Incidence of endocrine cancers is rising every year. Over the last decade, evidence has accumulated that demonstrates the anti-cancer effects of an anti-diabetic drug, metformin, in endocrine malignancies. We performed a literature review utilizing the PubMed, Medline and clinicaltrials.gov databases using the keyword ‘metformin’ plus the following terms: ‘thyroid cancer’, ‘thyroid nodules’, ‘parathyroid’, ‘hyperparathyroidism’, ‘adrenal adenoma’, ‘Cushing syndrome’, ‘hyperaldosteronism’, ‘adrenocortical cancer’, ‘neuroendocrine tumor (NET)’, ‘pancreatic NET (pNET)’, ‘carcinoid’, ‘pituitary adenoma’, ‘pituitary neuroendocrine tumor (PitNET)’, ‘prolactinoma’, ‘pheochromocytoma/paraganglioma’. We found 37 studies describing the preclinical and clinical role of metformin in endocrine tumors. The available epidemiological data show an association between exposure of metformin and lower incidence of thyroid cancer and pNETs in diabetic patients. Metformin treatment has been associated with better response to cancer therapy in thyroid cancer and pNETs. Preclinical evidence suggests that the primary direct mechanisms of metformin action include inhibition of mitochondrial oxidative phosphorylation via inhibition of both mitochondrial complex I and mitochondrial glycerophosphate dehydrogenase, leading to metabolic stress. Decreased ATP production leads to an activation of a cellular energy sensor, AMPK, and subsequent downregulation of mTOR signaling pathway, which is associated with decreased cellular proliferation. We also describe several AMPK-independent mechanisms of metformin action, as well as the indirect mechanisms targeting insulin resistance. Overall, repositioning of metformin has emerged as a promising strategy for adjuvant therapy of endocrine tumors. The mechanisms of synergy between metformin and other anti-cancer agents need to be elucidated further to guide well-designed prospective trials on combination therapies in endocrine malignancies.
Shilpa Thakur, Brianna Daley, and Joanna Klubo-Gwiezdzinska
Svenja Nölting, Edwin Garcia, Ghassan Alusi, Alessio Giubellino, Karel Pacak, Márta Korbonits, and Ashley B Grossman
Currently, there is no completely effective therapy available for metastatic phaeochromocytomas (PCCs) and paragangliomas. In this study, we explore new molecular targeted therapies for these tumours, using one more benign (mouse phaeochromocytoma cell (MPC)) and one more malignant (mouse tumour tissue (MTT)) mouse PCC cell line – both generated from heterozygous neurofibromin 1 knockout mice. Several PCC-promoting gene mutations have been associated with aberrant activation of PI3K/AKT, mTORC1 and RAS/RAF/ERK signalling. We therefore investigated different agents that interfere specifically with these pathways, including antagonism of the IGF1 receptor by NVP-AEW541. We found that NVP-AEW541 significantly reduced MPC and MTT cell viability at relatively high doses but led to a compensatory up-regulation of ERK and mTORC1 signalling at suboptimal doses while PI3K/AKT inhibition remained stable. We subsequently investigated the effect of the dual PI3K/mTORC1/2 inhibitor NVP-BEZ235, which led to a significant decrease of MPC and MTT cell viability at doses down to 50 nM but again increased ERK signalling. Accordingly, we next examined the combination of NVP-BEZ235 with the established agent lovastatin, as this has been described to inhibit ERK signalling. Lovastatin alone significantly reduced MPC and MTT cell viability at therapeutically relevant doses and inhibited both ERK and AKT signalling, but increased mTORC1/p70S6K signalling. Combination treatment with NVP-BEZ235 and lovastatin showed a significant additive effect in MPC and MTT cells and resulted in inhibition of both AKT and mTORC1/p70S6K signalling without ERK up-regulation. Simultaneous inhibition of PI3K/AKT, mTORC1/2 and ERK signalling suggests a novel therapeutic approach for malignant PCCs.
Christian Fottner, Timo Minnemann, Sarah Kalmbach, and Matthias M Weber
In order to determine the role of the IGF-I receptor (IGF-IR) in human pheochromocytomas we have compared the expression of the IGF-IR in normal tissues and in pheochromocytomas with regard to the IGF-IR mRNA levels and ligand binding. By semiquantitative reverse transcription polymerase chain reaction (RT-PCR), the mRNA of the IGF-IR could be detected in all samples of normal adrenomedullary cells (n=13) and pheochromocytomas (n=16). However, pheochromocytomas exhibited 2.8-fold higher mean IGF-IR mRNA levels than normal adrenomedullary cells (2.8±0.5×105 molecules/μg RNA vs 7.8±1.2×105 molecules/μg RNA; P < 0.001). This overexpression of the IGF-IR in pheochromocytomas could be confirmed at the protein level by binding studies. Radioligand assays and Scatchard analysis revealed a single class of high affinity IGF-IR binding sites with a similar dissociation constant (K d: 0.32±0.1 nmol/l vs 0.22±0.08 nmol/l) for both normal adrenomedullary cells and pheochromocytomas. However, specific 125I-labeled IGF-I binding and the calculated receptor concentration were significantly elevated in pheochromocytomas as compared with normal adrenomedullary cells (58.3±5 vs 24.3±12 nmol/kg protein; P < 0.05). In summary, our results demonstrate significant overexpression of the IGF-IR in human pheochromocytomas. This suggests a possible role of the IGF system in the pathogenesis of adrenal neoplasia and thus IGF-IR may be a target for future therapeutic approaches.
