NF2 Tumor Suppressor Gene Research Articles

Linking FOXM1 and PD-L1 to CDK4/6-MEK targeted therapy resistance in malignant peripheral nerve sheath tumors.

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, Ras-driven sarcomas characterized by loss of the NF1 tumor suppressor gene and hyperactivation of MEK and CDK4/6 kinases. MPNSTs lack effective therapies. We recently demonstrated remarkable efficacy of dual CDK4/6-MEK inhibition in mice with de novo MPNSTs, which was heightened by combined targeting of the immune checkpoint protein, PD-L1. The triple combination therapy targeting CDK4/6, MEK, and PD-L1 led to extended MPNST regression and improved survival, although most tumors eventually acquired drug resistance. Here, we consider the immune activation phenotype caused by CDK4/6-MEK inhibition in MPNSTs that uniquely involved intratumoral plasma cell accumulation. We discuss how PD-L1 and FOXM1, a tumor-promoting transcription factor, are functionally linked and may be key mediators of resistance to CDK4/6-MEK targeted therapies. Finally, the role of FOXM1 in suppressing anti-tumor immunity and potentially thwarting immune-based therapies is considered. We suggest that future therapeutic strategies targeting the oncogenic network of CDK4/6, MEK, PD-L1, and FOXM1 represent exciting future treatment options for MPNST patients.

Combined NF2/PTEN mutations as predictors of meningioma aggressiveness.

e14044 Background: In meningiomas, loss of the NF2 tumor suppressor gene function leads to dysregulation of cell proliferation and tumor formation. PTEN, another tumor suppressor gene correlated with worse prognosis in tumors like gliomas, has also been reported in meningiomas, but the impact of its mutation alone or in conjunction with NF2 loss on outcomes in these tumors is unexplored. We aimed to evaluate whether dual NF2/PTEN mutations comprise a more aggressive meningioma phenotype compared to tumors with only NF2 mutations. Identifying this high-risk genetic profile could allow for preventative and individualized treatment of these aggressive meningiomas. Methods: We reviewed patients who underwent meningioma resection at our institution from January 2018 through October 2022. Demographic information, tumor characteristics, pre- and post-operative clinical characteristics, and outcomes were collected. Meningioma specimens were analyzed by immunohistochemistry for WHO grading and Ki67 proliferation index and by sequencing for genomic alterations. We performed multivariable logistic regression analyses to identify clinical outcomes associated with proliferation index and genetic mutations. Results: We identified NF2 mutations in 24 meningiomas and dual NF2/PTEN mutations in 7 meningiomas. Mutation rates did not significantly differ based on demographic factors including sex, age, race, socioeconomic status, or prior cranial radiation status (p>0.05). The majority of tumors with these mutations (93%) were in non-skull base regions (i.e. convexity, parafalcine). Tumors with both NF2 and PTEN mutations were more likely to be WHO grade III tumors than those with the NF2 mutation alone (29% versus 9%). Tumors with dual mutations had higher likelihood of having Ki67 proliferation indices ≥ 10% (OR 5.98, p<0.01). While higher Ki67 index was significantly associated with features of more aggressive tumors including higher WHO grade and recurrence rates, dual mutation in NF2 and PTEN is associated with higher rate of recurrence (OR 13.13, p<0.001) and mortality (OR 5.14, p<0.05) compared to NF2 irrespective of Ki67 index. Notably, patients with mutations in NF2 alone or both NF2/PTEN did not differ in preoperative Karnofsky performance score, Simpson resection grade, or presence of post operative residual tumor. Conclusions: Our results demonstrated that concomitant NF2 and PTEN mutations in meningiomas were associated with higher WHO grades, tumor proliferation indices, recurrence rates, and mortality rates. This finding suggests that NF2/PTEN mutated meningiomas represent a distinct subset of tumors that demonstrate a more aggressive clinical and histopathological phenotype that may require more aggressive treatment and closer surveillance. Further investigation is warranted to confirm the prognostic relevance of NF2/PTEN mutations in meningioma and elucidate their underlying molecular mechanisms.

Nf1 deficiency modulates the stromal environment in the pretumorigenic rat mammary gland.

Neurofibromin, coded by the NF1 tumor suppressor gene, is the main negative regulator of the RAS pathway and is frequently mutated in various cancers. Women with Neurofibromatosis Type I (NF1)-a tumor predisposition syndrome caused by a germline NF1 mutation-have an increased risk of developing aggressive breast cancer with poorer prognosis. The mechanism by which NF1 mutations lead to breast cancer tumorigenesis is not well understood. Therefore, the objective of this work was to identify stromal alterations before tumor formation that result in the increased risk and poorer outcome seen among NF1 patients with breast cancer. To accurately model the germline monoallelic NF1 mutations in NF1 patients, we utilized an Nf1-deficient rat model with accelerated mammary development before presenting with highly penetrant breast cancer. We identified increased collagen content in Nf1-deficient rat mammary glands before tumor formation that correlated with age of tumor onset. Additionally, gene expression analysis revealed that Nf1-deficient mature adipocytes in the rat mammary gland have increased collagen expression and shifted to a fibroblast and preadipocyte expression profile. This alteration in lineage commitment was also observed with in vitro differentiation, however, flow cytometry analysis did not show a change in mammary adipose-derived mesenchymal stem cell abundance. Collectively, this study uncovered the previously undescribed role of Nf1 in mammary collagen deposition and regulating adipocyte differentiation. In addition to unraveling the mechanism of tumor formation, further investigation of adipocytes and collagen modifications in preneoplastic mammary glands will create a foundation for developing early detection strategies of breast cancer among NF1 patients.

