The reverse Warburg effect and 18F-FDG uptake in non-small cell lung cancer A549 in mice: a pilot study

The purpose of this study was to observe the effect of fasting and feeding on (18)F-FDG uptake in a mouse model of human non-small cell lung cancer.

In in vivo studies, (18)F-FDG small-animal PET scans were acquired in 5 mice bearing non-small cell lung cancer A549 xenografts on each flank with continuous feeding and after overnight fasting to observe the changes in intratumoral distribution of (18)F-FDG and tumor (18)F-FDG standardized uptake value (SUV). In ex vivo studies, intratumoral spatial (18)F-FDG distribution assessed by autoradiography was compared with the tumor microenvironment (including hypoxia by pimonidazole and stroma by hematoxylin and eosin stain). Five overnight-fasted mice and 5 fed mice with A549 tumors were observed.

Small-animal PET scans were obtained in fed animals on day 1 and in the same animals after overnight fasting; the lapse was approximately 14 h. Blood glucose concentration after overnight fasting was not different from fed mice (P = 0.42), but body weight loss was significant after overnight fasting (P = 0.001). Intratumoral distribution of (18)F-FDG was highly heterogeneous in all tumors examined, and change in spatial intratumoral distribution of (18)F-FDG between 2 sets of PET images from the same mouse was remarkably different in all mice. Tumor (18)F-FDG mean SUV and maximum SUV were not significantly different between fed and fasted animals (all P > 0.05, n = 10). Only tumor mean SUV weakly correlated with blood glucose concentration (R(2) = 0.17, P = 0.03). In ex vivo studies, in fasted mice, there was spatial colocalization between high levels of (18)F-FDG uptake and pimonidazole-binding hypoxic cancer cells; in contrast, pimonidazole-negative normoxic cancer cells and noncancerous stroma were associated with low (18)F-FDG uptake. However, high (18)F-FDG uptake was frequently observed in noncancerous stroma of tumors but rarely in viable cancer cells of the tumors in fed animals.

Host dietary status may play a key role in intratumoral distribution of (18)F-FDG. In the fed animals, (18)F-FDG accumulated predominantly in noncancerous stroma in the tumors, that is, reverse Warburg effect. In contrast, in fasted status, (18)F-FDG uptake was found in hypoxic cancer cells component (Pasteur effect). Our findings may provide a better understanding of competing cancer glucose metabolism hypotheses: the Warburg effect, reverse Warburg effect, and Pasteur effect.