Targeting glycans for the treatment of ischemia-reperfusion injury.

Context of research. Renal Ischaemia Reperfusion Injury (IRI) is a major cause of acute kidney failure and renal damage following transplantation, resulting in significant morbidity and mortality, and posing a significant burden on the healthcare system. IRI can be defined as the tissue damage induced by the restoration of blood flow following an ischaemic event, and is induced by a cascade of biological processes, the exact nature of which is still not fully understood. Despite extensive research and several therapeutic approaches undergoing clinical trials, to date no consistent clinically acceptable means of attenuating IRI is available.
Recent advances in polymer chemistry allowed to engineer synthetic glycopolymers - GPs, polymers which display sugar units onto macromolecular scaffolds - with 'bespoke' size, valency, and orientation of their lectin-recognition motifs.
Cell receptors rarely act as isolated entities, but rather tend to function as part of multireceptor complexes. With their enhanced avidity, coupled with their ability to span over multiple cell receptors, multivalent ligands - i.e. functional polymers - are emerging as very valuable probes to interrogate complex processes and address fundamental biological questions. Within this context GPs could potentially play a pivotal role, if they could be designed that engage selectively specific lectin receptors.
The proposed research builds on a preliminary study where we have shown that a novel class of GPs can selectively engage the Mannose Receptor (MR, CD206), a carbohydrate-binding receptor predominantly expressed by selected populations of macrophages, dendritic cells, non-vascular endothelium, and kidney mesangial cells. Importantly, we have also shown that MR appears to be implicated in the development of IRI and that MR-binding GPs can attenuate the extent of tissue damage caused by reperfusion following an ischaemic event.
Research objectives. In this work we therefore propose:
1) to engineer a family of MR-binding GPs with tuneable ability to engage MR and with different pharmacokinetic and pharmacodynamics profiles; and 2) to identify the biological mechanisms by which MR-binding GPs prevent IRI by a combination of in vitro and in vivo approaches focussing at both investigating prophylactic and therapeutic attenuation of IRI, and GP-mediated modulation of motility, differentiation and activation of key MR-expressing cells, e.g. macrophages.
Potential applications and benefits. Devising a means to attenuate or minimise IRI represents a significant unmet clinical need that could produce substantial healthcare and economic benefits. A major hurdle to the development of effective therapies for the management of IRI is the incomplete understanding of the biological mechanisms that lead to reperfusion tissue damage.
Successful completion of this work will allow not only to identify structure-function relationships of our new family of GPs within an ischaemia/reperfusion context, but also to utilise this knowledge to develop a 'chemical prototype' of a new class of therapeutics for the management of renal IRI.
From a biomaterials perspective, better understanding of the details by which IRI develops and how multivalent probes that intersect specific biological pathways can attenuate reperfusion damage may produce important insight into clinical applications of multivalent carbohydrate-presenting materials.
Moreover, although focussed on renal IRI, the outcome of the proposed research could potentially have implication on the management of IRI in other organs, such as liver, and heart following myocardial infarction and subsequent reperfusion. Additionally, in preliminary work we have also shown a role for MR in tubular damage due to other aetiological factors- such as a drug toxin (folic acid), indicating that the outcome of our research might not be restricted to IRI, but also have implications in a wider range of clinical settings.

Mannose Receptor (MR, CD206) has not been widely investigated as clinical target due to the lack of molecular probes able to selectively modulate its activity in vivo, and represents a novel biological target for the treatment/prevention of IRI. We have developed an initial family of novel synthetic glycopolymers (GPs) that bind MR with high affinity and protect against IRI in vivo. In the proposed research we will investigate the mechanism(s) by which GPs are protective in IRI by a combination of in vitro and in vivo approaches as a means to determine the contribution of MR to IRI. Accordingly, key research objectives will be:

1) Generation of MR-binding GPs. A library of MR-binding GPs will be engineered by a combination of controlled/living radical polymerisation (CRP) and Cu-catalysed azide-alkyne cycloaddition (CuAAC) with variable macromolecular size. This will allow to systematically modulate affinity to MR and pharmacokinetic profile, with the aim of establishing structure-function relationship for this novel class of biomaterials within the context of renal IRI.

