Genetics,Diagnosis, and Management of Medullary Thyroid Carcinoma and Pheochromocytoma/Paraganglioma

ObjectiveMedullary thyroid carcinoma (MTC) and pheochromocytoma/paraganglioma (PHEO/PGL) are rare neuroendocrine tumors. Because of the increased metastatic rates in certain genetic backgrounds, early diagnosis and treatment are essential to improved patient outcomes. Our objective was to summarize recent findings related to the genetics, diagnosis, and management of MTC and PHEO/PGL.MethodsA literature review was performed.ResultsMTC is primarily associated with mutations in the rearranged during transfection (RET) protooncogene. Determining the specific genetic mutation can guide patient management and screening. Early detection and appropriate surgical management of MTC is critical to prevent or limit metastatic spread, as treatment options for patients with metastatic disease are limited. PHEO/PGL also has a strong genetic component, with approximately 50% of cases linked to germline and somatic mutations in 15 genes. Although most PHEO/PGLs are benign, factors such as genetic background, size, tumor location, and high methoxytyramine levels are associated with higher rates of metastatic disease. The state-of-the-art diagnosis and localization of PHEO/PGLs is based on measurement of plasma metanephrines and methoxytyramine and functional imaging studies. For both PHEO/PGL and MTC, surgery is the only curative treatment. Treatment options for patients with metastatic disease are limited.ConclusionAs genetic testing becomes more widely available, the diagnosis of MTC and PHEO/PGL will be made earlier due to routine screening of at-risk patients. In addition, continued advances in basic science, diagnostic methods, and imaging techniques will improve understanding of the pathogenesis of these diseases and facilitate the introduction of novel treatment strategies for patients with metastatic disease. (Endocr Pract. 2014;20:176-187)     

A decade (2001-2010) of genetic testing for pheochromocytoma and paraganglioma

The identification of 9 susceptibility genes for paraganglioma/pheochromocytoma between 2001 and 2010 has led to the development of routine genetic tests. To study the evolution in genetic screening for paraganglioma/pheochromocytoma over the past decade, we carried out a retrospective study on the tests performed in our laboratory from January 2001 to December 2010. A genetic test for paraganglioma/pheochromocytoma was assessed for 2 499 subjects, 1 620 index cases, and 879 presymptomatic familial genetic tests. A germline mutation in a PGL/PCC susceptibility gene was identified in 363 index cases (22.4%): 269 in SDHx genes (137 in SDHB, 100 in SDHD, 30 in SDHC, 2 in SDHA), 64 in VHL, 23 in RET, and 7 in TMEM127. A presymptomatic paraganglioma/pheochromocytoma test was positive in 427 subjects. Advances in molecular screening techniques led to an increase in the total number of mutation-carriers diagnosed each year. Overall, during the last decade, our laboratory identified a germline mutation in 44.7% of patients with a suspect hereditary PGL/PCC and in 8% of patients with an apparently sporadic PGL/PCC. During the past decade, the discoveries of new paraganglioma/pheochromocytoma susceptibility genes and the subsequent progress of molecular screening techniques have enabled us to diagnose a hereditary paraganglioma/pheochromocytoma in about 22% of patients tested in routine practice. This genetic testing is of major importance for the follow-up of affected patients and for the genetic counselling of their families.     

Évaluation fonctionnelle par TEP 18F-FDopa des paragangliomes et phéochromocytomes non métastatiques : impact de la localisation lésionnelle et du statut génétique

