Somatic mutation and neoplastic transformation induced by (methyl-/sup 3/H)thymidine. [Hamsters]

A system for the study of neoplastic transformation as induced by the incorporation of (methyl-/sup 3/H)thymidine is described. Normal diploid golden Syrian hamster embryo fibroblasts were exposed to (methyl-/sup 3/H)thymidine for 17 hr, followed by a brief chase with deoxycytidine- and thymidine-containing growth medium. Analysis of cell curves suggested multihit mechanism with D/sub q/ and D/sub o/ equal to 0.012 and 0.04 ..mu..Ci/ml, respectively. Transformation studies demonstrate that expression of specific neoplastic phenotypes occurs at different post-treatment population doublings (PTPD), beginning with morphological alteration (PTPD 3-4), followed by enhanced fibrinolytic activity (PTPD 11-16) and the ability to clone in both medium containing 1% serum (PTPD 18-32) and soft agar (PTPD 25-32). All treated lines displayed tumorigenicity when examined at PTPD 46, whereas control cultures did not. Two tumor lines obtained from tumor explants were further characterized. Cells treated with equivalent tritium concentrations of (5-/sup 3/H)uridine display neither elevated somatic mutation nor enhanced morphological transformation. DNA damage occurring as a result of (/sup 3/H)thymidine incorporation was shown via mutagenicity studies at loci coding for hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) (HPRT) and the NA/sup +/ /K/sup +/ ATPase (EC 3.6.1.3). (methyl-/sup 3/H)thymidine incorporation resulted in induction of HPRT but not ouabain-resistant mutants. Presentmore » studies substantiate the importance of specific DNA/nuclear damage, induced by incorporation of tritiated thymidine, as a cause of neoplastic transformation.« less