Metformin inhibits cell proliferation and ACTH secretion in AtT20 cells via regulating the MAPK pathway.

We investigated the impact of metformin on ACTH secretion and tumorigenesis in pituitary corticotroph tumors. The mouse pituitary tumor AtT20 cell line was treated with varying concentrations of metformin. Cell viability was assessed using the CCK-8 assay, ACTH secretion was measured using an ELISA kit, changes in the cell cycle were analyzed using flow cytometry, and the expression of related proteins was evaluated using western blotting. RNA sequencing was performed on metformin-treated cells. Additionally, an in vivo BALB/c nude xenograft tumor model was established in nude mice, and immunohistochemical staining was conducted for further verification. Following metformin treatment, cell proliferation was inhibited, ACTH secretion decreased, and G1/S phase arrest occurred. Analysis of differentially expressed genes revealed cancer-related pathways, including the MAPK pathway. Western blotting confirmed a decrease in phosphorylated ERK1/2 and phosphorylated JNK. Combining metformin with the ERK1/2 inhibitor Ulixertinib resulted in a stronger inhibitory effect on cell proliferation and POMC (Precursors of ACTH) expression. In vivo studies confirmed that metformin inhibited tumor growth and reduced ACTH secretion. In conclusion, metformin inhibits tumor progression and ACTH secretion, potentially through suppression of the MAPK pathway in AtT20 cell lines. These findings suggest metformin as a potential drug for the treatment of Cushing's disease.

Neuromedin B receptor as a potential therapeutic target for corticotroph adenomas.

PURPOSE: Cushing's disease (CD) results from autonomous adrenocorticotropic hormone (ACTH) secretion by corticotroph adenomas, leading to excessive cortisol production, ultimately affecting morbidity and mortality. Pasireotide is the only FDA approved tumor directed treatment for CD, but it is effective in only about 25% of patients, and is associated with a high rate of hyperglycemia. Neuromedin B (NMB), a member of the bombesin-like peptide family, regulates endocrine secretion and cell proliferation. Here, we assessed NMB and NMB receptor (NMBR) expression in human corticotroph adenomas and the effects of NMBR antagonist PD168368 on murine and human corticotroph tumors. METHODS: To investigate NMB and NMBR expression, real-time qPCR and immunostaining on human pathological specimens of corticotroph, non-functional and somatotroph adenomas were performed. The effects of PD168368 on hormone secretion and cell proliferation were studied in vitro, in vivo and in seven patient-derived corticotroph adenoma cells. NMB and NMBR were expressed in higher extent in human corticotroph adenomas compared with non-functional or somatotroph adenomas. RESULTS: In murine AtT-20 cells, PD168368 reduced proopiomelanocortin (Pomc) mRNA/protein expression and ACTH secretion as well as cell proliferation. In mice with tumor xenografts, tumor growth, ACTH and corticosterone were downregulated by PD168368. In patient-derived adenoma cells, PD168368 reduced POMC mRNA expression in four out of seven cases and ACTH secretion in two out of five cases. A PD168368-mediated cyclin E suppression was also identified in AtT-20 and patient-derived cells. CONCLUSION: NMBR antagonist represents a potential treatment for CD and its effect may be mediated by cyclin E suppression.

Innovative tumour targeting therapeutics in Cushing's disease.

Cushing's disease (CD) is the most frequent form of endogenous hypercortisolism. Management of this devastating condition relies on pituitary surgery, while effective pharmacological treatment mainly focus on periphery targeting pharmaceuticals. Approved tumour-targeting drugs are limited to dopamine agonists and somatostatin analogues with frequently low efficacy and substantial side effects. Discoveries on the genetics and pathophysiology of corticotroph tumorigenesis brought forward new potential pharmacological targets. Compounds such as retinoic acid although promising in preclinical studies, are not as efficient in the clinic. Others, such as, silibinin, gefitinib and roscovitine are effective in preclinical models, but their efficacy and safety still needs to be determined in patients with CD.