ObjectiveParaganglioma (PGL) and pheochromocytoma (PCC) are neuroendocrine tumors most often benign associated with hereditary syndromes in about 30% of cases. This study aims to define the impact of tumor location and patient genotype on the clinical value of ¹⁸F-FDopa PET by assessing in detail the false negative occurrences.Patients and methodsA retrospective study was conducted on a cohort of 53 cases with non-metastatic sporadic or inherited PGL/PCC (SDHx or VHL related syndromes), investigated with ¹⁸F-FDopa PET.ResultsOverall detection sensitivity of ¹⁸F-FDopa PET was 88%. Seventy-three lesions were found using this technique, including 49 head-and-neck PGL (HNP), two thoracic PGL (1 sympathetic and 1 parasympathetic), eight extra-adrenal retroperitoneal PGL and 15 PCC. The 10 missed lesions were seven extra-adrenal abdominal PGL (2 SDHB, 2 SDHD), two HNP (1 sporadic, 1 SDHD) and one PCC (1 SDHD).Conclusion¹⁸F-FDopa PET is a sensitive technique for the evaluation of non-metastatic head and neck and adrenal PGLs. Exploration of extra-adrenal retroperitoneal PGL associated with SDHB or SDHD syndrome is the main limitation of this technique, encouraging the use of alternative functional imaging modalities like FDG-PET. Negativity of ¹⁸F-FDopa PET in the initial assessment of a PGL should prompt to search for a SDHx mutation.     

PLGA nanoparticles for peptide receptor radionuclide therapy of neuroendocrine tumors: a novel approach towards reduction of renal radiation dose

Background

Peptide receptor radionuclide therapy (PRRT), employed for treatment of neuroendocrine tumors (NETs) is based on over-expression of Somatostatin Receptors (SSTRs) on NETs. It is, however, limited by high uptake and retention of radiolabeled peptide in kidneys resulting in unnecessary radiation exposure thus causing nephrotoxicity. Employing a nanocarrier to deliver PRRT drugs specifically to the tumor can reduce the associated nephrotoxicity. Based on this, ¹⁷⁷Lu-DOTATATE loaded PLGA nanoparticles (NPs) were formulated in the present study, as a potential therapeutic model for NETs.

Methodology and Findings

DOTATATE was labeled with Lutetium-177 (¹⁷⁷Lu) (labeling efficiency 98%; R_f∼0.8). Polyethylene Glycol (PEG) coated ¹⁷⁷Lu-DOTATATE-PLGA NPs (50∶50 and 75∶25) formulated, were spherical with mean size of 304.5±80.8 and 733.4±101.3 nm (uncoated) and 303.8±67.2 and 494.3±71.8 nm (coated) for PLGA(50∶50) and PLGA(75∶25) respectively. Encapsulation efficiency (EE) and In-vitro release kinetics for uncoated and coated NPs of PLGA (50∶50 & 75∶25) were assessed and compared. Mean EE was 77.375±4.98% & 67.885±5.12% (uncoated) and 65.385±5.67% & 58.495±5.35% (coated). NPs showed initial burst release between 16.64–21.65% with total 42.83–44.79% over 21days. The release increased with coating to 20.4–23.95% initially and 60.97–69.12% over 21days. In-vivo studies were done in rats injected with ¹⁷⁷Lu-DOTATATE and ¹⁷⁷Lu-DOTATATE-NP (uncoated and PEG-coated) by imaging and organ counting after sacrificing rats at different time points over 24 hr post-injection. With ¹⁷⁷Lu-DOTATATE, renal uptake of 37.89±10.2%ID/g was observed, which reduced to 4.6±1.97% and 5.27±1.66%ID/g with uncoated and coated ¹⁷⁷Lu-DOTATATE-NP. The high liver uptake with uncoated ¹⁷⁷Lu-DOTATATE-NP (13.68±3.08% ID/g), reduced to 7.20±2.04%ID/g (p = 0.02) with PEG coating.

Conclusion

PLGA NPs were easily formulated and modified for desired release properties. PLGA 50∶50 NPs were a more suitable delivery vehicle for ¹⁷⁷Lu-DOTATATE than PLGA 75∶25 because of higher EE and slower release rate. Reduced renal retention of ¹⁷⁷Lu-DOTATATE and reduced opsonisation strongly advocate the potential of ¹⁷⁷Lu-DOTATATE-PLGA-PEG NPs to reduce radiation dose in PRRT.     

