Tracking anti‐fibrotic pathways of nilotinib and imatinib in experimentally induced liver fibrosis: An insight

The tyrosine kinase inhibitors imatinib and nilotinib have been suggested to have promising antifibrotic activity in experimental models of liver fibrosis. The aim of the present study was to investigate new pathways underlying this beneficial effect. Hepatic injury was induced in male Wistar rats by intraperitoneal injection of CCl₄ for 12 weeks. During the last 8 weeks of treatment, rats were also injected daily intraperitoneally with 20 mg/kg imatinib or 20, 10 or 5 mg/kg nilotinib. At the end of treatment, effects on fibrosis were assessed by measuring serum fibrotic markers and profibrogenic cytokines, as well as by histopathological examination. Possible anti‐inflammatory effects were estimated by measuring levels of inflammatory cytokines in liver tissue. Liver expression of α‐smooth muscle actin, transforming growth factor (TGF)‐β1 antibodies and platelet‐derived growth factor receptor β (PDGFRβ) was evaluated by immunohistochemical staining techniques. Nilotinib (5 and 10 mg/kg) significantly (P < 0.05) decreased all serum fibrotic markers measured, but 20 mg/kg of either nilotinib or imatinib had limited effects. At all doses tested, nilotinib significantly (P < 0.05) decreased the CCl₄‐induced increases in tissue inflammatory cytokines. Furthermore, 5 and 10 mg/kg nilotinib significantly decreased TGF‐β1 levels and tissue expression of its antibody, as well expression of PDGFRβ. In conclusion, low doses (5 and 10 but not 20 mg/kg) of nilotinib, rather than imatinib, can control hepatic fibrosis by regulating levels of proinflammatory cytokines, primarily interleukin (IL)‐1 and IL‐6. Nilotinib also controls the signalling pathways of profibrogenic cytokines by lowering TGF‐β1 levels and decreasing expression of PDGFRβ.     

Surgery‐induced changes in rat IL‐1β and acetylcholine metabolism: role of physostigmine

Pharmacological enhancement of cholinergic activity following administration of physostigmine is known to induce protective effects generally. However, it is unclear whether the effect of physostigmine on inflammation and acetylcholine (ACh) metabolism is related to different types of surgical intervention or anaesthesia alone. To investigate this, rats were subjected to partial liver resection (PLR) or sham surgery, with a control group receiving anaesthesia alone. Half of each treatment group received a single intra‐operative dose of physostigmine (0.04 mg/kg); the others received placebo. Acetylcholinesterase (AChE) activity and plasma and brain concentrations of interleukin (IL)‐1β and ACh were determined. Both PLR and sham operation induced a time‐dependent increase in plasma concentrations of IL‐1β compared with rats receiving anaesthesia alone (3.9‐ and 4.8‐fold increases, respectively). In the brain, IL‐1β concentrations had increased approximately twofold after surgery compared with the control group. Blood AChE was transiently decreased after surgery. Brain AChE activity increased 1.3‐fold (P = 0.014) only after PLR; consequently, cerebral ACh concentrations were significantly reduced. Physostigmine administration significantly reduced IL‐1β and AChE levels. Cerebral ACh concentrations were markedly increased from 544 ± 122 ng/mg protein following placebo administration to 654 ± 93 ng/mg protein after physostigmine administrations (P < 0.001). We conclude that a single dose of physostigmine intra‐operatively has a sustained anti‐inflammatory effect (up to 120 min after injection) that is especially pronounced under the conditions of PLR surgery. In addition to its protective peripheral action, physostigmine exerts a neuroprotective action by increasing levels of the neurotransmitter ACh.     

