© The Author 2007. Published by Oxford University Press.
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The 1p-Encoded Protein Stathmin and Resistance of Malignant Gliomas to Nitrosoureas
Affiliations of authors: Surgical and Molecular Neuro-oncology Unit (TTBN, TP, XJL, OA, DWK, JKP), Flow Cytometry Facility (DM), and Office of the Clinical Director (NOJ), National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD; Neuro-oncology Branch, National Cancer Institute, Bethesda, MD (SP, WZ, YK, JCZ, HAF); Dana-Farber/Brigham and Women's Cancer Center, Boston, MA (PYW); Brigham and Women's Hospital, Boston, MA (UDG, PMB); Proteomics Core Facility, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD (WWW, RFS)
Correspondence to: John K. Park, MD, PhD, 35 Convent Dr, MSC 3706, Bethesda, MD 20892 (e-mail: parkjk{at}ninds.nih.gov).
Background: Malignant gliomas are generally resistant to all conventional therapies. Notable exceptions are anaplastic oligodendrogliomas with loss of heterozygosity on chromosome 1p (1p+/–). Patients with 1p+/– anaplastic oligodendroglioma frequently respond to procarbazine, 1-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea, and vincristine. Because the underlying biologic basis for this clinical finding is unclear, we evaluated differentially expressed 1p-encoded proteins in 1p+/– and 1p+/+ malignant glioma cell lines and then examined whether their expression was associated with outcome of patients with anaplastic oligodendroglioma.
Methods: We used a comparative proteomic screen of A172 (1p+/–) and U251 (1p+/+) malignant glioma cell lines to identify differentially expressed 1p-encoded proteins, including stathmin, a microtubule-associated protein. 1p+/– and 1p+/+ anaplastic oligodendroglioma specimens from 24 patients were assessed for stathmin expression by immunohistochemistry. The relationship between stathmin expression and clinical outcome was assessed with Kaplan–Meier analyses. RNA inhibition and cDNA transfection experiments tested effects of stathmin under- and overexpression, respectively, on the in vitro and in vivo resistance of malignant glioma cells to treatment with nitrosourea. For in vivo resistance studies, 36 mice with intracranial and 16 mice with subcutaneous xenograft tumor implants were used (one tumor per mouse). Flow cytometry was used for cell cycle analysis. Immunoblotting was used to assess protein expression. All statistical tests were two-sided.
Results: Decreased stathmin expression in tumors was statistically significantly associated with loss of heterozygosity in 1p (P<.001) and increased recurrence-free survival (P<.001). The median recurrence-free survival times for patients with tumors expressing low, intermediate, or high stathmin levels were 45 months (95% confidence interval [CI] = 0 to 90 months), 17 months (95% CI = 10.6 to 23.4 months), and 6 months (95% CI = 1.7 to 10.3 months), respectively. Expression of stathmin was inversely associated with overall survival of nitrosourea-treated mice carrying xenograft tumors. Median survival of mice with stathmin+/– tumors was 95 days (95% CI = 68.7 to 121.3 days) and that of mice with stathmin+/+ tumors was 64 days (95% CI = 58.2 to 69.8 days) (difference = 31 days, 95% CI = 4.1 to 57.9 days; P<.001, log-rank test). Nitrosoureas induced mitotic arrest in malignant glioma cells, and this effect was greater in cells with decreased stathmin expression.
Conclusions: Loss of heterozygosity for the stathmin gene may be associated with improved outcomes of patients with 1p+/– anaplastic oligodendroglioma tumors.
| CONTEXT AND CAVEATS Prior knowledge Patients with anaplastic oligodendroglioma with loss of heterozygosity on chromosome 1p (1p+/–) frequently respond to combination chemotherapy with procarbazine, 1-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea, and vincristine. Study design Molecular study in malignant glioma cell lines, xenograft tumor mouse model systems, and human tumor specimens from patients with survival information available. Contribution Decreased expression of stathmin, a microtubule-associated protein whose gene is located on chromosome 1p, was associated with loss of heterozygosity in 1p and with increased recurrence-free survival. Implications Loss of heterozygosity of stathmin may be associated with outcome of patients with 1p+/– anaplastic oligodendroglioma. Limitations Although stathmin haploinsufficiency appears to contribute to the nitrosourea sensitivity of 1p+/– gliomas, other factors may also be involved. The immunohistochemical analysis was only semiquantitative, and tumor samples could be reproducibly classified into three expression categories, not two as would be predicted from gene copy number.
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Manuscript received October 4, 2006; revised February 8, 2007; accepted March 5, 2007.
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J Natl Cancer Inst 2007 99: 577.
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