JP5207169B2 - Ionizing radiolytic liposome, liposome preparation using the same, and method for preparing liposome - Google Patents

Description

  The present invention relates to an ionizing radiolytic liposome, a liposome preparation using the same, and a method for preparing the liposome.

  Liposomes are microscopic vesicles composed of concentric lipid bilayers. Liposomes are structurally large and spherical in size and shape, and usually range from a few hundred angstroms to millimeters compartment. The size of the vesicle is usually in the range of about 20-30000 nm in diameter. The liquid film between lamellas is usually about 3-10 nm. Liposomes are based on their overall size and lamellar structure properties in three categories: multilamellar vesicles (MLV's), single lamellar vesicles (SUV's) and large single lamellar vesicles (LUV). 's).

  Liposomes can be prepared by a number of methods, and these different types of liposomes can be prepared. For example, ultrasonic dispersion by the method of immersing a metal probe directly in a suspension of MLV's is a common method of SUV's preparation. The preparation of MLV class liposomes generally involves dissolving the lipid in a suitable organic solvent and then removing the solvent under gas or air flow. This leaves a thin film of dry lipid on the container surface. Thereafter, the aqueous solution is introduced into the container from the side of the container while stirring to release lipid molecules. This process disperses the lipid and causes lipid aggregation or liposome formation. LUVs can be made by slowly hydrating a thin layer of lipids using distilled water or an aqueous solution. Alternatively, liposomes can be prepared by lyophilization. This process involves drying the lipid solution into a film under a nitrogen stream. The film is then dissolved in a volatile frozen organic solvent, such as cyclohexane or t-butanol, frozen, and transferred to a lyophilizer to remove the solvent. Liposomes are formed as soon as an aqueous solution of the drug is added to the lyophilized lipid in order to prepare a pharmaceutical containing a water-soluble drug.

Such liposomes have been tried to be used as so-called sustained-release drugs in which a drug is encapsulated inside the liposome membrane and taken into the body, and then the drug (drug) is gradually released. For example, after administration of a drug to a patient, an attempt has been made to change the ratio of the biodegradable polymer and lipid constituting the liposome membrane in order to adjust the drug release rate (see, for example, Patent Document 1). . However, such a sustained-release drug is one in which the liposome membrane gradually degrades and releases the drug, for example, under a desired condition at a predetermined site in the living body, for example, a low pH condition. It is not decomposed by, and the control of release is insufficient.

In addition to the above-mentioned sustained release drug, for example, a liposome encapsulates a drug inside the liposome membrane, takes it into the body, reaches the site where treatment is required, and then irradiates with ionizing radiation. Attempts have been made to use the drug as a drug carrier that releases the drug at once. For example, it is attempted to polymerize a polymerizable colipid by containing a polymerizable colipid in the liposome membrane and exposing it to ionizing radiation, thereby destabilizing the liposome membrane and releasing the drug at once. (For example, refer to Patent Document 2).
However, this liposome is not preferable because it uses an artificial substance, that is, a foreign substance for the living body, as a constituent of the liposome membrane. In addition, since polymerizable lipids are used, and the substances after polymerization are expected to have a wide variety of molecular weights and chemical structures, they are not suitable as liposomes that are actually administered in vivo.

  Furthermore, for example, it has been attempted to release glucose from a liposome membrane composed of soybean lecithin by irradiation with γ rays (see, for example, Non-Patent Document 1). However, soy lecithin, which is a component of the liposome membrane, is an aggregate of various phospholipids and contains various other types of phospholipids, so that it is difficult to control the composition. Moreover, since the so-called sizing for adjusting the particle diameter is not performed, the average particle diameter and the distribution are unknown, so that it is difficult to control the drug release property. Furthermore, here, glucose having a molecular weight of 180 is released, but active agents such as anticancer agents have a molecular weight of about several hundred to 1,000, and the active agent is several tens Gy due to the irradiation of the above-mentioned γ rays. It is unclear whether release can be controlled.

