Maintenance Of Tumor Growth Research Articles

Allele-specific cancer cell killing in vitro and in vivo targeting a single-nucleotide polymorphism in POLR2A

Cancer is one of the diseases for which RNA interference is a potential therapeutic approach. Genes involved in the promotion or maintenance of tumor growth are obvious targets for RNAi. RNAi is also considered an attractive additional approach to conventional chemotherapy for cancer treatment. Moreover, siRNAs have shown a high specificity for their molecular target mRNAs as they can selectively inhibit cancer-promoting genes that differ by a point mutation. Loss of heterozygosity (LOH) reduces genes to hemizygosity in cancer cells and presents an absolute difference between normal and cancer cells. The regions of LOH are usually much larger than the tumor suppressor gene, which is lost, and has been shown to contain genes that are essential for cell survival. Single-nucleotide polymorphisms (SNPs) are the most common type of genetic variation in man. SNPs in essential genes that are frequently affected by LOH can be used as a target for a therapy against cancer cells with LOH. We have designed siRNAs against the gene of the large subunit of RNA polymerase II (POLR2A), a gene located in close proximity to the tumor suppressor gene p53, which frequently shows LOH in cancer cells. It is shown in vitro that siRNA can selectively inhibit POLR2A expression dependent on its genotype. Furthermore, cancer cell proliferation and tumor growth inhibition in nude mice was genotype dependent. We conclude that siRNA can be used for genotype-specific inhibition of tumor growth targeting an SNP in POLR2A in vivo.

Nitric Oxide-Mediated Oncogenic Loop

The gene encoding the small guanosine triphosphatase Ras was one of the first oncogenes to be discovered. Certain tumor cells require continuous presence of activated Ras oncogenes for continued proliferation. Ras has numerous targets, but protein kinase B (PKB, also known as AKT) is a critical one to sustain tumor growth. Lim et al . therefore explored what target or targets of AKT (it also has many) might account for sustained tumor growth. In an assay in which a mixture of cells was transplanted into mice (to provide a characteristic tumor microenvironment), the authors found that in the presence of tumor cells expressing the oncogenic form of Hras, the contribution of cells expressing an activated phosphoinositide 3-kinase (PI3K) subunit (to activate AKT) and LacZ (to allow detection of the cells by their blue staining) to tumors was inhibited if the AKT target eNOS (endothelial nitric oxide synthase) was depleted with short hairpin RNA (shRNA). If eNOS was depleted with shRNA, participation of such cells in tumor formation was rescued by wild-type eNOS but not by a mutant eNOS that was no longer phosphorylated by AKT. Activated eNOS makes nitric oxide, which promotes S -nitrosylation of cysteine residues in proteins, and one such target--bringing us back almost to where we started--is wild-type HRas, which is activated by such nitrosylation. Indeed, other evidence supports facilitation of the effects of oncogenic Ras by wild-type Ras proteins. Activation of AKT promoted nitrosylation of wild-type Ras, and, in assays of tumor initiation or maintenance in mice injected with transformed cells, loss of HRas inhibited tumor formation by cells with activated PI3K. This effect was overcome by expression of wild-type HRas, but an HRas in which the nitrosylated cysteine was mutated provided little recovery of tumor cell growth. In similar studies with human pancreatic tumor cells (a cancer highly dependent on Ras mutations), eNOS and the modified cysteine residue of HRas or NRas were shown to be required for initiation and maintenance of tumor growth in mice. Thus, the authors propose that oncogenic Ras proteins act through AKT and eNOS to activate wild-type Ras proteins and contribute to tumor growth. Inhibition of eNOS is thus a possible therapeutic target for human cancers such as pancreatic cancer that are promoted by Ras oncogenes. K.-H. Lim, B. B. Ancrile, D. F. Kashatus, C. M. Counter, Tumour maintenance is mediated by eNOS. Nature 452 , 646-649 (2008). [PubMed]

C-Myc is required for transformation of FDC-P1 cells by EGFRvIII

In contrast to wtEGFR, its truncated version EGFRvIII transformed non-tumorigenic FDC-P1 cells only when c-Myc was coexpressed. In nude mice, EGFRvIII/c-Myc coexpressing cells induced tumors, whereas wtEGFR-expressing EGF-dependent FDC-P1 cells did not. EGFRvIII function was required for both the induction and maintenance of tumor growth. Cellular proliferation was inhibited by a selective EGFR tyrosine kinase inhibitor indicating intrinsic tyrosine kinase activities for both receptors. Unlike wtEGFR, constitutive signaling by EGFRvIII was refractory to stimulation by the EGFR ligands EGF and TGF-α. Summarized, EGFRvIII is a constitutively active receptor tyrosine kinase whose transforming capacity is lower than that of EGF-stimulated wtEGFR.

