Littérature scientifique sur le sujet « Reactivation of vulnerabilities »

Oncogenic kinase inhibitors show short-lived responses in the clinic due to high rate of acquired resistance. We previously showed that pharmacologically exploiting oncogene-induced proteotoxic stress can be a viable alternative to oncogene-targeted therapy. Here, we performed extensive analyses of the transcriptomic, metabolomic and proteostatic perturbations during the course of treatment of Her2+ breast cancer cells with a Her2 inhibitor covering the drug response, resistance, relapse and drug withdrawal phases. We found that acute Her2 inhibition, in addition to blocking mitogenic signaling, leads to significant decline in the glucose uptake, and shutdown of glycolysis and of global protein synthesis. During prolonged therapy, compensatory overexpression of Her3 allows for the reactivation of mitogenic signaling pathways, but fails to re-engage the glucose uptake and glycolysis, resulting in proteotoxic ER stress, which maintains the protein synthesis block and growth inhibition. Her3-mediated cell proliferation under ER stress during prolonged Her2 inhibition is enabled due to the overexpression of the eIF2 phosphatase GADD34, which uncouples protein synthesis block from the ER stress response to allow for active cell growth. We show that this imbalance in the mitogenic and proteostatic signaling created during the acquired resistance to anti-Her2 therapy imposes a specific vulnerability to the inhibition of the endoplasmic reticulum quality control machinery. The latter is more pronounced in the drug withdrawal phase, where the de-inhibition of Her2 creates an acute surge in the downstream signaling pathways and exacerbates the proteostatic imbalance. Therefore, the acquired resistance mechanisms to oncogenic kinase inhibitors may create secondary vulnerabilities that could be exploited in the clinic.

Abstract Background BRAF inhibitors, such as vemurafenib, have shown efficacy in BRAF-mutant melanoma treatment but acquired-resistance invariably develops. Unveiling the potential vulnerabilities associated with vemurafenib resistance could provide rational strategies for combinatorial treatment. Methods This work investigates the metabolic characteristics and vulnerabilities of acquired resistance to vemurafenib in three generated BRAF-mutant human melanoma cell clones, analysing metabolic profiles, gene and protein expression in baseline and nutrient withdrawal conditions. Preclinical findings are correlated with gene expression analysis from publicly available clinical datasets. Results Two vemurafenib-resistant clones showed dependency on lipid metabolism and increased prostaglandin E2 synthesis and were more responsive to vemurafenib under EGFR inhibition, potentially implicating inflammatory lipid and EGFR signalling in ERK reactivation and vemurafenib resistance. The third resistant clone showed higher pyruvate-carboxylase (PC) activity indicating increased anaplerotic mitochondrial metabolism, concomitant with reduced GLUT-1, increased PC protein expression and survival advantage under nutrient-depleted conditions. Prostaglandin synthase (PTGES) expression was inversely correlated with melanoma patient survival. Increases in PC and PTGES gene expression were observed in some patients following progression on BRAF inhibitors. Conclusions Altogether, our data highlight heterogeneity in metabolic adaptations during acquired resistance to vemurafenib in BRAF-mutant melanoma, potentially uncovering key clinically-relevant mechanisms for combinatorial therapeutic targeting.

Abstract TP53 is the most frequently mutated tumor suppressor with somatic alterations found in approximately 50% of all human cancers. In the remaining TP53 wild-type (WT) tumors, functional inactivation of the p53 pathway may be achieved through a variety of other mechanisms, including gene deletion, epigenetic silencing, and/or alterations in prominent negative regulators, including MDM2/MDM4 and PPM1D. These alterations block p53 activity and lead to uncontrolled cell proliferation and oncogenesis in a majority of cancers, including the highly aggressive, universally fatal glial cell tumors of childhood, known as Diffuse Intrinsic Pontine Gliomas (DIPGs). DIPGs are inoperable due to their location within the brainstem. Available treatment options, including radiotherapy, have had a palliative effect at best, with almost all children succumbing to the disease within 18 months of diagnosis. Recent advances have led to an improved understanding of the biological underpinnings of this disease and identification of recurrent genetic alterations that represent potential therapeutic targets for these patients. Prominent among these targets in DIPGs with WT p53 status (50%) are MDM2/4 and PPM1D, whose suppression lead to p53 reactivation specifically in the WT p53 context. We have undertaken a combination of approaches to better understand the therapeutic potential of MDM2 and PPM1D inhibition in DIPG, characterizing the genomic, transcriptomic, and cell-state changes that drive resistance, and identifying novel vulnerabilities that can be exploited with combination therapies towards a cure.

