Engineering anti-Lewis-Y hu3S193 antibodies with improved therapeutic ratio for radioimmunotherapy of epithelial cancers

Background: The aim of the study was to explore Fc mutations of a humanised anti-Lewis-Y antibody (IgG1) hu3S193 as a strategy to improve therapeutic ratios for therapeutic payload delivery. Methods: Four hu3S193 variants (I253A, H310A, H435A and I253A/H310A) were generated via site-directed mutagenesis and radiolabelled with diagnostic isotopes iodine-125 or indium-111. Biodistribution studies in Lewis-Y-positive tumour-bearing mice were used to calculate the dose in tumours and organs for therapeutic isotopes (iodine-131, yttrium-90 and lutetium-177). Results: In-111-labelled I253A and H435A showed similar slow kinetics (t(1/2 beta), 63.2 and 62.2 h, respectively) and a maximum tumour uptake of 33.11 +/- 4.05 and 33.69 +/- 3.77 percentage injected dose per gramme (%ID/g), respectively. 111In-labelled I253A/H310A cleared fastest (t(1/2 beta), 9.1 h) with the lowest maximum tumour uptake (23.72 +/- 0.85 % ID/g). The highest increase in tumour-to-blood area under the curve (AUC) ratio was observed with the metal-labelled mutants (Y-90 and Lu-177). Lu-177-CHX-A" DTPA-hu3S193 I253A/H310A (6:1) showed the highest tumour-to-blood AUC ratio compared to wild type (3:1) and other variants and doubling of calculated dose to tumour based on red marrow dose constraints. Conclusions: These results suggest that hu3S193 Fc can be engineered with improved therapeutic ratios for Y-90- and Lu-177-based therapy, with the best candidate being hu3S193 I253A/H310A for Lu-177-based therapy.