High Glucose Activates AKT Signaling and Induces Upregulation of Genes Encoding Glycolytic Enzymes Glut-1 and HK-2 in Acute Lymphocytic Leukemia.

Background: Hyperglycemia represents a common side effect of steroid therapy and is not uncommon during treatment of patients with acute lymphocytic leukemia (ALL). Our recent retrospective study in 278 adult patients with ALL demonstrated that hyperglycemia during induction chemotherapy occurred in up to 37% of patients and was associated with a shorter median complete remission duration and a shorter median survival (Cancer 2004 Mar 15;100(6):1179–85). The serine/threonine AKT, a major downstream PI3K target, promotes continued cell growth and metabolism by increasing glucose uptake, stimulating glycolysis and ATP production. Recent data in transgenic models demonstrated that AKT activation resulted in transcriptional upregulation of enzymes essential for glycolysis including hexokinase (HK) and Glut-1 (Nature Med., 2004, 10:594). The purpose of this study was to determine whether high AKT activity in leukemic blasts in the setting of hyperglycemia promotes survival and chemoresistance of leukemic cells by stimulation of glycolysis.

Methods and Results: A 24-hour culture of REH cells in serum-free medium supplemented with 14mM glucose resulted in induction of AKT phosphorylation (by Western blot analysis) and increase in mRNA levels of Glut-1 and HK-2 (by quantitative TaqMan PCR). PI3K inhibitor LY294002 (15 μM) prevented AKT phosphorylation and decreased mRNA expression of Glut-1 and HK-2 in high-glucose conditions and enhanced doxorubicin- and dexamethasone-induced killing. We next investigated expression of AKT 1, Glut1, and HK2 mRNA in bone marrow samples from 14 adult patients with ALL (9 pre-B-, 2 B-, 3 pre-T-ALL). The results demonstrated elevated (> 2-fold compared with normal bone marrow or peripheral blood) levels of AKT in 7/14 patients, 6 of those showed increased levels of Glut1 and 5 of HK2. In addition, in samples from 2 patients with low baseline AKT expression high HK-2 mRNA levels were observed.

Conclusions: High expression of AKT, glucose transporter Glut-1 and the glycolytic enzyme HK-2 is prevalent in primary ALL blast cells. Our results suggest that high glucose further stimulates AKT signaling in ALL blast cells resulting in upregulation of glucose transporter Glut-1 and of the glycolytic enzyme HK-2. This effect was abrogated by inhibition of PI3K/AKT signaling, resulting in chemosensitization. These data provide rationale for use of PI3K/AKT inhibitors in the therapy of ALL. The hypothesis that tight blood glucose control improves outcome in ALL patients is currently being tested in a Phase III clinical trial at M.D. Anderson Cancer Center.