Structure-function studies on human Angiotensin-I converting enzyme (ACE)

Angiotensin-I converting enzyme [ACE, which contains two domains (N and C)] inhibitors are widely used to treat cardiovascular diseases, including high blood pressure, heart failure, coronary artery disease, fibrosis and kidney failure. However, current-generation ACE inhibitors, which were developed in the 1970's and 1980's, are hampered by common side effects. The N- and C-domains of ACE display different substrate specificities.

While there are many ACE inhibitors on the market that block both domains, there are no drugs that selectively inhibit the N-domain and thereby accrue the advantages of reducing fibrosis and inflammation in the heart, kidney and lung, without the concomitant side effects induced by blockade of the C-domain.

This underscores the importance of the determination of the 3D structure of ACE and the design of 2nd generation ACE-inhibitor complex/s that are safer and more effective. Our success in the determination of the crystal structure of human testis ACE (equivalent to the C-domain of somatic ACE) and the N-domain of somatic ACE (Angiotensin-I converting enzyme [ACE, which contains two domains (N and C)] inhibitors are widely used to treat cardiovascular diseases, including high blood pressure, heart failure, coronary artery disease, fibrosis and kidney failure. However, current-generation ACE inhibitors, which were developed in the 1970's and 1980's, are hampered by common side effects. The N- and C-domains of ACE display different substrate specificities.

While there are many ACE inhibitors on the market that block both domains, there are no drugs that selectively inhibit the N-domain and thereby accrue the advantages of reducing fibrosis and inflammation in the heart, kidney and lung, without the concomitant side effects induced by blockade of the C-domain.

This underscores the importance of the determination of the 3D structure of ACE and the design of 2nd generation ACE-inhibitor complex/s that are safer and more effective. Our success in the determination of the crystal structure of human testis ACE (equivalent to the C domain of somatic ACE) and the N-domain of somatic ACE (with various clinically important inhibitors as well as novel domain selective inhibitors) using X-ray crystallography have provided the platform for true structure-based design of better ACE inhibitors. This is a significant breakthrough in terms of the structural biology of the protease and, more importantly, the mechanism of ACE inhibition.

This paves the way for a more rigorous approach exploiting the differences between the domains through a structure based drug design approach of novel domain-selective inhibitors. Thus the sustained effort on ACE has provided a firm platform for our group for the new studies.

Our proposed experiments that builds on a body of previous and current work are directed at structural study of the full-length somatic ACE and crystal structures of complexes of ACE with domain selective inhibitors combining basic and translational research on an important medical problem.

In the longer term, the application seeks to exploit detailed structural knowledge for the synthesis of new ACE inhibitors with the aim of providing better drugs for the treatment of cardiovascular diseases in particular hypertension and fibrosis. A key feature will be the design of compounds that are specific for the N- or C-terminal domain of ACE with the expectation that this will provide selective compounds for therapy with fewer side effects.

This project addresses key unresolved issues concerning the structure and activities of the angiotensin converting enzyme (ACE) using a combination of structural molecular biology, homology modelling and biochemistry and is a natural extension of our ongoing research.

Our structure biology centred research work on ACE has been highly successful on the structures of different forms of the ACE protein, their substrate and inhibitor selectivity, and biological and potential clinical relevance. Key questions, however, remain unanswered and are the subject of the present proposal: what is the structure of the entire somatic ACE protein with both its active sites present? This is a considerable challenge for such a large and heavily glycosylated membrane protein. Encouraging preliminary data has been obtained in this direction.

Can we design domain selective ACE inhibitors? Again, this should certainly be feasible and significant proof-of-principle work has already been achieved but more structural data are needed to refine the information available. To achieve these ends, our laboratory is very well placed from the structure determination viewpoint and we have put in place some key international collaborations over the recent years [with Profs Ed Sturrock, Kelly Chibale at UCT, South Africa (ACE biochemistry, compound design and synthesis) and Dr. Vincent Dive, CEA, Paris (protease inhibitor design and synthesis)].

Although the aims are challenging, much novel and potentially exploitable data should emerge from the project as we make progress through the next ambitious stage of the work as described in the proposal.

The economic burden of cardiovascular diseases staggering, with estimated annual costs of $150 billion in the US, Euros 170 billion in the EU, and £30 billion in the UK.

Angiotensin-I converting enzyme (ACE) plays a critical role in the renin-angiotensin system (RAS) in relation to cardiovascular physiology and disease. This is mainly because of the drugs that block various components of this system and which are effective as treatments for hypertension, heart failure, fibrosis, prevention of vascular events caused by atherosclerosis (heart attack and stroke), and slowing kidney disease due to hypertension or diabetes.

Current ACE inhibitors have a wide range of licensed indications ranging from mild hypertension to post myocardial infarction. For the treatment of hypertension, the competing therapeutic approaches also include the use angiotensin II receptor antagonists and beta-blockers.

However, the development of novel, highly selective ACE inhibitors targeted to either the N or the C domain by structure-based drug design will produce a new generation of domain-specific ACE inhibitors with the potential for greater efficacy, fewer side effects, for the treatment of cardiovascular illnesses due to end-organ damage and organ fibrosis.

ACE has been the subject of intensive structural studies in many laboratories worldwide. Our group has a successful track record in this area, having made significant breakthroughs in determining the crystal structures of testis ACE, the N-terminal domain of sACE and the Drosophila homologue AnCE. Fundamental to this success has been the close collaboration between our laboratory at Bath (UK) and that of Professor Ed Sturrock at University of Cape Town, South Africa.

Thus we have a key advantage in the development of second generation ACE inhibitors (with efficacy and side effects), informed by structures of complexes with existing inhibitors- long term Aim.

As a consequence of this highly productive international collaboration, we are uniquely placed to deliver the proposed work, which has profound medical significance with a realistic chance of achieving real benefits for human health.