G Monges, P Biagini, J-F Cantaloube, C Chicheportiche, V Frances, D Brandini, P Parc, J-F Seitz, M Giovannini, R Sauvan, and J Hassoun
To investigate the hypothesis that gastrin might be synthesized by tumour tissues in cancer of the colon, samples from six human colon tumours, one hepatic metastasis, four normal colonic mucosal samples and two antral and one fundic gastric mucosal samples from nine patients were analysed to determine whether gastrin mRNA was present.
RNA was extracted from surgical specimens by ultracentrifugation on a CsC1 cushion, purified using the guanidinium thiocyanate method, reversetranscribed and amplified by polymerase chain reaction. Gastrin mRNA was detected in each colonic carcinoma sample (including the hepatic metastasis), while no such signal was observed in normal colon biopsies. Positive and negative controls (gastric antrum and fundus respectively) gave the expected results. In each of the positive samples, the chemiluminescent revelation of amplified products after Southern blotting corresponded to gastrin mRNA without the intron.
These findings demonstrate the ability of primary and metastatic human colonic tumours to produce gastrin mRNA. Since malignant cell lines have been reported to produce gastrin peptide, and since gastrin receptors were present in some cases, our results support the idea that gastrin may be involved in an autocrine mechanism.
Shu-Ching M Wang, Dennis H Dowhan, and George E O Muscat
Breast cancer is a heterogeneous disease, and the complexity of breast carcinogenesis is associated with epigenetic modification. There are several major classes of epigenetic enzymes that regulate chromatin activity. This review will focus on the nine mammalian protein arginine methyltransferases (PRMTs) and the dysregulation of PRMT expression and function in breast cancer. This class of enzymes catalyse the mono- and (symmetric and asymmetric) di-methylation of arginine residues on histone and non-histone target proteins. PRMT signalling (and R methylation) drives cellular proliferation, cell invasion and metastasis, targeting (i) nuclear hormone receptor signalling, (ii) tumour suppressors, (iii) TGF-β and EMT signalling and (iv) alternative splicing and DNA/chromatin stability, influencing the clinical and survival outcomes in breast cancer. Emerging reports suggest that PRMTs are also implicated in the development of drug/endocrine resistance providing another prospective avenue for the treatment of hormone resistance and associated metastasis. The complexity of PRMT signalling is further underscored by the degree of alternative splicing and the scope of variant isoforms (with distinct properties) within each PRMT family member. The evolution of PRMT inhibitors, and the ongoing clinical trials of PRMT inhibitors against a subgroup of solid cancers, coupled to the track record of lysine methyltransferases inhibitors in phase I/II clinical trials against cancer underscores the potential therapeutic utility of targeting PRMT epigenetic enzymes to improve survival outcomes in aggressive and metastatic breast cancer.
J Guillemot, E Thouënnon, M Guérin, V Vallet-Erdtmann, A Ravni, M Montéro-Hadjadje, H Lefebvre, M Klein, M Muresan, N G Seidah, Y Anouar, and L Yon
We have previously demonstrated that measurement of tissue concentrations of the secretogranin II (SgII or SCG2 as listed in the HUGO database)-derived peptide EM66 may help to discriminate between benign and malignant pheochromocytomas and that EM66 represents a sensitive plasma marker of pheochromocytomas. Here, we investigated the gene expression and protein production of SgII in 13 normal adrenal glands, and 35 benign and 16 malignant pheochromocytomas with the goal to examine the molecular mechanisms leading to the marked variations in the expression of EM66 in tumoral chromaffin tissue. EM66 peptide levels were 16-fold higher in benign than in malignant pheochromocytomas and had an area under the receiver-operating characteristic curve of 0.95 for the distinction of benign and malignant tumors. Q-PCR experiments indicated that the SgII gene was significantly underexpressed in malignant tumors compared with benign tumors. Western blot analysis using antisera directed against SgII and SgII-derived fragments revealed lower SgII protein and SgII-processing products in malignant tumors. Western blot also showed that low p-cAMP-responsive element-binding (CREB) concentrations seemed to be associated with the malignant status. In addition, the prohormone convertase PC1 and PC2 genes and proteins were overexpressed in benign pheochromocytomas compared with malignant pheochromocytomas. Low concentrations of EM66 found in malignant tumors are associated with reduced expression and production of SgII and SgII-derived peptides that could be ascribed to a decrease in SgII gene transcription, probably linked to p-CREB down-regulation, and to lower PC levels. These findings highlight the mechanisms leading to lower concentrations of EM66 in malignant pheochromocytoma and strengthen the notion that this peptide is a suitable marker of this neuroendocrine tumor.
