title: ARC-111 inhibits hypoxia-mediated hypoxia-inducible factor-1alpha accumulation.
abstract: ARC-111, a small-molecule topoisomerase I inhibitor, is a potent cytotoxic drug against multiple human cancer cell lines under normoxic conditions (Li et al., Cancer Res 2003; 63:8400-8407). In this study, we explore the potential of ARC-111 as a hypoxia-inducible factor-1alpha inhibitor under hypoxic conditions. The transcription factor, hypoxia-inducible factor-1alpha, is an essential regulator of tumorigenesis and an attractive molecular target for cancer therapy. We demonstrate that ARC-111 specifically inhibits hypoxia-induced accumulation of hypoxia-inducible factor-1alpha, but not other short half-life proteins in multiple human cancer cell lines. ARC-111 inhibits hypoxia-inducible factor-1alpha protein synthesis specifically and does not inhibit protein synthesis globally. We demonstrate that inhibition of hypoxia-inducible factor-1alpha accumulation by ARC-111 is independent of proteasomal degradation. In addition, we demonstrate using topoisomerase I-resistant cell lines that topoisomerase I is required for ARC-111-mediated hypoxia-inducible factor-1alpha inhibition. Experiments performed with nocodazole indicate that ARC-111 inhibits hypoxia-inducible factor-1alpha accumulation in a cell-cycle-independent manner. Analysis of AKT and mammalian target of rapamycin phosphorylation reveals that ARC-111 does not exhibit inhibitory effect on the phosphatidylinositol-3-kinase AKT mammalian target of rapamycin signaling pathway. It has been previously shown that topotecan, a topoisomerase I inhibitor, can also modulate hypoxia-induced hypoxia-inducible factor-1alpha accumulation (Rapisarda et al., Cancer Res 2003; 64:1475-1482). In addition to inhibiting hypoxia-induced accumulation of hypoxia-inducible factor-1alpha, ARC-111 exhibits antiproliferative effects against multiple human cancer cell lines. We demonstrate that topoisomerase I is required for the antiproliferative effects of ARC-111. Antiproliferative effects of ARC-111, however, are oxygen-independent, which is distinguishable from inhibition of hypoxia-inducible factor-1alpha accumulation by ARC-111, which is only observed under hypoxia. The results indicate that inhibiting hypoxia-inducible factor-1alpha accumulation and exhibiting antiproliferation of ARC-111 are through distinct mechanisms of action, which reinforce the potential anticancer effect of ARC-111 on hypoxic tumors.
authors.affiliation: Threshold Pharmaceuticals, Redwood City, California 94063, USA. fmeng@thresholdpharm.com
authors.forename: Fanying
authors.initials: F
authors.lastname: Meng
authors.forename: Xuan-Thao
authors.initials: XT
authors.lastname: Nguyen
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Cai
authors.forename: Jianxin
authors.initials: J
authors.lastname: Duan
authors.forename: Mark
authors.initials: M
authors.lastname: Matteucci
authors.forename: Charles P
authors.initials: CP
authors.lastname: Hart
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D007202:Indicators and Reagents; D009287:Naphthyridines / Q000494:pharmacology*; D009363:Neoplasm Proteins / Q000096:biosynthesis; D051058:Oncogene Protein v-akt / Q000502:physiology; D010100:Oxygen / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D011494:Protein Kinases / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases
chemical_list: D000970:Antineoplastic Agents; D004264:DNA Topoisomerases, Type I; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007202:Indicators and Reagents; D009287:Naphthyridines; D009363:Neoplasm Proteins; D051058:Oncogene Protein v-akt; D010100:Oxygen; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D058570:TOR Serine-Threonine Kinases; C481982:topovale; C546842:MTOR protein, human