Examination of the mechanisms underlying the discriminative stimulus properties of the atypical antipsychotic amisulpride.

Amisulpride is an atypical benzamide antipsychotic/antidepressant, whose mechanism of action is thought to depend mainly on dopamine D2/3 receptor activity, but also with some serotonin 5-HT2B/7 effects. The present study examined the role of D2/3 receptors and 5-HT2B/7 receptors in amisulpride's discriminative stimulus. Selective agonists and antagonists of the above receptors were tested in adult, male C57BL/6 mice trained to discriminate 10 mg/kg amisulpride from vehicle in a two-lever drug discrimination assay. After acquisition of the two-lever discrimination, the amisulpride generalization curve yielded an ED50 = 0.56 mg/kg (95% CI = 0.42-0.76 mg/kg). Substitution tests found that the D2/3 antagonist raclopride (62.7% Drug Lever Responding), D2/3 agonist quinpirole (56.6% DLR), 5-HT7 agonist LP-44 (50.1% DLR) and 5-HT7 antagonist SB-269970 (36.7% DLR) produced various degrees of partial substitution for the amisulpride stimulus, whereas the 5-HT2B agonist BW 723C86 (17.9% DLR) and 5-HT2B antagonist SB-204741 (21.1% DLR) yielded negligible amisulpride-like effects. In combination tests with amisulpride, quinpirole decreased percent responding from 98.3% to 57.0% DLR, LP-44 decreased percent responding from 97.6% to 76.7% DLR, and BW 723C86 reduced percent responding from 95.66% to 74.11% DLR. Taken together, the results from stimulus generalization and antagonism studies suggest that amisulpride has a complex discriminative cue that involves mainly mixed D2/3 receptor antagonist/agonist effects and, to a lesser degree, mixed 5-HT7 receptor agonist/antagonist and perhaps 5-HT2B receptor antagonist effects.

Diversity and Composition of Methanotroph Communities in Caves.

Methane oxidizing microorganisms (methanotrophs) are ubiquitous in the environment and represent a major sink for the greenhouse gas methane (CH4). Recent studies have demonstrated methanotrophs are abundant and contribute to CH4 dynamics in caves. However, very little is known about what controls the distribution and abundance of methanotrophs in subterranean ecosystems. Here, we report a survey of soils collected from > 20 caves in North America to elucidate the factors shaping cave methanotroph communities. Using 16S rRNA sequencing, we recovered methanotrophs from nearly all (98%) of the samples, including cave sites where CH4 concentrations were at or below detection limits (≤0.3 ppmv). We identified a core methanotroph community among caves comprised of high-affinity methanotrophs. Although associated with local-scale mineralogy, methanotroph composition did not systematically vary between the entrances and interior of caves, where CH4 concentrations varied. We also observed methanotrophs are able to disperse readily between cave systems showing these organisms have low barriers to dispersal. Lastly, the relative abundance of methanotrophs was positively correlated with cave-air CH4 concentrations, suggesting these microorganisms contribute to CH4 flux in subterranean ecosystems. IMPORTANCE Recent observations have shown the atmospheric greenhouse gas methane (CH4) is consumed by microorganisms (methanotrophs) in caves at rates comparable to CH4 oxidation in surface soils. Caves are abundant in karst landscapes that comprise 14% of Earth's land surface area, and therefore may represent a potentially important, but overlooked, CH4 sink. We sampled cave soils to gain a better understand the community composition and structure of cave methanotrophs. Our results show the members of the USC-γ clade are dominant in cave communities and can easily disperse through the environment, methanotroph relative abundance was correlated with local scale mineralogy of soils, and the relative abundance of methanotrophs was positively correlated with CH4 concentrations in cave air.

Zotatifin, an eIF4A-Selective Inhibitor, Blocks Tumor Growth in Receptor Tyrosine Kinase Driven Tumors.

