Characterization of Torin2, an ATP-competitive inhibitor of mTOR, ATM, and ATR

Small Molecular Inhibitors That Target ATM for Drug Discovery: Current Research and Potential Prospective

The protein kinase ataxia telangiectasia mutated (ATM) is a constituent of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, exerting a pivotal influence on diverse cellular processes, notably the signaling of double-strand DNA breaks (DSB) and stress response. The dysregulation of ATM is implicated in the pathogenesis of cancer and other diseases such as neurodegeneration. Hence, ATM is deemed a promising candidate for potential therapeutic interventions across a spectrum of diseases. Presently, while ATM small molecule inhibitors are not commercially available, various selective inhibitors have progressed to the clinical research phase. Specifically, AZD1390, WSD0628, SYH2051, and ZN-B-2262 are under investigation in clinical studies pertaining to glioblastoma multiforme and advanced solid tumors, respectively. In this Perspective, we encapsulate the structure, biological functions, and disease relevance of ATM. Subsequently, we concentrate on the design concepts and structure-activity relationships (SAR) of ATM inhibitors, delineating potential avenues for the development of more efficacious ATM-targeted inhibitors.

An expedited screening platform for the discovery of anti-ageing compounds in vitro and in vivo

BACKGROUND

Restraining or slowing ageing hallmarks at the cellular level have been proposed as a route to increased organismal lifespan and healthspan. Consequently, there is great interest in anti-ageing drug discovery. However, this currently requires laborious and lengthy longevity analysis. Here, we present a novel screening readout for the expedited discovery of compounds that restrain ageing of cell populations in vitro and enable extension of in vivo lifespan.

METHODS

Using Illumina methylation arrays, we monitored DNA methylation changes accompanying long-term passaging of adult primary human cells in culture. This enabled us to develop, test, and validate the CellPopAge Clock, an epigenetic clock with underlying algorithm, unique among existing epigenetic clocks for its design to detect anti-ageing compounds in vitro. Additionally, we measured markers of senescence and performed longevity experiments in vivo in Drosophila, to further validate our approach to discover novel anti-ageing compounds. Finally, we bench mark our epigenetic clock with other available epigenetic clocks to consolidate its usefulness and specialisation for primary cells in culture.

RESULTS

We developed a novel epigenetic clock, the CellPopAge Clock, to accurately monitor the age of a population of adult human primary cells. We find that the CellPopAge Clock can detect decelerated passage-based ageing of human primary cells treated with rapamycin or trametinib, well-established longevity drugs. We then utilise the CellPopAge Clock as a screening tool for the identification of compounds which decelerate ageing of cell populations, uncovering novel anti-ageing drugs, torin2 and dactolisib (BEZ-235). We demonstrate that delayed epigenetic ageing in human primary cells treated with anti-ageing compounds is accompanied by a reduction in senescence and ageing biomarkers. Finally, we extend our screening platform in vivo by taking advantage of a specially formulated holidic medium for increased drug bioavailability in Drosophila. We show that the novel anti-ageing drugs, torin2 and dactolisib (BEZ-235), increase longevity in vivo.

CONCLUSIONS

Our method expands the scope of CpG methylation profiling to accurately and rapidly detecting anti-ageing potential of drugs using human cells in vitro, and in vivo, providing a novel accelerated discovery platform to test sought after anti-ageing compounds and geroprotectors.

Modeling of Intracellular Taurine Levels Associated with Ovarian Cancer Reveals Activation of p53, ERK, mTOR and DNA-Damage-Sensing-Dependent Cell Protection

Taurine, a non-proteogenic amino acid and commonly used nutritional supplement, can protect various tissues from degeneration associated with the action of the DNA-damaging chemotherapeutic agent cisplatin. Whether and how taurine protects human ovarian cancer (OC) cells from DNA damage caused by cisplatin is not well understood. We found that OC ascites-derived cells contained significantly more intracellular taurine than cell culture-modeled OC. In culture, elevation of intracellular taurine concentration to OC ascites-cell-associated levels suppressed proliferation of various OC cell lines and patient-derived organoids, reduced glycolysis, and induced cell protection from cisplatin. Taurine cell protection was associated with decreased DNA damage in response to cisplatin. A combination of RNA sequencing, reverse-phase protein arrays, live-cell microscopy, flow cytometry, and biochemical validation experiments provided evidence for taurine-mediated induction of mutant or wild-type p53 binding to DNA, activation of p53 effectors involved in negative regulation of the cell cycle (p21), and glycolysis (TIGAR). Paradoxically, taurine's suppression of cell proliferation was associated with activation of pro-mitogenic signal transduction including ERK, mTOR, and increased mRNA expression of major DNA damage-sensing molecules such as DNAPK, ATM and ATR. While inhibition of ERK or p53 did not interfere with taurine's ability to protect cells from cisplatin, suppression of mTOR with Torin2, a clinically relevant inhibitor that also targets DNAPK and ATM/ATR, broke taurine's cell protection. Our studies implicate that elevation of intracellular taurine could suppress cell growth and metabolism, and activate cell protective mechanisms involving mTOR and DNA damage-sensing signal transducti.

Hydrogen peroxide modulates the expression of the target of rapamycin (TOR) and cell division in Arabidopsis thaliana

Hydrogen peroxide (H2O2) is naturally produced by plant cells during normal development and serves as a messenger that regulates cell metabolism. Despite its importance, the relationship between hydrogen peroxide and the target of rapamycin (TOR) pathway, as well as its impact on cell division, has been poorly analyzed. In this study, we explore the interaction of H2O2 with TOR, a serine/threonine protein kinase that plays a central role in controlling cell growth, size, and metabolism in Arabidopsis thaliana. By applying two concentrations of H2O2 exogenously (0.5 and 1 mM), we could correlate developmental traits, such as primary root growth, lateral root formation, and fresh weight, with the expression of the cell cycle gene CYCB1;1, as well as TOR expression. When assessing the expression of the ribosome biogenesis-related gene RPS27B, an increase of 94.34% was noted following exposure to 1 mM H2O2 treatment. This increase was suppressed by the TOR inhibitor torin 2. The elimination of H2O2 accumulation with ascorbic acid (AA) resulted in decreased cell division as well as TOR expression. The potential molecular mechanisms associated with the effects of H2O2 on the cell cycle and TOR expression in roots are discussed in the context of the results.

In silico Design, Synthesis and Biological Evaluation of Novel Thieno[3,2-d]pyrimidine Derivatives for Cancer Therapy - A Preliminary Study on the Inhibitory Potential towards ATR Kinase Domain and PIKK Family

Continuing our studies in the field of new heterocyclic compounds with biological interest, herein we report the synthesis and anticancer activity of new N- and S-substituted derivatives of tetracyclic pyrido[3',2' : 4,5]thieno[3,2-d]pyrimidines. In this regard, starting from the thieno[2,3-b]pyridine-2-carboxylates, the corresponding 8(9)-aminopyrido[3',2' : 4,5]thieno[3,2-d]pyrimidin-7(8)-ones, as well as chloro derivatives were obtained. Based on the latter, amino, hydrazino and S-alkyl derivatives of pyrido[3',2' : 4,5]thieno[3,2-d]pyrimidines were synthesized subsequently. The current study focuses on identifying the potential of thieno[3,2-d]pyrimidine derivatives primarily towards ATR kinase inhibition, through computational predictions, followed by synthesis and cancer cell viability studies, along with an aim to develop the core as PIKK inhibitors for cancer therapy.

A drug-resistant mutation in plant target of rapamycin validates the specificity of ATP-competitive TOR inhibitors in vivo

Kinases are major components of cellular signaling pathways, regulating key cellular activities through phosphorylation. Kinase inhibitors are efficient tools for studying kinase targets and functions, however assessing their kinase specificity in vivo is essential. The identification of resistant kinase mutants has been proposed to be the most convincing approach to achieve this goal. Here, we address this issue in plants via a pharmacogenetic screen for mutants resistant to the ATP-competitive TOR inhibitor AZD-8055. The eukaryotic TOR (Target of Rapamycin) kinase is emerging as a major hub controlling growth responses in plants largely thanks to the use of ATP-competitive inhibitors. We identified a dominant mutation in the DFG motif of the Arabidopsis TOR kinase domain that leads to very strong resistance to AZD-8055. This resistance was characterized by measuring root growth, photosystem II (PSII) activity in leaves and phosphorylation of YAK1 (Yet Another Kinase 1) and RPS6 (Ribosomal protein S6), a direct and an indirect target of TOR respectively. Using other ATP-competitive TOR inhibitors, we also show that the dominant mutation is particularly efficient for resistance to drugs structurally related to AZD-8055. Altogether, this proof-of-concept study demonstrates that a pharmacogenetic screen in Arabidopsis can be used to successfully identify the target of a kinase inhibitor in vivo and therefore to demonstrate inhibitor specificity. Thanks to the conservation of kinase families in eukaryotes, and the possibility of creating amino acid substitutions by genome editing, this work has great potential for extending studies on the evolution of signaling pathways in eukaryotes.

