The RORγt nuclear
receptor (NR) is of critical importance
for the differentiation and proliferation of T helper 17 (Th17) cells
and their production of the pro-inflammatory cytokine IL-17a. Dysregulation
of RORγt has been linked to various autoimmune diseases, and
small molecule inhibition of RORγt is therefore an attractive
strategy to treat these diseases. RORγt is a unique NR in that
it contains both a canonical, orthosteric and a second, allosteric
ligand binding site in its ligand binding domain (LBD). Hence, dual
targeting of both binding pockets constitutes an attractive alternative
molecular entry for pharmacological modulation. Here, we report a
chemical biology approach to develop a bitopic ligand for the RORγt
NR, enabling concomitant engagement of both binding pockets. Three
candidate bitopic ligands,
Bit-L15
,
Bit-L9
, and
Bit-L4
, comprising an orthosteric and allosteric
RORγt pharmacophore linked via a polyethylene glycol (PEG) linker,
were designed, synthesized, and evaluated to examine the influence
of linker length on the RORγt binding mode.
Bit-L15
and
Bit-L9
show convincing evidence of concomitant
engagement of both RORγt binding pockets, while the shorter
Bit-L4
does not show this evidence, as was anticipated during
the ligand design. As the most potent bitopic RORγt ligand,
Bit-L15
, antagonizes RORγt function in a potent manner
in both a biochemical and cellular context. Furthermore,
Bit-L15
displays an increased selectivity for RORγt over RORα
and PPARγ compared to the purely orthosteric and allosteric
parent compounds. Combined, these results highlight potential advantages
of bitopic NR modulation over monovalent targeting strategies.