Autophagy inhibition suppresses hormone production and cell growth in pituitary tumor cells: A potential approach to pituitary tumors

Pituitary tumors (PTs) represent about 10% of all intracranial tumors, and most are benign. However, some PTs exhibit continued growth despite multimodal therapies. Although temozolomide (TMZ), an alkylating chemotherapeutic agent, is a first-line medical treatment for aggressive PTs, some PTs are resistant to TMZ. Existing literature indicated the involvement of autophagy in cell growth in several types of tumors, including PTs, and autophagy inhibitors have anti-tumor effects. In this study, the expression of several autophagy-inducible genes, including Atg3, Beclin1, Map1lc3A, Map1lc3b, Ulk1, Wipi2, and Tfe3 in two PT cell lines, the mouse corticotroph AtT-20 cells and the rat mammosomatotroph GH4 cells were identified. Down regulation of Tfe3, a master switch of basal autophagy, using RNA interference, suppressed cell proliferation in AtT-20 cells, suggesting basal autophagy contributes to the maintenance of cellular functions in PT cells. Expectedly, treatment with bafilomycin A1, an autophagy inhibitor, suppressed cell proliferation, increased the cleavage of PARP1, and reduced ACTH production in AtT-20 cells. Treatment with two additional autophagy inhibitors, chloroquine (CQ) and monensin, demonstrated similar effects on cell proliferation, apoptosis, and ACTH production in AtT-20 cells. Also, treatment with CQ suppressed cell proliferation and growth hormone production in GH4 cells. Moreover, the combination of CQ and TMZ had an additive effect on the inhibition of cell proliferation in AtT-20 and GH4 cells. The additive effect of anti-cancer drugs such as CQ alone or in combination with TMZ may represent a novel therapeutic approach for PTs, in particular tumors with resistance to TMZ.

IGF-2-mediated hypoglycemia: a case series and review of the medical therapies for refractory hypoglycemia

Summary

Non-islet cell tumour hypoglycemia (NICTH), typically mediated by insulin-like growth factor 2 (IGF-2), is a rare but highly morbid paraneoplastic syndrome associated with tumours of mesenchymal or epithelial origin. Outside of dextrose administration and dietary modification which provide transient relief of hypoglycemia, resection of the underlying tumour is the only known cure for NICTH. Available medical therapies to manage hypoglycemia include glucocorticoids, recombinant growth hormone, and pasireotide. We report two cases of IGF-2 mediated hypoglycemia. The first was managed surgically to good effect, highlighting the importance of a timely diagnosis to maximise the likelihood of a surgical cure. The second patient had unresectable disease and was managed medically, adding to a growing number of cases supporting the efficacy of glucocorticoids and recombinant growth hormone in NICTH.

Learning points

Recurrent fasting hypoglycemia in the setting of a malignancy should raise suspicion of non-islet cell tumour hypoglycemia (NICTH), which is typically mediated by IGF-2. The initial workup for NICTH should include a serum glucose, C-peptide, insulin, insulin antibodies, beta-hydroxybutyrate, IGF-2, IGF-1, and sulphonylurea screen during a spontaneous or induced hypoglycemic episode. An IGF-2/IGF-1 ratio above 10 is highly suggestive of IGF-2-mediated hypoglycemia if the IGF-2 level is normal or elevated. False positives may be seen with sepsis and cachexia as both IGF-2 and IGF-1 are subnormal in these cases. A low IGF binding protein 3 (IGFBP3), such as in renal failure, may also result in a falsely normal or low IGF-2/IGF-1 ratio. Surgical resection of the associated tumour is curative in most NICTH cases. When the tumour is unresectable, moderate-dose glucocorticoids, low-dose glucocorticoids in combination with recombinant growth hormone, and pasireotide are medical therapies with promising results in controlling NICTH.

