Summary A previous publication (Leith et al., 1992) showed that administration of basic fibroblast growth factor 0.25 We recently reported in this journal that administration of basic fibroblast growth factor (FGF-2; q.i.d. x 7; 0.25 mg kg-') caused a significant increase in the growth rates of xenografted DLD-2 human colon cancers, and concomitantly decreased the percentage of hypoxia within these neoplasms (Leith et al., 1992). In that study, hypoxia levels were determined 1 day after the end of a 7 day period of FGF-2 administration, at a time when the volumes of control (given sham-injections with Hank's balanced salt solution) or FGF-2 treated tumours had increased from 211 mm3 to 992 and 1751 mm3 respectively. Although the FGF-2 treated tumours were about 1.8 times the volume of controls at the time of assay, the percentage of hypoxia within these neoplasm was 19.1% (13.5-26.9; 95% confidence limits) whereas the percentage in control neoplasms was 42.2% (34.2-52.1). In essence, increases in tumour volume can be uncoupled from changes in hypoxia by FGF-2 administration. In these studies however, the effects of the nonequivalent tumour volumes on interpretation of steady-state levels of hypoxia as a function of volume were not explicitly studied.Because of our lack of knowledge of how steady-state levels of hypoxia within unperturbed DLD-2 tumours might change as a function of volume, we performed further experiments to define these kinetics. Additionally, we examined hypoxia levels in FGF-2 treated DLD-2 tumours at several times during and after the administration of growth factor.
Materials and methods
Cell lineThe biological characteristics of the DLD-2 cell line have been previously described (Leith et al., 1992). For these experiments, stock cells stored in liquid nitrogen were grown in RPMI-1640 medium containing 10% foetal bovine serum (FBS), 1% sodium bicarbonate, 1% anti-PPLO reagent, 1% 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer, and 0.04% gentamicin (all reagents from the Grand Island Biological Co., Grand, Island, NY).Mice and production of xenografted tumours Young adult male mice were obtained from the Charles River Breeding Laboratories, North Wilmington, MA. Mice were housed, five per large cage, with dust covers, in a dedicated room in the Brown University Animal Care Facilities in a laminar flow hood (Thoren Industries, King of Prussia, PA). Mice were quarantined for 1 week, and were ear tagged for identification. To produce tumours (one tumour per animal), DLD-2 cells were trypsinised (0.05% trypsin, 0.54 mM EDTA) from exponentially growing cultures, and resuspended as single cells in Hank's basic salt solution (HBSS) at a concentration of 5 x 107 cells ml-'. Nought point two ml of the cell suspension was injected into the right flank regions of the mice.Volumetric procedures Tumours were measured in two orthogonal diameters and volumes (mm3) were calculated using the formula for a prolate ellipsoid [V (mm3) = L x W2/2] where L and W are respectively the major and minor d...