Targeting Ductal Carcinoma in Situ Cancer Stem Cells via Focal Adhesion Kinase

Abstract

Ductal carcinoma in situ (DCIS) of the breast is a non-invasive breast malignancy that accounts for around 20% of all screening-detected breast cancers in the UK. Management of the disease is currently aimed at preventing its progression to invasive cancer but despite treatment with surgery ± radiotherapy, 15-20% of patients with DCIS will suffer a disease recurrence within 10 years, 50% of which will be invasive.Evidence suggests that disease recurrence in breast cancer is due to a specialised sub- population of cells called cancer stem cells (CSCs). They are relatively resistant to current treatment strategies and therefore survive to reinitiate tumour growth at a later date via specialised self-renewal pathways. Targeting CSCs in DCIS should reduce disease recurrence and progression.Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase known to be overexpressed in DCIS and invasive breast cancer. FAK knockout in the PyMT mouse model of breast cancer has recently shown FAK to be integral to the self-renewal capacity of CSCs. The mechanism by which FAK affects self-renewal of CSCs has not previously been investigated in breast cancer, however evidence from neural plate development does suggest that FAK is linked to the canonical Wnt signaling pathway, which is a well- recognised control pathway of self-renewal. FAK has also been demonstrated to play a role in radio-resistance in various cancer cell lines, as CSCs are known to preferentially survive radiation FAK may also be a radio-resistance mechanism in DCIS CSCs. This evidence suggests that FAK is a valid target in the treatment of DCIS CSCs.Work presented here shows for the first time that molecular phenotypes can predict for DCIS recurrence as seen in invasive breast cancers and also suggests that patients with DCIS tumours that express higher levels of the activated, autophosphorylated form of FAK (pFAK) may have a higher risk of disease recurrence. Results show that the DCIS CSC- enriched cell population expresses more FAK and Wnt than non-enriched cells and self- renewal capacity of the CSC-enriched population is significantly decreased in DCIS cell lines and in cells taken from human DCIS tumour samples by FAK inhibition or siRNA knockdown. Data demonstrates that this is mediated, at least in part, by cross-talk between FAK and Wnt signaling. Results also show that the DCIS CSC-enriched cell population is relatively radio-resistant compared to the non-enriched cells. FAK inhibition or siRNA knockdown sensitises the DCIS CSCs to radiation, increasing DNA double strand breaks after FAK inhibition. The way in which FAK expression causes radio- resistance in DCIS still remains unclear although this data suggests that this may also be mediated through cross-talk with the canonical Wnt pathway.Findings presented here suggest that DCIS CSCs are successfully targeted through FAK via inhibiting self-renewal and sensitisation to DNA double strand breaks. In the future, pharmacological FAK inhibitors may provide patients with a novel treatment strategy to help prevent disease recurrence and improve outcome.

Date of Award	1 Aug 2014
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nigel Bundred (Supervisor) & Gillian Farnie (Supervisor)