Double-sided asymmetric metasurfaces achieving sub-microscale focusing from a GaN green laser diode.

We proposed and demonstrated a highly efficient sub-microscale focusing from a GaN green laser diode (LD) integrated with double-sided asymmetric metasurfaces. The metasurfaces consist of two nanostructures in a GaN substrate: nanogratings on one side and a geometric phase based metalens on the other side. When it was integrated on the edge emission facet of a GaN green LD, linearly polarized emission was firstly converted to the circularly polarized state by the nanogratings functioning as a quarter-wave plate, the phase gradient was then controlled by the metalens on the exit side. In the end, the double-sided asymmetric metasurfaces achieve a sub micro-focusing from linearly polarized states. Experimental results show the full width at half maximum of the focused spot size is about 738 nm at the wavelength 520 nm and the focusing efficiency is about 72.8%. Our results lay a foundation for the multi-functional applications in optical tweezers, laser direct writing, visible light communication, and biological chip.

Gold-Catalyzed Conversion of Highly Strained Compounds.

The past decade has witnessed the golden age of homogeneous gold-catalyzed reactions, especially those that involve the transformation of highly strained molecules into complex molecular architectures. Gold catalysts, with unique electronic properties and catalytic abilities, have elevated versatile reaction modes through π-interaction induced activation. On the basis of increasing research interest in this topic, together with the significant development of various ligands, including phosphine ligands and azacyclic or noncyclic carbene ligands, the understanding of the catalytic function of gold catalysts has become much deeper and more comprehensive. Different reaction needs thus could be adapted by a novel gold catalyst with a diversified ligand selection. Furthermore, the whole evolution of the gold catalysis on synthetic methodologies has realized and expanded its application into natural product synthesis as well as the potentiality of drug discovery, which endows this ancient metal with a magnificent renaissance. The reactivity of strained small ring molecules with high tension has always been an important research topic in organic chemistry. When the highly strained small ring is linked with a π-electron rich moiety or contains a heteroatom, the gold activation of the π-system or coordination with the heteroatom can initiate a cascade reaction, usually followed by ring opening or expansion. These processes can result in the rapid construction of complex and distinct molecular structures, many of which feature in biologically important molecules. In this review, we will mainly summarize the advances on diverse reaction types and molecular constructions accomplished by homogeneous gold catalysis using highly strained substrates, including methylenecyclopropanes (MCPs), vinylidenecyclopropanes (VDCPs), cyclopropenes as well as aziridine- and epoxide-containing molecules, focusing on the last 10 years. For functionalized alkynyl cyclopropanes, several early inspiring and elegant examples will be described in this review for systematically understanding these transformations.

E2F1-mediated AUF1 upregulation promotes HCC development and enhances drug resistance via stabilization of AKR1B10.

The AU-rich binding factor 1 (AUF1) is one of the well known adenylate-uridylate-rich element (ARE)-specific RNA-binding proteins (ARE-BPs) for which dysregulation has been reported in various human cancers. However, the involvement of AUF1 in the initiation and progression of hepatocellular carcinoma (HCC) is still elusive. In this study, we aimed at exploring the clinical significance, function, and mechanism of the abnormal expression of AUF1 in HCC. Using a bioinformatics analysis of The Cancer Genome Atlas (TCGA) and Liver Cancer Institute (LCI) database, we identified that AUF1 was abnormally highly expressed in HCC tissues and that the high expression of AUF1 was correlated with poor prognosis in patients with HCC. We also confirmed the increased AUF1 expression and its prognostic value in our HBV-related HCC cohorts. AUF1 overexpression in hepatoma cells promoted cell proliferation and increased the resistance of hepatoma cells toward doxorubicin, whereas knockdown of AUF1 exerted the opposite effects. Mechanistically, we demonstrated that AKR1B10 was a critical target of AUF1 and was essential for sustaining the AUF1-induced proliferation and drug resistance of hepatoma cells. AUF1 increased AKR1B10 expression by binding to the 3'UTR region of AKR1B10 mRNA and stabilizing AKR1B10 mRNA. Additionally, we demonstrated that E2F1 enhanced AUF1 expression in HCC at the transcription level. Our study revealed a novel role of AUF1 in promoting the development and drug resistance of HCC via the post-transcriptional regulation of AKR1B10 expression. The E2F1/AUF1/AKR1B10 axis can serve as a potential therapeutic target in HCC.

