Lyophilization and development of solid protein pharmaceuticals

Mechanism of protein stabilization by sugars during freeze-drying and storage: native structure preservation, specific interaction, and/or immobilization in a glassy matrix?

The purpose of this study is to investigate the mechanism of protein stabilization by sugars in the solid state. That is, explore whether the stabilization is controlled by "glass dynamics" or by native structure preservation through "specific interaction" between sugars and protein. The IgG1 antibody (150 kD) and recombinant human serum albumin (rHSA) (65 kD) were formulated with sorbitol, trehalose, and sucrose. Degradation of lyophilized formulations was quantified using size exclusion (SEC) and ion-exchange chromatography (IEX). The secondary structure of the protein in these formulations was characterized using Fourier Transform Infrared (FTIR) spectroscopy. The molecular mobility, as measured by the stretched relaxation time (tau(beta)) was obtained by fitting the modified stretched exponential (MSE) equation to the calorimetric data from the Thermal Activity Monitor (TAM). Compared with sucrose and trehalose, sorbitol could only slightly protect the protein against aggregation and had no effect on chemical degradation. The chemical degradation and aggregation rates of the protein decreased when the weight ratio of sucrose to protein increased from 0 to 2:1. Storage stability of the proteins showed a reasonably good correlation with the degree of retention of native structure of protein during drying as measured by the spectral correlation coefficient for FTIR spectra. The plots of tau(beta) as a function of fraction of sucrose passed through a maximum at 1:1 weight ratio of sucrose to protein. That is, the molecular mobility did not correlate with the stability of protein at high levels of sucrose content. Although the glass transition appears to be an important parameter for stability, protein stabilization by sugars in the solid state cannot be wholly explained by the glass dynamics mechanism, at least as measured by tau(beta). However, it is possible that the beta-relaxations rather than the alpha-relaxations (i.e., the tau we measured) are critical to stability. The data show that storage stability correlates best with "structure" as determined by FTIR spectroscopy. However, while a specific interaction between stabilizer and protein might be responsible for the preservation of native structure, the evidence supporting this position is not compelling.

Stabilizing Peptide Fusion for Solving the Stability and Solubility Problems of Therapeutic Proteins

PURPOSE

Protein aggregation is a major stability problem of therapeutic proteins. We investigated whether a novel stabilizing peptide [acidic tail of synuclein (ATS) peptide] could be generally used to make a more stable and soluble form of therapeutic proteins, particularly those having solubility or aggregation problems.

METHODS

We produced ATS fusion proteins by fusing the stabilizing peptide to three representative therapeutic proteins, and then compared the stress-induced aggregation profiles, thermostability, and solubility of them. We also compared the in vivo stability of these ATS fusion proteins by studying their pharmacokinetics in rats.

RESULTS

The human growth hormone-ATS (hGH-ATS) and granulocyte colony-stimulating factor-ATS (G-CSF-ATS) fusion proteins were fully functional as determined by cell proliferation assay, and the ATS fusion proteins seemed to be very resistant to agitation, freeze/thaw, and heat stresses. The introduction of the ATS peptide significantly increased the storage and thermal stabilities of hGH and G-CSF. The human leptin-ATS fusion protein also seemed to be very resistant to aggregation induced by agitation, freeze/thaw, and heat stresses. Furthermore, the ATS peptide greatly increased the solubility of the fusion proteins. Finally, pharmacokinetic studies in rats revealed that the ATS fusion proteins are also more stable in vivo.

CONCLUSION

Our data demonstrate that a more stable and soluble form of therapeutic proteins can be produced by fusing the ATS peptide.

Influence of the active pharmaceutical ingredient concentration on the physical state of mannitol--implications in freeze-drying

PURPOSE

The aim of this study was to investigate the effect of the concentration of the active pharmaceutical ingredient on the physical state of mannitol in frozen aqueous systems.

METHODS

A human monoclonal antibody was used as the model protein. Mannitol and sucrose were used as the bulking agent and the lyoprotectant, respectively. The thermal behavior of frozen mannitol-sucrose solutions during and after annealing, in the absence and presence of the protein, were characterized by low-temperature powder X-ray diffractometry and differential scanning calorimetry. The influence of the protein on the crystallization behavior of mannitol was also evaluated.

RESULTS

The excipient concentration had a pronounced effect on the glass transition temperature of maximally freeze-concentrated amorphous phase (T(g)'). At fixed excipient compositions, the protein had no effect on the T(g)' if the protein concentration was < or =20 mg/ml. However, at higher protein concentrations, there was a marked increase in T(g)' as a function of protein concentration. The inhibitory effect of the protein on mannitol crystallization was concentration dependent and was directly evident from X-ray diffractometry experiments. Annealing facilitated both mannitol nucleation and crystal growth even in the presence of the protein.

CONCLUSIONS

The ratio of mannitol to sucrose and the protein concentration have an impact on the T(g)' and may therefore influence the primary drying temperature. The protein inhibits both the nucleation and growth of mannitol crystals and this effect seems to be concentration dependent. The presence of the protein and the protein concentration dictate the processing conditions, i.e., annealing time, annealing temperature, and primary drying temperature.

Effects of sucrose and mannitol on asparagine deamidation rates of model peptides in solution and in the solid state

Asparagine (Asn) degradation kinetics in two model peptides, Gly-Gln-Asn-Gly-Gly (GQNGG) and Val-Tyr-Pro-Asn-Gly-Ala (VYPNGA), were studied at 50 degrees C in pH 7 buffer solutions in the presence and absence of 5% (w/v) sucrose or mannitol and at 50 degrees C and 30% relative humidity in solid samples lyophilized from these solutions. Solid formulations were characterized using Karl Fischer coulometric titration, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier-transform infrared spectrometry (FTIR), and solid-state nuclear magnetic resonance (NMR) spectroscopy. GQNGG and VYPNGA showed similar pseudo first-order deamidation rates in solution in the absence of sucrose and mannitol. Adding 5% sucrose or mannitol decreased the rates by no more than 17%. The model peptides degraded 2- to 80-fold more slowly in the solid formulations of sucrose and mannitol than in 5% solutions of these carbohydrates. Ratios of deamidation rates of the model peptides depended upon the solid matrix. In the mannitol solid, the ratio of deamidation rates of GQNGG and VYPNGA (GQNGG:VYPNGA) was approximately 8, while in the sucrose solid, the model peptides deamidated at similar rates (GQNGG:VYPNGA congruent with 1). DSC showed the mannitol formulations to be largely amorphous immediately after lyophilization with some ordered, crystalline-like structure; the extent of ordered structure increased during storage as shown by FTIR and ssNMR. In contrast, the sucrose formulation was largely amorphous after lyophilization and remained so during storage. Together, the results showed that 5% sucrose or mannitol in solution does not significantly change the rates of Asn deamidation of the model peptides, while sucrose stabilizes the model peptides against deamidation more than mannitol in the solid state.

