Effects of non-nearest neighbors on the thermodynamic stability of RNA GNRA hairpin tetraloops.

Currently, several models for predicting the secondary structure of RNA exist, one of which is free energy minimization using the Nearest Neighbor Model. This model predicts the lowest-free energy secondary structure from a primary sequence by summing the free energy contributions of the Watson-Crick nearest neighbor base pair combinations and any noncanonical secondary structure motif. The Nearest Neighbor Model also assumes that the free energy of the secondary structure motif is dependent solely on the identities of the nucleotides within the motif and the motif's nearest neighbors. To test the current assumption of the Nearest Neighbor Model that the non-nearest neighbors do not affect the stability of the motif, we optically melted different stem-loop oligonucleotides to experimentally determine their thermodynamic parameters. In each of these oligonucleotides, the hairpin loop sequence and the adjacent base pairs were held constant, while the first or second non-nearest neighbors were varied. The experimental results show that the thermodynamic contributions of the hairpin loop were dependent upon the identity of the first non-nearest neighbor, while the second non-nearest neighbor had a less obvious effect. These results were then used to create an updated model for predicting the thermodynamic contributions of a hairpin loop to the overall stability of the stem-loop structure.

Impact of Formulation and Suspension Properties on Redispersion of Aluminum-Adjuvanted Vaccines.

The adsorption of antigens to the surface of 2 commonly used insoluble adjuvants, aluminum phosphate and aluminum hydroxide, has been well characterized. In spite of the pharmaceutical benefits, alum-based vaccine formulations can present challenges in redispersion of the final product after storage. Inability to resuspend alum-based vaccines during administration results in inadequate dosing, thus rendering the product unusable. Here, the influence of formulation conditions on the resuspendability of aluminum adjuvant-containing vaccines was investigated. Particle size analysis by Micro-Flow Imaging (MFI™), zeta potential measurement, and sedimentation analysis by Turbiscan® were used to characterize suspension properties. Ionic strength, pH, and antigen concentration were found to significantly influence sedimentation behavior, particle size, and redispersion. Increasing ionic strength increased the sedimentation rate of adjuvants favoring resuspendability. The addition of bovine serum albumin to aluminum phosphate reduced resuspendability more significantly than the addition of lysozyme. Decreased resuspendability correlated with an increase in fine-to-large particle ratio and decrease in sedimentation rate. In summary, resuspendability of adjuvant drug product is favored by increased flocculation, decrease in fine-to-large particle ratio, and reduction in surface charge of antigen and adjuvant. A careful balance of these formulation conditions can therefore be an effective means to mitigate challenges of alum adjuvant redispersion.

Impact of extractables/leachables from filters on stability of protein formulations.

Aqueous extractables/leachables from three sterilizing-grade filter membranes [polyvinylidene fluoride (PVDF), polyethersulfone (PES), and mixed cellulose ester (MCE)] were found to significantly reduce the surface tension of aqueous solutions. To evaluate the effect of these extractables/leachables from filter membranes on stability of protein formulations, model IgG2 formulations (with or without added surfactant) were spiked with different levels of filter extractables from stock solutions as a stress study. The stock solutions of extractables were created by processing the filter membranes through autoclaving and soaking steps. The IgG2 formulations were subsequently subject to agitation and temperature stress. Extractables/leachables from the filters were found to have a significant protective (PVDF, PES) and destabilizing (MCE) impact on both visible and subvisible particulates formation under agitation stress for formulations that did not contain any additional surfactant such as polysorbate 80. The impact of filter extractables/leachables on chemical stability of the antibody formulation displayed a more complicated pattern, but was generally destabilizing, causing increases in aggregation, oxidation, and acidic species. In conclusion, extractables/leachables from filter membranes may have impact on protein formulation stability and caution should be exercised during protein filtration, especially when filtering small volumes and in preformulation or high-throughput screening studies.