The controlled polymerization of vinyl acetate has been recently achieved by several techniques, but PVAc with targeted M n and low dispersity up to very high monomer conversions and high degrees of ...polymerization was only obtained with Co(acac)2 as controlling agent in the so-called CMRP, a type of organometallic mediated radical polymerization (OMRP). Other techniques (including ATRP, ITP, TERP, and RAFT/MADIX) have shown a more or less pronounced slowdown in the polymerization kinetics, which was attributed to the higher strength of the C–X bond between the radical PVAc chain and the trapping agent (X) in the dormant species and to a consequent slower reactivation after a less frequent head-to-head monomer addition. The reason for the CMRP exception is clarified by the present contribution. First, a detailed investigation by 1H, 13C and multiplicity-edited HSQC and DEPT-135 NMR of the PVAc obtained by CMRP, in comparison with a regular polymer made by free radical polymerization under the same conditions, has revealed that Co(acac)2 does not significantly alter the fraction of head-to-head sequences in the polymer backbone and that there is no accumulation of Co(acac)2-capped chains with a head-to-head ω end. Hence, both dormant chains (following the head-to-head and the head-to-tail monomer additions) must be reactivated at similar rates. A DFT study shows that this is possible because the dormant chains are stabilized not only by the C–Co σ bond but also by formation of a chelate ring through coordination of the ω monomer carbonyl group. The head-to-head dormant chain contains an inherently stronger C–Co bond but forms a weaker 6-membered chelate ring, whereas the weaker C–Co bond in the head-to-tail dormant chain is compensated by a stronger 5-membered chelate ring. Combination of the two effects leads to similar activation enthalpies, as verified by DFT calculations using a variety of local, gradient-corrected, hybrid and “ad hoc” functionals (BPW91, B3PW91, BPW91*, M06 and M06L). While the BDE(C–X) of model H-VAc–X molecules X = Cl, I, MeTe, EtOC(S)S and Co(acac)2 are functional dependent, the BDE difference between head-to-head and head-to-tail dormant chain models is almost functional insensitive, with values of 5–9 kcal/mol for the ATRP, ITP and TERP models, 3–6 for the RAFT/MADIX model, and around zero for CMRP.
This work reveals the preponderance of an intramolecular metal chelation phenomenon in a controlled radical polymerization system involving the reversible trapping of the radical chains by a cobalt ...complex bis(acetylacetonato)cobalt(II). The cobalt‐mediated radical polymerization (CMRP) of a series of N‐vinyl amides was considered with the aim of studying the effect of the cobalt chelation by the amide moiety of the last monomer unit of the chain. The latter reinforces the cobaltpolymer bond in the order N‐vinylpyrrolidone<N‐vinyl caprolactam<N‐methyl‐N‐vinyl acetamide, and is responsible for the optimal control of the polymerizations observed for the last two monomers. Such a double linkage between the controlling agent and the polymer, through a covalent bond and a dative bond, is unique in the field of controlled radical polymerization and represents a powerful opportunity to fine tune the equilibrium between latent and free radicals. Possible hydrogen bond formation is also taken into account in the case of N‐vinyl acetamide and N‐vinyl formamide. These results are essential for understanding the factors influencing CoC bond strength in general, and the CMRP mechanism in particular, but also for developing a powerful platform for the synthesis of new precision poly(N‐vinyl amide) materials, which are an important class of polymers that sustain numerous applications today.
Growing the chain: In addition to reversible cobaltcarbon bond formation, an intramolecular metal chelation phenomenon occurs in the cobalt‐mediated radical polymerization (CMRP) of N‐vinyl amides (see scheme). The latter reinforces the metalpolymer bond and allows optimal control of the polymerizations of N‐vinyl caprolactam and N‐methyl vinyl acetamide. The detrimental effect of hydrogen bond formation in the CMRP of N‐vinyl acetamide and N‐vinyl formamide is also considered.
The tricarboxylic acid (TCA) cycle is a central metabolic pathway responsible for supplying reducing potential for oxidative phosphorylation and anabolic substrates for cell growth, repair and ...proliferation. As such it thought to be essential for cell proliferation and tissue homeostasis. However, since the initial report of an inactivating mutation in the TCA cycle enzyme complex, succinate dehydrogenase (SDH) in paraganglioma (PGL), it has become clear that some cells and tissues are not only able to survive with a truncated TCA cycle, but that they are also able of supporting proliferative phenotype observed in tumours. Here, we show that loss of SDH activity leads to changes in the metabolism of non-essential amino acids. In particular, we demonstrate that pyruvate carboxylase is essential to re-supply the depleted pool of aspartate in SDH-deficient cells. Our results demonstrate that the loss of SDH reduces the metabolic plasticity of cells, suggesting vulnerabilities that can be targeted therapeutically.