On the other hand, a composition for neutron capture therapy (BNCT) containing boron and a method for using the same have been tried (see, for example, Patent Document 3). In this method, after a boron-containing compound reaches a tumor, the tumor cells are attacked by α particles generated from boron by irradiation with neutrons. Moreover, it is described that this boron-containing compound is included in a liposome in which a specific compound is embedded in order to improve the amount reaching the tumor site.
However, this composition and method of use is only directed at improving the reach of this composition to the tumor site for boron neutron capture therapy (BNCT), and there is nothing about the degradability of the liposome membrane. Not oriented. Furthermore, this liposome is used for allowing a compound containing boron to reach the tumor site, and does not encapsulate a drug therein.

Therefore, it is desired to further improve the control of the release of the active agent by irradiating with ionizing radiation after encapsulating the drug inside the liposome membrane, taking it into the body, and reaching the site where treatment is required.
Special Table 2002-520120 JP 2004-346163 A JP-T 9-501146 Nakazawa, T. et al., Radiation-induced lipid peroxidation and membrane permeability in liposomes, Int. J. Radiat. Biol., 38 (1980) pp537-544

The present invention has been made in view of the above problems, and the present invention relates to liposomes with improved control of active drug release by irradiation with ionizing radiation, liposome preparations containing a drug in liposomes, and liposome membranes. It aims at providing the preparation method of a liposome by adjusting the molar ratio of a component.

In the liposome of the present invention, the membrane component comprises (A) an unsaturated phospholipid or derivative thereof in which the acyl group is a linoleic acid residue, (B) a saturated phospholipid or derivative thereof in which the acyl group is a stearic acid residue, and (C) A film comprising cholesterol or a derivative thereof and formed from the film component is at least partially decomposed by exposure to ionizing radiation. A ¹⁰ B-containing compound can be included (for example, encapsulated) in the membrane. Among these, for the component (A), an unsaturated phospholipid whose acyl group is an unsaturated linoleic acid residue is preferable, and for the component (B), a saturated phospholipid whose acyl group is a stearic acid residue is preferable. As for the component (C), cholesterol is preferable.

  In the liposome, the molar ratio of the component (A) to the whole membrane component is 0.05 or more and 0.5 or less, and the molar ratio of the component (C) is 0.3 or more and 0.6 or less. And the balance is preferably the component (B). The molar ratio of the component (A) is more preferably 0.1 or more and 0.2 or less. In the liposome, the total lipid molar concentration of the liposome is preferably 0.01 to 10 mM. It is preferable that the dose rate of the ionizing radiation is 0.01 to 1 Gy / min.

Furthermore, the liposome preparation of the present invention is characterized by containing (for example, encapsulating) a drug (drug) in the liposome. The liposome preparation of the present invention can also contain (for example, encapsulate) a ¹⁰ B-containing compound in the liposome. In this case, the liposome membrane can also be prepared so as to be resistant to thermal neutron rays. Moreover, as said drug, an anticancer agent is preferable.
Moreover, the preparation method of a liposome adjusts the molar ratio of said (A) component in 0.05-0.5, and adjusts the molar ratio of said (C) component in 0.3-0.6. The remainder is the component (B). That is, the above-mentioned liposome is obtained by irradiation of the liposome (membrane) formed from the liposome membrane component by adjusting the molar ratio of the component (A), the component (B) and the component (C). Degradability can be adjusted.

