Matthew L. Bush

AR42, a novel histone deacetylase inhibitor, as a potential therapy for vestibular schwannomas and meningiomas

Neurofibromatosis type 2 (NF2) is an autosomal-dominant disease that results in the formation of bilateral vestibular schwannomas (VSs) and multiple meningiomas. Treatment options for NF2-associated tumors are limited, and to date, no medical therapies are FDA approved. The ideal chemotherapeutic agent would inhibit both VS and meningiomas simultaneously. The objectives of this study are (1) to test the efficacy of AR42, a novel histone deacetylase inhibitor, to inhibit VS and meningioma growth and (2) to investigate this drugs mechanisms of action. Primary cultures of human VS and meningioma cells were established. Nf2-deficient mouse schwannoma and benign human meningioma Ben-Men-1 cells were also cultured. Cells were treated with AR42, and the drugs effects on proliferation and the cell cycle were analyzed using a methanethiosulfonate assay and flow cytometry, respectively. Human phospho-kinase arrays and Western blots were used to evaluate the effects of AR42 on intracellular signaling. The in vivo efficacy of AR42 was investigated using schwannoma xenografts. Tumor volumes were quantified using high-field, volumetric MRI, and molecular target analysis was performed using immunohistochemistry. AR42 inhibited the growth of primary human VS and Nf2-deficient mouse schwannoma cells with a half maximal inhibitory concentration (IC(50)) of 500 nM and 250-350 nM, respectively. AR42 also inhibited primary meningioma cells and the benign meningioma cell line, Ben-Men-1, with IC(50) values of 1.5 µM and 1.0 µM, respectively. AR42 treatment induced cell-cycle arrest at G(2) and apoptosis in both VS and meningioma cells. Also, AR42 exposure decreased phosphorylated Akt in schwannoma and meningioma cells. In vivo treatment with AR42 inhibited the growth of schwannoma xenografts, induced apoptosis, and decreased Akt activation. The potent growth inhibitory activity of AR42 in schwannoma and meningioma cells suggests that AR42 should be further evaluated as a potential treatment for NF2-associated tumors.

Preclinical validation of AR42, a novel histone deacetylase inhibitor, as treatment for vestibular schwannomas.

Recent studies indicate that vestibular schwannomas (VSs) rely on phosphatidylinositol 3‐kinase/AKT activation to promote cell proliferation and survival; therefore, targeting AKT may provide new therapeutic options. We have previously shown that AR42, a novel histone deacetylase inhibitor, potently suppresses VS growth in vitro at doses correlating with AKT inactivation. The objectives of the current study were translational: 1) to examine the end biologic effects of AR42 on tumor growth in vivo, 2) to validate AKT as its in vivo molecular target, 3) to determine whether AR42 penetrates the blood‐brain barrier (BBB), and 4) to study the pharmacotoxicity profile of AR42.

Histone Deacetylase Inhibitor AR-42 Differentially Affects Cell-cycle Transit in Meningeal and Meningioma Cells, Potently Inhibiting NF2-Deficient Meningioma Growth

Meningiomas constitute about 34% of primary intracranial tumors and are associated with increased mortality in patients with neurofibromatosis type 2 (NF2). To evaluate potential medical therapies for these tumors, we have established a quantifiable orthotopic model for NF2-deficient meningiomas. We showed that telomerase-immortalized Ben-Men-1 benign meningioma cells harbored a single nucleotide deletion in NF2 exon 7 and did not express the NF2 protein, merlin. We also showed that AR-42, a pan-histone deacetylase inhibitor, inhibited proliferation of both Ben-Men-1 and normal meningeal cells by increasing expression of p16(INK4A), p21(CIP1/WAF1), and p27(KIP1). In addition, AR-42 increased proapoptotic Bim expression and decreased anti-apoptotic Bcl(XL) levels. However, AR-42 predominantly arrested Ben-Men-1 cells at G(2)-M whereas it induced cell-cycle arrest at G(1) in meningeal cells. Consistently, AR-42 substantially decreased the levels of cyclin D1, E, and A, and proliferating cell nuclear antigen in meningeal cells while significantly reducing the expression of cyclin B, important for progression through G(2), in Ben-Men-1 cells. In addition, AR-42 decreased Aurora A and B expression. To compare the in vivo efficacies of AR-42 and AR-12, a PDK1 inhibitor, we generated and used luciferase-expressing Ben-Men-1-LucB cells to establish intracranial xenografts that grew over time. While AR-12 treatment moderately slowed tumor growth, AR-42 caused regression of Ben-Men-1-LucB tumors. Importantly, AR-42-treated tumors showed minimal regrowth when xenograft-bearing mice were switched to normal diet. Together, these results suggest that AR-42 is a potential therapy for meningiomas. The differential effect of AR-42 on cell-cycle progression of normal meningeal and meningioma cells may have implications for why AR-42 is well-tolerated while it potently inhibits tumor growth.