Comprehensive genetic analyses have identified germline
and
gene mutations as predominant causes of metastatic paraganglioma and pheochromocytoma. However, some suspicious cases remain unexplained. ...In this study, we performed whole-exome sequencing of a paraganglioma exhibiting an
-like molecular profile in the absence of
or
mutations and identified a germline mutation in the
gene, which encodes the mitochondrial 2-oxoglutarate/malate carrier. Germline
mutations were identified in six other patients, five of whom had metastatic disease. These mutations were associated with loss of heterozygosity, suggesting that
acts as a tumor-suppressor gene. Pseudohypoxic and hypermethylator phenotypes comparable with those described in
- and
-related tumors were observed both in tumors with mutated
and in
immortalized mouse chromaffin knockout cells generated by CRISPR-Cas9 technology. These data show that
is a novel paraganglioma susceptibility gene for which loss of function correlates with metastatic presentation.
A gene encoding a mitochondrial carrier is implicated in a hereditary cancer predisposition syndrome, expanding the role of mitochondrial dysfunction in paraganglioma.
.
Reversible-deactivation radical polymerization (RDRP) of methyl methacrylate (MMA) and styrene (St) was successfully mediated by copper(II) acetylacetonate, Cu(acac)2, or copper(II) ...hexafluoroacetylacetonate, Cu(hfa)2, in conjunction with 1-cyano-1-methylethyl diethyldithiocarbamate (MAN-DC) or 2-(N,N-diethyldithiocarbamyl)ethyl isobutyrate (EMA-DC) initiators/transfer agents in the absence of additional reducing agents. Linear first-order kinetic plots were obtained for the polymerization of MMA in the presence of Cu(hfa)2 or Cu(acac)2 and MAN-DC. Cu(hfa)2 provided better control than Cu(acac)2 for the polymerization of MMA, leading to PMMA with narrow molecular weight distribution, M w/M n ∼ 1.1. Polymerization of St was successfully carried out with either MAN-DC or EMA-DC in the presence of Cu(hfa)2, also resulting in polymers with low M w/M n values. In the absence of alkyl dithiocarbamates or copper acetylacetonates, the polymerizations resulted in only trace amounts of polymers or polymers with high values of M w/M n. Thus, the combination of alkyl dithiocarbamates and copper(II) acetylacetonates provides a convenient way to prepare well-controlled PMMA and PSt. NMR analysis of low-MW polymers reveals the presence of DC groups as chain ends. DFT calculations show that DC group transfer from a H-MMA-DC model of the growing chain to the Cu(II) complexes is energetically accessible and more favorable than Br atom transfer, thus rationalizing the need for the Cu(II)/dithiocarbamate combination for successful control and suggesting that the process takes place by reversible DC group transfer involving a CuII/CuIII couple. Attempts to synthesize complexes Cu(acac)2(DC) and Cu(hfa)2(DC), in combination with DFT calculations, suggest that these complexes are thermodynamically unstable relative to the bis(diketonate)copper(II) and dithiuram disulfide, but this does not preclude the involvement of the Cu(III) species as a spin trap in RDRP controlled by DC group transfer.
Accurate temperature rises prediction in gas insulated switchgears (GIS) is necessary to reduce the number of unsuccessful qualification tests for IEC standard 62271 validation. Numerical simulation ...is recently the most adapted tool used to achieve this goal. Due to the complexity of GIS geometries and to the physical phenomena interaction, the simulation involves several fields of engineering. This article proposes a multiphysics numerical model for temperature rise prediction on GIS busbars. It also highlights the benefit of temperature rises prediction with numerical simulations for cooling solutions design and validation.