Oncoprotein expression is controlled at the level of mRNA translation and is regulated by the eukaryotic translation initiation factor 4F (eIF4F) complex. eIF4A, a component of eIF4F, catalyzes the unwinding of secondary structure in the 5'-untranslated region (5'-UTR) of mRNA to facilitate ribosome scanning and translation initiation. Zotatifin (eFT226) is a selective eIF4A inhibitor that increases the affinity between eIF4A and specific polypurine sequence motifs and has been reported to inhibit translation of driver oncogenes in models of lymphoma. Here we report the identification of zotatifin binding motifs in the 5'-UTRs of HER2 and FGFR1/2 Receptor Tyrosine Kinases (RTKs). Dysregulation of HER2 or FGFR1/2 in human cancers leads to activation of the PI3K/AKT and RAS/ERK signaling pathways, thus enhancing eIF4A activity and promoting the translation of select oncogenes that are required for tumor cell growth and survival. In solid tumor models driven by alterations in HER2 or FGFR1/2, downregulation of oncoprotein expression by zotatifin induces sustained pathway-dependent anti-tumor activity resulting in potent inhibition of cell proliferation, induction of apoptosis, and significant in vivo tumor growth inhibition or regression. Sensitivity of RTK-driven tumor models to zotatifin correlated with high basal levels of mTOR activity and elevated translational capacity highlighting the unique circuitry generated by the RTK-driven signaling pathway. This dependency identifies the potential for rational combination strategies aimed at vertical inhibition of the PI3K/AKT/eIF4F pathway. Combination of zotatifin with PI3K or AKT inhibitors was beneficial across RTK-driven cancer models by blocking RTK-driven resistance mechanisms demonstrating the clinical potential of these combination strategies.

Registration Attendants Show Poor Readiness to Handle Advanced Care Planning Discussions.

Background: Emergency departments (ED) and other medical points of care are required to provide patients with advance directive (AD) information. Although many hospitals provide AD information in EDs, the comfort and preparation of the ED staff with this responsibility is unclear. Objective: To determine the attitudes, comfort levels, and prior training of ED staff with AD. Methods: The ED social workers, nurses, registration attendants, residents, and attending physicians at two academic hospitals completed a survey about their attitudes around, preparedness for, and experiences with advance care planning (ACP) discussions in the ED. Results: We received responses from 220 ED staff. Preparedness to discuss ACP with patients varied by profession. Eighty percent of social workers (n = 4/5) and 52% (n = 16/31) of attending physicians reported preparedness to handle ACP discussions. Registration attendants were the least prepared, and only 4% (n = 1/24) reported preparedness to discuss ACP. Attempts at ACP discussions with patients also differed by profession, with attending physicians being the most likely (77%, n = 24/31), whereas registration attendants were the least likely (8%, n = 2/24). Fifty-nine percent of surveyed staff (n = 130/220) believed that ACP was a component of emergency care, although only 13% (n = 29/220) had received training. Conclusion: The ED staff are in favor of ACP in the ED. Preparedness for, and attempts of ACP discussions with patients in the ED vary by profession. Attending physicians and social workers tend to be the most prepared, and they report the most frequent attempts at discussions with patients. Despite the fact that registration attendants are frequently tasked with asking about patient ADs, they show little confidence in asking about and discussing such matters. Our research indicates that registration attendants feel unprepared to guide discussions of ADs and should not do so without additional training.

mRNA translation is a therapeutic vulnerability necessary for bladder epithelial transformation.

Using genetically engineered mouse models, this work demonstrates that protein synthesis is essential for efficient urothelial cancer formation and growth but dispensable for bladder homeostasis. Through a candidate gene analysis for translation regulators implicated in this dependency, we discovered that phosphorylation of the translation initiation factor eIF4E at serine 209 is increased in both murine and human bladder cancer, and this phosphorylation corresponds with an increase in de novo protein synthesis. Employing an eIF4E serine 209 to alanine knock-in mutant mouse model, we show that this single posttranslational modification is critical for bladder cancer initiation and progression, despite having no impact on normal bladder tissue maintenance. Using murine and human models of advanced bladder cancer, we demonstrate that only tumors with high levels of eIF4E phosphorylation are therapeutically vulnerable to eFT508, the first clinical-grade inhibitor of MNK1 and MNK2, the upstream kinases of eIF4E. Our results show that phospho-eIF4E plays an important role in bladder cancer pathogenesis, and targeting its upstream kinases could be an effective therapeutic option for bladder cancer patients with high levels of eIF4E phosphorylation.