According to the liposome and liposome preparation of the present invention, the control of the release of the active agent by irradiation with ionizing radiation is improved. For example, after the drug is encapsulated inside the liposome membrane, taken into the body, and reaches the site where treatment is required, the release control of the active agent when irradiated with ionizing radiation is further improved. In addition, for example, by adjusting the components of the liposome membrane, after reaching the site where treatment is required, the liposome is decomposed by irradiating with ionizing radiation, and the drug is more effectively (for example, once) applied to the site requiring treatment. Can be given. Furthermore, for example, by using ionizing radiation having anticancer activity as ionizing radiation and using an anticancer agent as a drug, cancer cells that could not be treated with only ionizing radiation at a treatment site are treated with an anticancer agent released from liposomes. Can be removed.
Further, according to the liposome membrane of the present invention to liposomes and liposome formulations containing ^{10 B-containing} compound, it is possible to control the degradation of the liposome membrane, it is improved control of release of the active agent. In addition, thermal neutron rays have a small energy, so the influence on the human body can be reduced. Furthermore, since α particles generated by boron neutron supplementation reaction of ¹⁰ B-containing compounds and ⁷ Li nuclei themselves have anticancer activity, Can be increased.
Furthermore, according to the method for preparing a liposome of the present invention, since the liposome of the present invention is composed of three lipid components, the composition ratio can be changed, so that the degradability (membrane permeability) of the liposome is controlled. In particular, it can be controlled in the range of several Gy to several kGy.

  In the liposome of the present invention, the membrane component comprises (A) an unsaturated phospholipid or derivative thereof in which the acyl group is a linoleic acid residue, (B) a saturated phospholipid or derivative thereof in which the acyl group is a stearic acid residue, and (C) A film comprising cholesterol or a derivative thereof and formed from the film component is at least partially, preferably completely decomposed by exposure to ionizing radiation. The liposome of the present invention may contain unavoidable impurities to the extent that it does not affect the effect of the present invention, that is, the control of the release of the active agent by irradiation with ionizing radiation. This will be described in detail below.

  The term “liposome” means a microscopic vesicle composed of lipid bilayer (s). Structurally, liposomes are from long cylindrical to spherical in size and shape, and are usually 100 ± 10 nm in diameter, but may be as small as 25 nm and as large as 500 nm. Liposomes may contain one or more bilayer (s). Liposomes can contain drugs in liposomes.

The term “phospholipid” refers to a lipid having a phosphate ester and / or a phosphonate ester among lipids that are long chain molecules containing fatty acids capable of forming liposomes under appropriate liposome forming conditions. Specific examples include glycerophospholipid and sphingophospholipid. Among these, glycerophospholipid is preferable.

すなわち、アシル基が不飽和リノール酸残基である不飽和リン脂質若しくはその誘導体である。式中Ｒは、任意の置換基であってよいが、生体適合性を考慮すると、コリン残基、エタノールアミン残基、水素が好ましく、さらに、コリン残基、エタノールアミン残基、特にはコリン残基がより好ましい。すなわち、上記化学式中、２本のリノール酸残基（構造）を有し、Ｒがコリン残基であるジリノレオイルホスファチジルコリン（ＤＬＯＰＣ）が最も好ましい。このようなリノール酸リン脂質を使用することにより、Ｘ線感受性を高めることが可能になる。 The component (A) constituting the liposome membrane of the present invention is a compound represented by the following chemical formula:

That is, an unsaturated phospholipid or derivative thereof in which the acyl group is an unsaturated linoleic acid residue. In the formula, R may be an arbitrary substituent, but in consideration of biocompatibility, a choline residue, an ethanolamine residue, and hydrogen are preferable, and a choline residue, an ethanolamine residue, particularly a choline residue. Groups are more preferred. That is, in the above chemical formula, dilinoleoylphosphatidylcholine (DLOPC) having two linoleic acid residues (structure) and R being a choline residue is most preferable. By using such linoleic acid phospholipid, X-ray sensitivity can be increased.

  In addition, the ratio (molar ratio) of the unsaturated phospholipid (A) component in the liposome membrane is preferably 0.05 mol or more, more preferably 0.1 mol or more, relative to the entire liposome membrane. Moreover, as the upper limit, 0.5 mol or less is preferable, 0.3 mol or less is more preferable, and 0.2 mol or less is more preferable. That is, 0.1 to 0.2 mol is a more preferable range. If the ratio (molar ratio) of the unsaturated phospholipid as component (A) is less than 0.05 mol, the ionizing radiation sensitivity index (IRSI) described later is small, such being undesirable. Further, if the ratio (molar ratio) of the unsaturated phospholipid that is the component (A) exceeds 0.5, the ionizing radiation sensitivity index (IRSI) is similarly reduced, which is not preferable. Such unsaturated phospholipids can be prepared by known methods. Moreover, it is available as a commercial item.

