Valosin-Containing Protein Contributes to Plexiform Neurofibroma Formation and Represents a Novel Therapeutic Target

Neurofibromatosis type 1 (NF1) patients are predisposed to develop plexiform neurofibromas (PNFs). By cross-comparison of RNA sequencing and RUNX1-CHIP sequencing data on mouse PNFs, we found that transcripts encoding the NF1-interacting p97/valosin-containing protein (VCP) gene are overexpressed in PNFs. Co-immunoprecipitation confirmed that VCP bounded to neurofibromin. Western blot and immunostaining confirmed VCP overexpression in both mouse and human PNFs. Treatment of primary mouse PNF Schwann cells with CB-5083, a p97/VCP inhibitor, led to accumulation of poly-ubiquitinated proteins and generation of irresolvable proteotoxic stress. Pharmacological or genetic inhibition of VCP reduced mouse PNF cell-derived sphere number, and genetic inhibition of Vcp in Schwann cell precursors decreased tumor-like lesion numbers in a cell transplantation model. In vivo treatment with CB-5083 in Nf1^fl/fl;DhhCre PNF mice significantly inhibited cell proliferation, increased cell apoptosis and reduced PNF volume. The combination with a MEK inhibitor did not increase efficacy compared to the single agent, supporting the hypothesis that VCP functions in parallel to, and may be modulated by, RAS-MAPK signaling under stress or oncogenic conditions. The significant effects of VCP inhibition in this pre-clinical study suggest a potential novel therapy for patients with PNFs.