Systemic radiotherapy with monoclonal antibodies. An experimental study with human neuroblastoma xenografts in nude mice.

In this experimental study, feasibility and efficiency of systemic radiotherapy with the I-131 labelled monoclonal antibody BW575/9 (radioimmunotherapy) are investigated using human SK-N-SH neuroblastoma transplanted into nude mice. Series of six nude mice were treated with intravenous application of 400 microCi (group 1), 700 microCi (group 2) of the I-131 labelled and of the unlabelled MAb (group 3). An untreated group (group 4) served as control. Tumors of group (3) and (4) showed an identical growth. In group (1), tumor growth was arrested for seven days. In group (2), the tumor showed complete regression after eight days which lasted for 55 days. Thereafter, the tumor started to regrow. This growth characteristics are correlated with the doses achieved in the tumor using a medical internal radiation dose (MIRD) formulation. The biodistribution data necessary for MIRD calculation were obtained by previously performed experiments with the I-125 labelled MAb. The doses assessed in the tumor turned out to be five to ten times greater than those in normal tissues (liver, bone, etc.) These results confirm feasibility, selectivity and efficiency of radioimmunotherapy in the above described model. Moreover, this in vivo model seems suitable for further investigations concerning fundamental issues of radioimmunotherapy.