REGULATION OF BREAST CANCER STEM CELL ACTIVITY BY FOCAL ADHESION KINASE SIGNALLING

Abstract

Background: Despite improvements in breast cancer survival there are still more than 11,000 deaths each year in the UK alone. There is a particular need to improve treatment outcomes in triple negative breast cancer which currently have a poor prognosis. Breast Cancer Stem-like Cells (BCSC) have been shown to be associated with tumour development, metastasis and resistance to current treatment modalities and hence investigated as potential therapeutic targets. Focal Adhesion Kinase (FAK) is classically known for its role in cell adhesion, survival and metastasis with emerging evidence suggesting it regulates CSC activity. We aimed to explore the association of FAK with clinical outcome and investigate the effects of FAK inhibition on CSC activity. Methods: A retrospective case-control cohort of 244 samples was created across a range of molecular phenotypes. IHC expression of phosphorylated (pFAK) and total FAK (tFAK) was evaluated alongside CSC markers Aldehyde Dehydrogenase 1 (ALDH1) and Integrin Alpha 6 (ITGa6). FAK expression was evaluated across a range of ductal cell lines and within CSC populations. The effects of FAK inhibition on mammosphere formation and selfrenewal were evaluated across a range of cell lines and primary patient samples in conjunction with current adjuvant treatments. Finally, the effects of FAK inhibition on tumour growth, proliferation and CSC activity were determined in two triple negative PDX models. CSC activity was evaluated using the mammosphere and Aldefluor assays and tumour initiaiting capacity measured using the limiting dilution assay. Results: The expression of tFAK not pFAK correlates with reduced survival (HR4.9). Coexpression of tFAK and ALDH1 (HR16.7) or ITGa6 (HR12.8) was associated with the poorest prognosis. pFAK was higher in ALDH+ cells and invasive cell lines. Combined FAK inhibition and paclitaxel reduced mammosphere formation and self-renewal in two triple negative cell lines and 10 ER negative patient samples. These findings were replicated in two triple negative PDX models where combined FAK inhibition and paclitaxel treatment reduced primary tumour growth, proliferation and ex vivo CSC activity including sphere forming ability, ALDH+ expression and tumour initiating capacity. Conclusions: This work demonstrates that FAK and BCSC marker expression are associated with reduced breast cancer survival. Pharmacological FAK inhibition reduced CSC activity, particularly in the triple negative setting when used in conjunction with current therapies. This data suggests that FAK inhibition may be used in combination with chemotherapy to improve treatment outcomes in triple negative invasive breast cancer.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nigel Bundred (Supervisor) & Robert Clarke (Supervisor)