Gluathione is critical for the growth of lymphoma-initiating cells and lymphomagenesis in vivo

Many patients with lymphoid tumors do not respond to existing therapies or relapse quickly after initial remission. A minor fraction of tumor cells, the tumor-initiating cells (TICs), has self-renewal capacity, is particularly resistant to cancer therapies, and likely accounts for tumor relapse. Targeting critical pathways that are specific to TIC function may therefore improve cancer treatment. As TICs are the only tumor cells able to grow in soft gels, we are investigating the mechanisms underlying the growth in soft gels. The balance between reactive oxygen species (ROS) and antioxidants levels regulates numerous cellular processes, including cell signaling, proliferation and death. Here we show that culture of lymphoid cells in soft-agar hydrogels induces ROS production and kills all non-tumor lymphoid cells but allows the survival and proliferation of a minor fraction of lymphoma cells. Treatment with the antioxidant N-acetylcysteine inhibits lethality and even enables the growth of primary non-tumor lymphoid cells in soft-agar. A fraction of lymphoma cells overcomes ROS-induced lethality by increasing the production of the antioxidant glutathione (GSH), whereas non-tumor cells fail to induce this response. Pharmacological inhibition of GCL, the limiting enzyme in GSH biosynthesis, or knockdown of GCLC, the GCL catalytic subunit, dropped GSH production in lymphoma cells, sharply decreased their viability and proliferation in softagar, and inhibited their growth in immunodeficient mice. B-cells from ¿MYC mice, a mouse model of B-cell lymphoma, show increased ROS and GSH levels relative to Bcells from control mice. Importantly, pharmacological GCL inhibition impaired lymphoma growth in female ¿MYC mice, increasing their tumor-free survival. We also found higher ROS and GSH levels in tumor B-cells from B-cell lymphoma and leukemia patients than in non-tumor T-cells from the same subject or in B-cells from healthy donors, strongly suggesting that GCL inhibition cou