Mapping of homozygous deletions on human chromosome 10q23 has led to the isolation of a candidate tumor suppressor gene, PTEN, that appears to be mutated at considerable frequency in human cancers. In preliminary screens, mutations of PTEN were detected in 31% (13/42) of glioblastoma cell lines and xenografts, 100% (4/4) of prostate cancer cell lines, 6% (4/65) of breast cancer cell lines and xenografts, and 17% (3/18) of primary glioblastomas. The predicted PTEN product has a protein tyrosine phosphatase domain and extensive homology to tensin, a protein that interacts with actin filaments at focal adhesions. These homologies suggest that PTEN may suppress tumor cell growth by antagonizing protein tyrosine kinases and may regulate tumor cell invasion and metastasis through interactions at focal adhesions.

https://science.sciencemag.org/content/sci/275/5308/1943.full.pdf

PTEN, a Putative Protein Tyrosine Phosphatase Gene Mutated in Human Brain, Breast, and Prostate Cancer

http://orion.bme.columbia.edu/lulab/pdf/Altman_Silk-Based-Biomaterials_2003.pdf

Silk-based biomaterials

DNase I hypersensitive sites (DHSs) are markers of regulatory DNA and have underpinned the discovery of all classes of cis-regulatory elements including enhancers, promoters, insulators, silencers and locus control regions. Here we present the first extensive map of human DHSs identified through genome-wide profiling in 125 diverse cell and tissue types. We identify ∼2.9 million DHSs that encompass virtually all known experimentally validated cis-regulatory sequences and expose a vast trove of novel elements, most with highly cell-selective regulation. Annotating these elements using ENCODE data reveals novel relationships between chromatin accessibility, transcription, DNA methylation and regulatory factor occupancy patterns. We connect ∼580,000 distal DHSs with their target promoters, revealing systematic pairing of different classes of distal DHSs and specific promoter types. Patterning of chromatin accessibility at many regulatory regions is organized with dozens to hundreds of co-activated elements, and the transcellular DNase I sensitivity pattern at a given region can predict cell-type-specific functional behaviours. The DHS landscape shows signatures of recent functional evolutionary constraint. However, the DHS compartment in pluripotent and immortalized cells exhibits higher mutation rates than that in highly differentiated cells, exposing an unexpected link between chromatin accessibility, proliferative potential and patterns of human variation. An extensive map of human DNase I hypersensitive sites, markers of regulatory DNA, in 125 diverse cell and tissue types is described; integration of this information with other ENCODE-generated data sets identifies new relationships between chromatin accessibility, transcription, DNA methylation and regulatory factor occupancy patterns. This paper describes the first extensive map of human DNaseI hypersensitive sites — markers of regulatory DNA — in 125 diverse cell and tissue types. Integration of this information with other data sets generated by ENCODE (Encyclopedia of DNA Elements) identified new relationships between chromatin accessibility, transcription, DNA methylation and regulatory-factor occupancy patterns. Evolutionary-conservation analysis revealed signatures of recent functional constraint within DNaseI hypersensitive sites.

/pdf/the-accessible-chromatin-landscape-of-the-human-genome-2cq94d4b48.pdf

The accessible chromatin landscape of the human genome

Negative Regulation of PKB/Akt-Dependent Cell Survival by the Tumor Suppressor PTEN

The athymic (nude) mouse is a useful model for studying the biology and response to therapies of human tumors in vivo. A survey of recent literature revealed the use of 19 different formulas for determining the size of subcutaneous tumors grown as xenografts in nude mice (2 for determining tumor area, 3 for tumor diameter, and 14 for calculating tumor volume). We compared the volumes, areas, and diameters predicted by each of the 19 formulas with the actual weights of 50 tumors ranging from 0.46 to 22.0 g established in nude mice as xenografts from human cell lines. In addition to determining how well each formula predicted relative tumor size, we analyzed how well each formula estimated actual tumor mass. The ellipsoid volume formulas (π/6 x L x W x H and 1/2 x L x W x H) were best for estimating tumor mass (r=0.93), whereas measurements of diameter correlated poorly with tumor mass (r<0.66). Although determination of tumor area correlated well with tumor mass in small tumors (r=0.89), correlations of area with tumor mass for large tumors were poor (r=0.41). We conclude that determination of the ellipsoid volume from measurements of three axes consistently yields the most accurate estimations of both relative and actual tumor mass.

Determination of subcutaneous tumor size in athymic (nude) mice

To determine the prognostic significance of histologic variables in oligodendroglial neoplasms, the presence and degree of 15 such variables were correlated with postoperative survival rates in 71 patients. By univariate analysis, prognostically significant factors, in order of decreasing importance, were mitoses (log), necrosis, nuclear cytologic atypia, vascular hypertrophy, and vascular proliferation. When studied by stepwise regression, necrosis and the number of mitoses contained all of the prognostically useful information. When each of the five variables significant by univariate analysis was tested in the Cox model by adding a variable to the model containing the other four, necrosis was found to be the only independently significant variable. There were significant positive pairwise correlations between each of the five significant histologic variables except for cytologic atypia with necrosis. The only histologic variable with a significant association with older age was the number of mitoses. These results suggest that necrosis and, to a lesser extent, the mitotic count are features that, in the appropriate setting, can be used to identify the "anaplastic" oligodendroglioma.

