High-resolution immunoscintigraphy for in vivo imaging of thyroid cancer by using galectin-3 radio-immunotargeting

The high prevalence of benign thyroid nodules makes the preoperative detection of thyroid cancer comparable to "looking for a needle in a haystack". The anti-apoptotic molecule galectin-3 is preferentially expressed in malignant thyroid cells and represents a potential target for obtaining in vivo imaging of thyroid cancer by using galectin-3 specific radiolabeled antibodies. Aim of our work was to develop a high-resolution immunoscintigraphy for in vivo detection of primary and metastatic thyroid cancer based on galectin-3 radio-immunotargeting, which uses a 99mTc-labeled anti-galectin-3 monoclonal antibody and a position-sensitive portable mini- gamma camera as imaging capture device. Anti-galectin-3 mAb was labelled with high specific activity using the direct method. QC included SDS-PAGE, HPLC, and several stability tests. To evaluate the binding specificity of 99mTc-labelled mAb to galectin-3 in vivo, several experiments were performed. Initially 6 mice bearing galectin-3+ thyroid carcinoma xenografts (ARO-Gal-3+) were imaged with 100?Ci of 99mTc-labeled mAb (30µg protein) at 1, 3, 6, 9 and 24 hours post injection using a high-resolution mini-gamma camera. Control was 99mTc-HIG. Then, 6 mice were transplanted with galectin-3+ ARO cells (5-8x106 cells) and 6 mice were transplanted with galectin-3 knockout ARO cells (ARO-Gal-3-). Biodistribution was studied in 20 ARO-Gal-3+ xenografted mice injected with 100µCi of 99mTc-labeled mAb and sacrificed at 3, 6, 9, 12, 24 hours p.i. Best visualization of the ARO-Gal-3+ xenografts was obtained between 6 and 12hrs from injection, whereas ARO-Gal-3- tumors were not detected. Biodistribution showed a rapid blood clearance of the radiopharmaceutical within 3hrs from injection. Most of the radioactivity was measured in the liver and kidneys. Finally, a fresh metastatic cervical lymph node, surgically resected from a patient bearing a papillary thyroid carcinoma, was used as target for 99mTc-anti- Gal-3 mAb binding and imaging ex-vivo. Results of this experiment are showed that the HR- gamma camera detected thyroid cancer metastasis whereas a scanty tumor uptake of the radiopharmaceutical was visible in the control tumor section after displacement of 99mTc- labeled-Gal-3 binding by excess of unlabelled mAb. This technology opens new avenues in both imaging and treatment of thyroid cancer with the possibility to extend this application to the diagnosis and treatment of different galectin-3 positive human malignancies in future.