Combination of bexarotene and the retinoid CD1530 reduces murine oral-cavity carcinogenesis induced by the carcinogen 4-nitroquinoline 1-oxide
We investigated the effects of bexarotene (a retinoid X receptor agonist), CD1530 (a retinoic acid receptor γ selective agonist), and the combination of these two drugs for the prevention of oral carcinogenesis induced by the carcinogen 4-nitroquinoline 1-oxide (4-NQO) in a mouse model of human oral-cavity and esophageal squamous-cell carcinoma previously generated in our laboratory. We observed decreased numbers of neoplastic tongue lesions and reduced lesion severity in the 4-NQO plus CD1530 (4N+C) and 4-NQO plus bexarotene plus CD1530 (4N+B+C) groups compared with the 4-NQO group. RNA-Seq analyses showed increases in transcripts in cell proliferation/cell cycle progression pathways in the 4-NQO vs. the untreated group. In addition, β-catenin and matrix metallopeptidase 9 (MMP9) protein levels and reactive oxygen species (ROS), as assessed by 4-hydroxynonenal (4-HNE) staining, were elevated in tongue tissues 17 wk after the termination of the 4-NQO treatment. The 4N+B, 4N+C, and 4N+B+C groups showed dramatically lower levels of β-catenin, MMP9, and 4-HNE staining compared with the 4-NQO group. The major reduction in 4-HNE staining in the retinoid treatment groups suggests a novel mechanism of action, reduction of ROS, by which bexarotene and CD1530 inhibit carcinogenesis.