Nima Sharifi, Robert J Lechleider, and William L Farrar
The transforming growth factor-β (TGF-β) pathway plays dual roles in cancer, inhibiting epithelial cell growth under normal physiologic conditions, but promoting invasion and metastasis once growth inhibitory responses are lost. Two recent papers show that TGF-β receptor III is the most common TGF-β pathway component downregulated in prostate cancer. Here, we discuss the implications of these findings and what it may mean about the biology of this disease.
Danrong Ye, Yang Jiang, Yihan Sun, Yuefeng Li, Yefeng Cai, Qingxuan Wang, Ouchen Wang, Endong Chen, and Xiaohua Zhang
Thyroid cancer is associated with one of the most malignant endocrine tumors. However, molecular mechanisms underlying thyroid tumorigenesis and progression remain unclear. In order to investigate these mechanisms, we performed whole-transcriptome sequencing, which indicated that a differentially expressed gene, METTL7B, was highly expressed in thyroid cancers. We analyzed METTL7B expression using TCGA and performed qRT-PCR on tissue samples. Moreover, an analysis of clinicopathological characteristics revealed a positive correlation between METTL7B and lymph node metastasis. A series of in vitro experiments indicated that METTL7B enhanced migration and invasion of thyroid carcinoma cells. Further studies revealed that METTL7B may enhance TGF-β1-induced epithelial-mesenchymal transition (EMT). Our results indicate that METTL7B may promote metastasis of thyroid cancer through EMT and may therefore be considered as a potential biomarker for the diagnosis and prognosis of thyroid carcinoma.
Ali Salajegheh, Haleh Vosgha, Atiqur Md Rahman, Moein Amin, Robert Anthony Smith, and Alfred King-Yin Lam
miR-205 plays a crucial role in angiogenesis and has been found in association with several types of cancers. The aims of this study were to investigate the clinical and functional roles of miR-205 on as the major initiator and modulator of angiogenesis in thyroid cancer. 101 thyroid carcinomas, including 51 conventional and 37 follicular variants of papillary thyroid carcinomas, and 13 undifferentiated thyroid carcinomas in addition to 13 lymph nodes with metastatic thyroid carcinoma were recruited to be compared with 14 nodular goitre and seven normal thyroid tissues. Five thyroid carcinoma cell lines, of papillary and undifferentiated origin with and without history of metastasis, were also used. Expression of vascular endothelial growth factor A (VEGFA) and miR-205 were measured and exogenous miR-205 were transfected to observe the changes of VEGFA (by immunofluorescence and western blot techniques). Proliferation assay, cell cycle analysis and apoptosis assays were also used to evaluate the role of miR-205 in these events. Significant under-expression of miR-205 and over-expression of VEGFA mRNA and protein were noticed in thyroid cancer tissues and cell lines compared to normal thyroid control. Transfection of miR-205 into the cancer cell lines caused significant reduction of VEGFA protein and significant inhibition in cell proliferation, arrest in G0-G1 of the cell cycle and promotion of total apoptosis (P<0.05). The angiogenic and tumour-suppressive roles of miRNA-205 were demonstrated for the first time in thyroid cancer. The current experiments provided specific information on the functional consequences of VEGF manipulation via miRNA on cancer.
Carrie S Shemanko
Prolactin and prolactin receptor signaling and function are complex in nature and intricate in function. Basic, pre-clinical and translational research has opened up our eyes to the understanding that prolactin and prolactin receptor signaling function differently within different cellular contexts and microenvironmental conditions. Its multiple roles in normal physiology are subverted in cancer initiation and progression, and gradually we are teasing out the intricacies of function and therapeutic value. Recently, we observed that prolactin has a role in accelerating the time to bone metastasis in breast cancer patients and identified the mechanism by which prolactin stimulated breast cancer cell-mediated lytic osteoclast formation. The possibility that the prolactin receptor is a marker for metastasis, and specifically bone metastasis, is one that may have to be put into the context of the different variants of prolactin, different prolactin receptor isoforms and intricate signaling pathways that are regulated by the microenvironment. The more complete the picture, the better one can test biomarker identity and design clinical trials to test therapeutic intervention. This review will cover the recent advances and highlight the complexity of prolactin receptor biology.