Mammalian target of rapamycin inhibition protects glioma cells from temozolomide-induced cell death

Glioblastoma is an incurable brain tumor with a median survival below two years. Trials investigating targeted therapy with inhibitors of the kinase mTOR have produced ambiguous results. Especially combination of mTOR inhibition with standard temozolomide radiochemotherapy has resulted in reduced survival in a phase II clinical trial. To date, this phenomenon is only poorly understood. To recreate the therapeutic setting in vitro, we exposed glioblastoma cell lines to co-treatment with rapamycin and temozolomide and assessed cell viability, DNA damage and reactive oxygen species. Additionally, we employed a novel translatomic based mass spectrometry approach ("mePROD") to analyze acute changes in translated proteins. mTOR inhibition with rapamycin protected glioblastoma cells from temozolomide toxicity. Following co-treatment of temozolomide with rapamycin, an increased translation of reactive oxygen species (ROS)-detoxifying proteins was detected by mass spectrometry. This was accompanied by improved ROS-homeostasis and reduced DNA damage. Additionally, rapamycin induced the expression of the DNA repair enzyme O-6-methylguanine-DNA methyltransferase (MGMT) in glioblastoma cells with an unmethylated MGMT gene promotor. Inhibition of mTOR antagonized the cytotoxic effects of temozolomide in vitro. The induction of antioxidant defences and MGMT are two underlying candidate mechanisms. Further functional experiments in vitro and in vivo are warranted to characterize this effect that appears relevant for combinatorial therapeutic strategies.

PI3K signaling promotes formation of lipid-laden foamy macrophages at the spinal cord injury site

After spinal cord injury (SCI), infiltrating macrophages undergo excessive phagocytosis of myelin and cellular debris, forming lipid-laden foamy macrophages. To understand their role in the cellular pathology of SCI, investigation of the foamy macrophage phenotype in vitro revealed a pro-inflammatory profile, increased reactive oxygen species (ROS) production, and mitochondrial dysfunction. Bioinformatic analysis identified PI3K as a regulator of inflammation in foamy macrophages, and inhibition of this pathway decreased their lipid content, inflammatory cytokines, and ROS production. Macrophage-specific inhibition of PI3K using liposomes significantly decreased foamy macrophages at the injury site after a mid-thoracic contusive SCI in mice. RNA sequencing and in vitro analysis of foamy macrophages revealed increased autophagy and decreased phagocytosis after PI3K inhibition as potential mechanisms for reduced lipid accumulation. Together, our data suggest that the formation of pro-inflammatory foamy macrophages after SCI is due to the activation of PI3K signaling, which increases phagocytosis and decreases autophagy.

Differentiation-inducing factor-1 reduces lipopolysaccharide-induced vascular cell adhesion molecule-1 by suppressing mTORC1-S6K signaling in vascular endothelial cells

AIMS

Differentiation-inducing factor-1 (DIF-1), a compound in Dictyostelium discoideum, exhibits anti-cancer effects by inhibiting cell proliferation and motility of various mammalian cancer cells in vitro and in vivo. In addition, DIF-1 suppresses lung colony formation in a mouse model, thus impeding cancer metastasis. However, the precise mechanism underlying its anti-metastatic effect remains unclear. In the present study, we aim to elucidate this mechanism by investigating the adhesion of circulating tumor cells to blood vessels using in vitro and in vivo systems.

MAIN METHODS

Melanoma cells (1.0 × 105 cells) were injected into the tail vein of 8-week-old male C57BL/6 mice after administration of DIF-1 (300 mg/kg per day) and/or lipopolysaccharide (LPS: 2.5 mg/kg per day). To investigate cell adhesion and molecular mechanisms, cell adhesion assay, western blotting, immunofluorescence staining, and flow cytometry were performed.

KEY FINDINGS

Intragastric administration of DIF-1 suppressed lung colony formation. DIF-1 also substantially inhibited the adhesion of cancer cells to human umbilical vein endothelial cells. Notably, DIF-1 did not affect the expression level of adhesion-related proteins in cancer cells, but it did decrease the expression of vascular cell adhesion molecule-1 (VCAM-1) in human umbilical vein endothelial cells by suppressing its mRNA-to-protein translation through inhibition of mTORC1-p70 S6 kinase signaling.

SIGNIFICANCE

DIF-1 reduced tumor cell adhesion to blood vessels by inhibiting mTORC1-S6K signaling and decreasing the expression of adhesion molecule VCAM-1 on vascular endothelial cells. These findings highlight the potential of DIF-1 as a promising compound for the development of anti-cancer drugs with anti-metastatic properties.

Models of KPTN-related disorder implicate mTOR signalling in cognitive and overgrowth phenotypes

KPTN-related disorder is an autosomal recessive disorder associated with germline variants in KPTN (previously known as kaptin), a component of the mTOR regulatory complex KICSTOR. To gain further insights into the pathogenesis of KPTN-related disorder, we analysed mouse knockout and human stem cell KPTN loss-of-function models. Kptn -/- mice display many of the key KPTN-related disorder phenotypes, including brain overgrowth, behavioural abnormalities, and cognitive deficits. By assessment of affected individuals, we have identified widespread cognitive deficits (n = 6) and postnatal onset of brain overgrowth (n = 19). By analysing head size data from their parents (n = 24), we have identified a previously unrecognized KPTN dosage-sensitivity, resulting in increased head circumference in heterozygous carriers of pathogenic KPTN variants. Molecular and structural analysis of Kptn-/- mice revealed pathological changes, including differences in brain size, shape and cell numbers primarily due to abnormal postnatal brain development. Both the mouse and differentiated induced pluripotent stem cell models of the disorder display transcriptional and biochemical evidence for altered mTOR pathway signalling, supporting the role of KPTN in regulating mTORC1. By treatment in our KPTN mouse model, we found that the increased mTOR signalling downstream of KPTN is rapamycin sensitive, highlighting possible therapeutic avenues with currently available mTOR inhibitors. These findings place KPTN-related disorder in the broader group of mTORC1-related disorders affecting brain structure, cognitive function and network integrity.

Chemo-proteomics in antimalarial target identification and engagement

Humans have lived in tenuous battle with malaria over millennia. Today, while much of the world is free of the disease, areas of South America, Asia, and Africa still wage this war with substantial impacts on their social and economic development. The threat of widespread resistance to all currently available antimalarial therapies continues to raise concern. Therefore, it is imperative that novel antimalarial chemotypes be developed to populate the pipeline going forward. Phenotypic screening has been responsible for the majority of the new chemotypes emerging in the past few decades. However, this can result in limited information on the molecular target of these compounds which may serve as an unknown variable complicating their progression into clinical development. Target identification and validation is a process that incorporates techniques from a range of different disciplines. Chemical biology and more specifically chemo-proteomics have been heavily utilized for this purpose. This review provides an in-depth summary of the application of chemo-proteomics in antimalarial development. Here we focus particularly on the methodology, practicalities, merits, and limitations of designing these experiments. Together this provides learnings on the future use of chemo-proteomics in antimalarial development.

Rapamycin and Torin2 inhibit Candida auris TOR: Insights through growth profiling, docking, and MD simulations

The fungus Candida auris is a pathogen of utmost concern due to its rapid emergence across the globe, acquired antifungal drug tolerance, thermotolerance, and ability to survive in hospital settings and preserved foods. Recent incidences of comorbidity of corona patients with its infection in hospital settings highlighted the importance of understanding the pathobiology and drug tolerance of this fungus on priority. The Target of rapamycin (TOR) is a central regulator of growth across eukaryotes with an illustrated role in fungal pathology. The role of the TOR signalling pathway in the growth of C. auris is yet to be described. In-silico, analysis revealed the presence of highly conserved Tor kinase, components of TORC, and key downstream components in C. auris. Rapamycin and Torin2, the specific inhibitors of Tor reduce the growth of C. auris. An inhibition of Tor leads to cell cycle arrest at the G1 phase with a defect in cytokinesis. Interestingly, with an insignificant difference in growth at 30 and 37 °C, a sharp decline in growth is seen with Torin2 at 37 °C. The heterogeneous response emphasizes the importance of physiology-based differential cellular response at different temperatures. In addition, the inhibition of Tor suppresses the biofilm formation. In silico studies through docking and simulations showed rapamycin and torin2 as specific inhibitors of C. auris Tor kinase (CauTor kinase) and hence can be exploited for a thorough understanding of the TOR signalling pathway in pathobiology and drug tolerance of C. auris. HIGHLIGHTSConservation of TOR signalling pathway in Candida aurisRapamycin and torin2 are specific inhibitors of Cau TorUnderstanding of the role of TOR signalling pathway through the use of inhibitors rapamycin and torin2.Heterogenous response of C. auris to torin2 at different physiological conditions.Communicated by Ramaswamy H. Sarma.

