Project 1: Molecular and Genetic Features Across Mouse and Human Plexiform Neurofibromas to Inform Clinical Trials

  • D. Wade Clapp, MD Basic Science Co-Leader (Indiana University School of Medicine)
  • Jaishri Blakeley, MD Clinical Science Co-Leader (Johns Hopkins University)
  • Brigitte Widemann, MD Clinical Science Co-Leader (National Institutes of Health)
  • Lu Le, MD, PhD Basic Science Co-Leader (University of Texas, Southwestern)
  • Kent Robertson, MD, PhD Co-Investigator (Indiana University School of Medicine)

Description

Plexiform neurofibromas (PNs) are complex nerve and soft tissue tumors that affect 25-50% of people with NF1, cause serious lifelong morbidity and mortality due to organ compression, and progress to malignant peripheral nerve sheath tumors (MPNST) in ~8-13% of patients. Collaborative studies performed by Drs. Clapp and Parada in a genetically engineered mouse (GEM) model of PNs unexpectedly demonstrated a central role of infiltrating Nf1 haploinsufficient bone marrow-derived mast cells in promoting the growth of PN lesions in vivo. These novel data led to a clinical trial administering imatinib mesylate to target aberrant stem cell factor (SCF)/c-kit signaling in the tumor microenvironment, which induced objective clinical responses in a subset of patients. Based on the observation that young children with head, neck, and airway tumors were most likely to have partial tumor regression, Drs. Robertson, Blakeley, Widemann and Fisher are pursuing a registration trial in this patient population. More recently, studies in GEM models informed successful clinical trials of MEK inhibitors to directly inhibit aberrant Ras/Raf/MEK/ERK signaling in PN cells. The objective of Project 1 is to extend these promising data to investigate the developmental, molecular, and pharmacokinetic effects of c-kit and MEK inhibition alone and in combination. Our investigative team will characterize the adaptive responses of PNs to these kinase inhibitors in GEM models and in parallel studies in patients.

Aims

Aim 1:

Evaluate tumor and circulating markers before and after treatment with the MEK inhibitor selumetinib in pediatric and adult patients with NF1 associated plexiform neurofibromas.

Aim 2:

Evaluate the molecular adaptive responses, PK/PD and clinical response of plexiform neurofibromas in genetically engineered mice (GEM) with selumetinib alone, and in combination with imatinib mesylate.

Aim 3:

Utilize GEM models to identify the optimal therapeutic window(s) of c-kit (SCF) inhibition at distinct embryonic and adult stages of PN formation utilizing Nf1flox/- and Nf1flox/-;Scf flox/flox mice under the transcriptional control of a PLP tamoxifen + Cre transgene.

Translational Impact

The translational impact of this project involves: (1) defining therapeutic window(s) for c-kit inhibition at distinct embryonic and adult stages of PN formation; (2) investigating a rational approach to combinatorial therapy based on simultaneously interfering with paracrine growth signals emanating from the tumor microenvironment while also targeting aberrant Raf/MEK/ERK pathway activation in tumor cells; and (3) defining novel biomarkers by analyzing tumor specimens and blood obtained both prior to and after treatment.

Project 2: Targeted Therapies for Malignant Peripheral Nerve Sheath Tumors

  • Luis Parada, PhD Basic Science Co-Leader (Memorial Sloan Kettering Cancer Center)
  • Stephen X. Skapek, MD Clinical Science Co-Leader (University of Texas, Southwestern)
  • Ted Laetsch, MD Co-Investigator (University of Texas, Southwestern)
  • Noelle Williams, PhD Co-Investigator (University of Texas, Southwestern)
  • Xiankai Sun, PhD Co-Investigator (University of Texas, Southwestern)
  • Guiyang Hao, PhD Co-Investigator (University of Texas, Southwestern)

Description

Malignant peripheral nerve sheath tumors (MPNST) evolve from pre-existing plexiform neurofibromas, and we therefore hypothesize that these aggressive sarcomas continue to express some of the transcriptional programs present in the initiating fetal precursor population. This, in turn, might create novel synthetic lethal dependencies that can be exploited therapeutically. Indeed, Dr. Parada recently identified CXCR4 and CDK4/6 as key drivers of MPNST cell proliferation and tumor progression in GEM models. The major goals of Project 2 are to translate these provocative preclinical data and to harness functional imaging to develop better markers of early response in MPNST.

Aims

Aim 1:

To optimize CXCR4 and Cyclin D1-associated CDK4/6 inhibition in MPNST.

Aim 2:

To optimize functional imaging for early response assessment in MPNST.

Aim 3:

To conduct pilot, “Phase 0” studies of GEM-guided, molecularly-targeted therapy in MPNST.

Translational Impact

The translational impact of these studies encompasses the development of a biomarker profile to identify early markers of MPNST progression and evaluate efficacy of CXCR4 and CDK4/6 inhibitors in clinical trials.