Thermodynamic and dynamic factors involved in the stability of native protein structure in amorphous solids in relation to levels of hydration

The internal, dynamical fluctuations of protein molecules exhibit many of the features typical of polymeric and bulk small molecule glass forming systems. The response of a protein's internal molecular mobility to temperature changes is similar to that of other amorphous systems, in that different types of motions freeze out at different temperatures, suggesting they exhibit the alpha-beta-modes of motion typical of polymeric glass formers. These modes of motion are attributed to the dynamic regimes that afford proteins the flexibility for function but that also develop into the large-scale collective motions that lead to unfolding. The protein dynamical transition, T(d), which has the same meaning as the T(g) value of other amorphous systems, is attributed to the temperature where protein activity is lost and the unfolding process is inhibited. This review describes how modulation of T(d) by hydration and lyoprotectants can determine the stability of protein molecules that have been processed as bulk, amorphous materials. It also examines the thermodynamic, dynamic, and molecular factors involved in stabilizing folded proteins, and the effects typical pharmaceutical processes can have on native protein structure in going from the solution state to the solid state.

LC–UV method development and validation for the investigational anticancer agent imexon and identification of its degradation products

Imexon (4-imino-1,3-diazabicyclo[3,1,0]-hexan-2-one) is a member of the class of 2-cyanoaziridine derivatives, which have been of interest as immunomodulators and anticancer agents since the late 1970s. The pharmaceutical development of imexon necessitated the availability of an assay for the quantification and purity determination of imexon active pharmaceutical ingredient (API) and the drug in its pharmaceutical dosage form. A liquid chromatographic (LC) method with ultraviolet (UV) detection was developed, using a reverse phase column with phosphate buffer (pH 6; 50 mM) as mobile phase and UV detection at 230 nm. Although retention capacity for imexon was small (capacity factor of 0.5), the method was found to be linear over the concentration range of interest of 1.0-25 microg/mL, precise, accurate, and stability-indicating. Moreover, the use of LC-mass spectrometry (MS) and on-line photodiode array (PDA) detection enabled us to propose structures for four degradation products. Two of these products were also found as impurities in the API. The degradation products, including chloro- and hydroxy-derivatised products were shown to arise from nucleophilic reactions with the activated aziridine moiety of imexon. The developed LC-UV method was found suitable for the pharmaceutical quality control of imexon API and the drug in its pharmaceutical dosage form.

Evaluation of extrusion/spheronisation, layering and compaction for the preparation of an oral, multi-particulate formulation of viable, hIL-10 producing Lactococcus lactis

Three formulation techniques were compared in order to develop a multi-particulate formulation of viable, interleukin-10 producing Lactococcus lactis Thy12. First, freeze-dried L. lactis was compacted into mini-tablets. Next, liquid L. lactis culture was used as the granulation fluid for the production of pellets by extrusion/spheronisation. Finally, liquid L. lactis culture was layered on inert pellets as an alternative technique for the production of pellets. L. lactis viability and interleukin-10 production was evaluated. Viability dropped to 15.7% after compaction of freeze-dried L. lactis and to 1.0% after pelletisation of liquid L. lactis by extrusion/spheronisation. The viability in the mini-tablets and pellets, stored for 1 week at RT and 10% RH was reduced to 23 and 0.5% of initial viability, respectively. Storage for 1 week at RT and 60% RH resulted in complete loss of viability. Layering of L. lactis on inert pellets resulted in low viability (4.86%), but 1 week after storage at RT and 10% RH, 68% of initial viability was maintained. Increasing product temperature and cell density of L. lactis in the layering suspension did not significantly change viability after layering and storage. Interleukin-10 production capacity of L. lactis Thy12 was maintained after layering.

Partially Crystalline Systems in Lyophilization: II. Withstanding Collapse at High Primary Drying Temperatures and Impact on Protein Activity Recovery

In an accompanying article we have described the construction of the water-rich sections of raffinose-glycine-water and trehalose-glycine-water state diagrams. In this study, we use the information obtained from the state diagrams to identify the minimum weight fraction of the crystalline component in glycine-carbohydrate systems necessary to withstand collapse at high primary drying temperatures. We also determine the impact of primary drying, substantially above T'g, on the recovery of lactate dehydrogenase (LDH) activity. Ambient and variable temperature X-ray powder diffractometry and differential scanning calorimetry were used to characterize the frozen and freeze-dried systems. Aqueous solutions with glycine to carbohydrate (raffinose pentahydrate or trehalose dihydrate) weight ratios ranging from 0.2 to 2.0 were freeze dried. The protein formulations contained 20 mM citrate buffer (pH 6.0) and LDH (20 microg/mL). A glycine to anhydrous raffinose weight ratio >or=1.18 and a glycine to anhydrous trehalose weight ratio >or=1.56 were necessary to withstand macroscopic collapse in the system, when the primary drying was carried out at a product temperature at least 10 degrees C above the T'g. The recovery of LDH activity was almost complete in the reconstituted lyophile whether the primary drying was carried out above T'g (-10 degrees C) or below T'g (-32 degrees C). Thus, by judiciously combining crystalline and amorphous components, it was possible to primary dry at temperatures substantially above the T'g.