Silencing of hypoxia inducible factor‐1α by RNA interference inhibits growth of SK‐NEP‐1 Wilms tumour cells in vitro,and suppresses tumourigenesis and angiogenesis in vivo

Wilms tumour is the most common tumour of the pediatric kidney. Elevation of hypoxia‐inducible factor 1α (HIF‐1α) has been detected in 93% to 100% of human Wilms tumour specimens, suggesting a potential value of HIF‐1α as a therapeutic target for Wilms tumour. In the present study, a stable HIF‐1α‐silenced Wilms tumour cell strain was established by introducing HIF‐1α short‐hairpin RNA (shRNA) into SK‐NEP‐1 cells. Silencing of HIF‐1α significantly reduced single‐cell growth capacity, suppressed proliferation and arrested cell cycle of SK‐NEP‐1 cells. In addition, reduction of HIF‐1α expression induced apoptosis in SK‐NEP‐1 cells, which was accompanied by increased levels of cleaved caspase‐3, cleaved poly (ADP‐ribose) polymerase (PARP) and Bax as well as downregulation of Bcl‐2 in the cells. Furthermore, when inoculated subcutaneously in nude mice, HIF‐1α‐silenced SK‐NEP‐1 cells displayed retarded tumour growth and impaired tumour angiogenesis. In summary, the findings of this study suggest that HIF‐1α plays a critical role in the development of Wilms tumour, and it may serve as a candidate target of gene therapy for Wilms tumour.     

α‐Lipoic acid prolongs survival and attenuates acute kidney injury in a rat model of sepsis

Acute kidney injury is a frequent and serious complication in patients with severe sepsis. α‐Lipoic acid (ALA), a naturally occurring dithiol compound, has been shown to possess anti‐inflammatory and anti‐oxidative properties. In the present study we investigated whether ALA could attenuate acute kidney injury and improve survival in a rat model of sepsis. Rats were subjected to caecal ligation and puncture (CLP) to induce sepsis. α‐Lipoic acid (200 mg/kg) was administered by oral gavage either immediately (early treatment) or 12 h after the surgical procedure (delayed treatment). Both early and delayed ALA treatment effectively prolonged survival, improved pathological damage in kidney tissues and reduced serum blood urea nitrogen and creatinine levels in CLP‐induced septic rats. Furthermore, early treatment with ALA markedly inhibited the release of tumour necrosis factor‐α, interleukin (IL)‐6 and IL‐1β into the serum and reduced mRNA and protein expression of inducible nitric oxide synthase and high mobility group box 1 in kidney tissues from CLP‐induced rats. Finally, CLP‐induced nuclear factor‐κB activation in kidney tissues was significantly suppressed by early ALA treatment. Together, the results indicate that ALA is able to reduce mortality and attenuate acute kidney injury associated with sepsis, possibly by anti‐inflammatory actions. α‐Lipoic acid may be a promising novel agent for the treatment of conditions associated with septic shock.     

Suppression of tumour necrosis factor‐α by Schizonepeta tenuifolia water extract via inhibition of IκBα degradation and Jun N‐terminal kinase/stress‐activated protein kinase activation

Objectives The anti‐inflammatory effects of an aqueous extract of Schizonepeta tenuifolia on lipopolysaccharide (LPS)‐induced tumour necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) in vivo and in vitro have been investigated. Methods C57BL/6 mice were orally administered phosphate‐buffered saline (control) or S. tenuifolia water extract (50, 200, 500 or 1000 mg/kg) for 10 days before intraperitoneal administration of LPS (1.3 mg/kg). Blood samples were obtained 1 h after LPS challenge, followed by determination of TNF‐α and IL‐6 levels. Peritoneal macrophages from thioglycollate‐injected mice were obtained and stimulated with LPS and S. tenuifolia water extract for viability assay, cytokine analysis, real‐time RT PCR and Western blotting. Key findings Oral administration of S. tenuifolia water extract to mice significantly reduced LPS‐induced serum levels of TNF‐α, but not IL‐6. When peritoneal macrophages were treated in vitro with S. tenuifolia water extract, the inhibition of LPS‐induced TNF‐α was more pronounced than that of IL‐6 at the level of secreted protein and mRNA. S. tenuifolia water extract reduced the degradation of IκBα and the nuclear relocation of p65 NF‐κB, but the phosphorylation of IκBα was not affected. Inhibition of c‐Jun N‐terminal kinase/stress‐activated protein kinase (JNK/SAPK) by S. tenuifolia water extract led secondarily to the inhibition of phospho‐c‐Jun and phospho‐ATF‐2. Conclusions These results indicated that the downregulation of TNF‐α by S. tenuifolia water extract may have involved the inhibition of both IκBα degradation and activation of c‐Jun and ATF‐2 involving suppression of JNK/SAPK.     

