Tolerance to nicotinamide and carbogen with radiation therapy for glioblastoma

Fractionated irradiation combined with carbogen breathing and nicotinamide of two human glioblastomas grafted in nude mice

This study addressed the potential radiosensitizing effect of nicotinamide and/or carbogen on human glioblastoma xenografts in nude mice. U-87MG and LN-Z308 tumors were irradiated with either 20 fractions over 12 days or 5 fractions over 5 days in air-breathing mice, mice injected with nicotinamide, mice breathing carbogen, or mice receiving nicotinamide plus carbogen. The responses to treatment were assessed using local control and moist desquamation. In U-87MG tumors, the enhancement ratios (ERs) at the radiation dose required to produce local tumor control in 50% of the treated mice (TCD(50)) with nicotinamide and/or carbogen ranged from 1.13 to 1.24 for irradiation in 20 fractions over 12 days. In LN-Z308 tumors, the ERs at the TCD(50) with nicotinamide and/or carbogen ranged from 1.22 to 1.40 for irradiation in 5 fractions over 5 days and from 1.11 to 1.30 in 20 fractions over 12 days, respectively. Skin injury was slightly enhanced, with ERs ranged from 1.06 to 1.15 when radiation was combined with carbogen and/or nicotinamide. Thus carbogen and nicotinamide can slightly improve the radiation response of human glioblastoma xenografts.

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.

Combination of fractionated irradiation with nicotinamide and carbogen in R1H-tumours of the rat and its pulmonary metastases

BACKGROUND AND PURPOSE

The combination of radiotherapy with nicotinamide and carbogen is a promising method to improve treatment outcome. The aim of the present study was to investigate its effect on rat lungs, the R1H-tumour and its pulmonary metastases.

MATERIALS AND METHODS

Subcutaneous tumours and artificially induced pulmonary metastases of the rhabdomyosarcoma R1H of the rat were treated either with fractionated irradiation alone or in combination with nicotinamide and carbogen. Local metastatic control, net growth delay and lethal lung damage were used as endpoints.

RESULTS

Radiosensitivity of the lungs of WAG/Rij rats increased by a factor of 1.13, while no positive effect of the combined treatment either on subcutaneous R1H-tumours or on pulmonary metastases could be detected. This resulted in a therapeutic loss of 18% (P = 0.003).

CONCLUSION

The results indicate that deleterious effects of the combination of radiotherapy with nicotinamide and carbogen cannot be excluded under all circumstances.