Abstract Germline loss-of-function (LOF) variants in Elongator complex protein 1 (ELP1) are the most prevalent predisposing genetic events in childhood medulloblastoma (MB). ELP1 germline carriers develop SHH-MBs that exhibit coincident somatic PTCH1 mutations and universal loss-of-heterozygosity of the remaining ELP1 allele through chromosome 9q deletion. The molecular, biochemical, and cellular mechanisms by which germline ELP1/Elongator deficiency contribute to SHH-MB tumorigenesis remain largely unknown. Herein, we report that mice engineered to mimic germline Elp1 LOF (i.e., Elp1HET) seen in SHH-MB patients exhibit hallmark features of premalignancy events in cycling cerebellar granule neuron progenitors (GNPs), the lineage-of-origin for SHH-MB. Compared to wild-type counterparts, Elp1HET GNPs exhibit increased replication stress-associated DNA damage, homologous recombination-associated genomic instability, accelerated cell cycle kinetics, reduced p53-dependent apoptosis in response to genotoxic stress, and slowed differentiation. Orthotopic transplantation of Elp1HET GNPs harboring somatic Ptch1 inactivation into the cerebella of immunocompromised mice promotes onset of SHH-MB tumors with incomplete penetrance that exhibit reduced p53 transcriptional activity through a currently unknown mechanism(s). Concomitant Elp1 and Ptch1 gene targeting in p53-null GNPs reproduces highly penetrant cerebellar tumors recapitulating the molecular and phenotypic features of ELP1-associated SHH-MB. Finally, reactivation of the p53 pathway through preclinical treatment with an MDM2 inhibitor promotes cell death and prolongs the survival of patient-derived xenograft tumor (PDX) models harboring deleterious ELP1 mutations. Together, our findings reveal that germline Elp1 LOF heightens genomic instability and malignant transformation in cycling GNPs, providing a mechanistic model for the subgroup-restricted pattern of predisposition associated with pathogenic ELP1 germline carriers. These results provide essential mechanistic insight into the molecular and cellular basis of SHH-MB predisposition driven by ELP1 LOF and nominate therapies that overcome p53 pathway inhibition as a rational treatment option for affected children.

