Irinotecan treats a range of solid tumors, but its effectiveness is severely limited by gastrointestinal (GI) tract toxicity caused by gut bacterial β-glucuronidase (GUS) enzymes. Targeted bacterial ...GUS inhibitors have been shown to partially alleviate irinotecan-induced GI tract damage and resultant diarrhea in mice. Here, we unravel the mechanistic basis for GI protection by gut microbial GUS inhibitors using in vivo models.We use in vitro, in fimo, and in vivo models to determine whether GUS inhibition alters the anticancer efficacy of irinotecan. We demonstrate that a single dose of irinotecan increases GI bacterial GUS activity in 1 d and reduces intestinal epithelial cell proliferation in 5 d, both blocked by a single dose of a GUS inhibitor. In a tumor xenograft model, GUS inhibition prevents intestinal toxicity and maintains the antitumor efficacy of irinotecan. Remarkably, GUS inhibitor also effectively blocks the striking irinotecan-induced bloom of Enterobacteriaceae in immunedeficient mice. In a genetically engineered mouse model of cancer, GUS inhibition alleviates gut damage, improves survival, and does not alter gut microbial composition; however, by allowing dose intensification, it dramatically improves irinotecan’s effectiveness, reducing tumors to a fraction of that achieved by irinotecan alone, while simultaneously promoting epithelial regeneration. These results indicate that targeted gut microbial enzyme inhibitors can improve cancer chemotherapeutic outcomes by protecting the gut epithelium from microbial dysbiosis and proliferative crypt damage.
Gene-environment interactions underlie cancer susceptibility and progression. Yet, we still have limited knowledge of which environmental factors are important and how they function during ...tumorigenesis. In this respect, the microbial communities that inhabit our gastrointestinal tract and other body sites have been unappreciated until recently. However, our microbiota are environmental factors that we are exposed to continuously, and human microbiome studies have revealed significant differences in the relative abundance of certain microbes in cancer cases compared with controls. To characterize the function of microbiota in carcinogenesis, mouse models of cancer have been treated with antibiotics. They have also been maintained in a germfree state or have been colonized with specific bacteria in specialized (gnotobiotic) facilities. These studies demonstrate that microbiota can increase or decrease cancer susceptibility and progression by diverse mechanisms such as by modulating inflammation, influencing the genomic stability of host cells and producing metabolites that function as histone deacetylase inhibitors to epigenetically regulate host gene expression. One might consider microbiota as tractable environmental factors because they are highly quantifiable and relatively stable within an individual compared with our exposures to external agents. At the same time, however, diet can modulate the composition of microbial communities within our gut, and this supports the idea that probiotics and prebiotics can be effective chemoprevention strategies. The trajectory of where the current work is headed suggests that microbiota will continue to provide insight into the basic mechanisms of carcinogenesis and that microbiota will also become targets for therapeutic intervention.
Mammalian SWI/SNF-related complexes have been implicated in cancer based on some of the subunits physically interacting with retinoblastoma (RB) and other proteins involved in carcinogenesis. ...Additionally, several subunits are mutated or not expressed in tumor-derived cell lines. Strong evidence for a role in tumorigenesis in vivo, however, has been limited to SNF5 mutations that result primarily in malignant rhabdoid tumors (MRTs) in humans and MRTs as well as other sarcomas in mice. We previously generated a null mutation of the Brg1 catalytic subunit in the mouse and reported that homozygotes die during embryogenesis. Here, we demonstrate that Brg1 heterozygotes are susceptible to mammary tumors that are fundamentally different than Snf5 tumors. First, mammary tumors are carcinomas not sarcomas. Second, Brg1+/- tumors arise because of haploinsufficiency rather than loss of heterozygosity. Third, Brg1+/- tumors exhibit genomic instability but not polyploidy based on array comparative genomic hybridization results. We monitored Brg1+/-, Brm-/- double-mutant mice but did not observe any tumors resembling those from Snf5 mutants, indicating that the Brg1+/- and Snf5+/- tumor phenotypes do not differ simply because Brg1 has a closely related paralog whereas Snf5 does not. These findings demonstrate that BRG1 and SNF5 are not functionally equivalent but protect against cancer in different ways. We also demonstrate that Brg1+/- mammary tumors have relatively heterogeneous gene expression profiles with similarities and differences compared to other mouse models of breast cancer. The Brg1+/- expression profiles are not particularly similar to mammary tumors from Wap-T121 transgenic line where RB is perturbed. We were also unable to detect a genetic interaction between the Brg1+/- and Rb+/- tumor phenotypes. These latter findings do not support a BRG1-RB interaction in vivo.
