Preparation of radioiodinated ritodrine as a potential agent for lung imaging

Ritodrine (a beta-2 adrenergic receptor agonist) was successfully labeled with 125I via direct electrophilic substitution reaction at ambient temperature. 125I-ritodrine was obtained with a maximum labeling yield of 97 ± 0.163 % and in vitro stability up to 24 h. Biodistribution studies showed that maximum in vivo uptake of 125I-ritodrine in lungs was 20.4 ± 0.22 % injected activity/g tissue at 1 h post-injection, whereas the clearance from mice appeared to proceed mainly via the renal pathway. 125I-ritodrine is not a blood product and so it is more safe than the currently available 99mTc-MAA, and its lung uptake is higher than that of the recently discovered 99mTc(CO)5I and 99mTc-DHPM. As a conclusion, radioiodinated ritodrine could be used as a novel radiopharmaceutical for lung perfusion scan safer than the currently available 99mTc-MAA and more potential than the recently discovered 99mTc(CO)5I and 99mTc-DHPM.