Abstract 2937: An EGFR-STAT3 pathway promotes NF1 peripheral nerve tumorigenesis and transformation

Abstract

Abstract Neurofibromatosis type 1 (NF1) is a very common inherited disease, affecting 1:3500 individuals worldwide. Nearly all (95%) of NF1 patients develop benign neurofibromas and malignant peripheral nerve sheath tumors(MPNSTs). Currently, their prevention is not possible, partially because the molecular mechanisms of tumorigenesis and the molecules that mark benign neurofibroma formation are poorly understood. This study is to test the relevance of EGFR expression to neurofibroma formation, and to identify possible additional pathways and genes that might contribute to neurofibroma formation. We bred the Nf1 flox/flox;DhhCre mice, 100% of which form neurofibromas (Wu et al., 2008), to CNP-hEGFR mice and to Wa2 mice, an EGFR hypomorphic allele. To test the role of EGFR in tumorigenesis, we also used sleeping beauty (SB) insertional mutagenesis to obtain quadruple transgenic mice (Rosa26-lsl-SB11;T2/Onc; Nf1flox/flox;DhhCre). To define neurofibroma initiation and progression genes, we used Pyrosequencing to identify common insertion sites (CISs) that had more SB insertions that are most likely to harbor disease-related genes. We used ingenuity pathway analysis to predict pathways and genes that might contribute to neurofibroma formation. We used a “neurofibroma sphere” culture system, a method used for detecting self-renewing stem/progenitor cells, to determine inhibitory effects of a STAT3 inhibitor (FLLL32). We immunostained human and mouse sections with anti-pSTAT3 (tyr705) to determine STAT3 activation status. We found that mouse neurofibroma number and size increased in Nf1flox/flox;DhhCre mice with hEGFR expressed in nerve Schwann cells. Diminished EGFR signaling in Nf1 flox/flox;DhhCre, Wa2/+ mice decreased neurofibroma number, not size. We used insertional mutagenesis to identify other modifiers of neurofibroma tumorigenesis. Analysis of CISs identified hubs involving GSK3B, TNF, and STAT3. STAT3 was the most significant changed pathway. Inhibition of STAT3 by shRNA or a specific STAT3 inhibitor FLLL32 blocked human neurofibroma-sphere formation. Immunohistochemistry identified STAT3(p705) in human and mouse neurofibromas and MPNSTs. FLLL32 inhibited cell proliferation and stimulated cell death as well as reduced neurofibroma growth in vivo in the Nf1flox/flox;DhhCre mouse neurofibromas. STAT3 knockdown by shRNA prevented MPNST formation in vivo. Finally, reducing EGFR activity strongly reduced pSTAT3 in vivo. Thus, an EGFR-STAT3 pathway regulates neurofibroma number and neurofibroma growth, and promotes transformation. STAT3 inhibitors may be useful in NF1 therapeutics. (*This work was supported by the National Institutes of Health (R01 NS28840 to N.R. and P50 NS057531 to N.R. and D.L.) and an Ohio State University Comprehensive Cancer Center pelotonia idea award to J.W.) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2937. doi:1538-7445.AM2012-2937