Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K9/00—Medicinal preparations characterised by special physical form
  • A61K9/48—Preparations in capsules, e.g. of gelatin, of chocolate
  • A61K9/50—Microcapsules having a gas, liquid or semi-solid filling; Solid microparticles or pellets surrounded by a distinct coating layer, e.g. coated microspheres, coated drug crystals
  • A61K9/5089—Processes
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K9/00—Medicinal preparations characterised by special physical form
  • A61K9/10—Dispersions; Emulsions
  • A61K9/107—Emulsions ; Emulsion preconcentrates; Micelles
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K49/00—Preparations for testing in vivo
  • A61K49/22—Echographic preparations; Ultrasonic imaging preparations
  • A61K49/222—Echographic preparations; Ultrasonic imaging preparations characterised by a special physical form, e.g. emulsions, liposomes
  • A61K49/223—Microbubbles, hollow microspheres, free gas bubbles, gas microspheres
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K49/00—Preparations for testing in vivo
  • A61K49/22—Echographic preparations; Ultrasonic imaging preparations
  • A61K49/222—Echographic preparations; Ultrasonic imaging preparations characterised by a special physical form, e.g. emulsions, liposomes
  • A61K49/226—Solutes, emulsions, suspensions, dispersions, semi-solid forms, e.g. hydrogels
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K9/00—Medicinal preparations characterised by special physical form
  • A61K9/0012—Galenical forms characterised by the site of application
  • A61K9/0019—Injectable compositions; Intramuscular, intravenous, arterial, subcutaneous administration; Compositions to be administered through the skin in an invasive manner
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K9/00—Medicinal preparations characterised by special physical form
  • A61K9/10—Dispersions; Emulsions
  • A61K9/127—Synthetic bilayered vehicles, e.g. liposomes or liposomes with cholesterol as the only non-phosphatidyl surfactant
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K9/00—Medicinal preparations characterised by special physical form
  • A61K9/48—Preparations in capsules, e.g. of gelatin, of chocolate
  • A61K9/50—Microcapsules having a gas, liquid or semi-solid filling; Solid microparticles or pellets surrounded by a distinct coating layer, e.g. coated microspheres, coated drug crystals
  • A61K9/5005—Wall or coating material

Definitions

• the invention relates to a method for preparing size-controlled microparticles, such as gas-filled microvesides, in particular by usi ng a flow-focusing device.
• Gas-filled microvesides are generally employed as suitable contrast agents in ultrasound imaging techniques, known as Contrast Enhanced Ultrasound (CEUS) Imaging .
• the gas of these microvesides is typically entrapped or encapsulated in a stabilizing envelope comprising, for instance, emulsifiers, oils, thickeners or sugars.
• These stabilized gas bubbles are generally referred to in the art with various terminologies, depending typically from the stabilizing material employed for their preparation; these terms include, for instance, "microspheres", “microbubbles”, “microcapsules” or “microballoons”, globally referred to here as “gas-filled microvesides" (or “microvesides” i n short) .
• aqueous suspensions of gas-filled microvesides where the bubbles of gas are bounded, at the gas/liquid interface, by a very thin envelope (film) involving a stabilizing amphi philic material (typically a phospholipid) disposed at the gas to liquid interface.
• a stabilizing amphiphilic material typically a phospholipid
• These suspensions are typically prepared by contacting powdered amphiphilic materials, e.g. freeze-dried preformed liposomes or freeze- dried or spray-dried lipid solutions, with air or any other gas, and then with an aqueous carrier, while agitati ng to generate a suspension of gas-filled microvesides which can then be administered, preferably shortly after its preparation.
• the stabilizing layer may comprise, i n addition to the above cited phospholipids, also other amphiphilic materials, such as fatty acids.
• Ref. 1 discloses an alternative method for the production of gas-filled microvesides which comprises emulsifying a hydrophobic liquid, typically an oil, in an aqueous dispersion of the amphiphilic material to obtain an emulsion of liquid filled microdroplets; the emulsion is then lyophilized and the lyophilized residue is subsequently reconstituted in the presence of a gas and an aqueous solvent to form the microbubble suspension.
• a hydrophobic liquid typically an oil
• Aqueous emulsions containing liquid filled microdroplets can also be used as drug carriers.
• Either hydrophobic drugs or hydrophilic drug can be i ncorporated in a droplet coated by amphiphilic materials.
• the amphiphilic material forms a monolayer around the droplet.
• a double layer of amphiphilic material liposome is formed around an aqueous droplet.
• PDI polydispersity index
• a typical preparation method may provide microparticles with a mean diameter of about 2-3 mi crometer and a PDI of about 60% .
• microparticles, and particul arly gas-filled microvesicles with a relatively high PDI (such as 60%) are generally well suited for most of the actual i magi ng techniques, such PDI may nevertheless still be optimized for said imaging techniques. Moreover, for certain therapeutic ultrasound applications it is preferable to mi ni mize the PDI.
• Suitable methods for preparing monodi sperse microparticles include, for instance, the use of microflui dic techni ques, typically by using T-junctions or flow- focusing devi ces.
• a flow of a fi rst fluid component e.g . a gas or an oil
• i s focused by a flow of a second fluid component through a narrow orifi ce.
• the second fluid component is a liquid fluid comprising an envelope formi ng material (typically surfactants such as lipids, i ncluding
• phospholipids and/or fatty acids which entraps the fi rst fluid component to form the desired microparticles (in the form of gas-filled microvesicles or liquid droplets), which are stabili zed against coal escence and dissolution by said envelope forming material .
• the freshly formed microparticles may collide with a rel atively high kinetic energy and such collisions may result in the coalescence of the mi croparticles.
