Breast Tumor Targeting in a Mouse Model with a New Anti-MUC1 Monoclonal Antibody, PR81, Radiolabeled with 99mTc via the HYNIC

Tumor imaging, using monoclonal antibodies (MAb) carring radioisotopes, is a promising approach toward improving early diagnosis of cancer. The PR81 is a new murine anti-MUC1 MAb that was generated by imunizing BALB/c mice with homogenized human breast cancerous tissues. This study was performed to develop an indirect labeling of this antibody via the HYNIC with Tc-99m in order to use it in radioimmunoscintigraphy (RIS) of breast tumor in mouse model. A 20 molar excess of dissolved HYNIC was added to a solution of the MAb. The solution was stirred for 5 hr at room temperature followed by dialysis against citrate buffer overnight. The resulting conjugate was labeled with 99mTc using tricine as a co-ligand. The labeling efficiency determined by ITLC was 89.2% +/- 4.7. Radiocolloides measured by cellulose nitrate electrophoresis were 3.4% +/- 0.9. In vitro stability of labeled product determined in human serum by gel filtration chromatography (FPLC) was 78.6% +/- 5.7 over 24 hr. The integrity of labeled MAb was checked by means of SDS-PAGE and no significant fragmentation was seen. The results of cell-binding studies showed that both labeled and unlabeled PR81 were able to compete for binding to MCF-7 cells. Biodistribution studies and tumor imaging performed in female BALB/c mice with breast tumor xenografts at 4, 16 and 24 hr after the Tc-99m-HYNIC-PR81 injection were demonstrated definite localization of the compound at the site of tumors with high sensitivity. These findings show that the new radiopharmaceutical can be considered as a promising candidate for imaging of human breast cancer in nuclear medicine.