Protein drug stability: a formulation challenge

The increasing use of recombinantly expressed therapeutic proteins in the pharmaceutical industry has highlighted issues such as their stability during long-term storage and means of efficacious delivery that avoid adverse immunogenic side effects. Controlled chemical modifications, such as substitutions, acylation and PEGylation, have fulfilled some but not all of their promises, while hydrogels and lipid-based formulations could well be developed into generic delivery systems. Strategies to curb the aggregation and misfolding of proteins during storage are likely to benefit from the recent surge of interest in protein fibrillation. This might in turn lead to generally accepted guidelines and tests to avoid unforeseen adverse effects in drug delivery.

Comparative Investigation by Two Analytical Approaches of Enthalpy Relaxation for Glassy Glucose, Sucrose, Maltose, and Trehalose

PURPOSE

In an effort to understand the stability of glassy sugars such as glucose, sucrose, maltose, and trehalose, the molecular mobility below the glass transition temperature (Tg) was investigated by an enthalpy relaxation measurement with differential scanning calorimetry (DSC).

METHODS

The glassy sample was aged over several days at (Tg - 10) K to (Tg - 30) K, before a DSC heating scan was taken. The relaxed enthalpy (deltaHrelax) was estimated from the endothermic peak area. The enthalpy relaxation time was analyzed from the time course of deltaHrelax using two different approaches; Kohlrausch-Williams-Watts (KWW) and extended Adam-Gibbs (exAG).

RESULTS

TauKWW, which is defined as the mean average enthalpy relaxation time in a distribution, and tau(eff)0 and tau(eff)infinity, which correspond to the enthalpy relaxation time of the initial minimum and final maximum cooperative rearrangement region, were estimated by KWW and exAG, respectively. And three activation energies for enthalpy relaxation were calculated from the Arrhenius plot.

CONCLUSIONS

Although these deltaEs originated from different theoretical backgrounds, almost the same trend was observed for a comparison of the values of the four sugars. The finding that the deltaEs of glassy trehalose were the largest among the four sugars may support the reason that glassy trehalose is an effective stabilizer.

Role of hydrogen bonds in the fast dynamics of binary glasses of trehalose and glycerol: A molecular dynamics simulation study

Trehalose-glycerol mixtures are known to be effective in the long time preservation of proteins. However, the microscopic mechanism of their effective preservation abilities remains unclear. In this article we present a molecular dynamics simulation study of the short time, less than 1 ns, dynamics of four trehalose-glycerol mixtures at temperatures below the glass transition temperature. We found that a mixture of 5% glycerol and 95% trehalose has the most suppressed short time dynamics (fast dynamics). This result agrees with the experimental analysis of the mean-square displacement of the hydrogen atoms, as measured via neutron scattering, and correlates with the experimentally observed enhancement of the stability of some enzymes at this particular concentration. Our microscopic analysis suggests that the formation of a robust intermolecular hydrogen bonding network is most effective at this concentration and is the main mechanism for the suppression of the fast dynamics.

Sustained interferon-γ delivery from a photocrosslinked biodegradable elastomer

The application of protein therapeutics for long-term, localized delivery has been hindered by a lack of a delivery device that releases active protein at a concentration within their therapeutic window. A protein delivery system that uses an osmotic pressure delivery mechanism and a photocrosslinked biodegradable elastomer has been designed in an attempt to overcome this limitation. The elastomer is prepared through the UV initiated crosslinking of end terminal acrylated star-poly(epsilon-caprolactone-co-D,L-lactide). Interferon-gamma (IFN-gamma) was released from the optimum formulation at a constant rate of 23 ng/day over 21 days. A cell-based assay showed that over 83% of released IFN-gamma was bioactive. Furthermore, it was demonstrated that bovine serum albumin co-lyophilized with IFN-gamma was released at the same rate as IFN-gamma. This delivery formulation may be clinically useful for sustained, local protein drug delivery applications.

Fast dynamics and stabilization of proteins: binary glasses of trehalose and glycerol

We present elastic and inelastic incoherent neutron scattering data from a series of trehalose glasses diluted with glycerol. A strong correlation with recently published protein stability data in the same series of glasses illustrates that the dynamics at Q >or= 0.71 A(-1) and omega > 200 MHz are important to stabilization of horseradish peroxidase and yeast alcohol dehydrogenase in these glasses. To the best of our knowledge, this is the first direct evidence that enzyme stability in a room temperature glass depends upon suppressing these short-length scale, high-frequency dynamics within the glass. We briefly discuss the coupling of protein motions to the local dynamics of the glass. Also, we show that T(g) alone is not a good indicator for the protein stability in this series of glasses; the glass that confers the maximum room-temperature stability does not have the highest T(g).

Inulin is a promising cryo- and lyoprotectant for PEGylated lipoplexes

The aim of this study was to investigate whether the oligosaccharides dextran and inulin are able to prevent aggregation of lipoplexes based on 1,2-dioleoyl-3-trimethylammonium-propane and dioleoylphosphatidyl-ethanolamine with and without distearoylphosphatidylethanolamine-polyethyleneglycol (PEGylated and nonPEGylated lipoplexes, respectively) during storage. The lipoplexes, dispersed in the oligosaccharide solution were frozen and subsequently stored at subzero temperature or freeze dried and subsequently stored at 37 degrees C. When lipoplexes in frozen dispersions were stored below the glass transition temperature of the maximally freeze concentrated fraction (Tg') of the oligosaccharide solutions severe aggregation of the nonPEGylated lipoplexes was prevented for 3 months by both inulin and dextran. However, while dextran failed to stabilize the frozen PEGylated lipoplexes (as in most cases full aggregation occurred in short time) inulin successfully protected them against aggregation. Compared to dextran, inulin was also a superior lyoprotectant of PEGylated lipoplexes: during freeze drying and subsequent storage at 37 degrees C of the dried powders for 3 months the PEGylated lipoplexes maintained their original size when dispersed in inulin matrices while in dextran matrices they fully aggregated in most cases. It is hypothesized that the aggregation of the PEGylated lipoplexes in dextran solutions is caused by the well known incompatibility between dextrans and PEG. This is further supported by the observation that inulins and PEG are compatible. It is concluded that oligosaccharides can prevent severe aggregation of nonPEGylated lipoplexes. The same holds for PEGylated lipoplexes provided that the oligosaccharide is compatible with PEG. Finally, this work also shows that the higher Tg' of oligosaccharides makes them more versatile cryoprotectants than disaccharides like sucrose or trehalose as the frozen dispersions can be stored at higher temperatures for prolonged periods of time. Furthermore, it is proposed that oligosaccharides are also more versatile lyoprotectants than the disaccharides because they can be exposed to higher relative humidities without passing the glass transition temperature.