Abstract Metabolic reprogramming is a hallmark of cancer. MYC oncoproteins control many aspects of this response, by inducing the expression of genes involved in mitochondrial biogenesis, glycolysis, glutaminolysis and amino acid transport. This coordinated response allows cancer cells to meet the demands for macromolecules and energy necessary to sustain the anabolic state. Normal cells adapt to nutrient-limiting conditions, such as amino acid (AA) starvation, by activating the autophagy-lysosomal pathway that is necessary for the maintenance of amino acid pools and for providing other building blocks (e.g., ATP) that are needed for cell survival. Surprisingly, our ex vivo and in vivo studies of premalignant and neoplastic MYC-expressing B cells of Eμ-Myc transgenic mice, and of human MYC-driven B cell lymphoma (e.g., Burkitt lymphoma), revealed that MYC suppresses the catabolic autophagy-lysosomal pathway, and that, accordingly, Myc-expressing premalignant and neoplastic B cells are exquisitely sensitive to AA starvation. For example, analyses of the effects of low (6%) versus high (20%) protein diets revealed that limiting AA pools in vivo selectively reduces the numbers of circulating premalignant Eμ-Myc B220+ B cells without affecting B cell numbers in wild type littermate mice. Thus, MYC-driven tumor cells are unable to sufficiently adapt to a state of nutrient deprivation (Figure 1). Expression analyses revealed that this MYC suppresses the autophagy-lysosomal system by transcriptionally repressing genes that encode regulators and components of this pathway, and that this response is a hallmark of human malignancies with MYC involvement. Further, suppressing these genes has functional consequences, where MYC provokes marked reductions in autophagic flux that lead to marked increases in the levels of cargo such as p62/Sequestrin that are normally degraded by this pathway. A master regulator of autophagy and lysosomal biogenesis is TFEB that, like MYC, functions as a basic helix-loop-helix leucine zipper transcription factor and shares a similar DNA recognition sequence. Our studies suggest that MYC blocks TFEB function at three levels. First, MYC can directly repress TFEB transcription. Second, MYC can directly repress TFEB transcription targets by competing with TFEB for binding to the promoter-regulatory regions of autophagy-lysosome gene targets. Third, MYC-expressing B cells have activated mTORC1, which phosphorylates TFEB and blocks its nuclear localization. Notably, forced reactivation of the autophagy-lysosomal pathway via inducible expression of a of a constitutively active (mTORC1-resistant and nuclear) form of TFEB (TFEBS211A) disables the malignant state, where TFEBS211A triggers cell cycle arrest and senescence of both mouse and human MYC-driven lymphomas ex vivo, and compromises tumorigenic potential in vivo. Thus, TFEB acts as tumor suppressor for MYC-driven malignancies. We hypothesized that MYC-driven tumor cells compensate for the reductions in the autophagy pathway and maintain AA homeostasis by activating compensatory mechanisms, including AA transport and the proteasome. In support of this notion, the expression of AA transporters and components of the proteasome, and AA transport and proteasome activity, are markedly augmented in premalignant and neoplastic MYC-expressing B cells. Accordingly, MYC-expressing B cells are exquisitely sensitive to treatment with proteasome inhibitors. Collectively, these findings suggest that MYC drives the anabolic state by suppressing the catabolic autophagy-lysosomal pathway, and that to maintain AA pools MYC-driven cancer cells up-regulate AA transport and the proteasome. This scenario provides attractive opportunities for combination therapies that should disable MYC-driven malignancies, including protein-restricted diets and proteasome and TORC1. Figure 1. Premalignant Eμ-Myc and wild type (WT) littermates were treated for one week with low (6%) and high (20%) protein diets and B220+ cell numbers in peripheral blood were assessed. Figure 1. Premalignant Eμ-Myc and wild type (WT) littermates were treated for one week with low (6%) and high (20%) protein diets and B220+ cell numbers in peripheral blood were assessed. Disclosures No relevant conflicts of interest to declare.

Abstract Clinical sequencing efforts are rapidly identifying sarcoma gene fusions that have not been functionally validated for their transformation capacity and biological activity. An example is the new fusion of transcriptional coactivators, VGLL2-NCOA2, found in infantile rhabdomyosarcoma. To delineate VGLL2-NCOA2 tumorigenic mechanisms and identify therapeutic vulnerabilities, we implemented a cross-species comparative oncology approach with zebrafish, mouse allograft, and patient samples. We found that in our transgenic zebrafish and mouse allograft models, VGLL2-NCOA2 is sufficient to generate mesenchymal tumors that display features of immature skeletal muscle. Zebrafish and mouse VGLL2-NCOA2 tumors are consistent with the human disease histologically and transcriptionally, and express diagnostic rhabdomyosarcoma markers. We found a shared molecular feature of these tumors was a suppression of myogenic differentiation pathways and reactivation of developmental programs. To identify impacted developmental programs, we transcriptionally clustered zebrafish VGLL2-NCOA2 tumors with the trajectory of early zebrafish development. A subset of VGLL2-NCOA2 zebrafish tumors cluster with embryonic somitogenesis and pinpoint VGLL2-NCOA2 developmental targets, including a RAS family GTPase, ARF6. In VGLL2-NCOA2 zebrafish, mouse allograft, and patient tumors, ARF6 is highly expressed and is absent from mature skeletal muscle. ARF6 knockout in our C2C12-VGLL2-NCOA2 cell culture model suppresses VGLL2-NCOA2 soft agar colony formation capacity, suggesting a genetic cooperating event in the disease. Our data indicate that VGLL2-NCOA2 is an oncogene which leverages developmental programs for tumorigenesis, and that the reactivation or persistence of ARF6 could represent a therapeutic opportunity. Citation Format: Sarah Watson, Collette A. LaVigne, Lin Xu, Didier Surdez, Joanna Cyrta, Delia Calderon, Matthew V. Cannon, Matthew R. Kent, Katherine M. Silvius, Jack P. Kucinski, Emma N. Harrison, Whitney Murchison, Dinesh Rakheja, Franck Tirode, Olivier Delattre, James F. Amatruda, Genevieve C. Kendall. VGLL2-NCOA2 leverages developmental programs for pediatric sarcomagenesis. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3525.