Potencies of vitamin D analogs, 1α‐hydroxyvitamin D3, 1α‐hydroxyvitamin D2 and 25‐hydroxyvitamin D3, in lowering cholesterol in hypercholesterolemic mice in vivo

Vitamin D₃ and the synthetic vitamin D analogs, 1α‐hydroxyvitamin D₃ [1α(OH)D₃], 1α‐hydroxyvitamin D₂ [1α(OH)D₂] and 25‐hydroxyvitamin D₃ [25(OH)D₃] were appraised for their vitamin D receptor (VDR) associated‐potencies as cholesterol lowering agents in mice in vivo. These precursors are activated in vivo: 1α(OH)D₃ and 1α(OH)D₂ are transformed by liver CYP2R1 and CYP27A1 to active VDR ligands, 1α,25‐dihydroxyvitamin D₃ [1,25(OH)₂D₃] and 1α,25‐dihydroxyvitamin D₂ [1,25(OH)₂D₂]_, respectively. 1α(OH)D₂ may also be activated by CYP24A1 to 1α,24‐dihydroxyvitamin D₂ [1,24(OH)₂D₂], another active VDR ligand. 25(OH)D₃, the metabolite formed via CYP2R1 and or CYP27A1 in liver from vitamin D₃, is activated by CYP27B1 in the kidney to 1,25(OH)₂D₃. In C57BL/6 mice fed the high fat/high cholesterol Western diet for 3 weeks, vitamin D analogs were administered every other day intraperitoneally during the last week of the diet. The rank order for cholesterol lowering, achieved via mouse liver small heterodimer partner (Shp) inhibition and increased cholesterol 7α‐hydroxylase (Cyp7a1) expression, was: 1.75 nmol/kg 1α(OH)D₃ > 1248 nmol/kg 25(OH)D₃ (dose ratio of 0.0014) > > 1625 nmol/kg vitamin D₃. Except for 1.21 nmol/kg 1α(OH)D₂ that failed to lower liver and plasma cholesterol contents, a significant negative correlation was observed between the liver concentration of 1,25(OH)₂D₃ formed from the precursors and liver cholesterol levels. The composite results show that vitamin D analogs 1α(OH)D₃ and 25(OH)D₃ exhibit cholesterol lowering properties upon activation to 1,25(OH)₂D₃: 1α(OH)D₃ is rapidly activated by liver enzymes and 25(OH)D₃ is slowly activated by renal Cyp27b1 in mouse.     

Up‐regulation of Gadd45α after exposure to metal nanoparticles: The role of hypoxia inducible factor 1α

The increased development and use of nanoparticles in various fields may lead to increased exposure, directly affecting human health. Our current knowledge of the health effects of metal nanoparticles such as cobalt and titanium dioxide (Nano‐Co and Nano‐TiO₂) is limited but suggests that some metal nanoparticles may cause genotoxic effects including cell cycle arrest, DNA damage, and apoptosis. The growth arrest and DNA damage‐inducible 45α protein (Gadd45α) has been characterized as one of the key players in the cellular responses to a variety of DNA damaging agents. The aim of this study was to investigate the alteration of Gadd45α expression in mouse embryo fibroblasts (PW) exposed to metal nanoparticles and the possible mechanisms. Non‐toxic doses of Nano‐Co and Nano‐TiO₂ were selected to treat cells. Our results showed that Nano‐Co caused a dose‐ and time‐dependent increase in Gadd45α expression, but Nano‐TiO₂ did not. To investigate the potential pathways involved in Nano‐Co‐induced Gadd45α up‐regulation, we measured the expression of hypoxia inducible factor 1α (HIF‐1α) in PW cells exposed to Nano‐Co and Nano‐TiO₂. Our results showed that exposure to Nano‐Co caused HIF‐1α accumulation in the nucleus. In addition, hypoxia inducible factor 1α knock‐out cells [HIF‐1α (?/?)] and its wild‐type cells [HIF‐1α (+/+)] were used. Our results demonstrated that Nano‐Co caused a dose‐ and time‐dependent increase in Gadd45α expression in wild‐type HIF‐1α (+/+) cells, but only a slight increase in HIF‐1α (?/?) cells. Pre‐treatment of PW cells with heat shock protein 90 inhibitor, 17‐(Allylamino)?17‐demethoxygeldanamycin (17‐AAG), prior to exposure to Nano‐Co significantly abolished Nano‐Co‐induced Gadd45α expression. These results suggest that HIF‐1α accumulation may be partially involved in the increased Gadd45α expression in cells exposed to Nano‐Co. These findings may have important implications for understanding the potential health effects of metal nanoparticle exposure. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 490–499, 2015.     

Deleterious effects of non‐synonymous single nucleotide variants of human IL‐1β gene

The IL‐1β gene is currently topic of interest for its important role in the pathogenesis of intervertebral disk degeneration. The new sequencing technology makes it crucial to study the effects of variants in IL‐1β. Thus, 714 IL‐1β variants with evidence supporting were collected from the EMBL database. Among them, 62 were non‐synonymous single nucleotide variants (nsSNVs). Furthermore, six common nsSNVs were predicted to have damaging effects by SIFT, PolyPhen, PROVEAN and SNPs&GO. Based on the constructed three‐dimensional structure of pro‐IL‐1β, rs375479974 with a mutation of Phe to Ser was proposed to reduce the stability of the pro‐IL‐1β protein. The rs375479974 variant was found to cause least common stabilizing amino acid residues, decrease hydrophilic and increase hydrophobic surface areas in the greatest degree, and have the lowest free energy alterations in I‐Mutant 2.0 sequence analysis. When analyzing the interaction between the experimental 3D structure of mature IL‐1β and its neutralizing McAb canakinumab complex, the rs775174784 substitution of Leu with Phe was found to attenuate this interaction by reducing binding energy, while rs375479974 not. Molecular dynamics simulation results in intervertebral disk environment supported rs775174784's effects. These results suggest that both rs375479974 and rs775174784 may have potential clinical and drug target implications.     

Andrographolide inhibits hypoxia‐induced hypoxia‐inducible factor 1α and endothelin 1 expression through the heme oxygenase 1/CO/cGMP/MKP‐5 pathways in EA.hy926 cells

Andrographolide is a potent anti‐inflammatory agent found in Andrographis paniculata. Endothelin 1 (ET‐1) is an endothelium‐derived vasoconstrictor with pro‐inflammatory properties secreted in response to hypoxia. Mitogen‐activated protein kinase phosphatase 5 (MKP‐5) is a dual‐specificity phosphatase that dephosphorylates threonine and tyrosine residues of MAPKs. We showed previously that hypoxia‐induced HIF‐1α expression and ET‐1 secretion are dependent on p38 MAPK in EA.hy926 cells. Here, we investigate what role MKP‐5 plays in andrographolide's inhibition of hypoxia‐induced expression of HIF‐1α and ET‐1. Hypoxic conditions were created using the hypoxia‐mimetic agent CoCl₂. Andrographolide enhanced HO‐1 and MKP‐5 expression and cellular cGMP content in addition to inhibiting hypoxia‐induced ROS generation. Concomitantly, the HO‐1 byproduct CO and the cGMP analogue 8‐bromoguanosine 3′,5′‐cyclic monophosphate (8‐Br‐cGMP) increased MKP‐5 expression, and pretreatment with CO and 8‐Br‐cGMP inhibited hypoxia‐induced HIF‐1α and ET‐1 expression. Transfection of HO‐1 siRNA or pretreatment with the HO‐1 inhibitor ZnPP‐9 or 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one, a specific inhibitor of soluble guanylate cyclase, reduced andrographolide‐induced MKP‐5 expression. Moreover, silencing MKP‐5 or treatment with the phosphatase inhibitor vanadate abrogated andrographolide's suppressing hypoxia‐induced p38 MAPK activation and HIF‐1α expression. The inhibition of hypoxia‐induced HIF‐1α and ET‐1 expression by andrographolide is likely associated with HO‐1/CO/cGMP/MKP‐5 pathways, which is involved in inhibiting hypoxia‐induced p38 MAPK activation.     

