Suppression of PKK expression sensitizes DLBCL cells to treatment with chemotherapeutic agents. (A) SUDHL-6 cells expressing shControl or shPKK-1 were cultured in the medium containing 10% serum and treated with etoposide at the indicted concentrations for 36 hours. The relative live cells were analyzed by MTT assay. The absorbance readings from the cells treated with the vehicle (DMSO) were set at 100%. The mean results and SDs from 3 separate experiments are depicted. The difference between shPKK-expressing and the control cells was significant after the etoposide treatment at all concentrations tested (P < .01). (B) SUDHL-6 cells expressing shControl or an shPKK were treated with CHOP for 72 hours. The relative live cells were analyzed as described in panel A. The difference between the shPKK-expressing and the control cells was significant (P < .01, at each concentration). 1x CHOP consists of cyclophosphamide monophosphate, doxorubicin, vincristine, and prednisone at concentrations of 5.84pM, 1.5pM, 260pM, and 1.0μM, respectively.⁶²