JP2006306751A - Diagnostic imaging agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diagnostic imaging agent used in both MRI (magnetic resonance imaging) and ultrasonic diagnostic equipment, having high imaging ability in ultrasonic diagnostic images and transferable from blood vessels to tissues. <P>SOLUTION: The diagnostic imaging agent contains a liposoluble or amphiphilic paramagnetic material or a super paramagnetic material, a water insoluble material having ≤37°C boiling point and a water insoluble material having >37°C boiling point and is brought to be fine particles with a stabilizer. The agent gives imaging effects in MRI, has little danger in bumping and gives site-specific ultrasonic imaging effects using phase changes from liquid to gas. Owing to those effects, safe diagnosis/therapeutic techniques are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a diagnostic contrast agent used in combination with an image diagnostic apparatus.

  Image diagnostic modalities such as X-ray CT, MRI, and ultrasonic diagnostic equipment have long become essential tools in the medical field. These are images of differences in CT values, spin relaxation times, and acoustic impedances in vivo, and these differences in physical properties exclusively reflect the structure (form) of the body. Called. On the other hand, what performs imaging of a part which is structurally different even in the same structure is called “functional imaging”. Among these functional imaging, in particular, what visualizes the existence state of biological constituent molecules such as proteins is often called “molecular imaging”. Molecular imaging is one of the research areas that is currently attracting the most attention because it is expected to be applied to elucidation of life phenomena such as development and differentiation and diagnosis and treatment of diseases. In molecular imaging, a “molecular probe”, which is a substance having a structure with selectivity for biological constituent molecules, is often used. In this case, a structure that can be detected by some physical means is added to the molecular probe, Visualize the distribution of molecular probes at. Non-Patent Document 1 describes an example of a molecular probe for targeting a tumor. Peptides, antibodies, etc. are the main molecular probes.

  A combination with morphological imaging is indispensable for diagnosing diseased sites and pathological conditions using such molecular imaging. The positioning of morphological imaging at this time is primarily to identify the location of the lesion site in the tissue suggested by molecular imaging. In addition to specifying such a location, it is important not only for confirming whether the lesion site suggested biochemically by molecular imaging is physically different from other sites. In other words, when an object placed in the dark is illuminated with a light and the shape of the object is to be known, the light is applied from a plurality of angles to obtain more detailed information on the shape. From this point of view, it is desirable to use a plurality of modalities based on different principles for morphological imaging combined with molecular imaging. For this reason, in the early diagnosis of a disease, the usefulness of a system in which molecular imaging and morphological imaging are fused and which can cope with a plurality of morphological imaging modalities is extremely high. The construction of such a system requires a contrast agent that can be combined with a molecular probe and can be used in a plurality of morphological imaging modalities.

  Here, when comparing X-rays, MRI, and ultrasound, which are exclusively used for morphological imaging, X-rays and MRI perform imaging at medium and low speeds in a wide area, whereas ultrasound applies a probe. It features real-time imaging of a narrow area. From this, it is considered that a combination of either X-rays or MRI and ultrasound is effective as the plurality of morphological imaging modalities. When targeting a tissue other than a blood vessel, as such a contrast agent, a droplet having a particle size of 200 nm or less that can be transferred from a blood vessel to a tissue, as shown in Non-Patent Document 2, A shape having a high-boiling fluorocarbon as an ultrasonic contrast agent and an amphiphilic Gd chelate as an MRI contrast agent has been devised. More specifically, the present contrast agent is obtained by solubilizing high-boiling fluorocarbons such as perfluorooctyl bromide (PFOB) insoluble in water using a surfactant by high-pressure emulsification and having a particle size of 200 nm or less. The amphiphilic Gd chelate as shown in Non-Patent Document 3 is used as a part of the surfactant. Further, a fat-soluble iron oxide colloid as shown in Non-Patent Document 4 can also be used by enclosing it in a suitable emulsion. With such a configuration, the size can be transferred from the blood vessel to the tissue, and it functions as a contrast agent sensitive to both MRI and ultrasound.