Visual Deficits and Diagnostic and Therapeutic Strategies for Neurofibromatosis Type 1: Bridging Science and Patient-Centered Care.

Neurofibromatosis type 1 (NF1) is an inherited autosomal dominant disorder primarily affecting children and adolescents characterized by multisystemic clinical manifestations. Mutations in neurofibromin, the protein encoded by the Nf1 tumor suppressor gene, result in dysregulation of the RAS/MAPK pathway leading to uncontrolled cell growth and migration. Neurofibromin is highly expressed in several cell lineages including melanocytes, glial cells, neurons, and Schwann cells. Individuals with NF1 possess a genetic predisposition to central nervous system neoplasms, particularly gliomas affecting the visual pathway, known as optic pathway gliomas (OPGs). While OPGs are typically asymptomatic and benign, they can induce visual impairment in some patients. This review provides insight into the spectrum and visual outcomes of NF1, current diagnostic techniques and therapeutic interventions, and explores the influence of NF1-OPGS on visual abnormalities. We focus on recent advancements in preclinical animal models to elucidate the underlying mechanisms of NF1 pathology and therapies targeting NF1-OPGs. Overall, our review highlights the involvement of retinal ganglion cell dysfunction and degeneration in NF1 disease, and the need for further research to transform scientific laboratory discoveries to improved patient outcomes.

The histone lysine acetyltransferase KAT2B inhibits cholangiocarcinoma growth: evidence for interaction with SP1 to regulate NF2-YAP signaling

BackgroundCholangiocarcinoma (CCA) is a highly malignant cancer of the biliary tract with poor prognosis. Further mechanistic insights into the molecular mechanisms of CCA are needed to develop more effective target therapy.MethodsThe expression of the histone lysine acetyltransferase KAT2B in human CCA was analyzed in human CCA tissues. CCA xenograft was developed by inoculation of human CCA cells with or without KAT2B overexpression into SCID mice. Western blotting, ChIP-qPCR, qRT-PCR, protein immunoprecipitation, GST pull-down and RNA-seq were performed to delineate KAT2B mechanisms of action in CCA.ResultsWe identified KAT2B as a frequently downregulated histone acetyltransferase in human CCA. Downregulation of KAT2B was significantly associated with CCA disease progression and poor prognosis of CCA patients. The reduction of KAT2B expression in human CCA was attributed to gene copy number loss. In experimental systems, we demonstrated that overexpression of KAT2B suppressed CCA cell proliferation and colony formation in vitro and inhibits CCA growth in mice. Mechanistically, forced overexpression of KAT2B enhanced the expression of the tumor suppressor gene NF2, which is independent of its histone acetyltransferase activity. We showed that KAT2B was recruited to the promoter region of the NF2 gene via interaction with the transcription factor SP1, which led to enhanced transcription of the NF2 gene. KAT2B-induced NF2 resulted in subsequent inhibition of YAP activity, as reflected by reduced nuclear accumulation of oncogenic YAP and inhibition of YAP downstream genes. Depletion of NF2 was able to reverse KAT2B-induced reduction of nuclear YAP and subvert KAT2B-induced inhibition of CCA cell growth.ConclusionsThis study provides the first evidence for an important tumor inhibitory effect of KAT2B in CCA through regulation of NF2-YAP signaling and suggests that this signaling cascade may be therapeutically targeted for CCA treatment.

NF1-Driven Rhabdomyosarcoma Phenotypes: A Comparative Clinical and Molecular Study of NF1-Mutant Rhabdomyosarcoma and NF1-Associated Malignant Triton Tumor.

Alterations of the NF1 tumor suppressor gene is the second most frequent genetic event in embryonal rhabdomyosarcoma (ERMS), but its associations with clinicopathologic features, outcome, or coexisting molecular events are not well defined. Additionally, NF1 alterations, mostly in the setting of neurofibromatosis type I (NF1), drive the pathogenesis of most malignant peripheral nerve sheath tumor with divergent RMS differentiation (also known as malignant triton tumor [MTT]). Distinguishing between these entities can be challenging because of their pathologic overlap. This study aims to comprehensively analyze the clinicopathologic and molecular spectrum of NF1-mutant RMS compared with NF1-associated MTT for a better understanding of their pathogenesis. We investigated the clinicopathologic and molecular landscape of a cohort of 22 NF1-mutant RMS and a control group of 13 NF1-associated MTT. Cases were tested on a matched tumor-normal hybridization capture-based targeted DNA next-generation sequencing. Among the RMS group, all except one were ERMS, with a median age of 17 years while for MTT the mean age was 39 years. Three MTTs were misdiagnosed as ERMS, having clinical impact in one. The most frequent coexisting alteration in ERMS was TP53 abnormality (36%), being mutually exclusive from NRAS mutations (14%). MTT showed coexisting CDKN2A/B and PRC2 complex alterations in 38% cases and loss of H3K27me3 expression. Patients with NF1-mutant RMS exhibited a 70% 5-year survival rate, in contrast to MTT with a 33% 5-year survival. All metastatic NF1-mutant ERMS were associated with TP53 alterations. Patients with NF1-mutant ERMS lacking TP53 alterations may benefit from dose-reduction chemotherapy. On the basis of the diagnostic challenges and significant treatment and prognostic differences, molecular profiling of challenging tumors with rhabdomyoblastic differentiation is recommended.

