Appeal No. 1995-4572
Application 08/035,443
attached to liposome surface components, not to the PEG chains on the outer surface
of the liposomes. Similarly, Hawrot teaches of liposomes which encapsulate a drug to be
delivered and to which cell specific ligand targets have been attached on the outer surface.
In the second category of references relied upon by the examiner, Handley teaches
that polymyxin B is useful for neutralizing endotoxin. However, the problem encountered
with the use of polymyxin B is the very short half-life in the body due to rapid renal
clearance by the kidneys. In order to solve this problem, Handley found that by conjugating
polymyxin B to a carrier such as dextran or polyethylene glycol (PEG), one is able to
increase the size and molecular weight of the polymyxin B which increases its circulation
time in the bloodstream. Similarly, Davis describes increasing the blood circulation time
of various polypeptides by conjugating the polypeptides to biologically compatible
polymers, such as PEG.
The only reference which discloses polymyxin B as recited in the instant claims is
Handley. However, this reference makes no mention or suggestion of attaching the
polymyxin B-polyethylene glycol conjugate to a liposome. Handley suggests increasing the
molecular weight and size of polymyxin B so as to increase its blood circulation time and
avoid its rapid renal clearance, but includes no suggestion to further increase the
molecular weight and size of the polymyxin B by attaching a liposome to the conjugate.
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