Phospholipases may not be targets of choice for medicinal chemistry, but two inhibitors are now in clinical development for atherosclerosis

By Editorial Board member Dr Keith Suckling

Phospholipases do not appear high on the list of major druggable target types. There are significant challenges in medicinal chemistry to provide specificity and in enzymology to generate data that can support chemistry for reactions that take place at a lipid-water interface at which active concentrations of compounds are difficult to define. So it is perhaps surprising that there are now two phospholipase inhibitors in clinical development for the treatment of atherosclerosis - surprising because of the chemical challenges but also because the final proof of efficacy in patients requires extended outcome studies in around 16,000 subjects.

The first of these compounds is darapladib (GSK) for which Phase 2 results were presented last year [1]. Darapladib inhibits the enzyme known as lipoprotein-associated phospholipase A2. As the name suggests, this phospholipase is found in the circulation associated with LDL and is thought to catalyse the hydrolysis of oxidised phospholipids. The products of the hydrolysis promote the expression of adhesion molecules on the artery wall and chemokines in macrophages and so promote the development of the vulnerable plaque. Inhibition of this process would therefore be expected to be of benefit and recent studies in a pig model support this concept [2] and some of the Phase 2 data are consistent with it too. This mechanism would be expected to have a similar overall effect on the pathogenesis of atherosclerosis to a chemokine receptor antagonist, for example CCR2. Importantly this approach does not reduce plasma LDL, and is not expected to.

Other forms of phospholipase have been implicated in atherogenesis in recent years and in particular those known as secretory phospholipases [3], of which the Group V enzymes have been of particular interest. Animal data also supports a role for these enzymes in atherogenesis [4], but the mechanism is different. In this case the phospholipase modifies HDL and LDL particles making the former less able to support reverse cholesterol transport and the latter more susceptible to oxidation. Very recently Phase 2 data have been reported of the effects of an sPLA2 inhibitor, varespladib (A-002, Anthera Pharmaceuticals) [5]. This compound inhibits a range of sPLA2 s (sPLA2-IIa>sPLA2-X>sPLA2-V) and, in contrast to darapladib, does have an effect on plasma LDL concentration and also on hsCRP. Recent animal data are consistent with an effect of varespladib on atherogenesis in the mouse [6]

It is important to recognize that the effects of these two phospholipase inhibitors on the process of atherogenesis are quite different and as a result, at least in Phase 2, they require different end points to be studied. If this is not borne clearly in mind there is a danger of serious confusion amongst non-experts. In this respect we should no more talk about phospholipase inhibitors as a class than we might about PPAR agonists: there are so many differences. Nevertheless, for both mechanisms, it is necessary to show that they improve outcomes in patients, and at this point the differences are not important. A large outcome study is beginning for darapladib (STABILITY) with around 15,000 patients [7].

By Keith Suckling, PhD, Editorial Board member of Expert Opinion on Investigational Drugs

Reference List

1. Serruys P.W., Garcia-Garcia H.M., Buszman P., Erne P., Verheye S., Aschermann M., Duckers H., Bleie O., Dudek D., Botker H.E. et al. (2008). Effects of the direct lipoprotein-associated phospholipase A(2) inhibitor darapladib on human coronary atherosclerotic plaque. Circulation 118: 1172-1182.
2. Wilensky R.L., Shi Y., Mohler E.R., III, Hamamdzic D., Burgert M.E., Li J., Postle A., Fenning R.S., Bollinger J.G., Hoffman B.E. et al. (2008). Inhibition of lipoprotein-associated phospholipase A2 reduces complex coronary atherosclerotic plaque development. Nat Med 14: 1059-1066.
3. Kimura-Matsumoto M., Ishikawa Y., Komiyama K., Tsuruta T., Murakami M., Masuda S., Akasaka Y., Ito K., Ishiguro S., Morita H. et al. (2008). Expression of secretory phospholipase A2s in human atherosclerosis development. Atherosclerosis 196: 81-91.
4. Boyanovsky B., Zack M., Forrest K., and Webb N.R. (2009). The Capacity of Group V sPLA2 to Increase Atherogenicity of ApoE-/- and LDLR-/- Mouse LDL In Vitro Predicts its Atherogenic Role In Vivo. Arterioscler Thromb Vasc Biol ATVBAHA.
5. Rosenson RS, Hislop C, McConnell D, Elliot, M, Stasiv U, et al. (2009). Effects of 1-H-indole-3-glyoxamide (A-002) on concentration of secretory phospholipase A2 (PLASMA study): a phase II double-blind, randomised, placebo-controlled trial. Lancet 373: 649-658.
6. Fraser H., Hislop C., Christie R.M., Rick H.L., Reidy C.A., Chouinard M.L., Eacho P.I., Gould K.E., and Trias J. (2009). Varespladib (A-002), a Secretory Phospholipase A2 Inhibitor, Reduces Atherosclerosis and Aneurysm Formation in ApoE-/- Mice. J Cardiovasc Pharmacol.53, 60-65
7. GSK Press release: http://www.gsk.com/media/pressreleases/2008/2008_pressrelease_10144.htm

