PHARMACOKINETICS AND EFFICACY OF I-131 METAIODOBENZYLGUANIDINE IN 2 NEUROBLASTOMA XENOGRAFTS

The pharmacokinetics, biodistribution and efficacy of the radiopharmac eutical I-131-meta-iodobenzylguanidine (I-131-mIBG) were determined in murine xenografts of two human neuroblastoma cell lines, SK-N-SH and SK-N-BE(2c). These lines have similar capacities in vitro for active u ptake of I-131-mIBG, but different radiobiological characteristics. Gr oups of four mice were killed after injection of I-131-mIBG, and retai ned radioactivity in the tumour and normal tissues was measured at 8, 16, 24 and 48 h. Within each type there was heterogeneity of tumour up take, although average values were similar for both. The per cent inje cted dose per gram of:tumour retained at 24 h was (mean and 95% confid ence interval) 0.95 (0.67-1.23) for SK-N-SH and 0.76 (0.47-1.05) for S K-N-BE(2c). The growth of tumours in groups of seven animals following injection of 35, 70 or 105 MBq I-131-mIBG was compared with that of c ontrols. The specific regrowth delay (median and 95% confidence interv als) caused by 105 MBq I-131-mIBG was 4.2 (0.9-5.9) in SK-N-SH and 5.6 (0-11.3) in SK-N-BE(2c) bearing mice. SK-N-BE(2c) xenografts were sig nificantly more sensitive to external beam irradiation than SK-N-SH xe nografts.