Bioconjugate Chemistry
ARTICLE
transferring these systems to the in vivo situation. Nonetheless,
these initial in vitro insights already demonstrate quite clearly
that polymer-coated siRNA-containing PEC are able to specifi-
cally induce target-specific gene silencing in vitro, and they
thereby exemplify that even systems (physico-) chemically
optimized to eventually perform well in vivo compare well to
unstable and nonstealth systems primarily designed for gene
silencing in vitro.
dct - surface density of coating polymer (g/nm2 mol)
nct - number of coating molecules fixed on PEC surface
tct - characteristic reaction time of the slow coating process (min)
’ MEANING OF SUBSCRIPTS AND SUPERSCRIPTS
cp - coating polymer
pec - uncoated polyelectrolyte complexes
cc - coated PEC
ct - coating layer of PEC
’ CONCLUSIONS
’ DEFINITIONS
The synthesis and physicochemical properties of reactive
copolymers suitable for the coating of PEC and the physical
properties of coated and uncoated siRNA-containing PECs are
described. Results of stability measurements showed that often-
studied PEI-based PECs are not suitable for coating reactions
and consequently are likely suboptimal vectors for in vivo siRNA
delivery. We therefore set out to develop siRNA-containing
PECs based on GPL, as well as GPL PECs coated with HPMA-
based reactive hydrophilic copolymers. The synthesis and physico-
chemical characterization of HPMA-based copolymers contain-
ing TT reactive groups bound to the polymer chain via spacers
containing biodegradable disulfide bonds was described. The use
of the HPMA copolymers for siRNA/GPL complex coating
reactions resulted in attachment of (on average) 28 polymer
molecules to the nanoparticle surface, forming a 5-nm-thick
hydrophilic polymer protective layer that was selectively remo-
vable in reducing environments. Coating the siRNA/GPL vec-
tors with the stealthy hydrophilic polymer substantially enhanced
the stability of the vectors in aqueous media, and it might thereby
improve their potential for passive targeting to solid tumors by
means of the EPR effect. Preliminary results on the in vitro gene
silencing efficacy of the coated complexes furthermore showed
that they were able to specifically reduce target gene expression in
human epithelial breast adenocarcinoma cells, thereby suggest-
ing that these systems hold significant potential for further in
vitro and in vivo evaluation.
pec
ΔMwct = Mwcc - Mw
ΔRhct = Rhcc - Rh
pec
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’ AUTHOR INFORMATION
Corresponding Author
*To whom correspondence should be addressed. E-mail: kostka@
imc.cas.cz. Fax: þ420 296809410. Tel.: þ420 296809209.
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’ ACKNOWLEDGMENT
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nanoparticles bearing amino groups on the surface with hydrophilic
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The authors acknowledge financial support by the Grant Agency
of Academy of Sciences of the Czech Republic (IAAX00500803),
Academy of Sciences of the Czech Republic (KAN 200200651)
and by the European Union (grant LSHB-CT-2004-512087
and MediTrans - Targeted delivery of Nanomedicines).
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(14) Pola, R., Studenovskꢁy, M., Pechar, M., Ulbrich, K., Hovorka, O.,
’ LIST OF SYMBOLS
Mw - weight-average molecular weight (g/mol)
Mwa - apparent weight-average molecular weight (g/mol)
Rh - hydrodynamic radius (nm)
Rg - radius of gyration (nm)
ζ - zeta potential of PEC (mV)
F - particle density of PEC (g/mL)
c - concentration (g/mL)
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Vꢀetviꢀcka, D., and Ríhovꢁa, B. (2009) HPMA-copolymer conjugates
targeted to tumor endothelium using synthetic oligopeptides HPMA
copolymer-based conjugates targeted with specific oligopeptides. J. Drug
Targeting 17, 773–786.
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(15) Ulbrich, K., Subr, V., Strohalm, J., Plocovꢁa, D., Jelínkovꢁa, M.,
dn/dc - refractive index increment
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and Ríhovꢁa, B. (2000) Polymeric drugs based on conjugates of synthetic
q - scattering vector (m-1
)
and natural macromolecules I. Synthesis and physico-chemical charac-
j - ratio of positive to negative charges
terisation. J. Controlled Release 64, 63–79.
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dx.doi.org/10.1021/bc100197e |Bioconjugate Chem. 2011, 22, 169–179