Intratumoral heterogeneity is considered the major cause of drug unresponsiveness in cancer and accumulating evidence implicates non-mutational resistance mechanisms rather than genetic mutations in its development. These non-mutational processes are largely driven by phenotypic plasticity, which is defined as the ability of a cell to reprogram and change its identity (phenotype switching). Tumor cell plasticity is characterized by the reactivation of developmental programs that are closely correlated with the acquisition of cancer stem cell properties and an enhanced potential for retrodifferentiation or transdifferentiation. A well-studied mechanism of phenotypic plasticity is the epithelial-mesenchymal transition (EMT). Current evidence suggests a complex interplay between EMT, genetic and epigenetic alterations, and clues from the tumor microenvironment in cell reprogramming. A deeper understanding of the connections between stem cell, epithelial–mesenchymal, and tumor-associated reprogramming events is crucial to develop novel therapies that mitigate cell plasticity and minimize the evolution of tumor heterogeneity, and hence drug resistance. Alternatively, vulnerabilities exposed by tumor cells when residing in a plastic or stem-like state may be exploited therapeutically, i.e., by converting them into less aggressive or even postmitotic cells. Tumor cell plasticity thus presents a new paradigm for understanding a cancer’s resistance to therapy and deciphering its underlying mechanisms.

Abstract The FDA approval of the KRAS G12C inhibitor (G12Ci) sotorasib and the advancement of similar drugs into clinical trials marks a major milestone in treating KRAS G12C non-small cell lung cancer (NSCLC). However, not all patients respond (sotorasib - ORR = 37.1%, adagrasib - 43%, JDQ443 - 35%), motivating preclinical and clinical investigation into mechanisms of intrinsic and acquired resistance. For instance, clinical studies have reported on-target KRAS mutations and preclinical studies have demonstrated mitogen-activated protein kinase (MAPK) feedback reactivation including EGFP, SHP2, and WT RAS signaling. In response to targeted therapies, sub-populations of cells can enter quiescence or specific epigenetic-driven states that confer drug tolerance. However, epigenetic states defining drug-tolerant persister populations and contributing to adaptive resistance to KRAS G12Ci have not been reported. Using a lineage tracing barcoded system, we identify distinct and reversible subpopulations defined by specific chromatin and transcriptional states in KRAS NSCLC cell lines that contribute to KRAS G12Ci resistance in vitro, even prior to drug treatment. We observed that specific states, including activation of histone demethylation and SWI/SNF complex, may contribute to MAPK reactivation-driven resistance. These results suggest potential epigenetic vulnerabilities that can be exploited to improve the response to KRAS G12Ci. Moreover, we observed distinct persister subpopulations with resistance to KRAS G12Ci combination co-targeting orthogonal pathways (SHP2, CDK4/6, PI3K, and MCL-1), raising the possibility that distinct epigenetic-transcriptional states contribute to differential drug response and clonal evolution of persisters. Collectively, these results suggest that more complete tumor regression may be achieved by orthogonal strategies that target different resistant populations within the same tumor. Citation Format: Chendi Li, Qian Qin, Mohammed Usman Syed, Anahita Nimbalkar, Barbara Karakyriakou, Sarah E. Clark, Anne Y. Saiki, Paul E. Hughes, Chris Ott, Luca Pinello, Aaron N. Hata. Chromatin modification driving sub-clonal resistance to KRAS G12C combination therapies in KRAS mutant non-small cell lung cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3867.

