Title: Cancer Research UK Centre for Cancer Therapeutics - Tumour biology and metastasis team
Funder: Cancer Research UK

Abstract: pathways linked to cell motility and ECM proteolysis, since these are utilised by both activated endothelial cells during capillary sprouting, and by tumour cells during invasion. We are focussing initially on selected targets for which there is evidence for a role in tumour angiogenesis, while in collaborative studies aiming to identify novel targets for future therapeutic exploitation. Hypoxia in tumours is a major inducer of neoangiogenesis, and PI3K/PKB activation is an important intermediary in this response. The role of VEGF as a “survival factor” for newly formed vasculature is mediated through induction of bcl-2 and activation of PI3K/PKB. PI3 kinase is also critically important in endothelial cell survival and migration mediated by angiopoietin 1. Distinct PI3 kinases have been implicated in proliferation (p110a) and migration (p110b and d) of leucocytes, but it is not known which isoforms are utilised by endothelial cells (or tumour cells) for these processes. We have shown that selective inhibitors of certain PI3 kinase isoforms effectively block angiogenesis in vitro. In most cases, the effects were shown to be due to inhibition of endothelial cell proliferation, but in some instances there were distinct effects on cell differentiation, motility and proteolytic activity. Since PI3K is a key downstream element in signalling via both VEGF and Ang-1 endothelial cell survival factors, it is potentially a better target than the cognate receptors (Flk-1 or Tie2) of these individual angiogenic factors, which can to some extent compensate for each other when inhibited singly. Future work will explore the role of the different PI3K isoforms in more detail, take the most promising inhibitors through our angiogenesis test cascade into in vivo systems and define the interactions with other modulators of tumour angiogenesis in which we have interests e.g. hypoxia, c-erbB signalling pathways, MMPs). VEGF stimulation of endothelial cells via the type III (VEGF-R) receptor tyrosine kinases results in phosphorylation of a number of downstream proteins besides PI3 kinase, including PLCg and the MAPK pathway. In addition, we and others have shown that oncogenes such as ras, EGF receptor kinase, c-erbB-2 and c-Met upregulate angiogenic cytokines, which may thereby contribute to tumour progression. Inhibitors of the common signalling pathways involved therefore have the potential to be anti-angiogenic by both direct and indirect routes. Not all compounds that inhibit cell proliferation driven by these oncogenes are capable of inhibiting their other functions e.g. motility, invasion, angiogenesis) hence these are separately assessed with a view to selecting the optimal therapeutic profile. We have used panels of ligands and monoclonal antibodies with selectivity for c-erbB-2 and EGF receptor kinase as proof of principle that blocking of signalling through these receptors can differentially inhibit tumour cell motility, invasion, MMP activity and VEGF expression. We are now using specific inhibitors in our angiogenesis test cascade and tumour invasion/metastasis assays to define the signalling pathways linking type 1 tyrosine kinase receptor activation to angiogenic activity. Recent results have shown that the PLC inhibitor U73122 significantly reduces migration of human tumour cells and endothelial cells and we are working towards developing more potent and selective PLC? inhibitors in collaboration with Matilda Katan and Wynne Aherne's groups. Heat shock protein 90 (Hsp90) stabilises and chaperones to the correct cellular compartment a variety of key proteins including c-erbB family members, steroid receptors, mutant p53 and Raf-1. Inhibitors of Hsp90 e.g. 17AAG and geldanamycins) can have antitumour activity by depleting oncogenic client proteins. Certain geldanamycins also inhibit uPA protease cascades and tumour cell motility and invasion at concentrations lower than those required for anti-proliferative effects. This observation has encouraged us to evaluate novel Hsp90 inhibitors for anti-invasive and anti-angiogenic activity. Finally, in collaborative clinical studies we are exploring the potential value of measuring circulating angiogenic cytokines and proteases as indicators of prognosis and response to therapy, while in preclinical studies, aiming to define by microarray analysis specific pharmacodynamic markers of response to novel agents in both tumour and endothelial cell compartments.


Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS
Health categories: CANCER AND NEOPLASMS