JQ1, a Potent c-MYC Inhibitor Overcomes Rituximab-Chemotherapy Resistance in Lymphoma Pre-Clinical Models

Background: The poor clinical outcomes of patients with aggressive B-cell lymphoma in the post-rituximab era, stress the need to identify and/or optimize novel targeted agents. Several retrospective and prospective clinical studies had demonstrated that C-myc expression correlates with a poor clinical outcome in patients with newly diagnosed or relapsed/refractory diffuse large B-cell lymphoma (DLBCL).  To this end, we evaluated the therapeutic effects of targeting C-myc using JQ1, a novel bromodomain inhibitor in rituximab-sensitive or –resistant models.

Methods: A panel of rituximab-sensitive (RSCL) or rituximab-resistant (RSCL) cell lines was exposed to JQ1 (0-100 µM) for 24-72 hrs. Changes in cell viability and cell cycle distribution were evaluated using the Presto Blue assay and flow cytometry respectively. IC₅₀ values were calculated using the GraphPad Prism6 software. Subsequently lymphoma cells were exposed to JQ1 or vehicle and various chemotherapy agents such as doxorubicin (0.5, 1, 2µM), dexamethasone (1µM), Ibrutinib (1µM), bortezomib (10-20nM) or carfilzomib (10nM) for 48 hours. Coefficient of synergy was calculated using the CalcuSyn software.

Results: In vitro exposure of RRCL and to a lesser degree RSCL to JQ1 resulted in a dose- and time-dependent cell death. Strong synergistic activity was observed when JQ1 was combined with doxorubicin, dexamethasone bortezomib or carfilzomib in vitro. Cell cycle analysis demonstrated that in vitro of RSCL or RRCL to JQ1 resulted in G1 cell cycle arrest.

Conclusions: In summary, our data suggests that targeting C-myc expression using JQ1 results in anti-tumor activity against RSCL and RRCL. In addition, JQ1 exhibited synergistic activity when combined with chemotherapy agents (doxorubicin or dexamethasone) or targeted agents (bortezomib or carfilzomib). On going studies are aimed to study the mechanisms by which c-myc inhibition results in cell death in RSCL and RRCL.  JQ1 is a distinct targeted agent undergoing clinical evaluation in patients with relapsed/refractory lymphomas. Molecular studies dissecting the cellular pathways affected by JQ1 are important in order to further advance the clinical development of c-myc inhibitors in lymphoid malignancies. (Research, in part, supported by a NIH grant R01 CA136907-01A1 awarded to Roswell Park Cancer Institute and The Eugene and Connie Corasanti Lymphoma Research Fund)