• the consequences of such coalescence are that the dimensions of the formed microparticles may vary randomly, e.g . two, three and up to n-ti mes the volume of the desired microparticles volume. Thus, the size and PDI of the microparticles population may become uncontroll able.
• the Applicant has now found suitable preparation conditions which may be applied for limiting the coalescence of the microparticles prepared according to microfluidic methods.
• the coalescence phenomenon can be substantially reduced.
• the present invention relates to a method for preparing a suspension of microparticles stabilized by a layer of amphiphilic material which comprises:
• an initial portion of said outlet channel is kept at a temperature (°C) of not less than 20% lower with respect to the transition temperature of the amphiphilic material .
• the initial portion of the outlet channel is kept at a temperature (°C) of not less than 10% lower with respect to the transition temperature of the amphiphilic material .
• Said initial portion of the outlet channel preferably extends from the exit of the calibrated orifice until at least a zone where the flow of the aqueous suspension of microparticles reaches a substantially stationary velocity.
• the suspension flows from the calibrated orifice to the outlet channel through a calibrated channel.
• said initial portion may extend for at least 0.1 mm from the exit of the calibrated orifice (or channel), preferably for at least 1 mm, more preferably for at least 2 mm.
• the length of said initial portion may be up to the total length of the outlet channel of the microfluidic device, e.g. 100 mm from the exit of the calibrated orifice.
• said first fluid flow is a gas and said microparticles are gas-filled microvesicles.
• the contact zone and the calibrated orifice are kept at the desired temperature.
• the optional calibrated channel between the calibrated orifice and the outlet channel is preferably kept at said temperature.
• the obtained suspension is cooled down to a temperature below the transition temperature of the amphiphilic material within a relatively short period of time after the formation of the microparticles.
• the suspension is cooled within 10 seconds from the formation of the microparticles, preferably within 5 seconds and even more preferably within 2 seconds.
• the suspension is cooled at a temperature (°C) of at least 5% lower than T m , more preferably at least 10% lower, down to e.g. 50 % of T m .
• the cooling temperature is room temperature (e.g. 22 °C), particularly when the microparticles suspension is stored at room temperature.
• the cooling temperature may also be lower, e.g. corresponding to the storage temperature when the suspension is stored at lower temperatures (e.g. 10°C).
• Figure 1 is a schematic representation of the core portion of a flow-focusing device.
• Figure 2 shows an exemplary schematic representation (top view) of a chip useful for the flow-focusing process of the invention.
• Figure 3 shows an exemplary schematic drawing of a device useful for the process of the invention.
• Figure 4 illustrates experimental results of the temperature control during the formation of gas-filled microvesicles according to the invention.
• Figure 5 illustrates experimental results of the temperature control during the formation of gas-filled microvesides with other amphiphilic materials according to the invention.
• Figure 6 illustrates experimental results of the cooling effect on a suspension of gas-filled microvesides.
• FIG. 1 shows a schematic representation of the core portion 100 of a flow- focusing device (chip) useful in the process of the invention.
• the chip comprises a first feed channel 101 for feeding a first fluid flow 101' and two additional feed channels 102a and 102b for supplying the liquid flow containing the amphiphilic material .
• the first fluid flow (preferably a gas) and the the two liquid flows are directed towards the contact zone 103 and then through the calibrated orifice 104, shown as a dotted line in figure 1.
• the calibrated orifice is connected to a calibrated channel 104' having preferably the same cross-section as the orifice, which is in turn connected to an initial portion 105 of the outlet channel 106.
• the calibrated orifice 104 may be a nozzle directly connected to the initial portion 105 of outlet channel 106 i.e. without the calibrated channel in-between.
• the micro particles 103' are formed in the calibrated orifice and directed, through calibrated channel 104', to the initial portion 105 of the outlet channel 106.
• the hydraulic diameter of the outlet channel is generally larger than the hydraulic diameter of the calibrated orifice and typically increases from the initial diameter of the calibrated orifice to the final diameter of the outlet channel 106, corresponding substantially to the hydraulic diameter of a collecting tube (not shown), connecting the flow-focusing device to a container, e.g. a sealed vial .
• the velocity of the stream dramatically decreases from a relatively high velocity at the exit of the calibrated orifice down to the stationary state velocity of the suspension (that is typically reached downstream in the outlet channel and in the collection tube).
• This negative velocity gradient may cause the microparticles exiting from the calibrated orifice to collide onto microparticles flowing at a substantially lower velocity in the initial portion of the outlet channel . If the temperature of the microvesides is not sufficiently high, these collisions may cause an uncontrolled collapse of the microparticles, with the result of undesirably increasing the polydispersity of the preparation.
• such undesi red coalescence phenomenon may be substantially reduced by controlling the temperature of the microparticles in the initial portion 105 of the outlet channel of the device and preferably also in the contact zone 103 and in the calibrated orifice 104.
• the initial portion of the outlet channel is preferably kept at a temperature of not less than 20% lower with respect to the T m of the amphiphilic material contained in the liquid flow and forming the stabilizing envelope of the microparticles. More preferably, said temperature is not less than 10% lower with respect to the T m of the amphi philic material . While in general it is not necessary to have a temperature excessively higher than the T m , such temperature may be as high as necessary, compati bly with the heat degradation resistance of the amphiphilic materials; for instance, the temperature may be up to 20% higher than the T m of the amphiphilic material, preferably up to 10% higher. In preferred embodiments, said temperature is at or slightly above (e.g.
• the temperature control is particularly useful in the zone of the outlet channel where the flow of the aqueous suspension of microparticles has not yet reached a substantial stationary velocity, e.g. when the absol ute velocity gradient is higher than about 10 s "1 .
