Thalidomide induces phosphorylation of histone H2AX and increases rate of apoptosis caused by fludarabine in malignant lymphocytes of chronic lymphocytic leukemia in short-term cell cultures

In this study we attempted to assess interactions of thalidomide with fludarabine in terms of their effect on DNA damage and apoptosis of chronic lymphocytic leukemia (CLL) cells. The experiments were done in ex vivo short-term cell cultures of peripheral blood cells from newly diagnosed untreated patients. We analyzed phosphorylation of histone H2AX on Ser139 (γH2AX), reporter of DNA damage, and expression of activated caspase-3, as a marker of apoptosis. Modest increase in expression of γH2AX caused by thalidomide was observed in samples of some analyzed patients. The increase in expression of γH2AX was also seen in leukemic TK6 cells treated with thalidomide. While treatment of CLL cells with thalidomide alone had no significant effect on apoptosis the treatment with thalidomide + fludarabine had greater than the additive effect on frequency of apoptotic cells. The data suggest that oxidative DNA damage likely induced by thalidomide sensitizes CLL cells to undergo apoptosis in response to fludarabine.