Antifibrosis effects of triterpene acids of Eriobotrya japonica (Thunb.) Lindl. leaf in a rat model of bleomycin‐induced pulmonary fibrosis

Objective The aim of this study was to investigate the prophylactic effect and some mechanisms of action of triterpene acids of loquat (TAL) on bleomycin A5‐induced pulmonary fibrosis rats. Methods A model of pulmonary fibrosis was induced by injecting rats with a single dose of bleomycin A5 (5 mg/kg) into the trachea. From the second day, rats in the preventive groups were treated with TAL (50, 150 or 450 mg/kg) or dexamethasone (1.2 mg/kg). On the 28th day after medication, the rats were killed and haematoxylin‐eosin or masson staining was used to evaluate the degree of pulmonary fibrosis. Tumour necrosis factor‐α (TNF‐α) and transforming growth factor‐β1 (TGF‐β1) levels in alveolar macrophage culture supernatant were detected by ELISA. The mRNA expression of TNF‐α and TGF‐β1 in alveolar macrophage was observed by RT‐PCR. Key findings Lung histopathological examination showed TAL could ameliorate the structure of the lung and alleviate fibrogenesis. At the same time, TAL (150 or 450 mg/kg dose group) could reduce the expression of TNF‐α and TGF‐β1 in alveolar macrophage of rats with pulmonary fibrosis at either the protein or mRNA level. Conclusions TAL had a positive prophylactic effect on lung fibrosis, which might have been related to its reduction on TNF‐α or TGF‐β1 expression in the alveolar macrophage of pulmonary fibrosis rats.     

Tropisetron ameliorates early diabetic nephropathy in streptozotocin‐induced diabetic rats

It has been well established that oxidative stress and inflammation are involved in the pathogenesis of diabetic nephropathy. It has been shown that tropisetron exerts anti‐inflammatory and immunomodulatory properties. The current study was designed to investigate protective effects of tropisetron on early diabetic nephropathy in streptozotocin‐induced diabetic rats. Rats were divided into six groups: (i) untreated diabetic (streptozotocin group); (ii) untreated control; (iii) diabetic rats treated with tropisetron (3 mg/kg); (iv) normal rats treated with tropisetron (3 mg/kg); (v) diabetic rats treated with granisetron (3 mg/kg); and (vi) normal rats treated with granisetron (3 mg/kg); rats began receiving treatment at the time of diabetes induction for 2 weeks. At the termination of the experiments, bodyweight, kidney index, urinary albumin excretion, and glomerular filtration rate were measured. The levels of oxidative stress markers and tumour necrosis factor‐α were also determined. Streptozotocin‐treated animals showed significant loss of bodyweight and renal enlargement and dysfunction. Diabetic rats also exhibited an increase in malondialdehyde along with a significant decrease in glutathione, superoxide dismutase activity, and catalase activity. Furthermore, the diabetic animals demonstrated a significant rise in renal cortical, urinary tumour necrosis factor‐α, and urinary albumin excretion. Both granisetron and tropisetron decreased blood glucose in diabetic animals, but this decrease was not significant for granisetron. Treatment with tropisetron, but not granisetron, prevented increases in oxidative stress and tumour necrosis factor‐α, decreased urinary cytokine excretion and albuminuria, and improved renal morphological damage. In conclusion, the present study suggests that tropisetron may be a protective agent in early diabetic nephropathy, and its action is mediated, at least in part, by anti‐oxidative and anti‐inflammatory mechanisms that appear to be independent of the 5‐HT₃ receptor.     

