Current Research

Background to the Research of the Tumour Microcirculation Group

In the Tumour Microcirculation Group, we are studying the blood vessels that supply tumours with oxygen and nutrients and their role in cancer therapy. Tumours require a blood supply to grow and the blood vessels provide a route for the spread of tumour cells to other sites in the body. Therefore, targeting treatment to the blood vessels rather than the tumour cells is a potential means of killing tumours. This has the added advantages that preventing blood flow through a single vessel can kill a large number of tumour cells and that delivering vascular-damaging drugs to their site of action on the blood vessels is much easier than delivery directly to the tumour cells. In our model systems, we are investigating ways of targeting tumour blood vessels and we are studying the factors that affect the way the vessels behave. The vascular supply of tumours is abnormal, with regions of very poor blood flow. One of the consequences of this is that many of the tumour cells survive in very low levels of oxygen. Tumour cells can adapt to this condition and become resistant to therapy. However, it's also possible to exploit these unique tumour conditions for the development of new treatments.

Tumour Microcirculation

This programme of work is funded by Cancer Research UK and is concerned with the maturation phase of angiogenesis as it relates to the tumour microcirculation and its influence on response to vascular disrupting agents (VDAs). Alternative splicing of the VEGF-A gene influences tumour vascular maturation and impacts on vascular disrupting therapy; specifically VEGF188/9 is involved in recruitment of pericytes to tumour blood vessels, which in turn confers resistance to the effects of the tubulin-binding VDA, combretastatin A-4-P (CA-4-P). A short video showing the effects of CA-4-P on tumour blood vessels can be seen in the video below.

Fragments of VEGF120 tumours expanded rapidly in the chambers despite poor internal vascularization. Within 4 days of implantation, haemorrhage of the surrounding blood vessels was observed. In contrast, the rate of VEGF188 fragment growth was slower until the tumours were well vascularized, with narrower vessels and no haemorrhage. The different VEGF isoforms clearly have markedly different effects on the vascularization process of tumours, influencing both the morphology and function of tumour blood vessels.

One aim of the current research is to determine the mechanisms by which VEGF188/9 influences vascular maturation, including pericyte recruitment and integrity of endothelial-endothelial and endothelial-pericyte adherens junctions. Activation of Rho-GTPase signalling pathways has been found to account for much of the CA-4-P-induced re-modelling of the actin cytoskeleton of endothelial cells in vitro and contributes to tumour necrosis induction in vivo. In addition, deciphering the cell signalling pathways associated with the different VEGF isoforms and how they interact with CA-4-P under different tumour microenvironmental conditions will provide mechanistic information on resistance mechanisms to tubulin-binding VDAs.

Imaging

This programme of work is funded by Cancer Research UK and EPSRC, with additional funding from MRC and the Department of Health and is carried out jointly with Professor Martyn Paley, Department of Human Metabolism, as co-PI. The aim is to develop imaging bio-markers for evaluating VDAs and other vascular-targeted therapeutics in clinical trials. This programme focuses on developing magnetic resonance imaging (MRI) techniques, including magnetic resonance spectroscopy imaging (MRSI), as well as mass spectrometry imaging of tissue sections. Hyperpolarisation techniques, both for 129Xe gas and dynamic nuclear polariation (DNP) for 13C are being used to enhance signal intensity. Blood flow rate and oxygenation are the efficacy end-points of primary interest. For blood flow, the utility of 129Xe uptake into tissues, following inhalation of the hyperpolarised gas, is being evaluated. For oxygenation, the kinetics of metabolism of injected hyperpolarised 13C-pyruvate to 13C-lactate, as well as the decay of signal from 129Xe, which is oxygen dependent, are being investigated.

A range of techniques, including optical imaging, are being used to validate results from MRI/MRSI experiments. Mass spectrometry imaging (in collaboration with Professor Malcolm Clench, Sheffield Hallam University) is being used to evaluate the response of tumours to VDAs, with the aim of identifying novel markers of both efficacy and resistance. Nano-particle technology is being employed to investigate the maturation status of tumour blood vessels, which is known to strongly influence tumour response to VDAs, making it a potentially useful marker for selecting patients most likely to benefit from this type of treatment. These techniques are being developed in pre-clinical models of cancer, with the aim of translating them to clinical studies.

Other Projects

• A BBSRC CASE PhD studentship funds work with AstraZeneca to investigate the effects of growth factors and vascular-targeting agents on blood vessel development and function using optical imaging.

• We are also working with Professor Claire Lewis on the role of tumour-associated macrophages in the response of tumours to VDAs. Part of this work employs a novel zebrafish model of cancer in which macrophages express mCherry and hypoxic cells express GFP. Using optical imaging, this powerful genetic model will be used to determine the role of hypoxic macrophages in tumour development and response to treatment.

• The European Union provides funds for studying the effects of radiation on the cardiovascular system, which is relevant for breast cancer patients undergoing radiotherapy.

• Yorkshire Cancer Research funds a project concerned with the role of ischaemia-reperfusion injury and nitric oxide synthase in the mechanism of action of VDAs.