Protein aggregation and its inhibition in biopharmaceutics

Protein aggregation is arguably the most common and troubling manifestation of protein instability, encountered in almost all stages of protein drug development. Protein aggregation, along with other physical and/or chemical instabilities of proteins, remains to be one of the major road barriers hindering rapid commercialization of potential protein drug candidates. Although a variety of methods have been used/designed to prevent/inhibit protein aggregation, the end results are often unsatisfactory for many proteins. The limited success is partly due to our lack of a clear understanding of the protein aggregation process. This article intends to discuss protein aggregation and its related mechanisms, methods characterizing protein aggregation, factors affecting protein aggregation, and possible venues in aggregation prevention/inhibition in various stages of protein drug development.

Enthalpy relaxation of bovine serum albumin and implications for its storage in the glassy state

Two endothermic peaks could be observed for five commercial samples of bovine serum albumin (BSA). The smaller peak observed by differential scanning calorimetry (DSC) corresponded to enthalpy relaxation. This peak was followed on storage of BSA, in its glassy state, after it had been heated above its denaturation temperature. Enthalpy and peak temperature increased with duration of storage. On storage for one week at 60 degrees C, a sample at 8.3% moisture showed a peak at 100 degrees C with an energy value of approximately 2 J per g protein. BSA samples were heated within the DSC sufficiently to eliminate the lower enthalpy peak but without altering the denaturation enthotherm. The amount of physical aging shown by these BSA samples was similar to that of the heat-denatured samples. It was concluded that the heating endotherms of dry BSA reflect both the storage and thermal history of the sample. Possible implications of the enthalpy relaxation of BSA on the behavior of this important protein are considered.

DNA-coated microcrystals

Coprecipitation leads to self-assembly of bioactive DNA on the surface of salt, sugar or amino-acid crystals and provides a rapid inexpensive immobilization method suitable for preparing dry-powder formulations of nucleic acids, useful for storage, imaging and drug delivery.

Microparticulate formulations for the controlled release of interleukin-2

Interleukin 2 (IL-2) is a pleotropic growth factor essential to immune system function. Current methods of administration are limited by the necessity of hospitalization as well as dose-limiting toxicities and side effects. There is also the issue of low therapeutic concentrations at the desired site of action; for instance, in the case of solid tumor treatment. Here we describe the design of controlled-release vehicles for the local administration of IL-2 based on single (SE) and double emulsion (DE) poly(lactic-co-glycolic acid) (PLGA) systems and a newly developed class of spray-dried lipid-protein-sugar systems composed of L-alpha-dipalmitoylphosphatidylcholine (DPPC) and 0.2% Eudragit E 100. All three systems demonstrated the release of therapeutic drug quantities. Totals of 2.0, 0.5, and 2.8 microg of IL-2 (per mg of solid) were encapsulated in the SE, DE, and spray-dried formulations, respectively. The SE and DE released of 30 and 15% of the encapsulated protein, respectively, with delivery of biologically active IL-2 during the first 5 to 10 days. The lipid-protein-sugar-based system demonstrated extended sustained release of biologically active IL-2 for a period of 4 months. These systems provide a potential framework for long-term loco-regional immunotherapeutic treatment regimens.

Raman spectroscopic characterization of drying-induced structural changes in a therapeutic antibody: correlating structural changes with long-term stability

We characterized the secondary structure of a therapeutic recombinant humanized monoclonal antibody (rhuMAb), formulated with different concentrations of sucrose, trehalose, and histidine and in solution, lyophilized, and spray-dried states. Quantitative secondary structure estimates were obtained using amide I band Raman spectroscopy and a previously developed spectral deconvolution procedure. On lyophilization or spray drying in the absence of sugar, the antibody underwent significant structural perturbation. The beta-sheet content decreased with corresponding gain in the turn and unordered content. With increasing amount of sucrose or trehalose, the extent of structural perturbation decreased. Eventually, at sugar-to-protein molar ratios of > or =360, almost complete structural preservation was observed. Histidine also protected the antibody against lyophilization-induced structural changes. The extent of structural perturbation immediately after lyophilization or spray drying exhibited good correlation with the rate of aggregation for the antibody during long-term storage under accelerated conditions. The results demonstrate that amide I band Raman spectroscopy could be a quick and reliable way to screen excipients and their concentrations during lyophilized or spray dried formulation development.

Spray freezing into liquid nitrogen for highly stable protein nanostructured microparticles

The objectives of this study were to produce nanostructured protein microparticles with the spray freezing into liquid (SFL) cryogenic process and to demonstrate a smaller degree of protein denaturation and aggregation than observed in spray freeze drying (SFD). Nanostructured microparticles were formed by atomization of an aqueous buffer solution containing bovine serum albumin (BSA) with and without excipients beneath the surface of a cryogenic liquid. Lyophilization was used to sublime the water in the frozen particles. The resulting BSA dry powder was characterized by size exclusion chromatography, Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), light scattering, and specific surface area analysis. SEM revealed highly porous microparticle with features smaller than 500 nm. The specific surface area of the BSA microparticles ranged from 19.2 to 97.7 m(2)/g as a function of the total protein and excipient content in the aqueous feed solution. SFL produced less denaturation and aggregation of protein monomer than SFD, despite the extremely high surface areas in both processes. The intense atomization and ultra-rapid freezing in the SFL process lead to nanostructured BSA microparticles with high surface areas. Protein denaturation and aggregation are reduced in SFL relative to SFD. The more rapid freezing in SFL lowers the time for proteins to aggregate or diffuse to water-air and water-ice interfaces where they may be denatured.

