Bioactive black tea phytochemicals partially influenced doxorubicin sensitivity by modulation of NRF2-regulatory pathways in lung cancer

BACKGROUND: Lung cancer therapy resistance is often associated with the redox-regulatory nuclear factor erythroid 2-related factor-2 (NRF2)-Kelch-like ECH-associated protein1 (KEAP1) dysfunction. OBJECTIVE: This study investigated the impact of commercially available black tea (BT) phytochemicals (≥80 % theaflavins) from Camellia sinensis in sensitizing doxorubicin (Dox) against nonresponsive lung adenocarcinoma cells by modulation of non-canonical NRF2 regulators. METHODS: The methods included multidrug resistance (MDR) assay, comet assay, cell cycle analysis, zymography, semi-quantitative polymerase chain reaction, western blot and immunocytochemistry (ICC). RESULTS: BT pretreatment followed by Dox exposure was partially effective in Dox resistance-reversal in A549 cells by increasing drug uptake and downregulating MDR pumps. This combination induced DNA damage and cytotoxicity in A549 cells. It also reduced invasiveness and suppressed the expression of multidrug resistance protein-1, epidermal growth factor receptor, protein kinase B, and B cell lymphoma-2. In absence of wild-type KEAP1, non-KEAP1 regulators were thoroughly investigated by immunolocalization, and immunoblotting. BT restricted non-canonical NRF2 activators, such as p21 and apurinic/apyrimidinic endonuclease1 in A549 and acted oppositely in NCI-H23 cells. Additionally, NRF2-repressors, namely forkhead box O3, p53, glycogen synthase kinase-3β, and retinoid X receptor (RXR), were downregulated in NCI-H23 and upregulated in A549 cells. ICC exhibited that BT modulated the co-localization of NRF2 regulators, such as β-transducin repeat-containing protein and RXR, in A549 and NCI-H23 cells. CONCLUSION: Therefore, it might be indicated that BT improved Dox retention and increased the Dox responsiveness in A549 cells. BT-mediated selective suppression of the NRF2, re-stabilized the KEAP-1-independent NRF2 regulators and made the non-responsive A549 cells partially sensitive to Dox.