(9b) Calcium Phosphate Nanocarriers Produced By Flame Spray Pyrolysis for High-Loading Delivery of Biological Drugs

Nanoparticle-based drug delivery systems have been considered as an auspicious alternative for efficient delivery of biological drugs (such as proteins and peptides) [1], which is deemed challenging due to large size and enzymatic degradation susceptibility of biologics. However, the clinical translation of such therapeutic nanoformulations is still in its infancy due to (i) complex synthesis methods of nanocarriers, and (ii) poor loading efficiency of biologics in comparison to clinically relevant therapeutic doses [2].

Here, we aim to address these challenges by engineering calcium phosphate (CaP) nanocarriers with tailored properties by flame spray pyrolysis (FSP) [3,4]. FSP is a scalable process with high production rates and also allows for fine tuning of nanoparticles properties. CaP nanoparticles with different specific surface areas (SSA) are obtained by varying precursor concentration in the flame. Our main goal is the synthesis of nanoparticles with high loading capacity of biological drugs (proteins and peptides). Bovine serum albumin (BSA) and bradykinin are used as model protein and peptide, respectively, and are physisorbed on the as-prepared nanoparticles. Their concentration along with the incubation time are varied in order to investigate their influence on loading efficiency. High loading values, reaching 350 mg/g and 600 mg/g of CaP for BSA and bradykinin, respectively, are obtained.

Furthermore, as a proof of concept, we apply the developed protocol and physisorb LL-37 antimicrobial peptide on CaP nanoparticles. Maximum loading achieved here (~800 mg/g) outperforms all LL-37 loading values found in the literature both for inorganic and organic nanocarriers [5]. Typical fractal-like structure of flame made agglomerated/aggregated nanoparticles promotes high drug loading efficiency. Moreover, it is shown that CaP nanoparticles protect LL-37 from enzymatic degradation by Protease K in vitro and that the peptide retains its antimicrobial activity against Escherichia coli and Streptococcus pneumoniae after being physisorbed on nanoparticles. The antimicrobial activity of LL-37 loaded nanoparticles, as assessed by monitoring bacterial growth, outperforms that of the free peptide for E. coli, whereas similar behavior is observed for free LL-37 and LL-37 loaded CaP nanoparticles for S. pneumoniae.

In a nutshell, the potential of FSP for fabrication of nanocarriers with high drug loading capacity of biologicals is shown in this study, which will improve therapeutic efficiency by delivering high concentration of biological drugs at the diseased sites.

References

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3. Mädler L., Kammler H.K., Mueller R., Pratsinis S.E., Controlled synthesis of nanostructured particles by flame spray pyrolysis. Aerosol Sci. 2002;33:369-389.
4. Loher S., Stark W.J., Maciejewski M., Baiker A., Pratsinis S.E., Reichardt D., Maspero F., Krumeich F., Günther D., Fluoro-apatite and Calcium Phosphate Nanoparticles by Flame Synthesis. Mater. 2005;17:36-42.
5. Tsikourkitoudi V., Karlsson J., Merkl P., Loh E., Henriques-Normark B., Sotiriou G.A., Flame-made calcium phosphate nanoparticles with high drug loading for delivery of biologics. Molecules 2020;25: