The role of APOBEC3B in lung tumor evolution and targeted cancer therapy resistance

In this study, the impact of the apolipoprotein B mRNA-editing catalytic subunit-like (APOBEC) enzyme APOBEC3B (A3B) on epidermal growth factor receptor (EGFR)-driven lung cancer was assessed. A3B expression in EGFR mutant (EGFRmut) non-small-cell lung cancer (NSCLC) mouse models constrained tumorigenesis, while A3B expression in tumors treated with EGFR-targeted cancer therapy was associated with treatment resistance. Analyses of human NSCLC models treated with EGFR-targeted therapy showed upregulation of A3B and revealed therapy-induced activation of nuclear factor kappa B (NF-κB) as an inducer of A3B expression. Significantly reduced viability was observed with A3B deficiency, and A3B was required for the enrichment of APOBEC mutation signatures, in targeted therapy-treated human NSCLC preclinical models. Upregulation of A3B was confirmed in patients with NSCLC treated with EGFR-targeted therapy. This study uncovers the multifaceted roles of A3B in NSCLC and identifies A3B as a potential target for more durable responses to targeted cancer therapy.

Abstract 2197: Targeted cancer therapy induces APOBEC fueling the evolution of drug resistance

Introduction: Increasing our understanding of drivers of mutagenesis in lung cancer is critical in our efforts to prevent tumor reoccurrence and resistance.

Results: Using the multi-region TRACERx lung cancer study, we uncovered that APOBEC3B is significantly upregulated when compared with other APOBEC family members in EGFR driven lung cancer and identified subclonal enrichment of APOBEC mutational signatures. To model APOBEC mutagenesis in lung cancer, several novel EGFR mutant mouse models containing a human APOBEC3B transgene were generated. Using these models, it was uncovered that APOBEC3B expression is detrimental at tumor initiation when expressed continuously in a p53 wildtype background. This detrimental effect is likely due to elevated chromosomal instability, which was observed to increase significantly with APOBEC3B expression in an EGFR mutant TP53 deficient mouse model. Induction of subclonal expression of APOBEC3B in an EGFR mutant mouse model with tyrosine kinase inhibitor (TKI) therapy resulted in a significant increase in resistant tumor development. Significant downregulation of the base excision repair gene uracil-DNA glycosylase (UNG) was also observed in APOBEC3B expressing mice, which paralleled findings in patient tumors and cell lines treated with TKI therapy. Finally, a mouse mutational signature was identified in APOBEC3B expressing cell lines, reinforcing the idea that APOBEC driven mutagenesis contributes to TKI resistance.

Conclusion: This study demonstrates a unique principle by which targeted therapy induces changes within tumors ideal for APOBEC driven tumor evolution, fueling therapy resistance.

Citation Format: Manasi Mayekar, Deborah Caswell, Natalie Vokes, Emily K. Law, Wei Wu, William Hill, Eva Gronroos, Andrew Rowan, Maise Al Bakir, Clare Weeden, Caroline E. McCoach, Collin M. Blakely, Nuri Alpay Temiz, Ai Nagano, Daniel L. Kerr, Julia K. Rotow, Oriol Pich, Franziska Haderk, Michelle Dietzen, Carlos Martinez Ruiz, Bruna Almeida, Lauren Cech, Beatrice Gini, Joanna Przewrocka, Chris Moore, Miguel Murillo, Bjorn Bakker, Brandon Rule, Cameron Durfee, Shigeki Nanj, Lisa Tan, Lindsay K. Larson, Prokopios P. Argyris, William L. Brown, Johnny Yu, Carlos Gomez, Philippe Gui, Rachel I. Vogel, Elizabeth A. Yu, Nicholas J. Thomas, Subramanian Venkatesan, Sebastijan Hobor, Su Kit Chew, Nicholas McGranahan, Nnennaya Kanu, Eliezer M. Van Allen, Julian Downward, Reuben S. Harris, Trever Bivona, Charles Swanton. Targeted cancer therapy induces APOBEC fueling the evolution of drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2197.

