BCNU-resistant human glioma cells with over-representation of chromosomes 7 and 22 demonstrate increased copy number and expression of platelet-derived growth factor genes

Anticancer activity of extracts derived from the mature roots of Scutellaria baicalensis on human malignant brain tumor cells

Background

Flavonoid-rich extracts from the mature roots of Scutellaria baicalensis have been shown to exhibit antiproliferative effects on various cancer cell lines. We assessed the ability of an ethanolic extract of S. baicalensis root to inhibit the proliferation of malignant glioma cells.

Methods

Cell lines derived from primary and recurrent brain tumors from the same patient and cells selected for resistance to the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) were used to identify antiproliferative effects of this extract when used alone and in conjunction with BCNU.

Results and discussion

Results indicated that Scutellaria baicalensis not only inhibits cellular growth in recurrent and drug resistant brain tumor cell lines, but also demonstrates an increased inhibitory effect when used in conjunction with BCNU.

Conclusion

The results of this study support the efficacy of S. baicalensis as an anticancer agent for glioblastomas multiforme and a potential adjuvant treatment to current chemotherapeutic agents used in the treatment of both primary and recurrent GBMs. Further studies of the effects of individual flavonoids alone and in combination with each other and with currently used therapies are needed.

Chromosomal alterations cause the high rates and wide ranges of drug resistance in cancer cells

Conventional mutation-selection theories have failed to explain (i) how cancer cells become spontaneously resistant against cytotoxic drugs at rates of up to 10(-3) per cell generation, orders higher than gene mutation, even in cancer cells; (ii) why resistance far exceeds a challenging drug-a state termed multidrug resistance; (iii) why resistance is associated with chromosomal alterations and proportional to their numbers; and (iv) why resistance is totally dependent on aneuploidy. We propose here that cancer-specific aneuploidy generates drug resistance via chromosomal alterations. According to this mechanism, aneuploidy varies the numbers and structures of chromosomes automatically, because it corrupts the many teams of proteins that segregate, synthesize, and repair chromosomes. Aneuploidy is thus a steady source of chromosomal variation from which, in classical Darwinian terms, resistance-specific aneusomies are selected in the presence of chemotherapeutic drugs. Some of the thousands of unselected genes that hitchhike with resistance-specific aneusomies can thus generate multidrug resistance. To test this hypothesis, we determined the rates of chromosomal alterations in clonal cultures of human breast and colon cancer lines by dividing the fraction of nonclonal karyotypes by the number of generations of the clone. These rates were about 10(-2) per cell generation, orders higher than mutation. Chromosome numbers and structures were determined in metaphases hybridized with color-coded chromosome-specific DNA probes. Further, we tested puromycin-resistant subclones of these lines for resistance-specific aneusomies. Resistant subclones differed from parental lines in four to seven specific aneusomies, of which different subclones shared some. The degree of resistance was roughly proportional to the number of these aneusomies. Thus, aneuploidy is the primary cause of the high rates and wide ranges of drug resistance in cancer cells.

Tumor Necrosis Factor-α–Induced Protein 3 As a Putative Regulator of Nuclear Factor-κB–Mediated Resistance to O6-Alkylating Agents in Human Glioblastomas

Purpose

Pre-existing and acquired drug resistance are major obstacles to the successful treatment of glioblastomas.

Methods

We used an integrated resistance model and genomics tools to globally explore molecular factors and cellular pathways mediating resistance to O6-alkylating agents in glioblastoma cells.

Results

We identified a transcriptomic signature that predicts a common in vitro and in vivo resistance phenotype to these agents, a proportion of which is imprinted recurrently by gene dosage changes in the resistant glioblastoma genome. This signature was highly enriched for genes with functions in cell death, compromise, and survival. Modularity was a predominant organizational principle of the signature, with functions being carried out by groups of interacting molecules in overlapping networks. A highly significant network was built around nuclear factor-κB (NF-κB), which included the persistent alterations of various NF-κB pathway elements. Tumor necrosis factor-α–induced protein 3 (TNFAIP3) was identified as a new regulatory component of a putative cytoplasmic signaling cascade that mediates NF-κB activation in response to DNA damage caused by O6-alkylating agents. Expression of the corresponding zinc finger protein A20 closely mirrored the expression of the TNFAIP3 transcript, and was inversely related to NF-κB activation status in the resistant cells. A prediction model based on the resistance signature enabled the subclassification of an independent, validation cohort of 31 glioblastomas into two outcome groups (P = .037) and revealed TNFAIP3 as part of an optimized four-gene predictor associated significantly with patient survival (P = .022).

Conclusion

Our results offer strong evidence for TNFAIP3 as a key regulator of the cytoplasmic signaling to activate NF-κB en route to O6-alkylating agent resistance in glioblastoma cells. This pathway may be an attractive target for therapeutic modulation of glioblastomas.

