Succinate Dehydrogenase Subunit B Research Articles

Transaminitis Evaluation Leads to the Incidental Diagnosis of Familial Paraganglioma Due to SDHB Mutation

Background: Paragangliomas are rare neuroendocrine tumors. Patients with succinate dehydrogenase subunit B (SDHB) gene mutations are predisposed to developing paraganglioma/pheochromocytoma. We are presenting the case of an incidental finding of a paraganglioma during an evaluation for transaminitis. Clinical Case: A 23-year-old male with a medical history of right hydrocele repair as a teenager was evaluated with an ultrasound of the abdomen for elevated liver enzymes and right upper quadrant discomfort. The ultrasound revealed a large lobular solid vascular 13.8 x 8.1 x 11.3 cm mass in the mid abdomen. He underwent a CT of the chest, abdomen and pelvis which demonstrated a large retroperitoneal mass measuring 16 x 10 x 13.7 cm within the right mid abdomen. The mass was described as a large centrally necrotic peripherally enhancing right retroperitoneal mass displacing the IVC anteriorly. The patient subsequently underwent an image-guided biopsy of the mass and the pathology revealed it was a paraganglioma. The patient denied any history of hypertension, orthostasis, headaches or palpitations. Biochemical workup for plasma catecholamines, plasma metanephrines, 24-hour urine catecholamines and metanephrines and cortisol were unremarkable. His transaminitis also resolved. He underwent a retroperitoneal paraganglioma excision and the final pathology was consistent with paraganglioma and negative for capsular invasion. He was referred to a genetic counsellor for testing since paragangliomas can be inherited. He also mentioned a family history of breast cancer in his mother and HTN and prostate cancer in his father. His test revealed that he had a c.289A>T mutation in his SDHB gene. He was encouraged to share the information with his family to help them understand the implications of his genetic test result. He underwent a surveillance PET scan which showed multiple osseous lesions in his temporal calvarium, sphenoid, spine and sacrum suggestive of metastasis. Repeat imaging with a DOTATATE PET scan showed stable disease. His transaminitis was transient, and we did not find a correlation to his paraganglioma. His imaging tests showed no liver metastasis. A CT of the head showed no evidence of intracranial metastasis. The current plan is to continue surveillance. His older brother underwent a genetic testing. He tested positive for the same SDHB mutation and underwent biochemical and imaging tests which were unremarkable. He too will continue surveillance. Conclusions: Patients with a succinate dehydrogenase subunit B (SDHB) gene mutations are predisposed to developing paraganglioma/pheochromocytoma. The tumors produce catecholamines, but can be biochemically silent as in our patient. They are inherited in an autosomal dominant manner. Our case highlights the importance for genetic counseling which increases the chances of early screening and surveillance in affected family members for optimal multidisciplinary management of patients.

Carney Triad, Carney-Stratakis Syndrome, 3PAS and Other Tumors Due to SDH Deficiency.

Succinate dehydrogenase (SDH) is a key respiratory enzyme that links Krebs cycle and electron transport chain and is comprised of four subunits SDHA, SDHB, SDHC and SDHD. All SDH-deficient tumors are caused by or secondary to loss of SDH activity. As many as half of the familial cases of paragangliomas (PGLs) and pheochromocytomas (PHEOs) are due to mutations of the SDHx subunits. Gastrointestinal stromal tumors (GISTs) associated with SDH deficiency are negative for KIT/PDGFRA mutations and present with distinctive clinical features such as early onset (usually childhood or adolescence) and almost exclusively gastric location. SDH-deficient GISTs may be part of distinct clinical syndromes, Carney-Stratakis syndrome (CSS) or dyad and Carney triad (CT). CSS is also known as the dyad of GIST and PGL; it affects both genders equally and is inherited in an autosomal dominant manner with incomplete penetrance. CT is a very rare disease; PGL, GIST and pulmonary chondromas constitute CT which shows female predilection and may be a mosaic disorder. Even though there is some overlap between CT and CSS, as both are due to SDH deficiency, CSS is caused by inactivating germline mutations in genes encoding for the SDH subunits, while CT is mostly caused by a specific pattern of methylation of the SDHC gene and may be due to germline mosaicism of the responsible genetic defect.