• said zone may extend for a length of from about 0.1 mm to 100 mm from the calibrated orifice, preferably from 1.0 to 50 mm and more preferably from 2.0 to 30 mm.
• the temperature may similarly be controlled by applying the parameters specified above also to the contact zone and to the cali brated orifice (and, where present, to the calibrated channel).
• the controlled temperature provides a substantial reduction of the coalescence among the formed microparticles.
• the percentage of coalescence can be determined by calculati ng the total number of coalesced microparticles from the peaks of the size distri bution from the images obtained with the optical microscope at the outlet channel of the flow- focusing device, e.g. by:
• the percentage of coalescence can thus be calculated by normalizing the total number of coalesced microparticles by the total number of produced microparticles,
• coalescence % — X 100% .
• coalescence percentage of less than about 10%, preferably of less than about 5% and even more preferably of about 1% or less is desirable, down to coalescence percentages of e.g. 0.01% .
• the flow rate at which the device is operated may affect the coalescence of the microparticles.
• the so-called "dripping" regime as the velocity of the flows is relatively low (e.g. about 45 ⁇ _/ ⁇ for a calibrated orifice of about 600 ⁇ 2 ), and the microparticles size is typically larger (typically corresponding to the cross-section of the calibrated orifice), the coalescence phenomenon is relatively reduced.
• the so-called "jetting" regime the increased velocity of the flow (e.g.
• the flow-focusing device can be any of those known in the art, described for instance in (see e.g. Ref. 3) .
• the flow focusing device comprises a chip, such as the one described e.g. in Ref. 4.
• the chi p 200 may comprise a first inlet channel 201 through which the first fluid (preferably a gas) flow is supplied and two inlet channels 202' and 202" through which the liquid flow is supplied .
• Each of said inlet channels is connected to a respective reservoir through respective tubing (not shown) .
• the chip further comprises an outlet channel 203 connected through a respective tubing to a container (not shown) adapted for collecti ng the suspension of micropartides.
• the cross-section of the final portion of the inlet channels 201a and 202a, close to the calibrated orifice, is substantially reduced with respect to the remainder of the channel 201b and 202b.
• the cross- section of this final portion 201a and 202a may vary from 25 to 1 ⁇ 10 4 ⁇ 2 , preferably from 200 to 1 ⁇ 10 3 ⁇ 2 , advantageously corresponding substantially to the cross-section of the calibrated orifice.
• the cross-section of the initial portions of the inlet channels may vary from 1 ⁇ 10 3 to 1 ⁇ 10 6 ⁇ 2 , preferably from 1 ⁇ 10 4 to 1 ⁇ 10 5 ⁇ 2 , while their length may vary from 50 mm to 1 mm, preferably from 2 mm to 5 mm.
• the calibrated orifice and the calibrated channel will have a cross-sectional area of about 250 to 2500 ⁇ 2 .
• the cross-sections of the inlet channels and that of the outlet channel are
• the length of the cali brated channel 203a may vary from about 0.05 mm to about 10 mm, preferably from 1 mm to 5 mm, while the total length of the outlet channel may be up to 100 mm, preferably up to 50 mm and more preferably up to 30 mm.
• the chip is made out of two halves of quartz glass, fused silica, or any plastic (e.g. Poly(methyl methacrylate)) material .
• the channels can be produced by etching, either dry or wet, the internal surface of each half, for the whole desired depth and width.
• the surface may be etched at a constant depth of 14 ⁇ and with a width of 15-20 ⁇ for the respective calibrated portions close to the contact zone and a width of 0.5-1.0 mm for the remainder portions.
• Commercially available chi ps suitable for the use in the process of the invention are available for instance from Dolomite microfluidics (Royston, United Kingdom) or Micronit
• the suspension in order to maintain the monodispersity of the formed micropartides, the suspension may then rapidly be cooled down to a temperature below the T m of the amphi philic material, preferably once the flow of the suspension in the collection zone has reached a substantially stationary velocity.
• a unit 300 (e.g . a chip as described i n figure 2) comprising the core portion of a flow-focusing device may be kept at the desired temperature close or slightly above the T m of the amphiphilic material, as described above, e.g . by means of a thermostatic bath.
• the first fluid flow and the liquid flows comprising the amphiphilic material are supplied to unit 300 from respective reservoirs 301 and 302 to the unit 300 via respective supply tubing (with an internal diameter of e.g 100 to 1000 ⁇ preferably from 150 to 250 ⁇ ) .
• the outlet tubing 303 connects the outlet channel (not shown) of unit 300 (to a suitable collecti ng container 304, e.g. a sealed vial .
• the cooling of the suspension of microparticles within few seconds from the formation of the microparticles, preferably as soon as the flow of the suspension reaches a substantially stationary velocity.
• said cooling may be initiated within 180 seconds from the formation of the microvesicles, preferably within 60 seconds, more preferably within 10 seconds and even more preferably within 2 seconds.
• the stationary flow is generally reached within few milliseconds or even less after the microparticles formation; the cooling may thus be applied starting from 1 milliseconds after the formation of the microparticles.
• the cooling may advantageously be applied to the initial portion of the outlet tubing exiting the unit 300.
• an initial portion of the outlet tubing is advantageously subjected to cooling by suitable cooling means 305, e.g. a heat exchanger, in order to reduce the temperature of the suspension of gas-filled microparticles below T m of the amphi philic material forming the stabilizing envelope of the microvesicles.