AMPK protects endothelial cells against HSV-1 replication via inhibition of mTORC1 and ACC1

Herpes simplex virus type 1 (HSV-1) is a widespread contagious pathogen, mostly causing mild symptoms on the mucosal entry side. However, systemic distribution, in particular upon reactivation of the virus in immunocompromised patients, may trigger an innate immune response and induce damage of organs. In these conditions, HSV-1 may infect vascular endothelial cells, but little is known about the regulation of HSV-1 replication and possible defense mechanisms in these cells. The current study addresses the question of whether the host cell protein AMP-activated protein kinase (AMPK), an important metabolic sensor, can control HSV-1 replication in endothelial cells. We show that downregulation of the catalytic subunits AMPKα1 and/or AMPKα2 increased HSV-1 replication as monitored by TCID50 titrations, while a potent AMPK agonist, MK-8722, strongly inhibited it. MK-8722 induced a persistent phosphorylation of the AMPK downstream targets acetyl-CoA carboxylase (ACC) and the rapamycin-sensitive adaptor protein of mTOR (Raptor) and, related to this, impairment of ACC1-mediated lipid synthesis and the mechanistic target of the rapamycin complex-1 (mTORC1) pathway. Since blockade of mTOR by Torin-2 as well as downregulation of ACC1 by siRNA also decreased HSV-1 replication, MK-8722 is likely to exert its anti-viral effect via mTORC1 and ACC1 inhibition. Importantly, MK-8722 was able to reduce virus replication even when added after HSV-1. Together, our data highlight the importance of endothelial cells as host cells for HSV-1 replication upon systemic infection and identify AMPK, a metabolic host cell protein, as a potential target for antiviral strategies against HSV-1 infection and its severe consequences. IMPORTANCE Herpes simplex virus type 1 (HSV-1) is a common pathogen that causes blisters or cold sores in humans. It remains latent in infected individuals and can be reactivated multiple times. In adverse conditions, for instance, in immunocompromised patients, HSV-1 can lead to serious complications such as encephalitis, meningitis, or blindness. In these situations, infection of endothelial cells lining the surface of blood vessels may contribute to the manifestation of disease. Here, we describe the role of AMP-activated protein kinase (AMPK), a potent regulator of cellular energy metabolism, in HSV-1 replication in endothelial cells. While downregulation of AMPK potentiates HSV-1 replication, pharmacological AMPK activation inhibits it by limiting the availability of required host cell macromolecules such as proteins or fatty acids. These data highlight the role of metabolic host cell proteins as antiviral targets and reveal activation of endothelial AMPK as a potential strategy to protect from severe consequences of HSV-1 infection.

Promotion of degradative autophagy by 6-bromoindirubin-3'-oxime attenuates neuropathy

Damage to the central or peripheral nervous system causes neuropathic pain. Endoplasmic reticulum (ER) stress plays a role in peripheral neuropathy. Increase in ER stress is seen in diabetic neuropathy. Inducers of ER stress also give rise to peripheral neuropathy. ER stress leads to the formation of autophagosome but as their degradation is also stalled during ER stress accumulation of autophagosomes is seen. Accumulation of autophagosomes has deleterious effects on cells. In the present study, we show that treatment with tunicamycin (TM) (ER stress inducer) in mice leads to peripheral neuropathy as assessed by Von Frey and Hot plate method. Administration of a promoter of autophagy viz. 6-bromoindirubin-3'-oxime (6-BIO) subsequent to ER stress induced by TM exhibits a decrease in peripheral neuropathy. 6-BIO was also effective in reducing diabetic peripheral neuropathy. To understand the type of autophagy activated, SH-SY5Y cells were treated with 6-BIO after TM treatment. Levels of cathepsin D (CTSD), a marker for degradative autophagy was higher in cells treated with 6-BIO after TM treatment compared to only TM-treated SH-SY5Y cells while levels of Rab8A,-a marker for secretory autophagy was reduced. Furthermore, in parallel during ER stress secretory, we noted increased levels of lysozyme in autophagosomes destined for secretion. Cells treated with 6-BIO showed reduction of lysozyme in secretory autophagosomes. This shows that 6-BIO increased degradative autophagy and reduced the secretory autophagy. 6-BIO also reduced the caspase-3 activity in 6-BIO-treated cells. Thus, 6-BIO reduced neuropathy in animals by activating degradative autophagy and reducing the secretory autophagy.

Paired evaluation of machine-learning models characterizes effects of confounders and outliers

The true accuracy of a machine-learning model is a population-level statistic that cannot be observed directly. In practice, predictor performance is estimated against one or more test datasets, and the accuracy of this estimate strongly depends on how well the test sets represent all possible unseen datasets. Here we describe paired evaluation as a simple, robust approach for evaluating performance of machine-learning models in small-sample biological and clinical studies. We use the method to evaluate predictors of drug response in breast cancer cell lines and of disease severity in patients with Alzheimer's disease, demonstrating that the choice of test data can cause estimates of performance to vary by as much as 20%. We show that paired evaluation makes it possible to identify outliers, improve the accuracy of performance estimates in the presence of known confounders, and assign statistical significance when comparing machine-learning models.

Targeting ATM and ATR for cancer therapeutics: inhibitors in clinic

The DNA Damage and Response (DDR) pathway ensures accurate information transfer from one generation to the next. Alterations in DDR functions have been connected to cancer predisposition, progression, and response to therapy. DNA double-strand break (DSB) is one of the most detrimental DNA defects, causing major chromosomal abnormalities such as translocations and deletions. ATR and ATM kinases recognize this damage and activate proteins involved in cell cycle checkpoint, DNA repair, and apoptosis. Cancer cells have a high DSB burden, and therefore rely on DSB repair for survival. Therefore, targeting DSB repair can sensitize cancer cells to DNA-damaging agents. This review focuses on ATM and ATR, their roles in DNA damage and repair pathways, challenges in targeting them, and inhibitors that are in current clinical trials.

Sequential Treatment with Temozolomide Plus Naturally Derived AT101 as an Alternative Therapeutic Strategy: Insights into Chemoresistance Mechanisms of Surviving Glioblastoma Cells

Glioblastoma (GBM) is a poorly treatable disease due to the fast development of tumor recurrences and high resistance to chemo- and radiotherapy. To overcome the highly adaptive behavior of GBMs, especially multimodal therapeutic approaches also including natural adjuvants have been investigated. However, despite increased efficiency, some GBM cells are still able to survive these advanced treatment regimens. Given this, the present study evaluates representative chemoresistance mechanisms of surviving human GBM primary cells in a complex in vitro co-culture model upon sequential application of temozolomide (TMZ) combined with AT101, the R(-) enantiomer of the naturally occurring cottonseed-derived gossypol. Treatment with TMZ+AT101/AT101, although highly efficient, yielded a predominance of phosphatidylserine-positive GBM cells over time. Analysis of the intracellular effects revealed phosphorylation of AKT, mTOR, and GSK3ß, resulting in the induction of various pro-tumorigenic genes in surviving GBM cells. A Torin2-mediated mTOR inhibition combined with TMZ+AT101/AT101 partly counteracted the observed TMZ+AT101/AT101-associated effects. Interestingly, treatment with TMZ+AT101/AT101 concomitantly changed the amount and composition of extracellular vesicles released from surviving GBM cells. Taken together, our analyses revealed that even when chemotherapeutic agents with different effector mechanisms are combined, a variety of chemoresistance mechanisms of surviving GBM cells must be taken into account.

Blood-feeding adaptations and virome assessment of the poultry red mite Dermanyssus gallinae guided by RNA-seq

Dermanyssus gallinae is a blood-feeding mite that parasitises wild birds and farmed poultry. Its remarkably swift processing of blood, together with the capacity to blood-feed during most developmental stages, makes this mite a highly debilitating pest. To identify specific adaptations to digestion of a haemoglobin-rich diet, we constructed and compared transcriptomes from starved and blood-fed stages of the parasite and identified midgut-enriched transcripts. We noted that midgut transcripts encoding cysteine proteases were upregulated with a blood meal. Mapping the full proteolytic apparatus, we noted a reduction in the suite of cysteine proteases, missing homologues for Cathepsin B and C. We have further identified and phylogenetically analysed three distinct transcripts encoding vitellogenins that facilitate the reproductive capacity of the mites. We also fully mapped transcripts for haem biosynthesis and the ferritin-based system of iron storage and inter-tissue trafficking. Additionally, we identified transcripts encoding proteins implicated in immune signalling (Toll and IMD pathways) and activity (defensins and thioester-containing proteins), RNAi, and ion channelling (with targets for commercial acaricides such as Fluralaner, Fipronil, and Ivermectin). Viral sequences were filtered from the Illumina reads and we described, in part, the RNA-virome of D. gallinae with identification of a novel virus, Red mite quaranjavirus 1.

An affinity tool for the isolation of endogenous active mTORC1 from various cellular sources

The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of mammalian cell growth that is dysregulated in a number of human diseases, including metabolic syndromes, aging and cancer. Structural, biochemical and pharmacological studies that have increased our understanding of how mTORC1 executes growth control often relied upon purified mTORC1 protein. However, current immunoaffinity-based purification methods are expensive, inefficient, and do not necessarily isolate endogenous mTORC1, hampering their overall utility in research. Here we present a simple tool to isolate endogenous mTORC1 from various cellular sources. By recombinantly expressing and isolating mTORC1-binding Rag GTPases from E. Coli and using them as affinity probes, we demonstrate that mTORC1 can be isolated from mouse, bovine and human sources. Our results indicate that mTORC1 isolated by this relatively inexpensive method is catalytically active and amenable to scaling. Collectively, this tool may be utilized to isolate mTORC1 from various cellular sources, organs, and disease contexts, aiding mTORC1-related research.

Exploring SPK98 for the Selective Sensitization of ATM- or P53-Deficient Cancer Cells

Frequent mutation in the ATM/P53 signaling pathway has been documented in many human cancers. Reportedly, cancer cells with deficient P53/ATM pathways depend on functional Ataxia-telangiectasia and Rad3-related (ATR) protein for survival. This has prompted research in developing ATR inhibitors for the selective sensitization of cancer cells that are P53/ATM-deficient, but no clinical success has been attained thus far. This study explores the therapeutic potential of SPK98, an analogue of Torin2 in P53- and ATM-deficient cancer cells. Furthermore, the prospect of improving the therapeutic outcome of the genotoxic agent was also explored. SPK98 was shown to inhibit full-length human ATR protein purified from HEK293T cells. Cellular investigation using SPK98 demonstrated that it selectively sensitizes P53- and ATM-deficient cells at low concentrations compared to P53-/ATM-proficient cells. Furthermore, SPK98 drives the cancer cells toward cell death by promoting the formation of DNA double-strand breaks. Taken together, our findings suggest that SPK98 is a promising therapeutic molecule for P53- or ATM-deficient malignancy that merits additional preclinical investigation.

