Ovarian cancer is the leading cause of death from gynecological malignancy and the fourth leading cause of cancer death among American women, yet little is known about its molecular aetiology. Studies using comparative genomic hybridization (CGH) have revealed several regions of recurrent, abnormal, DNA sequence copy number that may encode genes involved in the genesis or progression of the disease. One region at 3q26 found to be increased in copy number in approximately 40% of ovarian and others cancers contains PIK3CA, which encodes the p110alpha catalytic subunit of phosphatidylinositol 3-kinase (PI3-kinase). The association between PIK3CA copy number and PI3-kinase activity makes PIK3CA a candidate oncogene because a broad range of cancer-related functions have been associated with PI3-kinase mediated signalling. These include proliferation, glucose transport and catabolism, cell adhesion, apoptosis, RAS signalling and oncogenic transformation. In addition, downstream effectors of PI3-kinase, AKT1 and AKT2, have been found to be amplified or activated in human tumours, including ovarian cancer. We show here that PIK3CA is frequently increased in copy number in ovarian cancers, that the increased copy number is associated with increased PIK3CA transcription, p110alpha protein expression and PI3-kinase activity and that treatment with the PI3-kinase inhibitor LY294002 decreases proliferation and increases apoptosis. Our observations suggest PIK3CA is an oncogene that has an important role in ovarian cancer.

PIK3CA is implicated as an oncogene in ovarian cancer

The epithelial ovarian carcinomas, which make up more than 85% of human ovarian cancer, arise in the ovarian surface epithelium (OSE). The etiology and early events in the progression of these carcinomas are among the least understood of all major human malignancies because there are no appropriate animal models, and because methods to culture OSE have become available only recently. The objective of this article is to review the cellular and molecular mechanisms that underlie the control of normal and neoplastic OSE cell growth, differentiation, and expression of indicators of neoplastic progression. We begin with a brief discussion of the development of OSE, from embryonic to the adult. The pathological and genetic changes of OSE during neoplastic progression are next summarized. The histological characteristics of OSE cells in culture are also described. Finally, the potential involvement of hormones, growth factors, and cytokines is discussed in terms of their contribution to our understanding of the physiology of normal OSE and ovarian cancer development.

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Ovarian surface epithelium: biology, endocrinology, and pathology.

The cancer stem cell hypothesis posits that malignant growth arises from a rare population of progenitor cells within a tumor that provide it with unlimited regenerative capacity. Such cells also possess increased resistance to chemotherapeutic agents. Resurgence of chemoresistant disease after primary therapy typifies epithelial ovarian cancer and may be attributable to residual cancer stem cells, or cancer-initiating cells, that survive initial treatment. As the cell surface marker CD133 identifies cancer-initiating cells in a number of other malignancies, we sought to determine the potential role of CD133+ cells in epithelial ovarian cancer. We detected CD133 on ovarian cancer cell lines, in primary cancers and on purified epithelial cells from ascitic fluid of ovarian cancer patients. We found CD133+ ovarian cancer cells generate both CD133+ and CD133− daughter cells, whereas CD133− cells divide symmetrically. CD133+ cells exhibit enhanced resistance to platinum-based therapy, drugs commonly used as first-line agents for the treatment of ovarian cancer. Sorted CD133+ ovarian cancer cells also form more aggressive tumor xenografts at a lower inoculum than their CD133− progeny. Epigenetic changes may be integral to the behavior of cancer progenitor cells and their progeny. In this regard, we found that CD133 transcription is controlled by both histone modifications and promoter methylation. Sorted CD133− ovarian cancer cells treated with DNA methyltransferase and histone deacetylase inhibitors show a synergistic increase in cell surface CD133 expression. Moreover, DNA methylation at the ovarian tissue active P2 promoter is inversely correlated with CD133 transcription. We also found that promoter methylation increases in CD133− progeny of CD133+ cells, with CD133+ cells retaining a less methylated or unmethylated state. Taken together, our results show that CD133 expression in ovarian cancer is directly regulated by epigenetic modifications and support the idea that CD133 demarcates an ovarian cancer-initiating cell population. The activity of these cells may be epigenetically detected and such cells might serve as pertinent chemotherapeutic targets for reducing disease recurrence.

Epigenetic regulation of CD133 and tumorigenicity of CD133+ ovarian cancer cells

Treatment of solid tumors despite improved techniques in detection, surgery, radiation therapy, and chemotherapy remains difficult. Therefore, strategies to improve efficacy in accord with safety are needed. Many epithelial cancers have been found to overexpress the receptor to epidermal growth fact

Epidermal growth factor receptor biology (IMC-C225)

The epidermal growth factor receptor (EGFR), a growth factor receptor involved in the regulation of cellular differentiation and proliferation, is highly expressed by many tumor cells. In light of a relationship between overexpression of EGFR and clinically aggressive malignant disease, EGFR has emerged as a promising target for cancer therapy. In recent years, several molecular strategies have been explored to modulate either the EGFR itself, or the downstream signal beyond the cell surface receptor. One of the most promising current strategies involves the use of anti-EGFR monoclonal antibodies (mAbs), either alone or in combination with conventional cytotoxic modalities such as chemotherapy or radiotherapy. This review focuses primarily on recent progress in the development of anti-EGFR mAbs, and examines their potential in the treatment of cancer.

Epidermal growth factor receptor inhibition in cancer therapy: biology, rationale and preliminary clinical results.

