Comprehensive establishment and characterization of orthoxenograft mouse models of malignant peripheral nerve sheath tumors for personalized medicine

Expanding a precision medicine platform for malignant peripheral nerve sheath tumors: New patient-derived orthotopic xenografts, cell lines and tumor entities

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft-tissue sarcomas with a poor survival rate, presenting either sporadically or in the context of neurofibromatosis type 1 (NF1). The histological diagnosis of MPNSTs can be challenging, with different tumors exhibiting great histological and marker expression overlap. This heterogeneity could be partly responsible for the observed disparity in treatment response due to the inherent diversity of the preclinical models used. For several years, our group has been generating a large patient-derived orthotopic xenograft (PDOX) MPNST platform for identifying new precision medicine treatments. Herein, we describe the expansion of this platform using six primary tumors clinically diagnosed as MPNSTs, from which we obtained six additional PDOX mouse models and three cell lines, thus generating three pairs of in vitro-in vivo models. We extensively characterized these tumors and derived preclinical models, including genomic, epigenomic, and histological analyses. Tumors were reclassified after these analyses: three remained as MPNSTs (two being classic MPNSTs), one was a melanoma, another was a neurotrophic tyrosine receptor kinase (NTRK)-rearranged spindle cell neoplasm, and, finally, the last was an unclassifiable tumor bearing neurofibromin-2 (NF2) inactivation, a neuroblastoma RAS viral oncogene homolog (NRAS) oncogenic mutation, and a SWI/SNF-related matrix-associated actin-dependent regulator of chromatin (SMARCA4) heterozygous truncated variant. New cell lines and PDOXs faithfully recapitulated histology, marker expression, and genomic characteristics of the primary tumors. The diversity in tumor identity and their specific associated genomic alterations impacted treatment responses obtained when we used the new cell lines for testing compounds against known altered pathways in MPNSTs. In summary, we present here an extension of our MPNST precision medicine platform, with new PDOXs and cell lines, including tumor entities confounded as MPNSTs in a real clinical scenario. This platform may constitute a useful tool for obtaining correct preclinical information to guide MPNST clinical trials.

Construction of a two-gene prognostic model related to ferroptosis in renal cell carcinoma

BACKGROUND

Renal cell carcinoma (RCC) is a common and aggressive tumor. A newly discovered form of programmed cell death, ferroptosis, plays an important role in tumor development and progression. However, a clear prognostic correlation between Ferroptosis-related genes (FRGs) and RCC has not yet been established. In this study, prognostic markers associated with FRGs were investigated to improve the therapeutic, diagnostic, and preventive strategies available to patients with renal cancer.

METHODS

The present study analyzed the predictive value of 23 FRGs in RCC through bioinformatics techniques, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) tools, Kaplan-Meier survival analysis, Cox regression modeling, tumor mutational burden (TMB), CIBERSORT, and half maximal inhibitory concentration (IC50) difference analysis.

RESULTS

We screened FRGs by differentially expressed genes (DEGs) and overall survival (OS). Four candidate genes were obtained by hybridization. Then, we constructed a two-gene prognostic signature (NCOA4 and CDKN1A) via univariate Cox regression and multivariate stepwise Cox regression, which classified RCC patients into high- and low-risk groups, and patients in the high-risk group were found to have worse OS and progression-free survival (PFS). We also found that patients with higher TNM stage, T stage, and M stage had higher risk scores than those with lower TNM stage, T stage, and M stage (P<0.05). Males had higher risk scores than females. This signature was identified as an independent prognostic indicator for RCC. These results were validated in both the test cohort and the entire cohort. In addition, we also constructed a nomogram that predicted the OS in RCC patients, the consistency index (C-index) of the nomogram was 0.731 [95% confidence interval (CI): 0.672-0.790], the areas under the receiver operating characteristic (ROC) curves (AUCs) were 0.728, 0.704, and 0.898 at 1-, 3-, and 5-year, respectively, which shows that nomogram has good prediction ability. and we also analyzed the immune status and drug sensitivity between the high- and low-risk groups.

CONCLUSIONS

We constructed a prognostic model associated with ferroptosis, which may provide clinicians with a reliable predictive assessment tool and offer new perspectives for the future clinical management of RCC.

Deep genomic analysis of malignant peripheral nerve sheath tumor cell lines challenges current malignant peripheral nerve sheath tumor diagnosis

Malignant peripheral nerve sheath tumors (MPNSTs) are soft-tissue sarcomas of the peripheral nervous system that develop either sporadically or in the context of neurofibromatosis type 1 (NF1). MPNST diagnosis can be challenging and treatment outcomes are poor. We present here a resource consisting of the genomic characterization of 9 widely used human MPNST cell lines for their use in translational research. NF1-related cell lines recapitulated primary MPNST copy number profiles, exhibited NF1, CDKN2A, and SUZ12/EED tumor suppressor gene (TSG) inactivation, and presented no gain-of-function mutations. In contrast, sporadic cell lines collectively displayed different TSG inactivation patterns and presented kinase-activating mutations, fusion genes, altered mutational frequencies and COSMIC signatures, and different methylome-based classifications. Cell lines re-classified as melanomas and other sarcomas exhibited a different drug-treatment response. Deep genomic analysis, methylome-based classification, and cell-identity marker expression, challenged the identity of common MPNST cell lines, opening an opportunity to revise MPNST differential diagnosis.