Allen (2002) Nature Rev. Cancer 2: 750-763 Winter et al., (2003) Magnetic Resonance in Medicine 50: 411-416 Grant et al., (1989) Magnetic Resonance in Medicine 11: 236-243 Sahoo et al., (2001) Langmuir 17: 7907-7911

Conventional techniques using high-boiling fluorocarbons as an ultrasound contrast agent generally have a problem in that the imaging ability is lower than that of microbubbles generally used as an ultrasound contrast agent. Although this problem visualizes the difference in acoustic impedance in an ultrasonic diagnostic apparatus, the acoustic impedance of living body (soft tissue), high-boiling fluorocarbon (PFOB), and microbubble (air) is about 1.6, about 0.9 and about 0.004 (10 ⁶ kg / m ² · s), and microbubbles have an acoustic impedance that is about 400 times different from that of living organisms, whereas high-boiling fluorocarbons have 2 This is because there is no difference between the two. In addition, microbubbles have the advantage that they can be separated from tissue signals by appropriate filtering because they produce a nonlinear response to ultrasonic irradiation and generate harmonics and subharmonics. Since high-boiling fluorocarbons are used in a liquid state, they are not suitable for highly sensitive measurement using such a nonlinear response.

  Due to the low sensitivity of ultrasound diagnostic devices, there are also limitations on therapeutic applications. When a disease site can be determined at an early stage by a tissue-selective contrast medium, minimally invasive treatment is desired from the viewpoint of balance between risk and effect. In order to reduce the invasiveness, it is necessary to treat the diseased part selectively. Usually, only the affected part is destroyed by external physical stimulation such as light, ultrasound and electromagnetic waves, or the drug is "activated" only by the affected part. Do. In such selective treatment, treatment is often performed while ensuring safety using an ultrasonic diagnostic apparatus capable of observing the affected area in real time. However, in the conventional technique, since a high-sensitivity contrast effect relating to ultrasound cannot be expected, there is a problem in that the affected area cannot be observed with high sensitivity using an ultrasonic diagnostic apparatus.

  As described above, as a means for providing a contrast agent having a size that is sensitive to both MRI and ultrasound and that can be transferred from a blood vessel to a tissue, the technique disclosed in Non-Patent Document 2 can be cited. However, the technique of Non-Patent Document 2 has a problem that high-sensitivity ultrasonic contrast using the non-linear response of microbubbles cannot be performed, and it cannot be used for minimally invasive treatment.

  As a result of intensive investigations for obtaining a contrast agent capable of migrating from blood to tissue, the present inventors have used a liquid microbubble precursor as an ultrasound contrast agent, It was conceived that the object can be achieved by using a fat-soluble or amphiphilic paramagnetic or superparamagnetic substance as a contrast agent and combining them into an emulsion form, and the present invention has been completed.

The imaging and therapeutic agent in the present invention can take the form of an emulsion in which a poorly water-soluble microbubble precursor and a hardly water-soluble paramagnetic or superparamagnetic substance are stabilized by a surfactant. The poorly water-soluble microbubble precursor is not particularly limited as long as it is a substance that forms microbubbles by irradiation with relatively weak ultrasonic waves of about 10 W / cm ² or less in the form of an emulsion and has low biotoxicity. Desirably, it is a fluorinated hydrocarbon. In addition, when a single component low boiling point fluorocarbon is used, if the fluorocarbon used has a low boiling point, it is vaporized before ultrasonic irradiation to generate microbubbles, which is difficult in terms of safety. On the other hand, when the boiling point of fluorinated hydrocarbons is high, high ultrasonic intensity is required, which is also difficult for safety. Therefore, fluorinated hydrocarbons with different boiling points are used, and only some of the components are nano-sized. It is possible to adopt a technique in which the remaining components are secondarily vaporized using the absorption of ultrasonic energy by the generated bubbles. In this case, at least one kind of fluorinated hydrocarbon having a temperature of 37 ° C. or lower and at least one kind of fluorinated hydrocarbon having a boiling point higher than 37 ° C. can be used.