Perspectives on Open Science and The Future of Scholarly Communication: Internet Trackers and Algorithmic Persuasion

The current digital content industry is heavily oriented towards building platforms that track users' behaviour and seek to convince them to stay longer and come back sooner onto the platform. Similarly, authors are incentivised to publish more and to become champions of dissemination. Arguably, these incentive systems are built around public reputation supported by a system of metrics, hard to be assessed. Generally, the digital content industry is permeable to non-human contributors (algorithms that are able to generate content and reactions), anonymity and identity fraud. It is pertinent to present a perspective paper about early signs of track and persuasion in scholarly communication. Building our views, we have run a pilot study to determine the opportunity for conducting research about the use of "track and persuade" technologies in scholarly communication. We collected observations on a sample of 148 relevant websites and we interviewed 15 that are experts related to the field. Through this work, we tried to identify 1) the essential questions that could inspire proper research, 2) good practices to be recommended for future research, and 3) whether citizen science is a suitable approach to further research in this field. The findings could contribute to determining a broader solution for building trust and infrastructure in scholarly communication. The principles of Open Science will be used as a framework to see if they offer insights into this work going forward.

Abstract LB124: APOBEC3B fuels evolution of resistance during targeted cancer therapy

Despite recent advances in cancer treatment, lung cancer remains the leading cause of cancer mortality worldwide. Lung adenocarcinoma is the most prevalent subtype of lung cancer. Genomic profiling of lung adenocarcinomas has led to the identification of several targetable oncogenic drivers. Therapies targeting the oncogenic-driver pathway using various tyrosine kinase inhibitors (TKIs), are effective initially but responses are often transient and tumors eventually regrow due to drug resistance. Furthermore, drug resistance can arise via the selection of pre-existing resistant clones or via the de novo acquisition of mutations that are not present before therapy. We set out to understand the mechanism for the de novo acquisition of drug resistance mutations in oncogene-driven lung cancers. To do so, we investigated the gene expression changes that occur upon inhibition of oncogenic pathways. We found that oncoprotein targeted therapy induces adaptations favorable for APOBEC genome mutagenesis. Treatment with small molecule inhibitors against EGFR and ALK promoted transcriptional upregulation of members of APOBEC family of cytidine deaminases and downregulation of the uracil glycosylase UNG, the key protein needed for removal of APOBEC-induced DNA lesions. These changes in mRNA levels resulted in functional effects that can impact nuclear DNA by increasing nuclear APOBEC activity and reducing nuclear uracil excision capacity. Determination of changes in APOBEC mRNA levels and nuclear APOBEC activity over time and depletion studies identified APOBEC3B as a driver of both baseline and targeted therapy-induced nuclear APOBEC activity in pre-clinical lung cancer models. We found that APOBEC3B mediates genetic evolution and emergence of resistance during targeted therapy. We identified NF-kB pathway induction and c-Jun downregulation as key mediators of these treatment-induced molecular changes. Furthermore, we find an upregulation of APOBEC3B in lung cancer patients with progressive disease and a high proportion of APOBEC-associated mutations in patient tumors treated with targeted therapy. Some putative resistance mutations in patient tumors were also in the APOBEC-preferred context. Our study identifies a novel targeted therapy-induced evolutionary process involving an APOBEC DNA deaminase that could serve as an attractive co-target to elicit more durable treatment responses.

Citation Format: Manasi K. Mayekar, Deborah Caswell, Natalie Vokes, Wei Wu, Caroline McCoach, Collin Blakely, Nuri Alpay Temiz, Daniel Lucas Kerr, Julia Rotow, Franziska Haderk, Lauren Cech, Beatrice Gini, Shigeki Nanjo, Lisa Tan, Johnny Yu, Carlos Gomez, Philippe Gui, Elizabeth Yu, Nicholas Thomas, Julian Downward, Reuben Harris, Eliezer Van Allen, Charles Swanton, Trever Bivona. APOBEC3B fuels evolution of resistance during targeted cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB124.

Impact of concurrent genomic alterations in epidermal growth factor receptor (EGFR)-mutated lung cancer

Comprehensive characterization of the genomic landscape of epidermal growth factor receptor (EGFR)-mutated lung cancers have identified patterns of secondary mutations beyond the primary oncogenic EGFR mutation. These include concurrent pathogenic alterations affecting p53 (60–65%), RTKs (5–10%), PIK3CA/KRAS (3–23%), Wnt (5–10%), and cell cycle (7–25%) pathways as well as transcription factors such as MYC and NKX2-1 (10–15%). The majority of these co-occurring alterations were detected or enriched in samples collected from patients at resistance to tyrosine kinase inhibitor (TKI) treatment, indicating a potential functional role in driving resistance to therapy. Of note, these co-occurring tumor genomic alterations are not necessarily mutually exclusive, and evidence suggests that multiple clonal and sub-clonal cancer cell populations can co-exist and contribute to EGFR TKI resistance. Computational tools aimed to classify, track and predict the evolution of cancer clonal populations during therapy are being investigated in pre-clinical models to guide the selection of combination therapy switching strategies that may delay the development of treatment resistance. Here we review the most frequently identified tumor genomic alterations that co-occur with mutated EGFR and the evidence that these alterations effect responsiveness to EGFR TKI treatment.

