The research activities of the Pathology Division of the Research Center for Innovative Oncology currently focus on the application of the morphological study of cancer tissue to the clinical course of the patient. These activities aim to (1) elucidate the biological activity of cancer and (2) establish new selection methods for patient treatment and (3) clarify the mechanism of metastasis. Prognostic factors and clinicopathological characteristics of various cancers have also been investigated in collaboration with the Diagnostic Pathology Section under the Clinical Laboratory Division of the National Cancer Center Hospital (NCCH) East.
Cancer tissue is composed of cancer and stromal cells. The cancer microenvironment generated by cancer-stromal interaction plays important roles not only in carcinogenesis but also in cancer progression. Stromal fibroblasts are the predominant cancer stromal cells; however, few studies have reported the heterogeneous origins and biological functions of cancer stromal fibroblasts. We confirmed in previous studies that bone-marrow-derived cells transform into cancer stromal fibroblasts in an animal model. To determine whether circulating fibroblast progenitor cells are present in the blood of lung cancer patients, mononuclear cells from pulmonary arterial blood were cultured. Results showed that almost all patients (94%) had fibroblast progenitor cells in their pulmonary arterial blood. Characterization of these cells confirmed that they have the potential to differentiate into bone and fat cells, indicating that these cells were mesenchymal progenitor cells (MPCs). To further characterize these MPCs, mononuclear cells from pulmonary arterial blood were exposed to anti-CD14, anti-CD105, anti-CD3, and anti-CD20 antibodies. CD105(+) cells generated MPCs, whereas CD14(+), CD3(+), and CD20(+) mononuclear cells generated MPCs. This indicates that the CD105(+) mononuclear cell fraction of the pulmonary arterial blood of adult lung cancer patients includes MPCs (96). As another source of cancer stromal fibroblasts, the vascular adventitia is thought to contribute to the development of various diseases. To determine whether the adventitia contains progenitor cells of cancer stromal fibroblasts, human vascular adventitial fibroblasts (hVAFs) from pulmonary arteries were cultured and their characteristics analyzed. The doubling time of hVAFs was 1.5 days, and the average number of passage was 11, independent of age and sex. The cultured hVAFs were positive for vimentin, collagen type-1, CD29, CD44, and CD105, but negative for hematopoietic and endothelial cell markers. The hVAFs also showed osteogenic and adipogenic differentiation. Myogenic differentiation was also confirmed by increased smooth muscle actin and calponin expression. This indicates that hVAFs contain MPCs (97).
Squamous cell carcinoma (SCC) is a malignant tumor morphologically and phenotypically similar to a normally differentiated squamous epithelium. This makes SCC an ideal model for identifying a marker of tumor-initiating cells (TICs) based on their morphology. Using A431 (human SCC cell line), we found that (1) podoplanin(+) cells generate both podoplanin(+) and podoplanin(-) cells; (2) podoplanin(-) cells rarely generate podoplanin(+) cells; (3) podoplanin(+) cells have higher colony formation efficiency and tumorigenicity than podoplanin(-) cells; (4) localization and morphology of podoplanin(+) cells in a xenografted tumor derived from podoplanin(+) cells are similar to those in human oral SCC tissue or a normal epithelium. Furthermore, podoplanin(+) A431 cells share sonic hedgehog and CD44 expression with stem cells in a normal squamous epithelium. Hence, podoplanin is a novel marker to enrich TICs with stem-cell-like properties from A431 (98). CD133 is reportedly a cancer-initiating cell marker in colorectal carcinoma. To evaluate the frequency of CD133 expression in colorectal cancer, the distribution of CD133-positive cancer cells and clinicopathological features were investigated in 189 consecutive colorectal cancer patients. Tumors with CD133 overexpression were found to be differentiated-type adenocarcinoma. Although there was no difference in recurrence-free survival between patients with and without CD133 overexpression, those with CD133 overexpression had significantly poorer overall survival (P = 0.03). importantly, the expression of this cancer-initiating cell marker may vary with cancer histological type (99).
The overexpression of enhancer of zeste homologue 2 (EZH2) occurs in various malignancies and is associated with a poor prognosis. An inverse correlation between EZH2 and RUNX3 gene expression was found in five different cancer cell lines. Chromatin immunoprecipitation assay showed an association between EZH2 bound to the RUNX3 gene promoter, trimethylated histone H3 at lysine 27, and histone deacetylase 1 (HDAC1) bound to the RUNX3 gene promoter in cancer cells. RNA interference-mediated knockdown of EZH2 resulted in a decrease in H3K27 trimethylation and unbound HDAC1, and an increase in RUNX3 gene expression. Restoration of RUNX3 expression was not associated with any change in DNA methylation status in the RUNX3 promoter region. RUNX3 was repressed by histone deacetylation and hypermethylation of a CpG island in the promoter region and was restored by trichostatin A or/and 5-aza-2'-deoxycytidine. The results showed that RUNX3 is a target for EZH2 repression and indicated an underlying mechanism of the functional role of EZH2 overexpression on cancer cell proliferation (100). Moreover, EZH2 overexpression is reversely correlated with E-cadherin down-regulation in human gastric cancer in both cell lines and human cancer tissues (101).
Tumor angiogenesis is regulated by VEGF activation. A new VEGF activation mechanism was found in that soluble VEGF receptor-1 was degraded by MMP-7 produced by cancer cells, resulting in the easy access of VEGF to the endothelial cell surface. This new mechanism will provide new insights into tumor angiogenesis as well as novel treatment strategies against cancer angiogenesis. Clinicopathological studies on gastrointestinal tract (102, 103), head and neck, pancreatic (104), and lung (105) tumors, and breast cancer (106) were also performed in collaboration with the clinical divisions of the NCCH East and other institutions (107, 108).
● A. Ochiai ●
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