Breast cancer can relapse up to 25 years later, despite initial surgical resection and adjuvant therapy. This indicates existence of a repository of dormant cells that give rise to clinically latent disease, and that these cells are highly resistant to current therapies. The mechanisms underlying dormancy are not well understood, but successful suppression or eradication of these dormant cells may prevent or delay recurrence. We describe an in vitro model that can be used in the discovery of potential therapies in a high throughput setting.
Our aim is to establish an in vitro preclinical model that mimics tumour dormancy for use in drug discovery. Therapies that can inhibit outgrowth of dormant tumour cells should prevent the development of secondary disease.
We have utilised a 3D culture technique where cells of varying metastatic capacity are seeded at very low density on Matrigel and show properties that mirror their metastatic behaviour in vivo1,2. There is no dormancy phenotype if cells are seeded at higher densities or on plastic in standard 2D culture. The low density 3D growth parallels metastatic behaviour in vivo.
We have validated our assay using inhibitors against focal adhesion kinase (FAK)1,2 and autophagy (using chloroquine)3,4 to demonstrate that inhibiting these genes/pathways can induce a dormant phenotype in aggressive cell lines, without cytotoxicity. We have conducted a preliminary high throughput screen and validated some positive candidates that may be key regulators of the dormancy phenotype.
Positive candidate molecules will be validated in in vivo dormancy models for their ability to delay the development of secondary disease to correlate our in vitro data. Our in vitro model can also be used to investigate molecular mechanisms underlying dormancy by targeting pathways, and tracking their phenotype and viability.