Evidence for mesenchymal-like sub-populations within squamous cell carcinomas possessing chemoresistance and phenotypic plasticity

Abstract

Variable drug responses among malignant cells within individual tumors may represent a barrier to their eradication using chemotherapy. Carcinoma cells expressing mesenchymal markers resist conventional and epidermal growth factor receptor (EGFR)-targeted chemotherapy. Here we evaluated whether mesenchymal-like subpopulations within human squamous cell carcinomas (SCCs) with predominantly epithelial features contribute to overall therapy resistance. We identified a mesenchymal-like subset expressing low E-cadherin (Ecad-lo) and high vimentin (Vim-hi) within upper aerodigestive tract SCCs. This subset was both isolated from cell lines and identified in xenografts and primary clinical specimens. The Ecad-lo subset contained more low-turnover cells, correlating with resistance to the conventional chemotherapeutic paclitaxel in vitro. Epidermal growth factor (EGF) induced less stimulation of the MAP kinase and PI3-kinase pathways in Ecad-lo cells, which was likely due to lower EGFR expression in this subset and correlated with in vivo resistance to the EGFR-targeted antibody cetuximab. The Ecad-lo and high E-cadherin (Ecad-hi) subsets were dynamic in phenotype, showing the capacity to repopulate each other from single cell clones. Taken together, these results provide evidence for a low-turnover, mesenchymal-like subpopulation in SCCs with diminished EGFR pathway function and intrinsic resistance to conventional and EGFR-targeted chemotherapies.

Detecting and targeting mesenchymal-like subpopulations within squamous cell carcinomas

“…Our previous work has identified similar resistance to both classes of compounds in an Ecad-lo, mesenchymal-like subpopulation present within individual SCC cell lines. 6 In this study, we demonstrate that salinomycin has efficacy against the mesenchymal-like subpopulation of SCC cells that is resistant to cisplatin, the single most widely used cytotoxic agent for HNSCC. 16 Salinomycin was highly toxic in vitro to both Ecad-hi and Ecad-lo subpopulations but only modestly selective for Ecad-lo vs. Ecad-hi cells.…”

“…6 In contrast, residual salinomycin-treated tumors showed a striking, widespread depletion of vimentin-positive cells (Fig. 5C, third row).…”

Molecular mechanisms of resistance to the EGFR monoclonal antibody cetuximab

“…196 In 2010, mesenchymal-like squamous cell carcinomas were shown to be resistant to cetuximab treatment. 193 Using immunohistochemistry, flow cytometry and gene expression profiling, researchers identified SCC cell lines that were epithelial-like and mesenchymal-like based on E-cadherin and vimentin expression levels. In this system, researchers identified cell lines that had sub-populations of both high E-cadherin/low vimentin and low E-cadherin/high vimentin levles.…”

“…191,192 These markers have been used by various investigators to characterize cells as either epithelial or mesenchymal; however, some researchers suggest that carcinomas do not fall into strict categories, and represent a mixed phenotype. 193,194 In a study by Fuchs et al, 12 human hepatocellular carcinoma cell lines were characterized as either epithelial or mesenchymal by western blot analysis of E-cadherin and vimentin protein levels. Based on this classification, mesenchymal cell lines were shown to be resistant to cetuximab, erlotinib and gefitinib, while epithelial cell lines remained sensitive to these EGFR inhibitors.…”

Induction of cytotoxic T lymphocytes against ovarian cancer‐initiating cells

“…The absorbance was measured at 590 nm by a micro-plate reader. 22,23 Cell viability rate was calculated as the percentage of MTT absorption as follows: % survival ¼ (mean experimental absorbance/mean control absorbance) Â 100.…”