Urinary bladder paraganglioma metastatic to the lung in a patient with SDHB gene mutation: A case report

Introduction: Paragangliomas are tumors originating from the neural crest. Most of them are benign and arise from various locations in the body. Extra-adrenal paragangliomas arise as sporadic cases in most settings or as part of heredofamilial syndromes in about one-quarter of cases. Succinate dehydrogenase subunit B (SDHB) gene mutations are associated with an aggressive clinical disease course of pheochromocytoma/paraganglioma.Methods: We present a 41-year-old male former smoker with a history of a growing right upper lung nodule on chest imaging. He had no cough or respiratory symptoms. Twenty-seven months prior, the patient underwent a cystoprostatectomy due to paraganglioma of the bladder. Genetic testing identified a pathogenic mutation in SDHB gene, c.166_170delCCTCA (p.Pro56Tyrfs*5). He underwent a wedge resection of the lung nodule.Results: Sectioning of the lung wedge revealed a well-circumscribed, firm tan nodule. Microscopically there were nests of large neoplastic cells with round nuclei and eosinophilic granular cytoplasm. Tumor cells were positive for synaptophysin and chromogranin and negative for pan-cytokeratin. S-100 protein highlighted sustentacular cells. Morphologically, the pulmonary neoplasm was similar to the primary tumor of the bladder. These features are consistent with a bladder paraganglioma metastatic to the lung, in a background of a hereditary paraganglioma syndrome.Conclusion: Extra-adrenal paraganglioma occurring in a setting of hereditary paraganglioma syndrome has a high risk of metastasis. Lifelong surveillance even after prompt resection of the primary tumor with negative margins is required to ensure early detection of metastasis and prevent complications associated with it.

Changes in DMI, SDHI, and QoI Fungicide Sensitivity in the Estonian Zymoseptoria tritici Population between 2019 and 2020.

Zymoseptoria tritici (Zt) populations adapt under the selection pressure of fungicides applied for disease control. The primary objective of this study was to assess fungicide sensitivity in the Estonian Zt population. A total of 282 Zt isolates from 2019 and 2020 were tested for sensitivity to azoles (DMIs; prothioconazole-desthio, epoxiconazole, mefentrifluconazole) and succinate dehydrogenase inhibitors (SDHIs; boscalid, fluxapyroxad). The efficacy of the tested fungicides varied considerably between the Estonian counties, but the Zt population is mainly sensitive to DMIs. Additionally, the frequencies of CYP51 gene alterations varied; D134G, V136C, A379G, and S524T had increased, but V136A and I381V showed a moderate decrease in 2020 in comparison to 2019. Sensitivity to SDHIs was stable, but boscalid was less effective than fluxapyroxad. SdhC gene mutations C-T33N, C-T34N, and C-N86S were common, but not linked with SDHI fungicide sensitivity assay results. Otherwise, mutation B-N225I in the SdhB subunit occurred in isolates with reduced sensitivity to SDHIs. Sensitivity to strobilurins was evaluated by the mutation G143A in the CytB gene, which was present in nearly half of the population. The data presented confirm the ongoing evolution of fungicide sensitivity in the Zt population in Estonia and highlight the importance of knowledge-based decisions for optimizing anti-resistance strategies in the field.

Development of Boscalid Resistance in Botrytis cinerea and an Efficient Strategy for Resistance Management.

Among succinate dehydrogenase inhibitors, only boscalid has been registered in China for controlling gray mold. In Shandong Province of China, it has been more than a decade since the first use of boscalid to control gray mold. In the current study, we monitored the resistance development process of Botrytis cinerea to boscalid, identified the mutation types that occurred in boscalid-resistant isolates, and proposed an original application technique to delay resistance development. A total of 720 B. cinerea isolates collected from tomato and cucumber in Shandong Province from 2014 to 2019 were determined to be sensitive to boscalid. The results showed that the sensitivity of the B. cinerea isolates to boscalid declined gradually over time, with a mean half maximal effective concentration of 0.3 ± 0.02 mg/liter in 2014 and 6.39 ± 1.66 mg/liter in 2019. The proportion of resistant isolates quickly increased from 0.81% in 2014 to 28.97% in 2019. Mutations of P225F, N230I, H272Y, and H272R in the SdhB subunit were responsible for boscalid resistance. Four concurrent mutations (G85A, I93V, M158V, and V168I) in the SdhC subunit were first discovered in Shandong Province, but they did not affect the level of boscalid resistance. Interestingly, this study found that the fruit dipping application, a precise topical application technique, could delay the development of boscalid resistance. Therefore, this application technique provides a new method for resistance management of B. cinerea.

Metastatic Paraganglioma of the Spine With SDHB Mutation: Case Report and Review of the Literature.