Abstract 2021: The RXR agonist MSU-42011 and the MEK inhibitor selumetinib reduce pERK levels in NF1-deficient cells and inhibit cytokine production in macrophages

Abstract Neurofibromatosis type 1 (NF1) is a common genetic disease that predisposes approximately 50% of affected individuals to develop plexiform neurofibromas (PNFs), which can progress to highly aggressive malignant peripheral nerve sheath tumors (MPNSTs) in approximately 10% of patients. NF1 is caused by mutations in the tumor suppressor gene NF1, which encodes for neurofibromin, a negative regulator of RAS activity. Selumetinib, a specific inhibitor of MEK1/2, is the only FDA-approved drug for NF1-associated PNFs. However, the anti-tumor effects of selumetinib are limited in MPNSTs and have dose-limiting side effects. Deficiency of the NF1 gene not only promotes tumorigenesis but also has broad effects on the immune cells and cytokine signaling driven by hyperactive RAS signaling. Because macrophages account for almost half of cells in NF1 lesions and their infiltration correlates with disease progression, we hypothesized that targeting tumor-promoting immune cells could be an alternative approach for treating NF1. The novel retinoid X receptor (RXR) agonist MSU-42011 reduces tumor growth in experimental Kras-driven cancers by decreasing pERK expression, reducing tumor-promoting immune cells like CD206+ macrophages and regulatory T cells, and increasing activated cytotoxic T cells. Here, we treated NF1-deficient cells and macrophages with MSU-42011 and selumetinib, either alone or in combination, using monoculture and conditioned media (CM) conditions. In human PNF cells and mouse MPNSTs, treatment with 200 nM MSU-40211 or 50 nM selumetinib for 3 hours reduced pERK protein levels compared with untreated controls, and the combination treatment enhanced this reduction in pERK protein levels. Additionally, there was a trend toward reduction in cell viability with increasing drug concentrations after 72 hours of the combination treatment. Moreover, CM from human and mouse PNF cells increased the mRNA expression of monocyte chemoattractant CCL2 (C-C motif chemokine ligand 2) and the secretion of IL-6 and TNFα in human THP1 monocytes/macrophages and bone marrow derived macrophages (BMDM). Notably, MSU-42011 and selumetinib alone inhibited CCL2 mRNA expression in THP1 macrophages and BMDM stimulated with CM from human and mouse PNF cells, respectively, and the inhibition of CCL2 mRNA expression was greatest with combination treatment. The combination of MSU42011 and selumetinib also significantly reduced tumor burden in a LL2 model of lung cancer driven by an activating Kras mutation. Based on the similarities in RAS activation and immune cell infiltration in NF1 and lung cancer, our next step is to confirm the immunomodulatory and anti-tumor effects of MSU-42011 and selumetinib in a syngeneic model of PNF and MPNST. Citation Format: Pei-Yu Hung, Jessica A. Moerland, Karen T. Liby. The RXR agonist MSU-42011 and the MEK inhibitor selumetinib reduce pERK levels in NF1-deficient cells and inhibit cytokine production in macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2021.

Fully accessible fitness landscape of oncogene-negative lung adenocarcinoma

Cancer genomes are almost invariably complex with genomic alterations cooperating during each step of carcinogenesis. In cancers that lack a single dominant oncogene mutation, cooperation between the inactivation of multiple tumor suppressor genes can drive tumor initiation and growth. Here, we shed light on how the sequential acquisition of genomic alterations generates oncogene-negative lung tumors. We couple tumor barcoding with combinatorial and multiplexed somatic genome editing to characterize the fitness landscapes of three tumor suppressor genes NF1, RASA1, and PTEN, the inactivation of which jointly drives oncogene-negative lung adenocarcinoma initiation and growth. The fitness landscape was surprisingly accessible, with each additional mutation leading to growth advantage. Furthermore, the fitness landscapes remained fully accessible across backgrounds with the inactivation of additional tumor suppressor genes. These results suggest that while predicting cancer evolution will be challenging, acquiring the multiple alterations that drive the growth of oncogene-negative tumors can be facilitated by the lack of constraints on mutational order.

NF2 alteration in mesothelioma.

The NF2 tumor suppressor gene is a frequent somatically mutated gene in mesothelioma, with 30%-40% mesotheliomas showing NF2 inactivation. NF2 encodes merlin, a member of the ezrin, radixin, and moesin (ERM) family of proteins that regulate cytoskeleton and cell signaling. Recent genome analysis revealed that NF2 alteration may be a late event in mesothelioma development, suggesting that NF2 mutation confers a more aggressive phenotype to mesothelioma cells and may not be directly caused by asbestos exposure. The Hippo tumor-suppressive and mTOR prooncogenic signaling pathways are crucial cell-signaling cascades regulated by merlin. Although the exact role and timing of NF2 inactivation in mesothelioma cells remain to be elucidated, targeting the NF2/merlin-Hippo pathway may be a new therapeutic strategy for patients with mesothelioma.