Kaposi's sarcoma-associated herpesvirus (KSHV) utilizes the NDP52/CALCOCO2 selective autophagy receptor to disassemble processing bodies

Kaposi's sarcoma-associated herpesvirus (KSHV) causes the inflammatory and angiogenic endothelial cell neoplasm, Kaposi's sarcoma (KS). We previously demonstrated that the KSHV Kaposin B (KapB) protein promotes inflammation via the disassembly of cytoplasmic ribonucleoprotein granules called processing bodies (PBs). PBs modify gene expression by silencing or degrading labile messenger RNAs (mRNAs), including many transcripts that encode inflammatory or angiogenic proteins associated with KS disease. Although our work implicated PB disassembly as one of the causes of inflammation during KSHV infection, the precise mechanism used by KapB to elicit PB disassembly was unclear. Here we reveal a new connection between the degradative process of autophagy and PB disassembly. We show that both latent KSHV infection and KapB expression enhanced autophagic flux via phosphorylation of the autophagy regulatory protein, Beclin. KapB was necessary for this effect, as infection with a recombinant virus that does not express the KapB protein did not induce Beclin phosphorylation or autophagic flux. Moreover, we showed that PB disassembly mediated by KSHV or KapB, depended on autophagy genes and the selective autophagy receptor NDP52/CALCOCO2 and that the PB scaffolding protein, Pat1b, co-immunoprecipitated with NDP52. These studies reveal a new role for autophagy and the selective autophagy receptor NDP52 in promoting PB turnover and the concomitant synthesis of inflammatory molecules during KSHV infection.

Inhibition of the AKT/mTOR pathway negatively regulates PTEN expression via miRNAs

PI3K/AKT/mTOR pathway plays important roles in cancer development, and the negative role of PTEN in the PI3K/AKT/mTOR pathway is well known, but whether PTEN can be inversely regulated by PI3K/AKT/mTOR has rarely been reported. Here we aim to investigate the potential regulatory relationship between PTEN and Akt/mTOR inhibition in MEFs. AKT1 ^E17K and TSC2 ^-/- MEFs were treated with the AKT inhibitor MK2206 and the mTOR inhibitors rapamycin and Torin2. Our results reveal that inhibition of AKT or mTOR suppresses PTEN expression in AKT1 ^E17K and TSC2 ^-/- MEFs, but the transcription, subcellular localization, eIF4E-dependent translational initiation or lysosome- and proteasome-mediated degradation of PTEN change little, as shown by the real time PCR, nucleus cytoplasm separation assay and immunofluorescence analysis. Moreover, mTOR suppression leads to augmentation of mouse PTEN-3'UTR-binding miRNAs, including miR-23a-3p, miR-23b-3p, miR-25-3p and miR-26a-5p, as shown by the dual luciferase reporter assay and miRNA array analysis, and miRNA inhibitors collaborately rescue the decline of PTEN level. Collectively, our findings confirm that inhibition of mTOR suppresses PTEN expression by upregulating miRNAs, provide a novel explanation for the limited efficacy of mTOR inhibitors in the treatment of mTOR activation-related tumors, and indicate that dual inhibition of mTOR and miRNA is a promising therapeutic strategy to overcome the resistance of mTOR-related cancer treatment.

Novel therapeutic approaches in GEP-NETs based on genetic and epigenetic alterations

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are heterogeneous malignancies with distinct prognosis based on primary tumor localization, grade, stage and functionality. Surgery remains the only curative option in localized tumors, but systemic therapy is the mainstay of treatment for patients with advanced disease. For decades, the therapeutic landscape of GEP-NETs was limited to chemotherapy regimens with low response rates. The arrival of novel agents such as somatostatin analogues, peptide receptor radionuclide therapy, tyrosine kinase inhibitors or mTOR-targeted drugs, has changed the therapeutic paradigm of GEP-NETs. However, the efficacy of these agents is limited in time and there is scarce knowledge of optimal treatment sequencing. In recent years, massive parallel sequencing techniques have started to unravel the genomic intricacies of these tumors, allowing us to better understand the mechanisms of resistance to current treatments and to develop new targeted agents that will hopefully start an era for personalized treatment in NETs. In this review we aim to summarize the most relevant genomic aberrations and signaling pathways underlying GEP-NET tumorigenesis and potential therapeutic strategies derived from them.

Autophagy in health and disease: From molecular mechanisms to therapeutic target

Macroautophagy/autophagy is an evolutionally conserved catabolic process in which cytosolic contents, such as aggregated proteins, dysfunctional organelle, or invading pathogens, are sequestered by the double-membrane structure termed autophagosome and delivered to lysosome for degradation. Over the past two decades, autophagy has been extensively studied, from the molecular mechanisms, biological functions, implications in various human diseases, to development of autophagy-related therapeutics. This review will focus on the latest development of autophagy research, covering molecular mechanisms in control of autophagosome biogenesis and autophagosome-lysosome fusion, and the upstream regulatory pathways including the AMPK and MTORC1 pathways. We will also provide a systematic discussion on the implication of autophagy in various human diseases, including cancer, neurodegenerative disorders (Alzheimer disease, Parkinson disease, Huntington's disease, and Amyotrophic lateral sclerosis), metabolic diseases (obesity and diabetes), viral infection especially SARS-Cov-2 and COVID-19, cardiovascular diseases (cardiac ischemia/reperfusion and cardiomyopathy), and aging. Finally, we will also summarize the development of pharmacological agents that have therapeutic potential for clinical applications via targeting the autophagy pathway. It is believed that decades of hard work on autophagy research is eventually to bring real and tangible benefits for improvement of human health and control of human diseases.

Glucose-driven TOR-FIE-PRC2 signalling controls plant development

Nutrients and energy have emerged as central modulators of developmental programmes in plants and animals^1-3. The evolutionarily conserved target of rapamycin (TOR) kinase is a master integrator of nutrient and energy signalling that controls growth. Despite its key regulatory roles in translation, proliferation, metabolism and autophagy^2-5, little is known about how TOR shapes developmental transitions and differentiation. Here we show that glucose-activated TOR kinase controls genome-wide histone H3 trimethylation at K27 (H3K27me3) in Arabidopsis thaliana, which regulates cell fate and development^6-10. We identify FERTILIZATION-INDEPENDENT ENDOSPERM (FIE), an indispensable component of Polycomb repressive complex 2 (PRC2), which catalyses H3K27me3 (refs. ^6-8,10-12), as a TOR target. Direct phosphorylation by TOR promotes the dynamic translocation of FIE from the cytoplasm to the nucleus. Mutation of the phosphorylation site on FIE abrogates the global H3K27me3 landscape, reprogrammes the transcriptome and disrupts organogenesis in plants. Moreover, glucose-TOR-FIE-PRC2 signalling modulates vernalization-induced floral transition. We propose that this signalling axis serves as a nutritional checkpoint leading to epigenetic silencing of key transcription factor genes that specify stem cell destiny in shoot and root meristems and control leaf, flower and silique patterning, branching and vegetative-to-reproduction transition. Our findings reveal a fundamental mechanism of nutrient signalling in direct epigenome reprogramming, with broad relevance for the developmental control of multicellular organisms.

A High-Throughput Screening Platform Identifies Novel Combination Treatments for Malignant Peripheral Nerve Sheath Tumors

Malignant peripheral nerve sheath tumors (MPNST) are soft-tissue sarcomas that are the leading cause of mortality in patients with Neurofibromatosis type 1 (NF1). Single chemotherapeutic agents have shown response rates ranging from 18% to 44% in clinical trials, so there is still a high medical need to identify chemotherapeutic combination treatments that improve clinical prognosis and outcome. We screened a collection of compounds from the NCATS Mechanism Interrogation PlatE (MIPE) library in three MPNST cell lines, using cell viability and apoptosis assays. We then tested whether compounds that were active as single agents were synergistic when screened as pairwise combinations. Synergistic combinations in vitro were further evaluated in patient-derived orthotopic xenograft/orthoxenograft (PDOX) athymic models engrafted with primary MPNST matching with their paired primary-derived cell line where synergism was observed. The high-throughput screening identified 21 synergistic combinations, from which four exhibited potent synergies in a broad panel of MPNST cell lines. One of the combinations, MK-1775 with Doxorubicin, significantly reduced tumor growth in a sporadic PDOX model (MPNST-SP-01; sevenfold) and in an NF1-PDOX model (MPNST-NF1-09; fourfold) and presented greater effects in TP53 mutated MPNST cell lines. The other three combinations, all involving Panobinostat (combined with NVP-BGT226, Torin 2, or Carfilzomib), did not reduce the tumor volume in vivo at noncytotoxic doses. Our results support the utility of our screening platform of in vitro and in vivo models to explore new therapeutic approaches for MPNSTs and identified that combination MK-1775 with Doxorubicin could be a good pharmacologic option for the treatment of these tumors.