Preclinical Assessment of MEK Inhibitors for Malignant Peripheral Nerve Sheath Tumors Reveals Differences in Efficacy and Adaptive Response

Malignant peripheral nerve sheath tumors (MPNSTs) are rare soft-tissue sarcomas refractory to standard therapies. Inactivation of NF1 and subsequent upregulation of RAS/RAF/MEK/ERK signaling exist in the majority of MPNSTs. However, the lack of preclinical assessment of MEK inhibitors in MPNSTs hinders the clinical application as well as the development of combination therapy. To guide further clinical studies, we evaluated different MEK inhibitors in terms of efficacy, safety, and mechanism of adaptive response in treating MPNSTs. Using a MPNST tissue microarray, we found that p-ERK could serve as a biomarker for predicting the prognosis of MPNST patients as well as an effective therapeutic target. Through in vitro and in vivo experiments, we identified trametinib as the most potent MEK inhibitor for the treatment of MPNSTs. Mechanistically, reduced reactivation of the MAPK pathway and compensatory activation of the parallel pathways contributed to better efficacy. Our results provide a basis for the further clinical application of MEK inhibitors as single agents or combinational therapies.

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

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

Malignant peripheral nerve sheath tumor: models, biology, and translation

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, invasive cancer that comprise around 10% of all soft tissue sarcomas and develop in about 8-13% of patients with Neurofibromatosis Type 1. They are associated with poor prognosis and are the leading cause of mortality in NF1 patients. MPNSTs can also develop sporadically or following exposure to radiation. There is currently no effective targeted therapy to treat MPNSTs and surgical removal remains the mainstay treatment. Unfortunately, surgery is not always possible due to the size and location of the tumor, thus, a better understanding of MPNST initiation and development is required to design novel therapeutics. Here, we provide an overview of MPNST biology and genetics, discuss findings regarding the developmental origin of MPNST, and summarize the various model systems employed to study MPNST. Finally, we discuss current management strategies for MPNST, as well as recent developments in translating basic research findings into potential therapies.

Modeling iPSC-derived human neurofibroma-like tumors in mice uncovers the heterogeneity of Schwann cells within plexiform neurofibromas

Plexiform neurofibromas (pNFs) are developmental tumors that appear in neurofibromatosis type 1 individuals, constituting a major source of morbidity and potentially transforming into a highly metastatic sarcoma (MPNST). pNFs arise after NF1 inactivation in a cell of the neural crest (NC)-Schwann cell (SC) lineage. Here, we develop an iPSC-based NC-SC in vitro differentiation system and construct a lineage expression roadmap for the analysis of different 2D and 3D NF models. The best model consists of generating heterotypic spheroids (neurofibromaspheres) composed of iPSC-derived differentiating NF1(-/-) SCs and NF1(+/-) pNF-derived fibroblasts (Fbs). Neurofibromaspheres form by maintaining highly proliferative NF1(-/-) cells committed to the NC-SC axis due to SC-SC and SC-Fb interactions, resulting in SC linage cells at different maturation points. Upon engraftment on the mouse sciatic nerve, neurofibromaspheres consistently generate human NF-like tumors. Analysis of expression roadmap genes in human pNF single-cell RNA-seq data uncovers the presence of SC subpopulations at distinct differentiation states.

Toward Understanding the Mechanisms of Malignant Peripheral Nerve Sheath Tumor Development

Malignant peripheral nerve sheath tumors (MPNSTs) originate from the neural crest lineage and are associated with the neurofibromatosis type I syndrome. MPNST is an unmet clinical need. In this review article, we summarize the knowledge and discuss research perspectives related to (1) the natural history of MPNST development; (2) the mouse models recapitulating the progression from precursor lesions to MPNST; (3) the role of the tumor microenvironment in MPNST development, and (4) the signaling pathways linked to MPNST development.

Chromosomal translocations inactivating CDKN2A support a single path for malignant peripheral nerve sheath tumor initiation

Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas with poor prognosis, developing either sporadically or in persons with neurofibromatosis type 1 (NF1). Loss of CDKN2A/B is an important early event in MPNST progression. However, many reported MPNSTs exhibit partial or no inactivation of CDKN2A/B, raising the question of whether there is more than one molecular path for MPNST initiation. We present here a comprehensive genomic analysis of MPNST cell lines and tumors to explore in depth the status of CDKN2A. After accounting for CDKN2A deletions and point mutations, we uncovered a previously unnoticed high frequency of chromosomal translocations involving CDKN2A in both MPNST cell lines and primary tumors. Most identified translocation breakpoints were validated by PCR amplification and Sanger sequencing. Many breakpoints clustered in an intronic 500 bp hotspot region adjacent to CDKN2A exon 2. We demonstrate the bi-allelic inactivation of CDKN2A in all tumors (n = 15) and cell lines (n = 8) analyzed, supporting a single molecular path for MPNST initiation in both sporadic and NF1-related MPNSTs. This general CDKN2A inactivation in MPNSTs has implications for MPNST diagnostics and treatment. Our findings might be relevant for other tumor types with high frequencies of CDKN2A inactivation.