Abstract 6089: Identification of novel YAP/TAZ pathway regulators in the triple-negative breast cancer cell line MDA-MB231 using single-cell CRISPR screening

Abstract The Hippo signaling cascade is a major pathway that integrates a broad spectrum of mechanosensory signals at the plasma membrane and regulates response via control of cell proliferation, self-renewal, differentiation, and apoptosis. Dysregulation of this pathway has been observed across a range of cancer types and results in an altered activity of its primary downstream effectors, the oncogenic transcription factors YAP/TAZ. For example, both germline and somatic loss-of-function mutations in the tumor suppressor gene NF2, a component of Hippo, induce hyperactivation of YAP/TAZ, transcriptional changes and ultimately result in tumor growth. The Hippo signaling pathway is an attractive target for drug discovery efforts, however, it is highly complex and still incompletely understood. Hence it is indispensable to get a deeper insight into the Hippo - YAP/TAZ signaling axis. To this end, we performed a genome-wide CRISPR knockout screen in the triple-negative breast cancer (TNBC) cell line MDA-MB231 (NF2LOF) expressing a YAP/TAZ reporter construct. We identified both negative and positive regulators of YAP/TAZ in breast cancer cells. In a second step, screening hits were further characterized in a focused single-cell CRISPR screen (Perturb-Seq), aiming at better understanding of the effects on YAP/TAZ activity regulation and downstream effects on gene expression. Here we present the technical details of our screening approaches and the results of perturbing known and novel regulators of YAP/TAZ on single cell level. We discuss the use of Perturb-Seq in the initial validation of hits from genome-wide screens and provide data that may serve as a basis for future drug discovery efforts, seeking for novel and effective treatments for triple-negative breast cancers and other malignancies with Hippo pathway alterations. Citation Format: Mareike Berlak, Zuzanna Makowska, Filippos Klironomos, Julia Kuehnlenz, Atanas Kamburov, Andreas Steffen, Martin Lange, Barbara Nicke, Ralf Lesche, Peter Staller, Charlotte Kopitz, Jan Naujoks. Identification of novel YAP/TAZ pathway regulators in the triple-negative breast cancer cell line MDA-MB231 using single-cell CRISPR screening [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 6089.

Abstract 3648: MSU-42011, alone and in combination with selumetinib, reduces pERK levels in NF1 cancer cells and decreases CCL2 expression in THP-1 macrophages

Abstract Neurofibromatosis type 1 (NF1) is a common genetic disease that predisposes approximately 50% of affected individuals to develop plexiform neurofibromas (PNFs), which can progress to highly aggressive malignant peripheral nerve sheath tumors (MPNSTs) in approximately 10% of patients. NF1 is caused by mutations in the tumor suppressor gene NF1, which encodes for neurofibromin, a negative regulator of RAS activity. Selumetinib, a specific inhibitor of MEK1/2, is the only FDA-approved drug for NF1-associated PNFs. However, the anti-tumor effects of selumetinib are limited in MPNSTs and have dose-limiting side effects. Deficiency of the NF1 gene not only promotes tumorigenesis but also has broad effects on the immune cells and cytokine signaling driven by hyperactive RAS signaling. Because macrophages account for almost half of cells in NF1 lesions and their infiltration highly correlates with disease progression, we hypothesized that targeting tumor-promoting immune cells could be an alternative approach for NF1 treatment. The novel retinoid X receptor (RXR) agonist MSU-42011 reduces tumor growth in experimental Kras-driven cancers by decreasing pERK expression, reducing tumor-promoting immune cells like CD206+ macrophages and regulatory T cells, and increasing activated cytotoxic T cells. Here, we tested MSU-42011 and selumetinib, either alone or in combination, to evaluate their efficacy against NF1 cancer cells and macrophages using monoculture and conditioned media (CM) treatments. Treatment with 200 nM MSU-40211, 50 nM selumetinib, and the combination for 3 hours reduced pERK protein levels by approximately 40%, 70% and 90%, respectively vs. untreated controls. Treatment for 72 hours with selumetinib and the combination reduced the viability of PNF cells in a dose-dependent manner. Moreover, CM from human PNF cells increased monocyte chemoattractant CCL2 (C-C motif chemokine ligand 2) mRNA expression in human THP1 monocytes and THP1 macrophages differentiated by PMA. Notably, MSU-42011 and selumetinib alone similarly inhibited CCL2 mRNA expression by 25% in THP1 macrophages stimulated with CM from PNF cells, and the inhibition of CCL2 mRNA expression was enhanced to 50% with combination treatment. Taken together, our data suggest that MSU-42011 should be tested in relevant preclinical models of NF1. Citation Format: Pei-Yu Hung, Lizbeth Lockwood, Karen T. Liby. MSU-42011, alone and in combination with selumetinib, reduces pERK levels in NF1 cancer cells and decreases CCL2 expression in THP-1 macrophages. [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 3648.

Comprehensive Genomic Profiling of NF2-Mutated Kidney Tumors Reveals Potential Targets for Therapy.

