cAMP phosphodiesterase-4: signalling complexes, regulation and potential therapeutic targets.

The death rate from respiratory diseases in the UK is twice the EU average and costs the NHS more than any other disease area. Chronic Obstructive Pulmonary Disease, the fourth leading cause of death in the world, causes around 26,000 deaths/year and asthma around 1500 deaths/yr in the UK. This debilitating illness is associated with lung damage caused by chronic inflammation due to the sustained activation of 'inflammatory' cells. Raising the levels of a substance called cAMP, inside these cells, can stop this. An effective way of doing this is to stop cAMP from being broken down by PDE4 enzymes. At the moment scientists have made inhibitor molecules that bind tightly to the 'mouth' on PDE4 where cAMP is digested, stopping it breaking down cAMP. However, a major problem using these as medicines are side-effects like nausea and vomiting.
It's now clear that there is a large family of PDE4 enzymes where only certain of these are found in cells causing inflammation and damage in lungs. We aim to identify the particular PDE4 enzymes that it is important to inhibit in order to stop damage and help repair lungs. Then we need to devise ways to inhibit these selectively, rather than all PDE4s, to produce medicines without side-effects. As all PDE4 enzymes have identical mouths for digesting cAMP we need to take a new approach to inhibit just the critical PDE4s. To do this we will exploit our discovery that individual PDE4s have unique 'postcodes' built into them. These post-codes allow particular PDE4s to be targeted to the right place inside cells for them to work properly. This happens because the individual postcode is recognised by distinct anchor proteins placed at strategically important sites in cells. This targeting to exactly the right place is essential for particular PDE4s to do their job. We aim to identify anchor proteins and relevant postcodes for the PDE4s that we need to inhibit to stop inflammation and lung damage. Then, when we've done this, we will design molecules that stop the postcode of critical PDE4s from being recognised by their anchors. These molecules will prevent PDE4s from going to the place in the cell where they help inflammation to occur. These should provide a new way of making medicines to treat COPD that we anticipate will not suffer side effects caused by medicines currently being developed.

cAMP is a pivotal second messenger able to exert a panoply of cell type specific effects. A multigene family of phosphodiesterases (PDEs) provide the sole means for degrading cAMP and are thus poised to play a key regulatory role in cells. Highly specialised regulatory properties, coupled with cell specific patterns of expression, provide each cell type with a sophisticated and unique means of regulating intracellular cAMP. This diversity offers potential for developing highly specific therapeutic agents. There is great interest in developing PDE4 family selective inhibitors for treatment of Chronic Obstructive Pulmonary Disease (COPD). However, the deployment of PDE4 inhibitors as therapeutics has been limited by side effects, such as nausea. It is now appreciated that PDE4 activity is attributable to a large family of isoforms. This has prompted the notion that selective inhibition of particular PDE4 isoforms may maximise therapeutic benefit whilst minimising side effects. Different cell types have unique complements of PDE4 isoforms and recent technological advances place us now at a stage where we can determine how individual PDE4 isoforms sculpt cAMP gradients in cells to underpin compartmentalised cAMP signalling and control specific cellular processes. Inherent in this is the concept pioneered by our laboratory that the intracellular targeting of individual types of PDE4 isoforms to specific signalling complexes is fundamental to their functioning. Thus, not only may altered expression, targeting and regulation of individual isoforms contribute to various pathological conditions but disrupting the intracellular targeting of specific PDE4 isoforms in cells may provide a novel means of generating therapeutics aimed at disease-related PDE4 isoforms while minimising side-effects. As a route to identifying novel therapeutic targets we propose to define the functional role, modes of intracellular targeting and and regulation of PDE4 isoforms associated with COPD.

Asthma causes around 74,000 emergency hospital admissions and 1500 deaths in the UK each year. However, Chronic Obstructive Pulmonary Disease has now overtaken asthma as a drain on healthcare resources. It is the fourth leading cause of death in the world, with numbers predicted to increase. In the UK, COPD causes around 30,000 deaths/year and is projected to become the third most common cause of death by 2020. It causes 300,000 emergency hospital admissions every year, representing >10% of all acute admissions. It currently costs the NHS £500 million in direct costs and almost £1 billion a year with indirect costs included. COPD causes working difficulties, with loss of >20 million working days/yr in the UK. Whilst there have been improvements in the management of this difficult disease, there is a pressing need for novel therapies to combat it, particularly as no existing treatment appears to reduce disease progression.
While the PDE4 selective inhibitor, Roflumilast has recently been approved for use in Europe and the USA, its path to approval has been problematic, reflecting difficulties due to side effects that limit the therapeutic window. Nevertheless, the proven anti-inflammatory action of PDE4 inhibitors demonstrates the functional importance of PDE4 isoforms. The side-effect issue probably relates to the fact that 4 PDE4 genes encode >20 isoforms with similar catalytic units such that active-site directed inhibitors, like Roflumilast, inhibit all PDE4 species to a greater or lesser extent, rather than preferentially targeting those associated with efficacy in ameliorating COPD. Different cell types have unique complements of PDE4 isoforms and recent technological advances place us now at a stage where we can determine how individual PDE4 isoforms sculpt cAMP gradients in cells to underpin compartmentalised cAMP signalling and control specific cellular processes. Inherent in this is the concept pioneered by our laboratory that the intracellular targeting of individual types of PDE4 isoforms to specific signalling complexes is fundamental to their functioning. Thus, not only may altered expression, targeting & regulation of individual isoforms contribute to various pathological conditions, but disrupting the intracellular targeting of specific PDE4 isoforms in cells may provide a novel means of generating therapeutics aimed at disease-related PDE4 isoforms while minimising side-effects. We are thus uniquely placed to build on and exploit our expertise in order to translate this into identifying novel therapeutic targets and approaches.
The general public will benefit. Collaborations such as the one proposed with the Akassoglou lab, are pivotal in future research development. They increase the UK knowledge base and therefore scientific output, student teaching and postdoctoral training, which are are substantial contributors to national wealth. In addition, such collaborations reduce costs through efficient sharing of intellectual and technical resources.
All materials generated as part of this proposal will be made freely available to other members of the scientific community.
Clinicians and patients will benefit indirectly from this work because the more we understand about the mechanisms underlying COPD, the nearer we become to an effective treatment.
Additionally, the researchers employed on this grant will acquire experience investigations into complex signalling modules and pathways and the multifaceted dynamic processes they involve. With this novel combination of competences the researchers will become competitive in the biomedical research field with an original profile. By working under the supervision of top scientists in their field and with authors of numerous highly quoted publications, they will learn how to conceive solid research projects and how to present scientific results in a clear and convincing form, with the perspective of publishing their work in high ranking peer-reviewed journals.