Development of a liver-targeted siRNA delivery platform with a broad therapeutic window utilizing biodegradable polypeptide-based polymer conjugates.

The greatest challenge standing in the way of effective in vivo siRNA delivery is creating a delivery vehicle that mediates a high degree of efficacy with a broad therapeutic window. Key structure-activity relationships of a poly(amide) polymer conjugate siRNA delivery platform were explored to discover the optimized polymer parameters that yield the highest activity of mRNA knockdown in the liver. At the same time, the poly(amide) backbone of the polymers allowed for the metabolism and clearance of the polymer from the body very quickly, which was established using radiolabeled polymers to demonstrate the time course of biodistribution and excretion from the body. The fast degradation and clearance of the polymers provided for very low toxicity at efficacious doses, and the therapeutic window of this poly(amide)-based siRNA delivery platform was shown to be much broader than a comparable polymer platform. The results of this work illustrate that the poly(amide) platform has a promising future in the development of a siRNA-based drug approved for human use.

An in vivo evaluation of amphiphilic, biodegradable peptide copolymers as siRNA delivery agents.

A series of amphiphilic, biodegradable polypeptide copolymers were prepared for the delivery of siRNA (short interfering ribonucleic acid). The molecular weight (or polymer chain length) of the linear polymer was controlled by reaction stoichiometry for the 11.5, 17.2, and 24.6 kDa polypeptides, and the highest molecular weight polypeptide was prepared using a sequential addition method to obtain a polypeptide having a molecular weight of 38.6 kDa. These polymers were used to prepare polymer conjugate systems designed to target and deliver an apolipoprotein B (ApoB) siRNA to hepatocyte cells and to help delineate the effect of polymer molecular weight or polymer chain length on siRNA delivery in vivo. A clear trend in increasing potency was found with increasing molecular weight of the polymers examined (at a constant polymer:siRNA (w/w) ratio), with minimal toxicity found. Furthermore, the biodegradability of these polymer conjugates was examined and demonstrates the potential of these systems as siRNA delivery vectors.

Acceleration of paraben sorption to polyethylene terephthalate: a freeze-thaw phenomenon.

The evaluation of preservative stability in a formulation throughout its life cycle (production, shipping, and storage) is an important part of product development and essential to ensuring that potential microbial contamination is satisfactorily controlled. This work investigates the unexpected losses of propyl and butylparaben in oral solutions packaged in polyethylene terephthalate (PET) bottles. The samples endured a temperature-cycling study that was designed to simulate extreme temperature fluctuations that could be encountered during product shipping and handling. An investigation into the preservative-package interaction indicated that the paraben preservatives precipitate as a result of the freezing process. The precipitated parabens at the bottom of the bottle dissolve as the solution warms. Without agitation of the solution, the local concentration of the parabens in the vicinity of the dissolving solids increases and is higher than in the oral solution at large. It appears that the combination of the localized high paraben concentration and increased temperature (50 degrees C) increases the kinetics of paraben sorption.

Use of thermal desorption mass spectrometry for the detection of free acid impurities in pharmaceutical products.

A method utilizing thermal desorption mass spectrometry (TDMS) for the detection and quantitation of free acid forms in pharmaceutical drug products formulated as salts is presented. Selective detection of neutral drug forms is possible because the volatility of a drug present in its free acid form is typically much higher than that of its corresponding salt forms, which have negligible volatility even at high temperatures. Tandem mass spectrometric detection allows selective quantitation of the desired free acid drug forms without significant interferences from formulation excipients. The application of the TDMS approach is demonstrated for a sodium salt of a representative, carboxylated drug molecule. Excellent sensitivity, specificity, and adequate linearity of detector signal as a function of micrograms of free acid added were demonstrated in the presence of the sodium salt of the drug and formulation excipients. The sensitivity of the method was demonstrated at free acid levels of 0.6% w/w (6 microg absolute mass). Tablet samples were analyzed by thermal desorption EI-MS/MS with reference to external standards using a commercially available quadrupole ion trap mass spectrometer. The relative drug form stabilities in three different tablet formulations were differentiated using this method; the salt-to-free acid form conversion ranged between less than the limit of detection to near complete conversion during the stability study.