Enhanced Fructose Utilization Mediated by SLC2A5 Is a Unique Metabolic Feature of Acute Myeloid Leukemia with Therapeutic Potential

Abstract

Rapidly proliferating leukemic progenitor cells consume substantial glucose, which may lead to glucose insufficiency in bone marrow. We show that acute myeloid leukemia (AML) cells are prone to fructose utilization with an upregulated fructose transporter GLUT5, which compensates for glucose deficiency. Notably, AML patients with upregulated transcription of the GLUT5-encoding gene SLC2A5 or increased fructose utilization have poor outcomes. Pharmacological blockage of fructose uptake ameliorates leukemic phenotypes and potentiates the cytotoxicity of the antileukemic agent, Ara-C. In conclusion, this study highlights enhanced fructose utilization as a metabolic feature of AML and a potential therapeutic target.

Keywords: GLUT5; SLC2A5; acute myeloid leukemia; fructose utilization.

Figure 1. Fructose utilization by AML cells

(A) ¹³C-fructose uptake by AML cells and normal monocytes. (B) Fructose-induced proliferation of AML cells and normal monocytes under the conditions of different glucose levels. Cells were grown in the media for 72 hours. For each glucose condition, p values were obtained by comparison with the cell proliferation in 0 mM fructose. (C) Western blot showing GLUT5 knockdown in K562 cells by siRNA targeting SLC2A5. (D) Uptake of ¹³C-fructose by K562 cells with or without SLC2A5 inhibition. (E) Fructose-induced proliferation of K562 cells with or without SLC2A5 inhibition. (F) GLUT5 expression between AML cells and normal monocytes. Relative GLUT5 expression was computed by dividing the value of GLUT5 signal intensity by the value of actin signal intensity. Normalized GLUT5 was obtained by normalizing each relative GLUT5 expression to the mean of relative GLUT5 expression of 4 cases of normal monocytes. (G) The expression of GLTU5-encoding gene SLC2A5 between normal hematopoietic cells of healthy controls and AML blast cells of patients. The data were obtained from a public microarray database. (H) Serum fructose concentration comparison between healthy controls and AML patients. (I) Serum fructose concentration of paired samples from 31 AML patients at diagnosis and at CR. Error bars represent mean ± SEM. * p < 0.05, ** p < 0.01 (Student’s t test). See also Figure S1 and Tables S1 and S2.

Figure 2. Prognostic value of SLC2A5 expression levels and fructose utilization rates in AML patients

(A) (Left) Meta-analysis of Cox hazard ratio of SLC2A5 expression levels in 5 data sets containing patients with intermediate-risk AML. Solid horizontal lines denoted 95% confidence intervals; boxes denoted the relative influence of each set over the results; diamond indicates the summary 95% confidence interval. The continuous SLC2A5 value was used in the analysis. (Right) Kaplan-Meier survival curves of 5 cohorts of patients in the left meta-analysis. Patients were separated into above-median (deep pink line) and below-median (deep sky blue line) of SLC2A5 expression. (B) AML patients were evenly divided into 3 groups according to the serum levels of fructose. (C) The complete remission and no remission rates of 3 AML groups in (B). See also Figure S2.

Figure 3. Enhanced fructose utilization mediated by SLC2A5 exacerbates the leukemic phenotypes of AML cells

(A) Measurement of the expression of SLC2A5/GLUT5 in U937 cells transfected with the control MigR1 retrovirus (U937-MigR1) or MigR1-SLC2A5 retrovirus (U937-SLC2A5) by Q-PCR and western blot. (B) Uptake of ¹³C-labeled fructose by U937-MigR1 and U937-SLC2A5 cells. (C–E) Proliferation of U937-MigR1 and U937-SLC2A5 cells in complete media containing 6 mM fructose without glucose or with distinct levels of glucose. (F–H) Colony formation of U937-MigR1 and U937-SLC2A5 cells in soft agar fed with complete media containing 6 mM fructose without glucose or with distinct levels of glucose. Cells were seeded at a density of 3,000/well (F) or 2,000/well (G) or 1,000/well (H). Colonies were assayed at day 23 (F) or day 16 (G and H). (I) Migration of U937-MigR1 and U937-SLC2A5 cells fed with complete medium containing 6 mM fructose without glucose or with different levels of glucose. (J) Invasion of U937-MigR1 and U937-SLC2A5 cells fed with complete medium containing 6 mM fructose without glucose or with different levels of glucose. Error bars represent mean ± SEM. * p < 0.05, ** p < 0.01 (Student’s t test). See also Figures S3 and S4 and Table S3.

