Quantification of longitudinal tissue pO2 gradients in window chamber tumours: impact on tumour hypoxia

We previously reported that the arteriolar input in window chamber tumours is limited in number and is constrained to enter the tumour from one surface, and that the pO2 of tumour arterioles is lower than in comparable arterioles of normal tissues. On average, the vascular pO2 in vessels of the upper surface of these tumours is lower than the pO2 of vessels on the fascial side, suggesting that there may be steep vascular longitudinal gradients (defined as the decline in vascular pO2 along the afferent path of blood flow) that contribute to vascular hypoxia on the upper surface of the tumours. However, we have not previously measured tissue pO2 on both surfaces of these chambers in the same tumour. In this report, we investigated the hypothesis that the anatomical constraint of arteriolar supply from one side of the tumour results in longitudinal gradients in pO2 sufficient in magnitude to create vascular hypoxia in tumours grown in dorsal flap window chambers. Fischer-344 rats had dorsal flap window chambers implanted in the skin fold with simultaneous transplantation of the R3230AC tumour. Tumours were studied at 9–11 days after transplantation, at a diameter of 3–4 mm; the tissue thickness was 200 μm. For magnetic resonance microscopic imaging, gadolinium DTPA bovine serum albumin (BSA-DTPA-Gd) complex was injected i.v., followed by fixation in 10% formalin and removal from the animal. The sample was imaged at 9.4 T, yielding voxel sizes of 40 μm. Intravital microscopy was used to visualize the position and number of arterioles entering window chamber tumour preparations. Phosphorescence life time imaging (PLI) was used to measure vascular pO2. Blue and green light excitations of the upper and lower surfaces of window chambers were made (penetration depth of light ~50 vs >200 μm respectively). Arteriolar input into window chamber tumours was limited to 1 or 2 vessels, and appeared to be constrained to the fascial surface upon which the tumour grows. PLI of the tumour surface indicated greater hypoxia with blue compared with green light excitation (P < 0.03 for 10th and 25th percentiles and for per cent pixels < 10 mmHg). In contrast, illumination of the fascial surface with blue light indicated less hypoxia compared with illumination of the tumour surface (P < 0.05 for 10th and 25th percentiles and for per cent pixels < 10 mmHg). There was no significant difference in pO2 distributions for blue and green light excitation from the fascial surface nor for green light excitation when viewed from either surface. The PLI data demonstrates that the upper surface of the tumour is more hypoxic because blue light excitation yields lower pO2 values than green light excitation. This is further verified in the subset of chambers in which blue light excitation of the fascial surface showed higher pO2 distributions compared with the tumour surface. These results suggest that there are steep longitudinal gradients in vascular pO2 in this tumour model that are created by the limited number and orientation of the arterioles. This contributes to tumour hypoxia. Arteriolar supply is often limited in other tumours as well, suggesting that this may represent another cause for tumour hypoxia. This report is the first direct demonstration that longitudinal oxygen gradients actually lead to hypoxia in tumours. © 1999 Cancer Research Campaig

Differential utilization of ketone bodies by neurons and glioma cell lines: a rationale for ketogenic diet as experimental glioma therapy

Background: Even in the presence of oxygen, malignant cells often highly depend on glycolysis for energy generation, a phenomenon known as the Warburg effect. One strategy targeting this metabolic phenotype is glucose restriction by administration of a high-fat, low-carbohydrate (ketogenic) diet. Under these conditions, ketone bodies are generated serving as an important energy source at least for non-transformed cells. Methods: To investigate whether a ketogenic diet might selectively impair energy metabolism in tumor cells, we characterized in vitro effects of the principle ketone body 3-hydroxybutyrate in rat hippocampal neurons and five glioma cell lines. In vivo, a non-calorie-restricted ketogenic diet was examined in an orthotopic xenograft glioma mouse model. Results: The ketone body metabolizing enzymes 3-hydroxybutyrate dehydrogenase 1 and 2 (BDH1 and 2), 3-oxoacid-CoA transferase 1 (OXCT1) and acetyl-CoA acetyltransferase 1 (ACAT1) were expressed at the mRNA and protein level in all glioma cell lines. However, no activation of the hypoxia-inducible factor-1alpha (HIF-1alpha) pathway was observed in glioma cells, consistent with the absence of substantial 3-hydroxybutyrate metabolism and subsequent accumulation of succinate. Further, 3-hydroxybutyrate rescued hippocampal neurons from glucose withdrawal-induced cell death but did not protect glioma cell lines. In hypoxia, mRNA expression of OXCT1, ACAT1, BDH1 and 2 was downregulated. In vivo, the ketogenic diet led to a robust increase of blood 3-hydroxybutyrate, but did not alter blood glucose levels or improve survival. Conclusion: In summary, glioma cells are incapable of compensating for glucose restriction by metabolizing ketone bodies in vitro, suggesting a potential disadvantage of tumor cells compared to normal cells under a carbohydrate-restricted ketogenic diet. Further investigations are necessary to identify co-treatment modalities, e.g. glycolysis inhibitors or antiangiogenic agents that efficiently target non-oxidative pathways

