Abstract 2124: Therapeutic targeting of cancer-associated fibroblasts by a novel protein, ProAgio, effectively decreases TNBC growth and metastasis to the lungs

Background: TNBC metastasis is responsible for a majority of the mortalities associated with breast cancer across the globe. Cancers metastasize to various distant organs such as lungs, liver, and bones, which accounts for a low 5-year survival rate. Lung offers the most favorable environment and is, therefore, the most common metastatic site in the majority of patients. Currently, there are no effective targeted therapies for breast cancer metastasis and hence there is a dire clinical need to establish treatment for this disease. It is noteworthy that tumor growth and metastasis is supported by the surrounding stroma, also known as the tumor microenvironment (TME) that promotes the proliferation of cancer cells by secreting various growth factors and cytokines. Despite growing awareness of the role of the TME in tumor progression, targeting cells that comprise the majority of the TME is still uncharted territory. TME is composed of a variety of cell types, with cancer-associated fibroblasts (CAFs) - cells that express high levels of integrin αVβ3 - being the predominant cell type. Here we report the development of a novel, rationally designed protein, ProAgio, which induces apoptosis of integrin αVβ3 expressing cells via a novel mechanism. Objectives: To test the efficacy of ProAgio in targeting the TME in TNBC. To elucidate the mechanism through which ProAgio exerts an anti-metastatic effect. Methods: We implanted 4T1 cells orthotopically in Balb/c mice and treated them with 10 doses of ProAgio (10mg/kg; i.p.) when the tumor volume reached around 250mm3. Another in vivo experiment was performed with the 4T1 model to see the effect of ProAgio in combination with a chemotherapeutic agent, doxorubicin (DOX) (3mg weekly i.p.). The tissues isolated were stained for collagen and α-SMA (CAF marker). Breast and lung fibroblasts were differentiated with TGF-β (5ng/mL) for two weeks and annexin V staining was used to measure their apoptosis. Results: Our data demonstrate that ProAgio inhibits breast tumor growth and metastasis to lungs by decreasing collagen and CAFs in 4T1 tumor-bearing mice. Histological analyses of the tissues exhibit decreased collagen and α-SMA in both breast tumor and lungs upon ProAgio treatment. Mechanistically, ProAgio induces integrin αVβ3-mediated apoptosis in breast and lung CAFs. In addition, ProAgio shows no effect on 4T1 breast cancer cells as they lack αVβ3 expression. Our study demonstrates that a combination of ProAgio and DOX exhibits improved anti-tumor efficacy and enhances survival in the 4T1 murine model. In conclusion, our study reports the first evidence of inducing apoptosis in CAFs and shows antitumor synergy for combined therapy, supporting the significant therapeutic potential of ProAgio as a stand-alone therapy and more effectively when combined with chemotherapy. Citation Format: Malvika Sharma, Ravi Chakra Turaga, Yi Yuan, Falguni Mishra, Zhi-Ren Liu. Therapeutic targeting of cancer-associated fibroblasts by a novel protein, ProAgio, effectively decreases TNBC growth and metastasis to the lungs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2124.