Quisinostat is a brain-penetrant radiosensitizer in glioblastoma.

Histone deacetylase (HDAC) inhibitors have garnered considerable interest for the treatment of adult and pediatric malignant brain tumors. However, owing to their broad-spectrum nature and inability to effectively penetrate the blood-brain barrier, HDAC inhibitors have failed to provide substantial clinical benefit to patients with glioblastoma (GBM) to date. Moreover, global inhibition of HDACs results in widespread toxicity, highlighting the need for selective isoform targeting. Although no isoform-specific HDAC inhibitors are currently available, the second-generation hydroxamic acid-based HDAC inhibitor quisinostat possesses subnanomolar specificity for class I HDAC isoforms, particularly HDAC1 and HDAC2. It has been shown that HDAC1 is the essential HDAC in GBM. This study analyzed the neuropharmacokinetic, pharmacodynamic, and radiation-sensitizing properties of quisinostat in preclinical models of GBM. It was found that quisinostat is a well-tolerated and brain-penetrant molecule that extended survival when administered in combination with radiation in vivo. The pharmacokinetic-pharmacodynamic-efficacy relationship was established by correlating free drug concentrations and evidence of target modulation in the brain with survival benefit. Together, these data provide a strong rationale for clinical development of quisinostat as a radiosensitizer for the treatment of GBM.

5-aminolevulinic acid, fluorescein sodium, and indocyanine green for glioma margin detection: analysis of operating wide-field and confocal microscopy in glioma models of various grades.

Introduction: Surgical resection remains the first-line treatment for gliomas. Several fluorescent dyes are currently in use to augment intraoperative tumor visualization, but information on their comparative effectiveness is lacking. We performed systematic assessment of fluorescein sodium (FNa), 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX), and indocyanine green (ICG) fluorescence in various glioma models using advanced fluorescence imaging techniques. Methods: Four glioma models were used: GL261 (high-grade model), GB3 (low-grade model), and an in utero electroporation model with and without red fluorescence protein (IUE +RFP and IUE -RFP, respectively) (intermediate-to-low-grade model). Animals underwent 5-ALA, FNa, and ICG injections and craniectomy. Brain tissue samples underwent fluorescent imaging using a wide-field operative microscope and a benchtop confocal microscope and were submitted for histologic analysis. Results: Our systematic analysis showed that wide-field imaging of highly malignant gliomas is equally efficient with 5-ALA, FNa, and ICG, although FNa is associated with more false-positive staining of the normal brain. In low-grade gliomas, wide-field imaging cannot detect ICG staining, can detect FNa in only 50% of specimens, and is not sensitive enough for PpIX detection. With confocal imaging of low-intermediate grade glioma models, PpIX outperformed FNa. Discussion: Overall, compared to wide-field imaging, confocal microscopy significantly improved diagnostic accuracy and was better at detecting low concentrations of PpIX and FNa, resulting in improved tumor delineation. Neither PpIX, FNa, nor ICG delineated all tumor boundaries in studied tumor models, which emphasizes the need for novel visualization technologies and molecular probes to guide glioma resection. Simultaneous administration of 5-ALA and FNa with use of cellular-resolution imaging modalities may provide additional information for margin detection and may facilitate maximal glioma resection.

Novel experimental model of brain arteriovenous malformations using conditional Alk1 gene deletion in transgenic mice.

OBJECTIVE: Hereditary hemorrhagic telangiectasia is the only condition associated with multiple inherited brain arteriovenous malformations (AVMs). Therefore, a mouse model was developed with a genetics-based approach that conditionally deleted the causative activin receptor-like kinase 1 (Acvrl1 or Alk1) gene. Radiographic and histopathological findings were correlated, and AVM stability and hemorrhagic behavior over time were examined. METHODS: Alk1-floxed mice were crossed with deleter mice to generate offspring in which both copies of the Alk1 gene were deleted by Tagln-Cre to form brain AVMs in the mice. AVMs were characterized using MRI, MRA, and DSA. Brain AVMs were characterized histopathologically with latex dye perfusion, immunofluorescence, and Prussian blue staining. RESULTS: Brains of 55 Tagln-Cre+;Alk12f/2f mutant mice were categorized into three groups: no detectable vascular lesions (group 1; 23 of 55, 42%), arteriovenous fistulas (AVFs) with no nidus (group 2; 10 of 55, 18%), and nidal AVMs (group 3; 22 of 55, 40%). Microhemorrhage was observed on MRI or MRA in 11 AVMs (50%). AVMs had the angiographic hallmarks of early nidus opacification, a tangle of arteries and dilated draining veins, and rapid shunting of blood flow. Latex dye perfusion confirmed arteriovenous shunting in all AVMs and AVFs. Microhemorrhages were detected adjacent to AVFs and AVMs, visualized by iron deposition, Prussian blue staining, and macrophage infiltration using CD68 immunostaining. Brain AVMs were stable on serial MRI and MRA in group 3 mice (mean age at initial imaging 2.9 months; mean age at last imaging 9.5 months). CONCLUSIONS: Approximately 40% of transgenic mice satisfied the requirements of a stable experimental AVM model by replicating nidal anatomy, arteriovenous hemodynamics, and microhemorrhagic behavior. Transgenic mice with AVFs had a recognizable phenotype of hereditary hemorrhagic telangiectasia but were less suitable for experimental modeling. AVM pathogenesis can be understood as the combination of conditional Alk1 gene deletion during embryogenesis and angiogenesis that is hyperactive in developing and newborn mice, which translates to a congenital origin in most patients but an acquired condition in patients with a confluence of genetic and angiogenic events later in life. This study offers a novel experimental brain AVM model for future studies of AVM pathophysiology, growth, rupture, and therapeutic regression.