Design and synthesis of macrocyclic bifunctional chelating agents to label monoclonal antibodies with radionuclide for targeted imaging and therapy of tumor.

An appropriate bifunctional chelating agent namely DOTA-Ph-Al was developed for the conjugation with biological vectors (monoclonal antibody, peptides). We hereby report the synthesis of p-bromoacetamidobenzyl derivative of DOTA and its conjugation to monoclonal antibody. Immunoconjugate was prepared by conjugation of pbromoacetamidobenzyl derivative of DOTA with antibody. Modified antibody was purified on size exclusion chromatography. DOTA-Ph-Al-mAb exhibited quantitative ^99mTc labeling (>96%) with specific activity 10–20 mCi/mg of protein and ⁹⁰Y-labeling with specific activity 2–5 mCi/mg. Immunoreactivity was determined by flow cytometry. Receptor ligand assay on murine cell line EAT and human tumor cell line U-87MG showed K_d =2.87 nM and 4.86 nM respectively. The stability in serum indicated that ^99mTc remained bound to antibodies up to 24h and 98% ⁹⁰Y was associated with the mAb for 5 days. Biodistribution characteristics of Ab-conjugate radiolabeled to ^99mTc and ⁹⁰Y radionuclide was examined in BALB/c mice grafted with EAT and athymic mice with U-87MG cell line demonstrated high tumor uptake with 5.5 ± 1.3 and 7.85 ± 1.2%ID/g at 4 and 24 h for ^99mTc-DOTA-Ph-Al-mAb in EAT tumors after post injection respectively. Maximal radiotracer uptake peaked 17.6 ± 2.5%ID/g in EAT tumor and 12.89 ± 0.66% ID/g in U-87MG tumor at 48h for ⁹⁰Y. The drug excreted through renal routes as the activity in the kidneys was 13.42 ± 0.33%ID/g at 1 h and 4.51± 1.2%ID/g at 4 h for ^99mTc-DOTA-Ph-Al-mAb.