Genetically Engineered Human Pituitary Corticotroph Tumor Organoids Exhibit Divergent Responses To Glucocorticoid Receptor Modulators (2022)

ABSTRACT Cushing’s disease (CD) is a serious endocrine disorder attributed to an ACTH-secreting pituitary neuroendocrine tumor (PitNET) that subsequently causes chronic hypercortisolemia. PitNET regression has been reported following treatment with the investigational selective glucocorticoid receptor (GR) modulator relacorilant, but the mechanisms behind that effect remain unknown. Human PitNET organoid models were generated from induced human pluripotent stem cells (iPSCs) or fresh tissue obtained from CD patient PitNETs (hPITOs). Genetically engineered iPSC derived organoids were used to model the development of corticotroph PitNETs expressing USP48 (iPSC USP48 ) or USP8 (iPSC USP8 ) somatic mutations. Organoids were treated with the GR antagonist mifepristone or the GR modulator relacorilant with or without somatostatin receptor (SSTR) agonists pasireotide or octreotide. In iPSC USP48 and iPSC USP8 cultures, mifepristone induced the predominant expression of SSTR2 with a concomitant increase in ACTH secretion and tumor cell proliferation. Relacorilant predominantly induced SSTR5 expression and tumor cell apoptosis with minimal ACTH induction. Hedgehog signaling mediated the induction of SSTR2 and SSTR5 in response to mifepristone and relacorilant. Relacorilant sensitized PitNET organoid responsiveness to pasireotide. Therefore, our study identified the potential therapeutic use of relacorilant in combination with somatostatin analogs and demonstrated the advantages of relacorilant over mifepristone, supporting its further development for use in the treatment of CD patients. HIGHLIGHTS Cushing disease (CD) is a serious endocrine disorder caused by an adrenocorticotropic hormone (ACTH)-secreting pituitary neuroendocrine tumor (PitNET) that leads to chronic hypercortisolemia Mifepristone (Korlym ® ), a non-selective glucocorticoid receptor (GR) antagonist, is an approved treatment for patients with Cushing disease, and competes with the binding of cortisol to the GR as well as the binding of progesterone to the progesterone receptor. Relacorilant is an investigational selective GR modulator in development for the treatment of Cushing syndrome that, unlike mifepristone, does not bind to the other hormone receptors. Unlike mifepristone, relacorilant does not significantly raise systemic cortisol levels, and cases of PitNET regression with relacorilant have been reported. However, the mechanisms behind these clinical differences remained unknown. PitNET organoids were generated from: 1) CRISPR-Cas9 gene editing of patient iPSCs, and 2) CD patient corticotroph PitNETs (hPITOs) and used to compare the diverse effects of mifepristone and relacorilant in a human-relevant model that recapitulates the PitNET microenvironment in vitro . Mifepristone and relacorilant have different effects on the induction of somatostatin receptor (SSTR) SSTR2 and SSTR5 expression, ACTH secretion and PitNET organoid proliferation and apoptosis. BRIEF COMMENTARY Background Cushing’s disease (CD), a serious endocrine disorder caused by an adrenocorticotropic hormone (ACTH)-secreting pituitary neuroendocrine tumor (PitNET) leads to chronic hypercortisolemia. Approved for the treatment for CD, Mifepristone (Korlym ® ) is a non-selective glucocorticoid receptor (GR) antagonist with additional competitive binding with progesterone for the progesterone receptor. Relacorilant, an investigational selective GR modulator in development for the treatment of CD, does not bind to the other hormone receptors. Translational Significance Patient-derived PitNET organoids recapitulate the tumor microenvironment in vitro. PitNET organoids revealed the advantages of relacorilant over mifepristone, supporting its further development for use in the treatment of CD.