Modeling tumors of the peripheral nervous system associated with Neurofibromatosis type 1: Reprogramming plexiform neurofibroma cells

Plexiform neurofibromas (pNFs) are benign tumors of the peripheral nervous system (PNS) that can progress towards a deadly soft tissue sarcoma termed malignant peripheral nerve sheath tumor (MPNST). pNFs appear during development in the context of the genetic disease Neurofibromatosis type 1 (NF1) due to the complete loss of the NF1 tumor suppressor gene in a cell of the neural crest (NC) - Schwann cell (SC) axis of differentiation. NF1(-/-) cells from pNFs can be reprogrammed into induced pluripotent stem cells (iPSCs) that exhibit an increased proliferation rate and maintain full iPSC properties. Efficient protocols for iPSC differentiation towards NC and SC exist and thus NC cells can be efficiently obtained from NF1(-/-) iPSCs and further differentiated towards SCs. In this review, we will focus on the iPSC modeling of pNFs, including the reprogramming of primary pNF-derived cells, the properties of pNF-derived iPSCs, the capacity to differentiate towards the NC-SC lineage, and how well iPSC-derived NF1(-/-) SC spheroids recapitulate pNF-derived primary SCs. The potential uses of NF1(-/-) iPSCs in pNF modeling and a future outlook are discussed.

Use of patient derived orthotopic xenograft models for real-time therapy guidance in a pediatric sporadic malignant peripheral nerve sheath tumor

Background:

The aim of this study was to test the feasibility and utility of developing patient-derived orthotopic xenograft (PDOX) models for patients with malignant peripheral nerve sheath tumors (MPNSTs) to aid therapeutic interventions in real time.

Patient & Methods:

A sporadic relapsed MPNST developed in a 14-year-old boy was engrafted in mice, generating a PDOX model for use in co-clinical trials after informed consent. SNP-array and exome sequencing was performed on the relapsed tumor. Genomics, drug availability, and published literature guided PDOX treatments.

Results:

A MPNST PDOX model was generated and expanded. Analysis of the patient’s relapsed tumor revealed mutations in the MAPK1, EED, and CDK2NA/B genes. First, the PDOX model was treated with the same therapeutic regimen as received by the patient (everolimus and trametinib); after observing partial response, tumors were left to regrow. Regrown tumors were treated based on mutations (palbociclib and JQ1), drug availability, and published literature (nab-paclitaxel; bevacizumab; sorafenib plus doxorubicin; and gemcitabine plus docetaxel). The patient had a lung metastatic relapse and was treated according to PDOX results, first with nab-paclitaxel, second with sorafenib plus doxorubicin after progression, although a complete response was not achieved and multiple metastasectomies were performed. The patient is currently disease free 46 months after first relapse.

Conclusion:

Our results indicate the feasibility of generating MPNST-PDOX and genomic characterization to guide treatment in real time. Although the treatment responses observed in our model did not fully recapitulate the patient’s response, this pilot study identify key aspects to improve our co-clinical testing approach in real time.

New Model Systems and the Development of Targeted Therapies for the Treatment of Neurofibromatosis Type 1-Associated Malignant Peripheral Nerve Sheath Tumors

Neurofibromatosis Type 1 (NF1) is a common genetic disorder and cancer predisposition syndrome (1:3000 births) caused by mutations in the tumor suppressor gene NF1. NF1 encodes neurofibromin, a negative regulator of the Ras signaling pathway. Individuals with NF1 often develop benign tumors of the peripheral nervous system (neurofibromas), originating from the Schwann cell linage, some of which progress further to malignant peripheral nerve sheath tumors (MPNSTs). Treatment options for neurofibromas and MPNSTs are extremely limited, relying largely on surgical resection and cytotoxic chemotherapy. Identification of novel therapeutic targets in both benign neurofibromas and MPNSTs is critical for improved patient outcomes and quality of life. Recent clinical trials conducted in patients with NF1 for the treatment of symptomatic plexiform neurofibromas using inhibitors of the mitogen-activated protein kinase (MEK) have shown very promising results. However, MEK inhibitors do not work in all patients and have significant side effects. In addition, preliminary evidence suggests single agent use of MEK inhibitors for MPNST treatment will fail. Here, we describe the preclinical efforts that led to the identification of MEK inhibitors as promising therapeutics for the treatment of NF1-related neoplasia and possible reasons they lack single agent efficacy in the treatment of MPNSTs. In addition, we describe work to find targets other than MEK for treatment of MPNST. These have come from studies of RAS biochemistry, in vitro drug screening, forward genetic screens for Schwann cell tumors, and synthetic lethal screens in cells with oncogenic RAS gene mutations. Lastly, we discuss new approaches to exploit drug screening and synthetic lethality with NF1 loss of function mutations in human Schwann cells using CRISPR/Cas9 technology.

