Computational and Experimental Evaluation of the Stability of a GLP-1-like Peptide in Ethanol-Water Mixtures.

Aggregation resulting from the self-association of peptide molecules remains a major challenge during preformulation. Whereas certain organic solvents are known to promote aggregation, ethanol (EtOH) is capable of disrupting interactions between peptide molecules. It is unclear whether it is beneficial or counterproductive to include EtOH in formulations of short peptides. Here, we employed molecular dynamics simulations using the DAFT protocol and MARTINI force field to predict the formation of self-associated dimers and to estimate the stability of a GLP-1-like peptide (G48) in 0-80% aqueous EtOH solutions. Both simulation and experimental data reveal that EtOH leads to a remarkable increase in the conformational stability of the peptide when stored over 15 days at 27 °C. In the absence of EtOH, dimerisation and subsequent loss in conformational stability (α-helix → random coil) were observed. EtOH improved conformational stability by reducing peptide-peptide interactions. The data suggest that a more nuanced approach may be applied in formulation decision making and, if the native state of the peptide is an α-helix organic solvent, such as EtOH, may enhance stability and improve prospects of long-term storage.

Injectables and Depots to Prolong Drug Action of Proteins and Peptides.

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

Inhibiting the fibrillation of a GLP-1-like peptide.

Aggregation, including the formation of fibrils, poses significant challenges for the development of therapeutic peptides. To prepare stable peptide formulations, some understanding of the mechanisms underpinning the fibrillation process is required. A thioflavin T fluorescence assay was first used to determine the fibrillation profile of a GLP-1-like peptide (G48) at conditions being considered to formulate the peptide. G48 concentrations ranged from 0 to 600 µM and three pH values (pH 3.7, 7.4 and 8.5) were evaluated. Kinetic data demonstrate that G48 displays a pH-dependent aggregation profile. At pH 3.7, which is below the isoelectric point of G48 (pI ~ 5), kinetics representative of amorphous aggregates forming via a nucleation-independent mechanism were seen. At pH 7.4 and 8.5 (pH > pI) typical nucleation-dependent aggregation kinetics were observed. The weight concentration of ß-sheet rich aggregates (FLmax) correlated inversely with net charge, so lower FLmax values were observed at pH 3.7 and 8.5 than at pH 7.4. Incorporation of a non-ionic surfactant (polysorbate 80) into the peptide solution suppressed the fibrillation of G48 at all pH values and maintained the native peptide conformation, whereas a phenolic co-formulant (ferulic acid) had minimal effects on fibril growth. Peptide fibrillation, which can occur within a range of formulation concentrations and pH values, can hence be inhibited by the judicious use of excipients.

Antibody loaded collapsible hyaluronic acid hydrogels for intraocular delivery.

Injectable gels have the potential to encapsulate drugs for sustained release of protein therapeutics for use in the eye. Hyaluronic acid (HA) is a biodegradable clinically used material and poly N-isopropylacrylamide (pNIPAAM) is a stimuli responsive polymer that can display a lower critical solution temperature (LCST) at physiological conditions. Two gel systems incorporating HA were prepared in the presence of the antibody infliximab (INF): i) 1% and 5% tyramine-substituted HA (HA-Tyr) was enzymatically crosslinked in the presence of INF to form HA-Tyr-INF and ii) NIPAAM was chemically crosslinked in the presence of HA and INF with 1 and 3% poly(ethylene glycol) diacrylate (PEGDA) to form PEGDA-pNIPAAM-HA-INF. The PEGDA-pNIPAAM-HA-INF hydrogels displayed LCSTs at temperatures ranging from 31.4 ±â€¯0.2 to 35.7 ±â€¯0.3 °C. Although all the gels prepared were injectable, INF-loaded gels with lower crosslinking density (1% PEGDA-pNIPAAM-HA and 1% HA-Tyr) showed lower elastic (G') and viscous (G″) moduli compared to higher crosslinked gels (3% PEGDA-pNIPAAM-HA-INF and 5% HA-Tyr-INF) resulting in differences in swelling ratio (SR). Moduli may be correlated with overall stiffness of the gel. All hydrogels demonstrated sustained release of INF in a two-compartment in vitro outflow model of the human eye called the PK-Eye. The 1% PEGDA-pNIPAAM-HA-INF hydrogel displayed the slowest release (24.9 ±â€¯0.4% INF release by day 9) in phosphate buffered saline (PBS, pH 7.4), which is a better release profile than the free drug alone (tested under the same conditions). These results suggest that PEGDA-pNIPAAM-HA has potential for the continued development of formulations to prolong the intraocular release of proteins.

Docetaxel-loaded liposomes: The effect of lipid composition and purification on drug encapsulation and in vitro toxicity.

Docetaxel (DTX)-loaded liposomes have been formulated to overcome DTX solubility issue, improve its efficacy and reduce its toxicity. This study investigated the effect of steric stabilisation, varying liposome composition, and lipid:drug molar ratio on drug loading and on the physicochemical properties of the DTX-loaded liposomes. Size exclusion chromatography (SEC) was used to remove free DTX from the liposomal formulation, and its impact on drug loading and in vitro cytotoxicity was also evaluated. Liposomes composed of fluid, unsaturated lipid (DOPC:Chol:DSPE-PEG2000) showed the highest DTX loading compared to rigid, saturated lipids (DPPC:Chol:DSPE-PEG2000 and DSPC:Chol:DSPE-PEG2000). The inclusion of PEG showed a minimum effect on DTX encapsulation. Decreasing lipid:drug molar ratio from 40:1 to 5:1 led to an improvement in the loading capacities of DOPC-based liposomes only. Up to 3.6-fold decrease in drug loading was observed after liposome purification, likely due to the loss of adsorbed and loosely entrapped DTX in the SEC column. Our in vitro toxicity results in PC3 monolayer showed that non-purified, DTX-loaded DOPC:Chol liposomes were initially (24h) more potent than the purified ones, due to the fast action of the surface- adsorbed drug. However, we hypothesize that over time (48 and 72h) the purified, DTX-loaded DOPC:Chol liposomes became more toxic due to high intracellular release of encapsulated DTX. Finally, our cytotoxicity results in PC3 spheroids showed the superior activity of DTX-loaded liposomes compared to free DTX, which could overcome the DTX poor tissue penetration, drug resistance, and improve its therapeutic efficacy following systemic administration.