Value of P-31 NMR spectroscopy in predicting the response of a xenograftedhuman hypopharynx carcinoma to irradiation

Purpose: An early indicator of tumor sensitivity to irradiation could provi de useful information on the effectiveness of therapy and may facilitate mo re individual designs of treatment protocols. The aim of the present study was to evaluate the potential of in vivo P-31 nuclear magnetic resonance sp ectroscopy in predicting the response of a xenografted human hypopharynx ca rcinoma to radiotherapy, Methods: The tumor had been serially heterotranspl anted to athymic mice. P-31 NMR spectra were collected before and at four i ntervals (24, 48, 72, and 120 h) after irradiation with 15 Gy or 30 Gy. Alt erations of phosphorus metabolism were compared with the growth delays, the histological appearance, and the mitotic activity of the treated tumors. R esults: Radiation with 30 Gy induced increases of the phosphodiester level (P < 0.001) as well as of the tumor pH (P < 0.05) and decreases of the phos phomonoester level (P < 0.001) within 48 h. The changes clearly preceded me asurable tumor responses and were accompanied by severe histological destru ction and marked depression of mitotic indices. However, none of these spec tral alterations was significantly correlated with individual delays of tum or growth. The only parameters allowing a prediction of radiation-induced t umor responses were the pre-treatment levels of phosphomonoesters and -dies ters. The P-31 NMR spectroscopic changes observed after therapy with 15 Gy were either unsystematic or insignificant. Conclusions: Pretreatment levels of tumor phospholipids were indicative of radiosensitivity in the xenograf ted human hypopharynx carcinoma investigated here. However, since phosphoru s metabolism varies considerably among different tumor lines, it seems unli kely that there exists a uniform P-31 NMR spectroscopic parameter predictin g tumor response to radiation therapy.