Evolution and clinical impact of co-occurring genetic alterations in advanced-stage EGFR-mutant lung cancers

A widespread approach to modern cancer therapy is to identify a single oncogenic driver gene and target its mutant-protein product (for example, EGFR-inhibitor treatment in EGFR-mutant lung cancers). However, genetically driven resistance to targeted therapy limits patient survival. Through genomic analysis of 1,122 EGFR-mutant lung cancer cell-free DNA samples and whole-exome analysis of seven longitudinally collected tumor samples from a patient with EGFR-mutant lung cancer, we identified critical co-occurring oncogenic events present in most advanced-stage EGFR-mutant lung cancers. We defined new pathways limiting EGFR-inhibitor response, including WNT/β-catenin alterations and cell-cycle-gene (CDK4 and CDK6) mutations. Tumor genomic complexity increases with EGFR-inhibitor treatment, and co-occurring alterations in CTNNB1 and PIK3CA exhibit nonredundant functions that cooperatively promote tumor metastasis or limit EGFR-inhibitor response. This study calls for revisiting the prevailing single-gene driver-oncogene view and links clinical outcomes to co-occurring genetic alterations in patients with advanced-stage EGFR-mutant lung cancer.

Saccharomyces jurei sp. nov., isolation and genetic identification of a novel yeast species from Quercus robur

Two strains, D5088^T and D5095, representing a novel yeast species belonging to the genus Saccharomyces were isolated from oak tree bark and surrounding soil located at an altitude of 1000 m above sea level in Saint Auban, France. Sequence analyses of the internal transcribed spacer (ITS) region and 26S rRNA D1/D2 domains indicated that the two strains were most closely related to Saccharomyces mikatae and Saccharomyces paradoxus. Genetic hybridization analyses showed that both strains are reproductively isolated from all other Saccharomyces species and, therefore, represent a distinct biological species. The species name Saccharomyces jurei sp. nov. is proposed to accommodate these two strains, with D5088^T (=CBS 14759^T=NCYC 3947^T) designated as the type strain.

mTORC2 Regulates Amino Acid Metabolism in Cancer by Phosphorylation of the Cystine-Glutamate Antiporter xCT

Mutations in cancer reprogram amino acid metabolism to drive tumor growth, but the molecular mechanisms are not well understood. Using an unbiased proteomic screen, we identified mTORC2 as a critical regulator of amino acid metabolism in cancer via phosphorylation of the cystine-glutamate antiporter xCT. mTORC2 phosphorylates serine 26 at the cytosolic N terminus of xCT, inhibiting its activity. Genetic inhibition of mTORC2, or pharmacologic inhibition of the mammalian target of rapamycin (mTOR) kinase, promotes glutamate secretion, cystine uptake, and incorporation into glutathione, linking growth factor receptor signaling with amino acid uptake and utilization. These results identify an unanticipated mechanism regulating amino acid metabolism in cancer, enabling tumor cells to adapt to changing environmental conditions.

Inactivation of Capicua drives cancer metastasis

Metastasis is the leading cause of death in people with lung cancer, yet the molecular effectors underlying tumor dissemination remain poorly defined. Through the development of an in vivo spontaneous lung cancer metastasis model, we show that the developmentally regulated transcriptional repressor Capicua (CIC) suppresses invasion and metastasis. Inactivation of CIC relieves repression of its effector ETV4, driving ETV4-mediated upregulation of MMP24, which is necessary and sufficient for metastasis. Loss of CIC, or an increase in levels of its effectors ETV4 and MMP24, is a biomarker of tumor progression and worse outcomes in people with lung and/or gastric cancer. Our findings reveal CIC as a conserved metastasis suppressor, highlighting new anti-metastatic strategies that could potentially improve patient outcomes.

Single-Cell Phosphoproteomics Resolves Adaptive Signaling Dynamics and Informs Targeted Combination Therapy in Glioblastoma

Intratumoral heterogeneity of signaling networks may contribute to targeted cancer therapy resistance, including in the highly lethal brain cancer glioblastoma (GBM). We performed single-cell phosphoproteomics on a patient-derived in vivo GBM model of mTOR kinase inhibitor resistance and coupled it to an analytical approach for detecting changes in signaling coordination. Alterations in the protein signaling coordination were resolved as early as 2.5 days after treatment, anticipating drug resistance long before it was clinically manifest. Combination therapies were identified that resulted in complete and sustained tumor suppression in vivo. This approach may identify actionable alterations in signal coordination that underlie adaptive resistance, which can be suppressed through combination drug therapy, including non-obvious drug combinations.

