(706d) Catalase Polymer Nanofilaments of Tunable Stiffness and Morphology

Filamentous polymer nanocarriers (f-PNC) can
be used to encapsulate the highly potent antioxidant enzyme catalase,
protecting this therapeutic from proteases and inhibitors found in many
biological settings [1]. The
primary factor that controls morphology of these f-PNC is the degree of
amphiphilicity of the constituent poly(ethylene glycol)-b-poly(lactic acid)
(PEG-PLA) diblock copolymers. While maintaining the same degree of
amphiphilicity through ratio of the molecular weights (MW) of PEG to PLA (i.e. 80%
PLA, a f-PNC producing polymer), different absolute MW diblocks were
synthesized. A ring opening polymerization of lactide initiated by different MW
PEG polymers resulted in diblock MWs that ranged from 12 kDa to 100 kDa, as
determined by ¹H-NMR and GPC. Thermal properties such as glass
transition temperature (T_g) and melt temperature (T_m)
were determined via differential scanning calorimetry (DSC). These polymers were
subsequently used to encapsulate catalase by previously established methods [1, 2]. Mass
and enzymatic activity loading of catalase, as well as the f-PNC
protection of the cargo enzyme from proteolysis, were determined. While we
found these measures to be relatively similar between different MW f-PNC,
it is known that characteristics such as carrier flexibility and length can
play a major role in f-PNC circulation profiles in vivo [3]. Therefore,
morphological analyses were performed by transmission electron microscopy (TEM)
as well as fluorescence microscopy. From fluorescence time-lapse microscopy, f-PNC
persistence lengths (l_p), which describe nanocarrier flexibility, as
well as contour lengths, were measured. Lower MW f-PNC had relatively
smaller l_p's and are thus more flexible at room temperature. Since
we found that the T_g was around 25°C for the lowest MW f-PNC,
and increased to 30°C for the highest MW f-PNC, we also determined the l_p's
at physiologic temperature, 37°C, well above the highest MW polymer T_g.
Heating increased flexibility (decreased l_p) of f-PNC overall,
however the highest MW f-PNC still had larger l_p's than lower
MW carriers. Contour lengths also significantly increased with increasing
polymer MW. Thus it would seem that polymer MW remains the most important
factor in determining nanocarrier morphology and stiffness. In conclusion,
several new preparations of catalase-loaded f-PNC are reported here,
with polymer MW tunable flexibility, offering several potential therapeutic
applications.

References:

[1]        E.A. Simone, T.D.
Dziubla, F. Colon-Gonzalez, D.E. Discher, V.R. Muzykantov, Effect of polymer
amphiphilicity on loading of a therapeutic enzyme into protective filamentous
and spherical polymer nanocarriers. Biomacromolecules 8(12) (2007) 3914-3921.

[2]        T.D. Dziubla, A. Karim, V.R. Muzykantov, Polymer
nanocarriers protecting active enzyme cargo against proteolysis. J Control
Release 102(2) (2005) 427-439.

[3]        Y. Geng, P. Dalhaimer, S. Cai, R. Tsai, M.
Tewari, T. Minko, D.E. Discher, Shape effects of filaments versus spherical
particles in flow and drug delivery. Nat Nano 2(4) (2007) 249-255.