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We have investigated the pharmacokinetics of TunR2, a modified tunicamycin-type antibiotic, in mice and cattle. TunR2 has previously been shown to be effective in a mycobacterial disease model using zebrafish, with a minimal activation of the eukaryotic unfolded protein response ( upr ) and a reduction in the in vivo mycobacterial burden. In this study, we presented statistically relevant pharmacokinetics of native tunicamycin (Tun) and two less toxic modified analogs, TunR2 and TunR1, using a well-defined clonal C57BL/6 mouse (both male and female). Blood samples were collected at multiple time points, and plasma concentrations were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Pharmacokinetic parameters were calculated using a two-compartment analysis. Our findings indicate that Tun and TunR1 tend to distribute in tissue compared to TunR2, which has a longer half-life than Tun. This translates into longer TunR2 activity time, potentially allowing for less frequent dosing than Tun or TunR1. We subsequently administered the modified TunR2 to Holstein cattle using a three-bolus intravenous regimen. We monitored blood, milk, urine, and feces over 90 days. In dairy cattle, the pharmacokinetics of TunR2 appear to be cumulative, and clear after 10 days. These findings provide critical new insights into the pharmacokinetics of TunR2. We concluded that TunR2 has considerable potential for treating bacterial infections, particularly as an antimicrobial adjuvant with well-established β-lactam antibiotics. Further studies are required to study safety and optimize dosing regimens for effective therapeutic use, as well as in combination with other antibiotics, such as β-lactams.

Background Multidrug resistance remains a major obstacle to successful treatment for patients with gastric cancer (GC). Recently, glycosylation has been demonstrated to play a vital role in the acquisition of multidrug resistance. As a potent inhibitor of glycosylation, tunicamycin (Tu) has shown marked antitumor activities in various cancers. In the present study, we attempted to determine the exact effect of Tu on the chemoresistance of GC. Methods The cytotoxic effects of drugs on GC cells were evaluated by cell viability assays, and apoptosis was detected by flow cytometry. PCR, western blot analysis, immunofluorescence staining and canonical inhibitors were employed to identify the underlying mechanisms of the specific effects of Tu on multidrug-resistant (MDR) GC cells. Results For the first time, we found that MDR GC cells were more sensitive to Tu-induced cell death than the parental cells and that the increased sensitivity might correlate with basal endoplasmic reticulum (ER) stress. In addition, Tu dramatically increased chemotherapy-induced apoptosis by evoking ER stress in GC cells, particularly MDR cells. Further study indicated that these effects were highly dependent on glycosylation inhibition by Tu, rather than its role as a canonical ER stress inducer. Besides, autophagy was markedly triggered by Tu, and blocking autophagy enhanced the combined effects of Tu and chemotherapy on MDR GC cells. Conclusions Our results suggest that tumor-targeted glycosylation inhibition may be a feasible strategy to reverse chemoresistance in GC patients.

N-linked glycosylation is a predominant post-translational modification of protein in eukaryotes, and its dysregulation is the etiology of several human disorders. The enzyme UDP-N-acetylglucosamine:dolichyl-phosphate N-acetylglucosaminephosphotransferase (GlcNAc-1-P-transferase or GPT) catalyzes the first and committed step of N-linked glycosylation in the endoplasmic reticulum membrane, and it is the target of the natural product tunicamycin. Tunicamycin has potent antibacterial activity, inhibiting the bacterial cell wall synthesis enzyme MraY, but its usefulness as an antibiotic is limited by off-target inhibition of human GPT. Our understanding of how tunicamycin inhibits N-linked glycosylation and efforts to selectively target MraY are hampered by a lack of structural information. Here we present crystal structures of human GPT in complex with tunicamycin. Structural and functional analyses reveal the difference between GPT and MraY in their mechanisms of inhibition by tunicamycin. We demonstrate that this difference could be exploited to design MraY-specific inhibitors as potential antibiotics.

APO2L/TRAIL (TNF-related apoptosis-inducing ligand) induces death of tumor cells through two agonist receptors, TRAIL-R1 and TRAIL-R2. We demonstrate here that N-linked glycosylation (N-glyc) plays also an important regulatory role for TRAIL-R1-mediated and mouse TRAIL receptor (mTRAIL-R)-mediated apoptosis, but not for TRAIL-R2, which is devoid of N-glycans. Cells expressing N-glyc-defective mutants of TRAIL-R1 and mouse TRAIL-R were less sensitive to TRAIL than their wild-type counterparts. Defective apoptotic signaling by N-glyc-deficient TRAIL receptors was associated with lower TRAIL receptor aggregation and reduced DISC formation, but not with reduced TRAIL-binding affinity. Our results also indicate that TRAIL receptor N-glyc impacts immune evasion strategies. The cytomegalovirus (CMV) UL141 protein, which restricts cell-surface expression of human TRAIL death receptors, binds with significant higher affinity TRAIL-R1 lacking N-glyc, suggesting that this sugar modification may have evolved as a counterstrategy to prevent receptor inhibition by UL141. Altogether our findings demonstrate that N-glyc of TRAIL-R1 promotes TRAIL signaling and restricts virus-mediated inhibition.