Targeting mutant KRAS.

The protein KRAS has for decades been considered a holy grail of cancer drug discovery. For most of that time, it has also been considered undruggable. Since 2018, five compounds have entered the clinic targeting a single mutant form of KRAS, G12C. Here, we review each of these compounds along with additional approaches to targeting this and other mutants. Remaining challenges include expanding the identification of inhibitors to a broader range of known mutants and to conformations of the protein more likely to avoid development of resistance.

A Highly Selective MNK Inhibitor Rescues Deficits Associated with Fragile X Syndrome in Mice.

Fragile X syndrome (FXS) is the most common inherited source of intellectual disability in humans. FXS is caused by mutations that trigger epigenetic silencing of the Fmr1 gene. Loss of Fmr1 results in increased activity of the mitogen-activated protein kinase (MAPK) pathway. An important downstream consequence is activation of the mitogen-activated protein kinase interacting protein kinase (MNK). MNK phosphorylates the mRNA cap-binding protein, eukaryotic initiation factor 4E (eIF4E). Excessive phosphorylation of eIF4E has been directly implicated in the cognitive and behavioral deficits associated with FXS. Pharmacological reduction of eIF4E phosphorylation is one potential strategy for FXS treatment. We demonstrate that systemic dosing of a highly specific, orally available MNK inhibitor, eFT508, attenuates numerous deficits associated with loss of Fmr1 in mice. eFT508 resolves a range of phenotypic abnormalities associated with FXS including macroorchidism, aberrant spinogenesis, and alterations in synaptic plasticity. Key behavioral deficits related to anxiety, social interaction, obsessive and repetitive activities, and object recognition are ameliorated by eFT508. Collectively, this work establishes eFT508 as a potential means to reverse deficits associated with FXS.

Rainforest-to-pasture conversion stimulates soil methanogenesis across the Brazilian Amazon.

The Amazon rainforest is a biodiversity hotspot and large terrestrial carbon sink threatened by agricultural conversion. Rainforest-to-pasture conversion stimulates the release of methane, a potent greenhouse gas. The biotic methane cycle is driven by microorganisms; therefore, this study focused on active methane-cycling microorganisms and their functions across land-use types. We collected intact soil cores from three land use types (primary rainforest, pasture, and secondary rainforest) of two geographically distinct areas of the Brazilian Amazon (Santarém, Pará and Ariquemes, Rondônia) and performed DNA stable-isotope probing coupled with metagenomics to identify the active methanotrophs and methanogens. At both locations, we observed a significant change in the composition of the isotope-labeled methane-cycling microbial community across land use types, specifically an increase in the abundance and diversity of active methanogens in pastures. We conclude that a significant increase in the abundance and activity of methanogens in pasture soils could drive increased soil methane emissions. Furthermore, we found that secondary rainforests had decreased methanogenic activity similar to primary rainforests, and thus a potential to recover as methane sinks, making it conceivable for forest restoration to offset greenhouse gas emissions in the tropics. These findings are critical for informing land management practices and global tropical rainforest conservation.

Targeting Oncogene mRNA Translation in B-Cell Malignancies with eFT226, a Potent and Selective Inhibitor of eIF4A.