Live cell imaging reveals distinct roles in cell cycle regulation for Nek2A and Nek2B.

Two splice variants of Nek2 kinase, a member of the NIMA-related family, have been identified as Nek2A and Nek2B. Nek2A regulates centrosome disjunction, spindle formation checkpoint signaling, and faithful chromosome segregation. A specific role for Nek2B has not yet been identified. Here, we have examined the distinct roles of Nek2A and Nek2B using timelapse video microscopy to follow the fate of cells progressing through the cell cycle in the absence of either Nek2A or Nek2B. We show that the down-regulation of Nek2B leads to a mitotic delay in the majority of cells. Upon exiting mitosis, cells exhibit mitotic defects such as the formation of multinucleated cells. Such phenotypes are not observed in cells that exit mitosis in the absence of Nek2A. These observations suggest that Nek2B may be required for the execution of mitotic exit

HIV protease inhibitors block Akt signaling and radiosensitize tumor cells both in vitro and in vivo.

In tumor cells with mutations in epidermal growth factor receptor (SQ20B), H-Ras (T24), or K-Ras (MIAPACA2 and A549), the inhibition of Akt phosphorylation increases radiation sensitivity in clonogenic assays, suggesting that Akt is a potential molecular target when combined with therapeutic radiation. Insulin resistance and diabetes are recognized side effects of HIV protease inhibitors (HPIs), suggesting that these agents may inhibit Akt signaling. Because activation of the phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway is common in human cancers, we hypothesized that HPIs can inhibit Akt activity resulting in increased tumor cell sensitivity to ionizing radiation-induced cell death. Five first-generation HPIs were subsequently tested and three of the five (amprenavir, nelfinavir, and saquinavir but not ritonavir or indinavir) inhibited Akt phosphorylation at Ser473 at serum concentrations routinely achieved in HIV patients. In both tumor cell colony formation assays and tumor regrowth delay experiments, combinations of drug and radiation exerted synergistic effects compared with either modality alone. In addition, in vivo, doses of amprenavir or nelfinavir comparable with the therapeutic levels achieved in HIV patients were sufficient to down-regulate phosphorylation of Akt in SQ20B and T24 xenografts. Finally, overexpression of active PI3K in cells without activation of Akt resulted in radiation resistance that could be inhibited with HPIs. Because there is abundant safety data on HPIs accumulated in thousands of HIV patients over the last 5 years, these agents are excellent candidates to be tested as radiation sensitizers in clinical trials

C-Raf-1 protein kinase is not essential for Ras transformation of mouse embryo fibroblasts.

Transfection of primary cells with mutated oncogenic ras plus a cooperating oncogene such as myc results in the acquisition of the transformed cell phenotype. The pathways downstream of Ras that are required for transformation are an active topic of research. The Raf-MEKK-MAP kinase pathway is triggered by activation of Ras and thought to be important in Ras transformation of rodent fibroblasts. To further explore the involvement of this pathway, fibroblasts from homozygous knock out c-Raf-1 mouse embryos (20 KO) and wild-type c-Raf-1 mouse embryos (16 WT) were transfected with H-ras and myc(v). The resulting cell line derived from the knock out cells grew slower both in tissue culture and had a longer latency period as tumors than the transformed cell line from the wild-type cells. Both cell lines were however able to form tumors in nude mice. These results suggest that c-Raf-1 is not required for Ras transformation in this system