すなわち、アシル基がステアリン酸残基である飽和リン脂質若しくはその誘導体である。式中Ｒは、任意の置換基であってよいが、生体適合性を考慮すると、コリン残基、エタノールアミン残基、水素が好ましく、さらに、コリン残基、エタノールアミン残基、特にはコリン残基がより好ましい。すなわち、上記化学式中、２本のステアリン酸残基（構造）を有し、Ｒがコリン残基であるジステアロイルホスファチジルコリン（ＤＳＰＣ）が最も好ましい。 The component (B) constituting the liposome membrane of the present invention is a compound represented by the following chemical formula:

That is, it is a saturated phospholipid or derivative thereof in which the acyl group is a stearic acid residue. In the formula, R may be an arbitrary substituent, but in consideration of biocompatibility, a choline residue, an ethanolamine residue, and hydrogen are preferable, and a choline residue, an ethanolamine residue, particularly a choline residue. Groups are more preferred. That is, in the above chemical formula, distearoylphosphatidylcholine (DSPC) having two stearic acid residues (structure) and R being a choline residue is most preferable.

  Further, the ratio (molar ratio) of the saturated phospholipid (B) component in the liposome membrane is preferably from the entire liposome membrane to the unsaturated phospholipid (C) and (C) relative to the entire liposome membrane. The total molar ratio with the component cholesterol can be subtracted (remainder). Moreover, 0.2 mol or more is preferable with respect to the whole liposome membrane, and 0.2-0.6 mol can also be made more preferable. Such saturated phospholipids can be prepared by known methods. Moreover, it is available as a commercial item.

すなわち、コレステロール若しくはその誘導体である。式中、Ｒは、任意の置換基であつてよいが、生体適合性を考慮すると、水素、又は低級炭化水素（例えば、炭素数１〜４の炭化水素）が好ましく、中でも水素がより好ましい。 Component (C) constituting the liposome membrane of the present invention is a compound represented by the following chemical formula:

That is, cholesterol or a derivative thereof. In the formula, R may be an arbitrary substituent, but considering biocompatibility, hydrogen or lower hydrocarbon (for example, hydrocarbon having 1 to 4 carbon atoms) is preferable, and hydrogen is more preferable.

Moreover, it is preferable that the ratio (molar ratio) of cholesterol or these derivatives which are (C) component in a liposome membrane shall be 0.2 or more with respect to the whole liposome membrane, and also 0.3 or more. The upper limit is preferably 0.65 or less, and more preferably 0.6 or less. Therefore, the range of 0.3 or more and 0.6 or less is a more preferable range. If the molar ratio of the component (C), cholesterol or a derivative thereof, is less than 0.2, the particle size of the liposome membrane is not stable, and if it exceeds 0.65, liposome formation becomes impossible.
Such cholesterol or derivatives thereof can be prepared by a known method. Moreover, it is available as a commercial item. In addition, the blending (use) of cholesterol is preferable in that cholesterol itself is a constituent component of the human body and hardly adversely affects the human body.

  The ratio (molar ratio) of each of the components (A) to (C) in the liposome membrane is such that the molar ratio of the component (A) is 0.05 or more and 0.5 or less, The ratio is 0.3 or more and 0.6 or less, and the balance is the component (B) (that is, the molar ratio of the component (B) is the following formula, the molar ratio of the component 1- (A)-(C) component The molar ratio of the component (A) is preferably 0.1 to 0.2 because the control of the liposome membrane by irradiation with ionizing radiation can be performed more easily.

The liposome of the present invention is substantially composed of the above-mentioned components (A) to (C), but contains components unavoidable for the production of the liposome membrane, such as impurities, in a range that does not hinder the effects of the present invention. May be. The total lipid concentration of the liposome (suspension) of the present invention is preferably lower in order to realize degradation of the liposome at a low dose, and the total lipid concentration is more preferably 10 mM or less. The lower limit of the total lipid concentration is preferably 0.01 mM or more.
The particle size of the liposome (suspension) of the present invention is preferably 200 nmφ or less, and more preferably 100 nmφ or less to reticuloendothelial cells existing in tissues such as liver and spleen. This is preferable because it suppresses the uptake of. The lower limit of the particle size of the liposome (suspension) is preferably 50 nmφ or more in diameter.

