Trastuzumab labeled to high specific activity with 111in by conjugation to G4 PAMAM dendrimers derivatized with multiple DTPA chelators exhibits increased cytotoxic potency on HER2-positive breast cancer cells

摘要

Purpose: To conjugate trastuzumab with/without NLS peptides to G4 PAMAM dendrimers derivatized with DTPA and determine the specific radioactivity (SA) for 111In labeling, HER2 immunoreactivity and cytotoxicity on breast cancer (BC) cells. Methods: G4 dendrimers were reacted with DTPA then conjugated through a thiol to maleimide-derivatized trastuzumab. The SA achievable was determined by incubating 2 to 20 μg with 60 MBq of 111In. HER2 immunoreactivity, internalization and nuclear importation were measured. The effect of 111In-DTPA-G4-trastuzumab (5.9 MBq/μg) on the clonogenic survival (CS) of SK-Br-3 or MDA-MB-231 cells with high or low HER2 density, respectively was compared to 111In-DTPA-NLS-trastuzumab (0.5 MBq/μg). DNA double-strand breaks (DSBs) were measured. Results: DTPA-G4-trastuzumab was labeled with 111In to a SA (23.6 MBq/μg) which was 100-fold higher than 111In-DTPA-NLS-trastuzumab. 111In-DTPA-G4-trastuzumab and 111In-DTPA-G4-NLS- trastuzumab retained HER2 immunoreactivity and were internalized and imported into the nucleus of BC cells. G4-radioimmunoconjugates were 2-4 fold and 9-fold more cytotoxic to SK-Br-3 and MDA-MB-231 cells, respectively than 111In-DTPA-NLS-trastuzumab which was associated with an increase in DNA DSBs. Conclusions: Conjugation of trastuzumab to G4 PAMAM dendrimers modified with 30 DTPA permitted high SA 111In labeling which increased their cytotoxic potency for BC cells with high or low HER2 density.