Genetic variation in offspring indirectly influences the quality of maternal behaviour in mice

Conflict over parental investment between parent and offspring is predicted to lead to selection on genes expressed in offspring for traits influencing maternal investment, and on parentally expressed genes affecting offspring behaviour. However, the specific genetic variants that indirectly modify maternal or offspring behaviour remain largely unknown. Using a cross-fostered population of mice, we map maternal behaviour in genetically uniform mothers as a function of genetic variation in offspring and identify loci on offspring chromosomes 5 and 7 that modify maternal behaviour. Conversely, we found that genetic variation among mothers influences offspring development, independent of offspring genotype. Offspring solicitation and maternal behaviour show signs of coadaptation as they are negatively correlated between mothers and their biological offspring, which may be linked to costs of increased solicitation on growth found in our study. Overall, our results show levels of parental provisioning and offspring solicitation are unique to specific genotypes.

Greater than the sum of its parts: single-nucleus sequencing identifies convergent evolution of independent EGFR mutants in GBM

Single-cell sequencing approaches are needed to characterize the genomic diversity of complex tumors, shedding light on their evolutionary paths and potentially suggesting more effective therapies. In this issue of Cancer Discovery, Francis and colleagues develop a novel integrative approach to identify distinct tumor subpopulations based on joint detection of clonal and subclonal events from bulk tumor and single-nucleus whole-genome sequencing, allowing them to infer a subclonal architecture. Surprisingly, the authors identify convergent evolution of multiple, mutually exclusive, independent EGFR gain-of-function variants in a single tumor. This study demonstrates the value of integrative single-cell genomics and highlights the biologic primacy of EGFR as an actionable target in glioblastoma.

Compensatory glutamine metabolism promotes glioblastoma resistance to mTOR inhibitor treatment

The mechanistic target of rapamycin (mTOR) is hyperactivated in many types of cancer, rendering it a compelling drug target; however, the impact of mTOR inhibition on metabolic reprogramming in cancer is incompletely understood. Here, by integrating metabolic and functional studies in glioblastoma multiforme (GBM) cell lines, preclinical models, and clinical samples, we demonstrate that the compensatory upregulation of glutamine metabolism promotes resistance to mTOR kinase inhibitors. Metabolomic studies in GBM cells revealed that glutaminase (GLS) and glutamate levels are elevated following mTOR kinase inhibitor treatment. Moreover, these mTOR inhibitor-dependent metabolic alterations were confirmed in a GBM xenograft model. Expression of GLS following mTOR inhibitor treatment promoted GBM survival in an α-ketoglutarate-dependent (αKG-dependent) manner. Combined genetic and/or pharmacological inhibition of mTOR kinase and GLS resulted in massive synergistic tumor cell death and growth inhibition in tumor-bearing mice. These results highlight a critical role for compensatory glutamine metabolism in promoting mTOR inhibitor resistance and suggest that rational combination therapy has the potential to suppress resistance.

Targeted therapy resistance mediated by dynamic regulation of extrachromosomal mutant EGFR DNA

Intratumoral heterogeneity contributes to cancer drug resistance, but the underlying mechanisms are not understood. Single-cell analyses of patient-derived models and clinical samples from glioblastoma patients treated with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) demonstrate that tumor cells reversibly up-regulate or suppress mutant EGFR expression, conferring distinct cellular phenotypes to reach an optimal equilibrium for growth. Resistance to EGFR TKIs is shown to occur by elimination of mutant EGFR from extrachromosomal DNA. After drug withdrawal, reemergence of clonal EGFR mutations on extrachromosomal DNA follows. These results indicate a highly specific, dynamic, and adaptive route by which cancers can evade therapies that target oncogenes maintained on extrachromosomal DNA.

mTOR complex 2 controls glycolytic metabolism in glioblastoma through FoxO acetylation and upregulation of c-Myc

Aerobic glycolysis (the Warburg effect) is a core hallmark of cancer, but the molecular mechanisms underlying it remain unclear. Here, we identify an unexpected central role for mTORC2 in cancer metabolic reprogramming where it controls glycolytic metabolism by ultimately regulating the cellular level of c-Myc. We show that mTORC2 promotes inactivating phosphorylation of class IIa histone deacetylases, which leads to the acetylation of FoxO1 and FoxO3, and this in turn releases c-Myc from a suppressive miR-34c-dependent network. These central features of activated mTORC2 signaling, acetylated FoxO, and c-Myc levels are highly intercorrelated in clinical samples and with shorter survival of GBM patients. These results identify a specific, Akt-independent role for mTORC2 in regulating glycolytic metabolism in cancer.