The role of particle engineering in relation to formulation and de-agglomeration principle in the development of a dry powder formulation for inhalation of cetrorelix

We formulated cetrorelix acetate, as an adhesive mixture for use in dry powder inhalation. To achieve the highest possible deposition efficiency we investigated both the influence of different micronization techniques and different inhalers. The Novolizer with an air classifier as the powder de-agglomeration principle and the ISF inhaler were used for in vitro deposition experiments (cascade impaction). Micronization by milling as the classical approach and micronization by spray drying and spray freeze drying as advanced particle engineering techniques were investigated to determine whether advanced techniques are necessary to obtain high fine particle fractions (FPF) for this specific drug. It was found that the effects obtained with a certain micronization technique depended on the complex interaction of the physical characteristics of the drug substance with the type of formulation chosen, as well as with the de-agglomeration principle used. The combination of particle engineering by spray drying and the use of the air classifier technology resulted in a fine particle fraction of 66%, while spray freeze drying yielded extremely fragile particles resulting in a FPF of only 25%. The behaviour of the milled material showed similar trends as the spray dried material but FPF values were lower. It was concluded that when a drug is to be formulated as a powder for inhalation with high fine particle fractions, it is profitable to use advanced particle engineering techniques, however the applied technique should be tuned with the characteristics of the formulation type and process as well as with device development.

Quantification of glycine crystallinity by near-infrared (NIR) spectroscopy

The object of this investigation was to use near-infrared (NIR) spectroscopy for quantification of glycine crystallinity. Glycine samples, with different degrees of crystallinity, were obtained by physically mixing different proportions of crystalline beta-glycine with amorphous glycine. NIR spectra were obtained, directly from samples in glass vials, over the wavelength range of 1100-2500 nm. A partial least squares (PLS) model was developed to correlate the NIR spectral changes with the degree of crystallinity. Using this model, a standard error of calibration (SEC) of 2.1% was obtained with an r(2) value of 0.996. Cross validation was used to test the precision of the quantitative model, resulting in a standard error of prediction (SEP) of 3.2%. These results indicate that NIR spectroscopy is well suited to the measurement of glycine crystallinity in lyophilized products. Employing the PLS model, the crystallinity of glycine in freeze-dried sucrose-glycine mixtures was evaluated. At a sucrose to glycine ratio >4, glycine crystallization during lyophilization was inhibited. Conversely, at ratios < or =0.67, glycine remained substantially crystalline. At intermediate compositions, the glycine was partially crystalline.

Cystatin incorporated in poly(lactide-co-glycolide) nanoparticles: development and fundamental studies on preservation of its activity

Preservation of biological activity is still a major challenge for successful formulation and delivery of protein drugs. Cystatin, a potential protein drug in cancer therapy, was incorporated in poly(lactide-co-glycolide) nanoparticles by the water-in-oil-in-water emulsion solvent diffusion technique. In order to preserve the biological activity of cystatin, a specific modification of the method of producing nanoparticles was introduced. The activity of cystatin was strongly influenced by the stirring rate during preparation and, to a lesser extent, by selected organic solvents. A synergistic effect of mechanical stirring and sonication, both at low energy levels, enabled nanoparticles to be formed without denaturing the cystatin. Nanoparticles produced by the optimised method ranged from 300 to 350 nm in diameter with 85% of the starting cystatin activity. The loading efficiency of cystatin depends on polymer type and ranged from 12 to 57%, representing an actual loading of 0.6-2.6% (w/w). Among various cryo-/lyoprotectants bovine serum albumin was identified as the most successful. The use of a protein protectant prior to nanoparticle formation was essential to maintaining the biologically active three-dimensional structure of cystatin. In addition, a specific type of poly(lactide-co-glycolide) polymer, particularly in terms of its functional groups, was identified to be important in retaining cystatin activity. Cystatin incorporated into nanoparticles in this way maintains its structural integrity, making it suitable for effective drug delivery.

Investigation of the stabilisation of freeze-dried lysozyme and the physical properties of the formulations

The long-term stability of a protein formulation requires that the glass transition temperature (Tg) of the formulation should be maximised and the perturbation of the protein native structure in the dried form after processing minimised. In the present study, the stabilisation of lysozyme structure conferred by excipients was monitored using second derivative Fourier transform infrared spectroscopy and the physical properties of protein formulations were investigated using differential scanning calorimetry. The results showed that the preservation of protein native structure during freeze-drying and the Tg of freeze-dried formulations were excipient- and excipient to enzyme mass ratio-dependent. The freeze-dried lysozyme appeared to be less effectively stabilised compared with the spray-dried enzyme when the excipients and the excipient to enzyme mass ratios were the same. In terms of the preservation of the secondary structure of lysozyme, glycerol and sucrose seemed to be more efficient than trehalose, although the Tg of trehalose-containing formulations were found to be higher than the Tg of the equivalent sucrose-based ones. With adding either trehalose or dextran to sucrose-containing formulations, the stabilisation of lysozyme native structure could be as effective as with sucrose alone, whilst the Tg could be enhanced. The results in this study suggested that lysozyme, processed by freeze-drying, is stabilised primarily by the water substitution mechanism.

Stability of crystallised and spray-dried lysozyme

Moisture and temperature promote protein degradation. The stabilities of commercial, crystallised and spray-dried lysozyme, a model protein, were assessed under these stresses to explore whether a crystalline protein had better storage stability than a conventionally produced one. Samples were maintained at different relative humidities (RH) and temperatures for 20 weeks and stabilities estimated in solid and aqueous states. Differential scanning calorimetry (DSC) and thermogravimetry (TGA) characterised solid samples. Fourier transform Raman (FT-Raman) spectroscopy analysed solid material and aqueous solutions. High sensitivity differential scanning calorimetry (HSDSC) and enzymatic assays were used to monitor solutions. DSC and HSDSC data revealed that crystals maintained thermal stability at high RH; spray drying appreciably changed melting characteristics. These results correlated with enzymatic assays that demonstrated good activity retention for crystals but less so for spray-dried material (e.g. 95 and 87% relative to fresh samples after 20 weeks at 40 degrees C/75% RH). FT-Raman analysis showed that crystallised lysozyme better-maintained protein conformational integrity compared to spray-dried samples in accelerated stability studies. Based on TGA data, spray-dried protein absorbed water on storage under humid conditions, which induced instability. Thus, crystallisation enhanced storage stability of lysozyme with negligible loss of activity.

