Purpose: Polymeric nanoparticles (NPs) are promising vehicles for the delivery of poorly soluble drugs. This study investigates the encapsulation of gedatolisib, an anti-cancer drug with limited aqueous and non-aqueous solubility, in polymeric NPs via Flash Nanoprecipitation. This simple and rapid method is particularly attractive due to its ability to produce NPs with narrow size distributions and high drug loading. At the same time, various factors must be taken into account to successfully produce NPs with the desired size, drug loading and release profiles. Gedatolisib is challenging to formulate using Flash Nanoprecipitation due to its weak hydrophobicity and low solubility in both aqueous and organic solvents, which results in low encapsulation efficiency and loss of NP size control. This work investigates the influence of the diblock copolymer, cosolute, and solvent-to-antisolvent ratio to improve the size control and drug encapsulation in polymeric NPs.
Methods: Polycaprolactone-b-polyethylene glycol (PCL-b-PEG) diblock copolymer was used to prepare NPs via Flash Nanoprecipitation. To study the role of the diblock copolymer on the particle size, PCL-b-PEG with different molecular weights and hydrophilic fractions (i.e., the ratio of the molecular weight of PEG to the total molecular weight of the diblock copolymer) were used. Pamoic acid, succinic acid, vitamin E or vitamin E succinate were mixed with an equal amount of gedatolisib and PCL-b-PEG in dimethylformamide to make drug-loaded NPs to investigate the effect of cosolutes on NP formation and stability. Hydrodynamic size, size distribution and surface zeta potentials of empty and gedatolisib-loaded NPs were characterized by dynamic light scattering. Robust methods were developed using high-performance liquid chromatography in order to determine the encapsulation efficiency as well as drug release profile.
Results: NP size control studies demonstrated that the polymers with a hydrophilic fraction of 40-50% gave the smallest NPs, with sizes of < 100 nm. More hydrophobic (i.e., hydrophilic fraction of less than 40%) polymers led to formation of larger NPs. This was confirmed by cloudy visual appearance of NPs made with PCL(6kDa)-PEG(2kDa) or PCL(8kDa)-PEG(2kDa). For cosolute studies, dynamic light scattering results showed that vitamin E succinate-based gedatolisib particles had a unimodal size distribution with NPs centered at 152 ± 4 nm, with a low polydispersity index of < 0.3 and a zeta potential of -18.5 ± 1.5 mV. NPs formed with either pamoic acid or vitamin E as cosolute were larger than 200 nm and had a bimodal size distribution with polydispersity index of >0.5. Succinic acid-based formulations resulted in the formation of macro-precipitates, not NPs. In solvent-to-antisolvent ratio studies, a higher fraction of the organic stream during the nanoprecipitation process resulted in larger sizes of gedatolisib-loaded NPs. All vitamin E succinate-based formulations had a high encapsulation efficiency of >80% and remained stable when stored at room temperature for 5 days. The 5-day cumulative drug release from the NPs was < 20%. Burst release was not observed from any of the formulations. Additional formulation and release studies are ongoing.
Conclusion: Gedatolisib-loaded polymeric NPs were successfully prepared, and it was found that size, drug encapsulation efficiency and stability varied with block copolymer length, cosolute and solvent-to-antisolvent ratio. NPs loaded with varying gedatolisib concentrations will be further explored for in vitro drug release and cell viability studies. Results of these studies will be applied to developing polymeric NP formulations for the treatment of a variety of cancers.
(Reference: Pinkerton NM, Grandeury A, Fisch A, et al. Formation of stable nanocarriers by in situ ion pairing during block-copolymer directed rapid precipitation. Mol Pharm2013 January 7; 10(1): 319–328.)
Patrick Sinko– Distinguished Professor, Rutgers University Ernest Mario School of Pharmacy, Piscataway, New Jersey