• suitable cooling means 305 e.g. a heat exchanger
• the length of the initial portion of the outlet tubing subjected to the cooling may vary e.g. from 1 cm to 100 cm, preferably from 5 cm to 10 cm, depending, for instance from the heating temperature of the unit 300, the efficacy of the applied cooling, the contact time and so on.
• transition temperature (T m ) of an amphiphilic material said temperature may be referred either to a single amphiphilic component or to a mixture of amphiphilic components.
• the amphiphilic material forming the stabilizing envelope is a mixture of different amphiphilic components
• said T m is generally referred to as the Tm of said mixture of amphiphilic components.
• the measured T m generally corresponds to a molar ratio weighted mean of the Tm of the individual components of the mixture.
• the transition temperature T m of a lipid reflects a change in the physical state of the lipid from the ordered gel phase to the disordered liquid crystalline phase.
• the hydrocarbon chains of the lipid are fully extended and closely packed.
• the hydrocarbon chains are randomly oriented and fluid like.
• the Tm of an aqueous lipid mixture may advantageously be measured by using differential scanning calorimetry (DSC). Calorimetric or thermal analysis allows for the measurement of heat flows related to transitions of a material as a function of time and temperature, and in a controlled atmosphere. DSC measures the difference of heat flow between a sample and an inert reference, by heating or cooling a sample at a constant rate in °C/min.
• T m of amphiphilic materials can be performed for instance by using a DSC- Q2000 device (TA Instruments, New Castle, DE USA). Parameters such as the temperature at which the transition starts and reaches its peak and the enthalpy of the transition are measured to determine the T m . Details of the measurements are provided in the experimental part.
• Suitable amphiphilic materials for use in a method of the invention comprise, for instance, phospholipids; lysophospholipids; fatty acids, such as palmitic acid, stearic acid, arachidonic acid or oleic acid; lipids bearing polymers, such as chitin, hyaluronic acid, polyvinylpyrrolidone or polyethylene glycol (PEG), also referred as "pegylated lipids"; lipids bearing sulfonated mono- di-, oligo- or polysaccharides; cholesterol, cholesterol sulfate or cholesterol hemisuccinate; tocopherol hemisuccinate; lipids with ether or ester-linked fatty acids; polymerized lipids; diacetyl phosphate; dicetyl phosphate; ceramides; polyoxyethylene fatty acid esters (such as polyoxyethylene fatty acid stearates), polyoxyethylene fatty alcohols, polyoxyethylene fatty alcohol ethers
• At least one of the compounds forming the envelope of the micropartides is a phospholipid, optionally in admixture with any of the other above cited materials.
• the term phospholipid is intended to encompass any amphiphilic phospholipid compound, the molecules of which are capable of forming a stabilizing film of material (typically in the form of a mono-molecular layer), particularly at the gas-water interface in the final microvesicles' suspension. Accordingly, these materials are also referred to in the art as "film-forming phospholipids".
• Amphiphilic phospholipid compounds typically contain at least one phosphate group and at least one, preferably two, lipophilic long-chain hydrocarbon group.
• Suitable phospholipids include esters of glycerol with one or preferably two (equal or different) residues of fatty acids and with phosphoric acid, wherein the phosphoric acid residue is in turn bound to a hydrophilic group, such a, for instance, choline (phosphatidylcholines - PC), serine (phosphatidylserines - PS), glycerol (phosphatidylglycerols - PG), ethanolamine (phosphatidylethanolamines - PE), inositol (phosphatidylinositol).
• choline phosphatidylcholines - PC
• serine phosphatidylserines - PS
• glycerol phosphatidylglycerols - PG
• ethanolamine phosphatidylethanolamines - PE
• inositol phosphatidylinositol
• Esters of phospholipids with only one residue of fatty acid are generally referred to in the art as the "lyso" forms of the phospholipid or "lysophospholipids".
• Fatty acids residues present in the phospholipids are in general long chain aliphatic acids, typically containing from 12 to 24 carbon atoms, preferably from 14 to 22; the aliphatic chain may contain one or more unsaturations or is preferably completely saturated.
• suitable fatty acids included in the phospholipids are, for instance, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, oleic acid, linoleic acid, and linolenic acid.
• saturated fatty acids such as myristic acid, palmitic acid, stearic acid and arachidic acid are employed.
• phospholipids are phosphatidic acids, i.e. the diesters of glycerol-phosphoric acid with fatty acids; sphingolipids such as sphingomyelins, i.e. those phosphatidylcholine analogs where the residue of glycerol diester with fatty acids is replaced by a ceramide chain; cardiolipins, i .e. the esters of 1,3- diphosphatidylglycerol with a fatty acid; glycolipids such as gangliosides GM1 (or GM2) or cerebrosides; glucolipids; sulfatides and glycosphingolipids.
• phosphatidic acids i.e. the diesters of glycerol-phosphoric acid with fatty acids
• sphingolipids such as sphingomyelins, i.e. those phosphatidylcholine analogs where the residue of glycerol diester with fatty acids
• phospholipids include either naturally occurring, semisynthetic or synthetically prepared products that can be employed either singularly or as mixtures.
• Examples of naturally occurring phospholipids are natural lecithins
• PC phosphatidylcholine
• Examples of semisynthetic phospholipids are the partially or fully hydrogenated derivatives of the naturally occurring lecithins.