The Role of Polycomb Repressive Complex in Malignant Peripheral Nerve Sheath Tumor

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft tissue sarcomas that can arise most frequently in patients with neurofibromatosis type 1 (NF1). Despite an increasing understanding of the molecular mechanisms that underlie these tumors, there remains limited therapeutic options for this aggressive disease. One potentially critical finding is that a significant proportion of MPNSTs exhibit recurrent mutations in the genes EED or SUZ12, which are key components of the polycomb repressive complex 2 (PRC2). Tumors harboring these genetic lesions lose the marker of transcriptional repression, trimethylation of lysine residue 27 on histone H3 (H3K27me3) and have dysregulated oncogenic signaling. Given the recurrence of PRC2 alterations, intensive research efforts are now underway with a focus on detailing the epigenetic and transcriptomic consequences of PRC2 loss as well as development of novel therapeutic strategies for targeting these lesions. In this review article, we will summarize the recent findings of PRC2 in MPNST tumorigenesis, including highlighting the functions of PRC2 in normal Schwann cell development and nerve injury repair, as well as provide commentary on the potential therapeutic vulnerabilities of a PRC2 deficient tumor cell.

Cell-type dependent enhancer binding of the EWS/ATF1 fusion gene in clear cell sarcomas

Clear cell sarcoma (CCS) is a rare soft tissue sarcoma caused by the EWS/ATF1 fusion gene. Here, we established induced pluripotent stem cells (iPSCs) from EWS/ATF1-controllable murine CCS cells harboring sarcoma-associated genetic abnormalities. Sarcoma-iPSC mice develop secondary sarcomas immediately after EWS/ATF1 induction, but only in soft tissue. EWS/ATF1 expression induces oncogene-induced senescence in most cell types in sarcoma-iPSC mice but prevents it in sarcoma cells. We identify Tppp3-expressing cells in peripheral nerves as a cell-of-origin for these sarcomas. We show cell type-specific recruitment of EWS/ATF1 to enhancer regions in CCS cells. Finally, epigenetic silencing at these enhancers induces senescence and inhibits CCS cell growth through altered EWS/ATF1 binding. Together, we propose that distinct responses to premature senescence are the basis for the cell type-specificity of cancer development.

The EWS-ATF1 fusion gene causes clear cell sarcoma (CCS). Here, the authors show that the downstream effects of EWS-ATF1 expression are strictly context dependent, and reveal the cell of origin for CCS to be Tppp3-expressing cells in peripheral nerves.

Establishment and Characterization of Histologically and Molecularly Stable Soft-tissue Sarcoma Xenograft Models for Biological Studies and Preclinical Drug Testing

Soft-tissue sarcomas (STS) represent a heterogeneous group of rare, malignant tumors of mesenchymal origin. Reliable in vivo sarcoma research models are scarce. We aimed to establish and characterize histologically and molecularly stable patient-derived xenograft (PDX) models from a broad variety of STS subtypes. A total of 188 fresh tumor samples from consenting patients with localized or advanced STS were transplanted subcutaneously in NMRI-nu/nu-immunodeficient mice. Once tumor growth was observed, the material was passaged to a next generation of mice. A patient-derived tumor sample was considered "successfully engrafted" whenever the sample was transplanted to passage 1. A PDX model was considered "established" when observing stable morphologic and molecular features for at least two passages. With every passage, histologic and molecular analyses were performed. Specific genomic alterations and copy-number profile were assessed by FISH and low coverage whole-genome sequencing. The tumor engraftment rate was 32% (61/188) and 188 patient samples generated a total of 32 PDX models, including seven models of myxofibrosarcoma, five dedifferentiated liposarcoma, five leiomyosarcoma, three undifferentiated pleomorphic sarcoma, two malignant peripheral nerve sheet tumor models, and single models of synovial sarcoma and some other (ultra)rare subtypes. Seventeen additional models are in early stages of engraftment (passage 1-2). Histopathologic and molecular features were compared with the original donor tumor and were stable throughout passaging. The platform is used for studies on sarcoma biology and suited for in vivo preclinical drug testing as illustrated by a number of completed and ongoing laboratory studies.

Targeted Inhibition of the Dual Specificity Phosphatases DUSP1 and DUSP6 Suppress MPNST Growth via JNK

PURPOSE

In neurofibromatosis type 1 (NF1) and in highly aggressive malignant peripheral nerve sheath tumors (MPNSTs), constitutively active RAS-GTP and increased MAPK signaling are important in tumorigenesis. Dual specificity phosphatases (DUSPs) are negative regulators of MAPK signaling that dephosphorylate p38, JNK, and ERK in different settings. Although often acting as tumor suppressors, DUSPs may also act as oncogenes, helping tumor cells adapt to high levels of MAPK signaling. We hypothesized that inhibiting DUSPs might be selectively toxic to cells from NF1-driven tumors.

EXPERIMENTAL DESIGN

We examined DUSP gene and protein expression in neurofibroma and MPNSTs. We used small hairpin RNA (shRNA) to knock down DUSP1 and DUSP6 to evaluate cell growth, downstream MAPK signaling, and mechanisms of action. We evaluated the DUSP inhibitor, (E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one (BCI), in MPNST cell lines and in cell-line and patient-derived MPNST xenografts.