Delays in Diagnosis of Congenital Hearing Loss in Rural Children

OBJECTIVE To examine the incidence of pediatric congenital hearing loss and the timing of diagnosis in a rural region of hearing healthcare disparity. STUDY DESIGN Data from the Kentucky newborn hearing-screening program was accessed to determine the incidence of congenital hearing loss in Kentucky, both in the extremely rural region of Appalachia and non-Appalachian region of Kentucky. We also performed a retrospective review of records of children with congenital hearing loss at our institution to determine the timing of diagnostic testing. RESULTS In Kentucky, during 2009-2011, there were 6970 newborns who failed hearing screening; the incidence of newborn hearing loss was 1.71 per 1000 births (1.28/1000 in Appalachia and 1.87/1000 in non-Appalachia); 23.8% of Appalachian newborns compared with 17.3% of non-Appalachian children failed to obtain follow-up diagnostic testing. Children from Appalachia were significantly delayed in obtaining a final diagnosis of hearing loss compared with children from non-Appalachian regions (P = .04). CONCLUSION Congenital hearing loss in children from rural regions with hearing healthcare disparities is a common problem, and these children are at risk for a delay in the timing of diagnosis, which has the potential to limit language and social development. It is important to further assess the causative factors and develop interventions that can address this hearing healthcare disparity issue.

Three-Dimensional Segmented Volumetric Analysis of Sporadic Vestibular Schwannomas: Comparison of Segmented and Linear Measurements

Objective To compare 3-D segmented volumetric analysis of vestibular schwannomas (VS) with traditional linear tumor measurement on serial magnetic resonance imaging (MRI) studies to assess volume and growth rates. Study Design Case series with retrospective chart review. Setting Tertiary care medical center. Methods This analysis identified 24 VS patients clinically followed with serial gadolinium enhanced images. Maximum linear dimensions (MLD) were obtained from gadolinium-contrasted T1 sequences from 3 serial MRI scans per RECIST guidelines. MLD was cubed (MLD3) and orthogonal analysis (OA) was carried out to provide volumetric estimates for comparison with segmented data. Segmented volumetric analysis (SVA) was performed with semi-automated 3-D conformal procedure. Tumor volume, percentage change in volume, and interval percentage change were compared using paired 2-tailed t tests. Results The average interval between MRIs was 2.6 years. Volume estimates differed significantly between SVA and OA and MLD3 at all intervals. Linear growth measurements averaged 0.5 mm/y (5.4%). Volumetric growth was 50 mm3/y (22.8%) with SVA, 110 mm3/y (19.6%) with OA, and 210 mm3/y (14.4%) with MLD3 estimates. Differences between MLD and both MLD3 and SVA were significant, but significance between MLD3 and SVA was only identified in interval analysis. Progression was identified in 75% more patients with SVA than OA, MLD3, or MLD. Conclusions VS assume complex configurations. Linear measurements inaccurately estimate tumor volume and growth compared with segmented analysis. SVA is a useful clinical tool that accurately assesses tumor volume. Use of outcomes such as tumor volume and percentage of volume change may be more sensitive in assessing tumor progression compared with linear measurements.

Assessment of Appalachian region pediatric hearing healthcare disparities and delays.

The purpose of this study was to examine the timing of diagnostic and therapeutic services in cochlear implant recipients from a rural Appalachian region with healthcare disparity.

Long-term hearing results in gamma knife radiosurgery for acoustic neuromas.

Objectives: There are many studies that have examined functional outcomes following Gamma Knife treatment; however, few have reported long‐term audiometric data. This study analyzed the long‐term hearing results of Gamma Knife radiosurgery in the treatment of acoustic neuromas.

