Comparison of Hprt variant frequencies and chromosome aberration frequencies in lymphocytes from radiotherapy and chemotherapy patients: A Prospective Study

Abstract

The autoradiographic 6-thioguanine-resistant mutant lymphocyte assay and a chromosome aberration assay were used to determine the time-course of appearance and persistence of elevated frequencies of hprt variants and dicentric chromosomes in patients receiving x-irradiation therapy. Twelve cancer patients, treated with 180-200 cGy/day, 5 days/wk, for 3-7 wk, were studied before treatment, at various weekly intervals during treatment, and after treatment. The hprt mutation assays were done with frozen/thawed lymphocytes isolated from aliquots of the same blood samples used for the chromosome aberration assays. The hprt variant frequencies (Vfs) of only 4 of the 7 patients assayed at 2 wk of treatment were elevated over pre-treatment Vfs, but during the 3rd and 4th weeks of treatment there were significant (P less than 0.01) 5- to 15-fold increases in all Vfs. By 6-32 wk after treatment Vfs had fallen to levels only slightly higher than the mean pre-treatment Vf. The frequencies of cells with dicentric chromosomes were significantly increased (P less than 0.01) after 1 wk of radiotherapy, continued to increase during therapy, and remained elevated after treatment. Five multiple sclerosis patients were also studied before and at 2 and 4 wk intervals after treatment with monthly i.v. doses of 750 mg/m2 of cyclophosphamide (CP). There were no significant elevations in chromosome aberrations at these post-treatment sample times. Previous assays for hprt mutants, done with aloquots of the same blood samples (Ammenheuser et al.: Mutat Res 204:509-520, 1988), had shown 8- to 20-fold increases in Vfs 2 wk after the 1st CP treatment. Our results demonstrate the complementary nature of these two human monitoring assays and emphasize the importance of careful selection of optimal sampling times.

Genotoxicity of Therapeutic Intervention in Children with Acute Lymphocytic Leukemia

“…In addition, the HPRT gene is an excellent biomarker of effect because mutations at the HPRT locus have no direct clinical consequences and have been shown to reflect genome-wide mutational events (13,14). This approach for somatic mutation analysis in humans has been widely used to determine in vivo background as well as acquired somatic cell Mfs in pediatric and adult populations exposed to known and unknown environmental mutagens (15)(16)(17)(18)(19)(20)(21).…”

The HPRT Short-Term Assay in Monitoring Individuals Exposed to Genotoxic Agents

“…For example, in the case of the radiotherapy study of Ammenheuser et al (4), effects could be observed because sampling was performed before, during, and after treatment, allowing the observation of a dose-related response due to the cumulative effect characteristic of radiation. When studying chemicals, this type of design is difficult to accomplish; in the best of the cases, patients are sampled only before and after treatment, or a control group is compared to an exposed group.…”

“…When these protocols are used, overlapping ranges are usually found, so that most of the exposed individuals cannot be distinguished from normals. Sampling time is another factor discussed by Ammenheuser et al (4,5) when studying individuals exposed to medical treatments. At least 15 days would be necessary for the mutations produced by exposure to be manifested in cells, and once treatments ended, there would be a period during which mutation frequency increases could be detected before the mutant cells are eliminated from the body by homeostatic mechanisms, as suggested from their studies (4,5).…”

Elevated Levels of Somatic Mutation as a Biomarker of Environmental Effects Contributing to Breast Carcinogenesis

“…The HPRT assay has also been used extensively to demonstrate a genotoxic effect of cancer chemotherapy upon circulating lymphocytes. In addition to the two mentioned above, seven studies have been published in which the frequency of lymphocytes with mutations at the GRANT X-linked HPRT locus was determined in newly diagnosed cancer patients prior to genotoxic therapy (Albertini, 1980;Lange and Prantner, 1982;Dempsey et al, 1985;Messing and Bradley, 1985;Sala-Trepat et al, 1990, Ammenheuser et al, 1991, Caggana et al, 1991. In all nine studies, the overall frequency of somatic mutation at the HPRT locus was higher in the cancer patients than in concurrent controls.…”