Antisense Oligonucleotides as a Novel Therapy for Cushing’s Disease

Background: Cushing’s disease (CD) is caused by high levels of blood cortisol resulting from excess secretion of ACTH from a corticotroph adenoma in the anterior pituitary gland. Clinical features include hypertension, diabetes, osteoporosis, and depression. If untreated CD has an increased mortality of five-fold owing to cardiovascular comorbidities, stroke or raised vulnerability to infection. Transsphenoidal surgery is considered the first-line treatment but remission is achieved in only 65% of cases and the relapse rate is high. Furthermore, medical treatments are often accompanied by unpleasant side-effects. Antisense therapy is a technique for suppressing gene expression at the level of translation using antisense oligonucleotides (ASOs) against the mRNA of interest. Aims: To investigate antisense therapy as a treatment for CD by targeting ASOs against ACTH-encoding POMC mRNA thereby reducing secretion of the hormone. To transfect mouse AtT20 cells (cells that secrete high levels of ACTH) with ASOs against POMC at varying doses to determine which is the most effective at reducing ACTH secretion. Methods: AtT-20 cells that secrete high levels of ACTH were used as the model system. ASOs were designed to specifically target exon 3 of the POMC gene. Transfection of AtT-20 was carried out using Lipofectamine. FACS was used to determine transfection efficiency. ACTH levels secreted by AtT-20 cells were determined by immunoassay. Statistical analysis was done using ANOVA with P values < 0.05 considered significant. Results: ASOs that targeted POMC exon 3 (ASO-2 and ASO-3) were transfected into AtT-20 cells at 10 and 100 nM. Control ASOs were ASO-1 (matched to POMC sense strand) and ASO-4 (a scrambled version of ASO-3). Experiments included untreated AtT-20 cells and AtT-20 cells treated with transfection reagent or ASOs alone. The results of six experiments indicated that ACTH secretion from AtT-20 cells was reduced after transfection with ASO-2 and ASO-3 at 100 nM (ANOVA, P = < 0.05) and 10 nM (ANOVA, P < 0.05) when compared with untreated AtT20 cells. ASO-1 and ASO-4 had no effect on ACTH secretion by AtT-20 cells (ANOVA, P > 0.05). Conclusions: Initial experiments have shown that ASOs against POMC can reduce ACTH secretion from AtT-20 cells and may be useful as a novel therapy for CD.