Assessment of Tumor Prevention in Type 1 Neurofibromatosis using a Nitroxide Compound

Abstract

Background: Type 1 Neurofibromatosis (NF1) is a genetic disorder linked to mutations of the NF1 gene. Clinical symptoms are varied, but hallmark features of the disease include skin pigmentation anomalies (café au lait macules, skinfold freckling) and dermal neurofibromas. Method: These dermal manifestations of NF1 have previously been reported in a mouse model where Nf1 +/-mice are topically treated with dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). We adopted this mouse model to test the protective effects of a nitroxide antioxidant, 5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl (CTMIO). Antioxidants have previously been shown to increase longevity in nf1-deficient fruitflies. Doses of 4µM and 40µM CTMIO provided ad libitum in drinking water were given to Nf1-deficient mice. Results: Consistent with previous reports, Nf1-deficient mice showed a 4.7-fold increase in papilloma formation (P < 0.036). However, neither dose of CTMIO had any significant affect on papilloma formation. A non-significant decrease in skin pigmentation abnormalities was seen with 4µM but not 40µM CTMIO. Subsequent analysis of genomic DNA isolated from papillomas indicated that DMBA/TPA induced tumors did not exhibit a local loss of heterozygosity (LOH) at the Nf1 locus. Conclusion: These data reveal that oral antioxidant therapy with CTMIO does not reduce tumor formation in a multistage cancer model, but also that this model does not feature LOH for Nf1. IntroductIonType 1 Neurofibromatosis (NF1) is an autosomal dominant genetic disorder that affects 1:3,000-1:3,500 individuals and can lead to disorders in a range of tissues.[1] NF1 has tumor-suppressor function and encodes for neurofibromin, a negative regulator of oncogenic protein Ras.[2] A number of specific tumor types are associated with NF1, including cutaneous and subcutaneous neurofibromas, plexiform neurofibromas, astrocytomas, and optic gliomas. While the cutaneous neurofibromas are often benign, their appearance is common during puberty and they can be cosmetically disfiguring and can have a dramatic impact on patient quality of life. Currently there are no preventative measures able to suppress the onset of dermal neurofibromas in NF1 patients. The causes of neurofibroma formation are linked to a clonal second hit on the NF1 gene. Assessment of tumor Prevention in type 1 neurofibromatosis using a nitroxide compound[3] For plexiform neurofibromas, a Krox20-cre; Nf1 flox/flox mouse model showed that double inactivation of NF1 in Schwann cells was critical for tumorigenesis.[4] However, this research also showed that interactions with Nf1 +/-mast cells were also important for potentiating tumor growth. A proportion of neurofibromas can progress to a more life-threatening outcome, a malignant peripheral nerve sheath tumor (MPNST). Coordinate loss of the master tumor suppressor P53 may be associated with progression to an MPNST. [5,6] The coincidence of tumor formation with puberty has historically led to speculation of an activation ...