• Preferred phospholipids are fatty acids di-esters of phosphatidylcholine, ethylphosphatidylcholine, phosphatidylglycerol, phosphatidic acid, phosphatidylethanolamine, phosphatidylserine,
• Examples of preferred phospholipids are, for instance, dilauroyl- phosphatidylcholine (DLPC), dimyristoyl-phosphatidylcholine (DMPC), dipalmitoyl- phosphatidylcholine (DPPC), diarachidoyl-phosphatidylcholine (DAPC), distearoyl- phosphatidylcholine (DSPC), dioleoyl-phosphatidylcholine (DOPC), 1,2 Distearoyl-sn- glycero-3-Ethylphosphocholine (Ethyl -DSPC), dipentadecanoyl -phosphatidyl choline (DPDPC), l-myristoyl-2-palmitoyl-phosphatidylcholine (MPPC), l-palmitoyl-2- myristoyl-phosphatidylcholine (PMPC), l-palmitoyl-2-stearoyl-phosphatidylcholine
• DAPG diarachidoylphosphatidyl-glycerol
• DMPG dimyristoylphosphatidylglycerol
• DPPG dipalmitoylphosphatidylglycerol
• distearoylphosphatidylglycerol DSPG and its alkali metal salts
• dioleoyl- phosphatidylglycerol (DOPG) and its alkali metal salts dimyristoyl phosphatidic acid (DMPA) and its alkali metal salts
• DPPA dipalmitoyl phosphatidic acid
• DSPA distearoyl phosphatidic acid
• DAPA diarachidoylphosphatidic acid
• dimyristoyl-phosphatidylethanolamine DMPE
• dipalmitoylphosphatidylethanolamine DPPE
• distearoyl phosphatidyl-ethanolamine DSPE
• dioleylphosphatidyl-ethanolamine DOPE
• diarachidoylphosphatidyl- ethanolamine DAPE
• DLPE dimyristoyl
• DOPS dioleoylphosphatidylserine
• DPSP dipalmitoyl sphingomyelin
• DSSP distearoylsphingomyelin
• DLPI dilauroyl-phosphatidylinositol
• DAPI diarachidoylphosphatidylinositol
• DMPI dimyristoylphosphatidylinositol
• DPPI dipalmitoylphosphatidylinositol
• DSPI distearoylphosphatidylinositol
• DOPI dioleoyl-phosphatidylinositol
• Suitable phospholipids further include phospholipids modified by linking a hydrophilic polymer, such as polyethyleneglycol (PEG) or polypropyleneglycol (PPG), thereto.
• PEG polyethyleneglycol
• PPG polypropyleneglycol
• Preferred polymer-modified phospholipids include "pegylated phospholipids", i .e. phospholipids bound to a PEG polymer. Examples of pegylated phospholipids are pegylated phosphatidylethanolamines ("PE-PEGs" in brief) i.e.
• phosphatidylethanolamines where the hydrophilic ethanolamine moiety is linked to a PEG molecule of variable molecular weight (e.g. from 300 to 20000 daltons, preferably from 500 to 5000 daltons), such as DPPE-PEG (or DSPE-PEG, DMPE-PEG, DAPE-PEG or DOPE-PEG).
• DPPE-PEG2000 refers to DPPE having attached thereto a PEG polymer having a mean average molecular weight of about 2000.
• Particularly preferred phospholipids are DAPC, DSPC, DPPC, DMPA, DPPA, DSPA, DMPG, DPPG, DSPG, DMPS, DPPS, DSPS and Ethyl-DSPC. Most preferred are DPPG, DPPS and DSPC.
• Mixtures of phospholipids can also be used, such as, for instance, mixtures of DPPE and/or DSPE (including pegylated derivatives), DPPC, DSPC and/or DAPC with DSPS, DPPS, DSPA, DPPA, DSPG, DPPG, Ethyl-DSPC and/or Ethyl-DPPC.
• a mixture of phospholipids may include phosphatidylcholine derivatives, phosphatidic acid derivatives and pegylated phosphatidylethanolamine, e.g. DSPC/DPPA/DPPE-PEG, DPPC/DPPA/DPPE-PEG, DSPC/DPPA/DSPE-PEG, DPPC/DPPA/DSPE-PEG, DAPC/DPPA/DPPE-PEG, DAPC/DPPA/DSPE-PEG, DAPC/DPPA/DSPE-PEG,
• the phospholipid is the main component of the stabilizing envelope of microvesicles, amounting to at least 50% (w/w) of the total amount of components forming the envelope of the gas-filled microvesicles, preferably at least 75%.
• substantially the totality of the envelope i .e. at least 90% w/w can be formed of phospholipids.
• the phospholipids can conveniently be used in admixture with any of the above listed amphiphilic compounds.
• lipids such as cholesterol, ergosterol, phytosterol, sitosterol, lanosterol, tocopherol, propyl gallate or ascorbyl palmitate, fatty acids such as myristic acid, palmitic acid, stearic acid, arachidic acid and derivatives thereof or butylated hydroxytoluene and/or other non-phospholipid compounds can optionally be added to one or more of the foregoing phospholipids, e.g in proportions preferably ranging from zero to 50% by weight, more preferably up to 25%.
• mixtures of amphiphilic materials comprising phosphilpids and fatty acids can advantageously be used, including DSPC/DPPG/palmitic acid, DSPC/DPPE-PEG/palmitic acid, DPPC/DPPE-PEG/palmitic acid, DSPC/DSPE- PEG/palmitic acid, DPPC/DSPE-PEG/palmitic acid, DSPC/DPPE-PEG/stearic acid, DPPC/DPPE-PEG/stearic acid, DSPC/DSPE-PEG/stearic acid or DPPC/DSPE- PEG/ stearic acid.
• micro particles prepared according to the method of the invention may optionally comprise a targeting ligand.
• targeting ligand includes within its meaning any compound, moiety or residue having, or being capable to promote, a targeting activity (e.g. including a selective binding) of the microparticles of a composition of the invention towards any biological or pathological site within a living body.
