The hypoxia-mimetic agent CoCl2 induces chemotherapy resistance in LOVO colorectal cancer cells

Hypoxia, which is an important factor that mediates tumor progression and poor treatment response, is particularly associated with tumor chemoresistance. However, the molecular mechanisms underlying hypoxia-induced colorectal cancer chemoresistance remain unclear. The present study aimed to explore the mechanism underlying hypoxia-induced chemotherapy resistance in LOVO colorectal cancer cells. LOVO cells were cultured in a hypoxic environment simulated by cobalt chloride (CoCl2), which is a chemical inducer of hypoxia-inducible factor-1 (HIF-1). HIF-1 is a transcription factor that has an important role in tumor cell adaptation to hypoxia, and controls the expression of several genes. Various CoCl2 concentrations are often used to simulate degrees of hypoxia. In the present study, following treatment with CoCl2, an MTT assay was conducted to determine the growth and drug sensitivity of LOVO cells. Reverse transcription-polymerase chain reaction and western blotting were used to detect the mRNA and protein expression levels of HIF-1 and factors associated with chemotherapy resistance, including multidrug resistance protein (MRP) and multidrug resistant 1 (MDR1), which encodes the major transmembrane efflux transporter P-glycoprotein (P-gp). In addition, the expression levels of apoptosis-related proteins, including B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax) and Bcl-2-associated agonist of cell death (Bad) were detected by western blotting. Flow cytometry (FCM) was used to visually observe Adriamycin (ADR) accumulation and retention, thus analyzing intracellular drug transportation in cells under hypoxic and normoxic conditions. CoCl2-simulated hypoxia was able to inhibit tumor cell proliferation, and upregulate the expression levels of HIF-1, MDR1/P-gp and MRP. In addition, proapoptotic members of the Bcl-2 protein family, Bax and Bad, were downregulated. The anti-apoptotic member Bcl-2 exhibited no significant change in expression, whereas the ratio of Bcl-2/Bax was increased. Results of FCM demonstrated that the intracellular retention of ADR was significantly decreased in the hypoxia group cells. In conclusion, the present study revealed that a CoCl2-simulated hypoxic microenvironment was able to effectively induce chemoresistance and reduce apoptosis in LOVO cells.