The purpose of this review is to provide a sufficiently detailed perspective on epidemiologic studies of primary brain tumors to encourage multidisciplinary etiologic and prognostic studies among surgeons, neuro-oncologists, epidemiologists, and molecular scientists. Molecular tumor markers that predict survival and treatment response are being identified with hope of even greater gains in this area from emerging array technologies. Regarding risk factors, studies of inherited susceptibility and constitutive polymorphisms in genes pertinent to carcinogenesis (for example, DNA repair and detoxification genes and mutagen sensitivity) have revealed provocative findings. Inverse associations of the history of allergies with glioma risk observed in 3 large studies and reports of inverse associations of glioma with common infections suggest a possible role of immune factors in glioma genesis or progression. Studies continue to suggest that brain tumors might result from workplace, dietary, and other personal and residential exposures, but studies of cell phone use and power frequency electromagnetic fields have found little to support a causal connection with brain tumors; caveats remain. The only proven causes of brain tumors (that is, rare hereditary syndromes, therapeutic radiation, and immune suppression giving rise to brain lymphomas) account for a small proportion of cases. Progress in understanding primary brain tumors might result from studies of well-defined histologic and molecular tumor types incorporating assessment of potentially relevant information on subject susceptibility and environmental and noninherited endogenous factors (viruses, radiation, and carcinogenic or protective chemical exposures through diet, workplace, oxidative metabolism, or other sources). Such studies will require the cooperation of researchers from many disciplines.
In 1997, the PTEN gene (phosphatase and tensin homolog deleted on chromosome 10) was identified as a tumor suppressor gene on the long arm of chromosome 10. Since then, important progress has been made with respect to the understanding of the role of the Pten protein in the normal development of the brain as well as in the molecular pathogenesis of human gliomas. This review summarizes the current state of the art concerning the involvement of aberrant Pten function in the development of different biologic features of malignant gliomas, such as loss of cell-cycle control and uncontrolled cell proliferation, escape from apoptosis, brain invasion, and aberrant neoangiogenesis. Most of the tumor-suppressive properties of Pten are dependent on its lipid phosphatase activity, which inhibits the phosphatidylinositol-3'-kinase (PI3K)/Akt signaling pathway through dephosphorylation of phosphatidylinositol-(3,4,5)-triphosphate. The additional function of Pten as a dual-specificity protein phosphatase may also play a role in glioma pathogenesis. Besides the wealth of data elucidating the functional roles of Pten, recent studies suggest a diagnostic significance of PTEN gene alterations as a molecular marker for poor prognosis in anaplastic astrocytomas and anaplastic oligodendrogliomas. Furthermore, the possibility of selective targeting of PTEN mutant tumor cells by specific pharmacologic inhibitors of members of the Pten/PI3K/Akt pathway opens up new perspectives for a targeted molecular therapy of malignant gliomas.
Radiotherapeutic doses for malignant gliomas are generally palliative because greater, supposedly curative doses would impart clinically unacceptable damage to nearby vital CNS tissues. To improve radiation treatment for human gliomas, we evaluated microbeam radiation therapy, which utilizes art array of parallel, microscopically thin (<100 μm) planar beams (microbeams) of synchrotron-generated X rays. Rats with i.e. 9L gliosarcoma tumors were exposed laterally to a single microbeam, 27 pm wide and 3.8 mm high, stepwise, to produce irradiation arrays with 50, 75, or 100 μm of on-center beam spacings and 150, 250, 300, or 500 Gy of in-slice, skin-entrance, single-exposure doses. The resulting array size was 9 mm wide and 10.4 mm high (using three 3.8-mm. vertical tiers); the beam's median energy was 70 keV. When all data were collated, the median survival was 70 days; no depletion of nerve cells was observed. However, when data from the highest skin-entrance dose and/or the smallest microbeam spacings were excluded, the median survival time of the subset of rats was 170 days, and no white matter necrosis was observed. Others have reported unilateral single-exposure broad-beam irradiation of i.e. 9L gliosarcomas at 22.5 Gy with a median survival of only 34 days and with severe depletion of neurons. These results suggest that the therapeutic index of unidirectional microbeams is larger than that of the broad beams and that an application for microbeam radiation therapy in treating certain malignant brain tumors may be found in the future.