RESULTS

DUSP1 and DUSP6 are expressed in NF1-deleted tumors. Knockdown of DUSP1 and DUSP6, alone or in combination, reduced MPNST cell growth and led to ERK and JNK hyperactivation increasing downstream TP53 and p-ATM. The DUSP inhibitor, BCI, diminished the survival of NF1-deleted Schwann cells and MPNST cell lines through activation of JNK. In vivo, treatment of an established cell-line xenograft or a novel patient-derived xenograft (PDX) of MPNSTs with BCI increased ERK and JNK activation, caused tumor necrosis and fibrosis, and reduced tumor volume in one model.

CONCLUSIONS

Targeting DUSP1 and DUSP6 genetically or with BCI effectively inhibits MPNST cell growth and promotes cell death, in vitro and in xenograft models. The data support further investigation of DUSP inhibition in MPNSTs.

MLN8237 treatment in an orthoxenograft murine model for malignant peripheral nerve sheath tumors

OBJECTIVE

Malignant peripheral nerve sheath tumors (MPNSTs) are soft-tissue sarcomas arising from peripheral nerves. MPNSTs have increased expression of the oncogene aurora kinase A, leading to enhanced cellular proliferation. This makes them extremely aggressive with high potential for metastasis and a devastating prognosis; 5-year survival estimates range from a dismal 15% to 60%. MPNSTs are currently treated with resection (sometimes requiring limb amputation) in combination with chemoradiation, both of which demonstrate limited effectiveness. The authors present the results of immunohistochemical, in vitro, and in vivo analyses of MLN8237 for the treatment of MPNSTs in an orthoxenograft murine model.

METHODS

Immunohistochemistry was performed on tumor sections to confirm the increased expression of aurora kinase A. Cytotoxicity analysis was then performed on an MPNST cell line (STS26T) to assess the efficacy of MLN8237 in vitro. A murine orthoxenograft MPNST model transfected to express luciferase was then developed to assess the efficacy of aurora kinase A inhibition in the treatment of MPNSTs in vivo. Mice with confirmed tumor on in vivo imaging were divided into 3 groups: 1) controls, 2) mice treated with MLN8237, and 3) mice treated with doxorubicin/ifosfamide. Treatment was carried out for 32 days, with imaging performed at weekly intervals until postinjection day 42. Average bioluminescence among groups was compared at weekly intervals using 1-way ANOVA. A survival analysis was performed using Kaplan-Meier curves.

RESULTS

Immunohistochemical analysis showed robust expression of aurora kinase A in tumor cells. Cytotoxicity analysis revealed STS26T susceptibility to MLN8237 in vitro. The group receiving treatment with MLN8237 showed a statistically significant difference in tumor size compared with the control group starting at postinjection day 21 and persisting until the end of the study. The MLN8237 group also showed decreased tumor size compared with the doxorubicin/ifosfamide group at the conclusion of the study (p = 0.036). Survival analysis revealed a significantly increased median survival in the MLN8237 group (83 days) compared with both the control (64 days) and doxorubicin/ifosfamide (67 days) groups. A hazard ratio comparing the 2 treatment groups showed a decreased hazard rate in the MLN8237 group compared with the doxorubicin/ifosfamide group (HR 2.945; p = 0.0134).

CONCLUSIONS

The results of this study demonstrate that MLN8237 is superior to combination treatment with doxorubicin/ifosfamide in a preclinical orthoxenograft murine model. These data have major implications for the future of MPNST research by providing a robust murine model as well as providing evidence that MLN8237 may be an effective treatment for MPNSTs.

Analysis of intratumor heterogeneity in Neurofibromatosis type 1 plexiform neurofibromas and neurofibromas with atypical features: Correlating histological and genomic findings

Plexiform neurofibromas (PNFs) are benign peripheral nerve sheath tumors involving large nerves present in 30%-50% Neurofibromatosis type 1 (NF1) patients. Atypical neurofibromas (ANF) are distinct nodular lesions with atypical features on histology that arise from PNFs. The risk and timeline of malignant transformation in ANF is difficult to assess. A recent NIH workshop has stratified ANFs and separated a subgroup with multiple atypical features and higher risk of malignant transformation termed atypical neurofibromatous neoplasms with uncertain biological potential (ANNUBP). We performed an analysis of intratumor heterogeneity on eight PNFs to link histological and genomic findings. Tumors were homogeneous although histological and molecular heterogeneity was identified. All tumors were 2n, almost mutation-free and had a clonal NF1(-/-) origin. Two ANFs from the same patient showed atypical features on histology and deletions of CDKN2A/B. One of the ANFs exhibited different areas in which the degree of histological atypia correlated with the heterozygous or homozygous loss of the CDKN2A/B loci. CDKN2A/B deletions in different areas originated independently. Results may indicate that loss of a single CDKN2A/B copy in NF1(-/-) cells is sufficient to start ANF development and that total inactivation of both copies of CDKN2A/B is necessary to form an ANNUBP.