In the present invention, the ¹⁰ B-containing compound encapsulated in the liposome membrane may be a compound containing ¹⁰ B, and examples thereof include BSH ( ¹⁰ B-enriched sodium mercaptododecaborate), BSSB, BSAA, BSAM, and BPA. . Among these, BSSB, BSAA, and BSAM are preferable from the viewpoint of low irritation to the liposome membrane.
BSSB can be prepared, for example, by oxidizing 2 mol of BSH with hydrogen peroxide or the like. BSAA can be prepared by the reaction of BSC and iodoacetic acid (IAA), and BSAM can be prepared by the reaction of BSC and iodoacetamide (IAM). FIG. 7 shows a synthesis example (preparation example) of a boron-containing compound.
In addition, the form of the ¹⁰ B-containing compound may be any form, but the ¹⁰ B cluster compound contains a large amount of ¹⁰ B per molecule (12), and the water solubility is extremely high. Therefore, it is preferable.

Amount of enclosed in liposomes of ^{10 B-containing} compound (concentration) dose thermal neutron beam irradiated can be appropriately determined depending on the reactivity with the liposome membrane of ^{10 B-containing} compound. ^{When a} large amount of the ¹⁰ B-containing compound is blended, the liposome membrane tends to be destabilized due to the interaction of the ¹⁰ B-containing compound itself with the liposome membrane and the difference in osmotic pressure inside and outside the liposome membrane. It is 6% by weight as ¹⁰ B with respect to the whole liposome membrane (formulation) (100% by weight). For example, it is determined as 0.5 to 6% by weight, preferably 1 to 5% by weight as ¹⁰ B with respect to the entire liposome membrane (formulation) (100% by weight).
Even when a ¹⁰ B-containing compound is encapsulated in the liposome, the components of the liposome membrane can be composed of the components (A), (B), and (C) described above, and the molar ratio thereof is also the same. Can be prescribed. For example, the molar ratio of (a) component: (b) component: (c) component is about 0.05 to 0.3: 0.1 to 0.65: 0.3 to 0.6.
In this case, as described later, it is possible to improve the control of the release of the active agent by effectively adjusting the direct and indirect effects involved in the degradation of the liposome membrane by thermal neutron irradiation. In addition, (A) component is indispensable for this liposome. Liposomes containing only component (B) and component (C) do not degrade at doses of 100 Gy or less.
The liposome membrane of the present invention can also be prepared so that it is preferably resistant to thermal neutron rays. In addition, the particle size (φ) of the liposome when encapsulating the ¹⁰ B-containing compound in the liposome can be adjusted to, for example, 10 nm to 200 nm, preferably 50 nm to 150 nm, more preferably 80 nm to 120 nm.

Next, in the liposome preparation of the present invention, a drug (drug) can be encapsulated in the liposome. Various drugs can be used as drugs (drugs) included in the liposome. For example, anticancer drugs (agents), antiangina drugs, antiarrhythmic drugs, antiasthmatic drugs, antibiotics, antidiabetic drugs, antifungal drugs, antihistamines, antihypertensive drugs, anthelmintic drugs, antitumor drugs, antivirals Drug, cardiac glycoside, herbicide, hormone, immunomodulator, monoclonal antibody, neurotransmitter, nucleic acid, protein, radiocontrast agent, radionuclide, sedative, analgesic, steroid, tranquilizer, vaccine, pressor, anesthesia Includes drugs such as drugs, peptides and the like. Of these, anticancer drugs (agents) have both effects on treatment of cancer cells with ionizing radiation and treatment on cancer cells by release of drugs (anticancer drugs) due to degradation of the liposome membrane by ionizing radiation. preferable. As the anticancer agent, for example, cisplatin, carboplatin and the like can be used. Of these, carboplatin is preferably used because its molecular weight (size) and water solubility are suitable for controlling the release of a drug by the degradation of the liposome membrane by ionizing radiation.
The concentration of these drugs (active ingredients) can be determined as appropriate. For example, the concentration is up to 5% by weight, for example, 2% to 3% by weight with respect to the whole liposome (membrane). Moreover, the dosage of such a liposome preparation is arbitrarily determined.