Paragangliomas (PGLs) are rare neuroendocrine tumors that can arise from any autonomic ganglion of the body. Most PGLs do not metastasize. Here, we present a rare case of metastatic PGL of the spine in a patient with a germline pathogenic succinate dehydrogenase subunit B (SDHB) mutation. In addition to a case report we provide a literature review of metastatic spinal PGL to highlight the importance of genetic testing and long-term surveillance of these patients. A 45-year-old woman with history of spinal nerve root PGL, 17 years prior, presented with back pain of several months' duration. Imaging revealed multilevel lytic lesions throughout the cervical, thoracic, and lumbar spine as well as involvement of the right mandibular condyle and clavicle. Percutaneous biopsy of the L1 spinal lesion confirmed metastatic PGL and the patient underwent posterior tumor resection and instrumented fusion of T7-T11. Postoperatively the patient was found to have a pathogenic SDHB deletion. Patients with SDHx mutation, particularly SDHB, have increased risk of developing metastatic PGLs. Consequently, these individuals require long-term surveillance given the risk for developing new tumors or disease recurrence, even years to decades after primary tumor resection. Surgical management of spinal metastatic PGL involves correcting spinal instability, minimizing tumor burden, and alleviating epidural cord compression. In patients with metastatic PGL of the spine, genetic testing should be considered.

A Rapid Molecular Detection System for SdhB and SdhC Point Mutations Conferring Differential Succinate Dehydrogenase Inhibitor Resistance in Clarireedia Populations.

Dollar spot, caused by the ascomycete fungus Clarireedia (formerly Sclerotinia), is one of the most resource-demanding diseases on amenity turfgrasses in North America. Differential resistance to the succinate dehydrogenase inhibitor (SDHI) fungicide class, conferred by singular point mutations on the SdhB, SdhC, and SdhD subunits of the succinate dehydrogenase enzyme (SDH), has been reported in dollar spot as well as many other plant-pathogenic fungal diseases. Four unique mutations were previously reported from Clarireedia field isolates collected from two different cool-season golf courses in Japan and Rhode Island: an amino acid substitution H267Y and a silent mutation (CTT to CTC) at codon 181 on the SdhB subunit gene, and amino acid substitutions G91R and G150R on the SdhC subunit gene. To properly diagnose and monitor SDHI resistance in the field, a rapid detection system for known mutations is crucial. As part of this study, additional SDHI-resistant Clarireedia isolates were collected from Rutgers University research plots and in vitro sensitivity to four SDHI active ingredients was assessed. SdhB, SdhC, and SdhD subunits of these isolates were sequenced to reveal an additional mutation on the SdhB subunit gene, H267R, not previously observed in Clarireedia. Cleaved amplified polymorphic sequence (CAPS) and derived CAPS molecular markers were developed to detect five mutations conferring SDHI resistance in Clarireedia isolates and validated using samples from two additional golf courses in Connecticut and Wisconsin experiencing SDHI field failure. This PCR-based molecular detection system will be useful for continued monitoring, assessment, and delay of SDHI resistance in the field.

Abstract 12938: An Unusual Case of Malignant Hypertension and Stress Cardiomyopathy Originating From the Urinary Bladder

A 39-year-old man with hypertension presented for an elective knee surgery. Within 15 minutes of induction of anesthesia, he developed malignant hypertension and acute hypoxia. Surgery wasaborted and he was subsequently transferred to our facility. High-sensitivity troponin was elevated. Chest X-ray demonstrated bilateral hilar opacities, consistent with pulmonary edema.Transthoracic echocardiography demonstrated mildly depressed left ventricular function with hypokinesis of the septum and inferolateral wall. Cardiac catheterization showed normal filling pressures and no coronary artery disease. Initial work up for secondary hypertension, including Duplex Doppler ultrasonography of renal artery and serum aldosterone level were unrevealing. Because of high index of suspicion, additional workup was pursued for adrenal hypertension. Hewas found to have severely elevated plasma normetanephrine level (36 nmol/L) and 24-hrurinary normetanephrine of 8,990 mcg while plasma metanephrine and epinephrine levels were within normal limits. Computed tomography of abdomen showed no adrenal mass but revealed contrast-enhancing mass in the bladder wall with surrounding lymphadenopathy, suggestive of metastatic paraganglioma. He underwent genetic evaluation which identified a heterozy gouspathogenic variant in the succinate dehydrogenase subunit B (SDHB) gene. He was treated withalpha- and beta-blockade and underwent partial cystectomy with lymph node dissection. Follow-up Gallium-68 DOTATATE scan was positive for uptake in several lymph nodes withsubsequent successful lymph node dissection. He is now asymptomatic. Discussion: This case illustrates the importance of a complete history in the evaluation of hypertension inyoung people. The presence of labile hypertension and acute cardiomyopathy which isprecipitated by stress or noncardiac surgery should prompt an evaluation of pheochromocytoma.The isolated elevation in plasma and urinary normetanephrine with normal plasma/urinarymetanephrine level is consistent with extra-adrenal production of catecholamines, which iscommon in the presence of SDHB mutation.