Figure 4. Enhanced fructose utilization mediated by SLC2A5 activates glycolytic flux

(A) Secretion of ¹³C-labeled pyruvate derived from ¹³C-fructose tracer by AML control cells and AML cells with ectopic SLC2A5. (B) Secretion of ¹³C-labeled lactate derived from ¹³C-fructose tracer by AML control cells and AML cells with ectopic SLC2A5. (C) Secretion of ¹³C-labeled alanine derived from ¹³C-fructose tracer by AML control cells and AML cells with ectopic SLC2A5. (D) Proposed metabolic scheme depicting increased glycolytic flux activated by enhanced fructose utilization mediated by SLC2A5. Error bars represent mean ± SEM. * p < 0.05, ** p < 0.01 (Student’s t test).

Figure 5. Response of AML cells to pharmacological blockage of fructose utilization

(A) Suppressed proliferation of U937-SLC2A5 cells treated with the fructose analogue 2,5-AM. Two carbon source conditions, 6 mM fructose and 6 mM fructose plus 0.75 mM glucose, were tested. P values were obtained by comparison with the proliferation of U937-SLC2A5 cells in 0 mM 2,5-AM. (B–C) The colony growth of U937-SLC2A5 cells in soft agar under the condition of 6 mM fructose (B) or 6 mM fructose plus 0.75 mM glucose (C) with or without 2,5-AM treatment. (D) Migration assay of U937-SLC2A5 cells with or without 2,5-AM treatment in medium containing 6 mM fructose or 6 mM fructose plus 0.75 mM glucose. (E) Proliferation of AML cells treated with 2,5-AM. Three carbon resource conditions were tested. (F–G) The synergistic effect between 2,5-AM and Ara-C in AML cells cultured in complete medium containing 6 mM fructose (F) or 6 mM fructose plus 0.75 mM glucose (G). Error bars represent mean ± SEM. * p < 0.05, ** p < 0.01 (Student’s t test). See also Figure S5 and Table S4.

Figure 6. Enhanced fructose utilization and the therapeutic potential of pharmacological blockage of this metabolic pathway in AML mice

(A) SLC2A5 expression in bone marrow cells between normal controls (n = 6) and AML mice (n = 6). (B) Serum fructose concentration measurements for normal controls (n = 6), AML mice treated with vehicle (n = 6), AML mice treated with 2,5-AM (n = 6) and AML mice treated with 2,5-AM and Ara-C (n = 6). (C) The percentage of BM blast cells in normal controls (n = 6), AML mice treated with vehicle (n = 6), AML mice treated with 2,5-AM (n = 6), AML mice treated with Ara-C (n = 6) and AML mice treated with 2,5-AM and Ara-C (n = 6). (D) The percentage of PB blast cells in normal controls (n = 6), AML mice treated with vehicle (n = 6), AML mice treated with 2,5-AM (n = 6), AML mice treated with Ara-C (n = 6) and AML mice treated with 2,5-AM and Ara-C (n = 6). (E) Spleen weight measurements for normal controls (n = 6), AML mice treated with vehicle (n = 6) and AML mice treated with 2,5-AM (n = 6). (F) WBC counts in PB for normal controls (n = 6), AML mice treated with vehicle (n = 8), AML mice treated with 2,5-AM (n = 8), AML mice treated with Ara-C (n = 6) and AML mice treated with 2,5-AM and Ara-C (n = 6). (G) RBC counts in PB for normal controls (n = 6), AML mice treated with vehicle (n = 8), AML mice treated with 2,5-AM (n = 8), AML mice treated with Ara-C (n = 6) and AML mice treated with 2,5-AM and Ara-C (n = 6). (H) HGB measurements in PB for normal controls (n = 6), AML mice treated with vehicle (n = 8), AML mice treated with 2,5-AM (n = 8), AML mice treated with Ara-C (n = 6) and AML mice treated with 2,5-AM and Ara-C (n = 6). (I) PLT counts in PB for normal controls (n = 6), AML mice treated with vehicle (n = 8), AML mice treated with 2,5-AM (n = 8), AML mice treated with Ara-C (n = 6) and AML mice treated with 2,5-AM and Ara-C (n = 6). (J) Overall survival curves of AML mice treated with vehicle (n = 9), AML mice treated with 2,5-AM (n = 10), AML mice treated with Ara-C (n = 9) and AML mice treated with 2,5-AM and Ara-C (n = 10). Abbreviation: BM, bone marrow; PB, peripheral blood; WBC, white blood cell; RBC, red blood cell; HGB, hemoglobin; PLT, platelet; HR, hazard ratio. Error bars represent mean ± SEM. * p < 0.05, ** p < 0.01, *** p < 0.001 (Student’s t test). See also Figure S6 and Table S5.