P53-MEDIATED RADIORESISTANCE DOES NOT CORRELATE WITH METASTATIC POTENTIAL IN TUMORIGENIC RAT EMBRYO CELL-LINES FOLLOWING ONCOGENE TRANSFECTION

Purpose: Changes in wild-type p53 protein function occur in the majori ty of human tumors, and may alter genomic stability and the cellular r esponse to ionizing radiation, Whether oncoproteins can render tumor c ells both radioresistant and metastatic, may have implications for cli nical strategies designed to improve local tumor control. In the studi es reported here, we tested the hypothesis that acquired radioresistan ce correlates with metastatic potential within a large panel of transf ormed rat embryo cell (REF) lines following transfection with activate d H-ras, mutant p53, and HPV16-E7 alleles. Methods and Materials: Rat embryo cells (REF cells) were transfected using the calcium-phosphate technique with an activated H-ras gene alone, or in combination with h uman papillomavirus HPV16-E7 and/or human or murine mutant p53 sequenc es, Other rat embryo cell clones expressing transfected HPV-E7 and act ivated ras sequences subsequently acquired endogenous p53 gene mutatio ns during culture in vitro. The relative expression of p21ras and p53 protein for each REF transformant was determined by Western blot analy sis following transfection. REF clones were phenotypically characteriz ed at early passage (i.e., passages 5-7) and late passage (i.e., passa ges 10-20) for their: (a) relative tumor growth rate, and (b) their ab ility to undergo spontaneous metastasis following intramuscular inject ion into the hind legs of SCID mice. In vivo phenotypic end points wer e then compared to previously measured parameters of in vitro radiosen sitivity for each cell line. Additionally, the expression of the cellu lar protease, plasminogen activator, was determined for a number of me tastatic and nonmetastatic cell Lines. Results: We found no evidence t hat selected oncogene-transfected REF transformants that were radiores istant in culture had a greater spontaneous metastatic potential than nonradioresistant REF transformants. Neither the level of expression o f the p21ras protein nor that of the p53 protein was correlated with t he spontaneous metastatic phenotype when tested at early passage. The metastatic phenotype appeared to be independent of p53 genotype. The m ajority of metastatic REF clones tested (7 out of 9 clones) expressed plasminogen activator following oncogene transfection, in contrast to nonmetastatic REF transformed cell lines. Conclusions: Our results sug gest that (a) intrinsic radioresistance does not correlate with sponta neous metastatic potential in oncogene-expressing REF transformant cel l lines, and (b), novel clinical strategies designed to overcome oncog ene-mediated radioresistance could potentially impact on overall survi val, as gains in local tumor control may not be offset by a greater ri sk of distant metastasis.