Aberrant Nuclear Translocation of E2F1 and Its Association in Cushing's Disease.

Nonsurgical medical treatments are often performed for Cushing's disease due to high recurrence rates. However, current medical treatment that targets corticotroph adenomas are limited. To develop a treatment that specifically targets corticotrophs in Cushing's disease, it is necessary to identify corticotroph lineage-specific proteins, which are involved in the Cushing's tumor phenotype. We have previously reported that the expression of E2F transcription factor 1 (E2F1), one of the cell cycle regulatory proteins, was increased in corticotrophs in Cushing's disease model mice and was involved in the regulation of POMC gene expression. Phosphorylation of Ser337 of E2F1 (pS337-E2F1) facilitates its binding to the POMC promoter, which was suggested to contribute to elevated POMC expression in corticotrophs. Here, we report that E2F1 expression is specific to the corticotroph lineage in normal human pituitaries and that the E2F1 protein is localized in the cytosol in normal corticotrophs. We show that pS337-E2F1 is localized in the nucleus specifically in Cushing's tumors, while it is localized in the perinuclear cytoplasm in the normal pituitary. This observation demonstrates that pS337 is a marker for Cushing's tumors and suggests that phosphorylation of E2F1 may be a target for developing a novel pharmacological treatment for tumorigenesis and hormone dysregulation of Cushing's disease.

Therapeutic difficulties in an aggressive ACTH-secreting pituitary adenoma.

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Successful management of a patient with active Cushing's disease complicated with coronavirus disease 2019 (COVID-19) pneumonia.

We provide the details of the successful management of a patient with active Cushing's disease complicated with coronavirus disease 2019 (COVID-19) pneumonia. The patient was a 27-year-old Japanese female healthcare worker who was scheduled to undergo pituitary surgery for Cushing's disease. She had been in close contact with an undiagnosed patient infected with COVID-19 and then developed COVID-19 pneumonia. Despite a lack of known risk factors associated with severe COVID-19 infection, the patient's dyspnea worsened and her respiratory condition deteriorated, as indicated by the need for 7 L/min oxygen supply by mask to maintain her oxygen saturation at >90%. Medical treatment was initiated to control hypercortisolism by the 'block and replace' regimen using steroidogenesis inhibitors and hydrocortisone. The COVID-19 pneumonia improved with multi-modal treatment including antiviral therapy. One month later, after a negative severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) test result and with appropriate protection against virus transmission to medical staff in the operating room and daily medical care nurses, trans-sphenoidal surgery was performed by our highly experienced pituitary surgeon. One month after the surgery, the patient's basal ACTH and cortisol levels and urinary free cortisol were all under the detection limit. Surgical remission was expected. Since hypercortisolism due to active Cushing's disease may worsen a COVID-19 infection, multi-disciplinary management that includes appropriate and prompt treatment strategies is mandatory in such cases.

Resistance to Dopamine Agonists in Pituitary Tumors: Molecular Mechanisms.

Pituitary neuroendocrine tumors (PitNET) are commonly benign tumors accounting for 10-25% of intracranial tumors. Prolactin-secreting adenomas represent the most predominant type of all PitNET and for this subtype of tumors, the medical therapy relies on the use of dopamine agonists (DAs). DAs yield an excellent therapeutic response in reducing tumor size and hormonal secretion targeting the dopamine receptor type 2 (D2DR) whose higher expression in prolactin-secreting adenomas compared to other PitNET is now well established. Moreover, although DAs therapy does not represent the first-line therapy for other PitNET, off-label use of DAs is considered in PitNET expressing D2DR. Nevertheless, DAs primary or secondary resistance, occurring in a subset of patients, may involve several molecular mechanisms, presently not fully elucidated. Dopamine receptors (DRs) expression is a prerequisite for a proper DA function in PitNET and several molecular events may negatively modify DR membrane expression, through the DRs down-regulation and intracellular trafficking, and DR signal transduction pathway. The current mini-review will summarise the presently known molecular events that underpin the unsuccessful therapy with DAs.

