Non-small cell lung cancer cells survived ionizing radiation treatment display cancer stem cell and epithelial-mesenchymal transition phenotypes

Abstract

Ionizing radiation (IR) is used for patients diagnosed with unresectable non small cell lung cancer (NSCLC), however radiotherapy remains largely palliative due to radioresistance. Cancer stem cells (CSCs), as well as epithelial-mesenchymal transition (EMT), may contribute to drug and radiation resistance mechanisms in solid tumors. Here we investigated the molecular phenotype of A549 and H460 NSCLC cells that survived treatment with IR (5Gy) and are growing as floating tumor spheres and cells that are maintained in a monolayer after irradiation.Non-irradiated and irradiated cells were collected after one week, seeded onto ultra low attachment plates and propagated as tumor spheres. Bulk NSCLC cells which survived radiation and grew in spheres express cancer stem cell surface and embryonic stem cell markers and are able to self-renew, and generate differentiated progeny. These cells also have a mesenchymal phenotype. Particularly, the radiation survived sphere cells express significantly higher levels of CSC markers (CD24 and CD44), nuclear β-catenin and EMT markers (Snail1, Vimentin, and N-cadherin) than non-irradiated lung tumor sphere cells. Upregulated levels of Oct-4, Sox2 and beta-catenin were detected in H460 cells maintained in a monolayer after irradiation, but not in radiation survived adherent A459 cells.PDGFR-beta was upregulated in radiation survived sphere cells and in radiation survived adherent cells in both A549 and H460 cell lines. Combining IR treatment with axitinib or dasatinib, inhibitors with anti-PDFGR activity, potentiates the efficacy of NSCLC radiotherapy in vitro.Our findings suggest that radiation survived cells have a complex phenotype combining the properties of CSCs and EMT. CD44, SNAIL and PDGFR-beta are dramatically upregulated in radiation survived cells and might be considered as markers of radiotherapy response in NSCLC.

Radiotherapy-induced plasticity of prostate cancer mobilizes stem-like non-adherent, Erk signaling-dependent cells

“…In contrast to reported sphere-forming growth of irradiated lung cancer cells 43 and IR-induced cell cycle entry of breast CSC, 61 the radiation-induced non-adherent CaP cells were proliferatively dormant even in conditions permissive for self-renewal of CSCs (not shown). This supports the notion that EMT-inducing factors reduce cell proliferation, 28,62 and circulating tumor cells (CTCs) with enhanced Twist1 need to downregulate Twist1 before regaining the ability to proliferate and form macrometastases.…”

“…The radiationinduced phenotypic heterogeneity, we report, might reflect transient cellular plasticity as well as stress-evoked responses of preexistent subsets cells seen in the parental DU145 and PC-3 cell populations. [40][41][42][43][44][45][46][47][48][49][50][51][52] Ionizing radiation can promote traits of EMT in normal human mammary epithelium, 41 lung carcinoma 42,43 and colorectal cancer cells. 44 Furthermore, besides their role in E-cadherin repression, 45,46 Slug and Snail have been implicated in radioresistance-associated EMT.…”

Adipose mesenchymal stromal cells minimize and repair radiation-induced oral mucositis

“…Different mechanisms have been reported as main pathways of such radio-resistance, such as cell cycle (CC) arrest (G2/M arrest) and activation of double stranded DNA (dsDNA) damage repair machinery; namely the homologous recombination repair (HRR) and nonhomologous end-joining repair (NHEJR) [95][96][97][98][99]. These mechanisms were also demonstrated to be responsible for the RT resistance of cancer stem cells (CSC), also known as cancer initiating cells, which have been linked to cancer disease recurrence and aggression [192,193]. Thus, the aim was to explore these pathways in irradiated aMSCs compared to 4T1 and NIH3T3-wt cells.…”

Lack of epithelial-to-mesenchymal transition induction in two bronchial epithelial cell lines after alpha and gamma irradiation

“…There are evidences supporting the involvement of EMT in the development of fibrosis and different types of cancer, including lung cancer (Bartis et al, 2014;Lee and Nelson, 2012;Zavadil and Böttinger, 2005). The EMT has been suggested to increase the invasiveness of already transformed tumour epithelial cells that have survived radiotherapy (Gomez-Casal et al, 2013;Xu et al, 2008). Important role in this process have the EMT-inducing transcription factors Snail, Twist and ZEB1.…”

“…The EMT hallmarks include loss of apicobasal orientation, decreased expression of adhesion molecules, matrix degradation and increased expression of mesenchymal markers (Lee and Nelson, 2012). There has been previously reported a connection between the EMT-inducing transcription factors twist, snail and zeb1 activation and the promotion of radioresistance in both non-small cell lung cancer (NSCLC) and breast cancer cells (Gomez-Casal et al, 2013;Zhang et al, 2014). Exposure of cells to IR is regarded as a sensitising factor for cells to undergo the TGF-β-induced EMT.…”