Paraganglioma of the Urinary Bladder Metastatic to the Lung in a Patient with SDHB Gene Mutation: A Case Report

Abstract Introduction/Objective Paragangliomas are tumors originating from the neural crest. Most tumors are benign and arise from various locations in the body. Extra-adrenal paragangliomas arise as sporadic cases in most settings or as part of heredofamilial syndromes in about one-quarter of cases. Succinate dehydrogenase subunit B (SDHB) gene mutations are associated with an aggressive clinical disease course of pheochromocytoma/paraganglioma. Methods We present a 41-year-old male former smoker with a history of a growing right upper lung nodule on chest imaging. He had no cough or respiratory symptoms. Twenty-seven months prior the patient underwent a cystoprostatectomy due to paraganglioma of the bladder. Genetic testing identified a pathogenic mutation in SDHB gene, c.166_170delCCTCA (p.Pro56Tyrfs*5). He underwent a wedge resection of the lung nodule. Results Sectioning of the lung wedge revealed a well circumscribed, firm tan nodule. Microscopically there were nests of large neoplastic cells with round nuclei and eosinophilic granular cytoplasm. Tumor cells were positive for synaptophysin and chromogranin and negative for pan-cytokeratin. S100 highlighted sustentacular cells. The pulmonary neoplasm was morphologically similar to the prior tumor of the bladder. These features are consistent with a metastatic urothelial paraganglioma to the lung, in a background of a hereditary paraganglioma syndrome. Conclusion Extra-adrenal paraganglioma occurring in a setting of hereditary paraganglioma syndrome has a higher risk of metastasis. Lifelong surveillance even after prompt resection of primary tumor with negative margins is required to ensure early detection of metastasis and prevention of complications associated with it.

Fungicide resistance in Cercospora species causing cercospora leaf blight and purple seed stain of soybean in Argentina

AbstractCercospora species cause cercospora leaf blight (CLB) and purple seed stain (PSS) on soybean. Because there are few resistant soybean varieties available, CLB/PSS management relies heavily upon fungicide applications. Sensitivity of 62 Argentinian Cercospora isolates to demethylation inhibitor (DMI), methyl benzimidazole carbamate (MBC), quinone outside inhibitor (QoI), succinate dehydrogenase inhibitor (SDHI) fungicides, and mancozeb was determined in this study. All isolates were sensitive to difenoconazole, epoxiconazole, prothioconazole, tebuconazole, and cyproconazole (EC50 values ranged from 0.006 to 2.4 µg/ml). In contrast, 51% of the tested isolates were sensitive (EC50 values ranged from 0.003 to 0.2 µg/ml), and 49% were highly resistant (EC50 > 100 µg/ml) to carbendazim. Interestingly, all isolates were completely resistant to azoxystrobin, trifloxystrobin, and pyraclostrobin, and insensitive to boscalid, fluxapyroxad, and pydiflumetofen (EC50 > 100 µg/ml). The G143A mutation was detected in 82% (53) of the QoI‐resistant isolates and the E198A mutation in 97% (31) of the carbendazim‐resistant isolates. No apparent resistance mutations were detected in the succinate dehydrogenase genes (subunits sdhB, sdhC, and sdhD). Mancozeb completely inhibited mycelial growth of the isolates evaluated at a concentration of 100 µg/ml. All Argentinian Cercospora isolates were sensitive to the DMI fungicides tested, but we report for the first time resistance to QoI and MBC fungicides. Mechanism(s) other than fungicide target‐site modification may be responsible for resistance of Cercospora to QoI and MBC fungicides. Moreover, based on our results and on the recent introduction of SDHI fungicides on soybean in Argentina, Cercospora species causing CLB/PSS are insensitive (naturally resistant) to SDHI fungicides. Insensitivity must be confirmed under field conditions.

Targeting pheochromocytoma/paraganglioma with polyamine inhibitors

BackgroundPheochromocytomas (PCCs) and paragangliomas (PGLs) are neuroendocrine tumors that are mostly benign. Metastatic disease does occur in about 10% of cases of PCC and up to 25% of PGL, and for these patients no effective therapies are available. Patients with mutations in the succinate dehydrogenase subunit B (SDHB) gene tend to have metastatic disease. We hypothesized that a down-regulation in the active succinate dehydrogenase B subunit should result in notable changes in cellular metabolic profile and could present a vulnerability point for successful pharmacological targeting. MethodsMetabolomic analysis was performed on human hPheo1 cells and shRNA SDHB knockdown hPheo1 (hPheo1 SDHB KD) cells. Additional analysis of 115 human fresh frozen samples was conducted. In vitro studies using N1,N11-diethylnorspermine (DENSPM) and N1,N12- diethylspermine (DESPM) treatments were carried out. DENSPM efficacy was assessed in human cell line derived mouse xenografts. ResultsComponents of the polyamine pathway were elevated in hPheo1 SDHB KD cells compared to wild-type cells. A similar observation was noted in SDHx PCC/PGLs tissues compared to their non-mutated counterparts. Specifically, spermidine, and spermine were significantly elevated in SDHx-mutated PCC/PGLs, with a similar trend in hPheo1 SDHB KD cells. Polyamine pathway inhibitors DENSPM and DESPM effectively inhibited growth of hPheo1 cells in vitro as well in mouse xenografts. ConclusionsThis study demonstrates overactive polyamine pathway in PCC/PGL with SDHB mutations. Treatment with polyamine pathway inhibitors significantly inhibited hPheo1 cell growth and led to growth suppression in xenograft mice treated with DENSPM. These studies strongly implicate the polyamine pathway in PCC/PGL pathophysiology and provide new foundation for exploring the role for polyamine analogue inhibitors in treating metastatic PCC/PGL. PrécisCell line metabolomics on hPheo1 cells and PCC/PGL tumor tissue indicate that the polyamine pathway is activated. Polyamine inhibitors in vitro and in vivo demonstrate that polyamine inhibitors are promising for malignant PCC/PGL treatment. However, further research is warranted.