Genomic alterations (GA) in NF2 tumor-suppressor gene have been associated with aggressive behavior in kidney tumors. We used comprehensive genomic profiling (CGP) to evaluate the frequencies of NF2 GA in histologic subtypes of kidney tumors and co-occurring GA in other genes and biomarkers. Advanced kidney tumors included 1875 clear cell (ccRCC), 405 papillary (pRCC), 108 chromophobe (chRCC), 171 sarcomatoid (sRCC), 61 collecting duct (cdRCC), 49 medullary (mRCC), 134 unclassified (uRCC), 906 urothelial carcinoma of renal pelvis (UC), and 147 Wilms tumors underwent hybrid-capture based CGP to evaluate all classes of GA. 192 (4.9%) of kidney tumors featured NF2 GA which were predominantly structural variant mutations (89%), followed by copy number alterations (9%). Gender and age were similar between NF2-mutant (NF2mut) and NF2-wild type (NF2wt) cohorts with male preponderance. NF2 GA frequency was highest in cdRCC (30%), sRCC (21%), uRCC (15%), and pRCC (12%) while lowest in ccRCC (3%), UC (3%) Wilms tumor (1%), and chRCC (0%). NF2 mutational status was associated with loss of Ch 22 (P < .001). NF2mut RCC harbored co-occurring GA including CDKN2A, CDKN2B, SETD2, and BAP1. VHL, PBRM1, PTEN, and FGFR3 GA were significantly more frequent in NF2wt than in NF2mut tumors. MTOR pathway GAs were uncommon in NF2mut tumors. No NF2 mutated RCC featured MSI-high or high TMB. sRCC was associated with high PD-L1 expression. PD-L1 SP142 tumoral (P = .04) and immune cells (P = .013) were more frequent in NF2mut as compared to NF2wt group. Among histologic subtypes of RCC, cdRCC, sRCC, pRCC, and uRCC are enriched in NF2 GA. Co-occurrent GA in CDKN2A/B, SETD2, and BAP1 may represent potential therapeutic targets. Higher level of PD-L1 expression in NF2mut cohort suggests that these tumors might be sensitive to immune checkpoint inhibitor therapies.

5 Targeting NF1/RAS pathway mutations in high-grade serous ovarian carcinoma (HGSOC) with a novel dual-mechanism ERK 1/2 inhibitor to improve chemotherapy sensitivity

Mutations in the NF1 tumor suppressor gene result in unregulated activation of the RAS/ERK pathway and increased cellular proliferation. Somatic NF1 mutations have been identified in up to one-third of HGSOC, and are associated with chemotherapy resistance. A novel dual-mechanism ERK 1/2 inhibitor, ASTX029, has been shown to have activity in non-ovarian solid tumor cell lines with BRAF, KRAS, and NRAS mutations. ASTX029 is unique in that it inhibits the kinase activity of ERK and blocks ERK from being phosphorylated itself by MEK. In this study we investigate the role of ASTX029 to improve platinum sensitivity in NF1/RAS pathway mutated HGSOC. We selected 3 human cancer cell lines consistent with HGSOC histology: OVSAHO, OVCAR3, and OVCAR7. OVSAHO was selected for its NF1 mutation, OVCAR3 for its RAS mutation, and OVCAR7 as a control. We treated all 3 cell lines with varying concentrations of carboplatin and ASTX029, both alone and in combination. The cytotoxic effect of carboplatin and ASTX029 were determined using a CellTiter Glo Luminenscent Cell Viability Assay. Combenefit software was used to evaluate for drug synergy and determine IC50 of both drugs. Phosphorylation of ERK (p-ERK) and RSK (p-RSK), an ERK substrate, were used as markers for effectiveness of inhibition of the NF1/RAS pathway and measured using Western Blot performed 6 and 24 hours after treatment. All 3 cell lines demonstrated decreased platinum sensitivity based on IC50, with OVSAHO having the lowest IC50. ASTX029 demonstrated exquisite cytotoxicity at very low concentrations in the OVSAHO cell line, both alone and in combination with carboplatin. OVCAR3 demonstrated moderate sensitivity to ASTX029, but IC50 was more than 10× greater than for OVSAHO. OVCAR7 demonstrated minimal sensitivity with even high doses of ASTX029, and IC50 was not reached. Synergy between carboplatin and ASTX029 was noted at various doses of both drugs for the OVSAHO cell line, using concentrations far below the IC50 of either drug. Synergistic effect was less pronounced for OVCAR3, and no synergy was noted for OVCAR7. Western blot demonstrated a decrease in p-ERK and p-RSK in a dose and time dependent fashion for OVSAHO and OVCAR3, consistent with effective inhibition of the RAS/ERK pathway. ASTX029, a novel dual-mechanism ERK 1/2 inhibitor, effectively blocks the RAS/ERK pathway in NF1/RAS pathway mutated HGSOC. ASTX029 demonstrates efficacy both as a single-agent and synergy when combined with carboplatin, and may indicate a potential new targeted therapy for chemotherapy resistant HGSOC.

EPCO-27. REVEALING TUMOR HETEROGENEITY AND IMMUNE MICROENVIRONMENT IN NF-1 GLIOMA BY SINGLE-CELL GENE EXPRESSION PROFILING

