PLATELET-DERIVED ENDOTHELIAL-CELL GROWTH-FACTOR IN HUMAN COLON-CANCERANGIOGENESIS - ROLE OF INFILTRATING CELLS

Background: Development of new blood vessels is essential for tumor gr owth and metastasis and depends on the production of angiogenic factor s by tumor and/or infiltrating cells, We previously showed that vascul ar endothelial growth factor (VEGF) expression and vessel count correl ate with metastasis in human colon cancer. Although most tumors with h igh vessel counts express high levels of VEGF, some do not. Recently, platelet-derived endothelial cell growth factor (PD-ECGF), another pot ent angiogenic factor, has been reported to be expressed in colon canc er. Purpose: In this study, we examined the role of PD-ECGF in colon c ancer angiogenesis and whether PD-ECGF is derived from the tumor or in filtrating cells. Methods: Immunostaining for PD-ECGF was performed on 96 colon cancer specimens, some of which were previously stained for VEGF and factor VIII, a marker that is specific for endothelial cells. Double staining was done by using antibodies to PD-ECGF and to CD68 ( macrophage specific) or CDS (lymphocyte specific) to confirm which inf iltrating cells produce PD-ECGF. Northern blot analysis for PD-ECGF me ssenger RNA (mRNA) was performed on four colon cancer specimens and co rresponding normal colon mucosae (same patients) and four human colon cancer cell lines (KM12SM, SW620, HT29, and NCI-H508) to determine whe ther colon cancer epithelium expresses PD-ECGF. Results: Immunohistoch emical analysis demonstrated that PD-ECGF was expressed in infiltratin g cells in most of the colon cancer specimens (80 [83%] of 96) but rar ely in tumor epithelium (five [5%] of 96). Double staining demonstrate d that infiltrating cells staining positive for both PD-ECGF and CD68 were more predominant than those staining positive for both PD-ECGF an d CD3. The intensity of staining for PD-ECGF in infiltrating cells cor related with vessel counts (Spearman's rank correlation coefficient (R ) = .29; P = .004), but did not correlate with the intensity of VEGF s taining (R = .176, P = .086) or metastasis (Mann-Whitney U test, P = . 253). PD-ECGF staining intensity was higher in specimens with a high v essel count (>50 at high magnification) and low VEGF-staining intensit y (less than or equal to 2+) than in specimens with a high vessel coun t (again, >50) and high VEGF-staining intensity (3+). Northern blot an alysis revealed that colon cancer specimens and normal mucosae express ed relatively high levels of PD-ECGF mRNA, whereas PD-ECGF mRNA transc ripts were not detectable in colon cancer cell lines. Conclusions and Implications: PD-ECGF expression in human colon cancer specimens is as sociated with vessel count and may be responsible for tumor vascularit y in those tumors with ion: VEGF expression. Infiltrating cells expres sing PD-ECGF mas contribute to angiogenesis, thus providing an additio nal mechanism for tumor neovascularization.