Kinetics and mechanisms of peptide aggregation. I: Aggregation of a cholecystokinin analogue

Novel formulations and drug delivery systems to administer biological solids

Recent advances in formulation sciences have expanded the previously limited design space for biological modalities, including peptide, protein, and vaccine products. At the same time, the discovery and application of new modalities, such as cellular therapies and gene therapies, have presented formidable challenges to formulation scientists. We explore these challenges and highlight the opportunities to overcome them through the development of novel formulations and drug delivery systems as biological solids. We review the current progress in both industry and academic laboratories, and we provide expert perspectives in those settings. Formulation scientists have made a tremendous effort to accommodate the needs of these novel delivery routes. These include stability-preserving formulations and dehydration processes as well as dosing regimes and dosage forms that improve patient compliance.

Just how prevalent are peptide therapeutic products? A critical review

How prevalent are peptide therapeutic products? How innovative are the formulations used to deliver peptides? This review provides a critical analysis of therapeutic peptide products and the formulations approved by the United States Food and Drug administration (FDA), the European Medicines Agency (EMA), and the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). This review also provides an in-depth analysis of dosage forms and administration routes for delivering peptide therapeutics, including injectables, oral dosage forms, and other routes of administration. We discuss the function of excipients in parenteral formulations in detail, since most peptide therapeutics are parenterally administered. We provide case studies of alternate delivery routes and dosage forms. Based on our analysis, therapeutic peptides administered as injectables remain the most commonly used dosage forms, particularly in the form of subcutaneous, intravenous, or intramuscular injections. In addition, therapeutic peptides are formulated to achieve prolonged release, often through the use of polymer carriers. The limited number of oral therapeutic peptide products and their poor absorption and subsequent low bioavailability indicate a need for new technologies to broaden the formulation design space. Therapeutic peptide products may also be delivered through other administration routes, including intranasal, implant, and sublingual routes. Therefore, an in-depth understanding of how therapeutic peptides are now formulated and administered is essential to improve peptide delivery, improve patient compliance, and reduce the healthcare burden for these crucial therapeutic agents.

Physicochemical and formulation developability assessment for therapeutic peptide delivery--a primer

Peptides are an important class of endogenous ligands that regulate key biological cascades. As such, peptides represent a promising therapeutic class with the potential to alleviate many severe disease states. Despite their therapeutic potential, peptides frequently pose drug delivery challenges to scientists. This review introduces the physicochemical, biophysical, biopharmaceutical, and formulation developability aspects of peptides pertinent to the drug discovery-to-development interface. It introduces the relevance of these properties with respect to the delivery modalities available for peptide pharmaceuticals, with the parenteral route being the most prevalent route of administration. This review also presents characterization strategies for oral delivery of peptides with the aim of illuminating developability issues with the drug candidate. A brief overview of other routes of administration, including inhaled, transdermal, and intranasal routes, is provided as these routes are generally preferred by patients over injectables. Finally, this review presents formulation techniques to mitigate some of the developability obstacles associated with peptide delivery. The authors emphasize opportunities for the thoughtful application of pharmaceutical science to the development of peptide drugs and to the general advancement of this promising class of pharmaceuticals.

Ethanol induced the formation of β-sheet and amyloid-like fibrils by surfactant-like peptide A6K

Self-assembly of natural or designed peptides into fibrillar structures based on β-sheet conformation is a ubiquitous and important phenomenon. Recently, organic solvents have been reported to play inductive roles in the process of conformational change and fibrillization of some proteins and peptides. In this study, we report the change of secondary structure and self-assembling behavior of the surfactant-like peptide A6K at different ethanol concentrations in water. Circular dichroism indicated that ethanol could induce a gradual conformational change of A6K from unordered secondary structure to β-sheet depending upon the ethanol concentration. Dynamic light scattering and atomic force microscopy revealed that with an increase of ethanol concentration the nanostructure formed by A6K was transformed from nanosphere/string-of-beads to long and smooth fibrils. Furthermore, Congo red staining/binding and thioflavin-T binding experiments showed that with increased ethanol concentration, the fibrils formed by A6K exhibited stronger amyloid fibril features. These results reveal the ability of ethanol to promote β-sheet conformation and fibrillization of the surfactant-like peptide, a fact that may be useful for both designing self-assembling peptide nanomaterials and clarifying the molecular mechanism behind the formation of amyloid fibrils.

