Innovative strategy for the selective inhibition of the pathological effects of a multifunctional therapeutic target: the case of USP8 – DruggingUSP8

The DruggingUSP8 project is led by a consortium of four academic and private partners, with complementary expertise in molecular and cellular biology, structural biology, clinical and drug discovery. It aims to specifically inhibit the pathological effects of a multifunctional enzyme, the ubiquitin specific protease USP8, while preserving its essential physiological functions through the discovery of chemical ligands.
Expression of mutated forms of USP8 unable to interact with a 14.3.3 regulatory chaperone is very frequently associated with Cushing's disease, a rare disease caused by the presence of an adenoma in the pituitary gland. This microadenoma is a benign tumor in most cases but which is not always detectable or operable. It is responsible for an increased secretion of corticotropic hormone (ACTH) and consequently an excessive production of cortisol by the adrenal glands, causing a series of very disabling symptoms, including faci-truncular obesity, skin weakness, amyotrophy, osteoporosis, depression, infertility, diabetes, hypertension, cardiovascular events. USP8 can activate an ACTH synthetic pathway, which identifies it as a very promising therapeutic target for the treatment of Cushing's disease.
The project includes in-depth characterization work of USP8 functions in intracellular signaling and ACTH secretion using molecular genetics, cell biology and proteomics strategies. The goal of this work is to identify new USP8 targets and partners and to better understand their physiological and pathological roles. At the same time, the involvement of a university hospital endocrinologist will allow the analysis of a collection of pituitary adenomas available at the Grenoble University Hospital, which, in terms of patient recruitment, is the second center in France in the national register of Cushing's disease. This analysis aims to characterize the presence of USP8 mutations in a new cohort as well as to perform histological section labeling to detect the existence of deregulated partners that may represent new molecular players in the etiology of the disease.
The Edelris Company, which is specialized in drug discovery, will screen its proprietary collection of more than 500,000 molecules using a completely innovative strategy making it possible to select chemical compounds capable of binding with great affinity to USP8. A complementary in silico screening approach will make it possible to predict their binding site, to define molecules likely to have an even stronger affinity and to select other types of commercial compounds capable of binding to USP8 from structural data.
The candidate molecules obtained by these two approaches will be sorted on a set of biological and pharmacological parameters, such as their binding activity to USP8, their ability to decrease the secretion of ACTH in cells in culture, or their pharmacokinetic and toxicological properties, distinguishing also catalytic ligands from chemical binders. These binders will be tested for their ability to prevent the association of USP8 with some of its substrates or partners involved in the secretion of ACTH while preserving other essential properties of the enzyme in healthy cells.
Through a close collaboration between the consortium partners, this project will provide proof of concept that chemical ligands make it possible to target the pathogenic effects of an enzyme. It will also enhance fundamental knowledge on USP8, validate this enzyme as a therapeutic target and select active molecules eligible for the development of new personalized treatments for Cushing's disease. These molecules will be patented to promote their pharmacological development as therapeutic drugs, and the results of this work will be published in open access journals to facilitate the transfer of knowledge to the community of clinicians, patients and researchers.