The mTOR kinase inhibitors, CC214-1 and CC214-2, preferentially block the growth of EGFRvIII-activated glioblastomas

PURPOSE

mTOR pathway hyperactivation occurs in approximately 90% of glioblastomas, but the allosteric mTOR inhibitor rapamycin has failed in the clinic. Here, we examine the efficacy of the newly discovered ATP-competitive mTOR kinase inhibitors CC214-1 and CC214-2 in glioblastoma, identifying molecular determinants of response and mechanisms of resistance, and develop a pharmacologic strategy to overcome it.

EXPERIMENTAL DESIGN

We conducted in vitro and in vivo studies in glioblastoma cell lines and an intracranial model to: determine the potential efficacy of the recently reported mTOR kinase inhibitors CC214-1 (in vitro use) and CC214-2 (in vivo use) at inhibiting rapamycin-resistant signaling and blocking glioblastoma growth and a novel single-cell technology-DNA Encoded Antibody Libraries-was used to identify mechanisms of resistance.

RESULTS

Here, we show that CC214-1 and CC214-2 suppress rapamycin-resistant mTORC1 signaling, block mTORC2 signaling, and significantly inhibit the growth of glioblastomas in vitro and in vivo. EGFRvIII expression and PTEN loss enhance sensitivity to CC214 compounds, consistent with enhanced efficacy in strongly mTOR-activated tumors. Importantly, CC214 compounds potently induce autophagy, preventing tumor cell death. Genetic or pharmacologic inhibition of autophagy greatly sensitizes glioblastoma cells and orthotopic xenografts to CC214-1- and CC214-2-induced cell death.

CONCLUSIONS

These results identify CC214-1 and CC214-2 as potentially efficacious mTOR kinase inhibitors in glioblastoma, and suggest a strategy for identifying patients most likely to benefit from mTOR inhibition. In addition, this study also shows a central role for autophagy in preventing mTOR-kinase inhibitor-mediated tumor cell death, and suggests a pharmacologic strategy for overcoming it.

EGFR mutation-induced alternative splicing of Max contributes to growth of glycolytic tumors in brain cancer

Alternative splicing contributes to diverse aspects of cancer pathogenesis including altered cellular metabolism, but the specificity of the process or its consequences are not well understood. We characterized genome-wide alternative splicing induced by the activating EGFRvIII mutation in glioblastoma (GBM). EGFRvIII upregulates the heterogeneous nuclear ribonucleoprotein (hnRNP) A1 splicing factor, promoting glycolytic gene expression and conferring significantly shorter survival in patients. HnRNPA1 promotes splicing of a transcript encoding the Myc-interacting partner Max, generating Delta Max, an enhancer of Myc-dependent transformation. Delta Max, but not full-length Max, rescues Myc-dependent glycolytic gene expression upon induced EGFRvIII loss, and correlates with hnRNPA1 expression and downstream Myc-dependent gene transcription in patients. Finally, Delta Max is shown to promote glioma cell proliferation in vitro and augment EGFRvIII expressing GBM growth in vivo. These results demonstrate an important role for alternative splicing in GBM and identify Delta Max as a mediator of Myc-dependent tumor cell metabolism.

A tale of two approaches: complementary mechanisms of cytotoxic and targeted therapy resistance may inform next-generation cancer treatments

Chemotherapy and molecularly targeted approaches represent two very different modes of cancer treatment and each is associated with unique benefits and limitations. Both types of therapy share the overarching limitation of the emergence of drug resistance, which prevents these drugs from eliciting lasting clinical benefit. This review will provide an overview of the various mechanisms of resistance to each of these classes of drugs and examples of drug combinations that have been tested clinically. This analysis supports the contention that understanding modes of resistance to both chemotherapy and molecularly targeted therapies may be very useful in selecting those drugs of each class that will have complementing mechanisms of sensitivity and thereby represent reasonable combination therapies.

