WO2014139168A1

WO2014139168A1 - Preparation process of polymeric microspheres

Info

Publication number: WO2014139168A1
Application number: PCT/CN2013/072749
Authority: WO
Inventors: Tuo Jin
Original assignee: Tuo Jin
Priority date: 2013-03-15
Filing date: 2013-03-15
Publication date: 2014-09-18

Abstract

The present invention disclosed a microsphere-producing process involving three essential elementary steps, 1) forcing the particle forming materials to pass through a porous wall; 2) solidifying the embryonic microspheres come out through the porous wall without breaking and fusing (between the particles); 3) collecting and/or outputting the solidified microspheres. This invention also comprises an apparatus to enable the unit operations of the invented process. The apparatus consists an embryonic microsphere-forming unit, a stirring-free microsphere hardening unit, and a microsphere collecting unit and a microsphere out-putting unit.

Description

Preparation Process of Polymeric Microspheres

FIELD OF THE INVENTION

This invention demonstrates a novel process (method) to prepare polymeric microspheres with designed uniform sizes. These microspheres may be used to encapsulate bioactive agents (including therapeutic agents) with high loading efficiency for controlled or sustained release delivery to human and other animals.

BACKRGOUND OF THE INVENTION

Polymeric microspheres are successfully used for controlled- or sustained- release delivery of active agents comprising therapeutics such as chemical drugs or therapeutic peptides. This type of dosage forms have also been used in the attempts to achieve controlled- or sustained-release delivery of proteins. The ability of polymeric microspheres to control or retard release rate of the active or therapeutic cargos loaded wherein offers a great compliance improvement to patients who have received frequent injections of medicine for prolonged period or even life time. With controlled- or sustained-release functions, the in vivo concentration of the medicines (drugs or vaccines) may well be maintained within the therapeutic window (a situation of which in vivo level of a drug/medicine is above the minimum effective concentration but below the minimum toxic concentration. Moreover, the frequency of the hateful injections may be greatly reduced.

Accompany with the benefits above are some drawbacks. A major challenge for preparing protein-loaded microsphere dosage forms is their sterilization process. Microspheres for sustained-release delivery of biologies are normally 10-100 μηι in diameter so that they cannot be sterilized by filtration through a membrane 0.2μηι in pore sizes, a method for sterilizing proteins conventionally. Radiation and heating are out of question too due to the susceptibility of proteins to such hazardous conditions which result in denaturing and/or degradation of the macromolecules. The only feasible method to prepare sterilized microspheres for controlled- or sustained- release delivery of proteins is to prepare this type of dosage forms under an aseptic condition, i.e. to incorporate the whole preparation process in an aseptic environment. Current manufacturing processes produce microspheres of relatively diversified diameters for which pre-lyophilization, sieving and powder-filling become necessary. Sieving and powder-filling are unit operations during which the medical products are exposed to the ambience and unable to be isolated within an aseptic environment. Moreover, the needs of saving to remove particles of undesired sizes results in reduced yield of manufacture, and powder-filling is difficult to achieve accurate load even with sophisticated machines. In addition to size dispersion, stirring, a unit operation to prevent microsphere fusion in the present manufacturing process, may also result in leaking of the ingredient to be encapsulated. The shear stress generated from stirring may break the newly formed microspheres and expose the encapsulated ingredients to the continuous phase. In addition, under-sized particles are regarded as a source of burst release. Clearly, a preparation process which enable manufacturer to produce microspheres of uniform and designable particle sizes, and to fill vials with the medicine in a fluid form will be greatly helpful for sterilized manufacturing.

BRIEF DESCRIPTION OF THE INVENTION

To enable microspheres be prepared in uniform and designable sizes, the particle-forming process involves three essential elementary steps, 1) forcing the particle forming materials to pass through a porous wall; 2) solidifying the embryonic microspheres come out through the porous wall without breaking and fusing (between the particles); 3) collecting and/or outputting the solidified microspheres. The porous wall may also be termed as a porous barrier or a porous membrane having desired pore sizes.

The porous wall may be in any form which allow the particle forming materials be pressed against and pass through. However, a cylindrical shape may offer some convenience for the microsphere-forming materials, normally in fluid form, to be pressed through. The glass particle named as "SPG membrane" made by a company called "SPG technology" is a good example.