Infrared spectroscopic studies of protein formulations containing glycine

Glycine is extensively used as an excipient in protein formulations. However, it absorbs significant infrared (IR) radiation in the conformationally sensitive amide I region (1700-1600 cm(-1)) of proteins. Furthermore, glycine can form a number of polymorphs, as well as an amorphous phase. Each of these forms possibly exhibits a different IR absorption spectrum. Accurate subtraction of glycine signals, in order to obtain reliable amide I spectra, was found to be possible only if the protein-to-glycine ratio was >/=1:1. In those cases, the solid-state conformation of the protein could be determined. In addition, a new method for estimating the degree of crystallinity of freeze-dried glycine is described, using IR bands in the 1350-1300 cm(-1) region.

Solid dispersions based on inulin for the stabilisation and formulation of Δ9-tetrahydrocannabinol

The aim of this study was to develop a dry powder formulation that stabilises the chemically labile lipophilic Delta(9)-tetrahydrocannabinol (THC), that rapidly dissolves in water in order to increase the bioavailability and that opens new routes of administration. It was investigated whether these aims can be achieved with solid dispersions consisting of a matrix of inulin, an oligo-fructose, in which THC is incorporated. These solid dispersions were prepared by lyophilisation of a solution of THC and inulin in a mixture of water and tertiary butyl alcohol (TBA). Both 4 and 8 wt.% of THC could be incorporated in a glassy matrix of inulin. In the solid dispersions only 0.4-0.5 wt.% of residual TBA was present after storage at 20 degrees C/45% relative humidity (RH) for 7 days. Unprotected THC was completely degraded after 40 days of exposure to 20 degrees C and 45% RH. However, solid dispersions exposed to the same conditions still contained about 80% non-degraded THC after 300 days. Dissolution experiments with tablets compressed from inulin glass dispersion material showed that THC and inulin dissolved at the same rate. Tablets weighing 125 mg and containing 2mg THC were prepared from a mixture of THC containing solid dispersion, polyvinylpolypyrrolidone (PVPP) and mannitol. Dissolution tests revealed that from these tablets 80% of the THC was dissolved within 3 min, which makes them promising for sublingual administration. It was concluded that THC can be strongly stabilized by incorporating it in a matrix of inulin. The aqueous dissolution rate was high which may improve bioavailability.

Effect of vacuum drying on protein-mannitol interactions: the physical state of mannitol and protein structure in the dried state

The purpose of the present studies was to systematically investigate protein-mannitol interactions using vacuum drying, to obtain a better understanding of the effect of protein/mannitol wt/wt ratios on the physical state of mannitol and protein secondary structure in the dried state. Solutions containing beta-lactoglobulin (betaLg):mannitol (1:1-1:15 wt/wt) were vacuum dried at 5 degrees C under 3000 mTorr of pressure. The physical state of mannitol was studied using x-ray powder diffractometry (XRPD), polarized light microscopy (PLM), Fourier-transform infrared (FTIR) spectroscopy, and modulated differential scanning calorimetry (MDSC). XRPD studies indicated that mannitol remained amorphous up to 1:5 wt/wt betaLg:mannitol ratio, whereas PLM showed the presence of crystals of mannitol in all dried samples except for the 1:1 wt/wt betaLg:mannitol dried sample. FTIR studies indicated that a small proportion of crystalline mannitol was present along with the amorphous mannitol in dried samples at lower (less than 1:5 wt/wt) betaLg:mannitol ratios. The T(g) of the dried 1:1 wt/wt betaLg:mannitol sample was observed at 33.4 degrees C in MDSC studies, which indicated that at least a part of mannitol co-existed with protein in a single amorphous phase. Evaluation of the crystallization exotherms indicated that irrespective of the betaLg:protein wt/wt ratio in the initial sample, the protein to amorphous mannitol ratio was below 1:1 wt/wt in all dried samples. Second-derivative FTIR studies on dried betaLg and recombinant human interferon alpha-2a samples showed that mannitol affected protein secondary structure to a varying degree depending on the overall mannitol content in the dried sample and the type of protein.

Citrate increases glass transition temperature of vitrified sucrose preparations

The aim of this study was to investigate the effect of sodium citrate on the properties of dried amorphous sucrose glasses. Addition of sodium citrate to a sucrose solution followed by freeze-drying or convective drying resulted in a glass transition temperature (Tg) that was higher than the well-studied sucrose Tg. This result was obtained either at reduced water content of the analysed sample or by removal of water during Modulated DSC analysis. After removal of the remaining water ( < 3.5% w/w), a Tg of approximately 105 degrees C was obtained at a mass ratio of sodium citrate to sucrose of 0.3. FTIR analysis showed a similar increase in Tg as was found with Modulated DSC analysis. The Tg values were derived from breaks in the vibrational frequency vs. temperature plots in the OH stretching and bending regions. Elevated average strength of hydrogen bonding in the sucrose/citrate glass was concluded from the downshift of the OH stretching band of 25 cm(-1) and from the reduced wavenumber temperature coefficient (WTC). The antisymmetric carboxylate stretch of citrate sensed the glass transition of the mixture, from which we conclude that citrate interacts with the sucrose OH via its carboxylate groups.