Recombinant inbred systems can advance research in behavioral ecology

Recombinant inbred (RI) systems such as the BXD mouse family represent a population with defined genetic architecture and variation that approximates those of natural populations. With the development of novel RI lines and sophisticated methods that conjointly analyze phenotype, gene sequence, and expression data, RI systems such as BXD are a timely and powerful tool to advance the field of behavioral ecology. The latter traditionally focused on functional questions such as the adaptive value of behavior but largely ignored underlying genetics and mechanisms. In this perspective, we argue that using RI systems to address questions in behavioral ecology and evolutionary biology has great potential to advance research in these fields. We outline key questions and how they can be tackled using RI systems and BXD in particular. The unique opportunity to analyze genetic and phenotypic data from studies conducted in different laboratories and at different times is a key benefit of RI systems and may lead the way to a better understanding of how adaptive phenotypes arise from genetic and environmental factors.

Longitudinal evaluation of MPIO-labeled stem cell biodistribution in glioblastoma using high resolution and contrast-enhanced MR imaging at 14.1 tesla

To optimize the development of stem cell (SC)-based therapies for the treatment of glioblastoma (GBM), we compared the pathotropism of 2 SC sources, human mesenchymal stem cells (hMSCs) and fetal neural stem cells (fNSCs), toward 2 orthotopic GBM models, circumscribed U87vIII and highly infiltrative GBM26. High resolution and contrast-enhanced (CE) magnetic resonance imaging (MRI) were performed at 14.1 Tesla to longitudinally monitor the in vivo location of hMSCs and fNSCs labeled with the same amount of micron-size particles of iron oxide (MPIO). To assess pathotropism, SCs were injected in the contralateral hemisphere of U87vIII tumor-bearing mice. Both MPIO-labeled SC types exhibited tropism to tumors, first localizing at the tumor edges, then in the tumor masses. MPIO-labeled hMSCs and fNSCs were also injected intratumorally in mice with U87vIII or GBM26 tumors to assess their biodistribution. Both SC types distributed throughout the tumor in both GBM models. Of interest, in the U87vIII model, areas of hyposignal colocalized first with the enhancing regions (ie, regions of high vascular permeability), consistent with SC tropism to vascular endothelial growth factor. In the GBM26 model, no rim of hyposignal was observed, consistent with the infiltrative nature of this tumor. Quantitative analysis of the index of dispersion confirmed that both MPIO-labeled SC types longitudinally distribute inside the tumor masses after intratumoral injection. Histological studies confirmed the MRI results. In summary, our results indicate that hMSCs and fNSCs exhibit similar properties regarding tumor tropism and intratumoral dissemination, highlighting the potential of these 2 SC sources as adequate candidates for SC-based therapies.

Abstract 1923: The mTOR kinase inhibitor, CC214, preferentially blocks the growth of EGFRvIII-activated glioblastomas

mTOR pathway hyper activation is a common feature in many cancers, including in nearly 90% of Glioblastomas. mTOR exists in two multiprotein complexes, which differ in regulation, function, and response to the allosteric mTOR inhibitor rapamycin. The failure of glioblastomas to clinically respond to rapamycin appears to be mediated both by inability of rapamycin to inhibit mTORC2 signaling, and by failure to fully suppress p4E-BP1, a critical effector of mTORC1. The new generation of mTOR kinase inhibitors (mTORki) has emerged as a new class of targeted cancer therapies capable of blocking mTOR more potently than rapalogs (such as Rapamycin). Here we demonstrate that CC214-1 and CC214-2, mTOR kinase inhibitors, have potent effects on the growth of glioblastoma in vitro and in vivo. Across a panel of GBM cell lines, CC214-1 was significantly more effective at suppressing 4E-BP1 phosphorylation and protein translation, and mTORC2 signaling than rapamycin, resulting in significantly more growth inhibition at equal levels of suppression of S6 phosphorylation. EGFRvIII, the constitutively active EGFR mutant frequently detected in GBMs strongly activates mTORC1 and mTORC2 signaling, potently sensitizing tumors to CC214-1. In contrast, PTEN expression suppressed mTOR signaling and reduced the response to CC214-1. In vivo CC214-2 significantly inhibited mTORC1 and mTORC2 signaling, significantly suppressing tumor growth by 50%. CC214-1 also potently activated autophagy. Addition of chloroquine suppressed autophagy resulting in significant CC214-1-dependent apoptotic cell death. These results demonstrate the potential activity of mTOR kinase inhibitors in GBM, and identify EGFRvIII expression and PTEN loss as molecular determinants of response. These data also suggest that mTOR kinase inhibitors, alone or in combination with autophagy inhibiting agents, are likely to have significant anti-tumor efficacy in GBM patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1923. doi:1538-7445.AM2012-1923

