Abstract
Immunotherapies are treatments that use a patient's immune system to combat disease. One important type of immunotherapy employed in cancer treatments is the delivery of monoclonal antibodies to block growth receptors. In this manuscript, we develop a methodology that enables accurate and simple evaluation of antibody-type drug delivery using MALDI-MSI. To overcome the mass-range limitation that prevents the detection of large therapeutic antibodies, we used in situ reduction and alkylation to break disulfide bonds to generate smaller fragments. These smaller fragments are more readily ionized and detected by MALDI-MSI without loss of spatial information on the parent drug. As a proof of concept study, we evaluated the distribution of cetuximab in 3D colon cell cultures. Cetuximab is a monoclonal antibody that binds to the extracellular domain of epidermal-growth-factor receptor (EGFR), which is often overexpressed in colorectal cancer (CRC) and mediates cell differentiation, proliferation, migration, and angiogenesis. Cetuximab directly inhibits tumor growth and metastasis and induces apoptosis. By performing on-tissue reduction followed by MALDI-MSI analysis, we successfully mapped the time-dependent penetration and distribution of cetuximab in spheroids derived from two different colon-cancer cell lines (HT-29 and DLD-1). The localization patterns were further confirmed with IF staining of the drug. Changes in other biomolecules following drug treatment were also observed, including the elevation of ATP in spheroids. The developed method has also been applied to map cetuximab distribution in patient-derived colorectal-tumor organoids (CTOs). Overall, we believe this powerful label-free approach will be useful for visualizing the heterogeneous distribution of antibody drugs in tissues and tumors and will help to monitor and optimize their use in the clinic.