No abstract

Summary In contrast to reports of extensive hypoxia in human gliomas in situ measured by P02 histography, non-invasive methods of assessing glioma oxygenation, including nitroimidazole binding, have yielded surprisingly contradictory results. In order to investigate the relationship of necrosis, hypoxia, nitroreductase activity and cellular respiration in human gliomas, subcutaneous models using the human glioma cell lines M059K, M006 and M01 Ob were developed in the murine SCID host. Intracranial growth of the M006 line was achieved in nude rats. The nitroreductive capacity of glioma cell lines was assessed and found to be similar to transplanted tumours previously reported in the literature. This suggests that if substantial numbers of viable hypoxic cells were present in situ in gliomas, then nitroimidazole-binding techniques should be capable of identifying them. Inter-tumour variability in the amount of necrosis was seen. M006 xenografts growing in subcutaneous and intracranial sites revealed extensive necrotic regions histologically, some of which were surrounded by cells labelled heavily for [3H]misonidazole, while other areas were lightly labelled. Similar binding patterns were seen for subcutaneous M059K tumours, while subcutaneous M01 Ob tumours display necroses of which almost all were surrounded by heavily labelled cells. The oxygen consumption rates of tumour cell lines grown in vivo, in which venous P02 concentrations are of the order of 2-5%, were two to sevenfold less than those of the same lines grown as monolayers in vitro under oxygen concentrations of 18%. We postulate that glioma cell lines behave as 'oxygen conformers', in that their rate of oxygen consumption appears to vary with the availability of oxygen. Together with the misonidazole-binding data, the results in this glioma tumour model are consistent with coordinate inhibition or down-regulation of respiration under moderate hypoxia.

We have shown previously that human glioblastoma multiforme cells vary in their ability to survive under hypoxic conditions. Under oxygen limiting conditions, hypoxia-tolerant cells decrease their oxygen consumption rate whereas hypoxia-sensitive cells continue to consume oxygen at a relatively steady rate until the oxygen supply becomes exhausted. We now show that hypoxia-tolerant and hypoxia-sensitive cells exhibit distinct patterns of mitochondrial function in response to hypoxic challenge. Hypoxia-tolerant cell lines retain stable mitochondrial membrane potential and ATP concentration when incubated under oxygen limiting conditions. In addition, hypoxia-tolerant cell lines are consistently more sensitive to a wide spectrum of inhibitors of mitochondrial function than are hypoxia-sensitive cells. In contrast, the hypoxia-sensitive cells are unable to maintain stable mitochondrial membrane potential and ATP levels when incubated at reduced oxygen tension. These results demonstrate significant differences in the mitochondrial function between these two phenotypes and reinforce previous data that suggest a regulatory role for mitochondria in the development of hypoxia tolerance.

No abstract

Summary Recently we reported the variable presence of hypoxia adjacent to necrosis in human glioma lines grown as subcutaneous tumours in severe combined immunodeficient (SCID) mice. To assess the basis for this observation. we examined the pattem of oxygenation in M006 and M006XLo glioma spheroids. We found a wide range of binding of [3H] aExduding two spheroids with a mixture of high and low grains ( Figure 3B).completely at each feeding. The number of spheroids w-as reduced at each feeding to stabilize the rate of consumption of nutrients. The first spheroids reached diameters of 0.8-1.2 mm. at x-hich they w-ere eliaible for experiments. w ithin 4-5 eeks. M006XLo sublineIn an effort to denrve a subline that w-as adapted to grow-th at lowambient oxy gen. the M006XLo subline x as established from small M006 spheroids that had been exposed continuously to 0.6%7 oxygen for 13 days. beainning 1 week after initiation in air. The spheroids were disaggregated wxith 0.25%c trypsin. and the cells w ere groxx n in monolayer culture for four passages (5 w eeks). then injected subcutaneously in SCID mice. A tumour x-as disaggregated to yield a new line designated M006XLo. w hich w as propagated in monolayer culture. Cells from the third passage were stored in liquid nitrogen. and each line x-as discarded after 3 months in culture and replaced from frozen stock.Clonally derived sublines (Franko et al. 1987). The desired oxygen level was obtained by a series of partial evacuations. each of which was followed by refilling of the chambers with 95% nitroaenlr5% carbon dioxide. Metabolic actixation of misonidazole during the degrassing procedure w-as minimized by precooling the medium and the chambers to 0°C and maintainingr this temperature during, the 30-to 40-min degassing process. The incubation period was 3 h for the spinner flask. and an additional 30 min for the aluminum chambers. w-hich is the time required for the medium in the dishes to return to 37' in the cabinet used for incubation. The oxygen tension in each chamber was measured at the end of the incubation period. as described previously (Franko et al. 1987). AutoradiographyThe spheroids were fixed in formalin and embedded in wax. and 4-gm serial sections w-ere taken throughout the spheroids. Slides w-ith sections near the centres of the majority of the spheroids were