Drug-drug interactions in oncology: from mechanisms to patient perception

Drug-drug interactions in oncology represent a highly problematic issue to resolve. The events that give rise to clinically significant drug-drug interactions are inherently driven by cancer patients that are often being medicated by more than one drug. Polypharmacy in oncology can result in alterations of chemotherapeutic pharmacokinetic profiles via multiple mechanisms affecting the pharmacodynamics of drugs that are closely related to their pharmacokinetic profiles. In their review article,Mani and colleagues critically analyze the mechanisms by which drug-drug interactions in oncology alter pharmacokinetics and also explore the emerging field of transcriptional control of enzyme/transporter action and its impact on altered drug clearance. Adding another layer of complexity to drug-drug interactions in oncology is the patient’s perception of the definition of a “drug”. Cancer patients undergoing treatment with chemotherapeutics who also consume over-the-counter medications, herbal remedies or supplements without informing their physician run the risk of unknowingly exposing themselves to potentially dangerous drug-drug interactions. In her Editorial article, Professor Marie Hanigan highlights the dangers of patients taking treatment advice from unreliable sources or misinterpretation of the scientific literature and calls for a more in-depth inquiry by the physician into the consumption of non-prescription medicines and other supplements by cancer patients. Professor Hanigan describes the lack of knowledge and confusion among cancer patients regarding the dangers of drug-drug interactions and addresses the challenges facing this large and complex field.

Finding and using patents for a bibliographical search

Patents are a valuable source of scientific information as well as business intelligence. In the case of the pharmaceutical industry, they provide early insights in a company's research programs and potential drug candidates. However, data contained in patents is often partial, biased and lacks the general objectiveness and perspective of peer-reviewed articles.
This laid the ground for Expert Opinion on Therapeutic Patents, which proposes critical reviews and analyses of patents (and articles) claiming the discovery of therapeutic compounds.

While authors have no problem at all compiling articles and data from the scientific literature, searching for patents often proves a hurdle. Here is an attempt at helping. A selection of databases and interfaces are briefly described.

Very much like for conventional scientific literature, several web-based interfaces propose search functionalities and access to patent databases. They are available to anyone and there is no need to be an IP professional to understand them. They may be free or require subscription. Search engines vary and it is recommended to read the instructions. However, they usually are obvious and easy enough to use, being not that different from Pubmed or Web of Science for example.
As ever, the selection of keywords is key to a successful search. Try several related or synonymous keywords. Also check if the search engine supports wildcard or truncated searches. The wildcard characters usually are *, ? and #. Boolean combinations and restricting searches to titles or abstracts can be necessary when a search returns too many irrelevant results.
In medicinal chemistry, searching for the molecular target is probably the best bet.

Researchers with access to SciFinder, Thomson Patents or Delphion for example will find these resources useful. Others can try:

• European Patent Office, which contains applications from most countries. You can save searches and save most original PDF files through the 'Save Full Document' link in the 'Original Document' tab.
  
• US Patent and Trademark Office, for US patents (an image can be downloaded)
• World Intellectual Property Organization proposes international patents applications. PDF and zipped TIFF images can be downloaded.
  
• Free Patents Online, for US, EU and some Japanese patents, as well as documents from the WIPO database. Powerful search engine (including a chemical search option) and access to the PDF files upon free registration.
• Google Patents, PDF available.

Patents filed in some countries, such as New Zealand and South Korea, are only accessible via their national patent offices (cf. links). However, chances are that these patents are also filed as WIPO patents.

I hope this demystifies patent searches.

Profile: Dr Micheal A. Morse

Dr Morse is a regular and invaluable contributor to Expert Opinion on Biological Therapy, having joined the Editorial Board in 2000 and accepting the position of Editor-in-Chief in 2007. He is currently Associate Professor of Medicine at Duke University, and is a G.I. Oncologist at Duke Comprehensive Cancer Center, where his clinical expertise lies in the treatment of gastrointestinal and hepatic malignancies, and malignant melanoma.