The PI3K/AKT/mTOR pathway is often activated in lymphoma through alterations in PI3K, PTEN, and B-cell receptor signaling, leading to dysregulation of eIF4A (through its regulators, eIF4B, eIF4G, and PDCD4) and the eIF4F complex. Activation of eIF4F has a direct role in tumorigenesis due to increased synthesis of oncogenes that are dependent on enhanced eIF4A RNA helicase activity for translation. eFT226, which inhibits translation of specific mRNAs by promoting eIF4A1 binding to 5'-untranslated regions (UTR) containing polypurine and/or G-quadruplex recognition motifs, shows potent antiproliferative activity and significant in vivo efficacy against a panel of diffuse large B-cell lymphoma (DLBCL), and Burkitt lymphoma models with ≤1 mg/kg/week intravenous administration. Evaluation of predictive markers of sensitivity or resistance has shown that activation of eIF4A, mediated by mTOR signaling, correlated with eFT226 sensitivity in in vivo xenograft models. Mutation of PTEN is associated with reduced apoptosis in vitro and diminished efficacy in vivo in response to eFT226. In models evaluated with PTEN loss, AKT was stimulated without a corresponding increase in mTOR activation. AKT activation leads to the degradation of PDCD4, which can alter eIF4F complex formation. The association of eFT226 activity with PTEN/PI3K/mTOR pathway regulation of mRNA translation provides a means to identify patient subsets during clinical development.

Belowground changes to community structure alter methane-cycling dynamics in Amazonia.

Amazonian rainforest is undergoing increasing rates of deforestation, driven primarily by cattle pasture expansion. Forest-to-pasture conversion has been associated with increases in soil methane (CH4) emission. To better understand the drivers of this change, we measured soil CH4 flux, environmental conditions, and belowground microbial community structure across primary forests, cattle pastures, and secondary forests in two Amazonian regions. We show that pasture soils emit high levels of CH4 (mean: 3454.6 ± 9482.3 µg CH4 m-2 d-1), consistent with previous reports, while forest soils on average emit CH4 at modest rates (mean: 9.8 ± 120.5 µg CH4 m-2 d-1), but often act as CH4 sinks. We report that secondary forest soils tend to consume CH4 (mean: -10.2 ± 35.7 µg CH4 m-2 d-1), demonstrating that pasture CH4 emissions can be reversed. We apply a novel computational approach to identify microbial community attributes associated with flux independent of soil chemistry. While this revealed taxa known to produce or consume CH4 directly (i.e. methanogens and methanotrophs, respectively), the vast majority of identified taxa are not known to cycle CH4. Each land use type had a unique subset of taxa associated with CH4 flux, suggesting that land use change alters CH4 cycling through shifts in microbial community composition. Taken together, we show that microbial composition is crucial for understanding the observed CH4 dynamics and that microorganisms provide explanatory power that cannot be captured by environmental variables.

The Oldest Highlands of Mars May Be Massive Dust Fallout Deposits.

The oldest terrains of Mars are cratered landscapes, in which extensive valleys and basins are covered by ubiquitous fluvial plains. One current paradigm maintains that an impact-generated megaregolith underlies these sediments. This megaregolith was likely largely generated during the Early Noachian (~4.1 to ~3.94 Ga) when most Martian impact basins formed. We examined the geologic records of NW Hellas and NW Isidis, which include this epoch's most extensive circum-basin outcrops. Here, we show that these regions include widespread, wind-eroded landscapes, crater rims eroded down by several hundred meters, pitted plains, and inverted fluvial and crater landforms. These surfaces exhibit few fresh craters, indicating geologically recent wind erosion. The deep erosion, topographic inversions, and an absence of dunes on or near talus across these regions suggest that sediments finer than sand compose most of these highland materials. We propose that basin-impact-generated hurricane-force winds created sediment-laden atmospheric conditions, and that muddy rains rapidly settled suspended sediments to construct extensive Early Noachian highlands. The implied high abundance of fine-grained sediments before these impacts suggests large-scale glacial silt production and supports the previously proposed Noachian "icy highlands" hypothesis. We suggest that subglacial meltwater interactions with the sedimentary highlands could have promoted habitability, particularly in clay strata.

Design of Development Candidate eFT226, a First in Class Inhibitor of Eukaryotic Initiation Factor 4A RNA Helicase.