Abstract 4321: EGFR signaling in glioblastoma regulates the expression of a brain specific isoform of alphaPIX/Arhgef6 to promote invasion

The gene Arhgef6 encodes the protein alphaPIX/Cool-2, a guanine nucleotide exchange factor specific for the Rho GTPases Rac1 and Cdc42. AlphaPIX is a protein of 90 kDa predominantly expressed in haemopoietic cells where it has been shown to have a role in cytoskeletal reorganization. However, Arhgef6 is also expressed in the brain and mutations in Arhgef6 have been linked to intellectual disability (ID) in humans. AlphaPIX mRNA was reported to be upregulated in glioblastoma multiforme (GBM), the most lethal form of brain cancer. We examined alphaPIX expression in several glioma cell lines and observed a smaller isoform migrating at 72 kDa. To characterize this isoform we performed 5′RACE from several glioma cell lines and show the smaller isoform is an amino-terminal truncated form of alphaPIX lacking the calponin homology (CH) domain. We demonstrate this isoform is expressed during post-natal brain development and its expression coincides with activation of mTOR. Examination of glioblastoma from both autopsy and biopsy clinical samples shows alphaPIX expression correlates with EGFR/PI3K/Akt/mTOR activation. EGF stimulation is shown to upregulate alphaPIX, and pharmacological inhibition of Akt inhibits alphaPIX expression. To examine the function of alphaPIX in glioblastoma we performed siRNA-mediated knockdown and demonstrate increased cell adhesion upon alphaPIX loss. In addition, knockdown of alphaPIX in glioma cells decreases invasive capacity and decreases the formation of invadopodia. These data demonstrate a previously uncharacterized isoform of alphaPIX is expressed during post-natal brain development, and is highly upregulated in GBM with activated EGFR signaling. A functional consequence of EGFR-mediated alphaPIX expression in glioma is increased invasion as a result of dysregulated cytoskeletal organization.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4321. doi:1538-7445.AM2012-4321

An LXR agonist promotes glioblastoma cell death through inhibition of an EGFR/AKT/SREBP-1/LDLR-dependent pathway

Glioblastoma (GBM) is the most common malignant primary brain tumor of adults and one of the most lethal of all cancers. Epidermal growth factor receptor (EGFR) mutations (EGFRvIII) and phosphoinositide 3-kinase (PI3K) hyperactivation are common in GBM, promoting tumor growth and survival, including through sterol regulatory element-binding protein 1 (SREBP-1)-dependent lipogenesis. The role of cholesterol metabolism in GBM pathogenesis, its association with EGFR/PI3K signaling, and its potential therapeutic targetability are unknown. In our investigation, studies of GBM cell lines, xenograft models, and GBM clinical samples, including those from patients treated with the EGFR tyrosine kinase inhibitor lapatinib, uncovered an EGFRvIII-activated, PI3K/SREBP-1-dependent tumor survival pathway through the low-density lipoprotein receptor (LDLR). Targeting LDLR with the liver X receptor (LXR) agonist GW3965 caused inducible degrader of LDLR (IDOL)-mediated LDLR degradation and increased expression of the ABCA1 cholesterol efflux transporter, potently promoting tumor cell death in an in vivo GBM model. These results show that EGFRvIII can promote tumor survival through PI3K/SREBP-1-dependent upregulation of LDLR and suggest a role for LXR agonists in the treatment of GBM patients.

Oncogenic EGFR signaling activates an mTORC2-NF-κB pathway that promotes chemotherapy resistance

Although it is known that mTOR complex 2 (mTORC2) functions upstream of Akt, the role of this protein kinase complex in cancer is not well understood. Through an integrated analysis of cell lines, in vivo models, and clinical samples, we demonstrate that mTORC2 is frequently activated in glioblastoma (GBM), the most common malignant primary brain tumor of adults. We show that the common activating epidermal growth factor receptor (EGFR) mutation (EGFRvIII) stimulates mTORC2 kinase activity, which is partially suppressed by PTEN. mTORC2 signaling promotes GBM growth and survival and activates NF-κB. Importantly, this mTORC2-NF-κB pathway renders GBM cells and tumors resistant to chemotherapy in a manner independent of Akt. These results highlight the critical role of mTORC2 in the pathogenesis of GBM, including through the activation of NF-κB downstream of mutant EGFR, leading to a previously unrecognized function in cancer chemotherapy resistance. These findings suggest that therapeutic strategies targeting mTORC2, alone or in combination with chemotherapy, will be effective in the treatment of cancer.

