Background: Our goal is to establish reproducible and robust
mouse models for use in breast cancer CTC/DTC research. Using a
species-specific tandem nested qRT-PCR approach, we are able to detect and
measure a panel of human specific markers relating to: detection of CTC/DTC,
prognostic markers of breast cancer, the ‘cancer stem cell’ phenotype and
epithelial-mesenchymal plasticity (EMP). EMP is hypothesised to be involved in
the generation and function of CTC/DTC.
Materials
& methods: Blood samples,
bone marrow and tumour tissue were collected from SCID mice orthotopically
xenografted with the MDA-MB-468 cell line, and a transplantable xenograft
derived from bone-metastatic breast cancer material passaged in vivo (ED-03). All samples from each
xenograft were assessed and comparisons made between blood, bone marrow and
tumour.
Results: Differences in relative expression levels between CTC,
DTC and tumour in the MDA-MB-468 model were observed for; CD24, CD44, SNAI1, CLDN3
and CLDN4. In the ED03 model, differences in relative expression levels of CDH1,
SNAI1, and CK20 were seen. Immunohistochemical analysis of human
pan-cytokeratin (hCK), vimentin (hVim) and mitochondria (hMito) on cytospin
slides of bone marrow from the MDA-MB-468 and ED-03 xenografts confirmed the
presence of DTC.
Conclusions:
Assessment of relative gene expression across a panel of markers was achieved
in two mouse models of minimal residual disease. Changes in CTC/DTC were
observed that correlate with current literature relating to the ‘cancer stem
cell’ phenotype. Increased expression in Snail1, a transcriptional repressor of
E-cadherin was seen, however no clear concordant change in E-cadherin were
detected. Relative expression changes were also observed in a subset of claudins
that are associated with the claudin-low breast cancer subtype. A small number
of markers displayed similar changes across both models. To our knowledge, these
are the first such analyses of human xenograft CTC and DTC.