Polyethylene glycol-induced precipitation of interferon alpha-2a followed by vacuum drying: development of a novel process for obtaining a dry, stable powder

Feasibility studies were performed on the development of a novel process based on polyethylene glycol (PEG)-induced precipitation of proteins followed by vacuum drying in the presence of sugars to obtain dry protein powders. Apparent solubility of interferon alpha-2a (IFNalpha2a) was determined in the presence of various PEGs and the effect of solution pH, ionic strength, and temperature was investigated. IFNalpha2a precipitate was dried at a shelf temperature of 25 degrees C at 100 mTorr either as it is or in the presence of mannitol and/or trehalose. The dried IFNalpha2a formulations were subjected to accelerated stability studies at 40 degrees C (3 months), and the stability was compared with that of a similar lyophilized formulation. The results indicated that more than 90% of the protein could be precipitated using 10% wt/vol PEG 1450 at pH 6.5 at a solution ionic strength of 71 mM. Vacuum drying of the precipitate only resulted in the formation of insoluble aggregates of IFNalpha2a; however, this was prevented by the addition of either mannitol or trehalose. The addition of excess mannitol resulted in low residual moisture content and better handling of the final dried product. Accelerated storage stability did not show any aggregation and showed less than 5% formation of oxidized IFNalpha2a in the dried formulation containing IFNalpha2a:trehalose:mannitol in a 1:10:100 wt/wt ratio upon storage at 40 degrees C for 3 months. The stability of this vacuum dried formulation was comparable with that of a similar lyophilized formulation.

Lyophilization: The process and industrial use

This article presents a general overview of lyophilization and discusses the underlying principles of the process through the basics of: formulation, freezing, primary drying and secondary drying. In this article lyophilization is defined as a stabilizing process in which the substance is first frozen and then the quantity of the solvent is reduced first by sublimation (primary drying) and then by desorption (secondary drying) to values that will no longer support biological growth or chemical reactions. Special mention was made of the industrial use of the process and emphasis was placed on the lyophilization of pharmaceutical products and food industry products. Lyophilization equipment, as well as the formulation of materials that can be lyophilized, are described in sufficient detail to give information on the restrictions and advantages of lyophlization. Processing economics and comparison with conventional drying methods are presented. A historical overview of the process and future developments presented from the industrial viewpoint give an insight on the previous application of lyophilization and the prospects of its broad industrial use.

Protection of Protein Secondary Structure by Saccharides of Different Molecular Weights during Freeze-Drying

The protective effects of saccharides with various molecular weights (glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltoheptaose, dextran 1060, dextran 4900, and dextran 10200) against lyophilization-induced structural perturbation of model proteins (BSA, ovalbumin) were studied. Fourier transform infrared (FT-IR) analysis of the proteins in initial solutions and freeze-dried solids indicated that maltose conferred the greatest protection against secondary structure change. The structure-stabilizing effect of maltooligosaccharides decreased in increasing the number of saccharide units. Larger molecules of dextran also showed a smaller structure-stabilizing effect. Increasing the effective saccharide molecular size by a borate-saccharide complexation reduced the protein structure-stabilizing effect of all of the saccharides except glucose. The results indicate that the larger saccharide molecules, and/or the complex formation with borate ion, reduce the free and accessible hydroxyl groups to interact with and stabilize the protein structure by a water-substitution mechanism.

Solute Crystallization in Mannitol–Glycine Systems—Implications on Protein Stabilization in Freeze‐Dried Formulations

The use of mannitol in combination with glycine has resulted in stable freeze-dried protein formulations. Our objectives were to (1) study solute crystallization in ternary systems containing mannitol, glycine, and water during all the stages of freeze drying as a function of processing conditions and formulation variables; (2) investigate the effect of sodium phosphate buffer salts on the crystallization of both mannitol and glycine and vice versa; and (3) investigate the effects of these excipients in a freeze-dried lactate dehydrogenase (LDH) formulation. X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC) were used to study the frozen aqueous solutions. Phase transitions during primary and secondary drying were monitored by simulating the entire freeze-drying process in situ in the sample chamber of the diffractometer. LDH activity after freeze drying was determined spectrophotometrically. In frozen aqueous solutions containing mannitol and glycine, each solute influenced the extent of crystallization of the other. The solutes crystallized as delta-mannitol and beta-glycine during primary drying. Glycine had a stronger tendency to crystallize, while it was easier to influence mannitol crystallization. The buffer salts inhibited the crystallization of mannitol and glycine. However, in some cases, during primary drying, glycine crystallization was followed by that of disodium hydrogen phosphate dodecahydrate. The latter underwent dehydration forming an amorphous anhydrate. It was possible to correlate the extent of crystallization of mannitol and glycine in the lyophile with the retention of protein activity. An increase in buffer concentration decreased the crystallinity of mannitol and glycine. This translated to increased retention of protein activity.

Sustained release of ascorbate-2-phosphate and dexamethasone from porous PLGA scaffolds for bone tissue engineering using mesenchymal stem cells

The purpose of this research was to develop porous poly(D,L-lactide-co-glycolide) (PLGA) scaffolds from which ascorbate-2-phosphate (AsAP) and dexamethasone (Dex) are continuously released for a month for osteogenesis of mesenchymal stem cells for bone tissue engineering. Porous PLGA matrices containing AsAP and Dex were prepared by solvent casting/particulate leaching method. In vitro release and water uptake studies were performed in Dulbecco's phosphate buffered saline at 37 degrees C and 15 rpm. Drug loading and release rates were determined by high performance liquid chromatography. Release studies of Dex and AsAP showed that, after an initial burst release lasting 4 and 9 days, respectively, release rates followed zero order kinetics with high correlation coefficients at least until 35 days. Incorporation of AsAP into the scaffolds increased the release rates of Dex and AsAP, and the scaffold water uptake. When mesenchymal stem cells (MSCs) were cultured in the AsAP and Dex containing scaffolds in vitro, the amount of mineralization was significantly higher than in control scaffolds. In conclusion, AsAP and Dex were incorporated into porous PLGA scaffolds and continuously released over a month and osteogenesis of MSCs was increased by culture in these scaffolds.

Effect of sodium tetraborate (borax) on the thermal properties of frozen aqueous sugar and polyol solutions

The effect of sodium tetraborate (Na(2)B(4)O(7), borax) on the thermal property of frozen aqueous sugar and polyol solutions was studied through thermal analysis. Addition of borax raised the thermal transition temperature (glass transition temperature of maximally freeze-concentrated solutes; T(g)') of frozen sucrose solutions depending on the borax/sucrose concentration ratios. Changes in the T(g)' of frozen mono- and disaccharide solutions suggested various forms of complexes, including those of a borate ion and two saccharide molecules. Borax exerted the maximum effect to raise the oligosaccharide and dextran T(g)'s at borax/saccharide molar ratios of approximately 1-2 (maltose and maltooligosaccharides), 2 (dextran 1060), 5 (dextran 4900), and 10 (dextran 10200). Further addition of borax lowered T(g)'s of the saccharide solutions. Borax also raised T(g) and T(g)' temperatures of frozen aqueous glycerol solutions. The decreased solute mobility in frozen solutions by the borate-polyol complexes suggested higher collapse temperature in the freeze-drying process and improved stability of biological systems in frozen solutions.

