Abstract
Purpose: :
Molecular genetic analyses and gene expression profiling (GEP) of uveal melanomas (UM) identify patients into those with high or low risk of metastatic disease. Furthermore, GEP demonstrates that aggressive melanoma cells show increased expression of genes associated with a more primitive developmental phenotype. This is consistent with the widely-accepted view that genes required for stem cell specification and lineage restriction during embryogenesis also play fundamental roles in cancer. On this basis, we hypothesised that aggressive monosomy 3 (M3) UM display more stem cell-like properties than the less aggressive disomy 3 tumors (D3).
Methods: :
Tumour biopsies from 17 patients were disaggregated and single cells were plated to non-adherent culture for 21 days in complex medium. The numbers of floating melanoma spheres (MS) were counted and the colony forming efficiency (CFE) calculated. Spheres were re-plated to adherent culture for the assessment of lineage differentiation. Lineage differentiation was also assessed in adherent cells plated immediately following disaggregation of the tumour biopsy. The chromosome 3 status of the tumor was determined by multiplex ligation dependent probe amplification (MLPA).
Results: :
MLPA classified 8 tumors as M3 and 9 tumors as D3. All M3 tumors formed MS in culture; mean CFE 0.068% (range 0.02-0.11%); however only 4/9 D3 tumors formed MS; mean CFE 0.028% (range 0-0.19%). One tumor formed nodules/spheres of cells in adherent culture that could be easily detached and propagated. Tumor cells variably expressed markers of smooth muscle fibroblasts (αSMA), melanocytes (MelanA/HMB45), neural cells (βIII tubulin/NFP), adipocyte like cells (Oil RedO) and the restricted neural crest lineage markers MITF and c-Kit. Of 7 primary tumor specimens (M3=4; D3=3) examined in detail, multiple lineage markers were more frequently observed in cells derived from M3 tumors.
Conclusions: :
In conclusion, UM cells can give rise to multiple cell lineages of neural crest origin. These data suggest the presence of stem cell like populations in UM and their involvement in the pathogenesis of these tumors.
Keywords: tumors • plasticity • pathobiology