CD28 Regulates Metabolism In Multiple Myeloma For Cell Survival and Proliferation

Multiple myeloma is an incurable hematological malignancy of transformed plasma cells. Many cellular interactions and soluble factors have been demonstrated to play a role in myeloma pathogenesis; however, novel targets to enhance therapeutic intervention are needed. We have demonstrated that CD28 signaling in myeloma cells supports their survival during chemotherapeutic challenge in vitro and in vivo. However, the cellular mechanisms by which CD28 confers this survival advantage to myeloma cells are not completely understood.

CD28 is best characterized as the canonical T cell co-stimulatory molecule. During T cell activation, CD28 signaling induces glycolysis, a metabolic program required for T cell proliferation and functional maturation. In the absence of glycolysis, T cells utilize fatty acid oxidation for energy production through the mitochondria. However, the way in which CD28 regulates metabolism in multiple myeloma is not well understood. Here we present evidence that CD28 signaling induces glut1 expression, and that poisoning the glycolytic pathway inhibits proliferation and survival of myeloma cells.

AMPK, an energy sensitive kinase known to regulate metabolism by driving fatty acid oxidation, is normally activated when cellular energy levels are low. Interestingly, poisoning glycolysis with a glucose analogue that cannot be processed (2DG) leads to AMPK inhibition in myeloma cells. Furthermore, pharmacological activation of AMPK by AICAR, an AMP analogue, is not sufficient to rescue myeloma cell proliferation from glycolytic inhibition and in fact increases cell death (p<.01 from no treatment, p<.05 from 2DG). This evidence suggests that multiple myeloma cells are absolutely dependent upon CD28-mediated glycolysis for proliferation and survival, and that myeloma cells cannot utilize fatty acid oxidation as a subsidiary metabolic pathway for proliferation in the absence of glycolysis. This understanding will allow us to target metabolism in multiple myeloma as a novel therapeutic strategy through pharmacological targeting of the CD28 pathway. This approach can be quickly translated into the clinic, as there are FDA approved drugs which activate AMPK (Metformin) and block CD28 signaling (Abatacept).