The agouti (a) locus acts within the microenvironment of the hair follicle to regulate coat color pigmentation in the mouse. We have characterized a gene encoding a novel 131 amino acid protein that ...we propose is the one gene associated with the agouti locus. This gene is normally expressed in a manner consistent with a locus function, and, more importantly, its structure and expression are affected by a number of representative alleles in the agouti dominance hierarchy. In addition, we found that the pleiotropic effects associated with the lethal yellow (Ay) mutation, which include pronounced obesity, diabetes, and the development of neoplasms, are accompanied by deregulated overexpression of the agouti gene in numerous tissues of the adult animal.
Tribological investigations of Mo–S–Te composite films were conducted on films grown at room temperature by pulsed laser deposition. The chemistry and microstructure of the films were characterized ...by X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and micro Raman spectroscopy. The films showed a granular morphology and a preferred basal plane growth of 2H-MoS
2 parallel to the substrate after annealing at high temperatures. The friction coefficients of the films were 0.05 at 300 °C and 0.10 at 450 °C for more than 10,000 cycles in air. Smeared hexagonal MoS
2 lubricant films were observed inside wear tracks while the tribochemical formation of wear debris occurred both inside and outside the wear tracks. The Te additives for increasing the film durability were proposed to slow oxidation of the lubricants at elevated temperatures by thermally-induced tellurium migration to the surface and the subsequent formation of the Te diffusion barrier. This mechanism could be significantly effective in high-temperature tribotests because of the increased tellurium mobility at high temperatures.
The Brg1 catalytic subunit of SWI/SNF-related complexes has been implicated in many developmental and physiological processes, but null homozygotes die as blastocysts prior to implantation. To ...circumvent this early embryonic lethality, we performed an ENU mutagenesis screen and generated a Brg1 hypomorph mutation in the ATPase domain. The mutant Brg1 protein is stable, assembles into SWI/SNF-related complexes, and exhibits normal ATPase activity but is unable to establish DNase I hypersensitivity sites characteristic of open chromatin. Mutant embryos develop normally until midgestation but then exhibit a distinct block in the development of the erythroid lineage, leading to anemia and death. The mutant Brg1 protein is recruited to the beta-globin locus, but chromatin remodeling and transcription are perturbed. Histone acetylation and DNA methylation are also affected. To our knowledge, Brg1 is the first chromatin-modifying factor shown to be required for beta-globin regulation and erythropoiesis in vivo. Not only does this mutation establish a role for Brg1 during organogenesis, it also demonstrates that ATPase activity can be uncoupled from chromatin remodeling.
Lethal yellow (Ay) is a mutation at the mouse agouti locus in chromosome 2 that causes a number of dominant pleiotropic effects, including a completely yellow coat color, obesity, an ...insulin-resistant type II diabetic condition, and an increased propensity to develop a variety of spontaneous and induced tumors. Additionally, homozygosity for Ayresults in preimplantation lethality, which terminates development by the blastocyst stage. The Aymutation is the result of a 170-kb deletion that removes all but the promoter and noncoding first exon of another gene called Raly, which lies in the same transcriptional orientation as agouti and maps 280 kb proximal to the 3' end of the agouti gene. We present a model for the structure of the Ayallele that can explain the dominant pleiotropic effects associated with this mutation, as well as the recessive lethality, which is unrelated to the agouti gene.
