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Estimating DNA Repair by Sequential Evaluation of Head and Neck Tumor Radiation Sensitivity Using the Comet Assay
David J. Terris, MD;
Edith Y. Ho;
Hani Z. Ibrahim, MD;
Mary Jo Dorie, PhD;
Mary S. Kovacs, BS;
Quynh T. Le, MD;
Albert C. Koong, MD, PhD;
Harlan A. Pinto, MD;
J. Martin Brown, DPhil
Arch Otolaryngol Head Neck Surg. 2002;128:698-702.
Background The alkaline comet assay is a microelectrophoretic technique for detecting
single-strand DNA breaks, and may be used as an indirect measure of hypoxia
by determining the radiation sensitivity of individual cells.
Objective To assess the ability of the comet assay to estimate the rate of DNA
repair after irradiation in patients with head and neck cancer.
Methods The comet assay was used to evaluate DNA damage in fine-needle aspirates
of lymph nodes containing metastatic squamous cell carcinoma in patients with
head and neck cancer 1, 2, and 3 minutes after treatment with 500 rad (5 Gy)
of irradiation. The amount of DNA damage (measured as the "tail moment" of
the comet) is proportional to the number of DNA single-strand breaks after
irradiation, which in turn depends on the oxygen concentration in each cell.
Results The mean ± SD of the median tail moment of the 1-minute postirradiation
comets was 29.4 ± 14.2 (n = 27). After 2 minutes, the mean median tail
moment decreased to 25.4 ± 13.6 (n = 25), representing a mean decrease
of 11.9% in those patients with both 1- and 2-minute comet assays. Assuming
a linear rate of repair, this decrease in DNA damage corresponds to a repair
half-life of 4.2 minutes. A 3-minute assay was also performed on samples from
a smaller number of patients (n = 9), with a mean value not significantly
different from that of the 2-minute assay of the samples from this group.
Conclusions The comet assay is a promising tool for evaluating radiation sensitivity
in individual cells. The rate of DNA repair early after irradiation is consistent
with data in the literature.
From the Division of Otolaryngology–Head and Neck Surgery (Drs
Terris and Ibrahim and Ms Ho) and the Departments of Radiation Oncology (Drs
Dorie, Le, Koong, and Brown and Ms Kovacs) and Medicine (Dr Pinto), Stanford
University Medical Center, Stanford, Calif.
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