Lyophilization and development of solid protein pharmaceuticals

Protective mechanism of stabilizing excipients against dehydration in the freeze-drying of proteins

PURPOSE

To investigate the influence of type and amount of excipient on the preservation of the native structure and the biologic activity of freeze-dried lysozyme and catalase.

METHODS

The secondary structure of protein in the dried form and in aqueous solution was obtained using second derivative infrared spectroscopy and circular dichroism spectra respectively whilst the activity was determined using bioassay.

RESULTS

Small molecular excipients (glycerol, sorbitol, 1,6-anhydroglucose, sucrose, and trehalose) were found to stabilize the activity and/or the native structure of freeze-dried lysozyme and catalase, despite the processing temperatures being above Tg' of excipent-protein mixtures. The preservation of catalase activity required excipient to be present at a lower excipient to enzyme mass ratio than that necessary to preserve native structure in the dried form. Combining dextran with sucrose synergistically protected the native structure of catalase but preserved the activity in an additive manner.

CONCLUSION

The results indicate that the stabilization of catalase and lysozyme by excipients during dehydration was mainly due to water substitution rather than the formation of glass; the latter appearing not to be a prerequisite during freeze-drying.

Preservation of lysozyme structure and function upon encapsulation and release from poly(lactic-co-glycolic) acid microspheres prepared by the water-in-oil-in-water method

When proteins are encapsulated in bioerodible polymers by water-in-oil-in-water (w/o/w) encapsulation techniques, inactivation and aggregation are serious drawbacks hampering their sustained delivery. Hen egg-white lysozyme was employed to investigate whether stabilizing it towards the major stress factors in the w/o/w encapsulation procedure would allow for the encapsulation and release of structurally unperturbed, non-aggregated, and active protein. When it was encapsulated in poly(lactic-co-glycolic) acid (PLGA) microspheres without stabilizing additives, lysozyme showed substantial loss in activity and aggregation. It has been shown that by co-dissolving various sugars and polyhydric alcohols with lysozyme in the first aqueous buffer, interface-induced lysozyme aggregation and inactivation can be minimized in the first emulsification step [J. Pharm. Pharmacol. 53 (2001) 1217]. Herein, it was found that those excipients, which were efficient in preventing interface-induced structural perturbations, were also efficient in minimizing lyophilization-induced structural perturbations (e.g. lactulose). The efficient excipients identified also reduced structural perturbations upon lysozyme encapsulation in PLGA microspheres and this led to reduced lysozyme inactivation and aggregation. However, the data obtained also show that later steps in the encapsulation procedure are detrimental to lysozyme activity. Lysozyme inactivation was completely prevented only by employing the efficient excipients in the second aqueous phase also. In summary, protein aggregation and inactivation were minimized by rationally selecting excipients efficient in stabilizing lysozyme against the major stress factors of w/o/w encapsulation.

Peroxide formation in polysorbate 80 and protein stability

Nonionic surfactants are widely used in the development of protein pharmaceuticals. However, the low level of residual peroxides in surfactants can potentially affect the stability of oxidation-sensitive proteins. In this report, we examined the peroxide formation in polysorbate 80 under a variety of storage conditions and tested the potential of peroxides in polysorbate 80 to oxidize a model protein, IL-2 mutein. For the first time, we demonstrated that peroxides can be easily generated in neat polysorbate 80 in the presence of air during incubation at elevated temperatures. Polysorbate 80 in aqueous solution exhibited a faster rate of peroxide formation and a greater amount of peroxides during incubation, which is further promoted/catalyzed by light. Peroxide formation can be greatly inhibited by preventing any contact with air/oxygen during storage. IL-2 mutein can be easily oxidized both in liquid and solid states. A lower level of peroxides in polysorbate 80 did not change the rate of IL-2 mutein oxidation in liquid state but significantly accelerated its oxidation in solid state under air. A higher level of peroxides in polysorbate 80 caused a significant increase in IL-2 mutein oxidation both in liquid and solid states, and glutathione can significantly inhibit the peroxide-induced oxidation of IL-2 mutein in a lyophilized formulation. In addition, a higher level of peroxides in polysorbate 80 caused immediate IL-2 mutein oxidation during annealing in lyophilization, suggesting that implementation of an annealing step needs to be carefully evaluated in the development of a lyophilization process for oxidation-sensitive proteins in the presence of polysorbate.

Improvement of dissolution rates of poorly water soluble APIs using novel spray freezing into liquid technology

PURPOSE

To develop and demonstrate a novel particle engineering technology, spray freezing into liquid (SFL), to enhance the dissolution rates of poorly water-soluble active pharmaceutical ingredients (APIs).

METHODS

Model APIs, danazol or carbamazepine with or without excipients, were dissolved in a tetrahydrofuran/water cosolvent system and atomized through a nozzle beneath the surface of liquid nitrogen to produce small frozen droplets, which were subsequently lyophilized. The physicochemical properties of the SFL powders and controls were characterized by X-ray diffraction, scanning electron microscopy (SEM), particle size distribution, surface area analysis, contact angle measurement, and dissolution.

