64 Cu-diacetyl-bis(N 4 -methylthiosemicarbazonate), 64 Cu-ATSM, continues to be investigated clinically as a PET agent both for delineation of tumor hypoxia and as an effective indicator of patient prognosis, but there are still aspects of the mechanism of action that are not fully understood. Methods: The retention of radioactivity in tumors after administration of 64 Cu-ATSM in vivo is substantially higher for tumors with a significant hypoxic fraction. This hypoxia-dependent retention is believed to involve the reduction of Cu-ATSM, followed by the loss of copper to cellular copper processing. To shed light on a possible role of copper metabolism in hypoxia targeting, we have compared 64 Cu retention in vitro and in vivo in CaNT and EMT6 cells or cancers after the administration of 64 Cu-ATSM or 64 Cu-acetate. Results: In vivo in mice bearing CaNT or EMT6 tumors, biodistributions and dynamic PET data are broadly similar for 64 Cu-ATSM and 64 Cu-acetate. Copper retention in tumors at 15 min is higher after injection of 64 Cu-acetate than 64 Cu-ATSM, but similar values result at 2 and 16 h for both. Colocalization with hypoxia as measured by EF5 immunohistochemistry is evident for both at 16 h after administration but not at 15 min or 2 h. Interestingly, at 2 h tumor retention for 64 Cuacetate and 64 Cu-ATSM, although not colocalizing with hypoxia, is reduced by similar amounts by increased tumor oxygenation due to inhalation of increased O 2 . In vitro, substantially less uptake is observed for 64 Cu-acetate, although this uptake had some hypoxia selectivity. Although 64 Cu-ATSM is stable in mouse serum alone, there is rapid disappearance of intact complex from the blood in vivo and comparable amounts of serum bound activity for both 64 Cu-ATSM and 64 Cu-acetate. Conclusion: That in vivo, in the EMT6 and CaNT tumors studied, the distribution of radiocopper from 64 Cu-ATSM in tumors essentially mirrors that of 64 Cu-acetate suggests that copper metabolism may also play a role in the mechanism of selectivity of Cu-ATSM.

Sugar alcohols are used in food products, yet their metabolic effects in humans are poorly known. We examined plasma glucose, insulin, and C-peptide responses and changes in carbohydrate and lipid oxidation after the ingestion of 25 g lactitol, xylitol, or glucose. Eight healthy, nonobese men were studied after an overnight fast. After the ingestion of lactitol or xylitol, the rise in plasma glucose, insulin, and C-peptide concentrations was less than after the ingestion of glucose (P < 0.02), with no difference between the two polyols. With the glycemic index of glucose as 100, the indexes of xylitol and lactitol were 7 and -1, respectively. A reactive hypoglycemia was observed 3 h after glucose ingestion, but not after the ingestion of sugar alcohols. There were no significant changes in the carbohydrate or lipid oxidation as determined by indirect calorimetry after the ingestion of sugar alcohols. After glucose ingestion, the rise in carbohydrate oxidation was nearly significant (P = 0.07). In conclusion, lactitol and xylitol cause smaller changes than does glucose in plasma glucose and insulin concentrations and thermogenic response. A small hormonal response and the lack of a thermogenic effect may be beneficial when these sugar alcohols are used in food products. The small glucose and insulin responses also suggest that lactitol and xylitol are suitable components of the diet for diabetic patients.

BackgroundInhibitors of the phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) pathway are currently in clinical trials. In addition to antiproliferative and proapoptotic effects, these agents also diminish tumor hypoxia. Since hypoxia is a major cause of resistance to radiotherapy, we sought to understand how it is regulated by PI3K/mTOR inhibition.MethodsWhole cell, mitochondrial, coupled and uncoupled oxygen consumption were measured in cancer cells after inhibition of PI3K (Class I) and mTOR by pharmacological means or by RNAi. Mitochondrial composition was assessed by immunoblotting. Hypoxia was measured in spheroids, in tumor xenografts and predicted with mathematical modeling.ResultsInhibition of PI3K and mTOR reduced oxygen consumption by cancer cell lines is predominantly due to reduction of mitochondrial respiration coupled to ATP production. Hypoxia in tumor spheroids was reduced, but returned after removal of the drug. Murine tumors had increased oxygenation even in the absence of average perfusion changes or tumor necrosis.ConclusionsTargeting the PI3K/mTOR pathway substantially reduces mitochondrial oxygen consumption thereby reducing tumor hypoxia. These alterations in tumor hypoxia should be considered in the design of clinical trials using PI3K/mTOR inhibitors, particularly in conjunction with radiotherapy.