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Research Articles: Therapeutics, Targets, and Development

Hypoxia-induced resistance to anticancer drugs is associated with decreased senescence and requires hypoxia-inducible factor-1 activity

¹ Department of Anatomy and Cell Biology, Queen's University, Kingston, Ontario, Canada; and ² Vascular Biology Program, Institute for Cell Engineering, Departments of Pediatrics, Medicine, Oncology, and Radiation Oncology, and McKusick-Nathans Institute of Genetic Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland

Requests for reprints: Charles H. Graham, Department of Anatomy and Cell Biology, Queen's University, Botterell Hall, Room 859, Kingston, Ontario, Canada K7L 3N6. Phone: 613-533-2852; Fax: 613-533-2566. E-mail: grahamc{at}queensu.ca

Abstract

Hypoxia in solid tumors is associated with the development of chemoresistance. Although many studies have focused on the effect of hypoxia on drug-induced apoptosis, the effect of nonapoptotic pathways on hypoxia-induced drug resistance has not been previously investigated. Here, we determined the effects of hypoxia on multiple forms of drug-induced death in human MDA-MB-231 breast carcinoma cells. Clonogenic assays showed that preexposure to hypoxia leads to resistance to various classes of chemotherapeutic agents, including anthracyclines (daunorubicin and doxorubicin), epipodophyllotoxins (etoposide), and anthracenediones (mitoxantrone). Results revealed a high degree of heterogeneity in nuclear and cytoplasmic alterations in response to acute drug exposure; however, the majority of exposed cells displayed morphologic and biochemical changes consistent with drug-induced senescence. Hypoxia decreased only the proportion of cells in the senescent population, whereas the small proportion of cells exhibiting features of apoptosis or mitotic catastrophe were unaffected. Similar results were obtained with human HCT116 colon carcinoma cells, indicating that the protective effect of hypoxia on drug-induced senescence is not unique to MDA-MB-231 cells. Treatment of MDA-MB-231 cells with small interfering RNA targeting the -subunit of hypoxia-inducible factor-1 (HIF-1), a key regulator of cellular adaptations to hypoxia, prevented hypoxia-induced resistance. HIF-1 small interfering RNA also selectively abolished the hypoxia-induced changes in the senescent population, indicating that the increased survival was due to protection against drug-induced senescence. These results support a requirement for HIF-1 in the adaptations leading to drug resistance and reveal that decreased drug-induced senescence is also an important contributor to the development of hypoxia-induced resistance. [Mol Cancer Ther 2008;7(7):1961–73]

Grant support: Canadian Institutes of Health Research (CIHR) grant MOP-57871. R. Sullivan was the recipient of a Natural Sciences and Engineering Research Council of Canada Postgraduate Scholarship and a CIHR Canada Graduate Scholarship Doctoral Award. L. Frederiksen was a recipient of a CIHR Postgraduate Scholarship.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

³ Supplementary material for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).

⁴ R. Sullivan and C.H. Graham, in preparation.

Received 2/26/08; accepted 4/ 8/08.