Activity of the Novel Succinate Dehydrogenase Inhibitor Fungicide Pydiflumetofen Against SDHI-Sensitive and SDHI-Resistant Isolates of Botrytis cinerea and Efficacy Against Gray Mold.

Succinate dehydrogenase inhibitor (SDHI) fungicides are currently the most frequently used fungicides for controlling gray mold. However, isolates of Botrytis cinerea resistant to SDHI fungicides have emerged in the field. Pydiflumetofen is a new SDHI fungicide that can control a variety of fungal diseases, but its efficacy against gray mold and whether the activity of pydiflumetofen is affected by the current SDHI-resistant isolates is currently unknown. The sensitivity of 291 single-spore B. cinerea isolates collected from 2017 to 2019 to pydiflumetofen was determined by spore germination inhibition assays. The mean EC50 value (fungicide concentration resulting in a 50% inhibition compared with that of the control) of pydiflumetofen was 0.06 ± 0.01, 0.07 ± 0.02, and 0.05 ± 0.02 mg/liter in 2017, 2018, and 2019, respectively. There was no significant difference in the sensitivity of B. cinerea to pydiflumetofen among the 3 years. Furthermore, pydiflumetofen at 300 mg/liter effectively controlled gray mold on cucumber leaves (80.9%), and its efficacy was superior to that of boscalid at 400 mg/liter (42.7%). The isolates carrying P225F, N230I, H272Y, and H272R mutations in the SdhB subunit were associated with the less sensitivity of B. cinerea to SDHI fungicides. After establishing the baseline sensitivity of B. cinerea to pydiflumetofen (EC50 of 0.03 ± 0.003 mg/liter), we found that the P225F and H272Y mutant isolates showed low to moderate levels of resistance to pydiflumetofen, and the H272R and N230I mutant isolates showed low levels of resistance. The reduced sensitivity to pydiflumetofen resulted from the positive correlation of pydiflumetofen with the other four SDHI fungicides (i.e., boscalid, fluopyram, isopyrazam, and benzovindiflupyr). These results suggest that pydiflumetofen provides effective control for the management of gray mold but must be used with caution.

MON-199 Targeting Pheochromocytoma/Paraganglioma with Polyamine Inhibitors

Background: Pheochromocytomas (PCCs) and paragangliomas (PGLs) are neuroendocrine tumors that are mostly benign. Metastatic disease occurs in about 10% of cases, and for these patients no effective therapies are available. Patients with mutations in the succinate dehydrogenase subunit B (SDHB) gene tend to have metastatic disease with very little treatment options. To find a new treatment strategy, we utilized a metabolomics approach to identify unique metabolic pathways. A metabolomic analysis was performed on human hPheo1 cells and shRNA SDHB knockdown hPheo1 (hPheo1 SDHB KD) cells. Additional analysis of 50 human fresh frozen PCC/PGL samples was conducted. Since the polyamine pathway surfaced in the metabolomics analysis, we hypothesized that treatment with polyamine inhibitors would be an effective option for aggressive PCC/PGL tumors. In vitro studies using N1,N11-diethylnorspermine (DENSPM) and N1,N12- diethylspermine (DESPM) treatments were carried out. DENSPM efficacy was assessed in xenograft models. Results: Components of the polyamine pathway were elevated in hPheo1 SDHB KD cells compared to wild-type cells. A similar observation was noted in SDHx PCC/PGLs tumor tissues compared to their SDHB wild-type counterparts. Specifically, spermidine, and spermine were significantly elevated in SDHx-mutated PCC/PGLs, with a similar trend in hPheo1 SDHB KD cells. Polyamine pathway inhibitors DENSPM and DESPM effectively inhibited growth of hPheo1 cells in vitro as well in mouse xenografts. Conclusions: This study demonstrates overactive polyamine pathway in PCC/PGL with SDHB mutations. Treatment with polyamine inhibitors significantly inhibited hPheo1 cell growth and led to growth inhibition in xenograft mouse models treated with DENSPM. These studies strongly implicate the polyamine pathway in PCC/PGL pathophysiology and provide new foundation for exploring the role for polyamine analogue inhibitors in treating metastatic PCC/PGL.