Homeobox genes encode transcription factors which regulate basic processes in development and cell differentiation and are grouped into classes and subclasses according to sequence similarities. Here, we analyzed the activities of the 20 members strong TALE homeobox gene class in early hematopoiesis and in lymphopoiesis including developing and mature B-cells, T-cells, natural killer (NK)-cells and innate lymphoid cells (ILC). The resultant expression pattern comprised eleven genes and which we termed TALE-code enables discrimination of normal and aberrant activities of TALE homeobox genes in lymphoid malignancies. Subsequent expression analysis of TALE homeobox genes in public datasets of Hodgkin lymphoma (HL) patients revealed overexpression of IRX3, IRX4, MEIS1, MEIS3, PBX1, PBX4 and TGIF1. As paradigm we focused on PBX1 which was deregulated in about 17% HL patients. Normal PBX1 expression was restricted to hematopoietic stem cells and progenitors of T-cells and ILCs but absent in B-cells, reflecting its roles in stemness and early differentiation. HL cell line SUP-HD1 expressed enhanced PBX1 levels and served as an in vitro model to identify upstream regulators and downstream targets in this malignancy. Genomic studies of this cell line therein showed a gain of the PBX1 locus at 1q23 which may underlie its aberrant expression. Comparative expression profiling analyses of HL patients and cell lines followed by knockdown experiments revealed NFIB and TLX2 as target genes activated by PBX1. HOX proteins operate as cofactors of PBX1. Accordingly, our data showed that HOXB9 overexpressed in HL coactivated TLX2 but not NFIB while activating TNFRSF9 without PBX1. Further downstream analyses showed that TLX2 activated TBX15 which operated anti-apoptotically. Taken together, we discovered a lymphoid TALE-code and identified an aberrant network around deregulated TALE homeobox gene PBX1 which may disturb B-cell differentiation in HL by reactivation of progenitor-specific genes. These findings may provide the framework for future studies to exploit possible vulnerabilities of malignant cells in therapeutic scenarios.

Passive immunization with broadly neutralizing antibodies (bNAbs) of HIV-1 appears a promising strategy for eliciting long-term HIV-1 remission. When administered concomitantly with the cessation of antiretroviral therapy (ART) to patients with established viremic control, bNAb therapy is expected to prolong remission. Surprisingly, in clinical trials on chronic HIV-1 patients, the bNAb VRC01 failed to prolong remission substantially. Identifying the cause of this failure is important for improving VRC01-based therapies and unraveling potential vulnerabilities of other bNAbs. In the trials, viremia resurged rapidly in most patients despite suppressive VRC01 concentrations in circulation, suggesting that VRC01 resistance was the likely cause of failure. ART swiftly halts viral replication, precluding the development of resistance during ART. If resistance were to emerge post ART, virological breakthrough would have taken longer than without VRC01 therapy. We hypothesized therefore that VRC01-resistant strains must have been formed before ART initiation, survived ART in latently infected cells, and been activated during VRC01 therapy, causing treatment failure. Current assays preclude testing this hypothesis experimentally. We developed a mathematical model based on the hypothesis and challenged it with available clinical data. The model integrated within-host HIV-1 evolution, stochastic latency reactivation, and viral dynamics with multiple-dose VRC01 pharmacokinetics. The model predicted that single but not higher VRC01-resistant mutants would pre-exist in the latent reservoir. We constructed a virtual patient population that parsimoniously recapitulated inter-patient variations. Model predictions with this population quantitatively captured data of VRC01 failure from clinical trials, presenting strong evidence supporting the hypothesis. We attributed VRC01 failure to single-mutant VRC01-resistant proviruses in the latent reservoir triggering viral recrudescence, particularly when VRC01 was at trough levels. Pre-existing resistant proviruses in the latent reservoir may similarly compromise other bNAbs. Our study provides a framework for designing bNAb-based therapeutic protocols that would avert such failure and maximize HIV-1 remission.

