Synchrotron diffraction reveals distinct collagen-associated distributions of EGFR-targeted antibody and affibody in pancreatic tumors

Significance: Tumor extracellular matrix may influence the distribution of targeted agents differently across molecular formats. We compared how an antibody and an affibody targeting the same receptor distribute relative to collagen associated tissue structure in pancreatic tumors. Methods: Cetuximab IRDye700DX, an epidermal growth factor receptor (EGFR) targeted fluorescent antibody, and ABY029, an EGFR targeted fluorescent affibody, were coadministered intravenously to 12 athymic nude mice bearing orthotopic pancreatic tumors: eight AsPC1 and four PANC1. Tumors were harvested at 3 or 24 h after injection, with four AsPC1 and two PANC1 mice at each time. Fluorescence images from 21 tissue slices were registered to scanning synchrotron X ray diffraction (XRD) maps to compare the distribution of each agent with local collagen associated diffraction intensity. Results: Cetuximab XRD correlations were negative in all 12 mice at every evaluated binning scale (100 to 400 microns, all adjusted P = 0.0039). Cohort average correlations were more negative for cetuximab than ABY029 at all four scales (paired adjusted P = 0.0137 to 0.0381). Conclusions: Cetuximab exhibited consistent inverse spatial associations with collagen-associated diffraction and stronger cohort-average associations than ABY029. These findings show that agents targeting the same receptor can differ in their relationships with local tissue structure and support spatially resolved assessment of tissue access when selecting molecular formats for imaging and therapy.