Production of the anti-HIV protein SLPI in plants

DESCRIPTION (provided by applicant): A New, Low-Cost Production Method for a Human Anti-HIV Protein SUMMARY: The human secretory leukocyte protease inhibitor (SLPI) is an 11.7 kDa mucosal protein well known for its anti-microbial (including anti-HIV), wound healing and anti-inflammatory (including anti- arthritis) activities. SLPI protein is found naturally in saliva and elsewhere in the human body. Individuals with high levels of this protein have notably reduced HIV transmission. At present, R&D Systems, Inc. produces this protein in E. coli and sells the product at a cost of approximately $2.5 million per gram, which restricts its use. The high cost associated with SLPI reflects high demand combined with limited supply, given that production of the non-glycosylated cationic protein expression in E. coli requires very extensive denaturation and renaturation to refold this disulfide-rich protein in its normal biologically active form. While biologically active human SLPI has been successfully overexpressed as a 16.4 KDa "polyhistidine-tagged" protein (HisSLPI) under regulation of baculovirus promoter (bv) in insect cells, insect cells cannot grow as fast as E. coli and have other drawbacks for commercial production of proteins. About 20 grams of SLPI will be necessary for a good size preclinical test, posing a severe financial challenge to thoroughly investigate of the HIV inhibitory properties of SLPI. In this STTR project, Edenspace Systems Corporation proposes to generate a new, low cost method of producing biologically active SLPI to facilitate preclinical testing and potential commercial production of this intriguing human anti-HIV protein. Edenspace's research partner, Dr. Mariam Sticklen at Michigan State University, has developed a plant-specific construct containing the gene for SLPI, with a polyhistidine tag for purification. This HisSLPI construct has been integrated into the tobacco genome, and multiple lines have been demonstrated to express the HisSLPI transcript. Work is in progress to see whether the plant-specific construct produces the correct SLPI protein that is biologically active. In Phase I, the HisSLPI construct will be modified to target the protein to several different organelles in the plant cell, thereby optimizing SLPI production and accumulation. SLPI protein will be purified from the tobacco biomass and examined for stability and activity against proteases. Following successful Phase I purification of biologically active SLPI from tobacco, production of the protein will be scaled up with a production cost objective of $1,000 per gram for preclinical studies of the anti-HIV properties of the protein during Phase II. Achievement of the goals of this STTR project is expected to provide the basis for low-cost commercial production of megagram quantities of a potentially important new anti-HIV agent. At the end of the Phase II project, at least 20 grams of purified SLPI will be provided to the Mayo Clinic HIV Research Center for preclinical testing (see attached letter from Dr. Andrew Badley of the Mayo Clinic). The human protein SLPI was isolated from saliva and shown to reduce HIV replication and block HIV binding to annexin II, a receptor on the surface of macrophages. While SLPI is an attractive target to develop as an HIV therapy, it is currently uneconomical to produce sufficient quantities for preclinical testing. By producing SLPI using transgenic tobacco plants, Edenspace proposes to manufacture enough SLPI for a preclinical trial with a research partner and develop a production system to produce SLPI for large scale (kilogram) purification.