Disorders of hepatic energy metabolism, which can be regulated by endoplasmic reticulum (ER) stress, lead to metabolic diseases such as hepatic steatosis and hypoglycemia. Tunicamycin, a pharmacological ER stress inducer, is used to develop an anti-cancer drug. However, the effects of tunicamycin on hepatic energy metabolism have not been well elucidated. Mice were intraperitoneally injected with tunicamycin or vehicle. Twenty-four hours later, hepatic triglyceride and glycogen content and serum lipids profiles were analyzed, as well as the expression of lipogenic and gluconeogenic genes. Tunicamycin significantly induced hepatic a yellowish color and ER stress, as well as increasing serum levels of aspartate transaminase and alanine transaminase. Besides, tunicamycin remarkably increased hepatic triglyceride content and suppressed the expression of apolipoprotein B100. In addition, tunicamycin-treated mice had lower serum levels of triglyceride, apolipoprotein B, low-density lipoprotein cholesterol and high-density lipoprotein cholesterol. Gene expression of peroxisome proliferator-activated receptor α was decreased by tunicamycin, but the protein level was increased. Furthermore, blood glucose level and hepatic glycogen content were decreased in tunicamycin-treated mice. Protein kinase B signaling was attenuated in the tunicamycin-treated liver, but the expression and activities of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase were unchanged. Tunicamycin alters hepatic energy homeostasis by increasing triglyceride accumulation and decreasing glycogen content.

Uncontrolled endoplasmic reticulum (ER) stress responses are proposed to contribute to the pathology of chronic inflammatory diseases such as type 2 diabetes or atherosclerosis. However, the connection between ER stress and inflammation remains largely unexplored. Here, we show that ER stress causes activation of the NLRP3 inflammasome, with subsequent release of the pro-inflammatory cytokine interleukin-1 β . This ER-triggered proinflammatory signal shares the same requirement for reactive oxygen species production and potassium efflux compared with other known NLRP3 inflammasome activators, but is independent of the classical unfolded protein response (UPR). We thus propose that the NLRP3 inflammasome senses and responds to ER stress downstream of a previously uncharacterized ER stress response signaling pathway distinct from the UPR, thus providing mechanistic insight to the link between ER stress and chronic inflammatory diseases.

Tunicamycins are nucleoside natural products and show antibacterial, antiviral and antitumor activities, which are attributed to their inhibition of enzymatic reactions between polyisoprenyl phosphate and UDP-GlcNAc or UDP-MurNAc-pentapeptide. Because of their various intriguing biological activities, tunicamycins have potential as therapeutic agents for infectious diseases or cancers. Structurally, tunicamycins have a unique structure composed of an undecodialdose skeleton, a lipid chain and a GlcNAc fragment linked by a 1,1-β,α-trehalose-type glycosidic bond. In this mini review, we summarize the total chemical syntheses and biosynthetic studies of tunicamycins.

Reduced ribosome biogenesis in response to environmental conditions is a key feature of cell adaptation to stress. For example, ribosomal genes are transcriptionally repressed when cells are exposed to tunicamycin, a protein glycosylation inhibitor that induces endoplasmic reticulum stress and blocks vesicular trafficking in the secretory pathway. Here, we describe a novel regulatory model, in which tunicamycin-mediated stress induces the accumulation of long-chain sphingoid bases and subsequent activation of Pkh1/2 signaling, which leads to decreased expression of ribosomal protein genes via the downstream effectors Pkc1 and Sch9. Target of rapamycin complex 1 (TORC1), an upstream activator of Sch9, is also required. This pathway links ribosome biogenesis to alterations in membrane lipid composition under tunicamycin-induced stress conditions. Our results suggest that sphingolipid/Pkh1/2-TORC1/Sch9 signaling is an important determinant for adaptation to tunicamycin-induced stress.

Tunicamycins (TUN) are well-defined, Streptomyces -derived natural products that inhibit protein N -glycosylation in eukaryotes, and by a conserved mechanism also block bacterial cell wall biosynthesis. TUN inhibits the polyprenylphosphate- N -acetyl-hexosamine-1-phospho-transferases (PNPT), an essential family of enzymes found in both bacteria and eukaryotes. We have previously published the development of chemically modified TUN, called TunR1 and TunR2, that have considerably reduced activity on eukaryotes but that retain the potent antibacterial properties. A mechanism for this reduced toxicity has also been reported. TunR1 and TunR2 have been tested against mammalian cell lines in culture and against live insect cells but, until now, no in vivo evaluation has been undertaken for vertebrates. In the current work, TUN, TunR1, and TunR2 are investigated for their relative toxicity and antimycobacterial activity in zebrafish using a well-established Mycobacterium marinum ( M. marinum ) infection system, a model for studying human Mycobacterium tuberculosis infections. We also report the relative ability to activate the unfolded protein response (UPR), the known mechanism for the eukaryotic toxicity observed with TUN treatment. Importantly, TunR1 and TunR2 retained their antimicrobial properties, as evidenced by a reduction in M. marinum bacterial burden, compared to DMSO-treated zebrafish. In summary, findings from this study highlight the characteristics of recently developed TUN derivatives, mainly TunR2, and its potential for use as a novel anti-bacterial agent for veterinary and potential medical purposes.

The β-lactams are the most widely used group of antibiotics in human health and agriculture, but this is under threat due to the persistent rise of pathogenic resistance. Several compounds, including tunicamycin (TUN), can enhance the antibacterial activity of the β-lactams to the extent of overcoming resistance, but the mammalian toxicity of TUN has precluded its use in this role. Selective hydrogenation of TUN produces modified compounds (TunR1 and TunR2), which retain the enhancement of β-lactams while having much lower mammalian toxicity. Here we show that TunR1 and TunR2 enhance the antibacterial activity of multiple β-lactam family members, including penems, cephems, and third-generation penicillins, to a similar extent as does the native TUN. Eleven of the β-lactams tested were enhanced from 2 to >256-fold against Bacillus subtilis, with comparable results against a penicillin G-resistant strain. The most significant enhancements were obtained with third-generation aminothiazolidyl cephems, including cefotaxime, ceftazidime, and cefquinome. These results support the potential of low toxicity tunicamycin analogs (TunR1 and TunR2) as clinically valid, synergistic enhancers for a broad group of β-lactam antibiotics.