Rural barriers to early diagnosis and treatment of infant hearing loss in Appalachia.

Objective The purpose of this study was to assess regional parental barriers in the diagnostic and therapeutic process after abnormal newborn hearing screening (NHS) testing. Study design Cross-sectional questionnaire study. Setting Tertiary medical center. Patients Parents of infants who failed NHS in Kentucky from January 2009 to February 2012. Main outcome measure Demographic information, county of origin, attitudes and perceptions regarding NHS, and barriers in the NHS diagnostic process. Results There were 460 participants in the study, which included 25.4% of parents from the Appalachian region. Twenty-one percent of Appalachian parents found the process on newborn hearing testing difficult. Appalachian parents were more likely to have no more than 12 years of education (odds ratio [OR], 1.7; p = 0.02) and Medicaid insurance (OR, 2.3; p < 0.001) compared with non-Appalachian parents. A higher percentage of Appalachian parents were unaware of the NHS results at the time of hospital discharge than non-Appalachians (14% versus 7%, p = 0.03). Distance from the diagnostic/therapeutic center represented was a significant barrier for Appalachian parents (OR, 2.8; p = 0.001). Compared with urban parents, a greater percentage of rural parents had never heard of a cochlear implant (p = 0.01). Appalachian parents expressed a strong interest in telemedicine and a desire for closer services. Conclusion Multiple barriers including education, distance, accessibility, and socioeconomic factors can affect timely diagnosis and treatment of congenital hearing loss for children residing in rural areas. Educational and telemedicine programs may benefit parents in Appalachia as well as parents in other rural areas.

Hemangioblastoma of the Cerebellopontine Angle

Tumors of the cerebellopontine angle (CPA) constitute 6% to 10% of all intracranial neoplasms. Most are vestibular schwannomas (VSs) and meningiomas, but as many as 1 in 5 CPA lesions are of other etiologies. 1,2 Hemangioblastomas (HMBs), which are highly vascular tumors of the central nervous system, represent up to 12% of infratentorial, intracranial tumors in adults and typically arise in the cerebellum, spinal cord, and brain-stem. 3 One in 4 HMBs is associated with von Hippel Lindau (VHL) disease. 4 A cerebellar HMB is found in 44% to 72% of patients with VHL disease 5 ; however, involvement of the CPA is uncommon. When present within the CPA, HMBs may mimic VSs because the 2 entities have similar magnetic resonance imaging (MRI) characteristics. Cystic changes are seen in 70% to 75% of all HMBs. 6,7 We report our experience with a large CPA HMB, which was initially thought to be an atypical cystic VS. Clinical and histologic findings of HMBs are discussed along with the potential for hearing preservation surgery when these lesions occur in the CPA.

Adult progressive sensorineural hearing loss: is preoperative imaging necessary before cochlear implantation?

Objective Preoperative evaluation of cochlear implant candidate includes routine imaging to identify anatomic abnormalities that may preclude or complicate implantation, such as cochlear aplasia, absent/narrowed internal auditory canals, cochlear ossificans, or significant traumatic fracture. The aim of this study is to determine if preoperative imaging is necessary in select cochlear implant candidates, thus defraying cost and ionizing radiation. Study Design Retrospective chart review. Setting Tertiary referral facility. Patients Adult patients with progressive sensorineural hearing loss without evidence of head trauma, meningitis, or congenital hearing loss who underwent cochlear implantation. Interventions Diagnostic and therapeutic. Main Outcome Measures Preoperative radiologic abnormalities, deviation from standard cochlear implant operation. Results One hundred eighteen cochlear implants met inclusion criteria; 23.7% of CT scans had a documented abnormality, including chronic otitis media (14.4%), otosclerosis (4.2%), and an enlarged vestibular aqueduct (3.4%). There were 6 eventful surgeries in patients with normal documented CT scan. Events included multiple insertion attempts (3.4%), CSF leak (2.5%), and no apparent round window (2.5%). In every case, a cochlear implant was able to be placed successfully. Conclusion In the appropriately selected patient, preoperative imaging is not necessary as it does not impact the cochlear implant surgery and will defray cost and ionizing radiation.