Abstract P4-01-13: Low tumor TLR9 expression results in resistance to growth inhibitory and autophagy responses to common breast cancer treatments

Abstract

Abstract Background: Toll like receptor-9 (TLR9) is an intracellular, innate immune system DNA-receptor, which is widely expressed in cancers. We previously demonstrated that low tumor TLR9 protein expression is associated with poor prognosis among triple negative breast cancer (TNBC) patients. A similar result is now detected also in larger, mRNA expression based datasets (Kmplot.com), which extend our initial observation to basal and luminal B clinical subtypes. The reason for TLR9 association with poor prognosis is not known.Aim: Since poor outcomes in early breast cancer are due to adjuvant treatment failures, we studied the role of TLR9 in breast cancer chemotherapy responses, growth inhibition and autophagy. Materials and Methods: Chemotherapy effects on the growth of control shRNA and TLR9 shRNA TNBC MDA-MB-231 and estrogen receptor expressing (ER+) T47-D cells were studied with cell confluency assays in vitro and in orthotopic mouse models in vivo. Autophagy was assessed with LC3I and II Western blots. Association of tumor TLR9 status with autophagy will be further studied in a cohort of neo-adjuvant treated patients, by comparing pre-treatment TLR9 expression with post-treatment LC3 vesicular expression, with immunohistochemistry. Autophagy gene expression will also be studied with RNAseq. Results: TLR9 shRNA cells were significantly less sensitive to the growth inhibitory effects of standard breast cancer chemotherapies than the corresponding control shRNA cells in vitro. The TLR9 shRNA T47-D cells were also significantly less sensitive to tamoxifen, than corresponding control shRNA cells. Docetaxel inhibited the growth of tumors formed by control shRNA cells, but not by TLR9 shRNA MDA-MB-231 cells in an orthotopic mouse model in vivo. Further chemotherapies and autophagy responses are being tested in this model as well. Standard chemotherapies induced accumulation of LC3IIB in control shRNA cells, but not in TLR9 cells, as demonstrated with Western blots. Conclusions: Decreased expression of tumor TLR9 is associated with 1) poor prognosis among basal and luminal B subtype patient samples, and in 2) decreased growth inhibitory and 3) decreased autophagy responses to common breast cancer chemotherapies and tamoxifen. Our results suggest that treatment responses, and thereby survival of patients with low-TLR9 tumors, may be improved by enhancing TLR9-associated autophagy. Citation Format: Katri Selander, Juha Klaper, Nataliia Petruk, Mauricio Ramm, Arja Jukkola, Eeva-Liisa Eskelinen. Low tumor TLR9 expression results in resistance to growth inhibitory and autophagy responses to common breast cancer treatments [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-01-13.