Suppression of substrate mode in GaN-based green laser diodes.

Parasitic substrate mode readily appears in GaN-based laser diodes (LDs) because of insufficient optical confinement, especially for green LDs. Substrate modes affect the behavior of a LD severely, including the laser beam quality, the optical output power, the longitudinal mode stability, and the maximum modulation speed. In this article, systematic studies on the n-cladding layer (CL) design to suppress the substrate mode of GaN-based green LDs were carried out. We established a contour map to describe the relationship between the optical confinement (determined by the thickness and the refractive index) of n-CL and the substrate mode intensity by simulating the near-field pattern and the far-field pattern. We found that it was difficult to obtain the Gaussian-shape far-field pattern using AlGaN as a cladding layer due to the appearance of cracks induced by tensile strain. However, this can be realized by introducing quaternary AlInGaN as a cladding layer since refractive index and strain can be tuned separately for quaternary alloy.

Room-temperature electrically pumped InGaN-based microdisk laser grown on Si.

Silicon photonics has been longing for an efficient on-chip light source that is electrically driven at room temperature. Microdisk laser featured with low-loss whispering gallery modes can emit directional lasing beam through a closely coupled on-chip waveguide efficiently, and hence is particularly suitable for photonics integration. The realization of electrically pumped III-nitride microdisk laser grown on Si has been impeded by the conventional undercut structure, poor material quality, and a limited quality of GaN microdisk formed by dry etching. Here we report a successful fabrication of room-temperature electrically pumped InGaN-based microdisk lasers grown on Si. A dramatic narrowing of the electroluminescence spectral line-width and a clear discontinuity in the slope of light output power plotted as a function of the injection current provide an unambiguous evidence of lasing. This is the first observation of electrically pumped lasing in InGaN-based microdisk lasers grown on Si at room temperature.

Green laser diodes with low threshold current density via interface engineering of InGaN/GaN quantum well active region.

By observing the morphology evolution of green InGaN/GaN quantum well (QW) and studying the catholuminescence (CL) property, we investigate indium-segregation-related defects that are formed at green InGaN/GaN QW interfaces. Meanwhile, we also propose the approach and suggest the mechanism to remove them for green InGaN/GaN QW grown on both GaN templates and free-standing GaN substrates. By engineering the interface of green InGaN/GaN QWs, we have achieved green laser diode (LD) structure with low threshold current density of 1.85 kA cm-2. The output power of the green LD is 58 mW at a current density of 6 kA cm-2 under continuous-wave operation at room temperature.

C(sp3 )-H Functionalizations Promoted by the Gold Carbene Generated from Vinylidenecyclopropanes.

The gold carbene generated from vinylidenecyclopropanes (VDCPs) can smoothly perform a C(sp3 )-H bond insertion reaction, stereoselectively affording the intramolecular C(sp3 )-H bond functionalized product, benzoxepine, with syn-configuration in moderate to good yields under mild conditions. The KIE investigation on this bond functionalization partially revealed that the carbene insertion step might be rate-determining. Using a chiral gold(I) catalyst, the first example on the asymmetric variant of gold carbene insertion into C(sp3 )-H bond has been disclosed, giving the desired products with excellent results.

Grignard reagent/CuI/LiCl-mediated stereoselective cascade addition/cyclization of diynes: a novel pathway for the construction of 1-methyleneindene derivatives.

Diynes containing a cyclopropane group smoothly undergo a novel intramolecular and stereoselective cascade addition/cyclization reaction to produce the corresponding 1-methyleneindene derivatives in moderate to good yields. This interesting transformation is mediated by Grignard reagent/CuI with LiCl as an additive under mild conditions. The obtained product can easily be further functionalized through cyclopropyl ring opening. A plausible reaction mechanism has also been presented on the basis of deuterium labeling and control experiments.

RNA binding protein TIAR modulates HBV replication by tipping the balance of pgRNA translation.

