THERAPEUTIC USEFULNESS OF WILD-TYPE P53 GENE INTRODUCTION IN A P53-NULL ANAPLASTIC THYROID-CARCINOMA CELL-LINE

Anaplastic thyroid carcinomas very often harbor the mutations in the t umor suppressor gene p53. We have previously shown that wildtype (wt) p53 gene introduction led to cell growth arrest, but not apoptosis, in p53-null anaplastic thyroid carcinoma cells. The present studies were designed to evaluate other therapeutic effects of wt-p53 gene introdu ction on p53-null thyroid carcinoma cells, as chemo- and radiosensitiz ation and inhibition of angiogenesis have also been described recently as additional therapeutic advantages of wt-p53 gene introduction in t umor cells with p53 mutations. A p53-null anaplastic thyroid carcinoma cell line, FRO, and a FRO subline stably expressing a temperature-sen sitive (ts) mutant of p53 (p53Val138): tsFRO, were used. ts-p53 functi ons as mutant and wt at nonpermissive (37 C) and permissive (32 C) tem peratures, respectively, tsFRO showed a prolonged cell doubling time c ompared to parental FRO when cultured at 32 C, but the cell growth rat e was similar between FRO and tsFRO at 37 C. The cytotoxic and clonoge nic assays demonstrated that although the sensitivity to three differe nt anticancer agents (cisplatin, 5-fluorocytosine, and doxorubicin) wa s unaltered, radiosensitivity was enhanced in tsFRO compared to FRO at 32 C. Unexpectedly, in studies on angiogenesis, expression levels of vascular endothelial growth factor (an angiogenic factor) messenger ri bonucleic acid were similar between FRO and tsFRO, and thrombospondin- 1 (an antiangiogenic factor) messenger ribonucleic acid and protein le vels were about 2.5-fold lower in tsFRO than FRO at 32 C, although any difference could not be detected in their ability to inhibit in vitro angiogenesis with the culture medium conditioned by tsFRO and FRO at 32 C. These results suggest that p53-defective thyroid carcinomas may benefit from the combination of p53 gene therapy and radiotherapy. How ever, further study will be necessary to clarify the pathological sign ificance of thrombospondin-1 in angiogenesis and thyroid tumor growth.