Anti-inflammatory effects of Torin2 on lipopolysaccharide-treated RAW264.7 murine macrophages and potential mechanisms

Context

Torin2 has various pharmacological properties. However, its anti-inflammatory activity has not been reported.

Objective

This study focused on the potential anti-inflammatory properties of Torin2 in lipopolysaccharide (LPS)-evoked RAW264.7 murine macrophages. The study aimed to shed light on the molecular mechanisms that ameliorate these effects.

Methods

Torin2 was applied to 100 ng/mL lipopolysaccharide-induced RAW 264.7 macrophages in vitro. Nitric oxide (NO) levels were detected using the Griess reagent kit. Prostaglandin E2 (PGE2), pro-inflammatory cytokines interleukin (IL)-1β, interleukin (IL)-6, and tumor necrosis factor in the supernatant fraction were determined using enzyme-linked immunosorbent assay (ELISA). Gene expression of pro-inflammatory cytokines, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS) were tested using real-time quantitative polymerase chain reaction (qPCR). Cyclooxygenase-2 and inducible nitric oxide synthase proteins, phosphorylation of mitogen-activated protein kinase (MAPK) subgroups, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38, I-kappa-B-alpha (IκBα), and nuclear factor-kappa-B (NF-κB), and activation in extracts were detected via western blotting. Nuclear factor-kappa-B/p65 nuclear translocation was tested using an immunofluorescence assay.

Results

The results demonstrated that pre-treatment with Torin2 profoundly attenuated the lipopolysaccharide-stimulated levels of nitric oxide and prostaglandin E2, pro-inflammatory cytokines, messenger ribonucleic acid (mRNA), and protein expression of cyclooxygenase-2 and inducible nitric oxide synthase. Collectively, Torin2 pre-treatment notably weakened lipopolysaccharide-induced damage by reducing the phosphorylation of nuclear factor-kappa-B, p38, c-Jun N-terminal kinase, extracellular signal-regulated kinase proteins, and nuclear factor-kappa-B/p65 nuclear translocation.

Conclusion

Numerous pieces of evidence indicated that Torin2 reversed inflammatory activation by regulating nuclear factor-kappa-B and mitogen-activated protein kinase signaling pathways and provided a tentative potential candidate for preventing and treating inflammatory diseases.

Targeting mTOR in the Context of Diet and Whole-body Metabolism

The mechanistic target of the rapamycin (mTOR) signaling pathway is the central regulator of cell growth and proliferation by integrating growth factor and nutrient availability. Under healthy physiological conditions, this process is tightly coordinated and essential to maintain whole-body homeostasis. Not surprisingly, dysregulated mTOR signaling underpins several diseases with increasing incidence worldwide, including obesity, diabetes, and cancer. Consequently, there is significant clinical interest in developing therapeutic strategies that effectively target this pathway. The transition of mTOR inhibitors from the bench to bedside, however, has largely been marked with challenges and shortcomings, such as the development of therapy resistance and adverse side effects in patients. In this review, we discuss the current status of first-, second-, and third-generation mTOR inhibitors as a cancer therapy in both preclinical and clinical settings, with a particular emphasis on the mechanisms of drug resistance. We focus especially on the emerging role of diet as an important environmental determinant of therapy response, and posit a conceptual framework that links nutrient availability and whole-body metabolic states such as obesity with many of the previously defined processes that drive resistance to mTOR-targeted therapies. Given the role of mTOR as a central integrator of cell metabolism and function, we propose that modulating nutrient inputs through dietary interventions may influence the signaling dynamics of this pathway and compensatory nodes. In doing so, new opportunities for exploiting diet/drug synergies are highlighted that may unlock the therapeutic potential of mTOR inhibitors as a cancer treatment.

Active APPL1 sequestration by Plasmodium favors liver-stage development

Intracellular pathogens manipulate host cells to survive and thrive. Cellular sensing and signaling pathways are among the key host machineries deregulated to favor infection. In this study, we show that liver-stage Plasmodium parasites compete with the host to sequester a host endosomal-adaptor protein (APPL1) known to regulate signaling in response to endocytosis. The enrichment of APPL1 at the parasitophorous vacuole membrane (PVM) involves an atypical Plasmodium Rab5 isoform (Rab5b). Depletion of host APPL1 alters neither the infection nor parasite development; however, upon overexpression of a GTPase-deficient host Rab5 mutant (hRab5_Q79L), the parasites are smaller and their PVM is stripped of APPL1. Infection with the GTPase-deficient Plasmodium berghei Rab5b mutant (PbRab5b_Q91L) in this case rescues the PVM APPL1 signal and parasite size. In summary, we observe a robust correlation between the level of APPL1 retention at the PVM and parasite size during exoerythrocytic development.

TARGET OF RAPAMYCIN is essential for asexual vegetative reproduction in Kalanchoë

The unique mechanism by which leaf margin cells regain potency and then form a plantlet in Kalanchoë spp. remains elusive but involves organogenesis and embryogenesis in response to age, day length, nutrient availability, and drought stress. In light of this, we investigated whether TARGET OF RAPAMYCIN (TOR), a conserved protein kinase in eukaryotes that controls cell growth and metabolism in response to nutrient and energy availability, may regulate plantlet formation. Kalanchoë daigremontiana TOR (KdTOR) was expressed in the leaf margin at the site of plantlet initiation, in the early plantlet cotyledons, and in the root tip of the developed plantlet. Both chemical and genetic inhibition of TOR Kinase activity in Kalanchoë daigremontiana leaves disrupted plantlet formation. Furthermore, downregulation of KdTOR in transgenic plants led to wide-ranging transcriptional changes, including decreased K. daigremontiana SHOOTMERISTEMLESS and K. daigremontiana LEAFYCOTYLEDON1 expression, whereas auxin treatments induced KdTOR expression in the plantlet roots. These results suggest that the KdTOR pathway controls plantlet development in cooperation with auxin, organogenesis, and embryogenesis pathways. The ancient and highly conserved TOR Kinase therefore controls diverse and unique developmental pathways, such as asexual reproduction within the land plant lineage.

Proteomic and Transcriptomic Profiling Reveals Mitochondrial Oxidative Phosphorylation as Therapeutic Vulnerability in Androgen Receptor Pathway Active Prostate Tumors

Simple Summary

Metastatic prostate cancer (PC) is the second leading cause of cancer deaths in males. The lack of preclinical models and molecular characterization for advanced stage PC is a key barrier in understanding the aggressive subsets androgen receptor (AR) pathway active or AR-null castration-resistant prostate cancers (CRPC). Our study aimed to assess the potential of patient-derived xenograft (PDX) models and an approach integrating proteomic and transcriptomic techniques to explore the underlying drivers of metastatic PC. Transcriptomic and proteomic profiling of 42 PDX prostate tumors uncovered both previously established and unexpected molecular features of aggressive PC subsets. Of these, we confirmed the functional role of mitochondrial metabolism in AR-positive CRPC.

Abstract

Metastatic prostate cancer (PC) is the second leading cause of cancer deaths in males and has limited therapeutic options. The lack of preclinical models for advanced stage PC represents one of the primary barriers in understanding the key genetic drivers of aggressive subsets, including androgen receptor (AR) pathway active and AR-null castration-resistant prostate cancers (CRPC). In our studies, we described a series of LuCaP patient-derived xenograft (PDX) models representing the major genomic and phenotypic features of human disease. To fully exploit the potential of these preclinical models, we carried out a comprehensive transcriptomic and proteomic profiling of 42 LuCaP PDX prostate tumors. The collected proteomic data (~6000 data points) based on 71 antibodies revealed many of the previously known molecular markers associated with AR-positive and AR-null CRPC. Genomic analysis indicated subtype-specific activation of pathways such as Wnt/beta-catenin signaling, mTOR, and oxidative phosphorylation for AR-positive CRPC and upregulation of carbohydrate metabolism and glucose metabolism for AR-null CRPC. Of these, we functionally confirmed the role of mitochondrial metabolism in AR-positive CRPC cell lines. Our data highlight how the integration of transcriptomic and proteomic approaches and PDX systems as preclinical models can potentially map the connectivity of poorly understood signaling pathways in metastatic prostate cancer.

Autophagy inducers lead to transient accumulation of autophagosomes in Arabidopsis roots

This study reveals that plant roots show a rapid termination of autophagy induction, offering a plant model for studying how excessive autophagy is deterred. In eukaryotes, autophagy is an intracellular mechanism that is important for recycling nutrients by degrading various macromolecules and organelles in vacuoles and lysosomes. Autophagy is induced when the nutrient supply to plant cells is limited. The protein kinase target of rapamycin (TOR) complex negatively regulates autophagy when nutrients are present in adequate amounts. The TOR inhibitor AZD8055 is an autophagy inducer that is useful for studying starvation-induced autophagy in plant cells. The mechanism by which AZD8055 increases the autophagic flux in plant cells has not been studied in detail. Here, we show that AZD8055-induced autophagy requires phosphatidylinositol 3-kinase activity and canonical AUTOPHAGY-RELATED (ATG) genes in Arabidopsis thaliana. Autophagic flux rapidly increased in seedlings treated with AZD8055. Unexpectedly, autophagy induction was transient in root cells and terminated earlier than in cotyledon cells. Transient induction is partly caused by a temporary effect of AZD8055 on phagophore initiation. These findings indicate a TOR-independent mechanism for terminating autophagy induction, thereby paving the way for elucidating how excess autophagy is prevented in plant roots.