SAT-LB313 A Unicorn With Double Horns - Metastatic Paraganglioma in a Patient With Beckwith-Wiedemann Syndrome and Hereditary Paraganglioma Syndrome Iv

Introduction: Beckwith-Wiedemann syndrome (BWS), a multisystem genomic imprinting disorder in chromosome 11p15.5 region, is an overgrowth syndrome often presenting with macroglossia, abdominal wall defects, hemihyperplasia, enlarged abdominal organs and an increased risk of tumors including neuroblastoma, rhabdomyosarcoma, unilateral Wilm’s tumor, hepatoblastoma, adrenal cortical carcinoma and pheochromocytoma. Six cases of benign bilateral pheochromocytomas and one case of pheochromocytoma with lymph node metastasis in BWS have been described in the literature. We describe the first case of BWS with distant metastatic paraganglioma harboring an SDHB (succinate dehydrogenase subunit B) mutation. Presentation: A 28-year-old male with BWS whose history included an omphalocele and diaphragmatic hernia in infancy, neuroblastoma resected at age 2, and left carotid paraganglioma (PGL) resected at age 22 presented with abdominal pain. CT A/P with contrast revealed a 3.3 x 4.4 cm hypervascular mass and multiple bone metastases. Workup revealed normal plasma/urine metanephrines, elevated plasma dopamine of 178 pg/ml (normal <20) and elevated chromogranin A of 190 ng/ml (normal <90). 68Ga-dotatate PET CT showed hypermetabolic 4.4 cm mass (SUV 83), right hypopharynx mass (SUV 49), and many dota avid areas throughout the skeleton. The abdominal mass was resected and pathology was consistent with PGL. Due to unusual presentation, patient underwent hereditary cancer genetic testing (67 gene panel) and pathogenic mutation (c.713delT) in the SDHB gene was identified, consistent with hereditary PGL syndrome IV. Conclusion: While pheochromocytomas and other tumors are commonly found in association with BWS, PGLs are not. This is the first documented case of a patient with BWS having distant metastatic PGL. Malignant transformation of hereditary and sporadic pheochromocytomas and paraganglioma (PPGLs) is more common in SDHx associated PPGLs (>40% of metastatic PPGLs are related to an SDHB mutation). Hereditary PGL syndromes should be suspected in the case of PGLs that are recurrent, early onset (<45 years), extra-adrenal and/or metastatic. With additional genetic testing, our patient with an already rare growth disorder was found to have hereditary PGL syndrome IV caused by a pathogenic mutation in the SDHB gene. This unique case highlights the rationale and importance of systematic genetic cancer screening in the diagnostic evaluation of PPGLs.

SAT-502 Clinical Hypothyroidism Associated with Lutetium 177-DOTATATE Therapy for Metastatic Paraganglioma: A Novel Adverse Effect of Peptide Receptor Radionuclide Therapy

Background: Peptide receptor radionuclide therapy (PRRT) is a relatively novel, emerging therapy for the treatment of metastatic pheochromocytoma and paraganglioma (PPGL). Lutetium 177 (177Lu)-DOTATATE (Lutathera ®) is a form of PRRT that is currently being evaluated for its treatment efficacy in metastatic PPGL. It acts by binding to somatostatin receptors 2 (SSTR2) which are present on PPGL and other tissues of neuroendocrine origin. Although subclinical thyroid dysfunction has been previously noted, development of clinical hypothyroidism post 177Lu-DOTATATE therapy has not been reported to date. Case: A 29-year-old male with Beckwith-Weidemann syndrome and metastatic, succinate dehydrogenase subunit B (SDHB) germline mutation-positive paraganglioma with normal metanephrines was enrolled at our center under the 177Lu-DOTATATE trial for the treatment of inoperable, metastatic PPGL (ClinicalTrials.gov NCT03206060). Prior to the first cycle of therapy, the patient underwent endocrine evaluation per protocol. He was noted to have suppressed thyroid stimulating hormone (TSH) of <0.01 mcIU/mL (normal: 0.27 - 4.2 mcIU/mL), and a normal free thyroxine (FT4) of 1.3 ng/dL (0.9 - 1.7 ng/dL), indicating subclinical hyperthyroidism. Thyroid auto-antibodies were not measured at that time point. The patient denied symptoms of hyper- or hypothyroidism. On physical examination, there was no thyromegaly or cervical lymphadenopathy. Serial monitoring of thyroid function tests (TFTs) was pursued. One month after the first cycle of 177Lu-DOTATATE therapy, the patient complained of new onset fatigue and weight gain. The TSH had markedly increased (73.04 mcIU/mL), along with a reduction in FT4 levels (0.3 mg/dL). Mass spectrometry measures revealed a low total T4 (1.3 ng/dL; 4.9 - 10.5 ng/dL), and a low total T3 (57 ng/dL; 87 - 169 ng/dL). Thyroid peroxidase antibodies were >1000 IU/mL (0.0 - 34.9 IU/mL), and anti-thyroglobulin antibodies were 668 IU/mL (0.0-40.0 IU/mL). Weight-based levothyroxine therapy was initiated and the follow-up TFTs normalized. The baseline diagnostic Gallium 68-DOTATATE scan performed prior to PRRT demonstrated an increased diffuse uptake in the entire thyroid gland (maximum standardized uptake value: 14.3) and post-treatment SPECT-CT scan revealed similar increased, diffuse 177Lu-DOTATATE uptake in the thyroid gland. The patient currently has stable metastatic disease and continues to be under 177Lu-DOTATATE therapy. Conclusion: We report the first known case of clinical hypothyroidism post 177Lu-DOTATATE therapy in a patient who likely had subclinical hyperthyroidism prior to treatment. The possible mechanism was development of thyroiditis. Further studies are necessary to evaluate the mechanisms of PRRT-induced endocrine abnormalities and their clinical implications.