Abstract Germline mutations in the NF1 tumor suppressor gene cause neurofibromatosis type 1 (NF-1), the most common human genetic cancer predisposition syndrome. NF1 patients are prone to develop peripheral and central nervous system tumors, with glioma occurring in 15-20% of patients. The molecular profiles of glioma from patients with NF-1 have been previously explored by large scale DNA and RNA bulk analyses, providing the first comprehensive genetic landscape of NF-1 glioma. However, the intra-tumoral architecture and the microenvironment organization remained largely concealed within the global bulk profile. Here, to characterize the complexity of molecular states of both malignant and non-malignant cells, we profiled NF-1 glioma gene expression at individual cell resolution. We performed single-nuclei RNA sequencing (Nucseq) on frozen NF-1 glioma specimens, including high-grade and low-grade tumors. The functional classification of the transcriptional programs activated in the individual tumor cells identified three main molecular states that partially overlapped with the cellular subtypes of sporadic glioblastoma. Tumor cells of low-grade NF-1 glioma exhibited marked enrichment of neuronal functions, suggesting that the gliomagenesis process in the context of NF1 inactivation might be supported by specialized neuronal activities. Conversely, the proliferative state characterized high-grade NF-1 glioma, indicating that cell cycle-associated pathways are drivers of tumor progression. The single-cell deconvolution of immune microenvironment in NF-1 low grade glioma revealed infiltration of CD8+ T lymphocytes and the active crosstalk of these cells with pro-inflammatory macrophages and mature dendritic cells, supporting a possible anti-tumor cell-mediated response. The identification of divergent tumor cell states as well as the characterization of the immune infiltrates provide new insights for accurate stratification of NF-1 glioma patients and to inform personalized therapeutics.

Reduction of sporadic and neurofibromatosis type 2-associated vestibular schwannoma growth in vitro and in vivo after treatment with the c-Jun N-terminal kinase inhibitor AS602801.

Vestibular schwannomas (VSs) are benign nerve sheath tumors that result from mutation in the tumor suppressor gene NF2, with functional loss of the protein merlin. The authors have previously shown that c-Jun N-terminal kinase (JNK) is constitutively active in human VS cells and plays a central role in their survival by suppressing accumulation of mitochondrial superoxides, implicating JNK inhibitors as a potential systemic treatment for VS. Thus, the authors hypothesized that the adenosine 5'-triphosphate-competitive JNK inhibitor AS602801 would demonstrate antitumor activity in multiple VS models. Treatment with AS602801 was tested in primary human VS cultures, human VS xenografts, and a genetic mouse model of schwannoma (Postn-Cre;Nf2flox/flox). Primary human VS cell cultures were established from freshly obtained surgical tumor specimens; treatment group media was enriched with AS602801. VS xenograft tumors were established in male athymic nude mice from freshly collected human tumor. Four weeks postimplantation, a pretreatment MRI scan was obtained, followed by 65 days of AS602801 (n = 18) or vehicle control (n = 19) treatment. Posttreatment MRI scans were used to measure final tumor volume. Tumors were then harvested. Finally, Postn-Cre;Nf2flox/flox mice were treated with AS602801 (n = 10) or a vehicle (n = 13) for 65 days. Posttreatment auditory brainstem responses were obtained. Dorsal root ganglia from Postn-Cre;Nf2flox/flox mice were then harvested. In all models, schwannoma identity was confirmed with anti-S100 staining, cell proliferation was measured with the EdU assay, and cell death was measured with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. All protocols were approved by the local institutional review board and Institutional Animal Care and Use Committees. Treatment with AS602801 decreased cell proliferation and increased apoptosis in primary human VS cultures. The systemic administration of AS602801 in mice with human VS xenografts reduced tumor volume and cell proliferation. Last, the AS602801-treated Postn-Cre;Nf2flox/flox mice demonstrated decreased cell proliferation in glial cells in the dorsal root ganglia. However, AS602801 did not significantly delay hearing loss in Postn-Cre;Nf2flox/flox mice up to 3 months posttreatment. The data suggest that JNK inhibition with AS602801 suppresses growth of sporadic and neurofibromatosis type 2-associated VSs. As such, AS602801 is a potential systemic therapy for VS and warrants further investigation.

Modeling YAP fusions: a paradigm for investigating rare cancers?

Loss of the NF2 tumor suppressor gene is a common finding in meningiomas, and more recently YAP1 fusions have been found in a subset of pediatric NF2 wild-type meningiomas. In the previous issue of Genes & Development, Szulzewsky and colleagues (pp. 857-870) showed that TEAD-dependent YAP1 activity by either the loss of the NF2 gene or YAP1-MAML2 fusion is an oncogenic process promoting meningioma tumorigenesis. Furthermore, pharmacological inhibition of YAP1-TEAD resulted in antitumor activity in both YAP1 fusion-positive and NF2 mutant meningiomas. Together, these data indicate that disruption of the YAP1-TEAD interaction raises a potential therapeutic option for these tumors that requires future investigation.

Molecular Targets in Lung Cancer: Study of the Evolution of Biomarkers Associated with Treatment with Tyrosine Kinase Inhibitors-Has NF1 Tumor Suppressor a Key Role in Acquired Resistance?

