Preparation of 99mTc(CO)3-Carboxymethylthioethyl iminodiacetic acid and evaluation as a potential renal imaging agent

The ligand, carboxymethylthioethyl iminodiacetic acid (CMT-IDA) has a suitable array of donor atoms for coordination with [99mTc(CO)3]+ core, wherein the resultant complex is expected to possess free carboxylic residues contributing towards hydrophilicity of the complex. The aim of the studies was to study the renal clearance of 99mTc(CO)3- labeled CMT-IDA and determine the potential of the complex towards its use as a renal tubular imaging agent.

CMT-IDA was radiolabeled with the [99mTc(CO)3(H2O)3]+ precursor and was characterized by reverse phase HPLC gradient elution system. Stability, hydrophilicity and plasma protein binding studies were carried out for the complex. Biodistribution studies were carried out in normal male Swiss mice at 10 min.p.i. and 2 h.p.i. The clearance was estimated from the activity observed in the urinary bladder by tying the urethra prior to injection of the complexes under study. Imaging studies were performed with male Swiss mice administered with [99mTc(CO)3(CMT-IDA)]-2 at 30 min. p.i. and blocking studies were carried out by intraperitoneal injection of probenecid 10 min. prior to the injection of the radiotracer.

[99mTc(CO)3(CMT-IDA)]-2 could be obtained in > 98% radiochemical purity. The complex showed renal clearance of 71.0� 5.9% ID at 10 min.p.i. which increased to 84.1� 10.6% ID at 2 h.p.i., with no major activity in blood, liver, heart, lungs, stomach and spleen. However, the intestinal uptake was high (10.3� 2.0% ID) at 2 h.p.i. Scintigraphic image of the animal injected with probenecid showed an increase in the activity in kidneys indicating excretion of the [99mTc(CO)3(CMT-IDA)]-2 complex via tubular pathway.

The complex, [99mTc(CO)3(CMT-IDA)]-2 has shown excellent renal clearance and thereby can be explored further for potential use as an agent towards assessing effective renal plasma flow.