Dysregulation of protein translation is a key driver for the pathogenesis of many cancers. Eukaryotic initiation factor 4A (eIF4A), an ATP-dependent DEAD-box RNA helicase, is a critical component of the eIF4F complex, which regulates cap-dependent protein synthesis. The flavagline class of natural products (i.e., rocaglamide A) has been shown to inhibit protein synthesis by stabilizing a translation-incompetent complex for select messenger RNAs (mRNAs) with eIF4A. Despite showing promising anticancer phenotypes, the development of flavagline derivatives as therapeutic agents has been hampered because of poor drug-like properties as well as synthetic complexity. A focused effort was undertaken utilizing a ligand-based design strategy to identify a chemotype with optimized physicochemical properties. Also, detailed mechanistic studies were undertaken to further elucidate mRNA sequence selectivity, key regulated target genes, and the associated antitumor phenotype. This work led to the design of eFT226 (Zotatifin), a compound with excellent physicochemical properties and significant antitumor activity that supports clinical development.

The Chaotic Terrains of Mercury Reveal a History of Planetary Volatile Retention and Loss in the Innermost Solar System.

Mercury's images obtained by the 1974 Mariner 10 flybys show extensive cratered landscapes degraded into vast knob fields, known as chaotic terrain (AKA hilly and lineated terrain). For nearly half a century, it was considered that these terrains formed due to catastrophic quakes and ejecta fallout produced by the antipodal Caloris basin impact. Here, we present the terrains' first geologic examination based on higher spatial resolution MESSENGER (MErcury Surface Space ENvironment GEochemistry and Ranging) imagery and laser altimeter topography. Our surface age determinations indicate that their development persisted until ~1.8 Ga, or ~2 Gyrs after the Caloris basin formed. Furthermore, we identified multiple chaotic terrains with no antipodal impact basins; hence a new geological explanation is needed. Our examination of the Caloris basin's antipodal chaotic terrain reveals multi-kilometer surface elevation losses and widespread landform retention, indicating an origin due to major, gradual collapse of a volatile-rich layer. Crater interior plains, possibly lavas, share the chaotic terrains' age, suggesting a development associated with a geothermal disturbance above intrusive magma bodies, which best explains their regionality and the enormity of the apparent volume losses involved in their development. Furthermore, evidence of localized, surficial collapse, might reflect a complementary, and perhaps longer lasting, devolatilization history by solar heating.

Discriminative stimulus properties of the typical antipsychotic haloperidol compared to other antipsychotic drugs in C57BL/6 mice.

Haloperidol (HAL) was developed in 1958 for the treatment of schizophrenia and is classified as a typical antipsychotic drug (APD). Effective in treating positive symptoms of schizophrenia, it does not treat negative symptoms and produces extrapyramidal motor side-effects. Atypical APDs like clozapine treat both positive and negative symptoms of schizophrenia, have reduced extrapyramidal motor side-effects and possess other clinical advantages. This study used a drug discrimination assay to allow a direct comparison between the subjective effects of HAL and other APDs. Eleven C57BL/6 mice were trained to discriminate 0.05 mg/kg HAL from the vehicle in a two-lever drug discrimination task. The HAL generalization curve (0.001563-0.2 mg/kg) yielded an ED50=0.0024 mg/kg (95% confidence interval: 0.0012-0.0048 mg/kg). The typical APD chlorpromazine produced full substitution at 4.0 mg/kg with 82.7% drug-lever responding (%DLR) with significant rate suppression and partial substitution (73.9% DLR) at 1.0 mg/kg with no rate suppression. The atypical APD clozapine produced partial substitution at 2.5 mg/kg (64.8% DLR) with significant rate suppression. The atypical APD amisulpride failed to substitute for HAL with a maximum %DLR of 57.9% at 40 mg/kg with no rate suppression. The atypical APD aripiprazole partially substituted with a maximum of 75.9% DLR at 1.25 mg/kg with significant rate suppression. These results demonstrate that HAL can be trained as a discriminative stimulus in C57BL/6 mice, and its discriminative cue appears to be unique and distinct from that of atypical APDs.

