Uptake of glucose analogues by colonic tumour cells during growth and after treatment with hydroxyurea

Factors influencing [F-18] 2-fluoro-2-deoxy-D-glucose (F-18 FDG) uptake in melanoma cells: the role of proliferation rate, viability, glucose transporter expression and hexokinase activity

Using human (SK-MEL 23, SK-MEL 24 and G361) and murine (B16) melanoma cell lines, the coregulatory potential of the uptake of the positron emission tomography (PET) tracer, [Fluorine-18] 2-fluoro-2-deoxy-D-glucose (F-18 FDG) has been investigated in relationship to tumor characteristics. Comparative studies among the four melanoma cell lines demonstrated that the lowest FDG uptake in SK-MEL 24 corresponded strongly to the data for DT (population doubling time) and MTT (tetrazolium salt) cell viability as well as hexokinase (HK) activity, but was not related to the glucose transporter 1 (GLUT 1) expression level. Furthermore, the FDG uptake in each melanoma cell line measured by cell cycle kinetics was significantly positively correlated to both the proliferation index (PI=S/G2M phase fractions) and the cell viability, though with one exception relating to the PI of the lowest FDG uptake cell line, SK-MEL 24. No positive correlation was found between the expression of GLUT 1 and FDG uptake in any individual cell line. However, the HK activities in SK-MEL 23 and 24 showed considerable positive relationships with FDG uptake. Our present study suggests that both the proliferation rate and the cell viability of melanoma cells may be key factors for FDG uptake and that HK activity, rather than GLUT 1 expression, seems to be a major factor.

Gleevec (STI571) influences metabolic enzyme activities and glucose carbon flow toward nucleic acid and fatty acid synthesis in myeloid tumor cells

Chronic myeloid leukemia cells contain a constitutively active Bcr-Abl tyrosine kinase, the target protein of Gleevec (STI571) phenylaminopyrimidine class protein kinase inhibitor. Here we provide evidence for metabolic phenotypic changes in cultured K562 human myeloid blast cells after treatment with increasing doses of STI571 using [1,2-13C2]glucose as the single tracer and biological mass spectrometry. In response to 0.68 and 6.8 microm STI571, proliferation of Bcr-Abl-positive K562 cells showed a 57% and 74% decrease, respectively, whereas glucose label incorporation into RNA decreased by 13.4% and 30.1%, respectively, through direct glucose oxidation, as indicated by the decrease in the m1/Sigma(m)n ratio in RNA. Based on the in vitro proliferation data, the IC50 of STI571 in K562 cultures is 0.56 microm. The decrease in 13C label incorporation into RNA ribose was accompanied by a significant fall in hexokinase and glucose-6-phosphate 1-dehydrogenase activities. The activity of transketolase, the enzyme responsible for nonoxidative ribose synthesis in the pentose cycle, was less affected, and there was a relative increase in glucose carbon incorporation into RNA through nonoxidative synthesis as indicated by the increase in the m2/Sigma(m)n ratio in RNA. The restricted use of glucose carbons for de novo nucleic acid and fatty acid synthesis by altering metabolic enzyme activities and pathway carbon flux of the pentose cycle constitutes the underlying mechanism by which STI571 inhibits leukemia cell glucose substrate utilization and growth. The administration of specific hexokinase/glucose-6-phosphate 1-dehydrogenase inhibitor anti-metabolite substrates or competitive enzyme inhibitor compounds, alone or in combination, should be explored for the treatment of STI571-resistant advanced leukemias as well as that of Bcr-Abl-negative human malignancies.