BACKGROUND: As in the case of other epithelial neoplasms, most ovarian cancers arise from single clones of cells that have undergone multiple genetic alterations. A comparison of normal and malignant ovarian epithelium has identified several differences in growth regulation by peptide growth factors, protooncogenes, and tumor suppressor genes. METHODS: Recent articles and abstracts have been reviewed. RESULTS: The malignant ovarian epithelial phenotype has been associated with (1) autocrine growth stimulation by transforming growth factor-alpha, (2) loss of autocrine growth inhibition by transforming growth factor-beta, (3) mutation or amplification of ras in 2-12% of cases, (4) amplification of myc in 23% of specimens, (5) expression of fms in 56% of cases with potential autocrine stimulation by macrophage colony stimulating factor, (6) paracrine stimulation by macrophage products including interleukin-1, interleukin-6 and tumor necrosis factor, (7) overexpression of c-erbB-2 (HER-2/neu) in 30% of cases, and (8) mutation with consequent overexpression of p53 in 50% of advanced ovarian cancers. A poor clinical prognosis is associated with expression or overexpression of the epidermal growth factor receptor, fms, and HER-2/neu. Antibodies against the extracellular domain of the HER-2/neu gene product p185 inhibit the growth of tumor cells that overexpress HER-2/neu and are associated with marked decreases in diacylglycerol levels. The intracellular kinase domain is required for growth inhibition. Antibodies that inhibit growth stimulate phosphorylation of intracellular substrates. Ricin A chain monoclonal antibody conjugates that react with p185 also inhibit the growth of tumor cells that overexpress p185. The intracellular kinase region is not required for immunotoxin-mediated killing. Coexpression of HER-2/neu and the epidermal growth factor receptor has been observed in 65% of epithelial ovarian cancers and in a limited number of normal tissue from a fraction of donors. CONCLUSIONS: Multiple alterations in growth factors, protooncogenes and growth factors have been detected in different epithelial ovarian cancers. Inappropriate signalling from receptor tyrosine kinases may be particularly important for ovarian oncogenesis. Drugs that affect tyrosine kinase and phosphatase activity deserve attention as potential therapeutic agents for ovarian cancer. The extracellular domains of the HER-2/neu gene product p185 and the epidermal growth factor receptor may provide useful targets for serotherapy.

https://acsjournals.onlinelibrary.wiley.com/doi/pdf/10.1002/cncr.2820710426

Cell growth regulation in epithelial ovarian cancer

BACKGROUND Previously, the authors found that immortalized ovarian cancer cell lines generally were resistant to the growth inhibitory effect of transforming growth factor-beta and frequently had lost the ability to produce or activate this growth factor. In this study, the authors examined whether early passage epithelial ovarian cancer cells obtained from ascites are growth-inhibited by or produce transforming growth factor-beta. METHODS Ovarian cancer cells were purified from ascites by percoll gradient density centrifugation, and inflammatory cells were removed using anti-CD45 antibody. The effect of transforming growth factor-beta on the proliferation of ovarian cancer cells was assessed using the thymidine incorporation assay. Immunohistochemical staining for transforming growth factor-beta 1 and beta 2 also was performed in these cells. RESULTS Transforming growth factor-beta (10 ng/ml) significantly inhibited [3H]thymidine incorporation in 19 of 20 (95%) primary ovarian cancers (P < 0.05). In cases in which significant inhibition was seen, the mean thymidine incorporation was 33 plus or minus 28% of control values. In addition, there was no difference in dose-dependent inhibition of proliferation between ovarian cancer cells and normal ovarian epithelial cells. Eleven of 18 ovarian cancers (61%) were found to express immunohistochemically detectable transforming growth factor-beta, but immunostaining was not observed in 39% of cases. CONCLUSIONS Although most primary ovarian cancer cells remain sensitive to the growth-inhibitory effect of transforming growth factor-beta, loss of production may interrupt the transforming growth factor-beta autocrine inhibitory loop and play a role in the development of some ovarian cancers.

Transforming growth factor-beta inhibits proliferation of human ovarian cancer cells obtained from ascites

The monoclonal antibody 4B5 binds to a mucin-like antigen elaborated by respiratory epithelium of patients with non-small cell bronchogenic carcinoma. Several immunoassay formats were used to determine the presence of the antigen in lavage specimens. A qualitative immunodrop binding assay showed immunoreactivity in 37 (64%) of 58 specimens from patients with non-small cell lung cancer. In contrast, only 11 (12%) of 93 specimens from patients with either metastatic carcinoma or benign pulmonary diseases exhibited 4B5 immunoreactivity. A quantitative radioimmunoassay using standardized amounts of mucin exhibited similar sensitivity and specificity. Positive immunoreactivity was associated significantly with tobacco use and the cytopathologic diagnoses of squamous metaplasia, atypia, or dysplasia. Conversely, no significant association was found between 4B5 immunoreactivity and age, gender, race, benign cytologic findings, frankly malignant cytologic findings, or stage of disease. The expression of 4B5 antigen in bronchial secretions from patients with bronchogenic carcinoma deserves additional evaluation as a potential marker of pulmonary carcinogenesis.

Robert C. Bast

Papers

Cell growth regulation in epithelial ovarian cancer

Transforming growth factor-beta inhibits proliferation of human ovarian cancer cells obtained from ascites

Sensitive and specific detection of the 4B5 antigen in bronchial lavage specimens from patients with primary bronchogenic carcinoma.