Induction of VEGF secretion in ovarian cancer by PDGF BB

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Background: We identified the PDGFR as a potential target in epithelial ovarian carcinoma (EOC). This led us to test whether inhibition of the receptor affects ovarian cancer cell proliferation and survival and regulates other processes critical to tumor growth and metastasis. We postulated that the PDGF-PDGFR axis regulates VEGF secretion in EOC. Methods: VEGF secretion in ovarian tumors, cancer cells, serum and ascites was measured by IHC, Western Blot and ELISA. The HOG Gyn03–62 protocol was a phase II protocol for patients with recurrent platinum resistant EOC. Patients were treated with imatinib and docetaxel. Serum and tumor samples from patients enrolled on this protocol were analyzed for VEGF. Results: VEGF expression was quantified by IHC in ovarian tumors. Of 21 PDGFR expressing ovarian tumors, seven specimens immunostained strongly for VEGF and six tumors demonstrated 2+ VEGF reactive extracellular (secreted) material. PDGF and VEGF secretion was measured in 17 specimens of malignant EOC ascites. The levels of PDGF BB and VEGF were strongly correlated (Pearson coefficient =0.728, p-value=0.001), suggesting that the two pathways interconnect. There was no correlation between PDGF AA and VEGF levels. VEGF levels were measured in 13 paired serum samples from patients enrolled in the clinical protocol HOG: Gyn03–62, before and after treatment. VEGF serum levels were stabilized or decreased in 9 of 13 EOC patients treated with imatinib. In conditioned media from primary cells, VEGF secretion was four fold higher for tumor derived cells than for cells derived from the normal ovarian epithelium. PDGF increased ten-fold VEGF secretion in PDGFR expressing immortalized ovarian cells (C272/hTert/E7 and C889/hTert), while imatinib reduced VEGF production to basal state. The effects of imatinib were mediated via inhibition of Akt and MAPK pathways, by stabilization of HIF1 alpha. In ovarian cancer cells overexpressing consitutively active Akt, imatinib inhibited only partially the secretion of VEGF compared to control cells, suggesting that the PI3K/Akt pathway is significantly implicated in PDGF-stimulated VEGF secretion. Conclusions: These results suggest that by blocking the PDGFR, imatinib inhibits VEGF production. This affects the tumor microenvironment favoring ovarian tumor growth and metastasis.

No significant financial relationships to disclose.

Cutting edge: IL-17F, a novel cytokine selectively expressed in activated T cells and monocytes, regulates angiogenesis and endothelial cell cytokine production

A novel secreted cytokine, termed IL-17F, was cloned using nested RACE PCR. This cytokine bears homology to IL-17. IL-17F was expressed only in activated CD4(+) T cells and activated monocytes. Recombinant human IL-17F did not stimulate the proliferation of hematopoietic progenitors or the migration of mature leukocytes. However, it markedly inhibited the angiogenesis of human endothelial cells and induced endothelial cells to produce IL-2, TGF-beta, and monocyte chemoattractant protein-1.