Monocyte- and Macrophage-Mediated Antibody Sequestration Attenuates Anti-Epidermal Growth Factor Receptor Antibody...

Tumor-associated monocytes and macrophages are abundant in the tumor microenvironment (TME) and can influence the therapeutic accessibility of antibody drugs. However, the impact of macrophage-mediated antibody sequestration on the therapeutic efficacy of anti-epidermal growth factor receptor (EGFR) therapy remains unclear. This study aimed to assess whether monocytes and macrophages attenuate anti-EGFR therapeutic efficacy by sequestering antibodies. We established a transwell-based co-culture platform using human THP-1 monocytes or macrophages and EGFR-positive DiFi colorectal cancer cells to evaluate macrophage-associated antibody sequestration. In vivo xenograft assays, flow cytometric uptake analyses and inhibitor-based functional studies were performed using the anti-EGFR monoclonal antibodies cetuximab and panitumumab. Xenograft models co-implanted with THP-1 cells demonstrated attenuated responses to anti-EGFR antibodies compared to tumor-only models. Monocytes and macrophages significantly reduced the growth-inhibitory effects of cetuximab and panitumumab in co-culture. Antibody uptake was increased in THP-1 cells and THP-1-derived macrophages. Fc receptor blockade and uptake-associated inhibitors partially suppressed antibody uptake and restored antibody-mediated anti-tumor activity, suggesting the involvement of FcγR-dependent and FcγR-independent pathways. Monocyte- and macrophage-mediated antibody sequestration attenuates anti-EGFR therapeutic efficacy by reducing antibody accessibility to tumor cells. The established co-culture platform provides a useful bioanalytical assay system to screen and evaluate antibody accessibility and macrophage-associated sequestration during the preclinical development of antibody therapeutics.