FOXA1 Case Study

  • FOXA1 is an emerging therapeutic target, with robust target validation, in oestrogen receptor (ER) positive breast cancer. 
  • CRT-DL, working with the laboratory of Dr Jason Carroll, has designed, developed and validated novel cell-based reporter assay to support the screening cascade.
  • Promising tool compounds have been generated facilitating the probing of FOXA1 biology. Therapeutic intervention of ER positive/FOXA1 dependent signalling may ultimately circumvent resistance to hormonal therapies, such as tamoxifen and aromatase inhibitors.

Treatment of hormone dependent breast cancers with a combination of surgery and adjuvant chemotherapy have led to significant increases in overall patient survival. However, despite these advancements in the management of the disease, there is an urgent requirement for novel treatment modalities. Deprivation of oestrogen and prevention of oestrogen receptor signalling by both selective oestrogen modulators and aromatase inhibitors have been successful therapeutic approaches. Resistance to therapy develops in many patients, the majority of whom retain oestrogen receptor activity.

FOXA1, a transcription factor required for oestrogen receptor mediated activation of target genes identified by our collaborator Dr Jason Carroll, has been shown to be pivotal in the tumourigenesis of oestrogen receptor positive luminal breast cancer (Figure 1). There is a clear clinical rationale for therapeutic targeting of this pathway, however due to the inherent challenges of “drugging”  transcription factors, CRT-DL developed cell based screening assays to identify inhibitors of this pathway.

Figure 1

The effective collaboration between CRT-DL and Dr Jason Carroll, Cancer Research UK Cambridge Research Institute has facilitated the establishment of a robust screening cascade, ultimately cumulating in the identification of inhibitors. Establishment of a project team that combines the scientific understanding of the target and pathway with the expertise in assay build and validation has been critical to the successful prosecution of this project. The team validated the role of FOXA1 in ER positive breast cancer proliferation. MCF-7 cells were transfected with a FOXA1/ER luciferase reporter in the laboratory of Dr Jason Carroll. This engineered cell line was utilised at CRT-DL to validate FOXA1 specificity using both RNA interference and ER antagonists.

Following validation of the assay, a collection of 180,000 diverse small molecules was screened and subsequently counter-screened to remove any cytotoxic or luciferase inhibitors. Subsequent cellular studies, both phenotypic and using the identified pharmacodynamic biomarker (PD biomarker) TFF1 and XBP, enabled the identification of potent compounds that modulated the FOXA1/oestrogen receptor pathway. The clear line of sight to the clinic for a modulator of the FOXA1/oestrogen receptor pathway, coupled with the lack of drug discovery competition, make this an attractive therapeutic target. Addressing the challenges of building a robust phenotypic screen has enabled identification of selective tool compounds that will underpin further investigations of FOXA1 biology and molecular target deconvolution.