The pregenomic RNA (pgRNA) of hepatitis B virus (HBV) serves not only as a bicistronic message RNA to translate core protein (Cp) and DNA polymerase (Pol), but also as the template for reverse transcriptional replication of viral DNA upon packaging into nucleocapsid. Although it is well known that pgRNA translates much more Cp than Pol, the molecular mechanism underlying the regulation of Cp and Pol translation efficiency from pgRNA remains elusive. In this study, we systematically profiled HBV nucleocapsid- and pgRNA-associated cellular proteins by proteomic analysis and identified TIA-1-related protein (TIAR) as a novel cellular protein that binds pgRNA and promotes HBV DNA replication. Interestingly, loss- and gain-of-function genetic analyses showed that manipulation of TIAR expression did not alter the levels of HBV transcripts nor the secretion of HBsAg and HBeAg in human hepatoma cells supporting HBV replication. However, Ribo-seq and PRM-based mass spectrometry analyses demonstrated that TIAR increased the translation of Pol but decreased the translation of Cp from pgRNA. RNA immunoprecipitation (RIP) and pulldown assays further revealed that TIAR directly binds pgRNA at the 5' stem-loop (ε). Moreover, HBV replication or Cp expression induced the increased expression and redistribution of TIAR from the nucleus to the cytoplasm of hepatocytes. Our results thus imply that TIAR is a novel cellular factor that regulates HBV replication by binding to the 5' ε structure of pgRNA to tip the balance of Cp and Pol translation. Through induction of TIAR translocation from the nucleus to the cytoplasm, Cp indirectly regulates the Pol translation and balances Cp and Pol expression levels in infected hepatocytes to ensure efficient viral replication.

Crystal structure of SARS-CoV-2 nsp10-nsp16 in complex with small molecule inhibitors, SS148 and WZ16.

SARS-CoV-2 nsp10-nsp16 complex is a 2'-O-methyltransferase (MTase) involved in viral RNA capping, enabling the virus to evade the immune system in humans. It has been considered a valuable target in the discovery of antiviral therapeutics, as the RNA cap formation is crucial for viral propagation. Through cross-screening of the inhibitors that we previously reported for SARS-CoV-2 nsp14 MTase activity against nsp10-nsp16 complex, we identified two compounds (SS148 and WZ16) that also inhibited nsp16 MTase activity. To further enable the chemical optimization of these two compounds towards more potent and selective dual nsp14/nsp16 MTase inhibitors, we determined the crystal structure of nsp10-nsp16 in complex with each of SS148 and WZ16. As expected, the structures revealed the binding of both compounds to S-adenosyl-L-methionine (SAM) binding pocket of nsp16. However, our structural data along with the biochemical mechanism of action determination revealed an RNA-dependent SAM-competitive pattern of inhibition for WZ16, clearly suggesting that binding of the RNA first may help the binding of some SAM competitive inhibitors. Both compounds also showed some degree of selectivity against human protein MTases, an indication of great potential for chemical optimization towards more potent and selective inhibitors of coronavirus MTases.

EP300 Selectively Controls the Enhancer Landscape of MYCN-Amplified Neuroblastoma.

Gene expression is regulated by promoters and enhancers marked by histone H3 lysine 27 acetylation (H3K27ac), which is established by the paralogous histone acetyltransferases (HAT) EP300 and CBP. These enzymes display overlapping regulatory roles in untransformed cells, but less characterized roles in cancer cells. We demonstrate that the majority of high-risk pediatric neuroblastoma (NB) depends on EP300, whereas CBP has a limited role. EP300 controls enhancer acetylation by interacting with TFAP2ß, a transcription factor member of the lineage-defining transcriptional core regulatory circuitry (CRC) in NB. To disrupt EP300, we developed a proteolysis-targeting chimera (PROTAC) compound termed "JQAD1" that selectively targets EP300 for degradation. JQAD1 treatment causes loss of H3K27ac at CRC enhancers and rapid NB apoptosis, with limited toxicity to untransformed cells where CBP may compensate. Furthermore, JQAD1 activity is critically determined by cereblon (CRBN) expression across NB cells. SIGNIFICANCE: EP300, but not CBP, controls oncogenic CRC-driven transcription in high-risk NB by binding TFAP2ß. We developed JQAD1, a CRBN-dependent PROTAC degrader with preferential activity against EP300 and demonstrated its activity in NB. JQAD1 has limited toxicity to untransformed cells and is effective in vivo in a CRBN-dependent manner. This article is highlighted in the In This Issue feature, p. 587.

