在淋巴瘤中利用MYC致癌应激实现治疗获益

Diffuse Large B-cell Lymphoma (DLBCL) is the most frequently occurring form of Non-Hodgkin's Lymphoma. Gene expression profiling identified two types of DLBCL based on germinal center reaction cell-of-origin: germinal center B cell-like (GCB) or activated B cell-like (ABC) DLBCL. Though GCB patients respond better than ABC to the standard immunochemotherapy regimen, one subtype of GCB patients paradoxically exhibit the lowest response rates. These represent a clinically and genetically distinct subset of DLBCL with both MYC and BCL2 translocations and overexpression, known as ‘double-hit' (DHIT)-GCB. Recently, the ViPOR phase I/II clinical trial in relapsed/refractory DLBCL, designed to target survival pathways in ABC, demonstrated unexpectedly that DHIT-GCB had a 50% complete response (CR) rate. In vitro drug sensitivity studies revealed that venetoclax, a BCL2 inhibitor in ViPOR, is significantly more toxic in DHIT-GCB cell lines than in other BCL2 translocated GCB lines lacking MYC translocations. Thus, we hypothesized that inhibition of BCL2 renders DHIT-GCB malignant cells vulnerable to MYC-induced toxicity, explaining the selective sensitivity of DHIT-GCB lymphomas to venetoclax. To test this, we employed the degradation tag (dTAG) system to controllably degrade MYC protein in malignant lymphoma cells. We used a knock-in approach to engineer GCB cell lines stably expressing a MYC-GFP-dTAG fusion protein from the endogenous MYC locus. BCL2 inhibition induced rapid apoptosis in these lines, but notably, concomitant degradation of MYC increased the proportion of live, non-apoptotic cells. To investigate how MYC modulates response to BCL2 inhibition in DHIT-GCB, we performed unbiased transcriptomic and genomic profiling studies in the MYC-dTAG lines. RNA-seq of MYC degradation in a time-course in DHIT-GCB cells validated that MYC gene expression signatures were the most strongly downregulated but, interestingly, showed upregulation of signatures for B-cell differentiation and proliferation. Genome-wide CRISPR screens sorted on viable, non-apoptotic cells treated with venetoclax +/- MYC degradation demonstrated that the strongest genetic regulators of differential response to venetoclax were DNA replication and damage and cell cycle genes. These results indicated that disruption of these pathways could synergize with high MYC to promote sensitivity of DHIT-GCB cells to venetoclax. Finally, functional assays with clinically available targeted therapies perturbing DNA damage and cell cycle highlighted how MYC levels relate to these processes in malignant B-cells and thus modulate response to BCL2 inhibition. These studies may suggest drug combinations strategies that would harness the synergism between MYC and BCL2 in DHIT-GCB, and hopefully improve therapeutic outcomes for these DLBCL patients.