Simple SummaryResistance to tyrosine kinase inhibitors in patients with EGFR-mutated non-small cell lung cancer is crucial in the development of the disease. Detecting the mechanisms of this resistance is fundamental in lung cancer research, so we evaluated the presence of EGFR mutations in circulating free DNA in plasma of patients with NSCLC under oncological treatment. We studied the role of EGFR and other driver mutations in their involvement in acquired resistance to treatment with EGFR-TKIs and we analyzed the role of liquid biopsy as a non-invasive diagnostic method. Our results showed that liquid biopsy is a very useful tool monitoring the evolution of the disease and the resistance to TKIs. The detection of other concomitant mutations in driver genes is also key in this regard, so we found that alterations in the NFI tumor suppressor gene could be playing a role in disease progression and resistance to targeted therapies.The application to clinical practice of liquid biopsy in patients with lung cancer has led to an advance in the diagnosis and monitoring of the disease. Detection of alterations in EGFR genes related to TKI treatment in EGFR-mutated non-small cell lung cancer patients is a routine method in pathology laboratories. The primary objective of this work was to analyze the presence of EGFR mutations in cfDNA of 86 patients with lung cancer undergoing oncological treatment related to response to treatment with TKIs. Secondarily, we evaluated the dynamics of EGFR mutations, the presence of the T790M alteration and its relationship with drug resistance and analyzed by NGS molecular alterations in cfDNA of patients with discordant progression. Our results demonstrate that understanding the mutational status of patients treated with TKIs over time is essential to monitor disease progression. In this context, liquid biopsy is a fundamental key. In addition, it is not only necessary to detect EGFR mutations, but also other concomitant mutations that would be influencing the development of the disease. In this sense, we have discovered that mutations in the NF1 tumor suppressor gene could be exerting an as yet unknown function in lung cancer.

Abstract 1131: Pharmacogenomic insight into targetable vulnerabilities and modifiers of response to MRTX1133 in KRASG12D-mutant models

Abstract The ability to effectively target mutated KRAS has remained elusive despite decades of research. Recently, the identification of selective KRASG12C inhibitors has provided an effective treatment option for patients harboring this particular mutation and has also provided insight toward targeting other KRAS mutants, including KRASG12D. MRTX1133 was identified via a structure-based drug design strategy as a potent, selective, and non-covalent KRASG12D inhibitor directed at the switch II binding pocket. MRTX1133 exhibited dose dependent KRAS pathway and tumor growth inhibition and demonstrated marked anti-tumor activity across a panel of models in vivo, including tumor regression &amp;gt;30% in 8 out of 11 pancreatic ductal adenocarcinoma (PDAC) models. While evaluation of MRTX1133 across a panel of cell and patient-derived xenograft models demonstrated strong single agent activity in the majority of models tested, a subset of models were less responsive. Focused sgRNA libraries targeting ~5,000 genes were tested in MRTX1133-anchored CRISPR/Cas9 screens in vitro and in vivo in PDAC and colorectal KRASG12D-mutant cell lines. Similar to what was seen in a targeted genetic screen with our selective KRASG12C inhibitor MRTX849, several genes that act either upstream or downstream of KRAS were depleted with MRTX1133 treatment which illuminate specific targetable vulnerabilities in the context of KRASG12D inhibition. sgRNAs targeting EGFR, PIK3CA, PTPN11, mTOR, and CDK2/4/6 were depleted in MRTX1133-treated (or vehicle-treated) cell lines or xenograft models, while hallmark tumor suppressor genes RB1, KEAP1, NF1 and PTEN were enriched. The enrichment of KEAP1 sgRNAs in PDAC models parallels findings with MRTX849 in preclinical models and is in line with emerging clinical data suggesting increased capacity to scavenge reactive oxygen species (ROS) may represent a mechanism of partial resistance to a non-covalent, non-electrophilic warhead-containing KRASG12D-selective inhibitor in PDAC. Treatment using small molecules targeting selected vulnerabilities in vitro and in vivo confirmed these genetic findings. Further evaluation of dependencies utilizing an integrated analysis of RNAseq data also revealed KRAS regulates and is critically dependent on pro-survival and cell cycle genes for cancer cell viability. These data lend further insight into tumor response to KRASG12D inhibition and provide key insight into the genes that mediate the mechanism of action of, as well as confer partial resistance to MRTX1133, and identify combination targets that can augment the anti-tumor effect of MRTX1133. Citation Format: Vickie Bowcut, Andrew Calinisan, David M. Briere, Lauren Hargis, Lars D. Engstrom, Jade Laguer, Darin Vanderpool, Xiaolun Wang, J David Lawson, Nicole Thomas, Robin Gunn, Christopher R. Smith, Julio Fernandez-Banet, Leo He, Adam Pavlicek, Lisa Rahbaek, Matthew A. Marx, Peter Olson, James G. Christensen, Jill Hallin. Pharmacogenomic insight into targetable vulnerabilities and modifiers of response to MRTX1133 in KRASG12D-mutant models [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 1131.

Aging accelerates while multiparity delays tumorigenesis in mouse models of high-grade serous carcinoma

ObjectivesThe “incessant ovulation” hypothesis links increased risk for tubo-ovarian high-grade serous carcinoma (HGSC) due to more ovulations and reduced risk conferred by pre-menopausal exposures like oral contraceptive use, multiparity, and breastfeeding. However, most women diagnosed with HGSC are postmenopausal, implying age is a major risk factor for HGSC. Our mouse model for HGSC, based on tamoxifen (TAM)-induced somatic inactivation of the Brca1, Trp53, Rb1, and Nf1 (BPRN) tumor suppressor genes in oviductal epithelium, recapitulates key genetic, histopathologic, and biological features of human HGSCs. We aimed to credential the model for future efforts to define biological and risk modification factors in HGSC pathogenesis. MethodsBPRN mice were treated with TAM to induce tumors at defined ages and parity status. ResultsBPRN mice aged 9-months prior to tumor induction had markedly shorter survival than 6–8 week old mice induced to form tumors (median 46.5 weeks versus 61.5 weeks, log-rank test P = 0.0006). No significant differences in cancer phenotypes were observed between multiparous versus nulliparous BPRN mice. However, using a modified tumor model with one wild-type Nf1 allele (BPRNfl/+), nulliparous mice had more advanced tumors than multiparous mice (Mantel-Haenszel Chi-square test of association, P = 0.01). ConclusionsOur findings show aging is associated with significantly shortened survival post tumor induction in the BRPN model and multiparity delays development and/or progression of HGSC in certain genetic contexts. The findings support relevance of our mouse model to gain mechanistic insights into how known factors exert their protective effects and to test novel approaches for HGSC prevention.