BAF Complex Maintains Glioma Stem Cells in Pediatric H3K27M Glioma.

Diffuse midline gliomas are uniformly fatal pediatric central nervous system cancers that are refractory to standard-of-care therapeutic modalities. The primary genetic drivers are a set of recurrent amino acid substitutions in genes encoding histone H3 (H3K27M), which are currently undruggable. These H3K27M oncohistones perturb normal chromatin architecture, resulting in an aberrant epigenetic landscape. To interrogate for epigenetic dependencies, we performed a CRISPR screen and show that patient-derived H3K27M-glioma neurospheres are dependent on core components of the mammalian BAF (SWI/SNF) chromatin remodeling complex. The BAF complex maintains glioma stem cells in a cycling, oligodendrocyte precursor cell-like state, in which genetic perturbation of the BAF catalytic subunit SMARCA4 (BRG1), as well as pharmacologic suppression, opposes proliferation, promotes progression of differentiation along the astrocytic lineage, and improves overall survival of patient-derived xenograft models. In summary, we demonstrate that therapeutic inhibition of the BAF complex has translational potential for children with H3K27M gliomas. SIGNIFICANCE: Epigenetic dysregulation is at the core of H3K27M-glioma tumorigenesis. Here, we identify the BRG1-BAF complex as a critical regulator of enhancer and transcription factor landscapes, which maintain H3K27M glioma in their progenitor state, precluding glial differentiation, and establish pharmacologic targeting of the BAF complex as a novel treatment strategy for pediatric H3K27M glioma. See related commentary by Beytagh and Weiss, p. 2730. See related article by Mo et al., p. 2906.

NFATc3 inhibits hepatocarcinogenesis and HBV replication via positively regulating RIG-I-mediated interferon transcription.

Nuclear factor of activated T cells 3 (NFATc3) has been reported to upregulate type I interferons (IFNs) expression, and the abnormal expression and activation of NFATc3 were closely related to tumorigenesis. However, the potential function of NFATc3 in hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) remains to be elucidated. In this study, we found that NFATc3 gene was frequently deleted and downregulated in HCC tumor tissues, and that the downregulation of NFATc3 was associated with poor prognosis of HCC patients. The gain- and loss-of-function experiments demonstrated that NFATc3 inhibited HCC cell proliferation and invasion, as well as HBV replication. Mechanistically, NFATc3 could bind to the promoters of IFNL1 and IFNB1 genes and prompt the production of IFNs and interferon-stimulated genes. Furthermore, retinoic acid-inducible gene-I (RIG-I) pathway activation increased NFATc3 expression and nuclear localization, and activated NFATc3 further enhanced RIG-I-mediated IFN responses. Collectively, our findings reveal a novel regulatory signaling cascade, the RIG-I/NFATc3/IFNs axis, which inhibits hepatocarcinogenesis and HBV replication by enhancing the immune response in hepatocytes, and this functional axis might potentially be exploited for therapeutic benefits in the clinical treatment of HBV-related HCC.

Development of Dimethylisoxazole-Attached Imidazo[1,2-a]pyridines as Potent and Selective CBP/P300 Inhibitors.