RESULTS

The X-ray diffraction pattern indicated that SFL powders containing either danazol or carbamazepine were amorphous. SEM micrographs indicated that SFL particles were highly porous. The mean particle diameter of SFL carbamazepine/SLS powder was about 7 microm. The surface area of SFL danazol/poloxamer 407 powder was 11.04 m2/g. The dissolution of SFL danazol/poloxamer 407 powder at 10 min was about 99%. The SFL powders were free flowing and had good physical and chemical stability after being stored at 25 degrees C/60%RH for 2 months.

CONCLUSIONS

The novel SFL technology was demonstrated to produce nanostructured amorphous highly porous particles of poorly water soluble APIs with significantly enhanced wetting and dissolution rates.

Preparation and characterization of microparticles containing peptide produced by a novel process: spray freezing into liquid

The objective of this study is to evaluate excipient type on the physicochemical properties of insulin microparticles produced by spray freezing into liquid (SFL). A novel process was developed to produce microparticles containing bioactive peptides and proteins. The microparticles were formed by atomization of an aqueous feed solution containing insulin beneath the surface of a cryogenic liquid (e.g. liquid nitrogen). In this study, bovine insulin was dissolved in deionized water alone or with tyloxapol, lactose or trehalose. The aqueous solution was sprayed directly into liquid nitrogen through a polyetheretherketone capillary nozzle under high pressure to form frozen microparticles. Lyophilization was used to sublime the ice. The SFL insulin powder was characterized by different techniques, including X-ray diffraction, reverse-phase high pressure liquid chromatography, size exclusion chromatography, scanning electron microscopy (SEM), particle size distribution and surface area. The mean diameter of the insulin microparticles was 5-7 microm. SEM revealed that the microparticles were highly porous, and the morphology of the microparticles was influenced by the excipient type. The total surface area of the insulin microparticles ranged from 20 to 40 m(2)/g, and the magnitude depended on the specific composition and total solids content of the aqueous feed solution. X-ray diffraction results indicated lack of crystallinity. No change in the level of the degradation product, A-21 desamido insulin, was found in the SFL insulin samples processed alone or with trehalose or tyloxapol. Similarly, no change in formation of high molecular weight transformation products (e.g. covalent insulin dimer) was detected in the samples processed with excipients. The results demonstrated that SFL is a feasible technique for forming porous microparticles containing insulin. The physicochemical properties of insulin were preserved by the SFL technique.

A novel particle engineering technology: spray-freezing into liquid

Spray-freezing into liquid (SFL) is a novel particle engineering technology where a feed solution containing an active pharmaceutical ingredient (API) and pharmaceutical excipient(s) is atomized beneath the surface of a cryogenic liquid, such as liquid nitrogen. Intense atomization results from the impingement that occurs between the liquid feed and the cryogenic liquid. The atomized feed droplets instantly solidify within the liquid nitrogen continuous phase to form a suspension. The frozen microparticles are then collected and lyophilized to obtain the dry SFL micronized powder. The novel SFL process has been used in this study to enhance the dissolution rates of two poorly water soluble APIs, carbamazepine and danazol. The SFL process has also been used to produce stable peptide particles of insulin.

Crystallization of mannitol below Tg' during freeze-drying in binary and ternary aqueous systems

PURPOSE

To characterize the phase transitions in a multicomponent system during the various stages of the freeze-drying process and to evaluate the crystallization behavior below Tg' (glass transition temperature of maximally freeze-concentrated amorphous phase) in frozen aqueous solutions and during freeze-drying.

METHODS

X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC) were used to study frozen aqueous solutions of mannitol with or without trehalose. By attaching a vacuum pump to the low-temperature stage of the diffractometer, it was possible to simulate the freeze-drying process in situ in the sample chamber of the XRD. This enabled real-time monitoring of the solid state of the solutes during the process.

RESULTS

In rapidly cooled aqueous solutions containing only mannitol (10% w/w), the solute was retained amorphous. Annealing of frozen solutions or primary drying. both below Tg', resulted in crystallization of mannitol hydrate. Similar effects were observed in the presence of trehalose (2% w/w). At higher concentrations (> or =5% w/w) of this noncrystallizing sugar. annealing below Tg' led to nucleation but not crystallization. However, during primary drying, crystallization of mannitol hydrate was observed.

CONCLUSIONS

The combination of in situ XRD and DSC has given a unique insight into phase transitions during freeze-drying as a function of processing conditions and formulation variables. In the presence of trehalose, mannitol crystallization was inhibited in frozen solutions but not during primary drying.

