Abstract
It is now widely accepted that the tumor microenvironment influences the fate of cancer cells and plays crucial roles in regulating tumor dormancy and chemoresistance. The standard cell culture system on plastic surfaces does not account for cell interactions with the extracellular matrix (ECM), and is thus a less reliable approach to analyze cellular activity ex vivo. In the present study, A549 lung cancer cells were cultured in a semi-solid growth substrate (Matrigel) to mimic the tumor microenvironment and to investigate the role played by ECM proteins, as well as to evaluate the mechanism of cell-ECM communication. A549 cells embedded in semi-solid Matrigel exhibited dormant cell characteristics, including decreased cell proliferation, migration and invasion rates, compared with the corresponding cells cultured on plastic plates. Exposure of A549 cells to Matrigel leads to resistance against conventional chemotherapeutic drugs (etoposide, paclitaxel, vinblastine, doxorubicin and 2-deoxy-D-glucose). Cell cycle distribution analysis indicated that a larger percentage of the cells embedded within semi-solid Matrigel was arrested in the G0/G1 phase. RT-qPCR analysis revealed that A549 cells cultured in semi-solid Matrigel exhibited a marked decrease in the expression levels of genes that are related to tumor progression and invasion (uPA, uPAR, MMP2, MMP7, MMP9 and CXCR4). The effects of altering various signaling pathways, such as p-ERK, p-Akt and p-STAT3, were evaluated, in order to assess whether these pathways could account for the observed responses of the cells. The inhibition of ERK1/2 and Akt activation using specific inhibitors induced G0/G1 arrest and drug resistance. These results demonstrated that Matrigel drove A549 cells into a drug-resistant dormancy state, most likely through inhibition of the ERK1/2 and PI3K/Akt pathways. Cell culture within semi-solid Matrigel offered a simple in vitro model for studying the mechanisms responsible for tumor dormancy and drug resistance. These studies may lead to therapeutic approaches that can eliminate dormant tumor cells and prevent disease recurrence.