A metadata approach for clinical data management in translational genomics studies in breast cancer

Background

Paragangliomas of the head and neck are highly vascular and usually clinically benign tumors arising in the paraganglia of the autonomic nervous system. A significant number of cases (10–50%) are proven to be familial. Multiple genes encoding subunits of the mitochondrial succinate-dehydrogenase (SDH) complex are associated with hereditary paraganglioma: SDHB, SDHC and SDHD. Furthermore, a hereditary paraganglioma family has been identified with linkage to the PGL2 locus on 11q13. No SDH genes are known to be located in the 11q13 region, and the exact gene defect has not yet been identified in this family.

Methods

We have performed a RNA expression microarray study in sporadic, SDHD- and PGL2-linked head and neck paragangliomas in order to identify potential differences in gene expression leading to tumorigenesis in these genetically defined paraganglioma subgroups. We have focused our analysis on pathways and functional gene-groups that are known to be associated with SDH function and paraganglioma tumorigenesis, i.e. metabolism, hypoxia, and angiogenesis related pathways. We also evaluated gene clusters of interest on chromosome 11 (i.e. the PGL2 locus on 11q13 and the imprinted region 11p15).

Results

We found remarkable similarity in overall gene expression profiles of SDHD -linked, PGL2-linked and sporadic paraganglioma. The supervised analysis on pathways implicated in PGL tumor formation also did not reveal significant differences in gene expression between these paraganglioma subgroups. Moreover, we were not able to detect differences in gene-expression of chromosome 11 regions of interest (i.e. 11q23, 11q13, 11p15).

Conclusion

The similarity in gene-expression profiles suggests that PGL2, like SDHD, is involved in the functionality of the SDH complex, and that tumor formation in these subgroups involves the same pathways as in SDH linked paragangliomas. We were not able to clarify the exact identity of PGL2 on 11q13. The lack of differential gene-expression of chromosome 11 genes might indicate that chromosome 11 loss, as demonstrated in SDHD-linked paragangliomas, is an important feature in the formation of paragangliomas regardless of their genetic background.     

Treatment of high-grade glioma with radiolabeled peptides

The management of high-grade glioma (HGG) patients in clinical routine represents a challenging task. HGG has a poor prognosis because of early recurrence or therapy-refractory disease following first-line standard therapy, which includes a multidisciplinary approach involving radical surgical resection followed by external beam radiation therapy in combination with chemotherapy.Glioma cells are known to express specific receptors or glycoproteins on their surface which can be used as biological targets for treatment. The application of radiopharmaceuticals consisting of a targeting and an effector domain has led to the introduction of new treatment approaches, aiming at a tumor-specific treatment sparing normal brain tissue.One of these new modalities is the peptide receptor radionuclide therapy (PRRT). Peptides labeled with radioactive nuclides can bind directly to the tumor cells and deliver high doses of radioactivity directly to the tumor tissue.This article reviews the literature for PRRT in HGG.     