Clinicopathologic correlations in the oligodendroglioma

Supratentorial glioblastoma multiforme (GBM) is a lethal malignancy. Subtotal surgical resection and post operative external beam radiotherapy palliate symptoms and prolong survival, but very few patients survive more than 3 years following diagnosis.‘,3,20*32,43,46,48*5’*58,66 Whereas the probability of survival of supratentorial anaplastic astrocytoma (AA) is slightly better, most patients will still succumb to the tumor.58-60*66 The resistance of these neoplasms to conventional therapies has prompted many physicians to undertake new clinical and laboratory investigations. These have included the use of chemotherapy,44 immunotherapy,40 multiple-fraction-perday radiotherapy,2’,34,49 radiotherapy with chemical radiosensitizers,6’ and neutron radiotherapy.45 As interest in the biology and treatment of malignant gliomas has increased, many conceptual verities have been proposed to guide therapeutic investigations, These include the significance of the cellular heterogeneity of AA and GBM,‘2,24 the presence of the blood-brain-barrier (BBB) as a functional obstruction to chemotherapy, and the local nature of these tumors. In this editorial, we focus on the last of these premises. We have selected this issue because of its major implications for any treatment that is directed at a specific portion of the brain rather than the whole brain: BBB disruption, intracarotid drug administration, and brain brachytherapy. Interstitial brachytherapy is used for primary and recurrent GBM and AA. The technique consists of the stereotactic computed tomography (CT) or magnetic resonance imaging (MRI) guided placement of coaxial catheters within and around the tumor. Radioactive sources are after-loaded into the catheters to deliver continuous low-dose rate irradiation. After a specified dose is delivered, the system is removed.22~27~28~39~45 Interstitial hyperthermia generated by implanted microwave antennae may be administered in conjunction with the radiation.52 One of the justifications invoked for brachytherapy is the concept of malignant gliomas as localizedlesions. Allusions to this concept abound in the literature. “Most malignant gliomas are localized to a single area of the brain, central nervous system (CNS) metastases from these tumors are uncommon and systemic metastases are rare.“29 “Since an astrocytoma is almost invariably a nonmetastatizing single mass, ideally it should lend itself best to regional treatment.“** “Because a primary brain tumor is most often a localized disease, hyperthermia, intratumoral chemotherapy, and interstitial irradiation, the stereotactic placement of radioactive sources directly into brain tumors, have been suggested as possible local treatments for brain tumors.“*’

The fallacy of the localized supratentorial malignant glioma.

Ependymomas: a clinicopathologic study.

Fifteen permanent cell lines derived from human gliomas which are individually distinct by immunologic and biochemical criteria were evaluated to determine if morphologic or cell biologic parameters distinguished the 4 lines which were tumorigenic in athymic nude mice. By subjective morphologic appraisal, the 4 tumorigenic lines were considered "malignant" or "borderline," but 4 of the non-tumorigenic lines were also classified in this way. By objective criteria, these 15 lines varied markedly in percentage of piled-up cells, chromatin pattern, pleomorphism, nuclear to cytoplasmic ratio, number of bizarre multinucleate giant cells, presence of abnormal mitotic figures, percentage of colony formation in soft agar, saturation density, population doubling time, and absolute plating efficiency. Among these criteria, percentage of colony formation in soft agar had the highest correlation coefficiency with tumorigenicity, and when this parameter was held constant the only additional characteristic which correlated significantly (p less than .05) was the number of bizarre multinucleate giant cells. When the 11 non-tumorigenic lines were ranked by these 2 criteria, 1 non-tumorigenic line (U-251 MGsp) had greater than .95 predicted probability of tumorigenicity. Although further tumorigenicity testing may increase the number of tumorigenic lines, the lines with few "malignant" characteristics may correspond to the population resembling cells of low grade astrocytomas seen within glioblastomas. The histologic pleomorphism of human gliomas is reflected in their morphologic and cell biologic diversity in culture.

Relationship of in vitro morphologic and growth characteristics of established human glioma-derived cell lines to their tumorigenicity in athymic nude mice.

Two patients with posttraumatic diencephalic seizures, characterized by autonomic dysfunction and extensor posturing, had partial responses to bromocriptine and complete responses to morphine. Probable synergism between the two agents was noted. These 2 cases suggest the potential effectiveness of this regimen for the treatment of diencephalic seizures, raise questions regarding the role of the dopaminergic and opioid systems in this disease entity, and support the hypothesis that diencephalic seizures represent a release phenomenon in the brain.

Dennis E. Bullard

Papers

Clinicopathologic correlations in the oligodendroglioma

The fallacy of the localized supratentorial malignant glioma.

Ependymomas: a clinicopathologic study.

Relationship of in vitro morphologic and growth characteristics of established human glioma-derived cell lines to their tumorigenicity in athymic nude mice.

Diencephalic seizures: responsiveness to bromocriptine and morphine.