Assessment of Temperature-Dependent Drug Release of Solubilizing Nanoformulations Using the SITUA

The evaluation of temperature-dependent drug release for solubilizing nanoformulations uses a modification of the stable isotope ultrafiltration assay (SITUA). This method is specific to parenterally administered solubilizing nanomedicines and can be used to assess drug release from the total dosage form for regulatory purposes of lot release. The principle upon which this method is based is the relationship between drug solubility and temperature in a plasma simulating media, 4.5% human serum albumin, that allows for discrimination of passing and failing lots based upon the release characteristics.

Plasma Stability and Plasma Metabolite Concentration-Time Profiles of Oligo(Lactic Acid)8-Paclitaxel Prodrug Loaded Polymeric Micelles

Paclitaxel (PTX) is a frequently prescribed chemotherapy drug used to treat a wide variety of solid tumors. Oligo(lactic acid)8-PTX prodrug (o(LA)8-PTX) loaded poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) micelles have higher loading, slower release and higher antitumor efficacy in murine tumor models over PTX-loaded PEG-b-PLA micelles. The goal of this work is to study plasma stability of o(LA)8-PTX-loaded PEG-b-PLA micelles and its pharmacokinetics after IV injection in rats. In rat plasma, o(LA)8-PTX prodrug is metabolized into o(LA)1-PTX and PTX. In human plasma, o(LA)8-PTX is metabolized more slowly into o(LA)2-PTX, o(LA)1-PTX, and PTX. After IV injection of 10 mg/kg PTX-equiv of o(LA)8-PTX prodrug loaded PEG-b-PLA micelles in Sprague-Dawley rats, metabolite abundance in plasma follows the order: o(LA)1-PTX > o(LA)2-PTX > o(LA)4-PTX > o(LA)6-PTX. Bile metabolite profiles of the o(LA)8-PTX prodrug is similar to plasma metabolite profiles. In comparison to equivalent doses of Abraxane®, plasma PTX exposure is two orders of magnitude higher for Abraxane® than PTX from o(LA)8-PTX prodrug loaded PEG-b-PLA micelles, and plasma o(LA)1-PTX exposure is fivefold higher than PTX from Abraxane®, demonstrating heightened plasma metabolite exposure for enhanced antitumor efficacy.

Bioequivalence assessment of high-capacity polymeric micelle nanoformulation of paclitaxel and Abraxane® in rodent and non-human primate models using a stable isotope tracer assay

The in vivo fate of nanoformulated drugs is governed by the physicochemical properties of the drug and the functionality of nanocarriers. Nanoformulations such as polymeric micelles, which physically encapsulate poorly soluble drugs, release their payload into the bloodstream during systemic circulation. This results in three distinct fractions of the drug-nanomedicine: encapsulated, protein-bound, and free drug. Having a thorough understanding of the pharmacokinetic (PK) profiles of each fraction is essential to elucidate mechanisms of nanomedicine-driven changes in drug exposure and PK/PD relationships pharmacodynamic activity. Here, we present a comprehensive preclinical assessment of the poly (2-oxazoline)-based polymeric micelle of paclitaxel (PTX) (POXOL hl-PM), including bioequivalence comparison to the clinically approved paclitaxel nanomedicine, Abraxane®. Physicochemical characterization and toxicity analysis of POXOL hl-PM was conducted using standardized protocols by the Nanotechnology Characterization Laboratory (NCL). The bioequivalence of POXOL hl-PM to Abraxane® was evaluated in rats and rhesus macaques using the NCL's established stable isotope tracer ultrafiltration assay (SITUA) to delineate the plasma PK of each PTX fraction. The SITUA study revealed that POXOL hl-PM and Abraxane® had comparable PK profiles not only for total PTX but also for the distinct drug fractions, suggesting bioequivalence in given animal models. The comprehensive preclinical evaluation of POXOL hl-PM in this study showcases a series of widely applicable standardized studies by NCL for assessing nanoformulations prior to clinical investigation.

