Knock-down of BCL6 / STAT6 Sensitizes Primary B Cell Lymphoma Cells for Treatment with Current Therapeutic Agents

Primary mediastinal B cell lymphoma (PMBL) is characterized by specific molecular hallmarks including the expression of B Cell Lymphoma factor 6 (BCL6) and the presence of the activated Signal Transducers and Activators of Transcription factor 6 (STAT6). Recently we have shown that combined targeting of BCL6 and activated STAT6 by specific chemical inhibitors in PMBL resulted in additive efficacy regarding their negative effects on cell viability. Given that despite general efficient immuno-chemotherapy in PMBL the delayed treatment-related sequelae remains still a main challenge, we analyzed the role of BCL6 and activated STAT6 in the sensitivity of PMBL cells to the current treatment components. We found that the knock-down of BCL6 / STAT6 by siRNA sensitized the PMBL cells to the effects of R-CHOP components in two of three PMBL cell lines. In one cell line, MedB-1, which is marked by less expression of BCL6 and mutated STAT6, the knock-down of BCL6 / STAT6 did not enhance the efficiency of Doxorubicin, Rituximab, and Vincristin. Thus, the targeting of BCL6 and STAT6 in addition or prior to the treatment with components of the current immuno-chemotherapy may sensitize the PMBL tumor cells for drug effects, at least in parts of PMBL cases.