Over-representation of specific regions of chromosome 22 in cells from human glioma correlate with resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea

BACKGROUND

Glioblastoma multiforme is the most malignant form of brain tumor. Despite treatment including surgical resection, adjuvant chemotherapy, and radiation, these tumors typically recur. The recurrent tumor is often resistant to further therapy with the same agent, suggesting that the surviving cells that repopulate the tumor mass have an intrinsic genetic advantage. We previously demonstrated that cells selected for resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) are near-diploid, with over-representation of part or all of chromosomes 7 and 22. While cells from untreated gliomas often have over-representation of chromosome 7, chromosome 22 is typically under-represented.

METHODS

We have analyzed cells from primary and recurrent tumors from the same patient before and after in vitro selection for resistance to clinically relevant doses of BCNU. Karyotypic analyses were done to demonstrate the genetic makeup of these cells, and fluorescent in situ hybridization analyses have defined the region(s) of chromosome 22 retained in these BCNU-resistant cells.

RESULTS

Karyotypic analyses demonstrated that cells selected for BCNU resistance were near-diploid with over-representation of chromosomes 7 and 22. In cells where whole copies of chromosome 22 were not identified, numerous fragments of this chromosome were retained and inserted into several marker and derivative chromosomes. Fluorescent in situ hybridization analyses using whole chromosome paints confirmed this finding. Additional FISH analysis using bacterial artificial chromosome probes spanning the length of chromosome 22 have allowed us to map the over-represented region to 22q12.3-13.32.

CONCLUSION

Cells selected for BCNU resistance either in vivo or in vitro retain sequences mapped to chromosome 22. The specific over-representation of sequences mapped to 22q12.3-13.32 suggest the presence of a DNA sequence important to BCNU survival and/or resistance located in this region of chromosome 22.

Genetic alterations associated with adult diffuse astrocytic tumors

Astrocytic tumors make up a wide range of neoplasms that differ in their location in the central nervous system, morphologic features, progressive and invasive behaviors, and the age and gender of people they affect. This report reviews the cytogenetic, molecular cytogenetic, and molecular genetic abnormalities associated with diffuse infiltrating astrocytomas in adults. This group of tumors is subdivided into low-grade astrocytomas (WHO grade II), anaplastic astrocytomas (WHO grade III), and glioblastoma multiforme (WHO grade IV).

The polymorphic human glutathione transferase T1-1, the most efficient glutathione transferase in the denitrosation and inactivation of the anticancer drug 1,3-bis(2-chloroethyl)-1-nitrosourea

A member of the Theta class of human glutathione transferases (GST T1-1) was found to display the greatest catalytic activity towards the cytostatic drug 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) of the GSTs studied. In this investigation (the most extensive to date), enzymes from four classes of the soluble human GSTs were heterologously expressed, purified, and kinetically characterized. From the 12 enzymes examined, only GST M2-2, GST M3-3 and GST T1-1 had significant activities with BCNU. This establishes that the activity is not a characteristic of a particular class of GSTs. Although GST M3-3 was previously reported to have the greatest activity with BCNU, the current investigation demonstrates that GST M2-2 is equally active and that GST T1-1 has an approximately 20-fold higher specific activity than either of the Mu class enzymes. A more rigorous kinetic analysis of GST T1-1 gave the following parameters with BCNU: a k(cat) of 0.035 +/-0.003s(-1) and a K(M) of 1.0 +/- 0.1mM. The finding that GST T1-1 has the highest activity towards BCNU is significant since GST T1-1 is expressed in the brain, a common target for BCNU treatment. Furthermore, the existence of a GST T1-1 null allele in up to 60% in some populations, may influence both the sensitivity of tumors to chemotherapy and the severity of adverse side-effects in patients treated with this agent.

Genetics of nervous system tumors

Genetic aberrations are being defined for the various glial tumors. Astrocytic tumors can evolve by two different pathways. The genetic aberrations now being defined for these two pathways are different and can be associated with the grade of malignancy. In oligodendrogliomas, the genetic lesions differ from the astrocytic tumors, and several markers have been linked to chemosensitivity response and survival. Genetic aberrations in ependymomas also differ from the astrocytic tumors or oligodendrogliomas. Although additional cases are needed to study the genetic aberrations, the abnormalities identified suggest that spinal cord tumors carry different markers than intracranial tumors and that the markers within the cranium may be different based on their location.

Genetics of brain neoplasms

Transformation of a normal cell into a malignant cell involves a series of events that damage the genome. Gliomas are the most common adult neoplasm of the central nervous system. To develop new therapeutic strategies requires an understanding of the specific lesions that occur and contribute to this malignant process. Initially, data reported from the analyses of human gliomas were quite variable. This has recently changed as more data have become available and the selection of tissue analyzed is coupled with clinical criteria. Specific genetic lesions are now defining different glioma pathways, and some aberrations may be indicative of therapeutic response. This review focuses on the specific genetic aberrations associated with astrocytic and oligodenroglial tumors.

