Glycoangiogenesis
Led by Professor Gordon Jayson
Angiogenesis has been proved as a clinically valid target for anti-cancer treatment. While phase III trials have focused on VEGF as a target, it is clear that other angiogenic cytokines should be inhibited and we have focused on FGF2 because of its obligate dependency on heparan sulphate (HS). We have shown that heparin octasaccharides inhibit angiogenesis in a number of in vivo models of angiogenesis and have developed an organic chemistry programme in which we are making octasaccharides. These will be evaluated in vitro and in vivo over the next year.
Angiogenesis, the formation of new blood vessels, has been validated as a target for anti-cancer treatment in several phase III trials in which patients with non-squamous non-small cell lung cancer, recurrent breast cancer or colorectal cancer were treated with a combination of cytotoxic chemotherapy and anti-VEGF antibodies. All trials showed that the combination was associated with an improved response rate. However, while the median survival of the patients was superior to that of patients who received conventional chemotherapy regimens, the overall survival was largely unchanged suggesting that impact of VEGF inhibition should be augmented by inhibiting other targets.
Development of anti-angiogenic oligosaccharides
We have focused on the HS-dependent growth factor family, the prototype of which is FGF2. The importance of this molecule has been highlighted recently in a study that showed that FGF2 is responsible for the development of resistance to VEGF inhibitors in vivo (Casanovas et al., Cancer Cell 2005; 8:299). If borne-out clinically the implication would be that the benefit of VEGF inhibitors could be increased if co-administered with antagonist of FGF function. We have previously shown that HS-proteoglycans are of prognostic significance in ovarian cancer (Davies et al., Clin Cancer Res 2004; 10: 5178) in that stromal syndecan 1 was associated with a worse prognosis while syndecan 3 was aberrantly expressed in the tumour endothelium.
This year we showed that the entire extra-cellular signalling mechanism for FGF2 is present in the ovarian cancer endothelium. In particular, using a novel molecular probe we showed that endothelial HS is able to activiate FGF2 (Whitworth et al., J Cancer Res Clin Oncol 2005; epub Aug 2005). In view of this we were keen to develop inhibitors of FGF2 based on the molecule’s dependency on HS.
Using size fractionated heparin oligosaccharides we investigated the anti-angiogenic potential of the species in models that were sequentially less dependent on FGF2. These data showed that heparin octasaccharides inhibited FGF2-induced angiogenesis but were also effective in models that were less dependent on FGF2 (Hasan et al., 2005; Clinc Cancer Res; 11: 8172).
One of the impediments to the clinical development of saccharides as anti-angiogenic agents is the availability and purity of potential drugs. We have therefore developed an organic chemistry programme in which we are making a defined octasaccharide that we have shown completely abrogates FGF2-induced HUVEC erk-1 phosphorylation in vitro (unpublished). The synthetic chemistry programme has led to the generation of tetrasaccharides and will develop octasaccharides and more complex species subsequently - the aim being to explore structure-function and structure-inhibition relationships using defined oligosaccharides.
The heparan sulphate-FGF axis in ovarian cancer
The above ex vivo tissue-based studies suggested that the ovarian tumour endothelium was the most active site of HS synthesis and we therefore carried out a detailed RNA in situ hybridisation (ISH) study to investigate the distribution of HS-synthetic enzymes in ovarian cancer. These data have shown that in fact the tumour cells express the synthetic enzymes at the RNA level to the greatest extent but that they also express heparanase and 2-O-sulphatase: enzymes that cleave and edit cell surface HS. The implcation is that HS synthesis is most tightly controlled in non-malignant lineages but that in cancer cells HS is made but then cleaved from the cell surface.
In a further arm of our programme to develop saccharide-based inhibitors of FGF we have initiated a detailed study of the expression of FGFs and FGF receptors in ovarian cancer and normal ovaries. The aim is to identify the FGFs and FGF receptors that are most abundantly expressed by cancer tissue and to investigate and target them. To date these studies have narrowed the number of FGFs that are differentially expressed in ovarian cancer and we will focus on these FGFs in forthcoming studies.
Phase I PK/PD anti-angiogenic trial programme
We have completed first-into-man phase I evaluations of an anti-αv integrin antibody and a di-Fab anti-KDR molecule. The anti-αv integrin antibody was well tolerated and we observed a prolonged partial response in a patient with cutaneous angiosarcoma. Biopsies showed that the antibody was bound and associated with the αv integrin. Interestingly we also observed down-regulation of phosphorylated MAP kinase and BCL-2 after treatment, potentially identifying intracellular mechanisms of action.
In this study we also carried out dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) of the patients receiving anti-αv integrin antibody. While these studies did not demonstrate a drug-related effect we were able to identify patients who were destined to develop progressive disease by examining the vascular characteristics of the tumours on DCE-MRI. These data raise the possibility that we can identify patients who will most benefit from anti-angiogenic agents through a radiological investigation.
As a result of these programmes we are now coordinating the translational research programme for two forthcoming MRC/NCRN ovarian cancer trials that investigate the benefit of anti-angiogenic agent-cytotoxic chemotherapy combinations in the disease. This will allow us to test and therefore also to validate our angiogenesis biomarkers at the phase III level.
Principal investigator
| Name | Job title | Email address |
|---|---|---|
| Gordon Jayson | Professor of Medical Oncology | gordon.jayson@manchester.ac.uk |