Elastase inhibitor for detection and treatment of inflammation and infection

An inhibitor of human neutrophil elastase (HNE) has recently received a US patent and is undergoing pre-clinical development, with Phase I clinical trials anticipated to start in 1998. The first clinical trials in patients are likely to be in cystic fibrosis (CF), where it is hoped that it will block the deterioration of the lung and help reduce bacterial infections and the production of mucus. EPI-HNE-4 (which stands for engineered protease inhibitor, human neutrophil elastase 4) is the first pharmaceutical agent to be discovered by phage display technology, and the lead HNE inhibitor from Dyax Corp. (Cambridge, MA, USA). Dyax hope it will be effective in treating pulmonary diseases where uncontrolled production of HNE are implicated, such as CF, bronchitis and emphysema. L. Edward Cannon, President of Dyax's Research Division, comments that for these conditions they believe inhibitors of HNE offer one of the first treatments to target the underlying inflammation rather than the infections that arise from them. EPI-HNE-4 was discovered through Dyax's proprietary phage display technology. The scaffold (starting point) was inter alpha-trypsin inhibitor (IATI), a small, stable protein for which a three-dimensional structural model was available. Another advantage was that IATI was known to be safe when administered therapeutically in humans. Any scaffold can be used, says Cannon, if the choice has the properties required; `all you have to do is modify the surface of the molecule to achieve the binding activity wanted.' Dyax actually made 50 million variants of IATI, from which they identified and chose the one lead inhibitor. Four amino acid changes were all that were needed to convert IATI into an elastase inhibitor. This technology has also allowed them to identify the specific chemical features required in any protein to inhibit HNE. Inhibitors of HNE are effective in animal models of emphysema: Dyax have shown that giving the HNE inhibitor to Syrian golden hamsters that have previously been given HNE reverses the otherwise fatal consequences of acute haemorrhage in the lungs, allowing them to survive. In another project, Dyax is developing EPI-HNE-4 as a targeting agent for imaging sites of inflammation and infection. The inhibitor can be labelled with the radioisotope technetium-99m (<sup>99m</sup>Tc), which is a strong γ-emitter. EPI-HNE-4 can be used as a diagnostic imaging agent because it rapidly penetrates to, and is retained at, sites of inflammation. One potential indication is the diagnosis of appendicitis; currently 25–30% of appendix operations are later found to be unnecessary. EPI-HNE-4 could also be used to find the anatomical site of `fever of unknown origin'; for example, when patients have an elevated temperature and physicians want to know where the site of inflammation or infection is to be able to treat the cause effectively. The only current alternative involves removing neutrophils from the body, labelling them with ^99mTc and then injecting them back into the patient, where they migrate to sites of inflammation. The approach takes a couple of days and requires considerable technical skill because neutrophils are extremely fragile. Using the new method, it is hoped that images could be produced within minutes, without the isolation and labelling of autologous cells.