Nimotuzumab is a humanized anti-epidermal growth factor receptor I (EGFR) monoclonal antibody. We have developed antibody drug conjugates (ADCs) with nimotuzumab conjugated to PEGylated-maytansine (PEG6-DM1). We generated conjugates with low (nimotuzumab-PEG6-DM1-Low: DAR = 3.5) and high (nimotuzumab-PEG6-DM1-High: DAR = 7.3) drug to antibody ratios (DAR). Quality control was performed using UV spectrophotometry, size exclusion HPLC, bioanalyzer, biolayer interferometry (BLI), and flow cytometry in EGFR-positive DLD-1, MDA-MB-468 (high density EGFR), and HT-29 (very low EGFR density) cells. Control antibody drug conjugates were developed using a human anti-maltose binding protein (MBP) antibody. BLI showed that the binding of nimotuzumab-PEG6-DM1-Low and nimotuzumab-PEG6-DM1-High was slightly but significantly affected by conjugation of the drug (nimotuzumab KD 0.89 ± 0.02 nM < nimotuzumab-PEG6-DM1-Low KD 1.94 ± 0.02 nM < nimotuzumab-PEG6-DM1-High KD 3.75 ± 0.03 nM). In vitro cytotoxicity was determined following incubation of cells with the immunoconjugates and IC50 values were determined. Nimotuzumab-PEG6-DM1-Low and nimotuzumab-PEG6-DM1-High were used to treat EGFR positive KRAS mutant DLD-1 colorectal cancer xenograft. DLD-1 cells were transduced with a red fluorescent protein (iRFP702) to allow the use of near infrared imaging (NIR) for tumor response monitoring. In vitro potency correlated with the number of drugs on antibody, with nimotuzumab-PEG6-DM1-High showing higher activity than nimotuzumab-PEG6-DM1-Low. Three doses (15 mg/kg) of the ADCs prolonged the survival of DLD-1-iRFP-702 tumor bearing mice as monitored by NIR. Nimotuzumab-PEG6-DM1-Low resulted in 4/6 complete cure while nimotuzumab-PEG6-DM1-High resulted in 2/5 complete cure. The novel ADCs were very effective in a colorectal cancer model in vivo.
Keywords: PEGylated maytansine; antibody drug conjugates; colorectal cancer; epidermal growth factor receptor I; near infrared imaging.