Pheochromocytomas and paragangliomas (PCCs/PGLs) are neural crest-derived tumours with a very strong genetic component. Here we report the first integrated genomic examination of a large collection ...of PCC/PGL. SNP array analysis reveals distinct copy-number patterns associated with genetic background. Whole-exome sequencing shows a low mutation rate of 0.3 mutations per megabase, with few recurrent somatic mutations in genes not previously associated with PCC/PGL. DNA methylation arrays and miRNA sequencing identify DNA methylation changes and miRNA expression clusters strongly associated with messenger RNA expression profiling. Overexpression of the miRNA cluster 182/96/183 is specific in SDHB-mutated tumours and induces malignant traits, whereas silencing of the imprinted DLK1-MEG3 miRNA cluster appears as a potential driver in a subgroup of sporadic tumours. Altogether, the complete genomic landscape of PCC/PGL is mainly driven by distinct germline and/or somatic mutations in susceptibility genes and reveals different molecular entities, characterized by a set of unique genomic alterations.
Although the alteration of cellular metabolism in cancer was reported by Warburg in the early 1930s, a regain of interest in cancer metabolism has more recently followed the discovery of germline or ...somatic mutations in genes coding for metabolic enzymes (succinate dehydrogenase, fumarate hydratase and isocitrate dehydrogenase) that are associated with tumor susceptibility. Mutations in these genes are found in numerous tumor types including paragangliomas, kidney cancers, leiomyomas, glioblastomas and acute myeloid leukemia. They lead to the accumulation of so‐called oncometabolites that behave as competitors of 2‐oxoglutarate‐dependent dioxygenases, involved in a broad spectrum of pathways such as hypoxic response and epigenetic reprogramming. Here, we review the diverse pathways affected by oncometabolites, their potential role in cancer formation, maintenance, metastasis and sensitivity to chemotherapies, as well as emerging new therapeutic strategies.
Succinate dehydrogenase is a key enzyme in the tricarboxylic acid cycle and the electron transport chain. All four subunits of succinate dehydrogenase are tumor suppressor genes predisposing to ...paraganglioma, but only mutations in the SDHB subunit are associated with increased risk of metastasis. Here we generated an
knockout chromaffin cell line and compared it with
deficient cells. Both cell types exhibited similar SDH loss of function, metabolic adaptation, and succinate accumulation. In contrast,
cells showed hallmarks of mesenchymal transition associated with increased DNA hypermethylation and a stronger pseudo-hypoxic phenotype compared with
cells. Loss of SDHB specifically led to increased oxidative stress associated with dysregulated iron and copper homeostasis in the absence of NRF2 activation. High-dose ascorbate exacerbated the increase in mitochondrial reactive oxygen species, leading to cell death in
cells. These data establish a mechanism linking oxidative stress to iron homeostasis that specifically occurs in
-deficient cells and may promote metastasis. They also highlight high-dose ascorbate as a promising therapeutic strategy for SDHB-related cancers. SIGNIFICANCE: Loss of different succinate dehydrogenase subunits can lead to different cell and tumor phenotypes, linking stronger 2-OG-dependent dioxygenases inhibition, iron overload, and ROS accumulation following SDHB mutation.
Malignant pheochromocytoma (PCC) and paraganglioma (PGL) are mostly caused by germline mutations of SDHB, encoding a subunit of succinate dehydrogenase. Using whole-exome sequencing, we recently ...identified a mutation in the FH gene encoding fumarate hydratase, in a PCC with an 'SDH-like' molecular phenotype. Here, we investigated the role of FH in PCC/PGL predisposition, by screening for germline FH mutations in a large international cohort of patients. We screened 598 patients with PCC/PGL without mutations in known PCC/PGL susceptibility genes. We searched for FH germline mutations and large deletions, by direct sequencing and multiplex ligation-dependent probe amplification methods. Global alterations in DNA methylation and protein succination were assessed by immunohistochemical staining for 5-hydroxymethylcytosine (5-hmC) and S-(2-succinyl) cysteine (2SC), respectively. We identified five pathogenic germline FH mutations (four missense and one splice mutation) in five patients. Somatic inactivation of the second allele, resulting in a loss of fumarate hydratase activity, was demonstrated in tumors with FH mutations. Low tumor levels of 5-hmC, resembling those in SDHB-deficient tumors, and positive 2SC staining were detected in tumors with FH mutations. Clinically, metastatic phenotype (P = 0.007) and multiple tumors (P = 0.02) were significantly more frequent in patients with FH mutations than those without such mutations. This study reveals a new role for FH in susceptibility to malignant and/or multiple PCC/PGL. Remarkably, FH-deficient PCC/PGLs display the same pattern of epigenetic deregulation as SDHB-mutated malignant PCC/PGL. Therefore, we propose that mutation screening for FH should be included in PCC/PGL genetic testing, at least for tumors with malignant behavior.
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