The realisation of targeted antitumour therapy

Better understanding of the pathways regulating proliferation and metastasis of cancer cells has led to the development of novel molecular-targeted therapies. The number of molecular-targeted agents approved for use in the clinic is growing, with many more in clinical trials. Most of these compounds can be broadly classified into two main categories: monoclonal antibodies and small-molecule tyrosine kinase inhibitors. The pathological processes targeted include vascular endothelial growth factor-dependent tumour angiogenesis and epidermal growth factor receptor-dependent tumour cell proliferation and survival. Unlike conventional chemotherapy, molecular-targeted agents offer the potential advantages of a relatively high therapeutic window and use in combination with other anticancer strategies without overlapping toxicity. It is hoped that these drugs will become valuable therapeutic tools within the multimodal approach to treating cancer. Recent progress in targeted antitumour therapy is discussed, with a focus on antiangiogenesis

Ovarian VEGF165b expression regulates follicular development, corpus luteum function and fertility

Angiogenesis and vascular regression are critical for the female ovulatory cycle. They enable progression and regression of follicular development, and corpora lutea formation and regression. Angiogenesis in the ovary occurs under the control of the vascular endothelial growth factor-A (VEGFA) family of proteins, which are generated as both pro-(VEGF165) and anti(VEGF165b)-angiogenic isoforms by alternative splicing. To determine the role of the VEGF165b isoforms in the ovulatory cycle, we measured VEGF165b expression in marmoset ovaries by immunohistochemistry and ELISA, and used transgenic mice over-expressing VEGF165b in the ovary. VEGF165b was expressed in the marmoset ovaries in granulosa cells and theca, and the balance of VEGF165b:VEGF165 was regulated during luteogenesis. Mice over-expressing VEGF165b in the ovary were less fertile than wild-type littermates, had reduced secondary and tertiary follicles after mating, increased atretic follicles, fewer corpora lutea and generated fewer embryos in the oviduct after mating, and these were more likely not to retain the corona radiata. These results indicate that the balance of VEGFA isoforms controls follicle progression and luteogenesis, and that control of isoform expression may regulate fertility in mammals, including in primates

The endogenous anti-angiogenic VEGF isoform, VEGF165b inhibits human tumour growth in mice

Vascular endothelial growth factor-A is widely regarded as the principal stimulator of angiogenesis required for tumour growth. VEGF is generated as multiple isoforms of two families, the pro-angiogenic family generated by proximal splice site selection in the terminal exon, termed VEGFxxx, and the anti-angiogenic family formed by distal splice site selection in the terminal exon, termed VEGFxxxb, where xxx is the amino acid number. The most studied isoforms, VEGF165 and VEGF165b have been shown to be present in tumour and normal tissues respectively. VEGF165b has been shown to inhibit VEGF- and hypoxia-induced angiogenesis, and VEGF-induced cell migration and proliferation in vitro. Here we show that overexpression of VEGF165b by tumour cells inhibits the growth of prostate carcinoma, Ewing's sarcoma and renal cell carcinoma in xenografted mouse tumour models. Moreover, VEGF165b overexpression inhibited tumour cell-mediated migration and proliferation of endothelial cells. These data show that overexpression of VEGF165b can inhibit growth of multiple tumour types in vivo indicating that VEGF165b has potential as an anti-angiogenic, anti-tumour strategy in a number of different tumour types, either by control of VEGF165b expression by regulation of splicing, overexpression of VEGF165b, or therapeutic delivery of VEGF165b to tumours

Participation of the PI-3K/Akt-NF-κB signaling pathways in hypoxia-induced mitogenic factor-stimulated Flk-1 expression in endothelial cells

BACKGROUND: Hypoxia-induced mitogenic factor (HIMF), a lung-specific growth factor, promotes vascular tubule formation in a matrigel plug model. We initially found that HIMF enhances vascular endothelial growth factor (VEGF) expression in lung epithelial cells. In present work, we tested whether HIMF modulates expression of fetal liver kinase-1 (Flk-1) in endothelial cells, and dissected the possible signaling pathways that link HIMF to Flk-1 upregulation. METHODS: Recombinant HIMF protein was intratracheally instilled into adult mouse lungs, Flk-1 expression was examined by immunohistochemistry and Western blot. The promoter-luciferase reporter assay and real-time RT-PCR were performed to examine the effects of HIMF on Flk-1 expression in mouse endothelial cell line SVEC 4–10. The activation of NF-kappa B (NF-κB) and phosphorylation of Akt, IKK, and IκBα were examined by luciferase assay and Western blot, respectively. RESULTS: Intratracheal instillation of HIMF protein resulted in a significant increase of Flk-1 production in lung tissues. Stimulation of SVEC 4–10 cells by HIMF resulted in increased phosphorylation of IKK and IκBα, leading to activation of NF-κB. Blocking NF-κB signaling pathway by dominant-negative mutants of IKK and IκBα suppressed HIMF-induced Flk-1 upregulation. Mutation or deletion of NF-κB binding site within Flk-1 promoter also abolished HIMF-induced Flk-1 expression in SVEC 4–10 cells. Furthermore, HIMF strongly induced phosphorylation of Akt. A dominant-negative mutant of PI-3K, Δp85, as well as PI-3K inhibitor LY294002, blocked HIMF-induced NF-κB activation and attenuated Flk-1 production. CONCLUSION: These results suggest that HIMF upregulates Flk-1 expression in endothelial cells in a PI-3K/Akt-NF-κB signaling pathway-dependent manner, and may play critical roles in pulmonary angiogenesis

Blood flow influences vascular growth during tumour angiogenesis

Many factors play a role in tumour angiogenesis. We observed growing tumour vessels in vivo to study the relationship between blood flow and vascular enlargement. Mammary adenocarcinoma was implanted into Fisher-344 rat with dorsal skin-fold transparent chambers. Vascular growth was observed and recorded on videotape through a microscope for 6 h. Vascular networks were photographed and traced every 30 min to identify changes over time. Tumour sections were stained with Masson's trichrome and anti-Factor VIII-related antigen. Tumour growth was rapid enough for differences to be seen each hour. Vessels with a high blood flow showed an increase in diameter within a few hours and new branches formed from these vessels. In contrast, vessels without an increase in blood flow showed no change in diameter. Vessels within the interstitium surrounding the tumour were lined by endothelium that was positive for anti-Factor VIII-related antigen staining. Vessels in the tumour had extremely rare endothelial cells detectable by Masson's trichrome or anti-Factor VIII-related antigen staining. In conclusion, increased blood flow may cause vascular enlargement and some primitive vessels seem to lack endothelium. 1999 Cancer Research Campaig