Tumours ferment glucose to lactate even in the presence of oxygen (aerobic glycolysis; Warburg effect). The pentose phosphate pathway (PPP) allows glucose conversion to ribose for nucleic acid synthesis and glucose degradation to lactate. The nonoxidative part of the PPP is controlled by transketolase enzyme reactions. We have detected upregulation of a mutated transketolase transcript (TKTL1) in human malignancies, whereas transketolase (TKT) and transketolase-like-2 (TKTL2) transcripts were not upregulated. Strong TKTL1 protein expression was correlated to invasive colon and urothelial tumours and to poor patients outcome. TKTL1 encodes a transketolase with unusual enzymatic properties, which are likely to be caused by the internal deletion of conserved residues. We propose that TKTL1 upregulation in tumours leads to enhanced, oxygen-independent glucose usage and a lactatebased matrix degradation. As inhibition of transketolase enzyme reactions suppresses tumour growth and metastasis, TKTL1 could be the relevant target for novel anti-transketolase cancer therapies. We suggest an individualised cancer therapy based on the determination of metabolic changes in tumours that might enable the targeted inhibition of invasion and metastasis.

Targeted therapies have demonstrated clinical benefit with limited impact on long-term disease specific survival in the treatment of renal cell cancer (RCC). New opportunities for the treatment of tumors that are resistant or have relapsed, are needed. Increased anaerobic glucose fermentation to lactate (aerobic glycolysis), leading to oxygen-and mitochondria-independent ATP generation is a hallmark of aggressive cancer growth. This metabolic shift results in increased lactate production via cycling through the pentose phosphate pathway (PPP), and plays an important role in tumor immune escape, progression and resistance to immune-, radiation-and chemo-therapy. This study explored the activity and impact of the oxidative and nonoxidative branches of the PPP on RCC to evaluate new therapeutic options. Activity was determined in the oxidative branch by glucose-6-phosphate-dehydrogenase (G6PD) activity, and in the nonoxidative branch by the total transketolase activity and the specific expression of the transketolaselike-1 (TKTL1) protein. Transketolase and G6PD activity were intensely elevated in tumor tissues. Transketolase, but not G6PD activity, was more elevated in metastasizing tumors and TKTL1 protein was significantly overexpressed in progressing tumors (p 5 0.03). Lethal tumors, where surrogate parameters such as grading and staging had failed to predict progression, showed intensive TKTL1 protein expression. RCC was found to have activated oxidative and nonoxidative glucose metabolism through the PPP, displaying a bioenergetic shift toward nonoxidative glucose fermentation in progressing tumors. The coexistence of cancer cells with differentially regulated energy supplies provides new insights in carcinogenesis and novel anticancer targets. ' 2008 Wiley-Liss, Inc.Key words: renal cell carcinoma; transketolase-like-1 enzyme; glucose-6-phosphate-dehydrogenase; Warburg effect; pentose phosphate pathway Worldwide, an estimated 208,000 new cases and 102,000 deaths result from kidney cancer each year. Metastatic spread is present in 30% of patients at the initial diagnosis, and will develop in 20-40% of patients with initially localized disease who have nephrectomy with curative-intent. 1,2 In summary, about 50% of patients with kidney cancer will develop metastatic disease, which has a 5-year survival of less than 10%. Treatment options in metastasized renal cell cancer (RCC) are limited. Conventional radiation and chemotherapy are of no significant benefit, and immunotherapy provides only a moderate response rate with curative results in only 5% of patients. 3 New antiangiogenic therapies, such as inhibitors of the VEGF receptor tyrosine kinase, seem promising, since they extend progression free survival time in advanced renal tumors. 4,5 Positron emission tomography (PET) studies have unequivocally identified increased glucose uptake as a hallmark of metastatic cancer, demonstrating altered glucose metabolism in progressing tumors and in therapy response. 6,7 Tumors are characterized by specific metabolic al...