Scientists at Protein Engineering Corp. have remodeled aninhibitor of an enzyme associated with lung diseases, creating ablocker that is orders of magnitude more potent than allprevious compounds.
The new elastase inhibitor, which should find use in suchrespiratory disorders as cystic fibrosis, bronchitis andemphysema, will be tested preclinically, and if promising, willenter clinical trials by the end of 1993, John Freeman, companypresident and co-founder, told BioWorld.
Elastase appears to be overactive in respiratory diseases,decreasing the elasticity of the lung. The new inhibitor wouldreplace an inhibitor called alpha-1-antitrypsin, which isexpensive and has a potential for contamination and asusceptibility to breakdown in the lungs of CF patients,according to the company.
Reporting in the current Proceedings of the National Academyof Sciences, the Cambridge, Mass., company showed how it useda method called "directed evolution" to create an elastaseblocker that is 50 times more potent than any inhibitorreported to date.
The technique causes a bacterial virus to express variants of anexisting protein, engineered to vary at key amino acids thatdetermine binding affinities. The viruses then make andexpress the new proteins on their surfaces, as directed by theirnew genetic instructions.
The variants that prove to be the most potent binding agentsare pulled out of the viral library by their immobilized targetmolecules -- in this case, human neutrophil elastase coatedonto beads.
Once isolated, the proteins can be made in quantity simply byallowing the virus bearing them to multiply in the bacterialhost.
The new elastase inhibitor binds to elastase 4 million timesmore tightly than its parent protein, aprotinin.
"We are the only ones I know of that have demonstrated thisimmense increase in affinity," said Freeman. "By making lots ofchanges in parallel rather than one at a time, we have greatlyaccelerated the process" of drug discovery, he said.
Other techniques to express new agents in viruses or bacteriagenerate entirely random sequences to create peptides.
Affymax N.V. (NASDAQ:AFMXF) screens for peptidetherapeutics by linking peptides to their encoding genes splicedinto plasmids. Because the peptide is linked to a plasmid, it canbe isolated and amplified from a mix of billions of randomlygenerated peptides by growing the plasmid in E. coli. Affymaxand other groups have a similar technique using peptideslinked to viruses.
Gilead Sciences Inc. (NASDAQ:GILD) makes billions of single-stranded nucleotides, called aptamers, from which the companyisolates the sequence of nucleic acids that specificallyrecognizes therapeutically important proteins, such as theblood clotting protein thrombin.
Privately held Protein Engineering Corp., however, believes afaster strategy is to work with larger proteins with somealready identified structural features. The tradeoff is having tohave some structural knowledge of the target, but the rewardis high potency, according to the company.
Protein Engineering, formed in 1987, is working on severalother protein-digesting enzyme targets, some for in-housedevelopment and some for corporate partners that Freemandeclined to identify.
Patents have been filed for the "keystone" technology, Freemansaid, and a sister patent application covering a method togenerate new DNA binding proteins has received notice ofallowance.
Robert Ladner, senior vice president, scientific director and co-founder, is an inventor on a score of protein engineeringtechniques and formerly was principle research scientist atGenex Corp. Freeman is an entrepreneur and private investor.
-- Roberta Friedman, Ph.D. Special to BioWorld
(c) 1997 American Health Consultants. All rights reserved.