A pair of sheep up in Seattle are being prepped asbellwethers for replacing injectable erythropoietin _biotech's first and only billion-dollar drug _ with asynthesize-your-own, gene-therapy approach. (SeeBioWorld Financial Watch, Aug. 14, 1995, p. 1.)
Those ovine laboratory animals will be turned intomodels of end-stage renal disease and kidney failure, inorder to test a process for implanting the gene forerythropoietin (EPO) into their systems, to correct theanemia from which human hemodialysis patients suffer.
Last year in the U.S. the number of Americans receivingdialysis grew by 15,286, to reach a total of 186,822, saidthe National Kidney Foundation's health informationofficer, Patricia O'Connor. (Meanwhile, their ranks weredepleted by 41,657 who died.) In most of thoseundergoing the thrice-weekly blood-filtering procedure,dialysis culminated with an infusion of recombinant EPOvia the access port, or fistula, by which the tubingreturned their cleansed blood to the body.
Recombinant EPO is the flagship drug developed anddistributed by Amgen Inc., of Thousand Oaks, Calif. TheFDA approved it on June 1, 1989, not only for dialysis-associated anemia, but for off-label warranted medicaluses. Thus, physicians prescribe EPO for the loss oferythrocytes (red blood cells) resulting from cancerchemotherapy, HIV infection and drug treatment forAIDS.
Red blood cells are sub-microscopic bags loaded withoxygen-rich hemoglobin, which the bloodstream carriesto the remotest recesses of the body. As red blood cellshave a shelf life of only 120 days or so, EPO triggers theirreplacement by the kidneys on a round-the-calendarschedule.
Also, if for whatever reason, such as anemia, or loss ofblood, oxygen levels decline, the erythropoietin hormone,a 30-kiloDalton glycoprotein, senses the O2 deficit, andsignals the kidneys that it's time to hurry up and generatemore new red blood cells.
Insert The Gene Instead Of Its Product
At the University of Washington, molecular biologist andgene therapist William Osborne mused that for such achronic, life-long administration of EPO to dialysispatients, implanting the gene for the hormone might be alogical alternative to injecting the product.
He and his co-workers put this idea to the test inlaboratory rodents, as they report in the current issue ofthe Proceedings of the National Academy of Sciences,(PNAS) dated Aug. 15. Their paper bears the title: "Genetherapy for long-term expression of erythropoietin inrats."
Clamping off a short segment of the left carotid artery intest animals, they scraped the endothelial cells from thevessel's inner lining, so the denuded walls would latch onto an infusion of rat vascular smooth-muscle cells. Thesecarried rat-EPO cDNA genes packaged in a retroviralvector.
Ten days later, the treated rats had a spurt in secretion ofreticulocytes _ newborn red blood cells _ "followed byclinically significant increases in hematocrit [red bloodcells levels in blood] and hemoglobin for up to 11weeks," PNAS reported.
Osborne's next step, begun last week, was to take twosheep and make them anemic and uremic, to mimickidney failure in humans. "We'll put in a vascular graftthat is seeded with ovine smooth muscle cells expressingthe EPO gene and its promoter in a retroviral vector."
His vascular graft is the device designed to permit genetherapy for EPO and other molecules in human patients."We've discovered a way," he explained, "of seedingthem within the plastic matrix of the graft with smoothmuscle cells transduced to express EPO."
"The interesting thing from our perspective," heobserved, "is that such grafts are already used in kidneydialysis patients because if they're on dialysis three timesa week, and get stuck in the arm, they wreck their ownveins. So they have to get a plastic prosthetic fistulaanyway. And of course they need EPO."
Osborne said that his arterial-venous shunt prosthesis"will last a minimum of one year. The kidney doctors tellus," he continued, "that their prosthetic grafts for needleaccess get trashed anyway within 18 months to two years"
He concluded: "The surgeon would simply sew in theprosthetic graft the same way he does for the dialysisaccess graft. Then the patient will be making his ownEPO, and won't be needing Amgen's EPO."
And For People . . .
For use in humans he visualizes a porous plastic cylinderfour to six millimeters in diameter, by perhaps 10centimeters long for treating an 80-kilogram patient with100 million transduced smooth muscle cells. Osborne isthe first inventor of this anastomosis-like device, forwhich the University of Washington has filed a patent.
He also has a grant application pending with the NationalInstitutes of Health (NIH) to fund eventual clinical trials,but added, "A venture-capital company in Chicago is alsointerested in getting us funding. We can do all thescience, but obviously we can't fund clinical studies."
Early in its development, Osborne recalled, "I proposedthis idea to Amgen, as a novel drug-delivery system. Theywere quite pleased, and gave us $75,000 for one year'spilot work. Then when we started doing that, and itlooked as if it was being successful, they switched off."
Hematologist David Dale is a co-author of the PNASpaper, and the university's point man with Amgen. Hetold BioWorld Today, "Amgen is not a device company.They have been interested in our work, and providedsupport for our research, as did the NIH.
Beyond EPO, Broader Applications
"They have not been particularly interested," Dalecontinued, "in developing this device, or really much elsein the way of devices. So they have encouraged us to seekother partners."
From Dale's perspective, "it's interesting because of thepotential breadth of application. We chose to use the EPOgene initially, because we knew a lot about its product.We're interested in devices to deliver granulocyte colony-stimulating factor [gCSF], and potentially othercytokines."
Osborne said: "We have transduced dogs, which mimicpeople, to express gCSF; it causes a 50 percent increasein neutrophil counts."
He concluded: "If our stuff goes successfully, within ayear to 18 months we could really think of going intopeople. It's pretty exciting." n
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.