The microspheres newly formed from the porous membrane, named embryonic microspheres hereafter, are soft and must be received by a continuous phase in which the embryonic microspheres can be suspended and solidified. The continuous phase must be immiscible with the microsphere-forming materials, yet able to extract the solvent or solvents in which the microsphere-forming materials are dissolved. To prevent the soft embryonic microspheres to fuse with each other or to break by shear stress, the present invention comprises such a unit operation in which the embryonic microspheres come out through the porous membrane and settle or flow to the bottom through a sufficient long path heading to a microsphere collector. During the sedimentation or forced pass, the embryonic microspheres are hardened due to extraction of the solvent from their matrix without shear stress and collision to each other. A long column may be applied to provide the long path of microsphere sedimentation.

Finally, the hardened microspheres should be transferred to a rinsing (washing) process to remove surfactants, salts or other additives used in the receiving phase. Since the more receiving phase is collected, the lower efficiency of microsphere rinsing is resulted, the hardened microspheres are best to be concentrated prior to transfer in order to minimize the receiving phase. A microsphere collector should be applied to collect and concentrate microspheres. After rinsing (washing), the microspheres may be filled in vials or other containers and subjected to freeze-drying or other drying processes. If the outputting of the microspheres is started simultaneously with addition of the receiving phase, continuous production may be achieved. As summary, the invented process to prepare microspheres of uniform and designed sizes comprises three essential unit operation, pressing/forcing microsphere-forming materials to pass through a porous membrane with designed pore size; solidifying embryonic microspheres by extracting the solvent during sedimentation or flow through a long path; collecting the hardened microspheres to minimize receiving phase prior to rinsing.

To achieve the invented process of microsphere preparation, an apparatus or equipment comprising a porous membrane of designed pore sizes (such as the cylindrical SPG membrane), a column or tube to guide the sedimentation or flow of embryonic microspheres through the solvent extraction path to a collector, and a collector at the bottom of which the hardened microspheres are accumulated the prior to rinsing is essential. The apparatus or equipment should also include a path to out-put the hardened/solidified microspheres to a rinsing/washing container. The path may be set to the bottom of the collector to drain the microspheres out or set inside of the collector to sock the microspheres out by the intrinsic pressure of the receiving phase. In the later case, the path or tube should have a bell-shaped or cone-shaped entrance to guide the microspheres in.

DETAILED DESCRIPTION OF FIGURES

The figures are served to help readers to understand this invention, so that they should not be used to limit this invention.

Figure 1. The apparatus/equipment for achieving the unit operations of the invented microsphere preparation process comprising a porous membrane of designed pore sizes (such as the cylindrical SPG membrane), a column or tube to guide the sedimentation or flow of embryonic microspheres through the solvent extraction path to a collector, a collector to accumulate hardened/solidified microspheres, and a tube with a draining valve or a bell-shape entrance to output the microspheres. The solvent extraction path can be set as vertical or other orientation. The socket tube for outputting microspheres may be set at the bottom of the collector or at inside of the collector. The microsphere collector has a rounded, cylindrical or cone shap bottom. The connection between the solvent extraction path and the microsphere collector can be different form and sizes if it allows microspheres to pass through. The diameter of solvent extraction path and the volume of microsphere collector may be enlarged to meet the needs of pilot production and massive manufacture.

Figure 2. Electron microscopic image of exenatide-loaded microspheres which were prepared by the process of this invention using the apparatus described in Figure 1. The particle diameter is as uniform as within 40-50 μηι.

Figure 3. Blood concentration curve of exenatide in monkeys resulted from injecting monthly-acting microsphere formulation prepared by the process of this invention and apparatus in Figure 1. Since the release kinetics was near to perfect, the dose (converted from monkey to human) to reach the targeted blood concentration (300 pg/ml) was only 25% of the commercial weekly-acting exenatide microsphere dosage form, Bydureon.

Figure 4. Electron and optical microscopic images of erythropoietin (EPO)-loaded microspheres which were prepared by the process of this invention using the apparatus described in Figure 1. Both of images confirmed formation of microspheres of uniform diameter.

Figure 5. Cumulative release curve of EPO from the microspheres which were prepared by the process of this invention and apparatus in Figure 1.

Figure 6. Activity los of EPO by antibody generation in monkeys after various formulations were injected.

DETAILED DESCRIPTION OF THE INVENTION

The challenges in manufacturing microspheres, especially those used for therapeutic injections, include difficulty to sterilize, diversifying in particle diameter, low encapsulation efficiency, and initial burst release. These challenges are interdependent on each other, so that cannot be solved one by one independently. The issues must be resolved simultaneously involving appropriate unit operations and rationally designed equipment. The present invention teaches a process and related equipment design to prepare microspheres of uniform diameters and highly efficient encapsulation of target ingredient using simplified operation.

