Metastatic breast cancer is the overwhelming cause of breast cancer mortality and is still incurable. The rapid development of immunotherapy is an exciting new area of research in metastatic breast cancer. However, the extreme immunosuppressive tumor environment poses a major challenge. A better understanding of how the immune system can be harnessed against metastatic cancer is required to improve patient outcomes. We previously showed that expression of the receptor tyrosine kinase Ron in the host, rather than Ron's tumor expression, contributed to tumor-associated immunosuppression and duo inhibition of Ron and CTLA-4 significantly reduced metastatic outgrowth. However, the actual mechanism remains unclear.

The present study provides evidence that the N-terminal truncated isoform, short-form Ron (SF-Ron), is the major contributor in suppressing the anti-tumor immune responses and promoting metastatic outgrowth. Genetic deletion of host SF-Ron nearly eliminated breast cancer metastasis in mice, lead to systemic immune-activation, increased recruitment of lymphocytes to the site of metastasis, and augmented tumor-specific T-cell responses. Lack of SF-Ron also leads to the accumulation of CD4+ T-cells in the metastatic lungs and endowed with anti-tumor potential. Importantly, mice treated with small molecule Ron kinase inhibitor that targets both Ron and SF-Ron, produced significantly higher, active, tumor-specific CD8+ T-cells. Our study indicates that blocking Ron, especially the SF-Ron, remodels the metastatic lung microenvironment to enhance anti-tumor immunity. This study sheds light on the potential non-redundant roles of full-length and SF-Ron isoforms in mediating breast cancer metastasis and anti-tumor immune responses; and highlights the relevance of combining Ron inhibitors with immunotherapeutic agents to potentially improve treatment efficacy for metastatic breast cancer patients.

Citation Format: Shu-Chin Alicia Lai, Harika Gundlapalli, Huseyin A Ekiz, Alana L Welm. Inhibition of short-form ron eliminates breast cancer metastases through an immune-mediated mechanism [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-24.