Identifying, Diagnosing, and Grading Malignant Peripheral Nerve Sheath Tumors in Genetically Engineered Mouse Models.

Patients with the autosomal dominant tumor susceptibility syndrome neurofibromatosis type 1 (NF1) commonly develop plexiform neurofibromas (PNs) that subsequently transform into highly aggressive malignant peripheral nerve sheath tumors (MPNSTs). Understanding the process by which a PN transforms into an MPNST would be facilitated by the availability of genetically engineered mouse (GEM) models that accurately replicate the PN-MPNST progression seen in humans with NF1. Unfortunately, GEM models with Nf1 ablation do not fully recapitulate this process. This led us to develop P0-GGFß3 mice, a GEM model in which overexpression of the Schwann cell mitogen neuregulin-1 (NRG1) in Schwann cells results in the development of PNs that progress to become MPNSTs with high frequency. However, to determine whether tumorigenesis and neoplastic progression in P0-GGFß3 mice accurately model the processes seen in NF1 patients, we had to first prove that the pathology of P0-GGFß3 peripheral nerve sheath tumors recapitulates the pathology of their human counterparts. Here, we describe the specialized methodologies used to accurately diagnose and grade peripheral nervous system neoplasms in GEM models, using P0-GGFß3 and P0-GGFß3;Trp53+/- mice as an example. We describe the histologic, immunohistochemical, and histochemical methods used to diagnose PNs and MPNSTs, how to distinguish these neoplasms from other tumor types that mimic their pathology, and how to grade these neoplasms. We discuss the establishment of early-passage cultures from GEM MPNSTs, how to characterize these cultures using immunocytochemistry, and how to verify their tumorigenicity by establishing allografts. Collectively, these techniques characterize the pathology of PNs and MPNSTs that arise in GEM models and critically compare the pathology of these murine tumors to their human counterparts.

Genetic Profiling and Genome-Scale Dropout Screening to Identify Therapeutic Targets in Mouse Models of Malignant Peripheral Nerve Sheath Tumor.

Malignant Peripheral Nerve Sheath Tumors (MPNSTs) are derived from Schwann cells or their precursors. In patients with the tumor susceptibility syndrome neurofibromatosis type 1 (NF1), MPNSTs are the most common malignancy and the leading cause of death. These rare and aggressive soft-tissue sarcomas offer a stark future, with 5-year disease-free survival rates of 34-60%. Treatment options for individuals with MPNSTs are disappointingly limited, with disfiguring surgery being the foremost treatment option. Many once-promising therapies such as tipifarnib, an inhibitor of Ras signaling, have failed clinically. Likewise, phase II clinical trials with erlotinib, which targets the epidermal growth factor (EFGR), and sorafenib, which targets the vascular endothelial growth factor receptor (VEGF), platelet-derived growth factor receptor (PDGF), and Raf, in combination with standard chemotherapy, have also failed to produce a response in patients. In recent years, functional genomic screening methods combined with genetic profiling of cancer cell lines have proven useful for identifying essential cytoplasmic signaling pathways and the development of target-specific therapies. In the case of rare tumor types, a variation of this approach known as cross-species comparative oncogenomics is increasingly being used to identify novel therapeutic targets. In cross-species comparative oncogenomics, genetic profiling and functional genomics are performed in genetically engineered mouse (GEM) models and the results are then validated in the rare human specimens and cell lines that are available. This paper describes how to identify candidate driver gene mutations in human and mouse MPNST cells using whole exome sequencing (WES). We then describe how to perform genome-scale shRNA screens to identify and compare critical signaling pathways in mouse and human MPNST cells and identify druggable targets in these pathways. These methodologies provide an effective approach to identifying new therapeutic targets in a variety of human cancer types.

Establishment and genomic characterization of a sporadic malignant peripheral nerve sheath tumor cell line.