Control of microsphere sizes

The microspheres of uniform size are formed by squeezing the forming material(s), normally a polymer solution carrying drug agents through porous wall (barrier or membrane) of designed pore sizes into a received phase, normally water-based solution. The drug agents may be chemicals or biologies. The biologies comprise proteins, peptides and nucleic acids such as siRNA or genes. The biologies may be loaded in the microsphere-forming polymer solution in the form of dispersed solution droplets or solid particles.

Solidification of embryonic microspheres

The microspheres newly formed from the porous membrane, named embryonic microspheres hereafter, must be received by a continuous phase in which the embryonic microspheres can be suspended and solidified. The continuous phase must be immiscible with the particle (microsphere)-forming materials so that the embryonic microspheres may be kept in shape. On the basis of the immiscibility, the continuous phase should be able to dissolve, in some extent, the solvent or solvents in which the microsphere-forming material or materials were dissolved. By extracting the solvent from the embryonic microspheres, the microspheres formed through the porous membrane may be solidified.

In order to maintain the designed uniform size, the soft embryonic microspheres must not fuse with each other or break by shear stress associated with stirring during the solidification process. The unit operation currently used in microsphere solidification comprises stirring of the receiving continuous phase during which the embryonic microspheres formed by passing through the porous membrane may touch and fuse with each other or break by the shear stress, resulting in dispersed particle sizes. Eliminating the stirring operation will, however, lead to even worse case that the embryonic microspheres drop to the bottom of the receiving phase and fuse to each other. In the present invention, a stirring-free path of solvent extracting phase (can be the receiving phase) is used to allow embryonic microspheres to settle or flow in parallel to avoid them to touch to each other. The solvent-extracting path can be mounted vertically or in other orientations, through which the embryonic microspheres are settling under gravity force or flow by other driving forces.

The stirring-free microsphere solidification may offer another advantage that the leaking of the soluble ingredient encapsulated in the microspheres may be avoided or reduced. Since the process is free of shear stress, the embryonic microspheres will not break, so that the chance for encapsulated soluble ingredient to be exposed to the continuous phase is greatly reduced. Surfactants, salts and other excipients required for facilitating microsphere formation may be added in the receiving phase as same as in a stirring container.

Temperature of receiving phase

To shorten the distance of microsphere sedimentation, temperature of the receiving continuous phase may be adjusted to increase solubility of the solvent or solvents with which the microsphere-forming materials are dissolved. For example, the water solubility of a commonly used solvent for preparing polymeric microspheres, dichloromethane, increases from 2% to 5% when water temperature drops from 25 °C to 2 °C. Increased solvent solubility will facilitate solvent extraction.

Microsphere collecting and outputting

The microspheres hardened by solvent extraction through the long path and settled in the bottom of the container should best be concentrated and output with minimal volume of the continuous phase. Minimizing the volume of the continuous phase is essential for improving the efficiency of rinsing the microspheres to remove the residues of the organic solvent in the matrix of microspheres and the excipients in the continuous phase. Design of the container for the continuous phase should facilitate the microsphere concentration. Figure 1 shows, but not limits to, a design of the bottom of the container by which hardened microspheres may be accumulated and concentrated. The center of the container for collecting microspheres may be deepened to allow microspheres to slide in and accumulated. The deepened part may be cylindrical, rounded, or cone shape.

Output of the accumulated microspheres may be achieved via various methods. Figure 1 shows, but not limits to, two output designs, draining the accumulated microspheres from the bottom, or socking them up through a pipe socket. The pipe socket has a bell-shaped or cone-shaped entrance. Another alternative may be that the hardened microspheres are output along the tangent of a flat bottom of the container of the continuous phase by stirring (not shown in Figure 1).

Preparation scale

The preparation scale of the microencapsulation process above may easily be adjusted by varying the volume of the receiving (continuous) phase, e.g. the diameter of the tube for the sedimentation path, and the size of the porous membrane mentioned above. The preparation scale can therefore vary from few hundreds of milligrams to kilograms.

Continuous production

For continuous production, the microsphere-receiving phase may be added in and drained (or socked from inside) out simultaneously and continuously. Two synchrotron valves to control the adding and draining (or socking) will be helpful. It is recommended that the adding and draining 9socking) the receiving phase slowly so that sedimentation or flow of the microspheres will not be affected.

Preparation of solid-in-microsphere

Some therapeutic agents, proteins for example, need to be protected prior to be encapsulated in polymeric microspheres most of them are made of hydrophobic materials. In this case, a common strategy is to pre-formulate the delicate agents into fine particles, so that the agents may be encapsulated into microspheres in solid form. This microencapsulation process is called "solid-in-oil-in-water" (S/O/W) process. The present invention may also be applied to S/O/W method. The modification of the present microencapsulation process to meet the requirements for S/O/W method is to suspend the p re-formulated fine particles in the solution of the polymeric materials of which the matrix of microspheres are formed.