Project 3: Efficacy of MEK Inhibition in Juvenile Myelomonocytic Leukemia

  • Kevin Shannon, MD Basic Science Co-Leader (University of California, San Francisco)
  • Mignon Loh, MD Clinical Science Co-Leader (University of California, San Francisco)
  • Benjamin Braun, MD, PhD Co-Investigator (University of California, San Francisco)
  • Elliot Stieglitz, MD Co-Investigator (University of California, San Francisco)

Description

Children with NF1 are predisposed to juvenile myelomonocytic leukemia (JMML), an aggressive myeloproliferative neoplasm (MPN) that responds poorly to chemotherapy. Hematopoietic stem cell transplantation (HSCT) cures ~50% of patients. Our studies of JMML specimens proved that NF1 functions as a tumor suppressor gene in hematopoietic cells, and provided the first direct evidence of deregulated Ras signaling in primary cancer cells from NF1 patients. These studies support the role of hyperactive Ras signaling in JMML pathogenesis, and our group and other researchers subsequently discovered mutations in NRAS, KRAS, PTPN11, and CBL in JMML patient specimens. Overall, >85% of JMML cases have mutations in one of these genes, including 15-20% with clinical NF1 or mutations in the NF1 gene. Despite the routine use of HSCT, up to 30% of JMML patients progress to acute myeloid leukemia (AML). Consistent with the molecular genetics of JMML, using the Mx1-Cre transgene to inactivate the conditional mutant Nf1flox allele generated by the Parada lab or to express oncogenic KrasG12D or NrasG12D in the hematopoietic compartment induces a JMML-like MPN in mice. Preclinical trials in these accurate GEM models revealed remarkable efficacy of MEK inhibitors. Importantly, however, this, treatment does not eradicate mutant bone marrow cells, but modulates their proliferation and differentiation in vivo. The overall goals of Project 3 are to translate these promising preclinical data in JMML patients though an innovative clinical trial that includes deep molecular analysis.

Aims

Aim 1:

To conduct a national phase II investigator-initiated trial of the MEK inhibitor trametinib in JMML and other refractory pediatric leukemias, and to interrogate molecular mechanisms of response and resistance. This trial will be executed in collaboration with the National Cancer Institute’s Cancer Therapy Evaluation Program (CTEP) and the Developmental Therapeutics Consortium (DVL) of the Children’s Oncology Group (COG).

Aim 2:

To use genetically accurate mouse models of MPN and acute myeloid leukemia (AML) characterized by Nf1 inactivation to investigate the efficacy and mechanisms of action of “second generation” therapies, and to functionally validate candidate mechanisms of drug resistance.

Translational Impact

The translational impact of these studies involves rigorously testing a novel therapeutic strategy for an aggressive pediatric cancer with deep molecular analysis of primary leukemia cells to ascertain mechanisms of response and resistance.

Project 4: Secondary Cancers among NF1 Cancer Survivors Outcome

  • Smita Bhatia, MD Clinical Science Co-Leader (University of Alabama, Birmingham)
  • Jean L. Nakamura, MD Basic Science Co-Leader (University of California, San Francisco)
  • Michael Fisher, MD Co-Investigator (Children’s Hospital of Philadelphia)
  • Lennie Wong, PhD Co-Investigator (City of Hope)

Description

Subsequent malignant neoplasms (SMNs) are histologically distinct cancers that develop months to years after patients receive radiation and/or chemotherapy to cure a primary malignancy. SMNs are a fundamental problem in cancer survivors. Compelling data generated by Drs. Nakamura and Shannon in GEM mice demonstrated that irradiation cooperates strongly with heterozygous Nf1 inactivation in the development of a spectrum of SMNs that recapitulate common SMNs in human patients with and without NF1. Project 4 will translate these novel data and will systematically assess the incidence of SMNs in NF1 patients and examine associated risk factors such as age at diagnosis, anatomic site of the primary tumor, and dose and duration of prior treatment. Data compiled by the NCI-funded Childhood Cancer Survivor Study (CCSS) will play an integral role in Project 4.

Aims

Aim 1:

To describe the magnitude of risk of second malignant neoplasms (SMNs) in individuals with NF1.

Aim 2:

To perform comparative oncogenomics to identify genetic alterations associated with radiation-induced tumorigenesis in individuals with NF1.

Aim 3:

To validate in model systems the biologic importance of candidate pathways in radiation-induced tumorigenesis and to determine whether radiotherapy promotes transformation of plexiform neurofibromas to MPNSTs in vivo.

Translational Impact

The translational impact of this work involves informing current clinical practice in the treatment of tumors arising in NF1 patients to reduce the risk of SMN, and generating insights into the underlying biology of SMN that will lead to new therapies for these common, aggressive, and largely refractory cancers.