Bortezomib down-modulates the survival factor interferon regulatory factor 4 in Hodgkin lymphoma cell lines and decreases the protective activity of Hodgkin lymphoma-associated fibroblasts

Bortezomib is a proteasome inhibitor active in classical Hodgkin lymphoma (cHL) cell lines, but poorly active in the clinic when used as a single agent, suggesting that the microenvironment could protect from drug efficacy. Therefore, we investigated the effects of bortezomib activity in the presence of HL-associated fibroblasts (HL-AFs) and sCD40L. We found that co-cultivation with human HL-AFs or the addition of sCD40L during bortezomib treatment protected cHL cells from apoptosis and cytotoxicity and rescued the down-regulation of the survival factor interferon regulatory factor 4 (IRF4). In contrast, bortezomib treatment before co-cultivation with HL-AFs inhibited in a dose-dependent manner cHL cell adhesion to HL-AFs and completely overcame HL-AF protection against drug activity. Consistently, we found that bortezomib treatment down-regulated the surface expression of CD49d and CD44, which mediate the adhesion of cHL cells to HL-AFs, and of CD54 and CD40, which mediate the adhesion to CD40L+ rosetting T-cells. These preclinical findings suggest that the low in vivo activity of bortezomib as a single agent may be due to a protective influence of the microenvironment. However, inclusion of bortezomib in the cHL drug regimen, by reducing IRF4 expression and interactions with the microenvironment, could increase the efficacy of current chemotherapeutic treatment of relapsed/refractory cHL.