Dr Morse’s research focuses on developing strategies to activate T cell responses against tumors by immunizing patients with dendritic cell based vaccines. His group has continued to develop modifications to these vaccines, including loading with antigen in the form of peptides, mRNA, viral vectors and maturing dendritic cells with cytokines. Most recently, they have focused on genetically altering the expression of co-stimulatory and adhesion molecules, and have also identified preliminary data which suggests that it may be important to activate antibody responses as well as T cells in order to initiate immune-mediated destruction of tumors. The group is also working on other methods of modulating immune response, including anti-CTLA4 antibodies and strategies that interfere with inhibitory molecules such as PDL1. Further areas of research include other anti-cancer therapies to weaken the tumor’s ability to impair immune response, including combinations of cancer vaccines along with chemotherapy, radiotherapy, and targeted therapies.

Dr Morse has contributed many papers to Expert Opinion on Biological Therapy during his time on the Editorial Board, including his recent papers listed below:

Countering tumor-induced immunosupression during immunotherapy for pancreatic cancer
Michael A Morse Joseph Robert Hall, Janet MD Plate
Expert Opinion on Biological Therapy, Mar 2009, Vol. 9, No. 3, Pages 331-339.

Update on anti-CTLA-4 antibodies in clinical trials
Lee F Langer, Timothy M Clay, Michael A Morse
Expert Opinion on Biological Therapy, Aug 2007, Vol. 7, No. 8, Pages 1245-1256.

Vascular endothelial growth factor and immunosupression in cancer: current knowledge and potential for new therapy
Benjamin F Johnson, Timothy M Clay, Amy C Hobeika, H Kim Lyerly, Michael A Morse
Expert Opinion on Biological Therapy, Apr 2007, Vol. 7, No. 4, Pages 449-460.

In vitro evaluation of immunotoxicity

Recommended in 2000 by EMEA's Committee of Proprietary Medicinal Products,the in vitro assessment of immunotoxic risk for drug candidates is an integral part of preclinical safety screenings. Indeed, immunosuppression, immunostimulation, hypersensitivity and autoimmunity are adverse effects that can be elicited by (bio)pharmaceuticals.
A number of assays, available from CROs and reagent companies, can be used to test the effects of drugs, whether intended or not, on the various players of cell-mediated immunity. In a technical article to be published in the April issue of Expert Opinion on Drug Discovery, Dr Maria Fuggetta critically reviews a selection of these assays and suggests how enhanced methodologies can improve the identification of immunological hazard.

‘JUPITER’ and the risk of heart disease

Statins are blockbuster drugs taken by millions around the world. Results from the ‘JUPITER’ clinical trial[1] indicate that these cholesterol-lowering agents could decrease the risk of heart disease even for persons with low cholesterol levels; meaning that millions more could benefit from popping a statin pill…

But could they really? What indicators and risk factors dictate the prescription of statins? How should vascular risk be measured? And what are the factors that count towards this risk? An Editorial in the January 2009 issue of CMRO discusses the JUPITER study and explores these interesting themes.

The trial suggests that hsCRP, a protein associated with inflammation, can be used to identify subjects without vascular disease who should receive statins despite a low or intermediate calculated risk. The CMRO editorial highlights the fact that risk assessment needs to be re-examined, and discusses the role of hsCRP-testing in what the authors call risk stratification. The authors also feel that guidelines (and clinical practice) may need changing if indeed statins do have a much wider role in preventing vascular disease than was previously thought.

Of course, if relatively healthy persons (‘low or intermediate risk’) are to be prescribed statins, then there are terrific cost implications too. The authors of the editorial remark that this is all the more so if the benefits observed from taking Crestor (used in the JUPITER trial) can not be reproduced by cheaper, generic statins.

At the heart of the ongoing scientific debate, the fundamental question remains: do statins have a convincing role in primary prevention of heart disease? Read the editorial (an open access article) here find out what the authors think.

[1] JUPITER: Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin

Impact of predictive pharmacokinetics

The implementation of studies aiming at predicting ADME properties at preclinical drug discovery stages has been central in the effort to reduce attrition rates.
In a clear and authoritative article reviewing the development, over the past three decades, of Discovery Metabolism and Pharmacokinetics research, Dr Summerfield analyses the key elements which moved the field forward and anticipates how new paradigms, such as translational medicine and systems thinking, will push it further.
He concludes that, although the predictive metabolism and pharmacokinetics approach already proved successful, a strong impact on drug pipelines will only be achieved when pharmacodynamics and toxicology are integrated in a similar way to drug discovery programmes.
The article will be available in the March issue of Expert Opinion on Drug Discovery