Molecular, Cellular and Genetic Analyses of Malignancies Associated with NF1

Division Of Basic Sciences - Nci

Investigators

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Abstract

Malignant Peripheral Nerve Sheath Tumors (MPNST) affect between 5-13% of Neurofibromatosis type 1 (NF1) patients and is a leading cause of mortality in this disease. We are using tumor cell lines from both mouse and human MPNSTs to test drugs for growth inhibition. We are focusing on late phase and FDA approved drugs and comparing their ability to inhibit MPNST growth to doxorubicin, one of the standard treatment options for MPNST. We are studying the changes in transcriptome and kinome caused by these drugs for rational design of synergistic combinations. Candidate combinations have been tested first in tumor cell lines in culture and will be tested in MPNST xenograft and genetically engineered mouse models. Because all the drugs we're testing have been through phase I clinical testing, we are comparing inhibitory effects at the Cmax found in patient serum at the maximum tolerated dose in humans. Successful synergistic combinations will be considered for clinical trials in MPNST patients. In addition to our examination of drugs that inhibit tumor signaling pathways, we are looking at the role of the immune system in MPNST tumorigenesis. The neurofibromin protein that is mutated in NF1 patients downregulates RAS signaling. Not only is RAS signaling important for MPNST growth, it also plays multiple important roles in the immune system. NF1 patients and mice that lack one copy of the gene for neurofibromin (NF1) have been shown to have several alterations in immune system with implications for tumorigenesis. Myeloid cells haploinsufficient for NF1 are hypersensitive to signaling through the RAS pathway and NF1 patients have higher levels of inflammatory cytokines in their blood. For these and other reasons, it is not clear whether MPNST patients would be amenable to immune therapies currently being developed for other cancers. We are using immune-competent mouse models of MPNST to characterize the interaction between the tumor and the immune system. We have found changes in the myeloid and lymphoid compartments in MPNST-bearing mice and are currently testing immune checkpoint therapy in immune competent syngenic orthografts of mouse MPNST. Depending on our findings, we will examine how immune-based therapies could complement therapies targeting tumor cell signaling for combination therapy in MPNST. NF1 patients are also at an increased risk for malignant gliomas and a subset of glioblastomas have mutation of the NF1 gene. New therapeutic options for malignant gliomas are desperately needed. Glioblastomas are more common in males than in females, but the mechanism of this difference is not understood. We have identified a modifier of gliomagenesis in our mouse model of NF1-associated brain tumors that affects males and females differently. Using human and mouse glioblastoma and astrocytic astrocytoma tumor lines and primary astrocytes, we are dissecting the mechanism of the sex-specific action of this modifier. In addition, because our mouse brain tumor lines are on purebred strain backgrounds, they are a powerful tool to study the immune system role in brain cancer. Our extramural collaborators are using these tumor lines to examine the role of cytokines in brain cancer and to test candidate therapies for glioblastoma. During the past fiscal year, we have continued our work to understand the transcriptional changes that occur when MPNST cells are effectively growth inhibited by HDAC inhibitors. This has led to new pathways that may be specifically targeted to block MPNST growth (manuscript in preparation). Through our basic research in mouse models, we continue to extend studies on an adaptor protein in the RAS signaling pathway, demonstrating through mouse genetic experiments that it inhibits both plexiform neurofibroma and MPNST development in mice. We are working to expand our understanding of this adaptor's normal function to develop new ideas for MPNST inhibition. Finally, our studies of the immune system in mouse models of MPNST confirm that immune function is altered in the presence of the tumor compared to wild-type or NF1 heterozygous mice. We tested a mouse version of a checkpoint inhibitor approved for use in humans in an orthotopic model of MPNST. This past fiscal year we have focused our studies on epigenetic modifiers encoded on the sex chromosome as a potential mechanism for the sex bias in malignant astrocytic gliomas. We have developed CRISPR and lentiviral tools to manipulate the level of a histone demethylase specific to the Y chromosome to study how it interacts with the sex-specific modifier of brain tumor development in mice (manuscript in preparation).