Parenteral Delivery of Peptides and Proteins - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 585

pathways, which are governed by CPPs. The current explanation for the intracellular
entry is that each CPP may be internalized by the endocytic route [466] . Two types
of endocytic uptake of CPPs have been proposed: the classical clathrin-mediated
endocytosis and the lipid raft-mediated caveolae endocytosis, [477-480] as shown in
Fig. 11.19 . Studies have also been carried out to demonstrate that possible penetra-
tion mechanisms for CPP like Tat and pAntp are through macropinosomes [481-484] .
Further studies suggest that internalization requires the expression of negatively
charged glycosaminoglycans on the cell-surface for electrostatic interaction with CPPs,
prior to endocytosis [485-487] . Endosome-localized CPPs have been shown to deliver
cargo, through the Golgi apparatus and endoplasmic reticulum (ER), prior to their cyto-
solic release [488] . Evidence also exists for nuclear delivery of CPP-internalized cargo
and resistance of CPP against degradation once internalized [485] . One remarkable
mechanism of endosomal escape for CPP has been investigated by the HIV viral pro-
tein hemagglutinin (HA2), which provided a novel mechanism of endosomal escape
for CPPs [486] .
In addition to interaction with the membrane, methods of cargo attachment and
cargo type and physicochemical properties of cargo such as size, overall charge, and
structure affect the whole construct's performance, including its uptake mechanism,
disassembly inside the cytoplasm, and release of the native protein [489-491] . Some
applications and examples of CPP in intracellular delivery of P/P drugs are presented
in Table 11.16 .
Although the mechanism of entry, trafficking route, and degradation pathway of
CPPs remains elusive, intracellular drug delivery using CPPs seems to be a promis-
ing solution to many hurdles of the current intracellular delivery systems. However,
for its clinical application more research work is essential in area like cell line speci-
ficity of CPPs.
11.6.6 Miscellaneous Delivery System
11.6.6.1 D��oFoam ���hno﻽o�y: � V�hi�﻽� fo� Cont�o﻽﻽�d D�﻽iv��y of
P�ot�in and P��tid� D�﻽�s
A major challenge in the development of sustained-release formulations for protein
and peptide drugs is to achieve high drug loading sufficient for prolonged thera-
peutic effect, coupled with a high recovery of the P/P. This challenge has been suc-
cessfully met in the formulation of several P/P drugs using the DepoFoam, a novel
multivesicular lipid-based drug delivery system. A unique feature of the DepoFoam
system is that inside each DepoFoam particle, discontinuous internal aqueous cham-
bers, bounded by a continuous, nonconcentric network of lipid membranes, render a
higher aqueous volume-to-lipid ratio and much larger particle diameters compared
with MLV [510-512] . DepoFoam technology can be used to develop sustained-
release formulations of therapeutic P/P over a period of few days to several weeks,
with versatility to modify rate of drug release, high drug loading, high encapsula-
tion efficiency of P/P drugs (up to 85%), low content of free drug in the suspension,
little chemical change in the drug caused by the formulation process, narrow particle