Update on Current Evidence for the Diagnosis and Management of Nonfunctioning Pituitary Neuroendocrine Tumors

Pituitary neuroendocrine tumors (PitNETs) are the third most frequently diagnosed intracranial tumors, with nonfunctioning PitNETs (nfPitNETs) accounting for 30% of all pituitary tumors and representing the most common type of macroPitNETs. NfPitNETs are usually benign tumors with no evidence of hormone oversecretion except for hyperprolactinemia secondary to pituitary stalk compression. Due to this, they do not typically present with clinical syndromes like acromegaly, Cushing's disease or hyperthyroidism and instead are identified incidentally on imaging or from symptoms of mass effects (headache, vision changes, apoplexy). With the lack of effective medical interventions, first-line treatment is transsphenoidal surgical resection, however, nfPitNETs often have supra- or parasellar extension, and total resection of the tumor is often not possible, resulting in residual tumor regrowth or reoccurrence. While functional PitNETs can be easily followed for recurrence using hormonal biomarkers, there is no similar parameter to predict recurrence in nfPitNETs, hence delaying early recognition and timely management. Therefore, there is a need to identify prognostic biomarkers that can be used for patient surveillance and as therapeutic targets. This review focuses on summarizing the current evidence on nfPitNETs, with a special focus on potential new biomarkers and therapeutics.

Paraganglioma with High Levels of Dopamine, Dopa Decarboxylase Suppression, Dopamine β-hydroxylase Upregulation and Intra-tumoral Melanin Accumulation: A Case Report with a Literature Review

Object Exclusively dopamine-producing pheochromocytoma/paraganglioma (PPGL) is an extremely rare subtype. In this condition, intratumoral dopamine β-hydroxylase (DBH), which controls the conversion of norepinephrine from dopamine, is impaired, resulting in suppressed norepinephrine and epinephrine production. However, the rarity of this type of PPGL hampers the understanding of its pathophysiology. We therefore conducted genetic and immunohistological analyses of a patient with an exclusively dopamine-producing paraganglioma. Methods Paraganglioma samples from a 52-year-old woman who presented with a 29.6- and 41.5-fold increase in plasma and 24-h urinary dopamine, respectively, but only a minor elevation in the plasma norepinephrine level was subjected to immunohistological and gene expression analyses of catecholamine synthases. Three tumors carrying known somatic PPGL-related gene variants (HRAS, EPAS1) were used as controls. Whole-exome sequencing (WES) was also performed using the patient's blood and tumor tissue. Results Surprisingly, the protein expression of DBH was not suppressed, and its mRNA expression was clearly higher in the patient than in the controls. Furthermore, dopa decarboxylase (DDC), which governs the conversion of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) to dopamine, was downregulated at the protein and gene levels. In addition, melanin, which is synthesized by L-DOPA, accumulated in the tumor. WES revealed no PPGL-associated pathogenic germline variants, but a missense somatic variant (c.1798G>T) in CSDE1 was identified. Conclusion Although pre-operative plasma L-DOPA was not measured, our histological and gene expression analyses suggest that L-DOPA, rather than dopamine, might have been overproduced in the tumor. This raises the possibility of pathophysiological heterogeneity in exclusively dopamine-producing PPGL.

The Impact of Multicultural Interfacility Video Case Conference: A Novel Education Model After the COVID Pandemic

Context

The COVID-19 pandemic challenged undertaking gradual educational activities for residency and fellowship trainees. However, recent technological advances have enabled broadening active learning opportunities through international online conferences.

Objective

The format of our international online endocrine case conference, launched during the pandemic, is introduced. The objective impact of this program on trainees is described.

Methods

Four academic facilities developed a semiannual international collaborative endocrinology case conference. Experts were invited as commentators to facilitate in-depth discussion. Six conferences were held between 2020 and 2022. After the fourth and sixth conferences, anonymous multiple-choice online surveys were administered to all attendees.

Results

Participants included trainees and faculty. At each conference, 3 to 5 cases of rare endocrine diseases from up to 4 institutions were presented, mainly by trainees. Sixty-two percent of attendees reported 4 facilities as the appropriate size for the collaboration to maintain active learning in case conferences. Eighty-two percent of attendees preferred a semiannual conference. The survey also revealed the positive impact on trainees' learning regarding diversity of medical practice, academic career development, and confidence in honing of presentation skills.

