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Hypoxanthine:Guanine Phosphoribosyltransferase Activity in Xenografts of Human Osteosarcoma¹

Departments of Hematology/Oncology [W. H. M.] and Biochemical and Clinical Pharmacology [J. A. H., P. J. L., P. J. H.], St. Jude Children's Research Hospital, Memphis, Tennessee 38101, and the Division of Hematology/Oncology [W. H. M.], Department of Pediatrics, University of Tennessee, Memphis, College of Medicine, Memphis, Tennessee 38163

It has recently been reported that human osteosarcomas may lack the purine salvage pathway enzyme, hypoxanthine:guanine phosphoribosyltransferase (EC 2.4.2.8). We have established a quantitative assay for measurement of this enzyme in human osteosarcoma xenografts with analysis of products by thin-layer chromatography. Nucleotidase or phosphatase activity was readily detected and could be abolished by preheating cytosol at 60°C for 10 min and performing the assay at pH 10. Alternatively, the use of 25 mM NaF at pH 7.4 also inhibited this activity. The pH optimum for this enzyme in red blood cell sonicates and tumor cytosols was pH 10. All six human osteosarcoma xenografts contained hypoxanthine:guanine phosphoribosyltransferase activity ranging from 0.97 to 4.06 nmol/min/mg of protein at pH 7.4. Control human red blood cell sonicates demonstrated activity of 0.83 nmol/min/mg of protein. These data demonstrate that human osteosarcoma xenografts contain substantial activities of this purine salvage pathway enzyme.

¹ Supported in part by American Cancer Society Grant IN99K, Studies of Childhood Tumors Grant P01 CA23099, and Cancer Center CORE Grant P30 CA21765 from the National Cancer Institute; Biomedical Research Support Grant S07 RR05584-21 from the Division of Research Resources; and the American Lebanese Syrian Associated Charities (ALSAC). Presented in part at the 76th Annual Meeting of the American Association for Cancer Research, Houston, TX, 1985 (1).

² To whom requests for reprints should be addressed, at St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38101.

Received 2/19/86. Revised 6/17/86. Accepted 6/19/86.