  There are no particular limitations on the poorly water-soluble MRI contrast agent in the present invention. When performing positive contrast, a sparingly water-soluble paramagnetic chelate such as Gd or a sparingly water-soluble superparamagnetic fine particle such as iron oxide having a primary particle diameter of 5 nm or less is used. When performing negative contrast, an oxidation of 10 nm or more is performed. It is desirable to use slightly water-soluble superparamagnetic fine particles such as iron.

  In addition, the imaging and therapeutic agent in the present invention can take the form of an emulsion in which a poorly water-soluble microbubble precursor is stabilized with a surfactant and an amphiphilic paramagnetic substance. There is no particular limitation on the amphiphilic paramagnetic substance, but it is desirable to use a paramagnetic atom chelate such as Gd bound to phospholipid.

  According to the present invention, the risk of bumping is low, and a contrast effect can be obtained selectively using a phase change from liquid to gas, and temperature monitoring in heat treatment can be performed. These effects can provide a safe diagnosis / treatment technique.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

An imaging and diagnostic agent in the form of an emulsion in which a slightly water-soluble microbubble precursor is stabilized with an amphiphilic paramagnetic substance and a surfactant. First, as an amphiphilic paramagnetic substance, Gd-diethylenetriaminepentaacetic acid (Gd- Gd-DTPA-PE obtained by chemically binding DTPA) to egg yolk phosphatidylethanolamine (PE), which is a phospholipid, was prepared according to Non-Patent Document 3.

  Thereafter, the following components were added, and homogenized for 1 minute at 9500 rpm at ice temperature in ULTRA-TURRAX T25 (Janke & Knukel, Staufen Germany) while slowly adding 20 ml of distilled water.

Gd-DTPA-PE 0.1g
Glycerol 2.0g
α-Tocopherol 0.02g
Cholesterol 0.1g
Lecithin 1.0g
Perfluoropentane Ng
Perfluoroheptane (0.2-N) g
(However, N has a value between 0 and 0.2)

  This emulsion was subjected to a high pressure emulsification treatment at 20 MPa for 2 minutes in Emulsiflex-C5 (Avestin, Ottawa Canada), and filtered through a 0.4 μm membrane filter. Through the above treatment, a substantially transparent microemulsion was obtained. It was measured by LB-550 (Horiba, Tokyo) that 98% or more of the obtained microemulsion had a diameter of 200 nm or less. An example of the results is shown in FIG. When it is necessary to obtain an emulsion larger than 200 nm depending on the purpose, the high pressure emulsification treatment can be omitted.

  The function of the obtained microemulsion as a contrast agent for MRI was evaluated as follows. First, 15 ml of a microemulsion having a Gd concentration of 0.1 and 0.5 mM was put in a plastic test tube having a diameter of 10 mm and imaged with a 1.5 T nuclear magnetic resonance imaging apparatus (Hitachi Medical Strates II). . The signal intensity ratio of the microemulsion to the physiological saline when TR / TE = 500/20 msec was 1.3 and 1.9, respectively. Furthermore, the relaxation time of the microemulsion was measured by the CPMG method. As a result, the T1 / T2 relaxation times of the microemulsions with Gd concentrations of 0.1 and 0.5 mM were 710/181 msec and 329/132 msec, respectively, which was significantly shorter than the control saline 1050/195 msec. It was. From the above results, it was found that the emulsion obtained this time was effective as an MRI contrast agent.