Glucocorticoid Receptor Antagonism Upregulates Somatostatin Receptor Subtype 2 Expression in ACTH-Producing Neuroendocrine Tumors: New Insight Based on the Selective Glucocorticoid Receptor Modulator Relacorilant.

Somatostatin exhibits an inhibitory effect on pituitary hormone secretion, including inhibition of growth hormone and adrenocorticotropic hormone (ACTH), and it can have antisecretory and antitumor effects on neuroendocrine tumors (NETs) that express somatostatin receptors. Although the precise mechanism remains unclear, the finding that glucocorticoids downregulate somatostatin receptor subtype 2 (SSTR2) expression has been used to explain the lack of efficacy of traditional SSTR2-targeting analogs in patients with ACTH-secreting NETs. Glucocorticoid receptor (GR) antagonism with mifepristone has been shown to reverse the glucocorticoid-induced downregulation of SSTR2; however, the effects of GR modulation on SSTR2 expression in ACTH-secreting NETs, particularly corticotroph pituitary tumors, are not well known. The current study presents new insight from in vitro data using the highly selective GR modulator relacorilant, showing that GR modulation can overcome dexamethasone-induced suppression of SSTR2 in the murine At-T20 cell line. Additional data presented from clinical case observations in patients with ACTH-secreting NETs suggest that upregulation of SSTR2 via GR modulation may re-sensitize tumors to endogenous somatostatin and/or somatostatin analogs. Clinical, laboratory, and imaging findings from 4 patients [2 ACTH-secreting bronchial tumors and 2 ACTH-secreting pituitary tumors (Cushing disease)] who were treated with relacorilant as part of two clinical studies (NCT02804750 and NCT02762981) are described. In the patients with ectopic ACTH secretion, SSTR2-based imaging (Octreoscan and 68Ga-DOTATATE positron emission tomography) performed before and after treatment with relacorilant showed increased radiotracer uptake by the tumor following treatment with relacorilant without change in tumor size at computed tomography. In the patients with Cushing disease who received relacorilant prior to scheduled pituitary surgery, magnetic resonance imaging after a 3-month course of relacorilant showed a reduction in tumor size. Based on these findings, we propose that GR modulation in patients with ACTH-secreting NETs upregulates previously suppressed SSTR2s, resulting in tumor-specific antisecretory and anti-proliferative effects. The effect of relacorilant on pituitary corticotroph tumors is being investigated in an ongoing phase 3 study (NCT03697109; EudraCT 2018-003096-35).

Immune checkpoint inhibitor therapy for ACTH-secreting pituitary carcinoma: a new emerging treatment?

BACKGROUND: Pituitary carcinomas are rare but aggressive and require maximally coordinated multimodal therapies. For refractory tumors, unresponsive to temozolomide (TMZ), therapeutic options are limited. Immune checkpoint inhibitors (ICI) may be considered for treatment as illustrated in the present case report. CASE: We report a patient with ACTH-secreting pituitary carcinoma, progressive after multiple lines of therapy including chemotherapy with TMZ, who demonstrated disease stabilization by a combination of ipilimumab (anti-CTLA-4) and nivolumab (anti-PD-1) ICI therapy. DISCUSSION: Management of pituitary carcinoma beyond TMZ remains ill-defined and relies on case reports. TMZ creates, due to hypermutation, more immunogenic tumors and subsequently potential candidates for ICI therapy. This case report adds support to the possible role of ICI in the treatment of pituitary carcinoma. CONCLUSION: ICI therapy could be a promising treatment option for pituitary carcinoma, considering the mechanisms of TMZ-induced hypermutation with increased immunogenicity, pituitary expression of CTLA-4 and PD-L1, and the frequent occurrence of hypophysitis as a side effect of ICI therapy.

