Tumorsphere assay provides a better in vitro method for cancer stem-like cells enrichment in A549 lung adenocarcinoma cells

Abstract

Cancer stem cells (CSCs) have been implicated in growth, metastasis, recurrence and chemo-/radio-resistance in several cancer types. Despite a plenty of literature about different in vitro techniques to enrich/isolate CSCs, their comparative characterization for stemness is not well established. In the present study, cells obtained following three in vitro assays [clonogenic assay, tumorsphere assay (TSA) and single cell assay (SCA)] were compared for their cancer stem-like cell characteristics in human lung adenocarcinoma (A549) cells. Expression of the pluripotent (OCT4, NANOG) and lung cancer stem cell marker (CD166) genes were studied in these cells. Results showed that in comparison to cells obtained from routine culture (CC), the cells obtained from TSA showed significantly higher expression of OCT-4 and NANOG. These results were further validated with quantification of cell surface cancer stem cell markers i.e. CD44+/CD24− in the cells obtained from different methods, which were higher in TSA and SCA. Additionally, functional characterization of cancer stem-like cells (CSLCs) using ALDH assay showed the highest % of ALDH+ cells in TSA. These results were in agreement with higher resistance of these cells against 5-Fluorouracil suggesting higher fraction of CSLCs in TSA than the other assays. These results showed that TSA provides a better method to enrich CSLCs in A549 lung adenocarcinoma cells.