Oxaliplatin resistance in colorectal cancer cells is mediated via activation of ABCG2 to alleviate ER stress induced apoptosis

Oxaliplatin (OXA), is a third generation platinum drug used as first-line chemotherapy in colorectal cancer (CRC). Cancer cells acquires resistance to anti-cancer drug and develops resistance. ATP-binding cassette (ABC) drug transporter ABCG2, one of multidrug resistance (MDR) protein which can effectively discharge a wide spectrum of chemotherapeutic agents out of cancer cells and subsequently reduce the intracellular concentration of these drugs. Role of ABCG2 and plausible molecular signaling pathways involved in Oxaliplatin-Resistant (OXA-R) colon cancer cells was evaluated in the present study. OXA resistant LoVo cells was developed by exposing the colon cells to OXA in a dose-dependent manner. Development of multi drug resistance in OXA-R cells was confirmed by exposing the resistance cells to oxaliplatin, 5-FU, and doxorubicin. OXA treatment resulted in G2 phase arrest in parental LoVo cells, which was overcome by OXA-R LoVo cells. mRNA and protein expression of ABCG2 and phosphorylation of NF-B was significantly higher in OXA-R than parental cells. Levels of ER stress markers were downregulated in OXA-R than parental cells. OXA-R LoVo cells exposed to NF-B inhibitor QNZ effectively reduced the ABCG2 and p-NF-B expression and increased ER stress marker expression. On other hand, invasion and migratory effect of OXA-R cells were found to be decreased, when compared to parental cells. Metastasis marker proteins also downregulated in OXA-R cells. ABCG2 inhibitor verapamil, downregulate ABCG2, induce ER stress markers and induces apoptosis. In vivo studies in nude mice also confirms the same.