Evaluation in a Mouse Model of a Thyroid-blocking Protocol for 131 I Antibody Therapy (Short Communication)

Abstract

Purpose

: We describe a murine model to evaluate variations of a published multicenter thyroid blocking protocol described for ¹³¹I antibody therapy, using doses of blocking agents proportional to those used in man. Variables include duration of super-saturated potassium iodide (SSKI) pretreatment and use of supplemental KC10₄.

Materials and Methods

: Whole-body activity measurements were performed 0, 24,48 and 72 hours following ¹³¹I-NaI administration in control and thyroid-blocked mice. Retained whole-body activity was calculated as a percentage of the injected dose (%ID), primarily reflecting radioiodine sequestered in the thyroid gland. In blocked groups, SSKI was begun one or 7 days preceding ¹³¹I-NaI therapy, and was supplemented in one half of the cases with KC10₄ from time of therapy.

Results

: In control mice, %ID was 11.23±1.47%, 10.15±l.ll%and9.29±1.50%at24,48 and 72 hrs respectively. %lDs of blocked groups were markedly lower than controls (p=.0001). In the one day SSKI pretreatment group, %ID was reduced from 1.73±0.58, 1.42±0.45 and 1.20±0.38 at 24, 48 and 72 hours to 0.49±0.08, 0.50±0.07 and 0.44±0.06 with addition of supplemental KC10₄. In the 7 day SSKI pretreatment group, %ID was reduced from 1.87±0.73,1.48±0.49and 1.36±0.57 at24,48 and 72 hours to0.60±0.36,0.45±0.13 and 0.41±0.14 with addition of supplemental KC10₄. %IDs in the 7 day pretreatment animals were not statistically different from those in the one day pretreatment groups (all p>>0.05).

Conclusion

: SSKI reduces retention of radioiodide approximately six-fold whereas supplemental KC10₄ enhances thyroid blocking an additional three-fold. Seven day SSKI pretreatment appears no more effective than one day pretreatment.