Targeting Corticotroph HDAC and PI3-Kinase in Cushing Disease.

CONTEXT: Cushing disease (CD) is a life-threatening disorder. Therapeutic goals include symptom relief, biochemical control, and tumor growth inhibition. Current medical therapies for CD by and large exert no action on tumor growth. OBJECTIVE: To identify drugs that inhibit corticotroph tumor adrenocorticotropic hormone (ACTH) secretion and growth. DESIGN: High throughput screen employing a novel "gain of signal" ACTH AlphaLISA assay. SETTING: Academic medical center. PATIENTS: Corticotroph tumor tissues from patients with CD. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Potent inhibitors of corticotroph tumor ACTH secretion and growth. RESULTS: From a kinase inhibitor library, we identified the dual PI3K/HDAC inhibitor CUDC-907 as a potent inhibitor of murine and human corticotroph tumor ACTH secretion (median effective concentration 1-5 nM), and cell proliferation (median inhibitory concentration 5 nM). In an in vivo murine corticotroph tumor xenograft model, orally administered CUDC-907 (300 mg/kg) reduced corticotroph tumor volume (TV [cm3], control 0.17 ± 0.05 vs CUDC-907 0.07 ± 0.02, P < .05) by 65% and suppressed plasma ACTH (ACTH [pg/mL] control 206 ± 27 vs CUDC-907 47 ± 7, P < .05) and corticosterone (corticosterone [ng/mL] control 180 ± 87 vs CUDC-907 27 ± 5, P < .05) levels by 77% and 85% respectively compared with controls. We also demonstrated that CUDC-907 acts through HDAC1/2 inhibition at the proopiomelanocortin transcriptional level combined with its PI3K-mediated inhibition of corticotroph cell viability to reduce ACTH secretion. CONCLUSIONS: Given its potent efficacy in in vitro and in vivo models of CD, combined with proven safety and tolerance in clinical trials, we propose CUDC-907 may be a promising therapy for CD.

Clinical, Laboratory, and Treatment Profiles of Silent Corticotroph Adenomas That Have Transformed to the Functional Type: A Case Series With a Literature Review.

Purpose: Silent corticotroph adenoma (SCA) is clinically non-functional pituitary adenoma with expression of corticotropin or Tpit. To further understand the characteristics of this rare type of SCA transforming to a functional SCA, we retrospectively reviewed SCAs that converted to typical Cushing's syndrome at a tertiary medical center and the relevant literature. Methods: Patients were identified based on the diagnosis of pituitary adenoma without symptoms of hypercortisolism at the initial visit with positive Immunohistochemical (IHC) staining for corticotropin or Tpit after surgery and subsequent transformation to functional SCAs during the follow-up period from March 1990 to January 2020 at Peking Union Medical College Hospital and in the literature. The characteristics of the clinical manifestations, biochemical results, imaging findings, pathology findings and outcome were analyzed. Results: Altogether, 16 patients were included in the study with an average age of 42.0 ± 12.48 (18-65) years at the first visit. Females were slightly predominant (F:M = 1.3:1). The median time of conversion from the nonfunctional to the functional type was 30 (13.0, 68.3) months. Once a functional SCA developed, the adrenocorticotropic hormone (ACTH) level and 24-h urine free cortisol were increased 3.8- (2.6, 12.9) and 5.3- (2.6, 19.3) fold, respectively, above the normal range. Approximately 50% of the patients had macrocystic changes on pituitary MRI. All 16 patients experienced 1-5 surgeries with a median of 2.5 (2.0, 4.0) surgeries. The proportion of patients with Ki-67 ≥ 3% increased from 22.2% (2/9) at the beginning to 50% (7/14) at the time of functional SCA diagnosis. Thirteen patients received radiotherapy, and 4 patients (30.8%) achieved remission. Four patients with refractory functional SCAs received temozolomide treatment with the normalization of cortisol in 4 cases and reduced tumor volume in 3 cases. Conclusion: In this study, all cases that transformed to functional SCAs were macroadenomas. Hypercortisolism was more severe in functional SCA patients. The tumors tended to have frequent recurrence and were highly invasive. Temozolomide could be a promising treatment for refractory functional SCA cases. Long-term follow-up is needed for nonfunctional SCAs since some cases have the potential to transform to clinical Cushing's syndrome.