Selected Articles from This Issue

Despite previous assumptions that constitutively high Wnt signaling promotes colorectal cancer in each stage of disease, recent studies have demonstrated that reduced Wnt signaling is associated with colorectal cancer invasiveness and poor prognoses. However, little work has been done to elucidate how diminished Wnt signaling underlies aggressive colorectal cancer phenotypes. Chen and colleagues used genetic manipulation strategies and orthotopic mouse models to show that abrogating Wnt signaling increases colorectal cancer invasiveness and decreases immune responsiveness in vivo. Disrupting Wnt signaling by targeting Wnt coreceptor LDL receptor-related protein 6 (LRP6) with CRISPR/Cas9 or transducing a dominant negative version of Wnt transcriptional effector lymphoid enhancer binding factor 1 (LEF1) increases tumor submucosal invasion and dissemination in mice. Using RNA-Seq, the authors revealed that reducing Wnt signaling elevates expression of markers associated with stemness and a mesenchymal phenotype, while repressing expression of immune-stimulatory molecules and collagens. The authors used TCGA data to demonstrate that the low Wnt signaling expression profile corresponds with poor survival in colorectal cancer patients, underscoring the potential clinical relevance of dampened Wnt signaling in colorectal cancer progression.Cholangiocarcinoma (CCA) is an aggressive biliary tract cancer for which effective therapeutics are lacking. Prostaglandin E2 (PGE2)-mediated inflammation is a critical component of CCA carcinogenesis and progression. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) chemically modifies and inactivates PGE2, but its expression is often diminished in CCA. In their work, Zhang and colleagues leveraged public data to show that expression of histone methyltransferase G9a negatively correlates with 15-PGDH expression. The authors validated the G9a-15-PGDH relationship in a mouse model of CCA in which the Notch intracellular domain and constitutively active Akt are expressed via hydrodynamic injection of sleeping beauty transposase-based plasmids. shRNA-mediated G9a silencing increases 15-PGDH expression in CCA cell lines, limiting cell proliferation in vitro and tumor growth in vivo. ChIP assays demonstrated that G9a is recruited to the 15-PGDH promoter by the Myc/Max/E-box complex, which prevents signal transducer and activator of transcription 4 (STAT4) from binding the promoter and inducing 15-PGDH expression. The work presented elucidates a previously unknown mechanism underlying CCA development and progression and reveals a novel potential target for CCA therapeutic strategies.Neurofibromatosis type 2 is characterized by growth of benign nervous system tumors, such as schwannomas, which can lead to deafness, brain stem compression, and death. Neurofibromatosis type 2 is caused by mutations in tumor suppressor gene NF2. Previously, Cho and colleagues demonstrated that NF2 loss promotes elevated TβR1 signaling, resulting in phosphorylation and degradation of tumor suppressor Raf kinase inhibitor protein (RKIP). While TGF-β inhibitors halt schwannoma growth, they are not ideal therapeutics given schwannomas occur around adolescence and TGF-β is required for development. Here, Cho and colleagues developed a novel TβR1 inhibitor, Nf18001, that abrogates TβR1-mediated RKIP degradation while maintaining canonical TGF-β signaling. The authors used human and mouse schwannoma cell lines to demonstrate that Nf18001 disrupts TβR1-RKIP interactions to sustain RKIP expression and lower NF2-mutant cell viability while not influencing normal fibroblast survival. Nf18001 arrests cell cycle progression in schwannoma cells, and augments Schwann cell differentiation marker expression while diminishing expression of markers associated with cell stemness. Nf18001 also displayed efficacy in a schwannoma allograft mouse model, where treatment slowed tumor growth.The pro-tumorigenic role of signal transducer and activator of transcription 3 (STAT3) in multiple myeloma has been established, but therapeutically targeting STAT3 has proven challenging. Similarly, given its canonical role in DNA damage repair, checkpoint kinase 1 (Chk1) inhibition has been tested in anti-cancer therapeutic regimens, but with ambiguous results. In their study, Zhou and colleagues employed a gene expression array to demonstrate that Chk1 inhibition diminishes expression of oncogenic STAT3 target genes in multiple myeloma cells, suggesting Chk1 inhibition may also effectively inhibit STAT3 activity. Subsequent work showed that Chk1 directly binds to STAT3 and phosphorylates it at tyrosine 705, enabling STAT3 dimerization and DNA binding. Chk1 inhibition — pharmacologically and via shRNA silencing — diminishes STAT3 tyrosine 705 phosphorylation and inhibits STAT3 DNA binding, reducing expression of STAT3 transcriptional targets. Chk1 inhibition abrogates STAT3 tyrosine 705 phosphorylation in IL-6–dependent, -independent, and bortezomib-resistant cells, as well as in patient primary myeloma mononuclear cells and multiple myeloma cells implanted into mice, suggesting Chk1 inhibition may provide therapeutic efficacy against multiple myeloma through a STAT3-related mechanism.