Abstract
PurposeTo investigate the role of heat-shock protein Hsp90 in adrenocorticotropic hormone (ACTH)-secreting cells, and to explore the potential clinical application of an inhibitor of Hsp90, 17-N-allylamino-17-demethoxygeldanamycin(17-AAG) in corticotropinomas [also known as “Cushing’s disease” (CD)].MethodsCulture of mouse pituitary tumor [AtT-20/D16v-F2 (ATCC® CRL-1795™)] cells and human pituitary ACTH-secreting tumor cells were employed. Hepatocellular carcinoma cell line (HLE) was used to evaluate EGFR inhibition by 17-AAG. Cell viability was evaluated using a commercial kit. The ACTH level was measured by a radioimmunoassay. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to measure expression of proopiomelanocortin (POMC) mRNA. Western blotting was done to measure protein levels.Results17-AAG suppressed the viability and proliferation, and promoted the apoptosis, of AtT-20/D16v-F2 cells. 17-AAG suppressed the synthesis and secretion of ACTH in AtT-20/D16v-F2 cells and down-regulated POMC transcription. 17-AAG acted in a similar pattern upon treatment with human pituitary ACTH-secreting tumor cells. Inhibition by 17-AAG was stronger in human pituitary ACTH-secreting tumor cells carrying the ubiquitin-specific protease-8 (USP8) mutant in comparison with cells carrying wild-type USP8.ConclusionsThe HSP90 inhibitor 17-AAG reduced the viability and secretory function of human pituitary ACTH-secreting tumor cells, and tumor cells carrying the USP8 mutant were more sensitive to 17-AAG than tumor cells carrying wild-type USP8. 17-AAG could be a potential treatment option for CD.
Highlights
Pituitary adenoma is one of the most common tumors appearing at sella
In the USP8 mutant group, 17-AAG inhibited POMC translation significantly (74% inhibition, p=0.02); While a trend towards reduced POMC expression was noted in the wild type group (63%inhibition, p=0.06), which meant the therapeutic validity manifested on function damage in tumor cells carrying the USP8 mutant were more sensitive
We found that the epidermal growth factor receptors (EGFRs) expression in model cells decreased after 17-AAG treatment, as well as HSP90
Summary
Pituitary adenoma is one of the most common tumors appearing at sella. Corticotropinoma accounts for about 2%−6% of pituitary adenomas [1]. Corticotropinoma (Cushing disease) is responsible for ~85% of cases of Cushing’s syndrome [2]. The clinical manifestations of hypercortisolemia are weight gain, fat redistribution, central obesity, purple striae, ecchymoses, muscle atrophy, and related complications [e.g., hypertension, diabetes mellitus, hyperlipidemia, mental/psychological disorders, osteoporosis, deep-vein thrombosis [2]]. First-line treatment for CD is transsphenoidal surgery, which carries a remission rate of 80%–90% and recurrence of approximately 10–20% [3]. Patients with persistent disease can undergo secondary procedure, which carries a remission rate of ≤50% [4]. Radiotherapy or medication are options for patients who cannot achieve remission by surgery [5]
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