  Subsequently, an example of the result of measuring the phase change from liquid to gas for function evaluation of the obtained microemulsion as an ultrasonic contrast agent will be described with reference to FIGS. FIG. 2 is a diagram showing an experimental system for performing ultrasonic irradiation and imaging. The experimental procedure will be described below. First, the water tank 1 is filled with degassed water 2 at 37 ° C. A vinyl tube 6 having an inner diameter of 2 mm filled with the microemulsion 5 is fixed to the support 3-1 using the fixtures 4-1 and 4-2. The microemulsion 5 is irradiated with 3 MHz pulsed ultrasonic waves (5 milliseconds ON / 55 milliseconds OFF) for 1 second using the ultrasonic transducer 7. The ultrasonic transducer 7 is driven by a waveform generator 8 and an amplifier 9. An ultrasonic image of the microemulsion 5 being irradiated with ultrasonic waves from the ultrasonic transducer 7 is acquired using a diagnostic probe 11 connected to the ultrasonic diagnostic apparatus 10. Note that Hitachi Medical Corp. EUB-8500 was used as the ultrasonic diagnostic apparatus, and EUP-53 (7.5 MHz) was used as the diagnostic probe.

  FIG. 3 shows the ultrasonic intensity (micron for diagnosis) required to produce a luminance change on the ultrasound image when the relative concentration of perfluoropentane relative to the total concentration of perfluoropentane and perfluoroheptane is changed. This shows the threshold value of the ultrasonic intensity that causes the generation of millimeter-sized bubbles corresponding to bumping. In addition, when the ultrasonic irradiation condition from the ultrasonic transducer 7 is changed to 1 ms ON / 59 ms OFF, 10 ms ON / 40 ms OFF, or 20 ms ON / 50 ms OFF, Results equivalent to those in FIG. 3 were obtained. Regarding the brightness change, the threshold value tended to increase as the relative density decreased. As for the bumping threshold, it can be seen that when the relative concentration is other than 0 and 1, that is, when a mixture of perfluoropentane and perfluoroheptane is used, it shows an almost constant value, and the value is the value of perfluoroheptane alone. The value was about double. By using a value having a relative density of about 0.6 to 0.9, it is possible to double the bumping threshold without changing the ultrasonic intensity threshold that causes a change in luminance. Also, a relative concentration of 0.6 or less can be used depending on the purpose. From the results shown in FIG. 3, it is possible to change the ultrasonic intensity that hardly causes bumping by the contrast agent using the low-boiling water-insoluble substance and the high-boiling water-insoluble substance in the present invention and that causes a luminance change in the ultrasonic diagnostic image. The effect of contrast agents with a phase change from liquid to gas is obvious.

  The same effect as in this example is obtained by combining pearl fluoropentane and perfluoroheptane, perfluoropentane and 2H, 3H perfluoropentane, isopentane and hexane, and isopentane and heptane as a combination of a low boiling water insoluble substance and a high boiling water insoluble substance. Also obtained using.

An imaging and diagnostic agent in the form of an emulsion in which a slightly water-soluble microbubble precursor is stabilized with a lipophilic superparamagnetic substance and a surfactant. First, as a lipophilic superparamagnetic substance, lauric acid is applied to the surface according to Non-Patent Document 4. Coated iron oxide fine particles were prepared. It was measured by LB-550 (Horiba, Tokyo) that 98% or more of the obtained fine particles have a diameter of 30 nm or less. The obtained fine particles were stored in a dispersed state in chloroform.

  Thereafter, the following components were added, and homogenized for 1 minute at 9500 rpm at ice temperature in ULTRA-TURRAX T25 (Janke & Knukel, Staufen Germany) while slowly adding 20 ml of distilled water.

