Small-Molecule Inhibitors of the CD40–CD40L Costimulatory Protein–Protein Interaction

Costimulatory interactions
are required for T cell activation and
development of an effective immune response; hence, they are valuable
therapeutic targets for immunomodulation. However, they, as all other
protein–protein interactions, are difficult to target by small
molecules. Here, we report the identification of novel small-molecule
inhibitors of the CD40–CD40L interaction designed starting
from the chemical space of organic dyes. For the most promising compounds
such as DRI-C21045, activity (IC50) in the low micromolar
range has been confirmed in cell assays including inhibition of CD40L-induced
activation in NF-κB sensor cells, THP-1 myeloid cells, and primary
human B cells as well as in murine allogeneic skin transplant and
alloantigen-induced T cell expansion in draining lymph node experiments.
Specificity versus other TNF-superfamily interactions (TNF-R1–TNF-α)
and lack of cytotoxicity have also been confirmed at these concentrations.
These novel compounds provide proof-of-principle evidence for the
possibility of small-molecule inhibition of costimulatory protein–protein
interactions, establish the structural requirements needed for efficient
CD40–CD40L inhibition, and serve to guide the search for such
immune therapeutics.