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive Schwann cell-derived neoplasms that occur sporadically or in patients with neurofibromatosis type 1 (NF1). Preclinical research on sporadic MPNSTs has been limited as few cell lines exist. We generated and characterized a new sporadic MPNST cell line, 2XSB, which shares the molecular and genomic features of the parent tumor. These cells have a highly complex karyotype with extensive chromothripsis. 2XSB cells show robust invasive 3-dimensional and clonogenic culture capability and form solid tumors when xenografted into immunodeficient mice. High-density single nucleotide polymorphism array and whole exome sequencing analyses indicate that, unlike NF1-associated MPNSTs, 2XSB cells have intact, functional NF1 alleles with no evidence of mutations in genes encoding components of Polycomb Repressor Complex 2. However, mutations in other genes implicated in MPNST pathogenesis were identified in 2XSB cells including homozygous deletion of CDKN2A and mutations in TP53 and PTEN. We also identified mutations in genes not previously associated with MPNSTs but associated with the pathogenesis of other human cancers. These include DNMT1, NUMA1, NTRK1, PDE11A, CSMD3, LRP5 and ACTL9. This sporadic MPNST-derived cell line provides a useful tool for investigating the biology and potential treatment regimens for sporadic MPNSTs.

PDE5 inhibition rescues mitochondrial dysfunction and angiogenic responses induced by Akt3 inhibition by promotion of PRC expression.

Akt3 regulates mitochondrial content in endothelial cells through the inhibition of PGC-1α nuclear localization and is also required for angiogenesis. However, whether there is a direct link between mitochondrial function and angiogenesis is unknown. Here we show that Akt3 depletion in primary endothelial cells results in decreased uncoupled oxygen consumption, increased fission, decreased membrane potential, and increased expression of the mitochondria-specific protein chaperones, HSP60 and HSP10, suggesting that Akt3 is required for mitochondrial homeostasis. Direct inhibition of mitochondrial homeostasis by the model oxidant paraquat results in decreased angiogenesis, showing a direct link between angiogenesis and mitochondrial function. Next, in exploring functional links to PGC-1α, the master regulator of mitochondrial biogenesis, we searched for compounds that induce this process. We found that, sildenafil, a phosphodiesterase 5 inhibitor, induced mitochondrial biogenesis as measured by increased uncoupled oxygen consumption, mitochondrial DNA content, and voltage-dependent anion channel protein expression. Sildenafil rescued the effects on mitochondria by Akt3 depletion or pharmacological inhibition and promoted angiogenesis, further supporting that mitochondrial homeostasis is required for angiogenesis. Sildenafil also induces the expression of PGC-1 family member PRC and can compensate for PGC-1α activity during mitochondrial stress by an Akt3-independent mechanism. The induction of PRC by sildenafil depends upon cAMP and the transcription factor CREB. Thus, PRC can functionally substitute during Akt3 depletion for absent PGC-1α activity to restore mitochondrial homeostasis and promote angiogenesis. These findings show that mitochondrial homeostasis as controlled by the PGC family of transcriptional activators is required for angiogenic responses.

The 5-hydroxytryptamine receptor 1F stimulates mitochondrial biogenesis and angiogenesis in endothelial cells.

A hallmark of acute kidney injury (AKI) is vascular rarefication and mitochondrial dysfunction. Promoting vascular recovery following AKI could facilitate kidney repair as the vasculature is responsible for oxygen and nutrient delivery to extravascular tissues. Little is known about mitochondrial biogenesis (MB) in endothelial cells, and the role of 5-HT1F receptor signaling in MB has only been studied in epithelial cells. Our laboratory has shown that stimulating MB through the 5-HT1F receptor promotes recovery from AKI and that 5-HT1F receptor knockout mice have decreased MB and poor renal recovery. We hypothesized that the 5-HT1F receptor plays a role in vascular homeostasis and mediates MB in renal endothelial cells. 5-HT1F receptor knockout mice had decreased renal vascular content, as evidenced by decreased CD31+ endothelial cells and αSMA+ vessels. Human glomerular endothelial cells (HEC) and mouse glomerular endothelial cells (MEC) expressed the 5-HT1F receptor. Treatment of HEC and MEC with 5-HT1F receptor agonists LY344864 or lasmiditan (0-500 nM) induced MB as evidenced by maximal mitochondrial respiration, a marker of MB. HEC and MEC treated with lasmiditan or LY344864 also had increased nuclear- and mitochondrial-encoded proteins (PGC1α, COX-1, and VDAC), and mitochondrial number, confirming MB. Treatment of HEC with LY344864 or lasmiditan enhanced endothelial branching morphogenesis and migration, indicating a role for 5-HT1F receptor stimulation in angiogenic pathways. We propose that stimulation of 5-HT1F receptor is involved in MB in endothelial cells and that treatment with 5-HT1F receptor agonists could restore stimulate repair and recovery following kidney injury.