Abstract:
G protein-coupled receptors (GPCRs) facilitate the majority of signal transductions across
cell membranes in humans, with numerous diseases attributed to inactivating GPCR mutations.
Many of these mutations result in misfolding during nascent receptor synthesis in the endoplasmic
reticulum (ER), resulting in intracellular retention and degradation. Pharmacological chaperones
(PCs) are cell-permeant small molecules that can interact with misfolded receptors in the ER and
stabilise/rescue their folding to promote ER exit and trafficking to the cell membrane. The neurokinin
3 receptor (NK3R) plays a pivotal role in the hypothalamic–pituitary–gonadal reproductive axis.
We sought to determine whether NK3R missense mutations result in a loss of cell surface receptor
expression and, if so, whether a cell-permeant small molecule NK3R antagonist could be repurposed
as a PC to restore function to these mutants. Quantitation of cell surface expression levels of seven
mutant NK3Rs identified in hypogonadal patients indicated that five had severely impaired cell
surface expression. A small molecule NK3R antagonist, M8, increased cell surface expression in four
of these five and resulted in post-translational receptor processing in a manner analogous to the
wild type. Importantly, there was a significant improvement in receptor activation in response to
neurokinin B (NKB) for all four receptors following their rescue with M8. This demonstrates that M8
may have potential for therapeutic development in the treatment of hypogonadal patients harbouring
NK3R mutations. The repurposing of existing small molecule GPCR modulators as PCs represents
a novel and therapeutically viable option for the treatment of disorders attributed to mutations in
GPCRs that cause intracellular retention.