Advances in the Medical Treatment of Cushing Disease.

Medical therapy has an adjunctive role in management of Cushing disease. Medical therapy is recommended for patients who received pituitary radiotherapy and are awaiting its salutary effects. Medications are used preoperatively to stabilize the condition of seriously ill patients before surgery. Medical therapy is used to control hypercortisolism in patients with uncertain tumor location. Medical therapies available for management of patients with Cushing disease include steroidogenesis inhibitors, centrally acting agents, and glucocorticoid receptor antagonists. All agents require careful monitoring to optimize clinical effectiveness and manage adverse effects. Novel agents in development may expand the armamentarium for management of this condition.

Glaucoma de ángulo abierto secundario a cortisona endógena por microadenoma hipofisario en un paciente joven, a propósito de un caso / Open angle glaucoma secondary to endogenous cortisone due to pituitary microadenoma in a young patient, a case report

CASO CLÍNICO: Varón de 31 años que fue derivado para valoración tras ser diagnosticado de síndrome de Cushing secundario a un microadenoma hipofisario. En la exploración se observó reducción de la agudeza visual y presión intraocular (PIO) de 48 mmHg en ambos ojos. El segmento anterior fue normal, la papila excavada y el ángulo abierto explorado mediante gonioscopia. Se realizó también campimetría que reveló una afectación avanzada. Se diagnosticó de glaucoma secundario a corticosteroides endógenos y se inició tratamiento médico a la espera de la extirpación del adenoma. La PIO no se normalizó tras la extirpación incompleta del adenoma, por lo que se optó por realizar trabeculectomía para controlarla. Como conclusiones: ante una hipertensión ocular con tumor hipofisario se debe sospechar glaucoma secundario a cortisona endógena; el tratamiento precoz del tumor es necesario para normalizar los niveles de la cortisona y controlar la PIO, el diagnóstico tardío o el tratamiento incompleto de estos tumores puede llevar a no obtener un control adecuado de la PIO

CASE REPORT: A 31-year-old male was referred for evaluation after being diagnosed with Cushing syndrome secondary to a pituitary microadenoma. He presented with a reduced visual acuity and high intraocular pressure (IOP) of 48mmHg in both eyes. The examination with biomicroscopy showed normal anterior segment, increased cup to disc ratio, and open angle. There was a moderate-advanced involvement in the visual field. The patient was diagnosed with glaucoma secondary to endogenous corticosteroids, and medical treatment was initiated pending the removal of the adenoma. The IOP did not return to normal after the incomplete removal of the adenoma, so a trabeculectomy was performed to control the IOP. As conclusions: In the case of an ocular hypertension with pituitary tumour, secondary glaucoma to endogenous cortisone should be suspected. Early treatment of the tumour is necessary to bring the cortisone and IOP levels back to normal. Late diagnosis or incomplete treatment of these tumours may lead to not obtaining adequate IOP control

Long-course temozolomide in aggressive pituitary adenoma: real-life experience in two tertiary care centers and review of the literature.