Mitochondrial Dysfunction Promotes Diabetes via A Previously Unrecognized Mechanism: Protein Succinylation

Mitochondrial dysfunction is a central contributor to the development of β‐cell failure and Type 2 Diabetes (T2D). Succinate dehydrogenase subunit B (SDHB) is a key component of the Succinate Dehydrogenase (SDH) protein complex that strongly impacts mitochondrial function via 1) oxidation of succinate to fumarate in the TCA cycle and 2) electron transfer in the electron transport chain as Complex II. Loss of SDH activity has been observed in diabetic β‐cells (humans and rodents); however, the relevance of this observation to diabetes pathogenesis remains poorly understood. Consistent with prior work, we found reduced SDHB expression in the pancreatic islets of human diabetics. To investigate the links between mitochondrial dysfunction, β‐cell failure and diabetes, we generated mice with a β‐cell‐specific knockout of SDHB (SDHBβKO). We found that SDHBβKO mice develop early onset diabetes. At 5 weeks, prediabetic SDHBβKO mice demonstrate mildly elevated glucose levels with low insulin levels and normal insulin sensitivity. These in vivo findings were confirmed by a reduction in glucose‐stimulated insulin secretion in SDHBβKO islets. Furthermore, glucose‐induced β‐cell replication was impaired in SDHBβKO mice; consistent with impaired adaptive β‐cell expansion. Given the prominent role of glucose metabolism in controlling β‐cell insulin secretion and replication, we assessed the mitochondrial bioenergetics by Seahorse Assay and found that basal and glucose‐stimulated respiration were significantly reduced in SDHBβKO islets. Notably, loss of SDH is expected to increase succinate accumulation and promote protein succinylation, a recently described bulky post‐translational modification. Indeed, SDHBβKO islets demonstrated a dramatic increase in succinate levels (16‐fold) and protein succinylation (6‐fold), providing a potential mechanism for global mitochondrial dysfunction. Accordingly, expression of the desuccinylation enzyme, Sirt5, was increased in SDHBβKO islets. Metabolomics by mass spectrometry and transcriptomics by high‐throughput RNA sequencing revealed significantly altered mitochondrial metabolism. Finally, protein succinylation levels were increased in islets of diabetic db/db mice indicating lysine‐succinylation may be characteristic of diabetes. Taken together, these results demonstrate a surprisingly necessary role for the SDH complex in β‐cell function and introduce a pathogenic mechanism of diabetes based upon β‐cell metabolic dysfunction.Support or Funding InformationStanford Diabetes Research Center (SRDC) Pilot &amp; Feasibility Grants Program (P30DK116074), Endocrinology Training grant (T32DK007217) and Child Health Research Institute at Stanford (UL1TR001085)

Glutaminases as a Novel Target for SDHB-Associated Pheochromocytomas/Paragangliomas.