Translation control of the immune checkpoint in cancer and its therapeutic targeting.

Cancer cells develop mechanisms to escape immunosurveillance, among which modulating the expression of immune suppressive messenger RNAs is most well-documented. However, how this is molecularly achieved remains largely unresolved. Here, we develop an in vivo mouse model of liver cancer to study oncogene cooperation in immunosurveillance. We show that MYC overexpression (MYCTg) synergizes with KRASG12D to induce an aggressive liver tumor leading to metastasis formation and reduced mouse survival compared with KRASG12D alone. Genome-wide ribosomal footprinting of MYCTg;KRASG12 tumors compared with KRASG12D revealed potential alterations in translation of mRNAs, including programmed-death-ligand 1 (PD-L1). Further analysis revealed that PD-L1 translation is repressed in KRASG12D tumors by functional, non-canonical upstream open reading frames in its 5' untranslated region, which is bypassed in MYCTg;KRASG12D tumors to evade immune attack. We show that this mechanism of PD-L1 translational upregulation was effectively targeted by a potent, clinical compound that inhibits eIF4E phosphorylation, eFT508, which reverses the aggressive and metastatic characteristics of MYCTg;KRASG12D tumors. Together, these studies reveal how immune-checkpoint proteins are manipulated by distinct oncogenes at the level of mRNA translation, which can be exploited for new immunotherapies.

Nociceptor Translational Profiling Reveals the Ragulator-Rag GTPase Complex as a Critical Generator of Neuropathic Pain.

Nociceptors, sensory neurons in the DRG that detect damaging or potentially damaging stimuli, are key drivers of neuropathic pain. Injury to these neurons causes activation of translation regulation signaling, including the mechanistic target of rapamycin complex 1 (mTORC1) and mitogen-activated protein kinase interacting kinase (MNK) eukaryotic initiation factor (eIF) 4E pathways. This is a mechanism driving changes in excitability of nociceptors that is critical for the generation of chronic pain states; however, the mRNAs that are translated to lead to this plasticity have not been elucidated. To address this gap in knowledge, we used translating ribosome affinity purification in male and female mice to comprehensively characterize mRNA translation in Scn10a-positive nociceptors in chemotherapy-induced neuropathic pain (CIPN) caused by paclitaxel treatment. This unbiased method creates a new resource for the field, confirms many findings in the CIPN literature and also find extensive evidence for new target mechanisms that may cause CIPN. We provide evidence that an underlying mechanism of CIPN is sustained mTORC1 activation driven by MNK1-eIF4E signaling. RagA, a GTPase controlling mTORC1 activity, is identified as a novel target of MNK1-eIF4E signaling. This demonstrates a novel translation regulation signaling circuit wherein MNK1-eIF4E activity drives mTORC1 via control of RagA translation. CIPN and RagA translation are strongly attenuated by genetic ablation of eIF4E phosphorylation, MNK1 elimination or treatment with the MNK inhibitor eFT508. We identify a novel translational circuit for the genesis of neuropathic pain caused by chemotherapy with important implications for therapeutics.SIGNIFICANCE STATEMENT Neuropathic pain affects up to 10% of the population, but its underlying mechanisms are incompletely understood, leading to poor treatment outcomes. We used translating ribosome affinity purification technology to create a comprehensive translational profile of DRG nociceptors in naive mice and at the peak of neuropathic pain induced by paclitaxel treatment. We reveal new insight into how mechanistic target of rapamycin complex 1 is activated in neuropathic pain pointing to a key role of MNK1-eIF4E-mediated translation of a complex of mRNAs that control mechanistic target of rapamycin complex 1 signaling at the surface of the lysosome. We validate this finding using genetic and pharmacological techniques. Our work strongly suggests that MNK1-eIF4E signaling drives CIPN and that a drug in human clinical trials, eFT508, may be a new therapeutic for neuropathic pain.

The DREADD agonist clozapine N-oxide (CNO) is reverse-metabolized to clozapine and produces clozapine-like interoceptive stimulus effects in rats and mice.