Spectroscopic investigations of metalloporphyrin-oligopeptide systems: evidence for peptide aggregation

Anionic pentapeptides consisting of a string of four glutamic acid residues terminated by either tyrosine (Glu4Tyr) or tryptophan (Glu4Trp) were synthesized, and their aggregation properties in buffered (pH = 7.0) aqueous solutions were investigated using two different approaches. In the first approach, the effects of the concentration of peptide used as its own probe (intrinsic probe) on its fluorescence emission, circular dichroism, surface tension, and solution pH yielded similar critical peptide concentrations of around 175 microM. This particular concentration was taken as evidence for peptide aggregation. In the second approach, peptide aggregation was investigated using cationic metalloporphyrins, tetrakis(N-methyl-4-pyridyl)porphyrin (Pd(II)TMPyP(4+) and Zn(II)TMPyP(4+)), as extrinsic probes. The effect of peptide concentration on porphyrin ground-state absorption confirmed peptide aggregation, but at a lower critical peptide concentration near 125 microM. This difference was attributed to the possible distortion introduced by the association of one (or more) large metalloporphyrin molecule with the peptide aggregates. Evidence for peptide aggregation was also demonstrated from the effect of peptide concentration on Pd(II)TMPyP(4+) triplet-state decay. The fast component (k(f), associated with electron transfer from the target Tyr and Trp residues to the porphyrin triplet state) was found to be independent of peptide concentration, implying no noticeable effect of peptide aggregation on the electron-transfer event. This was attributed to the fact that species formed by excitation of porphyrin associated with ion-pair complexes or bound to peptide aggregates and the diffusion together of the separate T(1) and peptide entities in the bulk phase are kinetically similar. On the other hand, the slower component (k(s)) of the decay, which is associated with the diffuse formation of an encounter complex between the free peptide and T(1) porphyrin (bulk phase), was peptide-dependent and displayed a critical peptide concentration near 125 microM, above which it became practically independent of peptide concentration. This invariance of k(s) was taken as an indication that the free peptide concentration in the bulk phase remains constant above 125 microM, the concentration at which peptide molecules prefer to associate as aggregates.

Alternate drug delivery routes for A-71623, a potent cholecystokinin-A receptor agonist tetrapeptide

A-71623 (BOC-Trp-Lys(epsilon-N-2-methylphenylaminocarbonyl)- Asp-(N-methyl)-Phe-NH2) is a tetrapeptide which has high affinity and selectivity for cholecystokinin receptors; it is a potent appetite suppresser in animal studies. Because of its low (< 1%) oral bioavailability, studies were performed to assess the feasibility of delivery of A-71623 by pulmonary, sublingual, and transdermal routes of administration. The pKa was determined to be 4.2 by spectrophotometric titration; aqueous solubility is increased by increasing pH and by increasing ethanol content. The solubility of A-71623 in ethanol/propellant mixtures was investigated; solubility ranged from 1.0 to 2.5 mg/mL in mixtures of ethanol, propellant 11 (trichlorofluoromethane), and propellant 12 (dichlorodifluoromethane). The log apparent octanol/water partition coefficient was 2.8 at pH 5 and 1.0 at pH 8. Maximum stability at 70 degrees C was seen in the range of pH values of 5.5-7.5; hydrolysis of the N-terminal BOC group appears to be the primary route of degradation. Increasing ethanol content increases the stability; Arrhenius analysis indicated a t90 of 150 days under ambient conditions in 25% ethanol. Intratracheal delivery of 3 mumol/kg A-71623 in 50% ethanol to rats showed rapid and efficient absorption of drug from the lungs, with a Cmax of 2.7 microM and an AUC of 85 microM*min. Similar studies in dogs showed bioavailabilities of 59% and 46% for 2 and 3 mumol/kg intratracheal doses, respectively, relative to intravenous administration. Sublingual administration of 1 mumol/kg A-71623 in a vehicle of 80% ethanol/2% Klucel/2.5% peppermint oil gave high prolonged plasma levels of A-71623, with a Cmax of 0.37 microM, indicating high bioavailability and favorable partitioning and distribution effects from the sublingual cavity for this formulation. Transdermal delivery was examined by in vitro diffusion through human skin; the permeability coefficient of A-71623 in 40% ethanol was 2.6 x 10(-5) cm/hr, suggesting that transdermal delivery of up to 2 mg/day may be feasible. In conclusion, the results provide preliminary indications that delivery of efficacious doses of A-71623, and perhaps other CCK analogs, by alternate routes of delivery is probably feasible.