Simvastatin Sensitizes Bcl-2-Negative DLBCL Cell Lines to CHOP: A Finding with Possible Clinical Implications for Treatment of Bcl-2-Negative DLBCL?

Abstract

It has previously been shown that addition of rituximab overcomes bcl-2-associated resistance to CHOP in DLBCL patients (Mounier 2003). However, the role of rituximab in the treatment of bcl-2 negative DLBCL is presently unclear. To better understand the molecular mechanisms for CHOP-resistance, the DLBCL cell lines Karpas 422, ULA, WSU-NHL, SU-DHL-8 and SU-DHL-5 were characterised with regard to CHOP- and rituximab-sensitivity. As compared to the other cell lines, Karpas 422 and ULA were CHOP-refractory and WSU-NHL showed an intermediate response to CHOP-treatment. However, SU-DHL-8 and SU-DHL-5 were sensitive to low levels of CHOP. Interestingly, the response to rituximab did not correspond to CHOP-sensitivity, as CHOP-refractory ULA were sensitive to rituximab alone while CHOP-sensitive SU-DHL-8 were refractory. Moreover, when assayed for expression of bcl-2 protein by western blot, SU-DHL-8 and SU-DHL-5 showed a low or undetectable expression while Karpas 422, ULA and WSU-NHL expressed high levels of bcl-2 protein. Hence, low levels of bcl-2 correlated to CHOP-sensitivity and with rituximab-resistance, consistent with results from clinical studies. The HMG-CoA reductase inhibitor simvastatin can induce apoptosis of Hodgkin lymphoma and myeloma cell lines, and statin use was associated with reduction in lymphoma risk in the international case-control study EPILYMPH (Fortuny 2006). Yet, statins have been shown to impair the antitumour effects of rituximab by inducing conformational changes of CD20 (Winiarska 2008), questioning the concomitant use of statins and rituximab. To evaluate the effect of simvastatin on the cell death of bcl-2-expressing and –non-expressing cell lines, ULA, SU-DHL-8 and Karpas 422 were incubated with increasing levels of simvastatin. Interestingly, already at levels as low as 2 μM (corresponding to a daily intake of 10 mg simvastatin), bcl-2-negative SU-DHL-8 cells showed signs of increased cell death. However, bcl-2 expressing ULA and Karpas 422 cells were resistant to levels of simvastatin as high as 50 μM. Moreover, low levels of simvastatin sensitized SU-DHL-8 cells to CHOP treatment. Taken together, our results may suggest that replacement of rituximab with simvastatin during CHOP-treatment of bcl-2 negative DLBCL could improve treatment responses. However, further studies are warranted to bring this notion to clinical reality.