Liposome Technology Inc. (LTI) announced Thursday that ithas been awarded a second U.S. patent on its Stealth liposometechnology.

The patent, No. 5,225,212, covers Stealth liposome compositionsand methods containing an encapsulated compound forintravenous or subcutaneous administration. The compositionsand methods apply to a variety of therapeutically activecompounds, including proteins and peptides.

Because the Stealth liposomes are long circulating in thebloodstream and act as a depot for the encapsulated drug, theycan maintain the compound at a therapeutically meaningfullevel for a period of days (if administered intravenously) toweeks (if administered subcutaneously).

LTI of Menlo Park, Calif., had collaborations with three topbiotechnology companies to explore the potential of using itsStealth liposomes to deliver various genetically engineeredtherapeutic proteins. It was working with Chiron Corp. oninterleukin-2, Genentech Inc. on CD4 and Amgen Inc. on anundisclosed protein. At this point, however, all three of thoseagreements are "more or less on hold," explained Frank Martin,LTI's vice president and chief scientific officer.

As it turns out, encapsulating large proteins -- especially non-glycosylated ones -- is a tricky business because they tend tobe sticky. "We've had trouble formulating them because theystick to the liposomes," Martin told BioWorld.

So before proceeding further with product development, hesaid, LTI scientists have to "figure out how to entrap them. ...It's a challenge to exploit the technology for the larger, non-glycosylated proteins."

But Martin emphasized that "the prospects of applying theStealth technology to peptides and polypeptides are very good.Most of the data in the patent are based on small peptides."

The company received it first patent covering its Stealthtechnology in May. That U.S. patent, No. 5,213,804, covers theliposomes' use in treating solid tumors with several specificanti-cancer drugs.

LTI (NASDAQ:LTIZ) has encapsulated one of those drugs,doxorubicin, as its product Doxil, which is now in Phase IIIclinical trials in Europe for treating AIDS-related Kaposi'ssarcoma (KS). LTI is also in U.S. Phase III trials on Doxil fortreating KS, Martin said, as well as another, open-labelprospective trial in KS patents who had received chemotherapypreviously (refractory patients).

LTI is continuing safety and dose-escalation studies of Doxil onpatients with solid tumors in the U.S. and Israel, Martin added.

-- Jennifer Van Brunt Senior Editor

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