Metformin reverses chemoresistance in non-small cell lung cancer via accelerating ubiquitination-mediated degradation of Nrf2

Sha Huang; Tianyu He; Sijia Yang; Hongxu Sheng; Xiuwen Tang; Feichao Bao; Yiqing Wang; Xu Lin; Wenfeng Yu; Fei Cheng; Wang Lv; Jian Hu

doi:10.21037/tlcr-20-1072

Metformin reverses chemoresistance in non-small cell lung cancer via accelerating ubiquitination-mediated degradation of Nrf2

Transl Lung Cancer Res. 2020 Dec;9(6):2337-2355. doi: 10.21037/tlcr-20-1072.

Authors

Sha Huang¹, Tianyu He¹, Sijia Yang¹, Hongxu Sheng¹, Xiuwen Tang², Feichao Bao³, Yiqing Wang¹, Xu Lin¹, Wenfeng Yu¹, Fei Cheng⁴, Wang Lv¹, Jian Hu¹

Affiliations

¹ Department of Thoracic Surgery, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
² Department of Biochemistry and Department of Thoracic Surgery of the First Affiliated Hospital, Zhejiang University School of Medicine, Zhejiang University, Hangzhou, China.
³ Department of Thoracic Surgery, Shanghai Chest Hospital, Shanghai Jiao Tong University, Shanghai, China.
⁴ Department of Pathology, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.

Abstract

Background: The therapeutic efficacy of cisplatin-based chemotherapy for non-small cell lung cancer (NSCLC) is limited by drug resistance. In NSCLC, hyperactivation of nuclear factor erythroid 2-related factor 2 (Nrf2) counteracts oxidative stress to promote chemoresistance. Metformin-mediated downregulation of Nrf2 plays a pivotal role in overcoming drug resistance in NSCLC cells. Therefore, a deeper understanding of the molecular mechanisms of combination therapy and the role of Nrf2 in chemotherapeutic response is critical to clinical translation.

Methods: The effects of combination therapy with metformin and cisplatin on cell proliferation and apoptosis, intracellular reactive oxygen species (ROS) levels, and xenograft tumor formation were analyzed in NSCLC cells. Co-immunoprecipitation (co-IP) and Phos-tag assays were used to explore the mechanism of metformin-mediated Nrf2 suppression. Immunohistochemical (IHC) staining was performed to detect Nrf2 expression in matched tumor samples before and after neoadjuvant chemotherapy.

Results: Metformin was observed to synergistically augment cisplatin-induced cytotoxicity by strongly inhibiting the level of Nrf2, thereby weakening the antioxidant system and detoxification ability of Nrf2 and enhancing ROS-mediated apoptosis in NSCLC. The synergistic antitumor effect of combination therapy is blocked by treatment with the ROS scavenger N-acetyl cysteine (NAC) as well as overexpression of Nrf2 and its downstream antioxidant protein. Mechanistically, metformin extensively dephosphorylates Nrf2 by attenuating the interaction between Nrf2 and extracellular signal-regulated kinases 1/2 (ERK1/2), which then restores its polyubiquitination and accelerates its proteasomal degradation. Moreover, for the first time, an association of non-decreased Nrf2 expression in patients after neoadjuvant chemotherapy with poor survival and chemoresistance in NSCLC was revealed.

Conclusions: Our findings illustrate the mechanism of metformin-mediated Nrf2 degradation through posttranslational modifications (PTMs), which weakens the ROS defense system in NSCLC. Fluctuations in Nrf2 expression have a strong predictive ability for chemotherapeutic response in neoadjuvant NSCLC patients. Targeting of the Nrf2 pathway could be a therapeutic strategy for overcoming chemoresistance, with metformin as the first choice for this strategy.

Keywords: Metformin; Nrf2; chemoresistance; lung cancer; posttranslational modification (PTM).