title: CX-5461 induces autophagy and inhibits tumor growth via mammalian target of rapamycin-related signaling pathways in osteosarcoma.
abstract: Osteosarcoma (OS) is the most common primary bone tumor, but molecular mechanisms of the disease have not been well understood, and treatment of metastatic OS remains a challenge. Rapid ribosomal RNA synthesis in cancer is transcribed by RNA polymerase I, which results in unbridled cell growth. The recent discovery of CX-5461, a selective RNA polymerase I inhibitor, exerted its inhibitory effect of ribosomal RNA synthesis and antiproliferative potency. Here, we demonstrate that CX-5461 induces G2arrest in the cell cycle and expression of microtubule-associated protein 1 light chain 3 II isoform in OS cell lines. Autophagic vacuoles could be observed in electron microscopy and 3-methyladenine prevented cell death mediated by CX-5461. Moreover, it significantly augmented phosphorylated AMP-Activated Protein Kinases α (p-AMPK α). (Thr172) expression in U2-OS cells and decreased p-Akt (Ser473) expression in MNNG cells, respectively, which repressed their downstream effector, mammalian target of rapamycin. On the other hand, CX-5461 increased p53 accumulation and messenger RNA level of its target genes, p21, MDM2, and Sestrin1/2 in U2-OS cells. Knockdown of p53 expression markedly impaired cell death as well as the expression of light chain 3-II and p21 induced by CX-5461. It also significantly enhanced doxorubicin-mediated cytotoxic effect in vitro and in vivo together with additive expression of p53, p21, and light chain 3-II in U2-OS cells. Our data indicate that CX-5461 might induce autophagy via mammalian target of rapamycin-associated signaling pathways dependent on p53 status and exert p53-dependent synergistic antitumor effect combined with doxorubicin in OS. These results suggest that CX-5461 might be promising in clinical therapy for OS, especially cases harboring wild-type p53.
authors.affiliation: Department of Joint Surgery and Sports Medicine, The First Affiliated Hospital.
authors.forename: Leiming
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Spine and Joint Surgery, Sheng Jing Hospital.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Spine and Joint Surgery, Sheng Jing Hospital.
authors.forename: Jiansong
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Department of Geriatrics, The First Affiliated Hospital, China Medical University, Shenyang, People's Republic of China.
authors.forename: Shuli
authors.initials: S
authors.lastname: Fan
authors.affiliation: Department of Joint Surgery and Sports Medicine, The First Affiliated Hospital.
authors.forename: Liguo
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Joint Surgery and Sports Medicine, The First Affiliated Hospital.
authors.forename: Xu
authors.initials: X
authors.lastname: Li
keywords: AMPK; RNA polymerase I inhibitor; combined chemotherapy