Clozapine-N-oxide (CNO) has long been the ligand of choice for selectively activating Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). However, recent studies have challenged the long-held assertion that CNO is otherwise pharmacologically inert. The present study aimed to 1) determine whether CNO is reverse-metabolized to its parent compound clozapine in mice (as has recently been reported in rats), and 2) determine whether CNO exerts clozapine-like interoceptive stimulus effects in rats and/or mice. Following administration of 10.0 mg/kg CNO, pharmacokinetic analyses replicated recent reports of back-conversion to clozapine in rats and revealed that this phenomenon also occurs in mice. In rats and mice trained to discriminate 1.25 mg/kg clozapine from vehicle, CNO (1.0-20.0 mg/kg) produced partial substitution for the clozapine stimulus on average, with full substitution being detected in some individual animals of both species at doses frequently used to activate DREADDs. The present demonstration that CNO is converted to clozapine and exerts clozapine-like behavioral effects in both mice and rats further emphasizes the need for appropriate control groups in studies employing DREADDs, and highlights the utility of the drug discrimination procedure as a tool with which to screen the off-target effects of novel DREADD agonists.

Structure-based Design of Pyridone-Aminal eFT508 Targeting Dysregulated Translation by Selective Mitogen-activated Protein Kinase Interacting Kinases 1 and 2 (MNK1/2) Inhibition.

Dysregulated translation of mRNA plays a major role in tumorigenesis. Mitogen-activated protein kinase interacting kinases (MNK)1/2 are key regulators of mRNA translation integrating signals from oncogenic and immune signaling pathways through phosphorylation of eIF4E and other mRNA binding proteins. Modulation of these key effector proteins regulates mRNA, which controls tumor/stromal cell signaling. Compound 23 (eFT508), an exquisitely selective, potent dual MNK1/2 inhibitor, was designed to assess the potential for control of oncogene signaling at the level of mRNA translation. The crystal structure-guided design leverages stereoelectronic interactions unique to MNK culminating in a novel pyridone-aminal structure described for the first time in the kinase literature. Compound 23 has potent in vivo antitumor activity in models of diffuse large cell B-cell lymphoma and solid tumors, suggesting that controlling dysregulated translation has real therapeutic potential. Compound 23 is currently being evaluated in Phase 2 clinical trials in solid tumors and lymphoma. Compound 23 is the first highly selective dual MNK inhibitor targeting dysregulated translation being assessed clinically.

Secondary Electrons as an Energy Source for Life.

Life on Earth is found in a wide range of environments as long as the basic requirements of a liquid solvent, a nutrient source, and free energy are met. Previous hypotheses have speculated how extraterrestrial microbial life may function, among them that particle radiation might power living cells indirectly through radiolytic products. On Earth, so-called electrophilic organisms can harness electron flow from an extracellular cathode to build biomolecules. Here, we describe two hypothetical mechanisms, termed "direct electrophy" and "indirect electrophy" or "fluorosynthesis," by which organisms could harness extracellular free electrons to synthesize organic matter, thus expanding the ensemble of potential habitats in which extraterrestrial organisms might be found in the Solar System and beyond. The first mechanism involves the direct flow of secondary electrons from particle radiation to a microbial cell to power the organism. The second involves the indirect utilization of impinging secondary electrons and a fluorescing molecule, either biotic or abiotic in origin, to drive photosynthesis. Both mechanisms involve the attenuation of an incoming particle's energy to create low-energy secondary electrons. The validity of the hypotheses is assessed through simple calculations showing the biomass density attainable from the energy supplied. Also discussed are potential survival strategies that could be used by organisms living in possible habitats with a plentiful supply of secondary electrons, such as near the surface of an icy moon. While we acknowledge that the only definitive test for the hypothesis is to collect specimens, we also describe experiments or terrestrial observations that could support or nullify the hypotheses. Key Words: Radiation-Electrophiles-Subsurface life. Astrobiology 18, 73-85.