2) Identify the mechanism by which MR-specific GPs mediate protection against renal IRI in vivo. At this stage we will establish (a) how the macromolecular structure of GPs affects their ability to attenuate IRI; (b) whether GPs can act as both prophylactic agents to prevent IRI and therapeutics to minimise tissue damage following ischaemia/reperfusion; (c) how GPs affect the evolution of IRI vs. time, providing key information on their mechanism of action; and (d) what cells are targeted by GPs in vivo, and how they are involved in the development of reperfusion injury.

3) Establish the effect of MR-specific GPs on the biology and activation of macrophages. Here we will investigate how MR-binding GPs modulate (a) macrophage migration, (b) polarisation, or (c) activation in vitro using primary mouse macrophages.

Ischaemia reperfusion injury (IRI) underlies various clinical diseases that result in significant morbidity and mortality, and which consume vast healthcare resources. This work ultimately aims at gaining a better understanding of the biological processes underlying IRI, and devising a means to attenuate or minimise it. This is a significant unmet clinical need that could produce substantial enhancement of quality of life and economic benefits across many diverse medical specialities, and be a world-leading advance in healthcare. A more effective therapy for IRI would also reduce risk of later-onset Chronic Kidney Disease (CKD) - which adds further to healthcare costs.
Benefits to policy makers. The cost for the management of acute kidney injury (AKI) is estimated at ~ £1 billion in England alone, just over 1% of the NHS budget, with many of the clinical cases recorded each year associated to IRI. With a steadily ageing population, it is expected that the burden on healthcare budgets will significantly increase in the next decades if efficient and cost-effective therapies are not discovered and clinically implemented. Policymakers will obtain far-reaching benefits if they invest in developing cutting-edge therapies now. Within this context additional benefit will come from further increasing visibility for MRC-funded research in this clinically key area. Moreover, in an economic climate where big pharma companies are restructuring their R&D operations and revising global priorities, MRC must seen as promoting high profile research to maintain the UK leading role, both in industry and academia, in key pharmaceutical areas.
Benefits to industry. If key mechanisms leading to kidney damage can be identified and modulated with appropriate synthetic probes, there will be a new class of therapeutics for the management of IRI, with associated IP and knowledge transfer to industry. Intellectual rights arising from the preliminary work leading to the present application are currently being protected by the commercialisation services at University of Nottingham and UCL, but devising a new therapeutic strategy for the prevention or treatment of IRI will likely result in further patents which will benefit the industry through the creation of spin-off companies and/or through licencing of the technology. Once the scientific aspects are investigated and understood, follow-on studies will focus on the development of our technology, preferably through collaboration with private partners. Ongoing collaborations with leading pharmaceutical companies - AstraZeneca, GSK, and Medimmune - will be exploited as fast-track routes towards commercialisation.
Further impact will originate from training of PDRAs with expertise ranging from functional materials to cell biology and nanomedicine. This will not affect only PDRAs, as knowledge will be shared with PhD students across research groups, further promoting development of a wider cohort of researchers with multidisciplinary skills. The availability of these highly skilled figures will contribute to further strengthen the UK-based pharma industry, to address effectively current and future grand challenges in materials, biology and medical research.
Benefit to the public. With the high prevalence of renal IRI amongst patients, efficient and cost-effective therapies will have an obvious and immediate effect on quality of life, both short-term, by reducing tissue damage following an ischaemic event, and long-term by reducing the risk of later-onset Chronic Kidney Disease (CKD) and dialysis.
Further benefits from the proposed research will originate from engaging strongly in dissemination activities. In addition to publication peer-reviewed international journals which will be made accessible to public outside of the academic community, research outcome will be disseminated via our After School Science Clubs and 'Test-tube' (www.test-tube.org.uk) projects, to maximise impact of our research.