• Targets with which targeting ligand may be associated include tissues such as, for instance, myocardial tissue (including myocardial cells and cardiomyocytes), membranous tissues (including endothelium and epithelium), laminae, connective tissue (including interstitial tissue) or tumors; blood clots; and receptors such as, for instance, cell-surface receptors for peptide hormones, neurotransmitters, antigens, complement fragments, and
• the targeting ligand may be synthetic, semi-synthetic, or naturally occurring.
• Materials or substances which may serve as targeting ligands include, for example, but are not limited to proteins, including antibodies, antibody fragments, receptor molecules, receptor binding molecules, glycoproteins and lectins; peptides, including oligopeptides and polypeptides; peptidomimetics; saccharides, including mono and polysaccharides; vitamins; steroids, steroid analogs, hormones, cofactors, bioactive agents and genetic material, including nucleosides, nucleotides and polynucleotides.
• the targeting ligand may be an amphiphilic compound per se (which is admixed with the other components of the microvesicle) or a compound bound to an amphiphilic molecule (e.g. a phospholipid) employed for the formation of the microparticles.
• an amphiphilic compound per se which is admixed with the other components of the microvesicle
• a compound bound to an amphiphilic molecule e.g. a phospholipid
• the targeting ligand may be bound to an amphiphilic molecule (e.g. a phospholipid) forming the stabilizing envelope of the microparticles through a covalent bond.
• an amphiphilic molecule e.g. a phospholipid
• microparticles envelope shall thus contain a suitable reactive moiety and the targeting ligand containing the complementary functionality will be linked thereto according to known techniques, e.g. by adding it to a dispersion comprising the amphiphilic components of the microparticles.
• the amphiphilic compound is a lipid bearing a hydrophilic polymer, such as those previously mentioned, preferably a pegylated phospholipid.
• the targeting ligand is linked to a suitable reactive moiety on the hydrophilic polymer.
• the amphiphilic compound may be combined with the desired targeting ligand before preparing the microvesicle, and the so obtained combination may be used for the preparation of the microvesicle.
• a microvesicle may first be manufactured, which comprises a compound (lipid or polymer-modified lipid) having a suitable moiety capable of interacting with a corresponding complementary moiety of a targeting ligand;
• the desired targeting ligand is added to the microvesicle suspension, to bind to the corresponding complementary moiety on the microvesicle.
• the targeting ligand may also be suitably associated with the microparticles via physical and/or electrostatic interactions.
• the liquid used in the method of the invention comprises an amphiphilic material (as above defined) at a concentration of e.g. from 5.0 to 20 mg/mL, preferably from 7.5 to 15 mg/mL, preferably dispersed in an aqueous carrier.
• Suitable aqueous carriers comprise water (preferably sterile water), aqueous solutions such as saline (which may advantageously be balanced so that the final product for injection is not hypotonic), or solutions of one or more tonicity adjusting substances.
• Tonicity adjusting substances comprise salts or sugars, sugar alcohols, glycols or other non- ionic polyol materials (e.g. glucose, sucrose, sorbitol, mannitol, glycerol,
• chitosan derivatives such as carboxymethyl chitosan, tri methyl chitosan or gelifying compounds, such as carboxymethylcellulose, hydroxyethyl starch or dextran.
• an additional oil phase may be added for incorporating therapeutic hydrophobic substances into the microvesicles.
• two additional conduits may be provided in the device for supplying the desired oil phase, as described for instance by Ref. 5.
• the formed gas-filled microvesicles will thus have a film of oil disposed at the interface between gas and the stabilizing layer of amphiphilic material, which can be loaded with a desired therapeutic agent.
• Suitable oils may include any
• biocompatible oil which is liquid at room temperature including, for instance, mono-, di- or tri-esters of glycerol with saturated or unsaturated (C2-C18) al kyl chains (including homo- or hetero-allkylesters), such as glycerol monobutyrin, glycerol monolinoleate, 1,2-dihexanoyl glycerol, 1,2 dioctanoyl glycerol, 1,2-dioleyl-sn- glycerol, triacetin, tributyrin, tricaproin, tricaprylin, tricaprin, and mixtures thereof; or natural oils such as soya oil, olive oil, safflower seed oil, sunflower seed oil, peanut oil and mixtures thereof.
• C2-C18 al kyl chains including homo- or hetero-allkylesters
• the first fluid flow is a gas or a precursor thereof.
• any biocompatible gas, gas precursor or mixture thereof may be employed for the preparation of the microvesicles (hereinafter also identified as "microvesicle-forming gas").
• the gas may comprise, for example, air; nitrogen; oxygen; carbon dioxide; hydrogen; nitrous oxide; a noble or inert gas such as helium, argon, xenon or krypton; a low molecular weight hydrocarbon (e.g.
• halogenated gases preferably fluorinated gases, such as or halogenated, fluorinated or perfluorinated low molecular weight hydrocarbons (e.g. containing up to 7 carbon atoms); or a mixture of any of the foregoing.
• a halogenated hydrocarbon preferably at least some, more preferably all, of the halogen atoms in said compound are fluorine atoms.
• Fluorinated gases are preferred, in particular perfluorinated gases.
• Fluorinated gases include materials which contain at least one fluorine atom such as, for instance fluorinated hydrocarbons (organic compounds containing one or more carbon atoms and fluorine); sulfur hexafluoride; fluorinated, preferably perfluorinated, ketones such as perfluoroacetone; and fluorinated, preferably perfluorinated, ethers such as perfluorodiethyl ether.
• Preferred compounds are perfluorinated gases, such as SF6 or perfluorocarbons (perfluorinated hydrocarbons), i.e. hydrocarbons where all the hydrogen atoms are replaced by fluorine atoms, which are known to form particularly stable gas-filled microvesicles suspensions.