Protective effect of isochlorogenic acid B on liver fibrosis in non‐alcoholic steatohepatitis of mice

Liver fibrosis is a common symptom of non‐alcoholic steatohepatitis (NASH) and a worldwide clinical issue. The miR‐122/HIF‐1α signalling pathway is believed to play an important role in the genesis of progressive fibrosis. Isochlorogenic acid B (ICAB), naturally isolated from Laggera alata, is verified to have antioxidative and hepatoprotective properties. The aim of this study was to investigate the effect of ICAB on liver fibrosis in NASH and its potential protective mechanisms. NASH was induced in a mouse model with a methionine‐ and choline‐deficient (MCD) diet for 4 weeks, and ICAB was orally administered every day at three doses (5, 10 and 20 mg/kg). Pathological results indicated that ICAB significantly improved the pathological lesions of liver fibrosis. The levels of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and hepatic hydroxyproline (Hyp), cholesterol (CHO) and triglyceride (TG) were also significantly decreased by ICAB. In addition, ICAB inhibited hepatic stellate cells (HSCs) activation and the expressions of hepatic genes involved in liver fibrosis including LOX, TGF‐β1, MCP‐1, COL1α1 and TIMP‐1. ICAB also attenuated liver oxidative stress through Nrf2 signalling pathway. What is more, the decreased levels of miR‐122 and over‐expression of hepatic HIF‐1α could be reversed by ICAB treatment. These results simultaneously confirmed that ICAB had a significant protective effect on fibrosis in NASH by inhibiting oxidative stress via Nrf2 and suppressing multiple profibrogenic factors through miR‐122/HIF‐1α signalling pathway.     

Synthesis of 1,4‐Anthracene‐9,10‐dione Derivatives and Their Regulation of Nitric Oxide,IL‐1β and TNF‐α in Activated RAW264.7 Cells

Mitoxantrone is an anthracenedione antineoplastic and immunosuppressive agent approved for multiple sclerosis treatment. Novel mono‐ and disubstituted anthraquinone derivatives, analogues of mitoxantrone, were synthesized through the addition of lipophilic amino alcohols and evaluated for their effect on IL‐1β, TNF‐α and nitric oxide production by LPS/IFN‐γ‐stimulated RAW264.7 cells. The disubstituted 1,4‐anthracene‐9,10‐dione 10 showed significant inhibition of nitric oxide, TNF‐α and IL‐1β production at the concentration of 5 μg/mL, with a much lower cytotoxicity than mitoxantrone. The monosubstituted 3 , 4 , 11, 12 and 13 also displayed a moderate to good inhibitory capacity on IL‐1β production. However, the methylated compounds 11, 12 and 13 failed to inhibit the TNF‐α production, and compound 13 was the only one to decrease the production of nitric oxide. None of these derivatives was toxic at the tested concentrations. Compounds 10 and 13 had better inhibitory capacity of the inflammatory mediators analyzed, with reliable viability of the cells.     

