A detailed investigation was undertaken of reported modifiers of the toxicity towards hypoxic cells of misonidazole. The modifiers tested were medium type, cell type, cell density, concentration of misonidazole, addition of serum, addition of sulfhydryl, addition of oxygen and pH. The latter 5 modifiers were found to be most important and were studied in many of the possible combinations. Serum has its greatest protective effect at low concentration (e.g. 0.5 mM) of misonidazole. In the absence of serum, the (log10) survival curve for misonidazole toxicity can be described mathematically as a function of time by a shoulder (DQ) inversely related to misonidazole concentration, and a slope (1/D0) related directly to log10 misonidazole concentration. Sulfhydryl's (cysteamine) protective effect dominates at high concentrations of misonidazole. The protective action of SH can change to potentiative in the absence of serum or at high pH. Addition of oxygen results in overall protection but no relative changes in the effect of the other modifiers. Drugs like ascorbate and disulfide may only potentiate toxicity to the level found in the absence of serum.

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PubMedDate not supplied

Binding of misonidazole to EMt6 and V79 spheroids.

Metabolism-induced binding of misonidazole was shown previously to be enhanced in hypoxic regions of V79 spheroids. Data are presented to show that the binding of misonidazole to EMT6 spheroids is similar to V79 in some respects and different in others. The binding rate in nitrogen was constant in all cells in EMT6 spheroids, whereas a 5-fold rise was found in binding rate across the outer 100 micrometers of V79 spheroids. A small enhancement of binding to the cells near the necrotic center in EMT6 spheroids in air was found, which was similar to the binding to chronically hypoxic cells in aerobic V79 spheroids. The binding rate in 1--5% oxygen was similar in EMT6 and V79 spheroids. Both showed a large rise in binding rate across the outer 120 micrometers and a constant binding rate to healthy cells interior to this. Since 1.5 oxygen should supply only the outer 40 micrometers of a typical spheroid, something beyond a simple oxygen diffusion limitation is required to explain the data. One possible explanation is the diffusion of some of the reactive product away from the hypoxic cells which produce it. This was tested by incubating a single cell suspension in misonidazole at 0.5% oxygen in the presence of absence of V79 spheroids. No evidence was found for an appreciable loss of reactive product from the spheroids.

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PubMedDate not supplied

Hypoxia and VEGF mRNA expression in human tumors.

High expression of circulating plasma vascular endothelial growth factor (VEGF) in patients with cancer is an indicator of poor treatment response. Similarly, hypoxia in tumors, as measured by oxygen needle electrodes, has been found to predict for tumor-treatment failure. These two predictors may be related because hypoxia is a potent stimulator of VEGF expression in vitro. However, the demonstration of a relationship between hypoxia and VEGF in human tumors has, to date, been indirect or even negative. The purpose of this study was to test whether this unexpected result was caused by factors unique to human tumors, or whether the prior results could have been influenced by the known complexities of VEGF regulation. Therefore, we undertook a direct assessment of VEGF induction in human tumors using in situ hybridization and compared its distribution with that of hypoxia, as measured by the distribution of adducts of the hypoxia marker EF5. The distribution of both markers was assessed in relationship to the distribution of blood vessels, as measured by antibodies to CD31. Our hypothesis was that VEGF mRNA and hypoxia would colocalize, assuming that detectability of the former was not limiting. Four squamous cell carcinomas, three sarcomas and one glioblastoma multiforme were studied. When VEGF mRNA signal was detectable, its maxima colocalized with regional maxima of EF5 binding. The strongest levels of both signals were sometimes adjacent to regions of tissue necrosis. However, we were unable to predict absolute levels of EF5 binding based on absolute levels of VEGF mRNA. Conversely, for all tumors studied, regions with relatively low levels of EF5 binding had relatively low or undetectable VEGF mRNA. We found moderate EF5 binding in some keratinized cells but VEGF mRNA was not expressed by these differentiated cells. The paradigm that hypoxia and VEGF expression are linked in human tumors is supported by the data presented herein. A better understanding of the biology behind VEGF expression, including its modulation by hypoxia, is important for optimizing its use as a prognostic indicator and/or modulating its presence with biologic therapies.

Biomarkers↗

PubMedDate not supplied

Hyperthermia-induced inhibition of respiration and mitochondrial protein denaturation in CHL cells.

Respiration of Chinese hamster lung V79 cells, as assayed by O2 consumption, increases linearly from 8 to 40 degrees C when plotted in the Arrhenius fashion but is strongly inhibited above 40 degrees C. The protein of mitochondria isolated from V79 cells undergoes structural transitions at 28 and 40 degrees C. This is supported by changes in the fluorescence excitation spectrum of conjugated pyrene maleimide and, to a lesser extent, intrinsic protein fluorophores. Electron spin resonance labelling studies with a derivative of tempo maleimide imply that extensive protein unfolding coincides with the 40 degrees C transition. The structural transition at 40 degrees C correlates well with inhibition of O2 consumption, is irreversible and is probably due to protein denaturation, while the change at 28 degrees C is reversible and has no effect on O2 consumption. Previous studies indicate the presence of a broad lipid transition extending from approximately 8 to 30 degrees C in mitochondrial membranes with all lipids being in the liquid-crystalline state above 30 degrees C. Thus, the onset of the lipid transition may induce the observed protein conformational change at 28 degrees C, but inhibition of respiration above 40 degrees C can be explained by protein denaturation alone. The region from 28 to 40 degrees C of stable protein conformation corresponds to the temperature range of V79 cell growth.

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PubMedDate not supplied

Comment on the hypothesis that hyperthermia facilitates reoxygenation.

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Animals↗