Matrix metalloproteinase-2 and matrix metalloproteinase-9 type IV collagenases in serum of patients with pleural effusions

Matrix metalloproteinases (MMPs) are proteolytic enzymes that are essentially involved in the turnover of the extracellular matrix (ECM). Recently, several MMPs were implicated in creating an environment that supports the initiation and maintenance of tumor growth. We verified MMP activity in the sera of patients with pleural effusions by gelatin zymography. Of these patients, 22 had malignant pleural effusion, consisting of 11 breast carcinomas and 11 lung carcinomas (7 squamous cell carcinomas and 4 adenocarcinomas), and 8 patients had benign effusions. The sera of 25 healthy subjects were used as controls. Zymography analysis showed three major gelatinolytic bands of 72, 92 and 220 kDa. The MMP-9/MMP-2 ratio was enhanced in cancer patients compared with benign diseases and healthy individuals. Furthermore, we determined the circulating levels of carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (Ca 19-9), carbohydrate antigen 15-3 (Ca 15-3). The serum levels of Ca 15-3 were above the cut-off levels in several cancer patients. No correlation between gelatinolytic activity and high tumoral marker values was found.

Role of Growth Factors in Pancreatic Endocrine Cells: Growth and Differentiation

Although previously thought to arise from neural ectoderm, the endocrine cells of the gastrointestinal system are now believed to derive from endoderm. The role of different growth factors in initiation of endocrine cell growth, commitment of the cells to a particular growth pathway, and the initiation and maintenance of tumor growth and remission remains unclear. This article briefly reviews factors controlling cell growth and differentiation of gastrointestinal endocrine cells and presents data on new candidate growth factors pertinent to the authors' model of induction of endocrine cell differentiation in the pancreas.

C- myc oncogene copy number in squamous carcinoma of the head and neck

Purpose: Altered resident cellular genetic sequences (oncogenes) may result in malignant transformation, maintenance of tumor growth, and metastatic propensity. In this pilot study, we have elected to probe c- myc oncogene in evaluating specimens from human squamous cell carcinoma. Materials and Methods: Samples were obtained from 24 patients with squamous cell carcinoma of the head and neck. The ratio of tumor DNA values to that of control DNA was used to estimate the c- myc copy number. Results: Data from material obtained from eight patients was analyzed to the point of c- myc copy number. Tumors varied from stage II through IV. Five originated in the oral cavity and three in the larynx. Analysis of primary tumors demonstrated that two of eight had increased c- myc copy numbers. Histologically positive neck specimens were encountered in five of the study patients. Three demonstrated elevated c- myc copy numbers, two of which had had increased copy number at the primary site. Conclusion: This study confirms that c- myc amplification can be present in squamous cell carcinoma of the head and neck. c- myc Amplification may also be present in neck metastasis. Oncogene amplification in neck metastasis may indicate an increased metastatic propensity for individual tumor cells demonstrating c- myc amplification.

Analysis of a deleted MC29 provirus: gag sequences are not required for fibroblast transformation.

Recovered avian myelocytomatosis virus HBI is an MC29-related virus that induces lymphoid tumors in chickens rather than the predominant neoplastic disease induced by wild-type MC29 (namely, endotheliomas). An analysis of the structure of the HBI provirus(es) in the tumors demonstrated that the provirus(es) could be either full size or deleted. One tumor was found to be clonal in that it contained a single provirus which had been partially deleted; this raised a question concerning the role of this provirus in the maintenance of tumor growth. To characterize the detailed structure of this provirus and determine its biological activity, it was molecularly cloned from tumor DNA. Sequencing confirmed that the provirus contained a deletion which effectively removed the whole gag gene. However, the provirus was shown to encode a myc-specific protein, presumably initiating from within the myc gene, and to be biologically active when it was transfected onto quail embryo fibroblasts. Our results suggest that myc alone is sufficient to transform quail embryo fibroblasts and to maintain tumor growth in vivo.

Factors influencing estrogen production and metabolism in postmenopausal women with endocrine cancer.

The role which steroid hormones play in the development and maintenance of human cancer is a problem which has attracted the attention of research investigators for many years. Oestrogens have come under particular scrutiny, since there is a good deal of indirect evidence that altered oestrogen production may be protective in some situations (e.g. the diminished risk of female breast cancer conferred by earlier castration) and disadvantageous in others (e,g, the enhanced risk of endometrial cancer attributable to increased oestrogen exposure in women bearing oestrogen-secreting tumours). Furthermore, in the last decade or so, studies of cellular receptors have clearly delineated the importance of oestrogens amongst other hormones in the maintenance of tumour growth. It is therefore entirely logical to investigate oestrogen metabolism in detail in the hope and expectation that some metabolic abnormality exists in women who are predisposed to these types of endocrine cancer, which may be revealed by careful biochemical examination. As a group, postmenopausal women are particularly important in this context, not only because of the increased incidence of breast and endometrial cancer at and around the menopause, but because it is at this time that major changes occur in the endocrine milieu which may relate directly to the risk of developing cancer.