Lauric acid coated iron oxide 0.5g
Glycerol 2.0g
α-Tocopherol 0.02g
Cholesterol 0.1g
Lecithin 1.0g
Perfluoropentane Ng
2H, 3H-perfluoroheptane (0.2-N) g
(However, N has a value between 0 and 0.2)

  This emulsion was subjected to a high pressure emulsification treatment at 20 MPa for 2 minutes in Emulsiflex-C5 (Avestin, Ottawa Canada), and filtered through a 0.4 μm membrane filter. A substantially transparent microemulsion was obtained by the above treatment. It was measured by LB-550 (Horiba, Tokyo) that 98% or more of the obtained microemulsion had a diameter of 200 nm or less.

  The function of the obtained microemulsion as a contrast agent for MRI was evaluated as follows. First, 15 ml of a microemulsion having an Fe concentration of 0.1 and 0.5 mM was put in a plastic test tube having a diameter of 10 mm and imaged with a 1.5 T nuclear magnetic resonance imaging apparatus (Hitachi Medical Strates II). The signal intensity ratio of the microemulsion to physiological saline when TR / TE = 2000/100 ms was set to 0.49 and 0.02, respectively. Furthermore, the relaxation time of the microemulsion was measured by the CPMG method. As a result, the T1 / T2 relaxation times of the microemulsions with Fe concentrations of 0.1 and 0.5 mM were 330/74 msec and 90/20 msec, respectively, which was significantly shorter than the control saline 1050/195 msec. It was. From the above results, it was found that the emulsion obtained this time was effective as an MRI contrast agent. The performance of the diagnostic agent of this example as an ultrasound contrast agent was equivalent to that of the diagnostic agent described in Example 1.

An imaging and diagnostic agent in the form of an emulsion in which a slightly water-soluble microbubble precursor is stabilized with an amphiphilic paramagnetic substance and a surfactant and coated with a polymer. First, as an amphiphilic paramagnetic substance, Gd -Gd-DTPA-PE obtained by chemically binding diethylenetriaminepentaacetic acid (Gd-DTPA) and egg yolk phosphatidylethanolamine (PE), which is a phospholipid, was prepared according to Non-Patent Document 3.

  Thereafter, the following ingredients were added together and homogenized for 1 minute at 9500 rpm at ice temperature in ULTRA-TURRAX T25 (Janke & Knkel, Staufen Germany) with slow addition of 20 ml of distilled water. 1,2-Diacyl-sn-Glycero-3-Phosphoethenolamine-N- [Methoxy (Polyethylene glycol) -2000] (hereinafter abbreviated as mPEG 2000 PE) is a product of Avanti (Alabama, USA) (catalog number: 880160).

Gd-DTPA-PE 0.1g
mPEG-2000-PE 0.05g
Glycerol 2.0g
α-Tocopherol 0.02g
Cholesterol 0.1g
Lecithin 1.0g
Perfluoropentane Ng
Perfluorohexane (0.2-N) g
(However, N has a value between 0 and 0.2)

  This emulsion was subjected to a high pressure emulsification treatment at 20 MPa for 2 minutes in Emulsiflex-C5 (Avestin, Ottawa Canada), and filtered through a 0.4 μm membrane filter. A substantially transparent microemulsion was obtained by the above treatment. It was measured by LB-550 (Horiba, Tokyo) that 98% or more of the obtained microemulsion had a diameter of 200 nm or less. In addition, instead of mPEG-2000-PE used in this example, 1,2-Distearoyl-sn-Glycero-3-Phosphoethanolamine-N- [Biotinyl (PolyethyleneGlycol) 2000] was used to chemically bond biotin as a molecular probe. The obtained contrast medium could be obtained.

