduced. Finally, we have observed that expression of either Lyn isoform in the tumor microenvironment can promote tumor growth and decrease survival in orthotopically transplanted mice. In contrast, our studies suggest that only LynB promotes metastasis to the lungs of transplanted mice, as determined by in vivo imaging of a hyper-metastatic, luciferase-expressing variant of E0771. Together, our findings suggest that Lyn kinase plays a role in the signaling response of myeloid cells, which are major factors in disease course and treatment response, to tumor-associated stimuli. Modulation of Lyn activity, specifically the LynB isoform, or the activity of its downstream signaling partners, is thus a potential strategy for influencing the trafficking and polarization of myeloid cells within breast tumors to benefit patients. Citation Format: Joseph T Greene, Ben F Brian, Aditi Bapat, Tanya S Freedman. Lyn kinase regulates myeloid-cell responses to mammary tumors [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr PR02.