PURPOSE: Aggressive pituitary adenomas (APAs) and pituitary carcinomas (PCs) are challenging for their invasive nature, resistance to treatment and recurrences. Temozolomide (TMZ) is used with benefit and well-tolerated toxicity profile in APAs and PCs. In most studies patients received ≤ 12 cycles but the best length of treatment is debated since other options after discontinuation are scarce and a second course is mainly unsuccessful. METHODS: We report outcomes of 8 patients with APAs and PCs treated with TMZ for more than 12 continuous cycles with a literature review. Data were retrospectively collected from Padua and Milan University Hospitals. TMZ was used as a single agent (150-200 p.o. mg/m2 daily, 5/28 days) for 14 to 45 cycles. RESULTS: Eight patients (7 M), 7 APAs and 1 PC. Previous treatments included neurosurgery and radiotherapy in all cases except two giant masses (ACTH-silent APA and prolactinoma). No patient had progression disease (PD) during long-term treatment nor toxicities. No one had complete response (CR) but four had partial response (PR). Four ACTH+ tumors maintained stable disease (SD) but the secretion pattern improved in all. After drug withdrawal, three had delayed PD (2 after 18 and one after 29 months, all ACTH+); two are still in SD. CONCLUSIONS: TMZ may be useful and well-tolerated in APAs and PCs as a long-term therapy. PR appears within the first cycles with no escape throughout the treatment; most patients achieve SD. We suggest extended protocols particularly in responsive ACTH+ PAs and PCs, when further therapies may be unsuccessful.

Molecular Mechanisms of Glucocorticoid Resistance in Corticotropinomas: New Developments and Drug Targets.

Cushing's disease is characterized by excessive adrenocorticotropin hormone (ACTH) secretion caused by a corticotroph tumor of the pituitary gland, leading to hypercortisolism and increased morbidity and mortality. The molecular causes of the disease are not completely understood, therefore more research is needed to discover novel molecular targets and more effective treatments. To date, the SSTR-analog pasireotide is the only approved drug for Cushing's Disease treatment that is directly targeting the source of the disease. Targeting directly the activity of glucocorticoid receptor or the factors modulating it might be a new valid option for the medical management of Cushing's disease. Here, we briefly review the molecular mechanisms involved in the glucocorticoid negative feedback and glucocorticoid resistance and examine novel targets and therapies that might effectively restore glucocorticoid sensitivity.

Effects of epigenetic pathway inhibitors on corticotroph tumour AtT20 cells.

Medical treatments for corticotrophinomas are limited, and we therefore investigated the effects of epigenetic modulators, a new class of anti-tumour drugs, on the murine adrenocorticotropic hormone (ACTH)-secreting corticotrophinoma cell line AtT20. We found that AtT20 cells express members of the bromo and extra-terminal (BET) protein family, which bind acetylated histones, and therefore, studied the anti-proliferative and pro-apoptotic effects of two BET inhibitors, referred to as (+)-JQ1 (JQ1) and PFI-1, using CellTiter Blue and Caspase Glo assays, respectively. JQ1 and PFI-1 significantly decreased proliferation by 95% (P < 0.0005) and 43% (P < 0.0005), respectively, but only JQ1 significantly increased apoptosis by >50-fold (P < 0.0005), when compared to untreated control cells. The anti-proliferative effects of JQ1 and PFI-1 remained for 96 h after removal of the respective compound. JQ1, but not PFI-1, affected the cell cycle, as assessed by propidium iodide staining and flow cytometry, and resulted in a higher number of AtT20 cells in the sub G1 phase. RNA-sequence analysis, which was confirmed by qRT-PCR and Western blot analyses, revealed that JQ1 treatment significantly altered expression of genes involved in apoptosis, such as NFκB, and the somatostatin receptor 2 (SSTR2) anti-proliferative signalling pathway, including SSTR2. JQ1 treatment also significantly reduced transcription and protein expression of the ACTH precursor pro-opiomelanocortin (POMC) and ACTH secretion by AtT20 cells. Thus, JQ1 treatment has anti-proliferative and pro-apoptotic effects on AtT20 cells and reduces ACTH secretion, thereby indicating that BET inhibition may provide a novel approach for treatment of corticotrophinomas.

Rapid disease progression in patient with mismatch-repair deficiency pituitary ACTH-secreting adenoma treated with checkpoint inhibitor pembrolizumab.