Temozolomide is an effective agent in the treatment of recurrent malignant gliomas. The standard dosage is 150200 mg/m(2) per day for 5 days in a 28-day cycle. A prior phase I study established a chronic daily temozolomide dose that significantly increased the total dose administered and suggested a superior response rate. In a prospective phase H trial, we treated 35 patients with recurrent malignant gliomas with temozolomide 75 mg/m(2) per day for 42 consecutive days in a 70-day cycle. Median age was 55 years (range, 27-73 years) and median Karnofsky performance score was 70 (range, 60-90). Twenty-eight (79%) patients had glioblastoma multiforme, 3 (9%) anaplastic astrocytoma, 2 (6%) anaplastic oligodendroglioma, and 2 (6%) anaplastic oligoastrocytoma. All but one had prior radiotherapy, and 27 had prior chemotherapy. There were 2 partial (anaplastic astrocytoma) and 3 minor (glioblastoma multiforme) radiographic responses; 17 patients had progressive disease at the end of the first cycle. In 55 cycles of temozolomide, there were 8 episodes of asymptomatic drug-related grade 3 toxicity: 6 lymphopenia, 1 neutropenia, and I thrombocytopenia. Median progression-free survival and overall survival were 2.5 and 8.7 months (2.3 and 7.7 months in glioblastoma multiforme patients). At 6 months, progression-free survival and overall survival rates were 27% and 67% (19% and 60% in glioblastoma multiforme). Quality of fife scores did not change significantly during treatment. We conclude that the extended low-dose schedule of temozolomide is well tolerated in heavily pre-treated patients; however, our results do not support an improved rate of response or survival.
Temozolomide is a novel second-generation oral alkylating agent with demonstrated efficacy and safety in patients with recurrent glioblastoma multiforme (GBM) and anaplastic astrocytoma (AA). A multicenter phase H trial was conducted to determine the efficacy and safety of temozolomide before radiotherapy in patients with newly diagnosed GBM and AA. Fifty-seven patients (51 adult, 6 pediatric) with newly diagnosed supratentorial GBM or AA were treated with temozolomide (200 mg/m(2) per day for 5 consecutive days every 28 days) for a maximum of 4 cycles. All patients were then treated with external beam radiotherapy. Twenty-two patients (39%) achieved objective response, including 6 (11%) with complete response (CR) and 16 (28%) with partial response (PR). Additionally, 18 (32%) patients had stable disease (SD). Of 21 patients (18 adult, 3 pediatric) with AA, 2 (10%) achieved CR, 5 (24%) achieved PR, and 8 (38%) had SD. Among adult patients with AA, the median progression-free and overall survival rates were 7.6 and 23.5 months, respectively. Among 36 patients (33 adult, 3 pediatric) with GBM, 4 (11%) had CR, 11 (31%) had PR, and 10 (28%) had SD. The median progression-free and overall survival rates among adult patients with GBM were 3.9 and 13.2 months, respectively. Temozolomide was safe and well tolerated in adult and pediatric patients. Grades 3 and 4 adverse events were reported in 16 (28%) and 7 (12%) patients, respectively. Temozolomide was safe and effective in treating newly diagnosed GBM and AA before radiotherapy. This pre-irradiation treatment, approach appears promising, but will require additional evaluation in comparative studies.
A phase II study of irinotecan (CPT-11) was conducted at Duke University Medical Center, Durham, NC, to evaluate the activity of this agent in children with high-risk malignant brain tumors. A total of 22 children were enrolled in this study, including 13 with histologically verified recurrent malignant brain tumors (glioblastoma multiforme [GBM] 4, anaplastic astrocytoma 1, ependymoma 5, and medulloblastoma/primitive neuroectodermal tumor 3), 5 with recurrent diffuse pontine glioma, and 4 with newly diagnosed GBM. All patients with recurrent tumor had prior chemotherapy and/or irradiation. Each course of CPT-11 consisted of 125 mg/m(2) per week given i.v. for 4 weeks followed by a 2-week rest period. Patients with recurrent tumors received therapy until disease progression or unacceptable toxicity. Patients with newly diagnosed tumors initially received 3 cycles of treatment to assess tumor response and then were allowed radiotherapy at physician's choice; patients who demonstrated a response to CPT-11 prior to radiotherapy were allowed to continue the drug after radiation until disease progression or unacceptable toxicity. A 25% to 50% close reduction was made for grade III-IV toxicity. Responses were assessed after every course by gadolinium-enhanced MRI of the brain and spine. Twenty-two patients received a median of 2 courses of CPT-11 (range, 1-16). Responses were seen in 4 of 9 patients with GBM or anaplastic astrocytoma (44%; 95% confidence interval, 11%-82%) (complete response in 2 patients with recurrent GBM lasting 9 months and 48+ months; partial response in one patient with a newly diagnosed midbrain GBM lasting 18 months prior to radiotherapy; and partial response lasting 11 months in I patient with recurrent anaplastic astrocytoma), 1 of 5 patients with recurrent ependymoma (partial response initially followed by stable disease lasting 11 months), and none of 5 patients with recurrent diffuse pontine glioma. Two of 3 patients with medulloblastoma/primitive neuroectodermal tumor had stable disease for 9 and 13 months. Toxicity was mainly myelosuppression, with 12 of 22 patients (50%) suffering grade II-IV neutropenia. Seven patients required dose reduction secondary to neutropenia. CPT-11, given in this schedule, appears to be active in children with malignant glioma, medulloblastoma, and ependymoma with acceptable toxicity. Ongoing studies will demonstrate if activity of CPT-11 can be enhanced when combined with alkylating agents, including carmustine and temozolomide.
