Purpose: NF-E2-related factor 2 (Nrf2) is a key transcription regulator for cellular response to oxidative stress in normal cells. In cancer cells, development of chemoresistance is associated with the constitutive activation of the Nrf2-mediated antioxidant defense system. Here, we investigated the role of Nrf2 in terms of cervical cancer cell proliferation and drug resistance.
Method: To investigate whether cancer cells activate the Nrf2 system, we examined 40 surgical cervical cancer samples and 12 normal control tissues. Plasmids containing Nrf2-small hairpin RNA (shRNA) or non-targeting vector-control shRNA were transfected into CaSki cells. Using Western blots and RT-PCR assays, the expression levels of Nrf2 mediated-target genes were measured in CaSki cells stably expressing Nrf2-shRNA. To evaluate how the Nrf2 knockdown affected susceptibility to chemotherapeutic drugs, MTT and flow cytometry assays were done in vitro and confirmed by a mouse xenograft model in vivo.
Results: The Nrf2-dependent defensive system was likely fully activated in cervical tumor tissues. Genetic knockdown of endogenous Nrf2 caused a global decrease in expression of Nrf2-regulated genes. This decrease in expression levels enhanced chemotherapeutic drug-induced apoptotic death in CaSki cells with a reduced cellular glutathione level. Additionally, the combination of cisplatin treatment and Nrf2 knockdown significantly suppressed tumor growth in vivo.
Conclusion: Our findings provide evidence that the inhibition of Nrf2 activity by shRNA might be a promising therapeutic strategy to enhance the efficacy of anticancer drugs and thus can be applied further during the course of chemotherapy in the treatment of cervical cancer.