Nephropreventing effect of hypoxia‐inducible factor 1α in a rat model of ischaemic/reperfusion acute kidney injury

Acute kidney injury (AKI) occurs in 5% of hospitalized patients and in 50% of sepsis patients with acute renal dysfunction. However, there have been no safe and effective therapeutic strategies. The hypoxia condition is closely related to renal injury and function under AKI. As hypoxia‐inducible factor 1α (HIF‐1α) is critical for the cellular response to hypoxia, we investigated the protective effect of HIF‐1α in a rat AKI model. We found that HIF‐1α injection improved the survival of rat with AKI, and the level of creatinine and blood urea nitrogen (BUN) was also increased. Our data showed that HIF‐1α treatment significantly alleviated ischaemic/reperfusion injury to kidney tubules and nephrocytes. We also found the downstream factors, such as EPOR, VEGF, and PHD3, were also upregulated by HIF‐1α. Finally, it was observed that HIF‐1α treatment also increased the percentage of adult resident progenitor cells (ARPC) in vitro and in vivo. In conclusion, HIF‐1α plays a protective role in the ischaemic AKI model through stimulating the proliferation of ARPC, and our study provided a potential therapeutic strategy for AKI.     

Drug resistance and cancer stem cells: the shared but distinct roles of hypoxia‐inducible factors HIF1α and HIF2α

Chemotherapy resistance is a major contributor to poor treatment responses and tumour relapse, the development of which has been strongly linked to the action of cancer stem cells (CSCs). Mounting evidence suggests that CSCs are reliant on low oxygen conditions and hypoxia‐inducible factors 1α and 2α (HIF1α and HIF2α) to maintain their stem cell features. Research in the last decade has begun to clarify the functional differences between the two HIFα subtypes (HIFαs). Here, we review and discuss these differences in relation to CSC‐associated drug resistance. Both HIFαs contribute to CSC survival but play different roles –HIF1α being more responsible for survival functions and HIF2α for stemness traits such as self‐renewal – and are sensitive to different degrees of hypoxia. Failure to account for physiologically relevant oxygen concentrations in many studies may influence the current understanding of the roles of HIFαs. We also discuss how hypoxia and HIFαs contribute to CSC drug resistance via promotion of ABC drug transporters Breast cancer resistance protein (BCRP), MDR1, and MRP1 and through maintenance of quiescence. Additionally, we explore the PI3K/AKT cell survival pathway that may support refractory cancer by promoting CSCs and activating both HIF1α and HIF2α. Accordingly, HIF1α and HIF2α inhibition, potentially via PI3K/AKT inhibitors, could reduce chemotherapy resistance and prevent cancer relapse.     

Conformational properties of hybrid peptides containing α‐ and ω‐amino acids*

Abstract: This review briefly surveys the conformational properties of guest ω‐amino acid residues when incorporated into host α‐peptide sequences. The results presented focus primarily on the use of β‐ and γ‐residues in αω sequences. The insertion of additional methylene groups into peptide backbones enhances the range of accessible conformations, introducing additional torsional variables. A nomenclature system, which permits ready comparisons between α‐peptides and hybrid sequences, is defined. Crystal structure determination of hybrid peptides, which adopt helical and β‐hairpin conformations permits the characterization of backbone conformational parameters for β‐ and γ‐residues inserted into regular α‐polypeptide structures. Substituted β‐ and γ‐residues are more limited in the range of accessible conformation than their unsubstituted counterparts. The achiral β,β‐disubstituted γ‐amino acid, gabapentin, is an example of a stereochemically constrained residue in which the torsion angles about the C^β–C^γ (θ₁) and C^α–C^β (θ₂) bonds are restricted to the gauche conformation. Hybrid sequences permit the design of novel hydrogen bonded rings in peptide structures.     

Synthesis,crystal structure and molecular conformation of Nα‐Boc‐l‐leucyl‐(Z)‐β‐(3‐pyridyl)‐α,β‐ dehydroalanyl‐l‐leucine methyl ester*

Abstract: A protected tridehydropeptide containing (Z)‐β‐(3‐pyridyl)‐α,β‐dehydroalanine (Δ^Z3Pal) residue, Boc‐Leu‐Δ^Z3Pal‐Leu‐OMe ( 1 ), was synthesized via Erlenmeyer azlactone method. X‐ray crystallographic analysis revealed that the peptide 1 adopts an extended conformation, which is similar to that of a Δ^ZPhe analog, Boc‐Leu‐Δ^ZPhe‐Leu‐OMe ( 2 ).