Application of a Scavenger Receptor A1-Targeted Polymeric Prodrug Platform for Lymphatic Drug Delivery in HIV

We have developed a macromolecular prodrug platform based on poly(l-lysine succinylated) (PLS) that targets scavenger receptor A1 (SR-A1), a receptor expressed by myeloid and endothelial cells. We demonstrate the selective uptake of PLS by murine macrophage, RAW 264.7 cells, which was eliminated upon cotreatment with the SR-A inhibitor polyinosinic acid (poly I). Further, we observed no uptake of PLS in an SR-A1-deficient RAW 264.7 cell line, even after 24 h incubation. In mice, PLS distributed to lymphatic organs following i.v. injection, as observed by ex vivo fluorescent imaging, and accumulated in lymph nodes following both i.v. and i.d. administrations, based on immunohistochemical analysis with high-resolution microscopy. As a proof-of-concept, the HIV antiviral emtricitabine (FTC) was conjugated to the polymer's succinyl groups via ester bonds, with a drug loading of 14.2% (wt/wt). The prodrug (PLS-FTC) demonstrated controlled release properties in vitro with a release half-life of 15 h in human plasma and 29 h in esterase-inhibited plasma, indicating that drug release occurs through both enzymatic and nonenzymatic mechanisms. Upon incubation of PLS-FTC with human peripheral blood mononuclear cells (PBMCs), the released drug was converted to the active metabolite FTC triphosphate. In a pharmacokinetic study in rats, the prodrug achieved ∼7-19-fold higher concentrations in lymphatic tissues compared to those in FTC control, supporting lymphatic-targeted drug delivery. We believe that the SR-A1-targeted macromolecular PLS prodrug platform has extraordinary potential for the treatment of infectious diseases.

Distinguishing Pharmacokinetics of Marketed Nanomedicine Formulations Using a Stable Isotope Tracer Assay

The pharmacokinetics of nanomedicines are complicated by the unique dispositional characteristics of the drug carrier. Most simplistically, the carrier could be a solubilizing platform that allows administration of a hydrophobic drug. Alternatively, the carrier could be stable and release the drug in a controlled manner, allowing for distribution of the carrier to influence distribution of the encapsulated drug. A third potential dispositional mechanism is carriers that are not stably complexed to the drug, but rather bind the drug in a dynamic equilibrium, similar to the binding of unbound drug to protein; since the nanocarrier has distributional and binding characteristics unlike plasma proteins, the equilibrium binding of drug to a nanocarrier can affect pharmacokinetics in unexpected ways, diverging from classical protein binding paradigms. The recently developed stable isotope tracer ultrafiltration assay (SITUA) for nanomedicine fractionation is uniquely suited for distinguishing and comparing these carrier/drug interactions. Here we present the the encapsulated, unencapsulated, and unbound drug fraction pharmacokinetic profiles in rats for marketed nanomedicines, representing examples of controlled release (doxorubicin liposomes, Doxil; and doxorubicin HCl liposome generic), equilibrium binding (paclitaxel cremophor micelle solution, Taxol generic), and solubilizing (paclitaxel albumin nanoparticle, Abraxane; and paclitaxel polylactic acid micelle, Genexol-PM) nanomedicine formulations. The utility of the SITUA method in differentiating these unique pharmacokinetic profiles and its potential for use in establishing generic nanomedicine bioequivalence are discussed.

Autophagy Monitoring Assay II: Imaging Autophagy Induction in LLC-PK1 Cells Using GFP-LC3 Protein Fusion Construct

Autophagy is a catabolic process involved in the degradation and recycling of long-lived proteins and damaged organelles for maintenance of cellular homeostasis, and it has also been proposed as a type II cell death pathway. The cytoplasmic components targeted for catabolism are enclosed in a double-membrane autophagosome that merges with lysosomes, to form autophagosomes, and are finally degraded by lysosomal enzymes. There is substantial evidence that several nanomaterials can cause autophagy and lysosomal dysfunction, either by prevention of autophagolysosome formation, biopersistence or inhibition of lysosomal enzymes. Such effects have emerged as a potential mechanism of cellular toxicity, which is also associated with various pathological conditions. In this chapter, we describe a method to monitor autophagy by fusion of the modifier protein MAP LC3 with green fluorescent protein (GFP; GFP-LC3). This method enables imaging of autophagosome formation in real time by fluorescence microscopy without perturbing the MAP LC3 protein function and the process of autophagy. With the GFP-LC3 protein fusion construct, a longitudinal study of autophagy can be performed in cells after treatment with nanomaterials.