Perturbation-Based Modeling Unveils the Autophagic Modulation of Chemosensitivity and Immunogenicity in Breast Cancer Cells

In the absence of new therapeutic strategies, chemotherapeutic drugs are the most widely used strategy against metastatic breast cancer, in spite of eliciting multiple adverse effects and having low responses with an average 5-year patient survival rate. Among the new therapeutic targets that are currently in clinical trials, here, we addressed the association between the regulation of the metabolic process of autophagy and the exposure of damage-associated molecular patterns associated (DAMPs) to immunogenic cell death (ICD), which has not been previously studied. After validating an mCHR-GFP tandem LC3 sensor capacity to report dynamic changes of the autophagic metabolic flux in response to external stimuli and demonstrating that both basal autophagy levels and response to diverse autophagy regulators fluctuate among different cell lines, we explored the interaction between autophagy modulators and chemotherapeutic agents in regards of cytotoxicity and ICD using three different breast cancer cell lines. Since these interactions are very complex and variable throughout different cell lines, we designed a perturbation-based model in which we propose specific modes of action of chemotherapeutic agents on the autophagic flux and the corresponding strategies of modulation to enhance the response to chemotherapy. Our results point towards a promising therapeutic potential of the metabolic regulation of autophagy to overcome chemotherapy resistance by eliciting ICD.

Targeting the mTOR pathway using novel ATP‑competitive inhibitors, Torin1, Torin2 and XL388, in the treatment of glioblastoma

Mechanistic target of rapamycin (mTOR), which functions via two multiprotein complexes termed mTORC1 and mTORC2, is positioned in the canonical phosphoinositide 3-kinase-related kinase (PI3K)/AKT (PI3K/AKT) pathways. These complexes exert their actions by regulating other important kinases, such as 40S ribosomal S6 kinases (S6K), eukaryotic translation initiation factor 4E (elF4E)-binding protein 1 (4E-BP1) and AKT, to control cell growth, proliferation, migration and survival in response to nutrients and growth factors. Glioblastoma (GB) is a devastating form of brain cancer, where the mTOR pathway is deregulated due to frequent upregulation of the Receptor Tyrosine Kinase/PI3K pathways and loss of the tumor suppressor phosphatase and tensin homologue (PTEN). Rapamycin and its analogs were less successful in clinical trials for patients with GB due to their incomplete inhibition of mTORC1 and the activation of mitogenic pathways via negative feedback loops. Here, the effects of selective ATP-competitive dual inhibitors of mTORC1 and mTORC2, Torin1, Torin2 and XL388, are reported. Torin2 exhibited concentration-dependent pharmacodynamic effects on inhibition of phosphorylation of the mTORC1 substrates S6K^Ser235/236 and 4E-BP1^Thr37/46 as well as the mTORC2 substrate AKT^Ser473 resulting in suppression of tumor cell migration, proliferation and S-phase entry. Torin1 demonstrated similar effects, but only at higher doses. XL388 suppressed cell proliferation at a higher dose, but failed to inhibit cell migration. Treatment with Torin1 suppressed phosphorylation of proline rich AKT substrate of 40 kDa (PRAS40) at Threonine 246 (PRAS40^Thr246) whereas Torin2 completely abolished it. XL388 treatment suppressed the phosphorylation of PRAS40^Thr246 only at higher doses. Drug resistance analysis revealed that treatment of GB cells with XL388 rendered partial drug resistance, which was also seen to a lesser extent with rapamycin and Torin1 treatments. However, treatment with Torin2 completely eradicated the tumor cell population. These results strongly suggest that Torin2, compared to Torin1 or XL388, is more effective in suppressing mTORC1 and mTORC2, and therefore in the inhibition of the GB cell proliferation, dissemination and in overcoming resistance to therapy. These findings underscore the significance of Torin2 in the treatment of GB.

DIF-1 inhibits growth and metastasis of triple-negative breast cancer through AMPK-mediated inhibition of the mTORC1-S6K signaling pathway

We have previously reported that the differentiation-inducing factor-1 (DIF-1), a compound identified in Dictyostelium discoideum, suppresses the growth of MCF-7 breast cancer cells by inactivating p70 ribosomal protein S6 kinase (p70S6K). Therefore, we first examined whether the same mechanism operates in other breast cancer cells, especially triple-negative breast cancer (TNBC), the most aggressive and refractory phenotype of breast cancer. We also investigated the mechanism by which DIF-1 suppresses p70S6K by focusing on the AMPK-mTORC1 system. We found that DIF-1 induces phosphorylation of AMPK and Raptor and dephosphorylation of p70S6K in multiple TNBC cell lines. Next, we examined whether AMPK-mediated inhibition of p70S6K leads to the suppression of proliferation and migration/infiltration of TNBC cells. DIF-1 significantly reduced the expression levels of cyclin D1 by suppressing the translation of STAT3 and strongly suppressed the expression levels of Snail, which led to the suppression of growth and motility, respectively. Finally, we investigated whether DIF-1 exerts anticancer effects on TNBC in vivo. Intragastric administration of DIF-1 suppressed tumor growth and spontaneous lung metastasis of 4T1-Luc cells injected into the mammary fat pad of BALB/c mice. DIF-1 is expected to lead to the development of anticancer drugs, including anti-TNBC, by a novel mechanism.

Exploring Molecular Descriptors and Fingerprints to Predict mTOR Kinase Inhibitors using Machine Learning Techniques

Mammalian Target of Rapamycin (mTOR) is a Ser/Thr protein kinase, and its role is integral to the autophagy pathway in cancer. Targeting mTOR for therapeutic interventions in cancer through autophagy pathway is challenging due to the dual roles of autophagy in tumor progression. The architecture of mTOR reveals two complexes - mTORC1 and mTORC2, each having multiple protein subunits. mTOR kinase inhibitors target the structurally and functionally similar catalytic subunits of both mTORC1 and mTORC2. In this paper, we have explored two different categories of molecular features - descriptors and fingerprints for developing predictive models using machine learning techniques. Random Forest variable importance measures and autoencoders are used to identify molecular descriptors and fingerprints, respectively. We have built various predictive models using identified features and their combination for predicting mTOR kinase inhibitors. Finally, the best model based on the Mathew correlation co-efficient value over the validation dataset is selected for screening kinase SARfari bioactivity dataset. In this study, we have identified twenty best performing descriptors for predicting mTOR kinase inhibitors. To the best of our knowledge, it is the first study on integrating traditional machine learning and deep learning-based approaches for feature extraction to predict mTOR kinase inhibitors.

DYRK1A Kinase Inhibitors Promote β-Cell Survival and Insulin Homeostasis

The rising prevalence of diabetes is threatening global health. It is known not only for the occurrence of severe complications but also for the SARS-Cov-2 pandemic, which shows that it exacerbates susceptibility to infections. Current therapies focus on artificially maintaining insulin homeostasis, and a durable cure has not yet been achieved. We demonstrate that our set of small molecule inhibitors of DYRK1A kinase potently promotes β-cell proliferation, enhances long-term insulin secretion, and balances glucagon level in the organoid model of the human islets. Comparable activity is seen in INS-1E and MIN6 cells, in isolated mice islets, and human iPSC-derived β-cells. Our compounds exert a significantly more pronounced effect compared to harmine, the best-documented molecule enhancing β-cell proliferation. Using a body-like environment of the organoid, we provide a proof-of-concept that small-molecule-induced human β-cell proliferation via DYRK1A inhibition is achievable, which lends a considerable promise for regenerative medicine in T1DM and T2DM treatment.

Targeting autophagy in disease: established and new strategies

Macroautophagy/autophagy is an evolutionarily conserved pathway responsible for clearing cytosolic aggregated proteins, damaged organelles or invading microorganisms. Dysfunctional autophagy leads to pathological accumulation of the cargo, which has been linked to a range of human diseases, including neurodegenerative diseases, infectious and autoimmune diseases and various forms of cancer. Cumulative work in animal models, application of genetic tools and pharmacologically active compounds, has suggested the potential therapeutic value of autophagy modulation in disease, as diverse as Huntington, Salmonella infection, or pancreatic cancer. Autophagy activation versus inhibition strategies are being explored, while the role of autophagy in pathophysiology is being studied in parallel. However, the progress of preclinical and clinical development of autophagy modulators has been greatly hampered by the paucity of selective pharmacological agents and biomarkers to dissect their precise impact on various forms of autophagy and cellular responses. Here, we summarize established and new strategies in autophagy-related drug discovery and indicate a path toward establishing a more efficient discovery of autophagy-selective pharmacological agents. With this knowledge at hand, modern concepts for therapeutic exploitation of autophagy might become more plausible.

Abbreviations: ALS: amyotrophic lateral sclerosis; AMPK: AMP-activated protein kinase; ATG: autophagy-related gene; AUTAC: autophagy-targeting chimera; CNS: central nervous system; CQ: chloroquine; GABARAP: gamma-aminobutyric acid type A receptor-associated protein; HCQ: hydroxychloroquine; LYTAC: lysosome targeting chimera; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NDD: neurodegenerative disease; PDAC: pancreatic ductal adenocarcinoma; PE: phosphatidylethanolamine; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol 3-phosphate; PROTAC: proteolysis-targeting chimera; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1.