Since solid particles may settle to the bottom of the container of the polymer solution, continuous stirring may be needed. One of the convenient methods is to apply a magnetic field around the polymer solution container to drive a magnetic stirring bar inside the polymer solution. In the examples of present invention, the magnetic field was created by mounting a coil of electric wire around the container and applying electric power to the coil. Pressured air (or other gas such as nitrogen) is then introduced into the container to press the polymer solution, wherein protein-loaded fine particles are suspended, to pass through the porous membrane. The operations for hardening and collecting of the embryonic microspheres containing the protein-loaded particles will be the same as above.

Annealing of hardened microspheres

To reduce initial burst of the release of encapsulated ingredients from the hardened microspheres, the surface of the microspheres may better be smoothed by an annealing treatment to eliminate pores formed in the solvent extraction step. The annealing treatment may be incorporated in the preparation process disclosed in the present invention.

For polymeric microspheres, annealing treatment is a process to induce phase transition or partial phase transition of the polymeric materials from hard glassy state to a soft gel state. Microspheres will be heated up to reach or over their phase transition temperature to soften the polymer to heal the pores on the microsphere surfaces. The temperature for annealing treatment is, however, affected by the medium used to suspend the microspheres. For example, if polylactic-co-glycolic acid (PLGA) is used to prepare microspheres, the annealing temperature may be lowered by suspending he microspheres in an aqueous solution containing polyethylene glycol (PEG). The concentration and molecular weight of PEG may be adjusted to achieve a designed annealing temperature. In addition to PEG, other reagents soluble in water but possessing some lipophilicity may also be used for lowering the temperature in the annealing treatment of PLGA microspheres.

Fluid filling

Another important advantage of the present invention is that filling of the vials with the microsphere drug product may be achieved by fluid filling. In the case of current manufacture processes, because particle sizes of the microspheres are diversified, a formulation has to be dried into powder and sieved to remove over- and lower-sized particles. Larger microspheres may plug the injection needles while smaller particles may result in burst release. Since the preparation process of the present invention enables manufacturing uni-sized microspheres, sieving and powder filling, the unit operations difficult to incorporate into an aseptic production line, may be avoided. The collected microspheres may be annealed (if necessary), rinsed, and mixed with a solution of viscosity-adjusting agent (carboxyl methyl cellulose for example), and then filled into product vials by fluid filling, an unit operation easier to achieve. Fluid filling may greatly simplify mixing and filling as compared with a powder filling process.

The apparatus

An apparatus to enable each unit operation of the invented process comprises a porous barrier to allow microsphere-forming solution to pass through to form embryonic microspheres, a path of receiving medium through which the embryonic microspheres are hardened via solvent extraction, and collector to collect hardened microspheres, the collector is connected with a draining tube at the bottom or mounted with a socket tube inside of the collector. The tube mounted inside having a bell shape or cone shape entrance. The system should also be equipped with a final formulation container to mix all the additives in the final formulation prior to filling into drug vials or trays.

EXAMPLES

The examples below are part of our on-going research of similar formulations and for helping readers to comprehend the invention better. The examples should not be used to limit applications of the present invention.

Example 1 Microsphere formulation of exenatide

Microsphere-forming polymer, PLGA/PLA, was dissolved in methylene dichloride; and exenatide was dissolved in DMSO. Then the two solutions were mixed and added in a container connected to a cylindrical porous membrane. Pressed air or nitrogen (or other gas) was applied in the container to squeeze the mixed solution through the porous membrane into a receiving phase containing polyvinyl alcohol (PVA) and NaCI. The receiving phase was contained in a column 1600-1800 tall and connected with a microspheres collecting bottle. The embryonic microspheres squeezed through the porous membrane were settled from the top to the bottom of column and the bottle under gravity force for approximately 30-40 second, during which the microspheres were hardened. The hardened microspheres were outputted through an inside socket tube with a bell-shape entrance under the water pressure within the tall column to another container for rinsing. The water rinsed microspheres were imaged using an electron microscope to confirm their uniform size (Figure 2), and then lyophilized for future use. The diameter of the particles is around 40-50 μηι.