Improved Ultrafiltration Method to Measure Drug Release from Nanomedicines Utilizing a Stable Isotope Tracer

An important step in the early development of a nanomedicine formulation is the evaluation of stability and drug release in biological matrices. Additionally, the measurement of encapsulated and unencapsulated nanomedicine drug fractions is important for the determination of bioequivalence (pharmacokinetic equivalence) of generic nanomedicines. Unfortunately, current methods to measure drug release in plasma are limited, and all have fundamental disadvantages including non-equilibrium conditions and process-induced artifacts. The primary limitation of current ultrafiltration (and equilibrium dialysis) methods for separation of encapsulated and unencapsulated drug and determination of drug release is the difficulty in accurately differentiating protein bound and encapsulated drug. Since the protein binding of most drugs is high (>70%) and can change in a concentration- and time-dependent manner, it is very difficult to accurately account for the fraction of non-filterable drug that is encapsulated within the nanomedicine and how much is bound to protein. The method in this chapter is an improvement of existing ultrafiltration protocols for nanomedicine fractionation in plasma, in which a stable isotope tracer is spiked into a nanomedicine containing plasma sample in order to precisely measure the degree of plasma protein binding. Determination of protein binding then allows for accurate calculation of encapsulated and unencapsulated nanomedicine drug fractions, as well as free and protein-bound fractions.

Synergistic combination therapy with nanoliposomal C6-ceramide and vinblastine is associated with autophagy dysfunction in hepatocarcinoma and colorectal cancer models

Autophagy, a catabolic survival pathway, is gaining attention as a potential target in cancer. In human liver and colon cancer cells, treatment with an autophagy inducer, nanoliposomal C6-ceramide, in combination with the autophagy maturation inhibitor, vinblastine, synergistically enhanced apoptotic cell death. Combination treatment resulted in a marked increase in autophagic vacuole accumulation and decreased autophagy maturation, without diminution of the autophagy flux protein P62. In a colon cancer xenograft model, a single intravenous injection of the drug combination significantly decreased tumor growth in comparison to the individual treatments. Most importantly, the combination treatment did not result in increased toxicity as assessed by body weight loss. The mechanism of combination treatment-induced cell death both in vitro and in vivo appeared to be apoptosis. Supportive of autophagy flux blockade as the underlying synergy mechanism, treatment with other autophagy maturation inhibitors, but not autophagy initiation inhibitors, were similarly synergistic with C6-ceramide. Additionally, knockout of the autophagy protein Beclin-1 suppressed combination treatment-induced apoptosis in vitro. In conclusion, in vitro and in vivo data support a synergistic antitumor activity of the nanoliposomal C6-ceramide and vinblastine combination, potentially mediated by an autophagy mechanism.

In vitro analysis of nanoparticle uptake by macrophages using chemiluminescence

This chapter provides a protocol for qualitative evaluation of nanoparticle internalization by phagocytic cells such as macrophages. This protocol uses luminol chemiluminescence to detect nanoparticle uptake. This protocol provides a preliminary qualitative look at phagocytosis which should be confirmed by other techniques such as electron microscopy, confocal microscopy, or as applicable to a given nanoparticle sample.

Method for analysis of nanoparticle effects on cellular chemotaxis

Chemotaxis is the phenomenon in which cells direct their movements in the presence of certain chemicals (chemoattractants or chemorepellents). Leukocyte recruitment (via chemotaxis) is an important component of the inflammatory response, both in physiological host defense and in a range of prevalent disorders that include an inflammatory component. Circulating leukocytes in the bloodstream migrate towards the site of inflammation in response to a complex network of proinflammatory signaling molecules (including cytokines, chemokines and prostaglandins). This chapter describes a method for rapid measure of the chemoattractant capacity of nanoparticulate materials. This method is an in vitro model for chemotaxis, in which promyelocytic leukemia cell migration through a filter is monitored using a fluorescent dye.