P1307: TESTING THE IMPORTANCE OF ANTIOXIDANTS ON THE PATHOGENESIS OF B CELL LYMPHOMA

Abstract

Background: Our group found that antioxidant supplementation of the diet – in doses that reduce reactive oxygen species (ROS) levels – markedly accelerates progression and metastasis of malignant melanoma and lung cancer in mice. These findings can help explain the puzzling outcome of clinical trials with antioxidants and led to a heated debate about the safety of supplements for cancer patients. The findings, combined with those of dozens of clinical antioxidant trials, suggest that cancer patients and survivors should avoid antioxidant supplements. Although multiple other cancer types including breast, colon, and pancreatic cancer has been found to respond similarly to antioxidants, little is known about the effects in hematologic malignancies. In the latter, high doses of VitC – that increase oxidative stress – have shown therapeutic effects in some studies, including in B cell lymphoma. However, other studies have raised doubts about high-dose VitC therapy. Thus, many questions remain about the impact of antioxidant administration for B cell lymphoma progression, in particular in ROS-lowering doses. Aims: Define the impact of antioxidant administration on B cell lymphoma cell proliferation and viability in vitro and on the progression and survival of lymphoma in vivo. Methods: For in vitro experiment, we performed analyses of cell proliferation, cell cycle, apoptosis, and ROS levels; RNA from cells following interventions was isolated for RNAseq analysis; real-time PCR was performed to confirm candidate genes; and ChIP-qPCR to study protein-DNA binding. For in vivo experiments, we used xenograft models by subcutaneous injection of human B lymphoma cell lines, and used λMYC mice as a model of endogenous B cell lymphoma (these mice harbor a mutant human MYC gene controlled by a reconstructed Igλ locus). In vivo antioxidants were administered both orally in the drinking water, and was injected in different doses and combinations. Results: The antioxidants N-acetylcysteine (NAC), vitamin C (VitC), L-Cystein, and glutathione in doses that reduce ROS levels markedly reduced the viability of human B cell lymphoma cell lines in a MYC-dependent fashion. Intraperitoneal injections of NAC and VitC dose-dependently reduced tumor growth in xenograft experiments. Knockdown of MYC restored tumor growth in the presence of antioxidants and switching-on MYC expression in B cells rendered them sensitive to NAC and VitC. Molecular analyses revealed that antioxidants increased the binding of EGR1 to MYC and stimulated EGR1/MYC binding to apoptotic gene promotors—thus stimulating apoptosis. Intraperitoneal injections or life-long oral antioxidant administration reduced tumor growth and improved survival in λMYC transgenic mice. Summary/Conclusion: High MYC expression renders B lymphoma cells sensitive to therapy with common soluble antioxidants and indicates that this strategy might be useful—alone or in combination with lower doses of standard chemotherapy—in patients with MYC-driven lymphomas such as the diffuse large B cell variant.