Transcriptome sequencing reveals two subtypes of cortisol-secreting adrenocortical tumours in dogs and identifies CYP26B1 as a potential new therapeutic target

Cushing's syndrome (CS) is a serious endocrine disorder that is relatively common in dogs, but rare in humans. In similar to 15%-20% of cases, CS is caused by a cortisol-secreting adrenocortical tumour (csACT). To identify differentially expressed genes that can improve prognostic predictions after surgery and represent novel treatment targets, we performed RNA sequencing on csACTs (n = 48) and normal adrenal cortices (NACs; n = 10) of dogs. A gene was declared differentially expressed when the adjusted p-value was 2 or < -2. Between NACs and csACTs, 98 genes were differentially expressed. Based on the principal component analysis (PCA) the csACTs were separated in two groups, of which Group 1 had significantly better survival after adrenalectomy (p = .002) than Group 2. Between csACT Group G1 and Group 2, 77 genes were differentially expressed. One of these, cytochrome P450 26B1 (CYP26B1), was significantly associated with survival in both our canine csACTs and in a publicly available data set of 33 human cortisol-secreting adrenocortical carcinomas. In the validation cohort, CYP26B1 was also expressed significantly higher (p = .012) in canine csACTs compared with NACs. In future studies it would be interesting to determine whether CYP26B1 inhibitors could inhibit csACT growth in both dogs and humans.

Automated summary

Cushing's syndrome (CS) is more common in dogs and is caused by cortisol-secreting adrenocortical tumours (csACTs) in a significant percentage of cases. By performing RNA sequencing on csACTs and normal adrenal cortices (NACs) of dogs, differentially expressed genes were identified that can improve prognosis and serve as treatment targets. Cytochrome P450 26B1 (CYP26B1) was found to be significantly associated with survival in both canine and human csACTs. Further research could explore the potential use of CYP26B1 inhibitors for inhibiting csACT growth in dogs and humans.