Evaluation of Anti-LGR5 Antibodies by ImmunoPET for Imaging Colorectal Tumors and Development of Antibody–Drug Conjugates

Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is highly expressed in colorectal tumors and marks colon cancer stem cells that drive tumor growth and metastasis. Recently, we showed that LGR5 is a promising target for antibody–drug conjugate (ADC) therapy. However, it is important to identify LGR5-positive tumors that would respond to ADC treatment. Prior to drug conjugation, we evaluated two different anti-LGR5 monoclonal antibodies (mAbs), 8F2 and 9G5, using 89Zr-immunoPET to select the optimal mAb for ADC development and tumor imaging. Binding, specificity, and internalization were compared, and mAbs were prescreened as ADC candidates against colon cancer cells using secondary ADCs. Both mAbs demonstrated strong, specific binding in 293T-LGR5 cells but not 293T-vector cells. In DLD-1 colorectal cancer cells, which express high levels of LGR5, the mAbs rapidly internalized into lysosomes and promoted ADC-induced cytotoxicity, with 8F2 exhibiting slightly higher potency. No binding wa...