Ce travail s'intéresse à l'étude du comportement en conditions statiques des failles dans la croûte supérieure continentale et plus particulièrement à l'effet des surpressions de fluides sur la réactivation des failles et le déclenchement des séismes. Pour ce faire, une analyse associant sismologie, géologie structurale, pétrophysique, géochimie et modélisation hydromécanique a été menée dans la région de l'Ubaye (Alpes du sud) où a eu lieu, en 2003-2004, un essaim sismique en relation avec des failles régionales affleurant plus au sud dans le massif cristallin de l'Argentera. Les mécanismes au foyer de 74 événements de cet essaim sismique ont été déterminés. À partir de ces mécanismes et d'autres données sismologiques ainsi que de modèles mécaniques basés sur la théorie de Mohr-Coulomb, cette étude a permis de confirmer que l'activité sismique de l'essaim était liée à la présence de surpressions de fluides et d'expliquer l'évolution spatio-temporelle des surpressions. Un modèle hydromécanique est proposé afin de concilier les évolutions spatio-temporelles de la sismicité et des surpressions de fluides. L'étude d'un affleurement d'une faille régionale de l'Argentera combinant analyse structurale, mesures pétrophysiques et modélisation hydromécanique a ensuite permis de préciser le comportement hydromécanique des failles aux profondeurs hypocentrales et plus particulièrement leur capacité à être compactées et à développer des surpressions de fluides. Finalement, l'initiation des séismes à la base de la zone sismogénique est explorée à partir d'analyses géochimiques et mécaniques menées sur de veines à paragénèse quartz-chlorite formées à la base de la zone sismogène. Ces résultats sont comparés avec ceux déduits de l'analyse de l'essaim sismique de l'Ubaye. Ce travail a permis d'étudier le comportement sismomécanique des failles et les interactions entre failles, fluides et séismes à travers la zone sismogène. Il met l'accent sur l'importance de coupler les approches sismologiques, hydrauliques et mécaniques dans l'étude des failles actives
This work adresses the behavior of faults in the upper continental crust under static conditions and moreparticularly the effect of fluid overpressures on fault reactivation and earthquake triggering. In order toreach this goal, an analysis combining seismology, structural geology, petrophysics, geochemistry andhydromechanical modeling has been carried out in the Ubaye region (southern French-Italian Alps) wherea seismic swarm related to regional faults exposed in the Argentera basement massif (located furthersouth) occurred in 2003-2004. Focal mechanisms of 74 events from this seismic swarm have beendetermined. Based on these mechanisms and other seismological data and on mechanical modeling basedon the Mohr-Coulomb theory, this study allows to confirm that the seismic activity of the swarm waslinked to the presence of overpressurized fluids and to explain the spatio-temporal evolution ofoverpressures. A hydromechanical model is proposed in order to account for the spatio-temporalevolutions of both seismicity and pore fluid overpressures. The study of an exposure of an Argenteraregional fault combining a structural analysis, petrophysical measurements and a hydromechanicalmodeling has allowed to decipher the hydromechanical behavior of faults at hypocentral depths, and moreparticularly to determine the ability of faults to be compacted and to develop fluid overpressures. Lastly,the initiation of earthquakes at or near the base of the seismogenic zone is explored through geochemicaland mechanical analyses of quartz-chlorite veins formed at the base of the seismogenic zone. Theseresults are then compared with those deduced from the analysis of the Ubaye seismic swarm. This workallows to study the seismo-mechanical behavior of faults and the interactions between faults, fluids andearthquakes across the seismogenic zone. It emphasizes the importance of associating seismological,hydraulic et mechanical analyses in the study of active faults

In more than 95% of all successfully conducted cyberattacks, the human factor is exploited as a vulnerability point. The following principle applies. Whenever a hacker uses external attack vectors and thus does not directly use the Internet as a medium, employees become the target of the attack. As a result, the current technical and intelligent defense mechanisms can only contribute to a limited extent to the increase the resilience of IT systems, as these technological approaches do not fully account for the behavioral, cognitive, and heterogeneous motivations that lead to human error in the security causal chain of information security using social engineering (SE) methods. In this paper, we present a strategic and iterative analysis tool to detect SE threats through systemic monitoring, to train and successfully defend against them. For this purpose, we use the so-called Course of Actions to practically check the security-compliant behavior of employees and to initialize the feedback processes for reactivating the human firewall based on the knowledge gained. This approach is already being applied to various types of organizations and critical infrastructure and can be seamlessly integrated into existing training and auditing programs.