Abstract 2917: Inhibition of Annexin A6 sensitizes triple negative breast cancer cells to radiation

Abstract

Abstract Introduction: Despite vast evidence that tumor genetics play a dominant role in determining radiosensitivity and ultimate benefit from radiation therapy (RT), current RT delivery algorithms have not successfully incorporated tumor biology. Instead, clinical decisions regarding the use of RT are still based on features of tumor aggressiveness such as stage, grade, degree of metastasis and type of surgery. We provide evidence showing that most aggressive basal-like TNBC cells characteristically expresses low levels of the Ca2+-dependent membrane-binding tumor suppressor Annexin A6 (AnxA6) as compared to mesenchymal-like TNBC cell lines. We have also shown that depletion of AnxA6 in TNBC cells induced severe morphological changes from the slow growing mesenchymal-like to rapidly growing basal-like phenotypes and that this was not only associated with enhanced anchorage independent cell proliferation, but significantly inhibited cell adhesion, motility and invasiveness. Given that rapidly proliferating cells are more radiosensitive, we hypothesized that the expression status of AnxA6 in triple negative breast cancer cells underlies their response to RT. Materials and Methods: For clonogenic assay, cells were grown to 70-80% confluency then were allowed to settle and attach for 8 hours before being exposed to irradiation at various doses. Dishes were then incubated at 37oC in 5% CO2 in a humidified incubator to form colonies for 14 days. Colonies (50 cells or more) were stained with crystal violet and enumerated under a Fisher Stereomaster II 10X stereoscopic microscope. Radiation induced cell cycle arrest was assessed by flow cytometry. Results: Our studies show that depletion of AnxA6, significantly increased the sensitivity of triple negative breast cancer cells via up-regulation of cell cycle pathways as demonstrated by lack of G2/M cell cycle arrest in cells with low level of AnxA6. Additionally, we demonstrate that knockdown of AnxA6 enhanced radiation induced DNA damage. Conclusions: Our findings demonstrate that reduced expression of AnxA6 enhances radiation sensitivity of triple negative breast cancer cells. Note: This abstract was not presented at the meeting. Citation Format: Gladys N. Nangami, Amos Sakwe, Josiah Ochieng. Inhibition of Annexin A6 sensitizes triple negative breast cancer cells to radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2917.