THE TYRPHOSTIN AG17 INDUCES APOPTOSIS AND INHIBITION OF CDK2 ACTIVITYIN A LYMPHOMA CELL-LINE THAT OVEREXPRESSES BCL-2

Tyrphostins are low molecular weight compounds that specifically inhib it protein tyrosine kinases. We studied the effects of tyrphostins on OCI-Ly8, a cell line derived from a patient with immunoblastic lymphom a that carries the t(14;18) translocation and overexpresses the B-cell lymphoma/leukemia-2 gene (bcl-2). To test the possibility that tyrpho stins induce apoptosis in these cells, overcoming the protection rende red by bcl-2, we screened 16 tyrphostins representing different famili es at a concentration of 0.5-50 mu M. We found that AG17 was the most potent in this regard. Cell cycle analysis demonstrated that AG17 indu ces arrest at the G(1) phase followed by apoptosis with general reduct ion of the intracellular level of tyrosine-phosphorylated proteins. To further elucidate the mechanism of action of AG17, we investigated it s effect on some of the key proteins that regulate the cell cycle. Bcl -2 and cdk2 protein levels were not altered with AG17, whereas cdk2 ki nase activity, as well as p21 and p16 protein levels, were reduced mar kedly. These results suggest that the target of AG17 is inactivation o f cdk2. Because lymphoma cells with the t(14;18) translocation and bcl -2 overexpression are resistant to chemotherapy, novel drugs selective ly able to induce apoptosis in these cells could offer a new approach to the treatment of lymphoma patients.