Pheochromocytoma/paragangliomas (Pheo/PGL) are rare endocrine cancers with strong genetic background. Mutations in the SDHB subunit of succinate dehydrogenase (SDH) predispose patients to malignant disease with limited therapeutic options and poor prognosis. Using a host of cellular and molecular biology techniques in 2D and 3D cell culture formats we show that SDH inhibition had cell line specific biological and biochemical consequences. Based on our studies performed on PC12 (rat chromaffin cell line), Hela (human cervix epithelial cell line), and H295R (human adrenocortical cell line) cells, we demonstrated that chromaffin cells were not affected negatively by the inhibition of SDH either by siRNA directed against SDHB or treatment with SDH inhibitors (itaconate and atpenin A5). Cell viability and intracellular metabolite measurements pointed to the cell line specific consequences of SDH impairment and to the importance of glutamate metabolism in chromaffin cells. A significant increase in glutaminase-1 (GLS-1) expression after SDH impairment was observed in PC12 cells. GLS-1 inhibitor BPTES was capable of significantly decreasing proliferation of SDH impaired PC12 cells. Glutaminase-1 and SDHB expressions were tested in 35 Pheo/PGL tumor tissues. Expression of GLS1 was higher in the SDHB low expressed group compared to SDHB high expressed tumors. Our data suggest that the SDH-associated malignant potential of Pheo/PGL is strongly dependent on GLS-1 expression and glutaminases may be novel targets for therapy.

TET-Mediated Hypermethylation Primes SDH-Deficient Cells for HIF2α-Driven Mesenchymal Transition

Loss-of-function mutations in the SDHB subunit ofsuccinate dehydrogenase predispose patients to aggressive tumors characterized by pseudohypoxicand hypermethylator phenotypes. The mechanisms leading to DNA hypermethylation and its contribution to SDH-deficient cancers remain undemonstrated. We examine the genome-wide distribution of 5-methylcytosine and 5-hydroxymethylcytosine andtheir correlation with RNA expression in SDHB-deficient tumors and murine Sdhb-/- cells. We report that DNA hypermethylation results from TET inhibition. Although it preferentially affects PRC2 targets and known developmental genes, PRC2 activity does not contribute to the DNA hypermethylator phenotype. We also prove, invitro and invivo, that TET silencing, although recapitulating the methylation profile of Sdhb-/- cells, is not sufficient to drive their EMT-like phenotype, which requires additional HIF2α activation. Altogether, our findings reveal synergistic roles of TET repression and pseudohypoxia in the acquisition of metastatic traits, providing a rationale for targeting HIF2α and DNA methylation in SDH-associated malignancies.

Targeting NRF2-Governed Glutathione Synthesis for SDHB-Mutated Pheochromocytoma and Paraganglioma.

Succinate dehydrogenase subunit B (SDHB) deficiency frequently occurs in cluster I pheochromocytomas and paragangliomas (PCPGs). SDHB-mutated PCPGs are characterized by alterations in the electron transport chain, metabolic reprogramming of the tricarboxylic cycle, and elevated levels of reactive oxygen species (ROS). We discovered that SDHB-deficient PCPG cells exhibit increased oxidative stress burden, which leads to elevated demands for glutathione metabolism. Mechanistically, nuclear factor erythroid 2-related factor 2 (NRF2)-guided glutathione de novo synthesis plays a key role in supporting cellular survival and the proliferation of SDHB-knockdown (SDHBKD) cells. NRF2 blockade not only disrupted ROS homeostasis in SDHB-deficient cells but also caused severe cytotoxicity by the accumulation of DNA oxidative damage. Brusatol, a potent NRF2 inhibitor, showed a promising effect in suppressing SDHBKD metastatic lesions in vivo, with prolonged overall survival in mice bearing PCPG allografts. Our findings highlight a novel therapeutic strategy of targeting the NRF2-driven glutathione metabolic pathway against SDHB-mutated PCPG.

Inflammation Associated Pancreatic Tumorigenesis: Upregulation of Succinate Dehydrogenase (Subunit B) Reduces Cell Growth of Pancreatic Ductal Epithelial Cells.

Pancreatic ductal adenocarcinoma (PDAC) is amongst the most fatal malignancies and its development is highly associated with inflammatory processes such as chronic pancreatitis (CP). Since the succinate dehydrogenase subunit B (SDHB) is regarded as tumor suppressor that is lost during cancer development, this study investigated the impact of M1-macrophages as part of the inflammatory microenvironment on the expression as well as function of SDHB in benign and premalignant pancreatic ductal epithelial cells (PDECs). Immunohistochemical analyses on pancreatic tissue sections from CP patients and control individuals revealed a stronger SDHB expression in ducts of CP tissues being associated with a greater abundance of macrophages compared to ducts in control tissues. Accordingly, indirect co-culture with M1-macrophages led to clearly elevated SDHB expression and SDH activity in benign H6c7-pBp and premalignant H6c7-kras PDECs. While siRNA-mediated SDHB knockdown in these cells did not affect glucose and lactate uptake after co-culture, SDHB knockdown significantly promoted PDEC growth which was associated with increased proliferation and decreased effector caspase activity particularly in co-cultured PDECs. Overall, these data indicate that SDHB expression and SDH activity are increased in PDECs when exposed to pro-inflammatory macrophages as a counterregulatory mechanism to prevent excessive PDEC growth triggered by the inflammatory environment.