Conclusion

We present an example of our successful virtual global case conference to enhance learning about rare endocrine cases. For the success of the collaborative case conference, we suggest smaller cross-country institutional collaborations. Preferably, they would be international, semiannually based, and with recognized experts as commentators. Since our conference has engendered multiple positive effects on trainees and faculty, continuation of virtual education should be considered even after the pandemic era.

Emerging role of signal transducer and activator of transcription 3 (STAT3) in pituitary adenomas

Pituitary adenomas are benign tumours that can cause an individual various clinical manifestations including tumour mass effects and/or the diverse effects of abnormal pituitary hormone secretion. Given the morbidity and limited treatment options for pituitary adenomas, there is a need for better biomarkers and treatment options. One molecule that is of specific interest is the signal transducer and activator of transcription 3 (STAT3), a transcription factor that plays a critical role in mediating cytokine-induced changes in gene expression. In addition, STAT3 controls cell proliferation by regulating mitochondrial activity. Not only does activation of STAT3 play a crucial role in tumorigenesis, including pituitary tumorigenesis, but a number of studies also demonstrate pharmacological STAT3 inhibition as a promising treatment approach for many types of tumours, including pituitary tumours. This review will focus on the role of STAT3 in different pituitary adenomas, in particular, growth hormone-producing adenomas and null cell adenomas. Furthermore, how STAT3 is involved in the cell proliferation and hormone regulation in pituitary adenomas and its potential role as a molecular therapeutic target in pituitary adenomas will be summarized.

L-type amino acid transporter 1, LAT1, in growth hormone-producing pituitary tumor cells

Pituitary tumors (PTs) can cause significant mortality and morbidity due to limited therapeutic options. L-type amino acid transporters (LATs), in particular, the LAT1 isoform, is expressed in a variety of tumor cells. Pharmacological inhibition or genetic ablation of LAT1 can suppress leucine transport into cancer cells, resulting in suppression of cancer cell growth. However, roles of LAT1 in PTs have not been elucidated. Therefore, we assessed LAT1 expression in PTs and evaluated a LAT1-specific inhibitor, JPH203, on rat somatomammotroph tumor cells, GH4 cells. GH4 cells dominantly express LAT1 mRNA rather than other LAT isoforms, whereas LAT2 transcripts were most abundant in normal rat pituitary tissues. JPH203 inhibited leucine uptake and cell growth in GH4 cells in a concentration-dependent manner, and appeared to be independent of the mechanistic target, the rapamycin pathway. Although JPH203 did not induce apoptosis, it suppressed growth hormone production in GH4 cells. Also, genetic downregulation of LAT1 showed similar effects on cell growth and hormone production. These results indicated that restriction of LAT1 substrates by JPH203 modulated both cell growth and hormone production. In conclusion, LAT1 may be a new therapeutic target for PTs because its inhibition leads to suppression of cell growth as well as hormone production. JPH203 may represent a promising drug for clinical use in patients with PTs, with the potential of hormonal control and tumor suppression.

MON-470 Pharmacological Inhibition of LAT1 Suppresses Proliferation and Hormone Synthesis in Rat Pituitary Tumor GH4 Cells [cc1] Synthesis May Be Better as Only mRNAs Were Measured