The cellular pathways and potential therapeutics of Polycystic Kidney Disease

Polycystic Kidney Disease (PKD) refers to a group of disorders, driven by the formation of cysts in renal tubular cells and is currently one of the leading causes of end-stage renal disease. The range of symptoms observed in PKD is due to mutations in cilia-localising genes, resulting in changes in cellular signalling. As such, compounds that are currently in preclinical and clinical trials target some of these signalling pathways that are dysregulated in PKD. In this review, we highlight these pathways including cAMP, EGF and AMPK signalling and drugs that target them and may show promise in lessening the disease burden of PKD patients. At present, tolvaptan is the only approved therapy for ADPKD, however, it carries several adverse side effects whilst comparatively, no pharmacological drug is approved for ARPKD treatment. Aside from this, drugs that have been the subject of multiple clinical trials such as metformin, which targets AMPK signalling and somatostatins, which target cAMP signalling have shown great promise in reducing cyst formation and cellular proliferation. This review also discusses other potential and novel targets that can be used for future interventions, such as β-catenin and TAZ, where research has shown that a reduction in the overexpression of these signalling components results in amelioration of disease phenotype. Thus, it becomes apparent that well-designed preclinical investigations and future clinical trials into these pathways and other potential signalling targets are crucial in bettering disease prognosis for PKD patients and could lead to personalised therapy approaches.

Sensors and Inhibitors for the Detection of Ataxia Telangiectasia Mutated (ATM) Protein Kinase

Recruitment and activation of the ataxia telangiectasia mutated (ATM) kinase regulate multiple cell-cycle checkpoints relevant to complex biological events like DNA damage repair and apoptosis. Molecularly specific readouts of ATM using protein assays, fluorescence, or radiolabeling have advanced significantly over the past few years. This Review covers the molecular imaging techniques that enable the visualization of ATM-from traditional quantitative protein assays to the potential use of ATM inhibitors to generate new imaging agents to interrogate ATM. We are confident that molecular imaging coupled with advanced technologies will play a pivotal role in visualizing and understanding the biology of ATM and accelerate its applications in the diagnosis and monitoring of disease, including radiation therapy and patient stratification.

Live imaging of intra-lysosome pH in cell lines and primary neuronal culture using a novel genetically encoded biosensor

Disorders of lysosomal physiology have increasingly been found to underlie the pathology of a rapidly growing cast of neurodevelopmental disorders and sporadic diseases of aging. One cardinal aspect of lysosomal (dys)function is lysosomal acidification in which defects trigger lysosomal stress signaling and defects in proteolytic capacity. We have developed a genetically encoded ratiometric probe to measure lysosomal pH coupled with a purification tag to efficiently purify lysosomes for both proteomic and in vitro evaluation of their function. Using our probe, we showed that lysosomal pH is remarkably stable over a period of days in a variety of cell types. Additionally, this probe can be used to determine that lysosomal stress signaling via TFEB is uncoupled from gross changes in lysosomal pH. Finally, we demonstrated that while overexpression of ARL8B GTPase causes striking alkalinization of peripheral lysosomes in HEK293 T cells, peripheral lysosomes per se are no less acidic than juxtanuclear lysosomes in our cell lines.Abbreviations: ARL8B: ADP ribosylation factor like GTPase 8B; ATP: adenosine triphosphate; ATP5F1B/ATPB: ATP synthase F1 subunit beta; ATP6V1A: ATPase H+ transporting V1 subunit A; Baf: bafilomycin A1; BLOC-1: biogenesis of lysosome-related organelles complex 1; BSA: bovine serum albumin; Cos7: African green monkey kidney fibroblast-like cell line; CQ: chloroquine; CTSB: cathepsin B; CYCS: cytochrome c, somatic; DAPI: 4',6-diamidino -2- phenylindole; DIC: differential interference contrast; DIV: days in vitro; DMEM: Dulbecco's modified Eagle's medium;‎ E8: embryonic day 8; EEA1: early endosome antigen 1; EGTA: ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid; ER: endoplasmic reticulum; FBS: fetal bovine serum; FITC: fluorescein isothiocyanate; GABARAPL2: GABA type A receptor associated protein like 2; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GOLGA2/GM130: golgin A2; GTP: guanosine triphosphate; HEK293T: human embryonic kidney 293 cells, that expresses a mutant version of the SV40 large T antigen; HeLa: Henrietta Lacks-derived cell; HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; HRP: horseradish peroxidase; IGF2R/ciM6PR: insulin like growth factor 2 receptor; LAMP1/2: lysosomal associated membrane protein 1/2; LMAN2/VIP36: lectin, mannose binding 2; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTORC1: mechanistic target of rapamycin kinase complex 1; PCR: polymerase chain reaction; PDL: poly-d-lysine; PGK1p: promotor from human phosphoglycerate kinase 1; PIKFYVE: phosphoinositide kinase, FYVE-type zinc finger containing; PPT1/CLN1: palmitoyl-protein thioesterase 1; RPS6KB1/p70: ribosomal protein S6 kinase B1; STAT3: signal transducer and activator of transcription 3; TAX1BP1: Tax1 binding protein 1; TFEB: transcription factor EB; TGN: trans-Golgi network; TGOLN2/TGN46: trans-Golgi network protein 2; TIRF: total internal reflection fluorescence; TMEM106B: transmembrane protein 106B; TOR: target of rapamycin; TRPM2: transient receptor potential cation channel subfamily M member 2; V-ATPase: vacuolar-type proton-translocating ATPase; VPS35: VPS35 retromer complex component.

Paxbp1 controls a key checkpoint for cell growth and survival during early activation of quiescent muscle satellite cells

Adult mouse muscle satellite cells (MuSCs) are quiescent in uninjured muscles. Upon muscle injury, MuSCs exit quiescence, reenter the cell cycle to proliferate and self-renew, and then differentiate and fuse to drive muscle regeneration. However, it remains poorly understood how MuSCs transition from quiescence to the cycling state. Here, we report that Pax3 and Pax7 binding protein 1 (Paxbp1) controls a key checkpoint during this critical transition. Deletion of Paxbp1 in adult MuSCs prevented them from reentering the cell cycle upon injury, resulting in a total regeneration failure. Mechanistically, we found an abnormal elevation of reactive oxygen species (ROS) in Paxbp1-null MuSCs, which induced p53 activation and impaired mTORC1 signaling, leading to defective cell growth, apoptosis, and failure in S-phase reentry. Deliberate ROS reduction partially rescued the cell-cycle reentry defect in mutant MuSCs. Our study reveals that Paxbp1 regulates a late cell-growth checkpoint essential for quiescent MuSCs to reenter the cell cycle upon activation.

The neurosteroid allopregnanolone protects retinal neurons by effects on autophagy and GABRs/GABAA receptors in rat glaucoma models

In an ex vivo rat glaucoma model using dissected retinas, the neurosteroid allopregnanolone (AlloP) protects retinal ganglion cells (RGCs) via GABR/GABAA receptors. To determine the involvement of macroautophagy/autophagy in neuroprotection by AlloP, we examined the effects of autophagy activators, rapamycin and torin 2, and autophagy inhibitors, bafilomycin A1 and SAR405, on retinal retinal morphology and expression of MAP1 LC3B/LC3B (microtubule-associated protein 1 light chain 3 beta) and SQSTM1 (sequestosome 1). Administration of rapamycin or torin 2 exerted partial histological neuroprotection, while combined administration of AlloP with bafilomycin A1 or SAR405 induced severe degeneration in a hyperbaric condition. Electron microscopic analyses showed that the addition of AlloP significantly increased autophagosomes and degenerative autophagic vacuoles in the retinal nerve fiber layer. Immunoblotting showed that the addition of AlloP or autophagic activators increased the lipidated form of LC3B (LC3B-II) and suppressed SQSTM1. Moreover, bafilomycin A1 increased LC3B-II and SQSTM1 protein levels in the presence of AlloP without changes in corresponding mRNAs compared to AlloP-treated retinas in a hyperbaric condition. These data indicate that AlloP likely induces a protective form of autophagy in this model. In an in vivo rat model of glaucoma, we also observed neuroprotective effects of AlloP. Injection of polystyrene microbeads into the anterior chamber increased intraocular pressure about 3-fold and induced RGC apoptosis. A single intravitreal injection of AlloP or autophagy activators prevented apoptosis and protected RGCs with autophagy activation. We conclude that AlloP may serve as a potential therapeutic agent for the treatment of glaucoma via diverse mechanisms.Abbreviations: 2HBCD: 2-Hydroxypropyl)-β-cyclodextrin; 3-MA: 3-methyladenine; AlloP: allopregnanolone; AP: autophagosome; AVd: degradative autophagic vacuoles; GCL: ganglion cell layer; INL: inner nuclear layer; IOP: intraocular pressure; IPL: inner plexiform layer; LC3B-I: cytosolic form of LC3B; LCB-II: lipidated form of LC3B; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mPTP: mitochondrial permeability transition pore; NDS: neuronal damage score; NFL: nerve fiber layer; OH: ocular hypertension; ON: optic nerve; ONL: outer nuclear layer; OPL: outer plexiform layer; p-STR: scotopic threshold response; RGC: retinal ganglion cells; RT-PCR: real-time reverse transcription polymerase chain reaction; SQSTM1: sequestosome 1; TUNEL: TdT-mediated dUTP Nick End Labeling.

