Molecular Insights into Mechanisms of Drug Resistance using Doxorubicin Resistant Hela Cells

Drug resistance poses a challenge to cancer therapy. In this work, we have modelled drug-induced changes in cancer cells, as observed in the clinical settings, by giving chronic doxorubicin treatment to cervical cancer derived cell line, HeLa. The cells so obtained are multi-drug resistant. We found the drug resistant cells to have higher levels of the drug transporter ATP Binding Cassette transporter B1 (ABCB1). These cells show low drug retention, which can be reversed using an ABCB1 inhibitor, suggesting ABCB1 is sufficient to confer the drug resistance phenotype to these cells. Recent literature has shown a correlation between drug resistance and stemness properties of cancer cells. Consistent with this, we observed increased anchorage independent colony formation and have higher levels of Bmi1, a stem cell marker. Bmi1 is also known to be involved in maintaining Epithelial to mesenchymal transition. Accordingly, we found a loss of E-cadherin expression in these cells. Expectedly, these cells show more metastatic lung nodules. A microarray analysis performed between parental HeLa and the drug resistant cells revealed changes in integrin and focal adhesion pathways. Integrin β1 (ITGB1) was up-regulated in the drug resistant cells. ITGB1 is reported to sense modified extra-cellular matrix in the tumor and lead to activation of Mitogen activated protein kinase (MAPK) and Akt signalling pathways, conferring drug resistance. Indeed, we found the levels of activated MAPK and Akt molecules to be up-regulated in drug resistant cells compared to parental cells. This model system allows us to dissect the molecular mechanisms which confer drug resistance and cause ABCB1 gene up-regulation.