• perfluorocarbon includes saturated, unsaturated, and cyclic
• perfluorocarbons are: perfluoroalkanes, such as perfluoromethane, perfluoroethane, perfluoropropanes, perfluorobutanes (e.g . perfluoro-n-butane, optionally in admixture with other isomers such as perfluoro-isobutane), perfluoropentanes, perfluorohexanes or perfluoroheptanes; perfluoroal kenes, such as perfluoropropene, perfluorobutenes (e.g . perfluorobut-2ene) or perfluorobutadiene; perfluoroalkynes (e.g.
• perfluorocycloalkanes e.g. perfluorocyclobutane, perfluoromethylcyclobutane, perfluorodi methylcyclobutanes,
• Preferred saturated perfluorocarbons include, for example, CF 4 , C 2 F 6 , C 3 F 8 , C 4 F 8 , C 4 F 10 , C 5 F 12 anc j C 6 F 14 .
• the mixture may comprise a conventional gas, such as nitrogen, air or carbon dioxide and a gas formi ng a stable microvesicle suspension, such as sulfur hexafluoride or a perfluorocarbon as indicated above.
• suitable gas mixtures can be found, for instance, in Ref. 6.
• the following combinations are particularly preferred : a mixture of gases (A) and (B) in which the gas (B) is a fluorinated gas, selected among those previously illustrated, including mixtures thereof, and (A) is selected from air, oxygen, nitrogen, carbon dioxide or mixtures thereof.
• the amount of gas (B) can represent from about 0.5% to about 95% v/v of the total mixture, preferably from about 5% to 80% .
• Particularly preferred gases are SF6, C3F8, C4F10 or mixtures thereof, optionally in admixture with air, oxygen, nitrogen, carbon dioxide or mixtures thereof.
• a precursor to a gaseous substance i .e. a material that is capable of being converted to a gas in vivo.
• the gaseous precursor and the gas derived therefrom are physiologically acceptable.
• the gaseous precursor may be pH-activated, photo-activated, temperature activated, etc.
• certain perfluorocarbons may be used as temperature activated gaseous precursors. These perfluorocarbons, such as perfluoropentane or perfluorohexane, have a liquid/gas phase transition temperature above room temperature (or the temperature at which the agents are produced and/or stored) but below body temperature; thus, they undergo a liquid/gas phase transition and may be converted to a gas within the human body.
• the component of the first fluid flow may be a liquid .
• said liquid is substantially immiscible with water.
• suitable liquids are for instance those listed in Ref. 1 including e.g. alkanes, such as branched or, preferably, linear (C5-C10) alkanes, e.g. pentane, hexane, heptane, octane, nonane, decane; alkenes, such as (C5-C10) al kenes, e.g. 1-pentene, 2-pentene, 1- octene; cyclo-al kanes, such as (Cs-C8)-cycloalkanes optionally substituted with one or two methyl groups, e.g .
• alkanes such as branched or, preferably, linear (C5-C10) alkanes, e.g. pentane, hexane, heptane, octane, nonane, decane
• alkenes such as (
• cyclopentane cyclohexane, cyclooctane, 1-methyl- cyclohexane
• aromatic hydrocarbons such as benzene and benzene derivatives substituted by one or two methyl or ethyl groups, e.g . benzene, toluene,
• ethylbenzene 1,2-dimethylbenzene, 1,3-dimethylbenzene
• alkyl ethers and ketones such as di-butyl ether and di-isopropylketone
• halogenated hydrocarbons or ethers such as chloroform, carbon tetrachloride, 2-chloro-l-(difluoromethoxy)-l, l,2- trifluoroethane (enflurane), 2-chloro-2-(difluoromethoxy)-l, l,l-trifluoroethane (isoflurane), tetrachloro-l,l-difluoroethane, and particularly perfluorinated hydrocarbons or ethers, such as perfluoropentane, perfluorohexane,
• perfluoroheptane perfluoromethylcyclohexane, perfluorooctane, perfluorononane, perfluorobenzene and perfluorodecalin, methyl perfluorobutyl ether,
• said liquid may be a biocompatible oil including, for instance, esters of glycerol or natural oils as illustrated above.
• said component may go through different transition phases during the manufacturi ng process and/or subsequent storage of the suspension.
• the component may be supplied as a liquid at room temperature, then transformed into a gas (or vapour) because of the heating above T m , and
• a liquid component may be heated above its boiling point (e.g. at or around the T m ), in order to supply it as a gas or vapour; upon cooling of the microparticles at room temperature, the component then condenses, thus providing the liquid-filled microdroplets.
• the resulting suspension of calibrated liquid-filled microdroplets may go under a subsequent lyophilization process, in order to obtain a lyophilized cake which can then be stored in a vial under an atmosphere of a gas (such as those illustrated above), as described for instance in Ref. 1.
• the cake can then be reconstituted with a suitable aqueous liquid by gentle agitation to obtain a suspension of gas-filled microvesides.
• a lyoprotective agent e.g. one of those illustrated in Ref. 1
• micro particles prepared according to the method of the invention may be used in a variety of diagnostic and/or therapeutic techniques, including in particular Ultrasound and Magnetic Resonance.
• Diagnostic techniques include any method where the use of the gas-filled microvesides allows enhancing the visualisation of a portion or of a part of an animal (including humans) body, including imaging for preclinical and clinical research purposes.
• imaging techniques may be employed in ultrasound applications, for example including fundamental and harmonic B-mode imaging, amplitude modulation, pulse or phase inversion imaging and fundamental and harmonic Doppler imaging; if desired three-dimensional imaging techniques may be used.