Progress towards a clinically-successful ATR inhibitor for cancer therapy

The DNA damage response (DDR) is now known to play an important role in both cancer development and its treatment. Targeting proteins such as ATR (Ataxia telangiectasia mutated and Rad3-related) kinase, a major regulator of DDR, has demonstrated significant therapeutic potential in cancer treatment, with ATR inhibitors having shown anti-tumour activity not just as monotherapies, but also in potentiating the effects of conventional chemotherapy, radiotherapy, and immunotherapy. This review focuses on the biology of ATR, its functional role in cancer development and treatment, and the rationale behind inhibition of this target as a therapeutic approach, including evaluation of the progress and current status of development of potent and specific ATR inhibitors that have emerged in recent decades. The current applications of these inhibitors both in preclinical and clinical studies either as single agents or in combinations with chemotherapy, radiotherapy and immunotherapy are also extensively discussed. This review concludes with some insights into the various concerns raised or observed with ATR inhibition in both the preclinical and clinical settings, with some suggested solutions.

Amino Acid Sensing in Metabolic Homeostasis and Health

Sensing and responding to changes in nutrient levels, including those of glucose, lipids, and amino acids, by the body is necessary for survival. Accordingly, perturbations in nutrient sensing are tightly linked with human pathologies, particularly metabolic diseases such as obesity, type 2 diabetes mellitus, and other complications of metabolic syndromes. The conventional view is that amino acids are fundamental elements for protein and peptide synthesis, while recent studies have revealed that amino acids are also important bioactive molecules that play key roles in signaling pathways and metabolic regulation. Different pathways that sense intracellular and extracellular levels of amino acids are integrated and coordinated at the organismal level, and, together, these pathways maintain whole metabolic homeostasis. In this review, we discuss the studies describing how important sensing signals respond to amino acid availability and how these sensing mechanisms modulate metabolic processes, including energy, glucose, and lipid metabolism. We further discuss whether dysregulation of amino acid sensing signals can be targeted to promote metabolic disorders, and discuss how to translate these mechanisms to treat human diseases. This review will help to enhance our overall understanding of the correlation between amino acid sensing and metabolic homeostasis, which have important implications for human health.

Comparing mTOR inhibitor Rapamycin with Torin-2 within the RIST molecular-targeted regimen in neuroblastoma cells

The prognosis for patients with relapsed or refractory high-risk neuroblastoma remains dismal and novel therapeutic options are urgently needed. The RIST treatment protocol has a multimodal metronomic therapy design combining molecular-targeted drugs (Rapamycin and Dasatinib) with chemotherapy backbone (Irinotecan and Temozolomide), which is currently verified in a phase II clinical trial (NCT01467986). With the availability of novel and more potent ATP competitive mTOR inhibitors, we expect to improve the RIST combination therapy. By comparing the IC50 values of Torin-1, Torin-2, AZD3147 and PP242 we established that only Torin-2 inhibited cell viability of all three MycN-amplified neuroblastoma cell lines tested at nanomolar concentration. Single treatment of both mTOR inhibitors induced a significant G1 cell cycle arrest and combination treatment with Dasatinib reduced the expression of cell cycle regulator cyclin D1 or increased the expression of cell cycle inhibitor p21. The combinatorial index depicted for both mTOR inhibitors a synergistic effect with Dasatinib. Interestingly, compared to Rapamycin, the combination treatment with Torin-2 resulted in a broader mTOR pathway inhibition as indicated by reduced phosphorylation of AKT (Thr308, Ser473), 4E-BP (Ser65), and S6K (Thr389). Furthermore, substituting Rapamycin in the modified multimodal RIST protocol with Torin-2 reduced cell viability and induced apoptosis despite a significant lower Torin-2 drug concentration applied. The efficacy of nanomolar concentrations may significantly reduce unwanted immunosuppression associated with Rapamycin. However, at this point we cannot rule out that Torin-2 has increased toxicity due to its potency in more complex systems. Nonetheless, our results suggest that including Torin-2 as a substitute for Rapamycin in the RIST protocol may represent a valid option to be evaluated in prospective clinical trials for relapsed or treatment-refractory high-risk neuroblastoma.

Glucose-TOR signaling regulates PIN2 stability to orchestrate auxin gradient and cell expansion in Arabidopsis root

The plant growth hormone auxin controls cell identity, cell division, and expansion. In the primary root of Arabidopsis there is a robust auxin gradient with a peak concentration at the tip of the meristem and a significant decrease throughout the elongation zone. The molecular mechanisms of how such a steep auxin gradient is established and maintained, and how this auxin gradient within the root dynamically adjusts in response to environmental stimuli are still largely unknown. Here, using a large-scale Arabidopsis mutant screening, we described the identification of PIN2 (PIN-FORMED 2), an auxin efflux facilitator, as a key downstream regulator in glucose-TOR (target of rapamycin) energy signaling. We demonstrate that glucose-activated TOR phosphorylates and stabilizes PIN2 and therefore influences the gradient distribution of PIN2 in the Arabidopsis primary root. Interestingly, dysregulation of TOR or PIN2 disrupts the glucose-promoted low auxin region located in the elongation zone that is essential for cell elongation. Taken together, our results shed light on how carbon and metabolic status can be tightly integrated with the hormone-driven processes to orchestrate complex plant growth programs.

Torin2 overcomes sorafenib resistance via suppressing mTORC2-AKT-BAD pathway in hepatocellular carcinoma cells

BACKGROUND

Sorafenib is an oral multi-kinase inhibitor that was approved by the US Food and Drug Administration for the treatment of patients with advanced hepatocellular carcinoma (HCC). However, resistance to sorafenib is an urgent problem to be resolved to improve the therapeutic efficacy of sorafenib. As the activation of AKT/mTOR played a pivotal role in sorafenib resistance, we evaluated the effect of a dual mTOR complex 1/2 inhibitor Torin2 on overcoming the sorafenib resistance in HCC cells.

METHODS

The sorafenib-resistant Huh7 and Hep3B cell lines were established from their parental cell lines. The synergistic effect of sorafenib and Torin2 on these cells was measured by cell viability assay and quantified using the Chou-Talalay method. Apoptosis induced by the combination of sorafenib and Torin2 and the alteration in the specific signaling pathways of interest were detected by Western blotting.

RESULTS

Sorafenib treatment inversely inhibited AKT in parental but activated AKT in sorafenib-resistant Huh7 and Hep3B HCC cells, which underscores the significance of AKT activation. Torin2 and sorafenib synergistically suppressed the viability of sorafenib-resistant cells via apoptosis induction. Torin2 successfully suppressed the sorafenib-activated mTORC2-AKT axis, leading to the dephosphorylation of Ser136 in BAD protein, and increased the expression of total BAD, which contributed to the apoptosis in sorafenib-resistant HCC cells.

CONCLUSIONS

In this study, Torin2 and sorafenib showed synergistic cytostatic capacity in sorafenib-resistant HCC cells, via the suppression of mTORC2-AKT-BAD pathway. Our results suggest a novel strategy of drug combination for overcoming sorafenib resistance in HCC.

Characterization of SPK 98, a Torin2 analog, as ATR and mTOR dual kinase inhibitor

A series of Torin2, a second-generation ATP-competitive inhibitor, analogues were biologically characterized to identify their potential for ATR and mTOR kinase inhibition. Compound SPK 98 was observed to inhibit ATR/mTOR kinase selectively over ATM kinase in HCT 116 cell line. In addition to that, SPK 98 on 30 min incubation with human, mice and rat liver microsomes showed improved properties with an increased half-life (a maximum T ½ of 157 min) and internal clearance in mouse as compared to Torin2. Further, SPK 98 was also noticed to indulge in inducing premature chromatin condensation as a result of ATR/mTOR kinase inhibition at 50 nM. In a nutshell, our work presents the identification and characterization of SPK 98, a small molecule inhibitor, which exhibits improved specific inhibition for ATR at a lower concentration than Torin2.

Genomic and pathological heterogeneity in clinically diagnosed small cell lung cancer in never/light smokers identifies therapeutically targetable alterations

Small-cell lung cancer (SCLC) occurs infrequently in never/former light smokers. We sought to study this rare clinical subset through next-generation sequencing (NGS) and by characterizing a representative patient-derived model. We performed targeted NGS, as well as comprehensive pathological evaluation, in 11 never/former light smokers with clinically diagnosed SCLC. We established a patient-derived model from one such patient (DFCI168) harboring an NRAS^Q61K mutation and characterized the sensitivity of this model to MEK and TORC1/2 inhibitors. Despite the clinical diagnosis of SCLC, the majority (8/11) of cases were either of nonpulmonary origin or of mixed histology and included atypical carcinoid (n = 1), mixed non-small-cell lung carcinoma and SCLC (n = 4), unspecified poorly differentiated carcinoma (n = 1), or small-cell carcinoma from different origins (n = 2). RB1 and TP53 mutations were found in four and five cases, respectively. Predicted driver mutations were detected in EGFR (n = 2), NRAS (n = 1), KRAS (n = 1), BRCA1 (n = 1), and ATM (n = 1), and one case harbored a TMPRSS2-ERG fusion. DFCI168 (NRAS^Q61K ) exhibited marked sensitivity to MEK inhibitors in vitro and in vivo. The combination of MEK and mTORC1/2 inhibitors synergized to prevent compensatory mTOR activation, resulting in prolonged growth inhibition in this model and in three other NRAS mutant lung cancer cell lines. SCLC in never/former light smokers is rare and is potentially a distinct disease entity comprised of oncogenic driver mutation-harboring carcinomas morphologically and/or clinically mimicking SCLC. Comprehensive pathologic review integrated with genomic profiling is critical in refining the diagnosis and in identifying potential therapeutic options.