Emerging therapeutic targets for neurofibromatosis type 1

INTRODUCTION

Neurofibromatosis type 1 (NF1) is an autosomal dominantly inherited tumor predisposition syndrome with an incidence of one in 3000-4000 individuals with no currently effective therapies. The NF1 gene encodes neurofibromin, which functions as a negative regulator of RAS. NF1 is a chronic multisystem disorder affecting many different tissues. Due to cell-specific complexities of RAS signaling, therapeutic approaches for NF1 will likely have to focus on a particular tissue and manifestation of the disease. Areas covered: We discuss the multisystem nature of NF1 and the signaling pathways affected due to neurofibromin deficiency. We explore the cell-/tissue-specific molecular and cellular consequences of aberrant RAS signaling in NF1 and speculate on their potential as therapeutic targets for the disease. We discuss recent genomic, transcriptomic, and proteomic studies combined with molecular, cellular, and biochemical analyses which have identified several targets for specific NF1 manifestations. We also consider the possibility of patient-specific gene therapy approaches for NF1. Expert opinion: The emergence of NF1 genotype-phenotype correlations, characterization of cell-specific signaling pathways affected in NF1, identification of novel biomarkers, and the development of sophisticated animal models accurately reflecting human pathology will continue to provide opportunities to develop therapeutic approaches to combat this multisystem disorder.

Genomic Status of MET Potentiates Sensitivity to MET and MEK Inhibition in NF1-Related Malignant Peripheral Nerve Sheath Tumors

Malignant peripheral nerve sheath tumors (MPNST) are highly resistant sarcomas that occur in up to 13% of individuals with neurofibromatosis type I (NF1). Genomic analysis of longitudinally collected tumor samples in a case of MPNST disease progression revealed early hemizygous microdeletions in NF1 and TP53, with progressive amplifications of MET, HGF, and EGFR To examine the role of MET in MPNST progression, we developed mice with enhanced MET expression and Nf1 ablation (Nf1^fl/ko;lox-stop-loxMET^tg/+;Plp-creERT^tg/+ ; referred to as NF1-MET). NF1-MET mice express a robust MPNST phenotype in the absence of additional mutations. A comparison of NF1-MET MPNSTs with MPNSTs derived from Nf1^ko/+;p53^R172H;Plp-creERT^tg/+ (NF1-P53) and Nf1^ko/+;Plp-creERT^tg/+ (NF1) mice revealed unique Met, Ras, and PI3K signaling patterns. NF1-MET MPNSTs were uniformly sensitive to the highly selective MET inhibitor, capmatinib, whereas a heterogeneous response to MET inhibition was observed in NF1-P53 and NF1 MPNSTs. Combination therapy of capmatinib and the MEK inhibitor trametinib resulted in reduced response variability, enhanced suppression of tumor growth, and suppressed RAS/ERK and PI3K/AKT signaling. These results highlight the influence of concurrent genomic alterations on RAS effector signaling and therapy response to tyrosine kinase inhibitors. Moreover, these findings expand our current understanding of the role of MET signaling in MPNST progression and identify a potential therapeutic niche for NF1-related MPNSTs.Significance: Longitudinal genomic analysis reveals a positive selection for MET and HGF copy number gain early in malignant peripheral nerve sheath tumor progression. Cancer Res; 78(13); 3672-87. ©2018 AACR.

Animal models for cancer cachexia

PURPOSE OF REVIEW

Cancer cachexia is a frequent syndrome that affects patient quality of life, anticancer treatment effectiveness, and overall survival. The lack of anticancer cachexia therapies likely relies on the complexity of the syndrome that renders difficult to design appropriate clinical trials and, conversely, on the insufficient knowledge of the underlying pathogenetic mechanisms. The aim of this review is to collect the most relevant latest information regarding cancer cachexia with a special focus on the experimental systems adopted for modeling the disease in translational studies.

RECENT FINDINGS

The scenario of preclinical models for the study of cancer cachexia is not static and is rapidly evolving in parallel with new prospective treatment options. The well established syngeneic models using rodent cancer cells injected ectopically are now used alongside new ones featuring orthotopic injection, human cancer cell or patient-derived xenograft, or spontaneous tumors in genetically engineered mice.

SUMMARY

The use of more complex animal models that better resemble cancer cachexia, ideally including also the administration of chemotherapy, will expand the understanding of the underlying mechanisms and will allow a more reliable evaluation of prospective drugs for translational purposes.

Dual mTORC1/2 inhibition induces anti-proliferative effect in NF1-associated plexiform neurofibroma and malignant peripheral nerve sheath tumor cells