In some cases, fine powders of Mg(OH)₂ or MgC0₃ were added to the polymer solution loaded with exenatide prior to subjecting to the porous membrane. To improve release kinetics, the hardened microspheres were annealed at elevated temperature up to the polymer's phase transition point (Tg). In case the drug stability wa in concern, Tg of the polymer was adjusted (lowered) by adding PEG into the annealing medium.

To examine the release kinetics, the microspheres were injected to normal monkeys subcutaneously, followed by blood taking and blood exenatide measurement at programed time. As shown in Figure 4, a month-long constant blood concentration was resulted by single injection of the microsphere formulation.

Example 2. Microsphere formulation of EPO

Pre-formulated polysaccharide fine particles in which EPO was loaded through an aqueous-aqueous emulsion or freezing-induced phase separation were mixed with the PLGA/PLA solution same as that in Example 1. The formed suspension was then loaded in the container connected to porous membrane (SPG membrane) and squeezed with pressed nitrogen through the membrane into a receiving phase same as that in Example 1. All the successive steps are the same as those in Example 1. The morphology of the microspheres were imaged using an electron microscope and an optical microscope to confirm their uniform sizes (See Figure 5). The particle diameters were around 70-80 μηι.

To examine PEO release kinetics and the protection effect of the formulation process, the EPO microspheres were subjected to an in vitro release test and antibody test in monkeys. As shown in Figure 6, a nearly linear release of EPO was observed from the in vitro test. Figure 7 compares the antibody responses of the EPO microspheres made according to the present invention and literature-report double emulsion method. Clearly, EPO microspheres prepared in the present invention had the similar antibody level as control groups of monkeys given NaCI solution and EPO solution dosage form.

Claims

1. A method to prepare microspheres of uniform sizes and high encapsulation efficiency, comprising

a) using a porous barrier to allow microsphere-forming solution to pass through to form embryonic microspheres;

b) involving a path of microsphere receiving medium through which the embryonic microspheres are hardened via solvent extraction;

c) collecting hardened microspheres.

2. The method of claim 1 , wherein the porous barrier may be cylindrical or round in shape.

3. The method of claim 1 , wherein the path of microsphere receiving medium are water-based and allow embryonic microspheres to path through without collision and fusion.

4. The method of claim 1 , wherein the microsphere-forming solution is a polymer solution immiscible with water.

5. The method of claim 1 , wherein the hardened microspheres are collected at the end of the path of microsphere-receiving medium.

6. The method of claim 3, wherein the path of microsphere-receiving medium may be set as vertical, horizontal or in between.

7. The method of claim 4, wherein the polymer solution may be loaded with bio-active agents.

8. The method of claim 7, wherein the bio-active agents may be chemical drugs or biologic agents.

9. The method of claim 8, wherein the biologic agents may be proteins, peptides, or nucleic acids.

10. The method of claim 8, wherein the biologic agents may be loaded in the polymer solution in the form of dispersed solution drops or solid fine particles.

1 1. The method of claim 10, wherein the fine particles are suspended in the polymer solution by stirring or shacking.

12. The method of claim 10, wherein the polymer solution with suspending fine particles is squeezed through the porous barrier to form embryonic microspheres.

13. The method of claim 5, wherein the end of the microsphere-receiving path may shape as round, cylindrical, cone-shaped or in between of them.

14. The method of claim 5, wherein collected hardened microspheres are output from the collector.

15. The method of claim 14, wherein the microsphere out-putting is achieved through a tube with a bell-shape or cone shape entrance from the inside of the collector, or through draining from the bottom of the collector.

16. The method of claim 14, wherein the out-putted microspheres are subjected to further treatment comprising annealing, rinsing, or lyophilization.

17. The method of claim 16, wherein polyethylene glycol may be added into the microsphere-treating medium to adjust the annealing temperature.

18. The method of 9, wherein the proteins or peptides comprise erythropoietin, growth hormone, interferon, factor VIII, exenatide, calcitonin, and GM-CSF.

19. The method of 9, wherein the nucleic acids comprise siRNA and genes.

20. An apparatus for accomplishing the method of claim 1 , comprising a porous barrier to allow microsphere-forming solution to pass through to form embryonic microspheres, a path of receiving medium through which the embryonic microspheres are hardened via solvent extraction, and collector to collect hardened microspheres.

21. The apparatus of claim 20, wherein the collector is connected with a draining tube at the bottom or mounted with a socket tube inside of the collector.

22. The apparatus of claim 21 , wherein the tube mounted inside having a bell shape or cone shape entrance.

23. The apparatus of claim 20, wherein the microsphere collector have a rounded, cylindrical of cone shape bottom.

24. The apparatus should also include a final formulation container to mix all the additives in the final formulation prior to filling into drug vials or trays.