Pituitary tumors (PTs) occur in almost 17 % of the population and they represent about 10 % of all intracranial tumors. Growth hormone-producing pituitary tumors account for about 12% of pituitary tumors. At present, many patients with this type of pituitary tumor suffer from symptoms and complications caused by abnormal hormone production and/or mass effects due to limited treatment options. L-type amino acid transporter 1 (LAT1/SLC7A5) delivers essential amino acids into cells, and higher expression of LAT1 has been detected in various types of cancer including gliomas and pancreatic cancers. Furthermore, several lines of evidence suggest that blockade of LAT1 in tumor cells suppresses mammalian target of rapamycin complex (mTORC) 1 activity, resulting in either cell growth arrest or apoptotic cell death. However, LAT1 expression has not been elucidated in normal pituitary glands or PTs. In addition, the effects of LAT1 inhibition on cell growth and hormone synthesis in PTs also remain unknown. Here we show that LAT1, with expression comparable to LAT2, LAT3 and LAT4 in the normal mouse pituitary gland, is predominantly expressed in rat pituitary tumor GH4 cells, which secrete GH and PRL. An LAT1-specific inhibitor, JPH203, provided by J-Pharma Co., Ltd., Yokohama Japan, suppressed growth of these cells as well as GH and PRL synthesis. Water-Soluble Tetrazolium salt (WST)-8 assay revealed that effective doses of JPH203 on cell proliferation were ranging from 5 to 40 μM. Analyzing Annexin V-Fluorescein isothiocyanate (FITC) binding by flow cytometry, we found that JPH203 (40μM) induced apoptosis within three days and growth arrest for at least three weeks in GH4 cells. JPH203 also reduced the amount of GH and PRL mRNAs 40 % and 50 %, respectively. These results indicate that LAT1 is a potential target of therapy for pituitary tumors. Next, the mechanisms of JPH203 action in GH4 cells were investigated. Unexpectedly, JPH203 did not have any apparent effects on the phosphorylation state of mTOR1 and its downstream effectors. In contrast, rapamycin decreased phosphorylation levels of these proteins, resulting in a reduction in cell proliferation. Our findings suggest that in pituitary tumor cells there could be differential amino acid sensing pathways, which regulate both cell growth and hormone synthesis. Further studies will be required to determine the mechanism of action of the LAT1 inhibitor in GH4 cells.

MON-406 Two Cases of Aggressive Corticotroph Pituitary Tumors Treated with Capecitabine and Temozolomide

Introduction: Aggressive corticotroph tumors exhibit continued growth despite multimodal therapy, including surgeries, radiotherapy and/or medical treatment. Temozolomide (TMZ), an oral alkylating agent, has been used to treat aggressive pituitary tumors; however, most patients only showed a partial response. Recent evidence suggests that TMZ administered with capecitabine (CAP) is effective and safe in treating patients with aggressive corticotroph tumors resistant to conventional therapy. Here, we present two patients with recurrence of aggressive corticotroph pituitary tumors after surgery and radiation therapy and good response to treatment with CAP and TMZ (CAPTEM). Clinical presentation: Case 1: A 54-year-old man presented with right-sided headache and dizziness. Examination revealed palsies of the right 3rd, 4th, 5th and 6th cranial nerves. MRI confirmed a 3.6 x 3.7 x 3.5 cm sellar/suprasellar mass with right cavernous sinus invasion, chiasmal compression and clival replacement. He had transsphenoidal surgery and pathology showed a sparsely granulated ACTH adenoma with necrosis. With evidence of hypopituitarism, he was placed on prednisone, levothyroxine and testosterone. He also received stereotactic radiotherapy to manage his residual adenoma. Three years later, he presented with new onset neck pain and imaging studies showed leptomeningeal disease and biopsy confirmed ACTH adenoma. He was treated with CAPTEM for one year which resulted in clinical remission with marked radiological improvement, and persistent tumor control 20 months after cessation of therapy. Case 2: A 48 year-old man seen post transsphenoidal surgery for management of his recurrent silent corticotroph adenoma. He presented at age 21 with vision loss and had his first craniotomy. At age 31, he had repeat craniotomy for tumor recurrence that was followed by radiation therapy. With documented hypopituitarism, he has been on hydrocortisone, levothyroxine and testosterone. Although he has been legally blind, he did notice further vision loss prior to his transsphenoidal surgery. MR sella showed a 3.0 x 3.6 x 2.5 cm sellar mass infiltrating the clivus, sphenoid sinus, both cavernous sinuses and extending and compressing the optic chiasm. Even though there was good debulkment of the sellar mass, rapid tumor regrowth was noted on follow up MRI 18 months later. As the neurosurgeon did not feel that the patient would benefit from further surgery, he was treated with a year of CAPTEM. This led to significant tumor shrinkage with no tumor regrowth four months after completion of therapy. Conclusion: Our cases represent the sixth and seventh cases of CAPTEM-treated aggressive corticotroph tumors with good response to therapy. TMZ in combination with CAP seems to be promising in the management of patients with aggressive corticotroph pituitary tumors, and potentially other aggressive pituitary adenomas.