Pheochromocytoma and Paraganglioma

Objective: Pheochromocytomas (PHEOs) and paragangliomas (PGLs) are neural crest cell tumors associated with catecholamine production and assessed by a metanephrine/methoxytyramine measurement. This review summarizes the genetics of these tumors.Methods: Case presentation, review of the relevant literature, and bullet point conclusions.Results: Genetic research over the past 10 years has led to a better understanding of the pathogenesis of these tumors, currently associated with 20 susceptibility genes (both somatic and germ-line mutations). Although most of these genes can be divided into two clusters (clusters 1 and 2), recent data suggest that all mutations converge on the hypoxia-inducible factor signaling pathway. Most of the susceptibility genes are well characterized and associated with specific clinical presentations, including biochemical phenotype, tumor location and behavior, as well as neoplasms or similar characteristics. Correct and early detection of hereditary PHEO/PGL is paramount, as early diagnosis leads to improved and focused treatment, along with better outcomes. However, missed or delayed diagnosis of hereditary PHEO/PGL forestalls proper treatment and results in multiple, recurrent, or metastatic tumors and avoidable complications in some patients.Conclusion: Early diagnosis allows prompt screening for potentially lethal cancers associated with specific gene mutations and makes genetic testing more readily available to first-degree and other relatives of an index patient. Thus, understanding the genetics of these tumors is an essential part of endocrinology.Abbreviations: HIF2A = hypoxia-inducible factor 2α MAX = Myc-associated factor X MEN2 = multiple endocrine neoplasia type 2 NF1 = neurofibromatosis type 1 PGL = paraganglioma PHEO = pheochromocytoma SDHAF2 = succinate dehydrogenase complex assemble factor 2 TMEM127 = transmembrane protein 127 VHL = von Hippel-Lindau     

Dual targeting of a mature plastoglobulin/fibrillin fusion protein to chloroplast plastoglobules and thylakoids in transplastomic tobacco plants

Plastoglobules (PG) are lipid droplets in chloroplasts and other plastid types having important functions in lipid metabolism. Plastoglobulins (PGL) also known as fibrillins (FBN) are evolutionary conserved proteins present at the PG surface but also to various extents at the thylakoid membrane. PGLs are thought to have structural functions in PG formation and maintenance. The targeting of an Arabidopsis PGL (PGL34) to PG required the full protein sequence with the exception of a short C-terminal stretch. This indicated that PGL targeting relies on correct folding rather than a discrete sequence. PGLs lack strongly hydrophic regions and may therefore extrinsically associate with PG and thylakoid membranes via interaction with hydrophilic headgroups of surface lipids. Here, we report on the expression of the Arabidopsis plastoglobulin of 35kD (PGL35 or FBN1a) expressed as a mature protein fused to HIVp24 (human immunodeficiency virus capsid particle p24) or HCV (hepatitis C virus core protein) in transplastomic tobacco. A PGL35–HIVp24 fusion targeted in part to plastoglobules but a larger proportion was recovered in the thylakoid fraction. The findings indicate that transplastomic PGL35–HIVp24 folded correctly after its synthesis inside the chloroplast and then dually targeted to plastoglobules as well as thylakoid membranes.     

Radiothérapie métabolique dans les tumeurs neuroendocrines par le DOTATATE marqué au lutétium 177 : expérience libanaise à propos de 6 cas avec revue de la littérature

The prevalence of neuroendocrine tumors (NET) is rare. Although some aggressive forms may exist, most NET shows a slow growth. The diagnosis is frequently made at a metastatic stage with more than 50% of hepatic metastasis. The only curative treatment is radical surgery and the other non-surgical therapeutic choices are chemotherapy, hepatic chemoembolization, alpha interferon, cold or non-radioactive somatostatin analogues and, more recently introduced, metabolic or internal radiotherapy with a somatostatin analogue coupled to an appropriate radioisotope. Nowadays, imagining of NET with a 68Ga-DOTATATE PET allows obtaining a better image quality and an effective dosimetry before treating with a somatostatin analogue coupled to an appropriate radioisotope such as 177Lu-DOTATATE. This latter can stabilize a rapidly progressive disease and improve quality of life enough and change it deeply. We are presenting our Lebanese experience by reporting six cases treated with 177Lu-DOTATATE after a PET/CT 68Ga-DOTATATE, and a review of literature.     