SIGNIFICANCE

This study demonstrates that EGFRvIII-activated mTORC2 signaling promotes GBM proliferation, survival, and chemotherapy resistance through Akt-independent activation of NF-κB. These results highlight the role of mTORC2 as an integrator of two canonical signaling networks that are commonly altered in cancer, EGFR/phosphoinositide-3 kinase (PI3K) and NF-κB. These results also validate the importance of mTORC2 as a cancer target and provide new insights into its role in mediating chemotherapy resistance, suggesting new treatment strategies.

Adipose-derived mesenchymal stem cells ameliorate chronic experimental autoimmune encephalomyelitis

Mesenchymal stem cells (MSCs) represent a promising therapeutic approach for neurological autoimmune diseases; previous studies have shown that treatment with bone marrow-derived MSCs induces immune modulation and reduces disease severity in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Here we show that intravenous administration of adipose-derived MSCs (ASCs) before disease onset significantly reduces the severity of EAE by immune modulation and decreases spinal cord inflammation and demyelination. ASCs preferentially home into lymphoid organs but also migrates inside the central nervous system (CNS). Most importantly, administration of ASCs in chronic established EAE significantly ameliorates the disease course and reduces both demyelination and axonal loss, and induces a Th2-type cytokine shift in T cells. Interestingly, a relevant subset of ASCs expresses activated alpha 4 integrins and adheres to inflamed brain venules in intravital microscopy experiments. Bioluminescence imaging shows that alpha 4 integrins control ASC accumulation in inflamed CNS. Importantly, we found that ASC cultures produce basic fibroblast growth factor, brain-derived growth factor, and platelet-derived growth factor-AB. Moreover, ASC infiltration within demyelinated areas is accompanied by increased number of endogenous oligodendrocyte progenitors. In conclusion, we show that ASCs have clear therapeutic potential by a bimodal mechanism, by suppressing the autoimmune response in early phases of disease as well as by inducing local neuroregeneration by endogenous progenitors in animals with established disease. Overall, our data suggest that ASCs represent a valuable tool for stem cell-based therapy in chronic inflammatory diseases of the CNS.

Different content of chitin-like polysaccharides in multiple sclerosis and Alzheimer's disease brains

Chitin is an insoluble N-acetyl-glucosamine polymer coating fungi cell wall and several human parasites. It is hydrolysed by chitotriosidase (Chit); however, as chitin is absent in humans, the significance of human Chit activity is unknown. The level of plasma Chit activity positively correlates with Alzheimer's disease (AD) and multiple sclerosis (MS). A recent study revealed the presence of potentially detrimental chitin-like substances in AD brain by Calcofluor histochemistry, whilst its search in MS brains has never been described to date. Through a comparative immunohistochemical analysis we confirm the presence of abundant chitin-like deposition in AD brains but fail to demonstrate it in MS brains. Interestingly, co-localization of beta-amyloid, Calcofluor and the nuclear marker DAPI was observed. Therefore, Chit production in MS patients is induced by mechanisms other than those operating in AD. Microglia-derived Chit activity in MS may counterbalance the naturally occurring glucosamine aggregation, protecting the brain from the chitin-like substance deposition.

Novel autoantigens recognized by CSF IgG from Hashimoto's encephalitis revealed by a proteomic approach

To identify the target of IgG autoimmune response in Hashimoto's encephalopathy (HE), we studied the binding of IgG present in serum and cerebro-spinal fluid (CSF) from six patients with HE and 15 controls to human central nervous system (CNS) white matter antigens by 2D-PAGE and immunoblotting and by immunohistochemistry. We found that CSF IgG from HE patients specifically recognized 3 spots, which were identified as dimethylargininase-I (DDAHI) and aldehyde reductase-I (AKRIAI). DDAHI was present in two isoforms recognized respectively by five and four HE patients; immunohistochemistry with anti-DDAHI antiserum depicted endothelial cells in normal human CNS. AKRIAI was recognized by three HE CSF and this enzyme was widely distributed on neurons and endothelia by immunohistochemistry. IgG from HE CSF immunostained both neuronal and endothelial cells in mouse CNS. The presence of these autoantibodies selectively in the CSF of HE patients may have important diagnostic and pathogenetic implications, since the autoimmune response to these enzymes may lead to vascular and/or neuronal damage, two major mechanisms involved in the pathogenesis of HE.