Approximately 30-50% of individuals with Neurofibromatosis type 1 develop benign peripheral nerve sheath tumors, called plexiform neurofibromas (PNFs). PNFs can undergo malignant transformation to highly metastatic malignant peripheral nerve sheath tumors (MPNSTs) in 5-10% of NF1 patients, with poor prognosis. No effective systemic therapy is currently available for unresectable tumors. In tumors, the NF1 gene deficiency leads to Ras hyperactivation causing the subsequent activation of the AKT/mTOR and Raf/MEK/ERK pathways and inducing multiple cellular responses including cell proliferation. In this study, three NF1-null MPNST-derived cell lines (90-8, 88-14 and 96-2), STS26T sporadic MPNST cell line and PNF-derived primary Schwann cells were used to test responses to AZD8055, an ATP-competitive “active-site” mTOR inhibitor. In contrast to rapamycin treatment which only partially affected mTORC1 signaling, AZD8055 induced a strong inhibition of mTORC1 and mTORC2 signaling in MPNST-derived cell lines and PNF-derived Schwann cells. AZD8055 induced full blockade of mTORC1 leading to an efficient decrease of global protein synthesis. A higher cytotoxic effect was observed with AZD8055 compared to rapamycin in the NF1-null MPNST-derived cell lines with IC50 ranging from 70 to 140 nM and antiproliferative effect was confirmed in PNF-derived Schwann cells. Cell migration was impaired by AZD8055 treatment and cell cycle analysis showed a G0/G1 arrest. Combined effects of AZD8055 and PD0325901 MEK inhibitor as well as BRD4 (BromoDomain-containing protein 4) inhibitors showed a synergistic antiproliferative effect. These data suggest that NF1-associated peripheral nerve sheath tumors are an ideal target for AZD8055 as a single molecule or in combined therapies.

Drug sensitivity and resistance testing identifies PLK1 inhibitors and gemcitabine as potent drugs for malignant peripheral nerve sheath tumors

Patients with malignant peripheral nerve sheath tumor (MPNST), a rare soft tissue cancer associated with loss of the tumor suppressor neurofibromin (NF1), have poor prognosis and typically respond poorly to adjuvant therapy. We evaluated the effect of 299 clinical and investigational compounds on seven MPNST cell lines, two primary cultures of human Schwann cells, and five normal bone marrow aspirates, to identify potent drugs for MPNST treatment with few side effects. Top hits included Polo-like kinase 1 (PLK1) inhibitors (volasertib and BI2536) and the fluoronucleoside gemcitabine, which were validated in orthogonal assays measuring viability, cytotoxicity, and apoptosis. DNA copy number, gene expression, and protein expression were determined for the cell lines to assess pharmacogenomic relationships. MPNST cells were more sensitive to BI2536 and gemcitabine compared to a reference set of 94 cancer cell lines. PLK1, RRM1, and RRM2 mRNA levels were increased in MPNST compared to benign neurofibroma tissue, and the protein level of PLK1 was increased in the MPNST cell lines compared to normal Schwann cells, indicating an increased dependence on these drug targets in malignant cells. Furthermore, we observed an association between increased mRNA expression of PLK1, RRM1, and RRM2 in patient samples and worse disease outcome, suggesting a selective benefit from inhibition of these genes in the most aggressive tumors.

The promise of signal transduction in genetically driven sarcomas of the nerve

Neurofibromatosis type 1 (NF1) is an autosomal dominant tumor predisposition syndrome. Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas arising from peripheral nerve sheaths, and the most commonly lethal feature associated with NF1. The hallmark of NF1 and NF1-related MPNST is the loss of neurofibromin expression. Loss of neurofibromin is considered a tumor-promoting event, and leads to constitutive activation of RAS and its downstream effectors. However, RAS activation alone is not sufficient for MPNST formation, and additional tumor suppressors and signaling pathways have been implicated in tumorigenesis of MPNST. Taking advantage of the rapid development of novel therapeutics targeting key molecular pathways across all cancer types, the best-in-class modulators of these pathways can be assessed in pre-clinical models and translated into clinical trials for patients with MPNST. Here, we describe the genetic changes and molecular pathways that drive MPNST formation and highlight the promise of signal transduction to identify therapies that may treat these tumors more effectively.

Clinical Factors That Affect the Establishment of Soft Tissue Sarcoma Patient-Derived Orthotopic Xenografts: A University of California, Los Angeles, Sarcoma Program Prospective Clinical Trial

Purpose

Given the diverse and aggressive nature of soft tissue sarcomas (STSs), a need exists for more-precise therapy. Patient-derived orthotopic xenografts (PDOXs) provide a unique platform for personalized treatment. Thus, identification of patient and treatment factors that predict PDOX establishment is important. This study assessed the feasibility of incorporating PDOXs into the clinical setting and identifying factors associated with PDOX establishment.

Patients and Methods

From May 2015 to May 2016, 107 patients with biopsy-proven or potential STS were enrolled. Tumor samples were obtained intraoperatively and orthotopically implanted into nude mice in the corresponding anatomic location. PDOXs were considered established after engraftment and serial passage. Factors associated with establishment were analyzed by logistic regression and time to establishment by time-to-event analysis.

Results

Only high-grade tumors established (32 of 72 [44.4%]). The establishment rate (ER) varied by neoadjuvant therapy and treatment response, with the highest ER among untreated high-grade tumors (26 of 42 [61.9%]). Tumors exposed to radiation preoperatively did not establish (zero of 11 [0%]), and tumors exposed to neoadjuvant chemotherapy had a lower ER(31.9%) than untreated tumors. Only STSs with minimal pathologic response to neoadjuvant treatment (≤ 30%) established a PDOX (six of 18 [33.3%]). Median establishment time was 54 days, which varied by neoadjuvant therapy but was not statistically significant (P = .180).

Conclusion

To our knowledge, in the largest STS PDOX study to date, we demonstrate a 62% ER among untreated high-grade tumors with a median establishment time of 54 days. Neoadjuvant therapy, particularly radiation, and pathologic response to treatment were associated with a reduced rate of PDOX establishment.

