Circulating tumour cells (CTCs) are emerging as a non-invasive and economical tumour sampling method allowing insight into patient prognosis, and to guide and monitor therapy.
To date, EpCAM targeted immunomagnetic isolation of CTCs is the most common approach. However, not all cancer cells express EpCAM and even within a certain cancer type or amongst the cancer cells from a single patient, expression of EpCAM may vary. Cells undergoing epithelial to mesenchymal transition (EMT) show decreased EpCAM expression.
Our aim is to investigate EMT phenotypes in ovarian cancer CTCs and improve immunomagnetic capture of these cells.
A literature screen with focus on proteins linked to EMT identified candidate target proteins commonly expressed on the cell surface of ovarian cancer cells. To test their value for immunomagnetic cell capture we used monoclonal antibodies against proteins to screen protein expression in a representative cohort of ten ovarian cancer cell lines.
We first confirmed that EpCAM alone is insufficient to target all ovarian cancer cells. In particular, two cell lines did not display any EpCAM expression, while the proportion of cells that expressed detectable EpCAM levels varied from 50-80% in the remaining eight cell lines. Other promising antibodies were against EGFR (>70% of cells from eight lines were EGFR positive), Her2 (≥60% of cells from five lines were Her2 positive) and N-cadherin (≥70% of cells of two lines were N-cadherin positive). We are currently evaluating which antibody combination will perform best in immunomagnetic isolation of ovarian CTCs by using either cultured cells spiked into lymphocytes or ovarian cancer patient’s blood samples.
In conclusion, our current data indicates that a cocktail of antibodies against EpCAM and EGFR with either Her2 or N-cadherin will significantly improve capture of ovarian CTCs.