External beam radiation therapy (EBRT) for patients with malignant pheochromocytoma and non-head and -neck paraganglioma: combination with 131I-MIBG

In patients with malignant pheochromocytoma and paraganglioma, 131I-MIBG radiotherapy can achieve an objective response rate of 30-50% with the dose limiting toxicity being hematologic. Patients with disseminated disease, who also have a few index bulky or symptomatic lesions, may benefit from the addition of targeted external beam radiotherapy alone or in combination with systemic 131I-MIBG. The records of patients with malignant paraganglioma who were treated with external beam radiotherapy at the University of Pennsylvania from February 1973 to February 2011 were reviewed in an institutional review board approved retrospective study. Of the 17 patients with tumors in the thorax, abdomen, or pelvis, 76% had local control or clinically significant symptomatic relief for at least 1 year or until death. As expected, the predominant toxicity was due to irradiation of tumor-adjacent normal tissues without clinically significant hematologic toxicity. Due to widespread systemic metastases with areas of bulky, symptomatic tumor, 5 of the 17 patients were treated with sequential 131I-MIBG (2 mCi/kg per treatment) and external beam radiotherapy to 9 sites. In these patients, all areas that were irradiated with external beam radiotherapy showed durable objective response despite all patients eventually experiencing out-of-field systemic progression requiring other treatment. Four of these patients remain alive with excellent performance status 16, 18, 23, and 24 months after external beam radiotherapy. External beam radiotherapy can be highly effective in local management of malignant paraganglioma and can be used in conjunction with 131I-MIBG due to nonoverlapping toxicities with excellent control of locally bulky tumors.     

Blood clearance and occupational exposure for <Superscript>177</Superscript>Lu-DOTATATE compared to <Superscript>177</Superscript>Lu-PSMA radionuclide therapy

The main target of this work is to examine blood clearance and external exposure for ¹⁷⁷Lu-DOTATATE compared with new emerging ¹⁷⁷Lu-PSMA therapy. Blood clearance and radiation exposure of 31 patients treated with 5.5?±?1.1 GBq ¹⁷⁷Lu-DOTATATE were compared to those of 23 patients treated with 7.4 GBq ¹⁷⁷Lu-PSMA. Dose rates were measured at several distances and time points up to 120 h after treatment. Blood samples were collected conjunctively after infusion. Caregiver’s cumulative dose was measured by means of an OSL (optically stimulated luminescence) dosimeter for 4–5 days and medical staff’s dose was also estimated using electronic personal dosimeters. Finger dose was determined via ring TLD (Thermoluminescence Dosimeter) for radiopharmacists and nurses. Dose rates due to ¹⁷⁷Lu-DOTATATE at a distance of 1 m, 4 h and 6 h after infusion, were 3.0?±?2.8 and 2?±?1.9 µSv/(h GBq), respectively, while those due to ¹⁷⁷Lu-PSMA were 3.1?±?0.8 and 2.2?±?0.9 µSv/(h GBq). Total effective dose of 17 caregivers was 100–200 µSv for ¹⁷⁷Lu-DOTATATE therapy. Mean effective doses to nurses and radiopharmacists were 5 and 4 µSv per patient, respectively, while those for physicists and physicians were 2 µSv per patient. For ¹⁷⁷Lu-DOTATATE, effective half-life in blood and early elimination phase were 0.31?±?0.13 and 4.5?±?1 h, while they were found as 0.4?±?0.1 and 5?±?1 h, respectively, for ¹⁷⁷Lu-PSMA. The first micturition time following ¹⁷⁷Lu-DOTATATE infusion was noted after 36?±?14 min, while the second and third voiding times were after 74?±?9 and 128?±?41 min, respectively. It is concluded that blood clearance and radiation exposure for ¹⁷⁷Lu-DOTATATE are very similar to those for ¹⁷⁷Lu-PSMA, and both treatment modalities are reasonably reliable for outpatient treatment, since the mean dose rate [2.1 µSv/(h GBq)] decreased below the dose rate that allows release of the patient from the hospital (20 µSv/h) after 6 h at 1 m distance.     

