Effects of antisense DNA on POMC mRNA and ACTH levels in cultured human corticotroph adenoma cells

Antisense oligonucleotides have been investigated in recent years as potential new therapeutic agents because of their ability to shut off gene expression. Antisense DNA and RNA oligomers can bind specifically to mRNA preventing protein translation. We have studied the ability of an antisense POMC oligomer to reduce the expression of POMC in human ACTH-secreting pituitary adenoma cells cultured from 2 uncommon ACTH-secreting macroadenomas. In separate experiments, tumor tissue was enzymatically dispersed, cultured for 4 days, and treated with and without an antisense POMC oligonucleotide for 18 hours. In addition, cells from one tumor were treated with dexamethasone and cells from the other tumor were treated with an unrelated oligomer as controls. RNA was prepared from cultured cells and POMC mRNA was quantitated in a RNase protection assay using a human POMC RNA probe. ACTH in the media was quantitated by RIA. Tumor cells responded to 250 nmol/L dexamethasone with diminished POMC mRNA and ACTH levels 18 hours after treatment (decreased by 28% and 67% of control respectively). In both tumors, a POMC antisense oligomer at a concentration of 50 μmol/L lowered POMC mRNA levels and detectable ACTH levels in the media 18 hours after treatment, with mRNA levels decreased by 76% and 62% of control and ACTH levels decreased by 58% and 48% of control. Conversely, tumor cells treated with an unrelated oligomer at a 50 μmol/L concentration showed minimal effect on POMC mRNA and ACTH levels 18 hours after treatment (decreased by 2.3% and 1.5% of control respectively). Our findings confirm the effects of antisense oligonucleotides in other systems and suggest that therapeutic investigations using these techniques may have application to syndromes of hormone excess.