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.