Inactivation of tesA reduces cell wall lipid production and increases drug susceptibility in mycobacteria

Phthiocerol dimycocerosates (PDIMs) and phenolic glycolipids (PGLs) are structurally related lipids noncovalently bound to the outer cell wall layer of Mycobacterium tuberculosis, Mycobacterium leprae, and several opportunistic mycobacterial human pathogens. PDIMs and PGLs are important effectors of virulence. Elucidation of the biosynthesis of these complex lipids will not only expand our understanding of mycobacterial cell wall biosynthesis, but it may also illuminate potential routes to novel therapeutics against mycobacterial infections. We report the construction of an in-frame deletion mutant of tesA (encoding a type II thioesterase) in the opportunistic human pathogen Mycobacterium marinum and the characterization of this mutant and its corresponding complemented strain control in terms of PDIM and PGL production. The growth and antibiotic susceptibility of these strains were also probed and compared with the parental wild-type strain. We show that deletion of tesA leads to a mutant that produces only traces of PDIMs and PGLs, has a slight growth yield increase and displays a substantial hypersusceptibility to several antibiotics. We also provide a robust model for the three-dimensional structure of M. marinum TesA (TesAmm) and demonstrate that a Ser-to-Ala substitution in the predicted catalytic Ser of TesAmm renders a mutant that recapitulates the phenotype of the tesA deletion mutant. Overall, our studies demonstrate a critical role for tesA in mycobacterial biology, advance our understanding of the biosynthesis of an important group of polyketide synthase-derived mycobacterial lipids, and suggest that drugs aimed at blocking PDIM and/or PGL production might synergize with antibiotic therapy in the control of mycobacterial infections.     

Peptide receptor radionuclide therapy of gastroenteropancreatic neuroendocrine tumors (GEP-NETs): From literature to practice

Well differentiated gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are characterized by the overexpression of specific biomarkers, especially somatostatin receptors subtype 2. Somatostatin receptor scintigraphy and currently, positron emission tomography using ⁶⁸Ga-labeled-somatostatin analogs are considered the gold standard for functional imaging of GEP-NETs. They are complementary to CT scan and to MRI, for the staging and restaging of these tumors and are useful to select patients for peptide receptor radionuclide therapy (PRRT), in a theranostic approach. Somatostatin analogues, radiolabeled with the beta-emitting radionuclides lutetium-177 and yttrium-90, have been developed for PRRT of GEP-NETs. The efficacy of this treatment depends on the intensity of uptake on pre-therapeutic scan, the extent of hepatic involvement, and a preserved global health status. Toxicity, mainly hematologic and renal can be reduced by a rigorous selection of patients and co-infusion of amino-acids. PRRT became possible since 2013 in some specialized centers in France, by the way of clinical research programs and temporary authorization from the Agence nationale de sécurité du médicament et des produits de santé to use PRRT. This decision took place after the communication of preliminary results of the NETTER-1 study, which confirmed the efficacy of LUTATHERA^® in the treatment of midgut NETs. A marketing authorization for this radiopharmaceutical is expected in France in 2017. This article reports the main data of the literature on the development of PRRT and its current use in France. It also reviews the indications and the side effects of the treatment, and presents the perspective of optimization of this promising therapeutic approach for the coming years. The other therapeutic options in GEP-NETs are also presented.     

Effect of image registration on 3D absorbed dose calculations in 177Lu-DOTATOC peptide receptor radionuclide therapy