Neurofibromatosis Type 1-Associated MPNST State of the Science: Outlining a Research Agenda for the Future

Malignant peripheral nerve sheath tumor (MPNST) is an aggressive soft tissue sarcoma for which the only effective therapy is surgery. In 2016, an international meeting entitled "MPNST State of the Science: Outlining a Research Agenda for the Future" was convened to establish short- and long-term research priorities. Key recommendations included the: 1) development of standardized, cost-efficient fluorodeoxyglucose positron emission tomography and whole-body magnetic resonance imaging guidelines to evaluate masses concerning for MPNST; 2) development of better understanding and histologic criteria for the transformation of a plexiform neurofibroma to MPNST; 3) establishment of a centralized database to collect genetic, genomic, histologic, immunohistochemical, molecular, radiographic, treatment, and related clinical data from MPNST subspecialty centers in a standardized manner; 4) creation of accurate mouse models to study the plexiform neurofibroma-to-MPNST transition, MPNST metastasis, and drug resistance; 5) use of trial designs that minimize regulatory requirements, maximize availability to patients, consider novel secondary end points, and study patients with newly diagnosed disease. Lastly, in order to minimize delays in developing novel therapies and promote the most efficient use of research resources and patient samples, data sharing should be incentivized.

Establishment of patient derived xenografts as functional testing of lung cancer aggressiveness

Despite many years of research efforts, lung cancer still remains the leading cause of cancer deaths worldwide. Objective of this study was to set up a platform of non-small cell lung cancer patient derived xenografts (PDXs) faithfully representing primary tumour characteristics and offering a unique tool for studying effectiveness of therapies at a preclinical level. We established 38 PDXs with a successful take rate of 39.2%. All models closely mirrored parental tumour characteristics although a selective pressure for solid patterns, vimentin expression and EMT was observed in several models. An increased grafting rate for tumours derived from patients with worse outcome (p = 0.006), higher stage (p = 0.038) and higher CD133⁺/CXCR4⁺/EpCAM⁻ stem cell content (p = 0.019) was observed whereas a trend towards an association with SUV_max higher than 8 (p = 0.084) was detected. Kaplan Meier analyses showed a significantly worse (p = 0.0008) overall survival at 5 years in patients with grafted vs not grafted PDXs also after adjusting for tumour stage. Moreover, for 63.2% models, grafting was reached before clinical recurrence occurred. Our findings strengthen the relevance of PDXs as useful preclinical models closely reflecting parental patients tumours and highlight PDXs establishment as a functional testing of lung cancer aggressiveness and personalized therapies.

Gene signature associated with benign neurofibroma transformation to malignant peripheral nerve sheath tumors

Benign neurofibromas, the main phenotypic manifestations of the rare neurological disorder neurofibromatosis type 1, degenerate to malignant tumors associated to poor prognosis in about 10% of patients. Despite efforts in the field of (epi)genomics, the lack of prognostic biomarkers with which to predict disease evolution frustrates the adoption of appropriate early therapeutic measures. To identify potential biomarkers of malignant neurofibroma transformation, we integrated four human experimental studies and one for mouse, using a gene score-based meta-analysis method, from which we obtained a score-ranked signature of 579 genes. Genes with the highest absolute scores were classified as promising disease biomarkers. By grouping genes with similar neurofibromatosis-related profiles, we derived panels of potential biomarkers. The addition of promoter methylation data to gene profiles indicated a panel of genes probably silenced by hypermethylation. To identify possible therapeutic treatments, we used the gene signature to query drug expression databases. Trichostatin A and other histone deacetylase inhibitors, as well as cantharidin and tamoxifen, were retrieved as putative therapeutic means to reverse the aberrant regulation that drives to malignant cell proliferation and metastasis. This in silico prediction corroborated reported experimental results that suggested the inclusion of these compounds in clinical trials. This experimental validation supported the suitability of the meta-analysis method used to integrate several sources of public genomic information, and the reliability of the gene signature associated to the malignant evolution of neurofibromas to generate working hypotheses for prognostic and drug-responsive biomarkers or therapeutic measures, thus showing the potential of this in silico approach for biomarker discovery.

Malignant Peripheral Nerve Sheath Tumors State of the Science: Leveraging Clinical and Biological Insights into Effective Therapies

Malignant peripheral nerve sheath tumor (MPNST) is the leading cause of mortality in patients with neurofibromatosis type 1. In 2002, an MPNST consensus statement reviewed the current knowledge and provided guidance for the diagnosis and management of MPNST. Although the improvement in clinical outcome has not changed, substantial progress has been made in understanding the natural history and biology of MPNST through imaging and genomic advances since 2002. Genetically engineered mouse models that develop MPNST spontaneously have greatly facilitated preclinical evaluation of novel drugs for translation into clinical trials led by consortia efforts. Continued work in identifying alterations that contribute to the transformation, progression, and metastasis of MPNST coupled with longitudinal follow-up, biobanking, and data sharing is needed to develop prognostic biomarkers and effective prevention and therapeutic strategies for MPNST.