The use of epigenetic bromodomain inhibitors as anticancer therapeutics has transitioned from targeting bromodomain extraterminal domain (BET) proteins into targeting non-BET bromodomains. The two most relevant non-BET bromodomain oncology targets are cyclic AMP response element-binding protein (CBP) and E1A binding protein P300 (EP300). To explore the growing CBP/EP300 interest, we developed a highly efficient two-step synthetic route for dimethylisoxazole-attached imidazo[1,2-a]pyridine scaffold-containing inhibitors. Our efficient two-step reactions enabled high-throughput synthesis of compounds designed by molecular modeling, which together with structure-activity relationship (SAR) studies facilitated an overarching understanding of selective targeting of CBP/EP300 over non-BET bromodomains. This led to the identification of a new potent and selective CBP/EP300 bromodomain inhibitor, UMB298 (compound 23, CBP IC50 72 nM and bromodomain 4, BRD4 IC50 5193 nM). The SAR we established is in good agreement with literature-reported CBP inhibitors, such as CBP30, and demonstrates the advantage of utilizing our two-step approach for inhibitor development of other bromodomains.

Probing the SAM Binding Site of SARS-CoV-2 Nsp14 In Vitro Using SAM Competitive Inhibitors Guides Developing Selective Bisubstrate Inhibitors.

The COVID-19 pandemic has clearly brought the healthcare systems worldwide to a breaking point, along with devastating socioeconomic consequences. The SARS-CoV-2 virus, which causes the disease, uses RNA capping to evade the human immune system. Nonstructural protein (nsp) 14 is one of the 16 nsps in SARS-CoV-2 and catalyzes the methylation of the viral RNA at N7-guanosine in the cap formation process. To discover small-molecule inhibitors of nsp14 methyltransferase (MTase) activity, we developed and employed a radiometric MTase assay to screen a library of 161 in-house synthesized S-adenosylmethionine (SAM) competitive MTase inhibitors and SAM analogs. Among six identified screening hits, SS148 inhibited nsp14 MTase activity with an IC50 value of 70 ± 6 nM and was selective against 20 human protein lysine MTases, indicating significant differences in SAM binding sites. Interestingly, DS0464 with an IC50 value of 1.1 ± 0.2 µM showed a bisubstrate competitive inhibitor mechanism of action. DS0464 was also selective against 28 out of 33 RNA, DNA, and protein MTases. The structure-activity relationship provided by these compounds should guide the optimization of selective bisubstrate nsp14 inhibitors and may provide a path toward a novel class of antivirals against COVID-19, and possibly other coronaviruses.

Probing the SAM Binding Site of SARS-CoV-2 nsp14 in vitro Using SAM Competitive Inhibitors Guides Developing Selective bi-substrate Inhibitors.

The COVID-19 pandemic has clearly brought the healthcare systems world-wide to a breaking point along with devastating socioeconomic consequences. The SARS-CoV-2 virus which causes the disease uses RNA capping to evade the human immune system. Non-structural protein (nsp) 14 is one of the 16 nsps in SARS-CoV-2 and catalyzes the methylation of the viral RNA at N7-guanosine in the cap formation process. To discover small molecule inhibitors of nsp14 methyltransferase (MT) activity, we developed and employed a radiometric MT assay to screen a library of 161 in house synthesized S-adenosylmethionine (SAM) competitive methyltransferase inhibitors and SAM analogs. Among seven identified screening hits, SS148 inhibited nsp14 MT activity with an IC 50 value of 70 ± 6 nM and was selective against 20 human protein lysine methyltransferases indicating significant differences in SAM binding sites. Interestingly, DS0464 with IC 50 value of 1.1 ± 0.2 µM showed a bi-substrate competitive inhibitor mechanism of action. Modeling the binding of this compound to nsp14 suggests that the terminal phenyl group extends into the RNA binding site. DS0464 was also selective against 28 out of 33 RNA, DNA, and protein methyltransferases. The structure-activity relationship provided by these compounds should guide the optimization of selective bi-substrate nsp14 inhibitors and may provide a path towards a novel class of antivirals against COVID-19, and possibly other coronaviruses.

Bromodomain protein BRD4 directs and sustains CD8 T cell differentiation during infection.

