UC Davis

Classical cadherins are essential cell-cell adhesion proteins that play crucial roles in various diseases. Regulating cell adhesion by modifying classical cadherin interactions holds promise for disease treatment. In this dissertation, I integrate computational simulations, single-molecule biophysics measurements, and cell experiments to elucidate the molecular mechanisms by which monoclonal antibodies modulate cadherin adhesion. First I resolve the molecular mechanisms by which the monoclonal antibodies 19A11 and 66E8 enhance E-cadherin interactions through the stabilization of strand-swap binding motifs, offering potential applications in preventing cancer metastasis. Next, I demonstrate that the monoclonal antibody CQY684 promotes P-cadherin internalization by trapping P-cadherin into an X-dimer binding motif, offering a pathway to deliver drugs to cancer cells that overexpress P-cadherin.

E-cadherin, a member of the classical cadherin family, is a crucial cell-cell adhesion protein with tumor-suppressing properties. Its adhesive state can be modified by monoclonal antibodies 19A11 and 66E8, potentially reducing cancer metastasis. However, the molecular mechanisms by which these antibodies strengthen E-cadherin binding are unclear. In chapters 2 and 3 of this dissertation, I use molecular dynamics simulations and single-molecule atomic force microscopy to reveal that both 19A11 and 66E8 strengthen E-cadherin interactions by forming crucial salt bridges near the strand-swap dimer binding motifs. This research elucidates the fundamental principles for E-cadherin binding enhancement through monoclonal antibodies.

In chapter 4 of this dissertation, I determine the molecular guidelines for engineering monoclonal antibodies that promote the endocytosis of classical cadherins, using P-cadherin as a model. P-cadherin is overexpressed in many malignant cancers and is a popular target for drug delivery antibodies. I show that the antibody CQY684, traps P-cadherin in an X-dimer conformation, strengthening this adhesive structure, and causing the dissociation of the essential adaptor protein p120-catenin from the P-cadherin cytoplasmic domain. This increases the turnover of P-cadherin, facilitating the endo-lysosomal trafficking of P-cadherin. These findings reveal a previously unknown outside-in signaling mechanism, which can be exploited by anti-cadherin antibodies for intracellular drug delivery.

Overall, this dissertation provides valuable insights into the molecular mechanisms by which monoclonal antibodies modify classical cadherin interactions, offering potential applications in cancer treatment and drug delivery.