Next, a method for producing a liposome membrane and including a drug in the liposome membrane will be described.
The liposome of the present invention can be prepared, for example, by the Bangham method (see J. Mol. Biol. 13, 238 (1965)).
First, a chloroform solution and a drug solution (model drug calcein solution) for each of the components (A) to (C) are prepared. Next, the molar ratio (for example, DLOPC: DSPC: CHOL) and total (lipid) mole number to be adjusted are determined for the solutions of these components (A) to (C), and each volume (A) is determined accordingly. A liposomal membrane can be prepared by taking a (lipid) solution of the component to component (C) in a container (an eggplant-shaped flask) and evaporating the solvent (chloroform) with, for example, a rotary evaporator.
To the liposome membrane obtained as described above, a drug solution (for example, calcein solution) is added in the minimum amount capable of forming multilamellar liposomes (MLV), and the solvent is distilled off by, for example, a rotary evaporator. Encapsulated multilamellar liposomes (MLV) can be made.

  Furthermore, in the present invention, sizing can be performed by filtering the MLV suspension obtained above with a filter to produce a single membrane liposome of a desired size (for example, ˜100 nmφ). The MLV suspension thus obtained may be purified before use.

The solution should be noted, in the case where the encapsulated drug (drug) and ^{10 B-containing} compound into the liposome membrane is dissolved mixed solution of the drug and ^{10 B-containing} compound, for example, a drug and ^{10 B-containing} compound in saline Can be performed using the same method as described above.

A liposome preparation containing such a drug is administered to a human body and then guided to a site requiring treatment. In addition, by binding a targeting reagent to the liposome membrane, the liposome preparation can be more accurately guided to the site requiring treatment. Specifically, for example, at least one peptide can be linked to the liposome and targeted to a tumor site via this peptide. Peptides that target liposomes to tumor sites include peptide sequences, peptide fragments, antibodies, antibody fragments and antigens. Antibodies specific for tumor cells can be linked to liposomes, thereby allowing selective targeting. Such antibodies selectively bind to antigens on tumor cells, thereby bringing the liposomes into close proximity to tumor tissue or malignant tissue. By binding the antibody to the tumor antigen, the liposome can be linked to the tumor tissue. Thereafter, as described below, ionizing radiation can cause release of liposome contents, such as antitumor substances. Certain antigens can also be bound to liposomes.
Thus, by binding the liposome to the target-directing substance, the drug can be effectively given (transported) to the site requiring treatment.

Next, the type and dose of ionizing radiation irradiated to the liposome will be described.
Examples of the ionizing radiation include charged particle beams such as α rays and β rays, and electromagnetic waves such as X rays and γ rays. Liposome degradation is caused by radical species generated by the effect of these ionizing radiations, so any ionizing radiation is effective. Of these, charged particle beam and X-ray are preferable. In the present invention, the neutron beam preferably does not include a thermal neutron beam.
The dose of radiation is not limited as long as the liposome membrane can be decomposed after administration to the human body, and is preferably 1 to 100 Gy, more preferably 1 to 20 Gy around the liposome. In addition, since it is a case where X-ray is used as ionizing radiation and linoleic acid unsaturated phospholipid is used as the component (A) constituting the liposome, it is preferable because very high radiation sensitivity is obtained.
As for the radiation dose rate (radiation dose per unit time), a lower dose rate is preferred because liposome decomposition is more likely to occur. The dose rate is preferably 1.0 Gy / min or less. The lower limit of the dose rate is preferably 0.01 Gy / min or more.

