Deep-breathing mice in the laboratory of Robert Debs promisethe breath of life -- literally -- to cystic fibrosis victims.
The animals inhaled the human gene for cystic fibrosistransmembrane conductance regulator (CFTR), a mutation ofwhich causes the disease. The healthy DNA sequence reachedthe rodents' lungs in a plasmid complexed to a liposomemicrocarrier about 100 nanometers (millionths of a millimeter)in diameter. Debs suspended the whole expression package inan aerosol mist and blew it into the mouses' nostrils for 90minutes.
"A full 60 days after a single aerosol administration," Debs toldBioWorld, "we see the human CFTR protein expressed in themajority of their airway epthelium lining cells." He added,"This, to my knowledge, is far and away the longest period ofexpression of the CFTR gene product in animal lungs."
His report of a successful earlier attempt, using only a markergene, to test aerosol delivery of gene therapy to the lungs,appeared in this week's Proceedings of the National Academyof Sciences (PNAS). The result: high-level, lung-specificmarker-gene expression in mice for at least 21 days.
Although his current CF-gene experiment is still ongoing, Debs,who is associate research physician at the University ofCalifornia, San Francisco, School of Medicine's Cancer ResearchInstitute, has already been contacted by a number ofbiotechnology and pharmaceutical companies to discuss thepossibility of early clinical trials. The university has licensedexclusive rights to his patent-pending techniques to a fledglingbiotechnology holding company, Megabios Corp. of SanFrancisco.William L. Brown, a Megabios vice-president, told BioWorldthat since its founding at the beginning of this year, hiscompany, with money from private investors, has been fundingDebs' research, as well as supporting complementary work onin vivo gene transfer at other university laboratories."Our primary business is research and in vivo gene therapy,"Brown said. "We find the cystic fibrosis thing very exciting."
Debs' track record stems from his development in the mid-1980s of aerosol-administered pentamidine to prevent Pneumocystis cariniipneumonia, a leading cause of AIDS death.
Other CF research groups, Debs said, are applying forpermission to initiate gene therapy trials using adenovirus as avector, rather than liposomes, and aerosol delivery via thetrachea, rather than inhalation.
Debs cited a broad spectrum of potential advantages for hisliposome delivery system:
-- The overall surface of his liposomes are cationic (positivelycharged) so they complex avidly with DNA, which is highlynegatively charged.
-- There is no theoretical limit on the size gene that can be socomplexed; only a limited amount of DNA can be cloned into aviral vector.
-- Delivery by inhalation, in contrast to intratracheal, is non-invasive and results in deeper penetration of material into thelungs.
-- Liposomes are non-infectious and appear non-immunogenic.
But don't hold your breath; Debs cautions that "effects ofrepeated aerosol administration of DNA/liposome complexesinto both normal and diseased lungs will need to be tested."
He also proposed making intrapulmonary targeting moreprecise by coupling monoclonal antibodies to the liposomesurface.
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.