title: Transient rRNA synthesis inhibition with CX-5461 is sufficient to elicit growth arrest and cell death in acute lymphoblastic leukemia cells.
abstract: Enhanced rRNA synthesis is a downstream effect of many of the signaling pathways that are aberrantly activated in cancer, such as the PI3K/mTOR and MAP kinase pathways. Recently, two new rRNA synthesis inhibitors have demonstrated therapeutic effects on cancer cells while sparing normal cells. One of them, CX-5461, is currently in phase 1 clinical trials for hematological malignancies. Here, we investigate the effectiveness of transient treatment with this drug on acute lymphoblastic leukemia cells. Our results show that short exposure to CX-5461 followed by drug washout is sufficient to induce persistent G2 cell-cycle arrest and irreversible commitment to cell death, in spite of rRNA synthesis returning to normal within 24 hours of drug washout. The magnitude of cell death after transient exposure is similar to continuous exposure, but the time to cell death is relatively delayed with transient exposure. In this report, we also investigate rational drug combinations that can potentiate the effect of continuous CX-5461 treatment. We show that the checkpoint abrogator UCN-01 can relieve CX-5461-induced G2 arrest and potentiate the cytotoxic effects of CX-5461. Finally, we show that ERK1/2 is activated upon CX-5461 treatment, and that pharmacological inhibition of MEK1/2 leads to enhanced cell death in combination with CX-5461. In summary, our results provide evidence for the effectiveness of CX-5461 pulse treatment, which may minimize drug related toxicity, and evidence for enhanced effectiveness of CX-5461 in combination with other targeted agents.
authors.affiliation: Department of Oncology and Pediatrics, Johns Hopkins University School of Medicine, Baltimore MD 21231, USA.
authors.forename: Sandeep S
authors.initials: SS
authors.lastname: Negi
authors.affiliation: Department of Oncology and Pediatrics, Johns Hopkins University School of Medicine, Baltimore MD 21231, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Brown
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D052160:Benzothiazoles / Q000494:pharmacology*; D015153:Blotting, Western; D016923:Cell Death / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D004357:Drug Synergism; D005434:Flow Cytometry; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects; D006801:Humans; D009287:Naphthyridines / Q000494:pharmacology*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000473:pathology*; D012335:RNA, Ribosomal / Q000187:drug effects*; D060888:Real-Time Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
chemical_list: D052160:Benzothiazoles; C557717:CX 5461; D009287:Naphthyridines; D019384:Nucleic Acid Synthesis Inhibitors; D012335:RNA, Ribosomal
keywords: CX-5461; MAP kinase; UCN-01; acute lymphoblastic leukemia; rRNA synthesis