Ethnic differences in antepartum glucose values that predict postpartum dysglycemia and neonatal macrosomia

BACKGROUND AND OBJECTIVE

Gestational diabetes (GDM) occurs more often in women from certain ethnic groups and is also associated with fetal macrosomia. In this study, we investigated the ability of a gestational diabetes screening test (GDS), the 2 h 75 g-Oral Glucose Tolerance Test (OGTT), and glycated hemoglobin (HbA1c) in predicting postpartum dysglycemia and fetal macrosomia in women of Caucasian, Filipino, Chinese and South-Asian descent.

METHODS

848 women diagnosed with carbohydrate intolerance in pregnancy who completed a 2 h 75 g- OGTT within 6 months postpartum, were included in the study. Receiver Operating Characteristic curve analysis was used to test the ability of antepartum GDS, HbA1c and OGTT in predicting postpartum hyperglycemia, type 2 diabetes (T2D) and neonatal macrosomia (birth weight >4000 g).

RESULTS

20.2% had postpartum hyperglycemia while 3.8% had T2D. Those with postpartum dysglycemia were more likely to be non-Caucasian (South-Asian > Filipino > Chinese), have higher antepartum glucose values, require insulin during pregnancy and have cesarean births. Of HbA1c and the antepartum glucose values, a fasting glucose of ≥5.25 mmol/L was predictive of fetal macrosomia in Caucasians. 1 h glucose of ≥11.05 mmol/L was predictive of postpartum hyperglycemia, while 2 h glucose of ≥9.75 mmol/L was predictive of T2D; ethnicity influenced the predictive ability of these tests.

CONCLUSIONS

Ethnicity influences the ability of antepartum glucose and HbA1c to predict the risk of macrosomia and postpartum dysglycemia. This information will help detect those most at risk of T2D.

Women with a history of gestational diabetes on long-term follow up have normal vascular function despite more dysglycemia, dyslipidemia and adiposity

AIMS

Previous gestational diabetes (GDM) is a risk factor for type 2 diabetes and increased metabolic risk, but the link with vascular dysfunction is not clear. This study examined vascular function in women 4-10 years after a diagnosis of GDM who had a normal oral glucose tolerance test (OGTT) in the first postpartum year.

METHODS

We studied 90 women with a history of GDM and 59 age-matched controls, examining differences in insulin resistance as measured by the Homeostatic Model Assessment (HOMA-IR) and glucose responses during an OGTT, adiposity, lipid profile and C-reactive protein (CRP). Using pulse wave analysis, we also measured cardiac function, vascular compliance, and systemic vascular resistance.

RESULTS

Women with a history of GDM had higher measures of adiposity (body mass index 28.9 ± 6.5 vs. 26.6 ± 6.9 kg/m(2), P=0.04, waist-hip ratio 0.85 ± 0.06 vs. 0.79 ± 0.07, P<0.001), dyslipidemia (LDL cholesterol 2.78 ± 0.64 vs. 2.41 ± 0.56 mmol/L, P<0.001, total cholesterol: HDL cholesterol 3.93 ± 1.2 vs. 3.21 ± 0.82 mmol/L, P<0.001) and abnormal glucose metabolism (50% vs. 12%, P<0.001). However, there was no difference in CRP, HOMA-IR, or measures of cardiovascular function including pulse rate, pulse pressure, mean arterial pressure, cardiac output, systemic vascular resistance, small and large artery elasticity index. After controlling for adiposity, blood pressure, lipids and CRP, glycemic status did not contribute to vascular function.

