Micelle-templated, poly(lactic-co-glycolic acid) nanoparticles for hydrophobic drug delivery.

PURPOSE: Poly(lactic-co-glycolic acid) (PLGA) is widely used for drug delivery because of its biocompatibility, ability to solubilize a wide variety of drugs, and tunable degradation. However, achieving sub-100 nm nanoparticles (NPs), as might be desired for delivery via the enhanced permeability and retention effect, is extremely difficult via typical top-down emulsion approaches. METHODS: Here, we present a bottom-up synthesis method yielding PLGA/block copolymer hybrids (ie, "PolyDots"), consisting of hydrophobic PLGA chains entrapped within self-assembling poly(styrene-b-ethylene oxide) (PS-b-PEO) micelles. RESULTS: PolyDots exhibit average diameters <50 nm and lower polydispersity than conventional PLGA NPs. Drug encapsulation efficiencies of PolyDots match conventional PLGA NPs (ie, ~30%) and are greater than those obtained from PS-b-PEO micelles (ie, ~7%). Increasing the PLGA:PS-b-PEO weight ratio alters the drug release mechanism from chain relaxation to erosion controlled. PolyDots are taken up by model glioma cells via endocytotic mechanisms within 24 hours, providing a potential means for delivery to cytoplasm. PolyDots can be lyophilized with minimal change in morphology and encapsulant functionality, and can be produced at scale using electrospray. CONCLUSION: Encapsulation of PLGA within micelles provides a bottom-up route for the synthesis of sub-100 nm PLGA-based nanocarriers with enhanced stability and drug-loading capacity, and tunable drug release, suitable for potential clinical applications.

One Step Encapsulation of Small Molecule Drugs in Liposomes via Electrospray-Remote Loading.

Resiquimod is a Toll-like receptor (TLR) 7/8 agonist that has previously been used as a vaccine adjuvant, as a topical treatment of viral lesions and skin cancer, and as an antiviral treatment. We report on the combined application of remote loading and electrospray to produce liposomal resiquimod, with the broader goals of improving drug encapsulation efficiency and scalability of liposome production methods. Drug loading in liposomes increased from less than 1% to greater that 3% by mass when remote loading was used, whether the liposomes were generated by thin-film hydration or electrospray methods. Dynamic light scattering (DLS) determined mean vesicle diameters of 137 ± 11 nm and 103 ± 4 for the thin-film and electrospray methods, respectively. Transmission electron microscopy (TEM) images showed spherical vesicles with sizes consistent with the DLS measurements. In vitro drug release profiles found that most of the drug remained within the liposomes at both pH 5.5 and 7.4. The in vitro bioactivity of the liposomal drug was also demonstrated by the increase in nitrite production when RAW macrophages were exposed to the drug. Our findings indicate that the remotely loaded liposomes formed via the scalable electrospray method have characteristics comparable to those produced via conventional batch methods. The methods discussed here are not limited to the enhanced delivery of resiquimod. Rather, they should be readily adaptable to other compounds compatible with remote loading.

Scalable, semicontinuous production of micelles encapsulating nanoparticles via electrospray.

Nanoparticle encapsulation within micelles has been demonstrated as a versatile platform for creating water-soluble nanocomposites. However, in contrast to typical micelle encapsulants, such as small molecule drugs and proteins, nanoparticles are substantially larger, which creates significant challenges in micelle synthesis, especially at large scale. Here, we describe a new nanocomposite synthesis method that combines electrospray, a top-down, continuous manufacturing technology currently used for polymer microparticle fabrication, with bottom-up micellar self-assembly to yield a scalable, semicontinuous micelle synthesis method: i.e., micellar electrospray. Empty micelles and micellar nanocomposites containing quantum dots (QDs), superparamagnetic iron oxide nanoparticles (SPIONs), and their combination were produced using micellar electrospray with a 30-fold increase in yield by weight over batch methods. Particles were characterized using dynamic light scattering, transmission electron microscopy, and scanning mobility particle sizing, with remarkable agreement between methods, which indicated size distributions with variations of as little as ~5%. In addition, new methodologies for qualitatively evaluating nanoparticle loading in the resultant micelles are presented. Micellar electrospray is a broad, scalable nanomanufacturing approach that should be easily adapted to virtually any hydrophobic molecule or nanoparticle with a diameter smaller than the micelle core, potentially enabling synthesis of a vast array of nanocomposites and self-assembled nanostructures.

Delivery of host cell-directed therapeutics for intracellular pathogen clearance.

Intracellular pathogens present a major health risk because of their innate ability to evade clearance. Their location within host cells and ability to react to the host environment by mutation or transcriptional changes often enables survival mechanisms to resist standard therapies. Host-directed drugs do not target the pathogen, minimizing the potential development of drug resistance; however, they can be difficult to deliver efficiently to intracellular sites. Vehicle delivery of host-mediated response drugs not only improves drug distribution and toxicity profiles, but can reduce the total amount of drug necessary to clear infection. In this article, we will review some host-directed drugs and current drug delivery techniques that can be used to efficiently clear intracellular infections.

Electrospray encapsulation of toll-like receptor agonist resiquimod in polymer microparticles for the treatment of visceral leishmaniasis.

Leishmaniasis is a disease caused by the intracellular protozoan, Leishmania. A current treatment for cutaneous leishmaniasis involves the delivery of imidazoquinolines via a topical cream. However, there are no parenteral formulations of imidazoquinolines for the most deadly version of the disease, visceral leishmaniasis. This work investigates the use of electrospray to encapsulate the imidazoquinoline adjuvant resiquimod in acid sensitive microparticles composed of acetalated dextran (Ac-DEX) or Ac-DEX/Tween blends. The particles were characterized and tested both in vitro and in vivo. Solutions of Ac-DEX and resiquimod in ethanol were electrosprayed to generate approximately 2 µm Ac-DEX particles containing resiquimod with an encapsulation efficiency of 85%. To prevent particle aggregation, blends of Ac-DEX with Tween 20 and Tween 80 were investigated. Tween 80 was then blended with the Ac-DEX at ∼10% (w/w) of total polymer and particles containing resiquimod were formed via electrospray with encapsulation efficiencies between 40% and 60%. In vitro release profiles of resiquimod from Ac-DEX/Tween 80 particles exhibited the acid-sensitive nature of Ac-DEX, with 100% drug release after 8 h at pH 5 (phagosomal pH) and after 48 h at pH 7.4 (physiological pH). Treatment with Ac-DEX/Tween 80 particles elicited significantly greater immune response in RAW macrophages over free drug. When injected intravenously into mice inoculated with Leishmania, parasite load reduced significantly in the bone marrow compared to blank particles and phosphate-buffered saline controls. Overall, electrospray appears to offer an elegant, scalable way to encapsulate adjuvant into an acid sensitive delivery vehicle for use in treating visceral leishmaniasis.