Steady-state tryptophan fluorescence spectroscopy study to probe tertiary structure of proteins in solid powders

The purpose of this work was to obtain information about protein tertiary structure in solid state by using steady state tryptophan (Trp) fluorescence emission spectroscopy on protein powders. Beta-lactoglobulin (betaLg) and interferon alpha-2a (IFN) powder samples were studied by fluorescence spectroscopy using a front surface sample holder. Two different sets of dried betaLg samples were prepared by vacuum drying of solutions: one containing betaLg, and the other containing a mixture of betaLg and guanidine hydrochloride. Dried IFN samples were prepared by vacuum drying of IFN solutions and by vacuum drying of polyethylene glycol precipitated IFN. The results obtained from solid samples were compared with the emission scans of these proteins in solutions. The emission scans obtained from protein powders were slightly blue-shifted compared to the solution spectra due to the absence of water. The emission scans were red-shifted for betaLg samples dried from solutions containing GuHCl. The magnitude of the shifts in lambda(max) depended on the extent of drying of the samples, which was attributed to the crystallization of GuHCl during the drying process. The shifts in the lambda(max) of the Trp emission spectrum are associated with the changes in the tertiary structure of betaLg. In the case of IFN, the emission scans obtained from PEG-precipitated and dried sample were different compared to the emission scans obtained from IFN in solution and from vacuum dried IFN. The double peaks observed in this sample were attributed to the unfolding of the protein. In the presence of trehalose, the two peaks converged to form a single peak, which was similar to solution emission spectra, whereas no change was observed in the presence of mannitol. We conclude that Trp fluorescence spectroscopy provides a simple and reliable means to characterize Trp microenvironment in protein powders that is related to the tertiary conformation of proteins in the solid state. This study shows that the use of fluorescence spectroscopy of proteins can be extended from simple protein aqueous solutions to protein powders, precipitates, and semidried protein samples to gain understanding of protein tertiary structure in these physical states.

In-situ near-infrared spectroscopy monitoring of the lyophilization process

PURPOSE

The purpose of this work was to demonstrate the feasibility of using near-infrared spectroscopy (NIRS) to monitor the freeze-drying process in-situ.

METHODS

The experiment was performed in a pilot-scale freeze-dryer, in which the NIRS probe was interfaced using a lead-through to the lyophilizer. Special equipment for the sample presentation was developed. NIRS measurements were made using a FT (Fourier transform)-NIR spectrometer fitted with a single fiber reflectance probe.

RESULTS

The physical changes, that is, freezing, sublimation, and desorption, generated significant spectral changes. There was good agreement between NIRS monitoring and product temperature monitoring about the freezing process and the transition from frozen solution to ice-free material. The NIRS monitoring also provided new information about the process that was not possible to detect with product temperature monitoring, such as the rate of the desorption process and the steady-state where the drying was complete. The NIRS monitoring yields significantly more information about the actual process and essentially explains the observed changes of the product temperature during the lyophilization process.

CONCLUSIONS

NIRS monitoring is a viable tool for in-situ monitoring, both qualitatively and quantitatively. It can facilitate investigations of the drying process within a sample. The small volume monitored makes sample presentation very important.

Thermal stability of vaccines

Worldwide vaccination programs against infectious diseases and toxins are estimated to save approximately 3 million lives yearly. Tragically, however, another 3 million individuals (primarily children) die of vaccine-preventable diseases. A significant portion of this problem results from the thermal instability of many of the currently used vaccines. This review argues that modern methods of physical and chemical analysis permit for the first time characterization of the degradative pathways of thermally labile vaccines. A rigorous description of these pathways permit a more rational and systematic approach to the stabilization of vaccines. A direct result of the replacement of currently employed, primarily empirical, approaches to vaccine stabilization with a more molecular-based methodology should be the development of more universally available vaccinations against life-threatening diseases. This has the potential to have a dramatic impact on world health.

Investigations into the stabilisation of drugs by sugar glasses: I. Tablets prepared from stabilised alkaline phosphatase

The aim of this study was to investigate the formulation of sugar glass stabilised alkaline phosphatase from bovine intestine (BIAP) into tablets. Two major subjects of tablet formulation were investigated. First, the compaction behaviour of the inulin sugar glass was investigated. Secondly, the effect of the compaction process on the physical stability of sugar glass stabilised BIAP was investigated, comparing inulin and trehalose glass. The tabletting properties of freeze-dried inulin without BIAP were studied first. Freeze-dried inulin conditioned at either 20 degrees C/0% relative humidity (RH) or 20 degrees C/45% RH was compacted at various pressures. As expected, the yield pressure of the material conditioned at 0% RH was higher (68 MPa) than after conditioning at 45% RH (39 MPa). Tablets made of the material stored at 0% RH showed severe capping tendency, especially at high compaction pressures. In contrast, material conditioned at 45% RH gave tablets without any capping tendency and a friability of less than 1%. Sugar glasses of BIAP and either inulin or trehalose were prepared by freeze-drying (BIAP/sugar 1/19 (w/w)). The material was subsequently compacted. Tablets and powders were stored at 60 degrees C/0% RH. The activity of the incorporated BIAP was measured at various time intervals. It was found that inulin was by far superior to trehalose as stabiliser of BIAP in tablets. The poor stabilising capacities of trehalose after compaction are explained by crystallisation of trehalose induced by the compaction process and moisture in the material. The results clearly show that inulin is an excellent stabiliser for BIAP. The tabletting properties are adequate, showing sufficient tablet strengths and low friability. Furthermore, the good (physical) stability of inulin glass with respect to exposure to high relative humidities makes it practical to work with.

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.