Pre-Clinical Investigation of Targeted Therapies for Double Hit Diffuse Large B-Cell Lymphoma (DH-DLBCL)

Background: Molecular studies divide DLBCL into three subtypes with distinct pathogenesis and clinical outcomes: activated B-cell (ABC), germinal center B-cell (GCB) and primary mediastinal lymphoma (PML). Florescence in situ hybridization (FISH) studies identified another subgroup of DLBCL, classified as DH-DLBCL, with a poor clinical outcome harboring concurrent gene rearrangements of the c-MYC, BCL2 and/or BCL6 proto-oncogenes, resulting in the over-expression of c-Myc, Bcl2 and Bcl6 proteins. DH-DLBCL has inferior response rates (RR) to rituximab-based chemotherapy, and a shorter progression-free survival (PFS)/overall survival (OS). DH-DLBCL is characterized by de-regulation of apoptosis and cell cycle progression, resulting in rapid cellular proliferation and resistance to apoptotic stimuli. In ABC-DLBCL, anti-apoptotic factor MCL-1 is implicated in poor prognosis leading to resistance to standard chemotherapy. C-MYC transcriptionally upregulates Mcl1. Translocation of c-MYC in DH-DLBCL may contribute to the aggressive phenotype and chemotherapy resistance via the MCL-1 pathway. We hypothesize that dual inhibition of both anti-apoptotic proteins BCL2 and MCL1 is an effective strategy in inducing lymphoma cell death in DH-DLBCL.

Materials & Methods: At the pre-clinical level, we studied novel therapeutic strategies targeting key-regulatory pathways abnormally enhanced by the dual BCL2/BCL6 and c-MYC gene rearrangements or amplification using DH lymphoma cell lines (Val, DOHH-2, ROS-50). We evaluated the therapeutic value of three novel agents targeting BCL2 (ABT199), c-MYC (JQ-1), and cell cycle regulatory proteins (p21) and other BCL2 family members affecting ABT199 activity (carfilzomib (CFZ), an irreversible proteasome inhibitor) in a panel of DH-DLBCL cell lines. We retrospectively evaluated our single institution outcome experience over the last 15 years in DH-DLBCL patients. Using the lymphoma translational database that includes 611 DLBCL patients, we identified 30 patients (M=17/F=13) with aberrations in c-MYC and BCL2 or BCL6 by FISH. Demographic characteristics and clinical data were collected and analyzed.

Results: In vitro, ABT199, JQ-1, and CFZ induced cell death in a dose- and time-dependent manner. Significant synergistic activity was observed by combining ABT199 with CFZ and to a lesser degree with JQ-1. Subsequently, we studied the outcome of DHL patients treated at our institute. Mean age at diagnosis was 63 years, mostly Caucasians (N=28). Using the Han's algorithm, 21 of the DH-DLBCL were GCB, 8 were non-GCB, and 1 unclassifiable. 22 patients had rearrangement of c-MYC and BCL2/ or BCL-6 by FISH and 8 had gain/amplification/aneuploidy at these loci. At diagnosis, 96% (n=29) patients presented with stage III/IV, 67% (n=20) with High-intermediate/High IPI score, and 77% (n=23) had extra nodal disease. Front-line chemo-immunotherapy included 1) standard doxorubicin-containing regimens: R-CHOP (N=11) or R-EPOCH (N=8), or 2) intensified regimens: R-DHAC (N=3) and R+HyperCVAD/R+HDMTXCytarabine (N=8). Prophylaxis IT chemotherapy was administered to 21 (70%) patients. The complete remission (CR) rate was 67% (n=20) and 37% (n=11) patients underwent HDC-ASCS (N=9)/allo-BMT (N=2) in first (N=9) or second-remission (N=2). The use of intensified regimens was associated with a non-statistically significant improvement is PFS and OS. Similarly, an improvement in OS was observed among patients receiving HDC-ASCT/allo-BMT as consolidation. As previously noted, CNS prophylaxis was associated with an improvement in OS. Mcl-1 and other Bcl-2 family members expression levels are been determined by IHC. These results highlight the poor clinical outcome of this patient population and the need for alternative therapeutic options.

Conclusion: Our data suggests that ABT199 exhibited strong synergistic activity with CFZ. Dual targeting of BCL2 and c-MYC pathways results in synergistic activity in DHL cell lines. Of interest, this pharmacological interaction could be related to the effects of proteasome inhibition on MCL1 and p21 levels in lymphoma cells, further enhancing the activity of ABT199. Using combination therapy to inhibit c-MYC and the proteasome and in turn decreasing MCL1 will render ABT-199 more effective and be a more potent combination in causing apoptosis and lymphoma cell death. Further pre-clinical work is ongoing.