Frequent down-regulation and lack of mutation of the KAI1 metastasis suppressor gene in epithelial ovarian carcinoma

OBJECTIVE

KAI1 is a recently identified metastasis suppressor gene on human chromosome 11p11.2. It belongs to a structurally distinct family of cell surface glycoproteins. Decreased KAI1 expression seems to be involved in the progression of human prostate, lung, pancreatic, and possibly breast cancer, and recently a reduced KAI1 protein expression has been demonstrated in several ovarian carcinoma cell lines. The aim of this study is to determine whether the KAI1 gene is altered in human epithelial ovarian carcinomas. In addition, its prognostic significance in this tumor is also evaluated.

METHODS

To detect KAI1 expression, 102 tumor samples from benign, borderline, primary invasive, metastatic, and recurrent epithelial ovarian tumors were prepared for immunohistochemical study with C-16, an anti-KAI1 polyclonal antibody. In addition, cellular RNA from 24 primary invasive and 7 recurrent tumors was also analyzed for KAI1 expression by using a reverse transcriptase PCR (RT-PCR) technique. The PCR single-strand conformation polymorphism method and direct DNA sequencing were used to detect KAI1 mutation in the 44 primary invasive and 8 recurrent ovarian carcinomas.

RESULTS

In immunohistochemical study, decrease of KAI1 protein expression was associated with the progression of ovarian tumor. However, it had no relation to the stage of primary invasive cancers because of its frequent occurrence in early stage tumors. KAI1 expression was also frequently down-regulated in primary invasive and recurrent tumors in RT-PCR analysis. Except for a missense change at codon 241 (ATC to GTC), which causes the substitution of a valine for an isoleucine in the amino acid sequence and occurs in both normal and tumor tissues, no mutation of the KAI1 gene was found in any of the 52 carcinomas. Although there was a trend for deteriorating survival from patients with KAI1-preserved tumors to those with KAI1-decreased and -negative tumors, statistically it was not significant (P = 0.079).

CONCLUSION

KAI1 may play a role in the malignant progression of epithelial ovarian carcinoma through the down-regulation of expression rather than gene mutation. Since the decreased expression presented frequently in early stage tumors, it may be an early event in the progression of this tumor and its prognostic significance needs further investigation with a larger number of cases.

Heterogeneity of chemosensitivity in six clonal cell lines derived from a spontaneous murine astrocytoma and its relationship to genotypic and phenotypic characteristics

Heterogeneity in drug sensitivity must, in part, account for the relative lack of success with single agent chemotherapy for glioblastoma multiforme (GBM). In order to develop in vitro model systems to investigate this, clones derived from the VM spontaneous murine astrocytoma have been characterised with regard to drug sensitivity. Six clonal cell lines have been tested for sensitivity to a panel of cytotoxic drugs using an intermediate duration 35S-methionine uptake assay. These lines have previously been extensively characterised with regard to morphological, antigenic, kinetic, tumourigenic potential in syngeneic animals and chromosomal properties and display considerable heterogeneity. The present study indicates that heterogeneity extends to sensitivity to all classes of cytotoxic drugs. The greatest difference in sensitivity between the clones was seen in response to cell cycle-specific drugs like the Vinca alkaloids (14-fold and 20-fold for vincristine (VCR) and vindesine (VIND) respectively), while the nitrosoureas, CCNU and BCNU displayed a smaller fold difference in sensitivity (4.3 and 3.6-fold difference respectively). All the clones were considerably more resistant to the adriamycin (ADM), cis-platinum (C-PLAT) and the Vinca alkaloids than the parental cell line although the difference in sensitivity between the clones and parental cell line were less marked for the nitrosoureas and procarbazine (PCB). It has also been possible to examine the relationship between drug sensitivity and the phenotypic and genotypic properties of these clonal cell lines. There is a relationship between chromosome number and sensitivity of a wide variety of cytotoxic drugs including the nitrosoureas, Vinca alkaloids, PCB, C-PLAT, BLEO but not ADR or 5-FU. Clones with small numbers of chromosomes were more resistant than clones with gross polyploidy. Similarly, sensitivity to Vinca alkaloids and ADM, but not other classes of drugs, was greatest in cells with numerous cytoplasmic processes and which did not express large amounts of cell surface fibronectin. Preliminary experiments have been conducted on reconstituting clonal mixtures of cells with different sensitivity to Vinca alkaloids and results from these studies indicate that the drug resistance phenotype is dominant, with clonal mixtures of sensitive and resistant cell adopting the sensitivity of the more resistant partner. These cell lines should prove to be useful models for examining the cell biological basis of drug resistance in glioma and may lead to the identification and exploitation of novel cellular targets in new therapies for GBM.