The selective tyrosine kinase inhibitor,STI571, inhibits growth of anaplastic thyroid cancer cells

To establish a molecular targeting therapy for anaplastic thyroid carcinomas, we studied the effect of the specific tyrosine kinase inhibitor, STI571, on anaplastic thyroid cancer cell lines highly expressing c-ABL ARO (mutated p53) and FRO (undetectable p53). These lines showed marked inhibition of cell growth after treatment with STI571. In contrast, the growth of papillary thyroid cancer cell lines that harbor wild-type p53 and have low levels of c-ABL was not affected by STI571. Fluorescent-activated cell sorting analysis revealed that STI571 treatment increased the fraction of FRO and ARO cells in S and G(2)/M phases, respectively, indicating induction of S and G(2)/M transition arrest. These changes were accompanied by inhibition of c-ABL phosphorylation/activation and increased expression of p21(cip1) in FRO and p27(kip1) in both FRO and ARO cells. Treatment with STI571 also led to reduction of cyclin A, B1, and CDC2 levels. The growth of FRO cells implanted into immunocompromised mice was significantly inhibited by STI571. Taken together, these results suggest that selective suppression of c-ABL activity by STI571 may represent a potential anticancer strategy for p53-mutated undifferentiated thyroid carcinomas.