  The function of the obtained microemulsion as a contrast agent for MRI was evaluated as follows. First, 15 ml of a microemulsion having a Gd concentration of 0.1 and 0.5 mM was put into a plastic test tube having a diameter of 10 mm and imaged with a 1.5 T nuclear magnetic resonance imaging apparatus (Hitachi Medical Strates II). . The signal intensity ratio of the microemulsion to the physiological saline when TR / TE = 500/20 msec was 1.3 and 1.9, respectively. Furthermore, the relaxation time of the microemulsion was measured by the CPMG method. As a result, the T1 / T2 relaxation times of the microemulsions with Gd concentrations of 0.1 and 0.5 mM are 700/170 msec and 320/130 msec, respectively, which are significantly shorter than the control saline 1050/195 msec. It was. From the above results, it was found that the emulsion obtained this time was effective as an MRI contrast agent. The performance of the diagnostic agent of this example as an ultrasound contrast agent was equivalent to that of the diagnostic agent described in Example 1.

The figure which shows an example of the particle size distribution of the contrast agent of this invention. The figure which shows the experimental system for producing and observing vaporization of the contrast agent of this invention. An example of a result of measuring an ultrasonic intensity threshold necessary for causing a luminance change on an ultrasonic diagnostic image and an ultrasonic intensity threshold necessary for causing bumping when the contrast medium of the present invention is irradiated with ultrasonic waves FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water tank 2 Deaerated water 3 Support tool 4 Fixing tool 5 Contrast agent 6 Vinyl tube 7 Ultrasonic transducer 8 Waveform generator 9 Amplifier 10 Ultrasonic diagnostic apparatus 11 Diagnostic probe

Claims (13)

  A contrast agent used together with an MRI and an ultrasonic diagnostic apparatus, comprising a water-insoluble substance that is a liquid when administered to a living body and that undergoes a phase change by ultrasonic irradiation to become a gas.   The medical agent for diagnostic imaging according to claim 1, wherein a water-insoluble substance having a boiling point of 37 ° C or lower that is vaporized by ultrasonic irradiation and a boiling point of 37 ° C or lower that has a boiling point higher than 37 ° C and is vaporized by the ultrasonic irradiation. An agent for diagnostic imaging, comprising a water-insoluble substance that is secondarily vaporized by ultrasonic absorption by the water-insoluble substance.   3. The diagnostic imaging agent according to claim 2, wherein the water-insoluble substance having a boiling point of 37 ° C. or lower is any one of a linear hydrocarbon, a branched hydrocarbon, a linear halogenated hydrocarbon, and a branched halogenated hydrocarbon. A diagnostic agent for imaging.   3. The diagnostic imaging agent according to claim 2, wherein the water-insoluble substance having a boiling point higher than 37 ° C. is any one of linear hydrocarbon, branched hydrocarbon, linear fluorinated hydrocarbon, and branched fluorinated hydrocarbon. A diagnostic agent for imaging.   4. The diagnostic agent for imaging according to claim 3, wherein the water-insoluble substance having a boiling point higher than 37 ° C. comprises at least one hydrogen atom or halogen atom of the water-insoluble substance having a boiling point of 37 ° C. or lower according to claim 2. A diagnostic imaging agent characterized by having a structure substituted with an alkyl group or a halogenated alkyl group.   4. The diagnostic agent for imaging according to claim 3, wherein the water-insoluble substance having a boiling point higher than 37 ° C. is obtained by replacing at least one halogen atom of the water-insoluble substance having a boiling point of 37 ° C. or less as claimed in claim 2 with a hydrogen atom. An agent for diagnostic imaging characterized by having a substituted structure.   The diagnostic imaging agent according to claim 3, further comprising a surfactant.   8. The diagnostic imaging agent according to claim 7, wherein the surfactant has a structure containing a water-soluble polymer.   9. The diagnostic imaging agent according to claim 8, wherein the water-soluble polymer contains polyethylene glycol.   3. The diagnostic imaging agent according to claim 2, comprising a paramagnetic substance physically or chemically bonded to a surfactant.   The diagnostic imaging agent according to claim 10, wherein the paramagnetic substance contains a gadolinium atom.   The diagnostic imaging agent according to claim 1, comprising a fat-soluble superparamagnetic substance.   13. The diagnostic imaging agent according to claim 12, wherein the superparamagnetic substance contains iron oxide.

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