Icaritin suppresses CAD-mediated liver cancer development by targeting miR-18b-5p in a xenograft mouse model

Cancer cells show abnormal nucleotide metabolism and prefer the de novo synthesis pathway. As the key enzymes, Carbamoyl-phosphate synthetase 2, Aspartate transcarbamoylase, and Dihydroorotase (CAD) is overactivated in cancer and promotes pyrimidine de novo synthesis, supplying cancer cells with DNA and RNA biosynthesis precursors. Therefore, the development of drugs targeting CAD might inhibit cancer progression and transformation. Icaritin (ICT) is an isoprenoid flavonoid derivative with a wide range of anticancer activities, however, the mechanism of ICT in regulating pyrimidine biosynthesis in cancer remains unclear. MicroRNAs are involved in carcinogenesis by regulating the expression of target genes, and ICT has been shown to regulate the expression of miRNAs leading to suppressing cancer progression. Using both human normal hepatocytes and liver cancer cells, we found that CAD expression was significantly elevated in cancer cells. Interestingly, although ICT treatment reduced CAD protein levels in liver cancer cells, it increased CAD transcriptional activity. Dual-luciferase reporter assays confirmed miR-18b-5p as a direct regulator of CAD. By transfecting miR-18b-5p mimics or inhibitors, we showed ICT upregulates miR-18b-5p to suppress CAD, inhibiting liver cancer cell proliferation, migration, and colony formation. Furthermore, in a human liver cancer xenograft mouse model, ICT treatment markedly reduced tumor growth and decreased Ki-67 expression, consistent with the in vitro results, CAD protein expression was downregulated, while its mRNA level was upregulated, further supporting a post-transcriptional regulatory mechanism. Overall, ICT plays an anti-liver cancer role by increasing miR-18b-5p at the post-transcriptional level to inhibit CAD expression, which may interfere with the de novo synthesis of pyrimidine and development of liver cancer.