In response to infection, pathogen-specific CD8 T cells differentiate into functionally diverse effector and memory T cell populations critical for resolving disease and providing durable immunity. Through small-molecule inhibition, RNAi studies, and induced genetic deletion, we reveal an essential role for the chromatin modifier and BET family member BRD4 in supporting the differentiation and maintenance of terminally fated effector CD8 T cells during infection. BRD4 bound diverse regulatory regions critical to effector T cell differentiation and controlled transcriptional activity of terminal effector-specific super-enhancers in vivo. Consequentially, induced deletion of Brd4 or small molecule-mediated BET inhibition impaired maintenance of a terminal effector T cell phenotype. BRD4 was also required for terminal differentiation of CD8 T cells in the tumor microenvironment in murine models, which we show has implications for immunotherapies. Taken together, these data reveal an unappreciated requirement for BRD4 in coordinating activity of cis regulatory elements to control CD8 T cell fate and lineage stability.

Lysine Demethylase 5A is Required for MYC Driven Transcription in Multiple Myeloma.

Lysine demethylase 5A (KDM5A) is a negative regulator of histone H3K4 trimethylation, a histone mark associated with activate gene transcription. We identify that KDM5A interacts with the P-TEFb complex and cooperates with MYC to control MYC targeted genes in multiple myeloma (MM) cells. We develop a cell-permeable and selective KDM5 inhibitor, JQKD82, that increases histone H3K4me3 but paradoxically inhibits downstream MYC-driven transcriptional output in vitro and in vivo. Using genetic ablation together with our inhibitor, we establish that KDM5A supports MYC target gene transcription independent of MYC itself, by supporting TFIIH (CDK7)- and P-TEFb (CDK9)-mediated phosphorylation of RNAPII. These data identify KDM5A as a unique vulnerability in MM functioning through regulation of MYC-target gene transcription, and establish JQKD82 as a tool compound to block KDM5A function as a potential therapeutic strategy for MM.

Dispersible and manipulable magnetic L10-FePt nanoparticles.

Oriented single-domain magnetic nanoparticles with a high remanence ratio Mr/Ms and maximum magnetic energy product (BH)max have attracted immense attention. However, nanoparticles easily agglomerate due to their extremely small size, which impedes the process of orientation. So manipulating the orientation of nanoparticles is still a key challenge. Here, L10-FePt single-domain nanoparticles were successfully synthesized by a chemical method in the liquid phase and nanoparticle-based anisotropic nanocomposites were obtained by dispersing the nanoparticles in liquid epoxy resin under an external magnetic field. The main factors that impact the orientation of L10-FePt single-domain nanoparticles were investigated further. It is found that the dispersibility of nanoparticles has a great impact on the degree of orientation, so do the applied magnetic field and the concentration of nanoparticles. Nanocomposites with homodisperse nanoparticles oriented under a suitable external magnetic field exhibit excellent magnetic performance, such as high coercivity Hc and remanence Mr, which gives the nanocomposites a higher (BH)max than the isotropic samples. The anisotropic nanocomposites show great potential in multifarious permanent magnet applications and fundamental research.

Development and preclinical validation of a novel covalent ubiquitin receptor Rpn13 degrader in multiple myeloma.

Proteasome inhibition is an effective treatment for multiple myeloma (MM); however, targeting different components of the ubiquitin-proteasome system (UPS) remains elusive. Our RNA-interference studies identified proteasome-associated ubiquitin-receptor Rpn13 as a mediator of MM cell growth and survival. Here, we developed the first degrader of Rpn13, WL40, using a small-molecule-induced targeted protein degradation strategy to selectively degrade this component of the UPS. WL40 was synthesized by linking the Rpn13 covalent inhibitor RA190 with the cereblon (CRBN) binding ligand thalidomide. We show that WL40 binds to both Rpn13 and CRBN and triggers degradation of cellular Rpn13, and is therefore first-in-class in exploiting a covalent inhibitor for the development of degraders. Biochemical and cellular studies show that WL40-induced Rpn13 degradation is both CRBN E3 ligase- and Rpn13-dependent. Importantly, WL40 decreases viability in MM cell lines and patient MM cells, even those resistant to bortezomib. Mechanistically, WL40 interrupts Rpn13 function and activates caspase apoptotic cascade, ER stress response and p53/p21 signaling. In animal model studies, WL40 inhibits xenografted human MM cell growth and prolongs survival. Overall, our data show the development of the first UbR Rpn13 degrader with potent anti-MM activity, and provide proof of principle for the development of degraders targeting components of the UPS for therapeutic application.