Peptide receptor radionuclide therapy (PRRT) is an effective MRT (molecular radiotherapy) treatment, which consists of multiple administrations of a radiopharmaceutical labelled with ¹⁷⁷Lu or ⁹⁰Y. Through sequential functional imaging a patient specific 3D dosimetry can be derived. Multiple scans should be previously co-registered to allow accurate absorbed dose calculations. The purpose of this study is to evaluate the impact of image registration algorithms on 3D absorbed dose calculation.A cohort of patients was extracted from the database of a clinical trial in PRRT. They were administered with a single administration of ¹⁷⁷Lu-DOTATOC. All patients underwent 5 SPECT/CT sequential scans at 1 h, 4 h, 24 h, 40 h, 70 h post-injection that were subsequently registered using rigid and deformable algorithms. A similarity index was calculated to compare rigid and deformable registration algorithms. 3D absorbed dose calculation was carried out with the Raydose Monte Carlo code.The similarity analysis demonstrated the superiority of the deformable registrations (p < .001).Average absorbed dose to the kidneys calculated using rigid image registration was consistently lower than the average absorbed dose calculated using the deformable algorithm (90% of cases), with percentage differences in the range [−19; +4]%. Absorbed dose to lesions were also consistently lower (90% of cases) when calculated with rigid image registration with absorbed dose differences in the range [−67.2; 100.7]%. Deformable image registration had a significant role in calculating 3D absorbed dose to organs or lesions with volumes smaller than 100 mL.Image based 3D dosimetry for ¹⁷⁷Lu-DOTATOC PRRT is significantly affected by the type of algorithm used to register sequential SPECT/CT scans.     

Paraganglioma of the Head and Neck: A Review

ObjectiveTo review the epidemiology, presentation, diagnosis, and management of head and neck paragangliomas.MethodsA literature review of english language papers with focus on most current literature.ResultsParagangliomas (PGLs) are a group of neuroendocrine tumors that arise in the parasympathetic or sympathetic ganglia. Head and neck PGLs (HNPGLs) comprise 65% to 70% of all PGLs and account for 0.6% of all head and neck cancers. The majority of HNPGLs are benign, and 6% to 19% of all HNPGLs develop metastasis outside the tumor site and significantly compromise survival. PGLs can have a familial etiology with germline sequence variations in different susceptibility genes, with the gene encoding succinate dehydrogenase being the most common sequence variation, or they can arise from somatic sequence variations or fusion genes. Workup includes biochemical testing to rule out secretory components, although it is rare in HNPGLs. In addition, imaging modalities, such as computed tomography and magnetic resonance imaging, help in monitoring in surgical planning. Functional imaging with DOTATATE-positron emission tomography, 18F-fluorodeoxyglucose, or 18F-fluorohydroxyphenylalanine may be necessary to rule out sites of metastases. The management of HNPGLs is complex depending on pathology, location, and aggressiveness of the tumor. Treatment ranges from observation to resection to systemic treatment. Similarly, the prognosis ranges from a normal life expectancy to a 5-year survival of 11.8% in patients with distant metastasis.ConclusionOur review is a comprehensive summary of the incidence, mortality, pathogenesis, presentation, workup and management of HNPGLs.     

Biosynthesis of Cell Envelope-Associated Phenolic Glycolipids in Mycobacterium marinum

Phenolic glycolipids (PGLs) are polyketide synthase-derived glycolipids unique to pathogenic mycobacteria. PGLs are found in several clinically relevant species, including various Mycobacterium tuberculosis strains, Mycobacterium leprae, and several nontuberculous mycobacterial pathogens, such as M. marinum. Multiple lines of investigation implicate PGLs in virulence, thus underscoring the relevance of a deep understanding of PGL biosynthesis. We report mutational and biochemical studies that interrogate the mechanism by which PGL biosynthetic intermediates (p-hydroxyphenylalkanoates) synthesized by the iterative polyketide synthase Pks15/1 are transferred to the noniterative polyketide synthase PpsA for acyl chain extension in M. marinum. Our findings support a model in which the transfer of the intermediates is dependent on a p-hydroxyphenylalkanoyl-AMP ligase (FadD29) acting as an intermediary between the iterative and the noniterative synthase systems. Our results also establish the p-hydroxyphenylalkanoate extension ability of PpsA, the first-acting enzyme of a multisubunit noniterative polyketide synthase system. Notably, this noniterative system is also loaded with fatty acids by a specific fatty acyl-AMP ligase (FadD26) for biosynthesis of phthiocerol dimycocerosates (PDIMs), which are nonglycosylated lipids structurally related to PGLs. To our knowledge, the partially overlapping PGL and PDIM biosynthetic pathways provide the first example of two distinct, pathway-dedicated acyl-AMP ligases loading the same type I polyketide synthase system with two alternate starter units to produce two structurally different families of metabolites. The studies reported here advance our understanding of the biosynthesis of an important group of mycobacterial glycolipids.     