Endostatin, the 20-kDa C-terminal fragment of collagen XVIII, has previously been shown to inhibit growth and induce regression of different experimental tumors in rodents. In this study, we show that recombinant murine and human endostatin, produced in 293 EBNA cells and yeast, respectively, inhibit ectotopic as well as orthotopic growing BT4Cn gliosarcomas in BD-IX rats. In rats in which s.c. gliomas were grown for a total of 29 days, systemic treatment with recombinant murine endostatin induced about 50% reduction of intratumoral blood flow and tumor size after only 10 days of therapy. In contrast, the blood flow to irrelevant organs was unaffected by endostatin, indicating its specificity of action. Tumors were not observed to increase in size or regrow after cessation of therapy. Furthermore, endostatin-treated rats with i.c. tumors had significantly longer survival time than did untreated controls. In the treated rats, endostatin therapy resulted in a reduced tumor blood vessel volume and an increased tumor cell density with an increased apoptotic index within a given tumor volume, as verified by flow cytometry and by staining with deoxynucleotidyltransferase-mediated dUTP nick-end labeling. This work verifies the general anti-angiogenic and antitumor effects of endostatin and indicates that the protein may also be considered as a treatment strategy for malignant brain tumors.
The Consensus Conference on Brain Tumor Definition was facilitated by the Central Brain Tumor Registry of the United States and held on November 10, 2000, in Chicago, Illinois, to reach multidisciplinary agreement on a standard definition of brain tumors for collecting and comparing data in the U.S. The Brain Tumor Working Group, convened in 1998 to determine the status of brain tumor collection in the U.S., outlined 4 recommendations of which the first 2 guided the discussion for the Consensus Conference: (1) standardization of a definition of primary brain tumors that is based on site alone, rather than on site and behavior, and that can be used by surveillance organizations in collecting these tumors; and (2) development of a reporting scheme that can be used for comparing estimates of primary brain tumors across registries. Consensus was reached on the collection of all primary brain tumor histologies found and reported in the brain or CNS ICD-O site codes (C70.0-C72.9 and C75.1-C75.3), including those coded benign and uncertain as well as those coded malignant. In addition, a comprehensive listing of histologies occurring in the brain and CNS, based on the CBTRUS grouping scheme, was formulated to provide a template for reporting in accordance with the second recommendation of the Brain Tumor Working Group. With consensus achieved on the first 2 recommendations, the stage is set to move forward in estimating additional resources necessary for the collection of these tumors, including funding, training for cancer registrars, identifying quality control measures, and developing computerized edit checks, as outlined in the last 2 recommendations of the Brain Tumor Working Group.
Histone deacetylase inhibitors that increase histone acetylation on transformed cells are being investigated as unique anticancer drugs. The aim of this investigation was to evaluate an anti proliferative activity of the histone deacetylase inhibitors sodium butyrate (NaBT) and trichostatin A on 5 glioma cell lines, T98G, A172, U-87 MG, U-118 MG, and U-373 MG, with the examination of the altered expressions in p21 and gelsolin genes. Treatment with 5-mM NaBT and 40 ng/ml trichostatin A for 48 h caused more than a 50% growth inhibition in 5 cell lines as measured by cell proliferation assays. An increase in histone acetylation was confirmed in each cell line. After treatment with 5 mM NaBT, T98G, A172, and U118 cells undergo apoptosis as indicated by DNA ladder formation. Treatment with NaBT and trichostatin A also decreased DNA synthesis as examined by the fluorescence-activated cell sorting analysis in T98G and U87 cells. In addition to the suppression of cell growth, the up regulation of p21 and gelsolin expression was observed after treatment with NaBT, especially in T98G cells. Maximum expression of p21 and gelsolin was observed within 24 h after treatment. Results from our in vitro studies indicate that the treatment of human glioma cells with one of the histone deacetylase inhibitors suppresses cell growth with decreasing DNA synthesis and stimulates apoptosis, and that associated molecular mechanisms responsible for these effects include increased histone acetylation as well as enhanced expression of p21 and gelsolin.
Although no optimal treatment is currently available for malignant brain tumors, as the molecular mechanisms underlying brain tumor development have been delineated, new chemotherapeutic agents that act directly on specific molecular targets have become available. Defining a specific molecular target raises the possibility that the molecular effects of a given agent can be analyzed in patients in a clinical trial. Specifically, whereas standard phase I and R clinical trials classically determine the safety and efficacy of agents by using indirect global end points, these new biological agents afford the opportunity to incorporate molecular end points into phase I and II clinical trials to determine whether the agent under investigation is actually doing what it was intended to do. This work presents avenues for improving current brain tumor clinical trial designs based on the molecular specificity of new agents and the unique features of brain tumors. Specifically, the authors recommend brain-applicable phase I and II clinical trial strategies that take advantage of the targeted nature of new agents to maximize information about their efficacy, toxicity, and molecular effects.