Impact of the physical-chemical properties of poly(lactic acid)-poly(ethylene glycol) polymeric nanoparticles on biodistribution

Nanoparticle (NP) formulations are inherently polydisperse making their structural characterization and justification of specifications complex. It is essential, however, to gain an understanding of the physico-chemical properties that drive performance in vivo. To elucidate these properties, drug-containing poly(lactic acid) (PLA)-poly(ethylene glycol) (PEG) block polymeric NP formulations (or PNPs) were sub-divided into discrete size fractions and analyzed using a combination of advanced techniques, namely cryogenic transmission electron microscopy, small-angle neutron and X-ray scattering, nuclear magnetic resonance, and hard-energy X-ray photoelectron spectroscopy. Together, these techniques revealed a uniquely detailed picture of PNP size, surface structure, internal molecular architecture and the preferred site(s) of incorporation of the hydrophobic drug, AZD5991, properties which cannot be accessed via conventional characterization methodologies. Within the PNP size distribution, it was shown that the smallest PNPs contained significantly less drug than their larger sized counterparts, reducing overall drug loading, while PNP molecular architecture was critical in understanding the nature of in vitro drug release. The effect of PNP size and structure on drug biodistribution was determined by administrating selected PNP size fractions to mice, with the smaller sized NP fractions increasing the total drug-plasma concentration area under the curve and reducing drug concentrations in liver and spleen, due to greater avoidance of the reticuloendothelial system. In contrast, administration of unfractionated PNPs, containing a large population of NPs with extremely low drug load, did not significantly impact the drug's pharmacokinetic behavior - a significant result for nanomedicine development where a uniform formulation is usually an important driver. We also demonstrate how, in this study, it is not practicable to validate the bioanalytical methodology for drug released in vivo due to the NP formulation properties, a process which is applicable for most small molecule-releasing nanomedicines. In conclusion, this work details a strategy for determining the effect of formulation variability on in vivo performance, thereby informing the translation of PNPs, and other NPs, from the laboratory to the clinic.

Case Study 2: Practical Analytical Considerations for Conducting In Vitro Enzyme Kinetic Studies

Characterization of enzyme kinetics in an experiment is dependent on measurement of a change in concentration of either the substrate (loss of parent) or the product (formation of metabolite). Modern analytical techniques such as ultrahigh pressure liquid chromatography, high resolution mass spectrometry, etc. have allowed accurate characterization of minute changes in concentration. Therefore, complex kinetic data such as a sigmoidal phase at low substrate concentrations or terminal half-life in a PK curve can be evaluated by stretching the limits of analytical quantification. This chapter presents some elementary dos and don'ts and provides insight into some of the underlying principles for utilizing the best possible analytical techniques when investigating enzyme kinetics. The objective of this case study is to answer the following questions: (a) Why is it necessary to determine lower and upper limits of quantification (LLOQ and ULOQ, respectively) of a bioanalytical assay, specifically for enzyme kinetic assays? How do you utilize LLOQ and ULOQ to correctly interpret your kinetic data? (b) Why should one use a linear fit and not a quadratic fit for standard curves? (c) Is quantification of an analyte possible without a reference standard? Can one assume equal signal intensities regardless of analytical technique (MS, UV)? (d) In the absence of reference standards, can you still determine kinetic constants? (e) With the need to keep substrate depletion at less than 20% for linearity assumptions, does bioanalytical variability matter? (f) What buffer do you use for your enzyme systems? How do you choose your buffer ? Does choice of bioanalytical methods (LC, MS) dictate your choice of buffer ?

Selection and analytical applications of aptamers binding microbial pathogens

DNA aptamers specifically recognizing microbial cells and viruses have a range of analytical and therapeutic applications. This article describes recent advances in the development of aptamers targeting specific pathogens (e.g., live bacteria, whole viral particles, and virally-infected mammalian cells). Specific aptamers against pathogens have been used as affinity reagents to develop sandwich assays, to label and to image cells, to bind with cells for flow-cytometry analysis, and to act as probes for development of whole-cell biosensors. Future applications of aptamers to pathogens will benefit from recent advances in improved selection and new aptamers containing modified nucleotides, particularly slow off-rate modified aptamers (SOMAmers).