Secreting pituitary adenomas are tumors for which few treatment options are available, including surgical treatment and management of hormonal imbalance due to altered pituitary secretion. In case of inoperable relapse, radiotherapy or chemotherapeutic treatment can be considered; the effectiveness of these treatments, however, remains limited. In the immunotherapy era, it is necessary to select patients who can benefit from immunotherapeutic treatment. Mismatch repair deficiency is strongly associated with responsiveness to anti-PD-1 in other cancers and can be detected using immunohistochemistry for MLH1, MSH2, MHS6, and PMS2. In this case report, we report a case of rapid disease progression to pembrolizumab in a patient with a MMRd pituitary adrenocorticotropic hormone (ACTH)-secreting adenoma. For the best of our knowledge, we described for the first time, a poor efficacy of pembrolizumab in a patient with ACTH-secreting pituitary adenoma having mismatch repair deficiency probably caused by high levels of cortisol in this patient. Prospective study should be performed to assess the activity of immune checkpoint inhibitor alone or in association with temozolomide in this subsetting of pituitary adenomas.

Regulation of the EGFR Pathway by HSP90 Is Involved in the Pathogenesis of Cushing's Disease.

Purpose: To 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)]. Methods: Culture 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. Results: 17-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. Conclusions: The 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.

Lapatinib decreases the ACTH production and proliferation of corticotroph tumor cells.

Cushing's disease is almost always caused by hypersecretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma. A mutation in the deubiquitinase gene USP8 has been found in human ACTH-producing pituitary adenoma cells. This mutational hotspot hyperactivates USP8, rescuing epidermal growth factor receptor (EGFR) from lysosomal degradation and ensuring its sustained signaling in Cushing's disease. An EGFR inhibitor would be an effective anti-tumor agent in EGFR-related tumors. We investigated the effect of a potent dual tyrosine kinase inhibitor, lapatinib, on ACTH production and cell proliferation in AtT-20 mouse corticotroph tumor cells. Lapatinib decreased proopiomelanocortin (Pomc) mRNA levels and ACTH levels in AtT-20 cells and also inhibited cell proliferation, induced apoptosis, and decreased pituitary tumor-transforming gene 1 (Pttg1), a hallmark of pituitary tumors, mRNA levels. KSN/Slc nude mice were subcutaneously inoculated with AtT-20 cells. After 1 week, the mice were randomized either to control or lapatinib groups. The inhibitor decreased the tumor weight of AtT-20 allografts in vivo versus control mice. Lapatinib also significantly decreased Pomc and Pttg1 mRNA levels in the tumor and plasma ACTH and corticosterone levels in vivo. Thus, lapatinib decreases the ACTH production and proliferation of corticotroph tumor cells. An EGFR-targeting therapy could be an important treatment for Cushing's disease.

Tumor-Directed Therapeutic Targets in Cushing Disease.

Context: The most frequent cause of endogenous hypercortisolism is Cushing disease (CD), a devastating condition associated with severe comorbidities and high mortality. Effective tumor-targeting therapeutics are limited. Design: Search in PubMed with key words "corticotroph" and "Cushing's disease" plus the name of the mentioned therapeutic agent and in associated references of the obtained papers. Additionally, potential therapeutics were obtained from ClinicalTrials.gov with a search for "Cushing disease." Results: At present, the tumor-targeted pharmacological therapy of CD is concentrated on dopamine agonists (cabergoline) and somatostatin analogs (pasireotide) with varying efficacy, escape from response, and considerable side effects. Preclinical studies on corticotroph pathophysiology have brought forward potential drugs such as retinoic acid, silibinin, and roscovitine, whose efficacy and safety remain to be determined. Conclusions: For many patients with CD, effective tumor-targeted pharmacological therapy is still lacking. Coordinated efforts are pivotal in establishing efficacy and safety of novel therapeutics in this rare but devastating disease.