Recombinant human erythropoietin increases the radiosensitivity of xenografted human tumours in anaemic nude mice.

PURPOSE: The effect of recombinant human erythropoietin (Epo) on the radiosensitivity of human tumour xenografts growing in anaemic nude mice was studied. METHODS AND MATERIALS: Anaemia was induced by total body irradiation (TBI) of mice prior to tumour transplantation. The development of anaemia was prevented by Epo (1000 U/kg s.c.) given 3 times weekly starting 2 weeks prior to TBI (5 Gy). Epo treatment did not influence the growth rate of the tumours, which were transplanted into the subcutis of the hind leg of mice. Thirteen days after TBI (tumour volume of approx. 40 mm3), a single-dose irradiation (12 Gy) of the tumour was performed resulting in a growth delay with subsequent regrowth of the tumours. RESULTS: In Epo-treated animals the tumour growth delay was significantly longer compared to anaemic mice. However, the radiosensitivity of tumours in non-anaemic animals' (non-Epo-treated) tumours could not fully be restored. CONCLUSION: These data give evidence for restored radiosensitivity after correction of anaemia with Epo.

Quiescent S-phase cells as indicators of extreme physiological conditions in human tumor xenografts.

PURPOSE: During the last 20 years, evidence has been accumulating for the existence in animal and human tumors of quiescent S-phase cells, i.e. cells with an S-phase DNA content that do not actively synthesize DNA. In cell culture studies, quiescent S-phase cells have been observed under physiological conditions typical for poorly vascularized regions of tumors such as reduced pH, hypoxia, and glucose deprivation. Therefore, we studied the possible correlation between the frequency of quiescent S-phase cells and the oxygenation status as determined polarographically in a number of human tumor xenografts. METHODS AND MATERIALS: Five human tumor xenografts on nude mice were used. Oxygenation was measured polarographically with an Eppendorf pO2-Histograph in 24 to 30 individual tumors for each entity. Mice were injected intraperitoneally with 1 mg/30 g bodyweight bromodeoxyuridine (BrdU), tumors were excised 30 min later and prepared into a single-cell suspension. After immunofluorescence staining with an antibody against BrdU and staining of the DNA with propidium iodide, cells were measured in a FACScan flow cytometer and the frequency of cells in the S-phase compartment that did not incorporate BrdU was determined. RESULTS: In most cases, the frequency of measurements of an oxygen partial pressure <5 mm Hg in the tumor tissue increased with tumor volume. Likewise, the frequency of quiescent S-phase cells was generally higher in larger tumors. Taking all five tumor entities together, there was a highly significant correlation between tumor oxygenation and the occurrence of quiescent S-phase cells. CONCLUSIONS: Our data confirm earlier findings that inactive S-phase cells do exist in vivo. Because their frequency seems to be dependent (directly or indirectly) on the degree of oxygenation and has been shown to increase not only with hypoxia, but also with reduced pH and glucose deprivation in vitro, the frequency of inactive S-phase cells may be considered a summary indicator for extreme physiological conditions in tumors.

The effect of combined nicotinamide and carbogen treatments in human tumour xenografts: oxygenation and tumour control studies.

BACKGROUND AND PURPOSE: This was an investigation to study the effect of giving carbogen and nicotinamide (CON) on pO2 and the radiation response of human xenografted tumours. MATERIALS AND METHODS: The human xenografts were two sarcomas (ENE2 and ES3) and a glioblastoma (HTZ17). Nicotinamide (500 mg/ kg, i.p.) was administered 60 min before PO2 measurements and irradiation, while carbogen was given for 5 min before and during these treatments. Tumour pO2 was measured with an Eppendorf electrode and radiation response was assessed by local tumour control following irradiation with 10 daily fractions. RESULTS: All three xenografts were found to be poorly oxygenated (about 80% of all pO2 values were < or =2.5 mmHg). CON treatment improved the oxygenation status in all three tumours such that 65, 52 and 71% of the pO2 values were < or =2.5 mmHg in ENE2, ES3 and HTZ17, respectively. However, only in ES3 was this decrease significant. The TCD50 doses for all tumours were around 52-54 Gy. No significant improvement was seen with CON in ENE2 (TCD50 = 48 Gy) and HTZ17 (TCD50 = 56 Gy), but for the ES3 xenograft a significant decrease to 42 Gy was found. CONCLUSIONS: The three tumours used in this study appeared to show the same level of hypoxia as measured both by pO2 and radiation response. However, only one tumour showed a significant improvement after CON treatment, suggesting that not all hypoxic human tumours might benefit from this type of therapy.

Experimental studies on the possible influence of invasive oxygen measurements on tumour radiosensitivity.

The effects of tissue damage associated with invasive pO2 measurements on radiation sensitivity were investigated using a xenografted squamous cell carcinoma model. For the tumour cure experiments, single dose irradiations were given following different regimens of polarographic pO2 measurements associated with different degrees of mechanical tissue damage. With a dose of 32 Gy, 57% of animals were cured. Following 3 tracks of needle measurements, 73% of tumours were locally controlled, and 75% were cured after 8 needle tracks. The polarographic measurements gave virtually identical oxygenation data for recurrent or cured tumours (both median pO2 1.0 mmHg), respectively. There was thus no evidence of decreased radiosensitivity associated with tissue damage after invasive pO2 measurements. The pre-therapeutic oxygenation status gave no evidence for a prediction of radiation response on an individual basis.

Effect of specific activity on neuroblastoma uptake of I-123-meta-iodobenzylguanidine in nude mice xenografted with SK-N-SH cells.

The effect of specific activity of meta[I-123]iodobenzylguanidine ([I-123]MIBG) on neuroblastoma uptake was studied in a nude mouse model (NMRI nu/nu) xenografted subcutaneously with SK-N-SH cells. Groups of eight animals received [I-123]MIBG intravenously with a specific activity of greater than or equal to 260 GBq/mu mol (no-carrier-added), 3.7 GBq/mu mol, 37 MBq/mu mol, and 0.37 MBq/mu mol, respectively. All animals in the group injected with 0.37 MBq/mu mol died immediately after the injection. Al 4 and 24 h, there was no significant effect of specific activity on tumor uptake of [I-123]MIBG in the different groups. The uptake of non-tumor tissue was in general lower with 37 MBq/mu mol compared to higher specific activities. The differences in blood, heart, liver, spleen and lungs were statistically significant at 24 h, whereas at 4 h significant differences were only present in the heart, liver and lungs. The results suggest that for the treatment of children with neuroblastoma a lower specific activity of radioiodinated MIBG may minimize the radiation exposure to non-tumor tissue but not to the tumor. Higher mass of MIBG >0.5 mu mol/g, however, is considered as lethal dose in our nude mice model and corresponding doses may cause toxic side effects in human.