Temporal Dynamics of PD-L1 Surface in RKO Cells: Characterizing the Reversible Impact of the Small-Molecule Dimerizer BMS-202.

Background/Objectives. Programmed death-ligand 1 (PD-L1) is a critical immune checkpoint protein that enables tumors to evade immune surveillance by suppressing T cell activation. Monoclonal antibodies are currently used to modulate PD-1/PD-L1 interactions. However, several immune-associated adverse effects were ascribed to those treatments. This led to the necessity for small-molecule alternatives like BMS-202. Methods. In this study, we investigated the temporal dynamics of cell-surface PD-L1 in response to the small-molecule dimerizer BMS-202. Treatment with a non-cytotoxic concentration of BMS-202 at 5 µM triggered a transient reduction in surface PD-L1 concentration, reaching its lowest level at 15 min. In the attempt to characterize the fate of PD-L1 following exposure to the BMS-202 dimerizer, we employed a low-pH wash internalization assay. Results. The results demonstrated a transient increase in intracellular PD-L1 within 5-15 min of compound exposure, followed by rapid recovery of surface PD-L1 levels. These findings suggest that BMS-202-induced changes in surface PD-L1 are acute and reversible, with levels returning to baseline within 24 h post-exposure. Conclusions. These findings reveal a dynamic regulatory mechanism where small-molecule-induced dimerization triggers rapid protein trafficking and transient surface depletion. Understanding these temporal dynamics is essential for the development of next-generation small-molecule immune checkpoint inhibitors.