JQ1, a c-MYC Inhibitor Targets Hexokinase II and Enhances the Cytotoxic Effects of Chemotherapeutic Agents in Diffuse Large B-Cell Lymphoma (DLBCL)

Background: Results from thecollaborative trial in relapsed aggressive lymphoma (CORAL) study demonstrated a poor clinical among patients treated with second-line chemo-immunotherapy in the post-rituximab era, stressing the need to identify and/or optimize novel targeted agents. C-myc expression was found correlate with a poor clinical outcome in patients with newly diagnosed or relapsed/refractory DLBCL. Previously, we found that JQ1 overcomes rituximab-chemotherapy resistance in lymphoma pre-clinical models. JQ1 exhibited synergistic activity when combined with chemotherapy agents. We also demonstrated that hexokinase II was highly expressed in rituximab resistant cell lines (RRCL), and its expression was associated with a deregulation in the glucose metabolism and an increase in the apoptotic threshold leading to chemotherapy resistance. In our current work, we evaluated molecular studies dissecting the cellular pathways affected by JQ1.

Methods: A panel of rituximab-sensitive (RSCL) and RRCL cell lines were exposed to escalating doses of JQ1 (0-8μM) for 24, 48 and 72h. Changes in cell viability and cell cycle distribution were evaluated using the Presto Blue assay and flow cytometry respectively. IC₅₀ was calculated by Graphpad Prism 6 software. Loss of mitochondrial membrane potential (∆ψm) following JQ1 exposure was assessed by DiOC6 staining. Changes in c-MYC, HKII, HKI, Voltage dependent anion channel protein (VDAC) and p21 expression levels were determined by western blotting. HKII was silencing using siRNA interference in RRCL (Raji-4RH) and changes in HKII, HKI, VDAC, c-MYC and p21 protein expression was determined. HKII knockdown or scramble Raji-4RH cells were exposed to different chemotherapy agents and JQ1; cell viability and mitochondrial membrane potential was accessed.

Result:JQ1 induced a dose-and time- dependent cell death in cell lines. In vitro exposure cells to JQ1 resulted in a loss of mitochondrial potential and induced G1 cell cycle arrest. In vitro exposure to JQ1 decreased c-MYC and HKII expression levels and induced of p21 expression. Complete silencing of HKII re-sensitized cell to chemotherapy (doxorubicin, vincristine and bortezomib). On the other hand, HKII knockout abrogated JQ1 anti-tumor activity.

Conclusion: Our data suggests that JQ1 had anti-tumor activity against rituximab-sensitive or resistant pre-clinical models. The inhibition of HKII following JQ1 exposure may contribute to lower the mitochondrial membrane potential and enhance the chemotherapeutic effect. Our finding highlights a better understanding in the molecular events triggered by JQ1 as a potential role in the treatment of B-cell malignancies.