Peri-gestational risk factors for pediatric brain tumors in Neurofibromatosis Type 1.

BACKGROUND: Individuals with Neurofibromatosis Type 1 (NF1) are strongly predisposed to developing pediatric brain tumors (PBTs), especially optic pathway gliomas (OPGs). Although developmental factors have been implicated in the origins of PBTs in both human and animal studies, associations between early-life factors and PBTs have not been evaluated in individuals with NF1. Our objective was to evaluate associations between peri-gestational characteristics and PBTs in this population. METHODS: We conducted a cross-sectional study, ascertaining questionnaire and medical record data for 606 individuals<18years old who enrolled in the NF1 Patient Registry Initiative (NPRI) from 6/9/2011-6/29/2015. One hundred eighty-four individuals had reported PBT diagnoses, including 65 who were identified with OPG diagnoses. Cox proportional hazards regression was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for associations between PBT and OPG diagnoses and peri-gestational characteristics (prematurity, birth weight, parental age, plurality, family history of NF1, assisted reproductive technology, maternal vitamin supplementation, and parental smoking). RESULTS: We observed no significant associations between any of the assessed characteristics and PBTs overall or OPGs with the exception of birth weight. After controlling for potential confounding variables, we observed a significant positive association between birth weight quartile and OPGs with a HR of 3.32 (95% CI 1.39-7.94) for the fourth (≥3915.5g) compared to the first (≤3020g) quartile (p for trend=0.001). CONCLUSIONS: Consistent with results for PBTs in the general population, these results suggest that higher birth weights increase OPG risk in individuals with NF1.

PET imaging for attention deficit preclinical drug testing in neurofibromatosis-1 mice.

Attention system abnormalities represent a significant barrier to scholastic achievement in children with neurofibromatosis-1 (NF1). Using a novel mouse model of NF1-associated attention deficit (ADD), we demonstrate a presynaptic defect in striatal dopaminergic homeostasis and leverage this finding to apply [(11)C]-raclopride positron-emission tomography (PET) in the intact animal. While methylphenidate and l-Deprenyl correct both striatal dopamine levels on PET imaging and defective attention system function in Nf1 mutant mice, pharmacologic agents that target de-regulated cyclic AMP and RAS signaling in these mice do not. These studies establish a robust preclinical model to evaluate promising agents for NF1-associated ADD.

Preclinical in vivo evaluation of rapamycin in human malignant peripheral nerve sheath explant xenograft.

Neurofibromatosis type 1 (NF1) patients are prone to the development of malignant tumors, the most common being Malignant Peripheral Nerve Sheath Tumor (MPNST). NF1-MPNST patients have an overall poor survival due to systemic metastasis. Currently, the management of MPNSTs includes surgery and radiation; however, conventional chemotherapy is not very effective, underscoring the need for effective biologically-targeted therapies. Recently, the NF1 gene product, neurofibromin, was shown to negatively regulate the phosphoinositide-3-kinase (PI3K)/Protein Kinase-B (Akt)/mammalian Target Of Rapamycin (mTOR) pathway, with loss of neurofibromin expression in established human MPNST cell lines associated with high levels of mTOR activity. We developed and characterized a human NF1-MPNST explant grown subcutaneously in NOD-SCID mice, to evaluate the effect of the mTOR inhibitor rapamycin. We demonstrate that rapamycin significantly inhibited human NF1-MPNST mTOR pathway activation and explant growth in vivo at doses as low as 1.0 mg/kg/day, without systemic toxicities. While rapamycin was effective at reducing NF1-MPNST proliferation and angiogenesis, with decreased CyclinD1 and VEGF respectively, there was no increase in tumor apoptosis. Rapamycin effectively decreased activation of S6 downstream of mTOR, but there was accompanied increased Akt activation. This study demonstrates the therapeutic potential and limitations of rapamycin in NF1-associated, and likely sporadic, MPNSTs.

Neurofibromin regulates somatic growth through the hypothalamic-pituitary axis.

