Pretargeted Radioimmunotherapy: A Method for Targeted Delivery of Therapeutic Radionuclides to Tumors
Transcript
– Pretargeted radioimmunotherapy or PRIT utilizes an immunoconjugate or an antibody construct that binds to a radioactive ligand while presenting a high affinity towards a tumor specific cell surface antigen. To pre-target, take the desired concentration of these antibodies in a syringe treated with serum albumin proteins. Serum treatment prevents the binding of these antibodies to the syringe walls.
Next, place a colorectal tumor-bearing mouse model under a heat lamp to dilate its tail vein. Inject the antibodies into the dilated vein. As these immunoconjugates reach the tumor site, their high affinity towards the tumor-specific cell surface antigen promotes their accumulation within the tissue.
Subsequently, take an appropriate dose of the radioactive ligand. Administer the radioligand into the dilated tail vein of the pre-targeted mouse. Once these molecules reach the tumor site, they combine with the antibodies. The high dose of radiation emitted during the radioactive decay of these ligands kills the targeted tumor while minimizing exposure to normal cells.
In the following protocol, we will show pretargeted radioimmunotherapy using trans-cyclooctene-modified antibodies and Lutetium-177-labeled tetrazene radioligands in a colorectal cancer mouse model.
– Sort female athymic nude mice with colorectal cancer xenograft so that the average tumor volume in each cohort is roughly equal. To do so, list the animal identification numbers, ear notch pattern, and tumor volume in three separate columns of a spreadsheet program. Sort the data from smallest to largest tumor volume. In a fourth column, assign each animal a cage number.
Cycle through the cages in a snakelike pattern until all the animals are assigned to cage. Once the cages are assigned, sort the data by cage number. To inject the immunoconjugate, draw doses of 150 microliters of huA33-TCO solution in syringes pre-treated with 1% bovine serum albumin in PBS, and store these syringes on ice. To inject the radioligand, first draw doses in 150 microliters of 0.9% sterile saline containing 1.1 molar equivalence of the radiolabeled Tz-PEG7-DOTA relative to the amount of huA33-TCO administered.
Use calipers to measure the longest side of the oblong tumor as well as the width, which is perpendicular to the length. Weigh each mouse on a balance to track weight gain or weight loss over time. Finally, calculate the volume using the formula for volume of an ellipsoid, assuming that the height is approximately equal to the width.
