Bclw Overexpression Predicts Aggressive Disease in B-Cell Lymphomas

B-cell lymphomas encompass a phenotypically and genetically heterogenous subgroup within hematologic malignancies. Despite this heterogeneity, the ability to evade apoptosis is a unifying feature across B-cell lymphomas, and alterations within the Bcl-2 family of apoptosis regulatory proteins is a key mechanism for this evasion. While overexpression of the anti-apoptotic Bcl-2 family member BCL2 has been widely described in multiple B-cell lymphomas, altered expression of other anti-apoptotic proteins within this family, including BCLX, MCL1, A1 and, in particular, BCLW has been under-investigated. This is highlighted by clinical trials of the BCL2 inhibitor, venetoclax, which found poor single agent activity in B-cell lymphomas that were thought to be highly BCL2-dependent. Therefore, we investigated the contributions of anti-apoptotic Bcl-2 proteins in B-cell lymphomas. Analysis of gene expression profiling datasets of patient samples of major B-cell lymphoma subtypes as compared to normal B-cells demonstrated differential overexpression of anti-apoptotic Bcl-2 proteins, with BCL2, BCLX and BCLW being significantly overexpressed in multiple B-cell lymphoma subtypes. Focusing on aggressive B-cell lymphoma subtypes, BCLW was consistently overexpressed across all major B-cell lymphoma subtypes. Notably, BCLW overexpression was maintained in high grade follicular lymphoma compared to low grade, whereas BCL2 levels decreased as grade increased. These findings indicate that BCLW overexpression is selected for in more aggressive B-cell lymphoma subtypes. BCLW overexpression in aggressive B-cell lymphoma cell lines conferred resistance to the non-specific BH3 mimetic navitoclax as well as to venetoclax. Further, analysis of diffuse large B-cell lymphoma (DLBCL) cell lines demonstrated that the combination of high BCLW/low BCL2 in GCB DLBCL and high BCLW/moderate BCL2 in non-GCB DLBCL is also associated with decreased navitoclax sensitivity, suggesting that high BCLW may confer treatment resistance. In accordance with this, analysis of patient outcomes in DLBCL demonstrates that patients exhibiting high BCLW levels with low BCL2 levels have poorer survival than those with low BCLW. Moreover, Cox regression analysis showed BCLW was an independent determinant of overall survival in DLBCL. Together, our results indicate that BCLW predicts for more aggressive disease in B-cell lymphomas and increased resistance to therapy.