Abstract
Expression of the anti-apoptotic B-cell lymphoma 2 (BCL-2) protein in patients with diffuse large B-cell lymphoma (DLBCL) strongly correlates with resistance to standard therapy with cyclophosphamide, vincristine, doxorubicin, prednisolone, and rituximab (R-CHOP). Although studies focus mainly on the contribution of BCL-2, here we also investigate the contribution of other anti-apoptotic proteins to CHOP-therapy resistance in DLBCL. Functional dynamic BCL-2 homology (BH)3 profiling was applied to DLBCL cell lines upon CHOP treatment or single CHOP compounds. Cell-specific anti-apoptotic dependencies were validated with corresponding BH3-mimetics. We found high expression of anti-apoptotic BCL-2, MCL-1, and BCL-XL in DLBCL cell lines and patients. CHOP treatment resulted in both enhanced and altered anti-apoptotic dependency. Enhanced sensitivity to different BH3-mimetics after CHOP treatment was confirmed in specific cell lines, indicating heterogeneity of CHOP-induced resistance in DLBCL. Analysis of single CHOP compounds demonstrated that similar changes could also be induced by doxorubicin or vincristine, providing evidence for clinical combination therapies of doxorubicin or vincristine with BH3-mimetics in DLBCL. In conclusion, we show for the first time that CHOP treatment induces increased anti-apoptotic dependency on MCL-1 and BCL-XL, and not just BCL-2. These results provide new perspectives for the treatment of CHOP-resistant DLBCL and underline the potential of BH3 profiling in predicting therapy outcomes.
Highlights
The B-cell lymphoma 2 (BCL-2) family of proteins is a group of pro- and anti-apoptotic proteins with key roles in the regulation of intrinsic apoptosis
diffuse large B-cell lymphoma (DLBCL) Cells Are Dependent on BCL-2 or MCL-1, but Not BCL-XL
We first validated the importance of different anti-apoptotic BCL-2 family protein expression in our representative DLBCL cell line panel with different genetic backgrounds (5 GCB and 3 activated B-cell (ABC)) and correlated anti-apoptotic protein expression to their functional anti-apoptotic dependency as determined by BH3 profiling (Figure 1, Figures S1 and S2)
Summary
The B-cell lymphoma 2 (BCL-2) family of proteins is a group of pro- and anti-apoptotic proteins with key roles in the regulation of intrinsic apoptosis. Proteins of the BCL-2 family share a general structure of one or more BCL-2 homology (BH) domains, of which expression of the BH3 domain is a universally shared feature Expression of this BH3 domain is essential for protein-protein interactions, thereby allowing dimerization of pro-apoptotic sensitizer proteins (e.g., BAD, NOXA and HRK) with anti-apoptotic proteins (e.g., BLC-2, BCL-XL, MCL-1 and BCL-W). The effect of standard (prolonged) CHOP treatment itself on DLBCL-specific pro- and anti-apoptotic signaling is currently unknown To this end, we studied the effect of CHOP therapy on anti-apoptotic dependency in DLBCL using functional dynamic BH3 profiling [11]. Our results showed that CHOP resistance is not exclusively mediated through BCL-2, but by multiple other anti-apoptotic proteins These results highlight the heterogeneity of anti-apoptotic dependency in DLBCL, which likely depends on other anti-apoptotic proteins in addition to BCL-2. These results could have implications for clinical trials evaluating efficacy of BH3 mimetics
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