| Author |
Komoto S, Kimura R, Yoshino Y, Morimoto K, Shinoda T, Shirouzu M, Ishikawa Y, Matsunaga T, Endo S, Ikari A.
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| Abstract |
Claudin-2 (CLDN2) is a tight junction-associated transmembrane protein that is highly expressed in lung adenocarcinoma and contributes to chemoresistance. Here, we screened Food and Drug Administration-approved small-molecule drugs to identify compounds capable of reducing CLDN2 expression and enhancing anticancer drug-induced cytotoxicity in cancer cells. A structure based virtual screening targeting CLDN2 predicted that saquinavir (SQV), a human immunodeficiency virus (HIV) protease inhibitor, binds to the second extracellular loop of CLDN2 protein. Consistent with the prediction, SQV markedly decreased CLDN2 protein levels without affecting its mRNA expression in human lung adenocarcinoma A549 cells. In contrast, ritonavir, another HIV protease inhibitor, or raltegravir, an HIV integrase inhibitor, has no significant effect, indicating that inhibition of viral enzymes is not directly involved in the regulation of CLDN2 expression. A cycloheximide-chase assay revealed that SQV reduces the stability of CLDN2 protein. Pharmacological inhibition experiments further revealed that SQV-induced CLDN2 downregulation is mediated by enhanced clathrin-dependent endocytosis and subsequent lysosomal degradation. In three-dimensional spheroid models, SQV reduced oxidative stress and expression of nuclear factor erythroid 2-related factor 2 protein expression without altering spheroid size, cell viability, or hypoxic stress. Notably, SQV enhanced the cytotoxic effects of multiple anticancer agents, including doxorubicin, cisplatin, and SN-38, in lung adenocarcinoma cell line-derived spheroids and patient-derived organoids. We suggest that SQV improves chemoresistance by reducing CLDN2 expression and oxidative stress in lung adenocarcinoma.
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