Semisolid, self-catalyzed poly(ortho ester)s as controlled-release systems: protein release and protein stability issues

Semisolid, self-catalyzed poly(ortho ester)s (POEs), are investigated as potential sustained-release systems for proteins. In this study, some factors influencing protein release kinetics and protein instability were evaluated. As model proteins, lysozyme, alpha-lactalbumin, bovine serum albumin, and vascular endothelial growth factor, which were lyophilized from various buffer solutions in the absence and presence of lyoprotectants, were used. For all protein formulations, the release kinetics followed the visually observed polymer dissolution profile. In the absence of any buffers in the protein formulation, the release was continuous. Formulations containing a buffer below pH 7 accelerated POE degradation, resulting in faster protein release. In contrast, a strong buffer capacity at pH 7 reduced the POE degradation and resulted in a biphasic release pattern. Moreover, proteins with a high isoelectric point (pI > 7) appeared to catalyze the POE degradation, and the effect of the buffer strength and pH was much smaller than for proteins with low pI (< 7). In the absence of lyoprotectants, all proteins tested showed an increasing fraction of covalent protein aggregates during the release. Protein formulations containing a lyoprotectant, such as sucrose or trehalose, did not show a significantly increased aggregation, whereas there was a minor influence of the large solid loadings on the release kinetics. In conclusion, this semisolid, self-catalyzed POE showed good promise as a sustained-release matrix for bioactive proteins.

Recent trends in stabilizing protein structure upon encapsulation and release from bioerodible polymers

Sustained release of pharmaceutical proteins from biocompatible polymers offers new opportunities in the treatment and prevention of disease. The manufacturing of such sustained-release dosage forms, and also the release from them, can impose substantial stresses on the chemical integrity and native, three-dimensional structure of proteins. Recently, novel strategies have been developed towards elucidation and amelioration of these stresses. Non-invasive technologies have been implemented to investigate the complex destabilization pathways that can occur. Such insights allow for rational approaches to protect proteins upon encapsulation and release from bioerodible systems. Stabilization of proteins when utilizing the most commonly employed procedure, the water-in-oil-in-water (w/o/w) double emulsion technique, requires approaches that are based mainly on either increasing the thermodynamic stability of the protein or preventing contact of the protein with the destabilizing agent (e.g. the water/oil interface) by use of various additives. However, protein stability is still often problematic when using the w/o/w technique, and thus alternative methods have become increasingly popular. These methods, such as the solid-in-oil-in-oil (s/o/o) and solid-in-oil-in-water (s/o/w) techniques, are based on the suspension of dry protein powders in an anhydrous organic solvent. It has become apparent that protein structure in the organic phase is stabilized because the protein is "rigidified" and therefore unfolding and large protein structural perturbations are kinetically prohibited. This review focuses on strategies leading to the stabilization of protein structure when employing these different encapsulation procedures.

Effects of a citrate buffer system on the solid-state chemical stability of lyophilized quinapril preparations

PURPOSE

The objective of this study was to examine the effect of a citric acid-citrate buffer system on the chemical instability of lyophilized amorphous samples of quinapril hydrochloride (QHCI).

METHODS

Molecular dispersions of QHCI and citric acid were prepared by colyophilization from their corresponding aqueous solutions with a molar ratio of QHCI to citric acid from 1:1 to 6:1 and solution pH from 2.49 to 3.05. Solid samples were subjected to a temperature of 80 degrees C and were analyzed for degradation using high-performance liquid chromatography. The glass transition temperature, Tg, of all samples was measured by differential scanning calorimetry.

RESULTS

Samples were first examined by varying the Tg and maintaining the initial solution pH constant. At pH 2.49 the rate of reaction was found to be less dependent on the sample Tg, whereas at pH > or = 2.75 the rate decreased with an increase in Tg. In a second set of experiments at a constant Tg of approximately 70 degrees C, the reaction rate increased as the pH increased.

CONCLUSION

The overall solid-state chemical reactivity of amorphous quinapril depends on the relative amount of QHCI and Q+-, the zwitterionic form of quinapril. At high proportions of Q+- (higher pH values) the reaction rate seems to be strongly influenced by the Tg of the mixture, and hence the molecular mobility, whereas at higher proportions of QHCI (lower pH) the reaction rate is less sensitive to Tg, presumably because of different mechanistic rate determining steps for the two sets of conditions.

Development of a synthetic cyclized peptide derived from alpha-fetoprotein that prevents the growth of human breast cancer

The peptide, EMTPVNPG, derived from alpha-fetoprotein, inhibits estrogen-stimulated growth of immature mouse uterus and estrogen-dependent proliferation of human breast cancer cells. However, the biological activities of the peptide diminish over time in storage, even when in the lyophilized state, probably because of peptide aggregation through hydrophobic interaction among monomers. Two analogs of EMTPVNPG were designed with the intent of minimizing aggregation and retaining biological activity during prolonged storage. EMTOVNOG, where O is 4-hydroxyproline, is a linear peptide generated by substituting 4-hydroxyproline for the two prolines, thereby increasing peptide hydrophilicity. This analog exhibited a dose-dependent inhibition of estrogen-stimulated growth of immature mouse uterus similar to that of EMTPVNPG (maximal activity at 1 microg/mouse). A second analog, cyclo-(EMTOVNOGQ), a hydrophilic, cyclic analog with increased conformational constraint, was as potent as the other peptides in its inhibition of estrogen-dependent growth of immature mouse uterus, and had an expanded effective dose range. Both linear and cyclized hydroxyproline-substituted analogs exhibited indefinite shelf-life. Furthermore, both analogs inhibited the estrogen-dependent growth of MCF-7 human breast cancer growing as a xenograft in SCID mice. These analogs may become significant, novel agents for the treatment of breast cancer.