MoS2–Sb2O3–C composite films exhibit adaptive behavior, where surface chemistry changes with environment to maintain the good friction and wear characteristics. In previous work on nanocomposite ...coatings grown by PVD, this type of material was called a “chameleon” coating. Coatings used in this report were applied by burnishing mixed powders of MoS2, Sb2O3 and graphite. The solid lubricant MoS2 and graphite were selected to lubricate over a wide and complementary range including vacuum, dry air and humid air. Sb2O3 was used as a dopant because it acts synergistically with MoS2, improving friction and wear properties. The MoS2–Sb2O3–C composite films showed lower friction and longer wear life than either single component MoS2 or C film in humid air. Very or even super low friction and long wear-life were observed in dry nitrogen and vacuum. The excellent tribological performance was verified and repeated in cycles between humid air and dry nitrogen. The formation of tribo-films at rubbing contacts was studied to identify the lubricating chemistry and microstructure, which varied with environmental conditions. Micro-Raman spectroscopy and Auger electron spectroscopy (AES) were used to determine surface chemistry, while scanning electron microscopy and transmission electron microscopy were used for microstructural analysis. The tribological improvement and lubrication mechanism of MoS2–Sb2O3–C composite films were caused by enrichment of the active lubricant at the contact surface, alignment of the crystal orientation of the lubricant grains, and enrichment of the non lubricant materials below the surface. Sb2O3, which is not lubricious, was covered by the active lubricants (MoS2 – dry, C – humid air). Clearly, the dynamics of friction during environmental cycling cleaned some Sb2O3 particles of one lubricant and coated it with the active lubricant for the specific environment. Mechanisms of lubrication and the role of the different materials will be discussed.
Multilayered MoS2/Sb2O3 thin films were prepared by pulsed laser deposition on steel substrates. A rotary multi-target holder was used to switch the laser targets for alternative growth of MoS2 and ...Sb2O3 layers providing nanometers thickness. The tribological properties of the films were measured in dry and wet environments and the wear scars were observed using a scanning electron microscope. The multilayer films showed a much longer wear life than pure MoS2 films in wet air tribotests. Focused ion beam and transmission electron microscopies were used to investigate the cross-sectional microstructures of wear scars. Lubricious MoS2/Sb2O3 tribofilms were built up on wear scar surfaces, and produced low friction. Micro-cracks occurred along the interface between the tribofilm and the neighboring/topmost Sb2O3 underlayer, where the Sb2O3 layer effectively inhibited the crack propagation perpendicular to the interface. The orientation of MoS2 crystals in as-deposited films was mostly random and friction-induced stress oriented the MoS2 basal planes parallel to the surface. The reorientation was confined to the topmost MoS2 layer and was not observed below the first intact Sb2O3 layer.
Oxides are inherently stable in air at elevated temperatures and may serve as wear resistant matrices for solid lubricants. Aluminum oxide is a particularly good candidate for a matrix because it has ...good diffusion barrier properties and modest hardness. Most thin film deposition techniques that are used to grow alumina require high temperatures to impart crystallinity. Crystalline films are about twice as hard as amorphous ones. Unfortunately, the mechanical properties of most engineering steels are degraded at temperatures above 250–350 °C. This work is focused on using energetic reactive ion bombardment during simultaneous pulsed laser deposition to enhance film crystallization at low temperatures.
Alumina films were grown at several background gas pressures and temperatures, with and without Ar ion bombardment. The films were nearly stoichiometric except for depositions in vacuum. Using nitrogen ion bombardment, nitrogen was incorporated into the films and formed the Al–O–N matrix. Nitrogen concentration could be controlled through selection of gas pressure and ion energy. Crystalline Al–O–N films were grown at 330 °C with a negative bias voltage to the substrate, and showed improved hardness in comparison to amorphous films.
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