Background:
Understanding the heterogenous CTC biology might help to answer key issues addressing
the complexity of metastatic processes and therapy resistance. Here we demonstrate
single CTC transcriptional profiling, providing early insight into intra-patient CTC
heterogeneity and allowing comparisons to breast cancer cell lines widely used for
examining therapy resistance.
Methods:
A PCR panel consisting of 30 different endocrine resistance and phenotypic markers
was designed and tested for single cell profiling by using different breast cancer
cell lines (MCF-7, MCF-7/TAMR and MDA-MB-231). In addition, CTCs were enriched from
a diagnostic leukapheresis product obtained from a patient suffering from metastatic
breast cancer resistant to endocrine therapy using the ParsortixTM system. RNA of single uncultured and cultured CTCs was extracted, reversely transcribed
into cDNA and subsequently pre-amplified. Next, gene expression profiles were generated
by multiplex real-time PCR.
Results:
Multimarker analysis was possible in single cells with intense signals of KR19 and
ACTB (61,5% of cell lines (n = 13), 17,9% of uncultured CTCs (n = 39) and 33% of cultured
CTCs (n = 15)). We found that single cell line cells and pools of 5 cells reproducibly
clustered together. Moreover, single cell transcriptomic profiles of each cell line
were consistent with penotypic and endocrine biomarker patterns (e.g. ER, HER2, VIM).
Gene expression profiles of CTCs and cultured CTCs revealed intra-patient heterogeneity
with clustering into subgroups concerning phenotypic (EpCAM, CD44) and endocrine markers
(ER, HER2).
Conclusion:
Multimarker RNA profiling of enriched single CTCs and cultured CTCs may provide important
insights into intra-patient tumoral heterogeneity relevant for therapy resistance.