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

The pharmacokinetics, biodistribution and efficacy of the radiopharmaceutical 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 uptake of I-131-mIBG, but different radiobiological characteristics. Groups of four mice were killed after injection of I-131-mIBG, and retained radioactivity in the tumour and normal tissues was measured at 8, 16, 24 and 48 h. Within each type there was heterogeneity of tumour uptake, although average values were similar for both. The per cent injected dose per gram of:tumour retained at 24 h was (mean and 95% confidence interval) 0.95 (0.67-1.23) for SK-N-SH and 0.76 (0.47-1.05) for SK-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 controls. The specific regrowth delay (median and 95% confidence intervals) 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 significantly more sensitive to external beam irradiation than SK-N-SH xenografts.