CONCLUSION

Despite a higher incidence of adiposity, dyslipidemia, and impaired glycemia, women with a history of GDM who had a normal postpartum OGTT did not have impaired vascular function 4-10 years postpartum, when compared to healthy controls.

The role of diabetes in acromegaly associated neoplasia

Background

The risk and mortality due to cancer in patients with acromegaly have been previously investigated. Although GH/IGF-1 excess provides a probable pathophysiological explanation, the degree of IGF-1 excess and the role in acromegaly-associated neoplasms of diabetes, a common comorbidity in acromegaly with known association with cancer, remains unclear.

Methods

Acromegalic patients treated in three Canadian referral centers (Toronto, Montreal, Edmonton) were included. All available clinical information was recorded including: age, initial and last percentage of the upper limit of normal (%ULN) IGF-1 levels, comorbidities and other neoplasms (benign and malignant).

Results

408 cases were assessed. 185 were women (45.3%), 126 (30.9%) developed extra-pituitary neoplasms: 55 malignant and 71 benign. The most frequent anatomic site was the gastrointestinal tract (46 [11.3%]), followed by head and neck (36 [8.8%]) and multiple locations (14 [3.4%]). 106 (26.0%) cases had diabetes. Initial IGF-1 was significantly higher in men older than 50 (380.15 vs. 284.78, p = 0.001) when compared to men younger than 50. Diabetics showed significantly higher initial IGF-1 (389.38 vs. 285.27, p = 0.009), as did diabetics older than 50 compared with those without diabetes. 45.3% (48/106) of cases with diabetes developed extra-pituitary neoplasms vs. 24.3% (71/292) without diabetes (p = 0.001, OR: 2.576 95%CI 1.615–4.108). 22.6% (24/106) of cases with diabetes developed malignant tumors vs. 9.2% (27/292), (p < 0.001, OR 2.873, 95%CI 1.572–5.250).

Conclusions

These data suggest that acromegalic patients with diabetes are more likely to develop extra-pituitary neoplasms and their initial IGF-1 levels are higher. The contribution of IGF-1 vs. diabetes alone or in combination in the development of extra-pituitary neoplasms warrants further investigation.

Emerging trends in the diagnosis and treatment of acromegaly in Canada

OBJECTIVE

To evaluate demographic data and quality of care of patients with acromegaly in Canada and their evolution over time and secondly, to evaluate predictors of co-morbidities and treatment outcomes.

DESIGN AND PATIENTS

Retrospective analyses of clinical, biochemical and treatment outcome data of 649 patients with acromegaly (males: 50·7%) followed from 1980 to 2010 (mean 10·2 years, SD 13·7) in eight tertiary care centres from six Canadian provinces.

RESULTS

In comparison to 1980-1994, the number of patients referred with acromegaly in the last 15 years was higher with female preponderance (52·8% vs 41·4%, P = 0·01) and an older age at diagnosis (46·4 ± 14 vs 41·3 ± 12 years, P < 0·0001). Diabetes was present in 28%, hypertension in 37% and sleep apnoea in 33% of cases. Pretreatment IGF-1 levels, but not GH levels were significant predictors of diabetes (P = 0·0002) and hypertension (P < 0·0001). Eighty-nine per cent of patients underwent pituitary surgery, 64·5% had medical therapy and 22% received radiotherapy. Radiotherapy was less utilized in the past 15 years (16% vs 45%, P < 0·0001). Multimodal therapy achieved remission or control of acromegaly in 70% of patients. Patients in remission or disease control had lower initial random GH (P = 0·04) and IGF-1 levels (P < 0·0001). Hypopituitarism was present in 23% of patients and cancer in 8·5%.

CONCLUSIONS

There was an increase over time of referral for acromegaly management with female predilection. Initial higher IGF-1, but not GH levels, were predictive of co-morbidities and persistent active disease after treatment. Disease remission or control was attained in 70% of patients utilizing multimodal therapy.