The VHL gene is epigenetically inactivated in pheochromocytomas and abdominal paragangliomas

Pheochromocytoma (PCC) and abdominal paraganglioma (PGL) are neuroendocrine tumors that present with clinical symptoms related to increased catecholamine levels. About a third of the cases are associated with constitutional mutations in pre-disposing genes, of which some may also be somatically mutated in sporadic cases. However, little is known about inactivating epigenetic events through promoter methylation in these very genes. Using bisulphite pyrosequencing we assessed the methylation density of 11 PCC/PGL disease genes in 96 tumors (83 PCCs and 13 PGLs) and 34 normal adrenal references. Gene expression levels were determined by quantitative RT-PCR. Both tumors and normal adrenal samples exhibited low methylation index (MetI) in the EGLN1 (PDH2), MAX, MEN1, NF1, SDHB, SDHC, SDHD, SDHAF2 (SDH5), and TMEM127 promoters, not exceeding 10% in any of the samples investigated. Aberrant RET promoter methylation was observed in two cases only. For the VHL gene we found increased MetI in tumors as compared with normal adrenals (57% vs. 27%; P < 0.001), in malignant vs. benign tumors (63% vs. 55%; P < 0.05), and in PGL vs. PCC (66% vs. 55%; P < 0.0005). Decreased expression of the VHL gene was observed in all tumors compared with normal adrenals (P < 0.001). VHL MetI and gene expressions were inversely correlated (R = −0.359, P < 0.0001). Our results show that the VHL gene promoter has increased methylation compared with normal adrenals (MetI > 50%) in approximately 75% of PCCs and PGLs investigated, highlighting the role of VHL in the development of these tumors.     

AN AGGRESSIVE TEMPORAL BONE SDHC PARAGANGLIOMA ASSOCIATED WITH INCREASED HIF-2α SIGNALING

Objective: To describe a patient with a germline succinate dehydrogenase (SDHC) gene mutation presenting with primary hyperparathyroidism and a large catecholamine-producing temporal bone paraganglioma (PGL).Methods: Evaluation of a SDHC mutation–positive PGL tumor biology using staining for tyrosine hydroxylase (TH), hypoxia-inducible factors 1α (HIF-1α) and 2α (HIF-2α).Results: A 66-year-old man was noted to have a lytic skull base mass during work-up for his primary hyperparathyroidism. Biochemical evaluation with 24-hour urine catecholamines and metanephrines revealed marked elevation of norepinephrine and normetanephrine. Genetic testing revealed a germline SDHC mutation. A partial excision of skull base tumor was performed, which upon further examination revealed PGL. Immunohistochemistry of skull base PGL demonstrated heavy expression of TH and HIF-2α but reduced expression of HIF-1α. The remaining skull base PGL was treated with adjuvant radiation therapy. The patient's normetanephrine levels significantly decreased after surgery and radiation.Conclusion: Here, we report an unusual case of a patient presenting with a germline SDHC mutation–related functional PGL along with concomitant primary hyperparathyroidism. The present case illustrates that overexpression of HIF-2α but not of HIF-1α is linked to the pathogenesis of SDHC mutation–related PGL, and it may be responsible for the aggressive clinical behavior of a usually indolent course of SDHC-related PGLs.Abbreviations:HIF = hypoxia-inducible factorMEN2A = multiple endocrine neoplasia type 2aPCC = pheochromocytomaPGL = paragangliomaPTH = parathyroid hormoneSDH = succinate dehydrogenaseTH = tyrosine hydroxylase