• Microvesides for diagnostic use may be administered (e.g. by injection) at a concentration of from about 0.01 to about 1.0 ⁇ _ of gas per kg of patient, depending e.g. on their respective composition, the tissue or organ to be imaged and/or the chosen imaging technique.
• This general concentration range may of course vary depending on specific imaging applications, e.g. when signals can be observed at very low doses such as in amplitude modulation and pulse inversion imaging.
• Possible other diagnostic imaging applications include scintigraphy, light imaging, and X-ray imaging, including X-ray phase contrast imaging.
• Therapeutic techniques include any method of treatment (as above defined) of a patient which comprises the use of microparticles either as such (e.g. ultrasound mediated treatment ischemic strokes, clot lysis etc.) or in combination with a therapeutic agent (e.g. for the delivery of a bioactive compound to a selected site or tissue, such as in gene therapy or in the use as vaccine), and which is capable of exerting or responsible to exert a biological effect in vitro and/or in vivo, either by itself or upon specific activation by various physical methods (including e.g.
• Microvesicles for therapeutic treatments may typically be administered in a concentration of from about 0.01 to about 5.0 ⁇ _ of gas per kg of patient, depending e.g. from their respective composition, the type of subject under treatment, the tissue or organ to be treated and/or the therapeutic method applied.
• the materials were added with the above molar ratios at a concentration of 20 mg/mL to a 2: 1 (volume ratio) chloroform/methanol mixture under stirring at 60°C until complete dissolution the amphiphilic material .
• the solvent was then evaporated under reduced pressure and the obtained film was dried overnight under reduced pressure.
• the dried material was then redispersed (at concentrations of from 5 to 15 mg/mL, as detailed in the part "preparation of microvesicles") in a mixture of glycerol, propylene glycol, and water (GPW, volume ratio of 5: 5:90) at 60 °C under stirring for 30 minutes.
• TRIS buffer (20 mM) was added to adjust the pH value at 7.
• the dispersion was then sonicated by using a tip sonicator (Branson Sonifier 250) to homogenously disperse the material .
• the preparations were then filtered using a polycarbonate filter (0.45 ⁇ pore size), cooled down to room temperature and degassed.
• Transition temperatures of amphiphilic materials were determined by using commercial Differential Scanning Calorimetry DSC-Q2000, with Tzero aluminum crucibles (TA Instruments, New Castle, DE USA). System calibration, including temperature and heat flow, was carried out with Indium metal (enthalpy of fusion 28.71 J/g ⁇ 0.5 J/g; onset temperature of fusion 156.6 °C ⁇ 0.25 °C).
• Dispersions of the amphiphilic material (pure or mixtures) in GPW/TRIS were prepared according to the procedure described above for the DSC measurements (about 30 ⁇ _ each, concentration 10 mg/mL).
• DSC measurements were carried out by heating at a constant temperature rate of 2 °C/min over a temperature range from 20 °C to 80 °C. Nitrogen was used as purging gas at a flow rate of 50 mL/min.
• Microvesicles were synthesized using a commercially available microfluidic flow- focusing device (Dolomite microfluidics, small droplet chip, 14 ⁇ etch depth, part no. 3200136), mounted in a commercially available chip holder (Dolomite microfluidics, part numbers: 3000024, 3000109, 3000021) allowing for the leak tight connection of the chip to the gas and liquid supply tubing (Peek Upchurch, 1/16 inch O.D, 150 ⁇ I.D.).
• the microvesicles formation channel had a width of 17 ⁇ and a length of 135 ⁇ .
• the overall channel depth was 14 ⁇ .
• the chip and its holder were positioned in an optically transparent temperature controlled water bath that was mounted on an inverted microscope equipped with a 20 times magnification objective (Olympus, LMPLAN 20x) and a CCD camera (Lumenera, LM156M).
• the liquid co-flow rate was controlled using a syringe pump (Harvard PHD4400).
• the gas (SF6) was pressure controlled using a pressure regulator (Omega, PRG101-25) connected to a pressure sensor (Omega, DPG1000B-30G). Individual microvesicles were automatically detected from the recorded optical images to measure their sizes offline on a PC using Matlab software (The Mathworks Inc., Natick, MA).
• Figures 4a to 4e show the results obtained using a liquid co-flow of the DSPC/DPPA/DPPE-PEG5000 suspension (Tm 55 °C) as prepared above, with concentrations of amphiphilic material ranging from 5 to 15 mg/mL (fig. 4a-4e, respectively) and at different temperatures of the thermostatic bath containing the microfluidic chip (similar to the one illustrated in figure 2).
• Squares ( ⁇ ) indicate experiments conducted under the dripping regime, while triangles (A) indicate experiments conducted under the more preferred jetting regime.
• the percentage of coalescence (C [%]) of microvesicles is generally lower in the dripping regime compared to the jetting regime.
• the advantageous effect of reducing coalescence by increasing the temperature is apparent.
• Figure 5 shows the results obtained using a liquid co-flow of the
• setup A the suspension was passed through a heat exchanger (at 20 °C) 3 ms after microvesicle formation, to suddenly reduce the temperature of the suspension below T m , particularly at room
• tubing exiting from the chip in the thermostatic bath was passed through a heat exchanger after approximately 0.5 mm from the chip's exit.
• setup B (late-cooled suspension)
• the suspension was passed through the same heat exchanger only 3 minutes after microvesicle formation.
• the tubing exiting from the chip was replaced by a tubing with an inner diameter of 1 mm and this tubing was kept in the thermostatic bath for a length of approximately 20 cm and then passed through a heat exchanger.

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