To study the role of the neurofibromatosis-1 (NF1) gene in mammalian brain development, we recently generated mice in which Nf1 gene inactivation occurs in neuroglial progenitor cells using the brain lipid binding protein (BLBP) promoter. We found that Nf1(BLBP)CKO mice exhibit significantly reduced body weights and anterior pituitary gland sizes. We further demonstrate that the small anterior pituitary size reflects loss of neurofibromin expression in the hypothalamus, leading to reduced growth hormone releasing hormone, pituitary growth hormone (GH) and liver insulin-like growth factor-1 (IGF1) production. Since neurofibromin both negatively regulates Ras activity and positively modulates cAMP levels, we examined the signaling pathway responsible for these abnormalities. While BLBP-mediated expression of an activated Ras molecule did not recapitulate the body weight and hypothalamic/pituitary defects, treatment of Nf1(BLBP)CKO mice with rolipram to increase cAMP levels resulted in a partial restoration of the body weight phenotype. Furthermore, conditional expression of the Ras regulatory GAP domain of neurofibromin also did not rescue the body weight or Igf1 mRNA defects in Nf1(BLBP)CKO mice. Collectively, these data demonstrate a critical role for neurofibromin in hypothalamic-pituitary axis function and provide further insights into the short stature and GH deficits seen in children with NF1.

The natural history and treatment of epilepsy in a murine model of tuberous sclerosis.

PURPOSE: Patients with tuberous sclerosis complex (TSC) often have severe epilepsy that is intractable to available therapies. The development of novel treatments for epilepsy in TSC would benefit greatly from a suitable animal model, but most animal models of TSC to date have few reported neurological abnormalities, such as epilepsy. We previously described a novel model of TSC, due to conditional inactivation of the Tsc1 gene in glia (Tsc1(GFAP)CKO mice), in which mice develop epilepsy and premature death. Here, we characterize the natural history of the epilepsy in Tsc1(GFAP)CKO mice in more detail and report acute effects of treatment with standard antiepileptic drugs on seizures in these mice. METHODS: Video-EEG recordings were obtained from Tsc1(GFAP)CKO mice on a weekly basis, starting at 4 weeks of age until death, to monitor progression of interictal EEG abnormalities and seizures. In separate experiments, Tsc1(GFAP)CKO mice were monitored for interictal EEG abnormalities and seizures before and during treatment with phenobarbital, phenytoin, or saline. RESULTS: Tsc1(GFAP)CKO mice developed seizures around 4-6 weeks of age and subsequently had progressive worsening of the interictal EEG background and seizure frequency over a month, culminating in death. Treatment with phenobarbital or phenytoin caused a reduction in seizure frequency, but did not improve EEG background or prevent death. CONCLUSIONS: Tsc1(GFAP)CKO mice develop progressive epilepsy. Acute treatment with standard antiepileptic drugs suppresses seizures in these mice, but does not affect long-term prognosis. Tsc1(GFAP)CKO mice represent a good model to test other drugs that may have true antiepileptogenic actions in TSC.

Harnessing preclinical mouse models to inform human clinical cancer trials.

The urgent need for better cancer treatments has stimulated interest in employing small-animal models to evaluate potential drug therapies. Robust mouse models of many human cancers have been generated using sophisticated technologies for engineering germ-line mutations. As we enter into an age of targeted therapeutics, these strains provide novel platforms for validating new anticancer drugs, assessing therapeutic index, identifying surrogate markers of tumor progression, and defining epigenetic and environmental influences on tumorigenesis.

Disruption of 14-3-3 binding does not impair Protein 4.1B growth suppression.

Meningiomas are common central nervous system tumors; however, the mechanisms underlying their pathogenesis are largely unknown. Collaborative studies from our laboratory demonstrated a direct association of 14-3-3 with the meningioma tumor suppressor Protein 4.1B, which was not observed with other members of the Protein 4.1 family, including the NF2 meningioma tumor suppressor, merlin/schwannomin. Given the role of 14-3-3 in the regulation of cell proliferation and apoptosis, we sought to determine the functional significance of 14-3-3 binding to Protein 4.1B growth suppression. Based on comparative binding studies performed with additional members of the Protein 4.1 family, we generated specific missense mutations within the minimal growth suppressor fragment of Protein 4.1B (DAL-1, differentially expressed in adenocarcinoma of the lung). Complementary in vitro GST affinity chromatography and in vivo interaction experiments demonstrated that the F359Y mutation abrogated binding to 14-3-3, but did not impair DAL-1 binding to other known Protein 4.1B interacting proteins. Similar to wild-type DAL-1, the expression of the F359Y DAL-1 14-3-3-binding mutant resulted in reduced Protein 4.1B-deficient IOMM-Lee and CH157-MN meningioma cell line colony formation. Moreover, similar to wild-type DAL-1, the stable expression of the DAL-1 F359Y mutant significantly reduced cell proliferation in independently isolated IOMM-Lee clones, as assessed by thymidine incorporation. Collectively, these results suggest that binding to 14-3-3 is not essential for the growth suppressor function of Protein 4.1B in meningiomas.