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

The efficacy of affinity-based treatments for cancer and other diseases is often limited by poor distribution throughout the targeted tissue. Although lower-affinity antibodies will penetrate more uniformly, these often reach lower concentrations because of their rapid clearance from the tissue. To increase retention and improve distribution, we created low-affinity photocrosslinkable affibodies that can diffuse into dense tumor matrices with limited tumor barrier formation and then be photocrosslinked in place to cell receptors to increase retention. In testing with 3D tumor spheroids, the addition of a 50 nM photocrosslinkable affibody showed a similar level of accumulation at the edges of the spheroid but a higher level near the middle of the spheroid than the wild-type (non-photocrosslinkable) affibody. These results show that target affinity affects protein transport in tumor microenvironments and that covalently cross-linking the ligands to cells may improve both their transport and retention.