C5aR plus MEK inhibition durably targets the tumor milieu and reveals tumor cell phagocytosis.

Plexiform neurofibromas (PNFs) are nerve tumors caused by loss of NF1 and dysregulation of RAS-MAPK signaling in Schwann cells. Most PNFs shrink in response to MEK inhibition, but targets with increased and durable effects are needed. We identified the anaphylatoxin C5a as increased in PNFs and expressed largely by PNF m acrophages. We defined pharmacokinetic and immunomodulatory properties of a C5aR1/2 antagonist and tested if peptide antagonists augment the effects of MEK inhibition. MEK inhibition recruited C5AR1 to the macrophage surface; short-term inhibition of C5aR elevated macrophage apoptosis and Schwann cell death, without affecting MEK-induced tumor shrinkage. PNF macrophages lacking C5aR1 increased the engulfment of dying Schwann cells, allowing their visualization. Halting combination therapy resulted in altered T-cell distribution, elevated Iba1+ and CD169+ immunoreactivity, and profoundly altered cytokine expression, but not sustained trumor shrinkage. Thus, C5aRA inhibition independently induces macrophage cell death and causes sustained and durable effects on the PNF microenvironment.

Germline genomic findings in children and young adults with melanocytic tumors.

In this retrospective study, we examined the prevalence and spectrum of germline variants in selected cancer predisposition genes in 38 children and young adults with melanocytic lesions at St. Jude Children's Research Hospital. Diagnoses included malignant melanoma (n = 16; 42%), spitzoid melanoma (n = 16; 42%), uveal melanoma (n = 5; 13%), and malignant melanoma arising in a giant congenital melanocytic nevus (n = 1; 3%). Six patients (15.8%) harbored pathogenic germline variants: one with bi-allelic PMS2 variants, one with a heterozygous 17q21.31 deletion, and one each with a pathogenic variant in TP53, BRIP1, ATM, or AXIN2. Overall, 15.8% of patients harbored a cancer-predisposing genetic variant.

Collaboration to Promote Research and Improve Clinical Care in the Evolving Field of Childhood Cancer Predisposition.

Germline pathogenic variants in cancer susceptibility genes are identified in up to 18% of all children with cancer. Because pediatric cancer predisposition syndromes (CPS) themselves are rare and underrecognized, there are limited data to guide the diagnosis and management of affected children and at-risk relatives. Furthermore, the care of affected children requires distinct considerations given the early onset of cancers, lifelong risks of additional cancers, and potential late effects of therapy. Herein, we discuss efforts to leverage existing infrastructure, organize experts, and develop a new consortium to optimize care and advance research for children with CPS. A 2016 workshop organized by the American Association for Cancer Research united many experts in childhood cancer predisposition and resulted in publication of multiple consensus guidelines for tumor surveillance. More recently, several of these authors established the Consortium for Childhood Cancer Predisposition (C3P), a multi-institutional collaboration that provides a structure for systematic research in cancer predisposition, screening, and prevention in children. The Consortium intends to work with other cooperative groups to merge longitudinal data from children with CPS throughout the continuum of the cancer risk period, as well as cancer treatment and survivorship care, to optimize overall outcomes.

WNT5A inhibition alters the malignant peripheral nerve sheath tumor microenvironment and enhances tumor growth.

Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft-tissue sarcomas that cause significant mortality in adults with neurofibromatosis type 1. We compared gene expression of growth factors in normal human nerves to MPNST and normal human Schwann cells to MPNST cell lines. We identified WNT5A as the most significantly upregulated ligand-coding gene and verified its protein expression in MPNST cell lines and tumors. In many contexts WNT5A acts as an oncogene. However, inhibiting WNT5A expression using shRNA did not alter MPNST cell proliferation, invasion, migration, or survival in vitro. Rather, shWNT5A-treated MPNST cells upregulated mRNAs associated with the remodeling of extracellular matrix and with immune cell communication. In addition, these cells secreted increased amounts of the proinflammatory cytokines CXCL1, CCL2, IL6, CXCL8, and ICAM1. Versus controls, shWNT5A-expressing MPNST cells formed larger tumors in vivo. Grafted tumors contained elevated macrophage/stromal cells, larger and more numerous blood vessels, and increased levels of Mmp9, Cxcl13, Lipocalin-1, and Ccl12. In some MPNST settings, these effects were mimicked by targeting the WNT5A receptor ROR2. These data suggest that the non-canonical Wnt ligand WNT5A inhibits MPNST tumor formation by modulating the MPNST microenvironment, so that blocking WNT5A accelerates tumor growth in vivo.

Cdkn2a Loss in a Model of Neurofibroma Demonstrates Stepwise Tumor Progression to Atypical Neurofibroma and MPNST.

Plexiform neurofibromas are benign nerve sheath Schwann cell tumors characterized by biallelic mutations in the neurofibromatosis type 1 (NF1) tumor suppressor gene. Atypical neurofibromas show additional frequent loss of CDKN2A/Ink4a/Arf and may be precursor lesions of aggressive malignant peripheral nerve sheath tumors (MPNST). Here we combined loss of Nf1 in developing Schwann cells with global Ink4a/Arf loss and identified paraspinal plexiform neurofibromas and atypical neurofibromas. Upon transplantation, atypical neurofibromas generated genetically engineered mice (GEM)-PNST similar to human MPNST, and tumors showed reduced p16INK4a protein and reduced senescence markers, confirming susceptibility to transformation. Superficial GEM-PNST contained regions of nerve-associated plexiform neurofibromas or atypical neurofibromas and grew rapidly on transplantation. Transcriptome analyses showed similarities to corresponding human tumors. Thus, we recapitulated nerve tumor progression in NF1 and provided preclinical platforms for testing therapies at each tumor grade. These results support a tumor progression model in which loss of NF1 in Schwann cells drives plexiform neurofibromas formation, additional loss of Ink4a/Arf contributes to atypical neurofibromas formation, and further changes underlie transformation to MPNST. SIGNIFICANCE: New mouse models recapitulate the stepwise progression of NF1 tumors and will be useful to define effective treatments that halt tumor growth and tumor progression in NF1.