The development of resistance to therapeutic regimens is a major problem for cancer therapy, as it precludes complete ablation of the tumour and leaves highly malignant and drug resistant cells remaining at the tumour site. These then drive local and distant tumour recurrence, the main cause of cancer mortality. Recent evidence has demonstrated the important role that cancer stem cells play in this process, as they express heightened resistance to current therapies compared to the majority non-stem cell population. They thus survive and drive tumour recurrence.
In the course of my current project, I have identified two cancer stem cell populations in squamous cell carcinoma (SCC). One has an epithelial phenotype and a CD44highESAhigh marker profile, and the other has a more mesenchymal phenotype and a CD44highESAlow marker profile. Cells are able to switch in both directions between these two phenotypes through the processes of epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET). The epithelial phenotype exhibits much faster growth and the mesenchymal phenotype has greatly enhanced invasive capacity. Importantly, the results obtained in vitro were reproducible using an in vivo transplantation system, with the only difference being that the in vivo murine system is inferior in terms of the amount of useful information generated about the cell types under investigation.I also now have evidence to demonstrate that both the epithelial and mesenchymal cancer stem cell phenotypes exhibit therapeutic resistance, but differences in their responses to individual drugs suggests differing underlying mechanisms of therapeutic resistance.
Therefore, new methods of targeting both phenotypes are required in order to develop therapies that clear all malignant cells and thus prevent tumour recurrence. I aim to develop an in vitro cell line model that enables high-throughput testing of compounds for their ability to target both cancer stem cell thenotypes. I will also use this model to assess the mechanisms of therapeutic resistance. In addition to work using cell lines, I will develop in vitro assays on fresh tumour specimens to enable comparison with data gained using cell lines and thus provide evidence that cell lines are a relevant model for therapeutic development.
Biddle A et al. (2016) Phenotypic Plasticity Determines Cancer Stem Cell Therapeutic Resistance in Oral Squamous Cell Carcinoma. EBioMedicine 4:138–145
Shigeishi H et al. (2014) Elevation in 5-FU-induced apoptosis in Head and Neck Cancer Stem Cells by a combination of CDHP and GSK3β inhibitors. J Oral Pathol Med Aug 28 [Epub ahead of print] doi: 10.1111/jop.12230
Biddle A et al. (2013) CD44 staining of cancer stem-like cells is influenced by down-regulation of CD44 variant isoforms and up-regulation of the standard CD44 isoform in the population of cells that have undergone epithelial-to-mesenchymal transition. PLoS One 8(2):e57314. doi: 10.1371/journal.pone.0057314.
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