Photocrosslinkable, Low-Affinity Affibodies Show Improved\nTransport and Retention in 3D Tumor Spheroids

The\nefficacy of affinity-based treatments for cancer and other\ndiseases is often limited by poor distribution throughout the targeted\ntissue. Although lower-affinity antibodies will penetrate more uniformly,\nthese often reach lower concentrations because of their rapid clearance\nfrom the tissue. To increase retention and improve distribution, we\ncreated low-affinity photocrosslinkable affibodies that can diffuse\ninto dense tumor matrices with limited tumor barrier formation and\nthen be photocrosslinked in place to cell receptors to increase retention.\nIn testing with 3D tumor spheroids, the addition of a 50 nM photocrosslinkable\naffibody showed a similar level of accumulation at the edges of the\nspheroid but a higher level near the middle of the spheroid than the\nwild-type (non-photocrosslinkable) affibody. These results show that\ntarget affinity affects protein transport in tumor microenvironments\nand that covalently cross-linking the ligands to cells may improve\nboth their transport and retention.