Molecular Targeting and Inactivation of Glutaminase and CDK4/6 in Mantle Cell Lymphoma

Abstract

Mantle Cell Lymphoma (MCL) is an aggressive B‐cell non‐Hodgkin's lymphoma (NHL) subtype that accounts for 7% of all NHL cases. Upon relapse, standard salvage regimens are ineffective and the disease is considered clinically incurable. Hence, novel therapeutic strategies that effectively target deregulated pathways that contribute to MCL pathogenesis are warranted. The hallmark of MCL is a chromosomal translocation t (11:14) event that results in the constitutive expression of the G1‐phase cell cycle regulatory oncogene, cyclin D1 (CCND1), resulting in uncontrolled cell proliferation. Cyclin D1 binds to and activates cyclin dependent kinases 4 and 6 (CDK4/6) and the complex phosphorylates the tumor suppressor gene product retinoblastoma (RB), a negative regulator of the cell cycle. MCL patients whose tumors express cyclin D1 have reduced survival. Uncontrolled cell proliferation results in metabolic alterations of tumor cells to support the energy and biosynthetic needs of unregulated cell growth. Adaptations by malignant cells involve changes in the expression of genes involved in metabolism. This results in both increased glucose and glutamine uptake and metabolism in tumor cells. Recent studies in metabolically reprogrammed tumor cells have shown increased levels of glutaminase, the enzyme involved in the first steps of glutamine metabolism. We hypothesize that molecular targeting of proliferation and glutamine metabolism will induce synergistic tumor cell death. In vitro studies with a MCL cell line were completed using Palbociclib, a potent and selective inhibitor of CDK4/6 which was recently approved by the FDA for the treatment of HR+/HER2− metastatic breast cancer. MTT assays were also carried out using BPTES which inhibits enzymatic activity by binding to the glutaminase tetramer, stabilizing it in an inactive conformation. Cell viability assays show that treatment of MCL cells with Palbociclib resulted in a dose dependent reduction in cell viability. Treatment with 5μM BPTES alone resulted in a slight reduction in cell viability. However, treatment with 5μM BPTES sensitizes cells to treatment with different concentrations of Palbociclib. Studies are ongoing using different concentrations of BPTES with a series of concentrations of Palbociclib to determine the synergistic effects of the combination treatment. As studies continue, quantification of synergy will be relayed using the Chou‐Talalay method with computerized simulation. Preliminary cell cycle assays using flow cytometry show that treatment of cells with Palbociclib induce G1‐phase cell cycle arrest. Establishing a treatment regimen that achieves a synergistic therapeutic effect may allow for integration of a novel molecular targeted approach to treating MCL.Support or Funding InformationButler University Holcomb research award, AFPE Gateway to Research awardThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.