Mouse models of brain tumors and their applications in preclinical trials.

Primary brain tumors, including gliomas and medulloblastomas, often represent the most devastating and difficult-to-treat tumors, and are thought to arise from glial cells and/or their precursors or the external granule cell layer, respectively. The majority of genetic alterations characteristic of the human brain tumors are thought to occur in genes encoding proteins involved in signal transduction or cell cycle regulation. Accurate recapitulation of these genetic alterations using genetically engineered mouse models allows for in vivo modeling of brain tumors with similar histopathology, etiology, and biology. These mouse models, in turn, increase our understanding of brain tumor initiation, formation, progression, and metastasis, providing an experimental system to discover novel therapeutic targets and test various therapeutic agents.

Molecular imaging of alkylguanine-DNA alkyltransferase: further evaluation of radioiodinated derivatives of O6-benzylguanine.

PURPOSE: An inverse correlation has been established between tumor levels of the DNA repair protein alkylguanine-DNA alkyltransferase (AGT) and a positive outcome after alkylator chemotherapy. Quantitative imaging of AGT could provide important information for patient-specific cancer treatment. Several radiolabeled analogues of O6-benzylguanine (BG), a potent AGT inactivator, have been developed and shown to be capable of labeling pure AGT protein. Herein, two of these analogues--O6-3-[*I]iodobenzylguanine ([*I]IBG) and O6-3-[*I]iodobenzyl-2'-deoxyguanosine ([*I]IBdG)--were further evaluated in two murine xenograft models. (AcO)2-[131I]IBdG, a peracetylated derivative of IBdG, also was investigated as an alternative agent. METHODS: Several biodistribution studies of radioiodinated IBG and IBdG were performed in TE-671 human rhabdomyosarcoma and DAOY human medulloblastoma murine xenograft models. Mice were treated with BG or its nucleoside analogue dBG to deplete the tumor AGT content. The effect of unlabeled IBG and that of 7,8-benzoflavone (BF), an inhibitor of the cytochrome P-450 isozyme CYP1A2, on the tumor uptake of the tracers was determined. The uptake of (AcO)2-[131I]IBdG along with that of [125I]IBdG in DAOY cells in vitro was determined in the presence and absence of a nucleoside transporter inhibitor, dipyridamole. RESULTS: Pretreatment of mice either with BG or dBG failed to reduce tumor levels of [*I]IBG or [*I]IBdG even though such treatments completely depleted tumor AGT content. Treatment of mice with BF increased tumor uptake of [125I]IBG by 56%; however, differentiation of tumors with and without AGT still was not possible. (AcO)2-[131I]IBdG, a peracetylated derivative of IBdG, had a higher uptake in vitro in DAOY tumor cells. However, its uptake, like that of [125I]IBdG, was blocked by dipyridamole. CONCLUSIONS: Taken together, these results suggest that labeled agents that are more specific for cellular AGT and that are more metabolically stable are needed.

Subarachnoid hemorrhage from brain tumors in childhood.

Six children are reported in whom subarachnoid hemorrhage was an initial symptom of brain tumor. In our neurosurgical clinics, this represented 3.6% of pediatric brain tumors and showed a frequency equal to aneurysmal rupture among nontraumatic subarachnoid hemorrhage of children. In pediatric patients, hemorrhages from brain tumors occur predominantly in the posterior fossa. The medulloblastoma, which had been believed to bleed rarely, is now realized to be a common source of tumor hemorrhages in such cases. The introduction of CT scan facilitates early recognition of hemorrhagic stroke from brain tumors and prompt management for acute intracranial hypertension and brainstem dysfunction. Although the patients achieve favorable recovery from their initial catastrophic condition, the ultimate prognosis, in the majority of cases, is still rather poor because such hemorrhages usually develop from a malignant tumor. The present and other recent reports indicate that the incidence of hemorrhagic stroke from brain tumors in pediatric patients is much higher than has been thought and is an important cause of subarachnoid hemorrhage in this age group.

Sustained tumour opacification in infants during cerebral angiography.

Total body opacification in infants following the intravenous injection of a large dose of water soluble contrast medium has long been recognised, but no example of increased radiodensity of abdominal or intracranial tumours has been reported using this technique. This paper reports the sustained opacification of intracranial tumours in three infants during cerebral angiography. Two of the tumours were papillomas of the choroid plexus of the lateral ventricle and the third a medulloblastoma of the fourth ventricle. Three possible explanations of this phenomenon are briefly considered: 1. That the amount of contrast medium was sufficient to cause total body opacification and the visibility of the tumours was due to a combination of their vascularity and the iodine concentration in the circulation blood. 2. That the observed phenomenon is peculiar to these tumours. 3. That the sustained opacity of these these tumours is due to the same cause or causes as the density enhancement of some intracranial tumours demonstrated by computerised tomography after intravenous injection of contrast medium.