  In addition, when a diagnostic substance is included in the liposome membrane, the diagnostic substance released from the liposome can be scanned and recorded using a molecular imaging technique after the diagnostic substance is released by irradiation. . This allows early detection of tumors and other malignant tumors. Alternatively, radiosensitive liposomes can be stained using dyes, fluorescent molecules, radioisotopes and the like. Moreover, the liposome membrane of the present invention is composed of the three lipid components (A) to (C) as described above, but the liposomal degradability (membrane permeability) can be changed by changing the composition ratio. Can be controlled (several Gy to several kGy). Therefore, for example, by putting reagents A and B inside and outside the liposome membrane and increasing the permeability of the liposome by ionizing radiation, A and B can be brought into contact and reacted to cause color development. The dose can be estimated based on the degree of color development. Furthermore, when the dose rate of the liposome of the present invention is increased, the dose necessary for releasing the encapsulated substance also increases, and therefore it may be used for measuring the dose rate.

Next, a method for releasing a drug from a liposome preparation containing a drug (drug) and a ¹⁰ B-containing compound in the liposome membrane will be described.
When a liposome preparation containing a ¹⁰ B-containing compound in a liposome is irradiated with thermal neutron rays, the ¹⁰ B-containing compound absorbs the thermal neutron rays and α is obtained by so-called boron neutron capture reaction ( ¹⁰ B (n, α) reaction). Lines, ⁷ Li nuclei, etc. are emitted. The energy of heavy charged particles (a kind of ionizing radiation) such as α rays (particles) and ⁷ Li nuclei (particles) is applied to membrane components, particularly lipid components, and the liposome membrane is directly decomposed (direct effect). . In addition, α-rays (particles) generated by boron neutron capture reaction, ⁷ Li nuclei (particles), and addition reactions by OH radicals generated around the tracks of secondary electrons and hydrogen abstraction reactions cause the liposome membrane components to become free radicals and be decomposed. (Indirect effect). As described above, the irradiation of the thermal neutron beam raises the permeability of the liposome membrane or breaks the membrane, and the encapsulated drug is released.
Of the above-mentioned degradation of the liposome membrane, the degradation due to the direct effect is carried out in all components (components A, B, C) of the liposome membrane, and the degradation due to the indirect effect mainly involves lipid molecules having unsaturated bonds. It is presumed to be obtained in the component (A) of the liposome membrane.
The thermal neutrons are other ionizing radiation, for example, the amount of energy in comparison with such γ-rays is small, it is captured very efficiently by ^{10 B} of ^{10 B-containing} compound, also direct effects and, as described above Since the indirect effect can be adjusted, the controlled release of the active agent can be improved.

The thermal neutron beam used in the present invention is irradiated after the liposome preparation reaches the site requiring treatment. The amount of thermal neutron irradiation can be determined by the type and amount of the ¹⁰ B-containing compound contained in the liposome. For example, the irradiation amount of the thermal neutron beam is 1.0 × 10 ^{9 to} 3.0 × 10 ⁹ n / cm ² / s, and preferably 1.0 × 10 ^{9 to} 1.6 × 10 ⁹ n / cm ² / s. The irradiation time is 30 minutes to 6 hours, preferably 30 minutes to 1 hour.

It should be noted that α rays and ⁷ Li (atomic nuclei) generated by the boron neutron supplementation reaction ( ¹⁰ B (n, α) reaction) have a high cell killing ability and a short range. Therefore, the α-ray and ⁷ Li (nucleus) itself can effectively enhance the anticancer property together with the release of the anticancer agent.

  Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to this.

(Preparation of ionizing radiation-sensitive liposomes)
The liposome of the present invention was produced by the Bangham method (J. Mol. Biol. 13, 238 (1965)).

(1) Preparation of chloroform solution and drug solution (model drug calcein solution) of component (A) to component (C) First, 100 mg of powdered 1,2-distearoyl-sn-glycero- as component (B) 3-phosphatidylcholine (hereinafter referred to as “DSPC”) (manufactured by NOF Corporation, trade name: COATSOME MC-8080) is accurately taken in a glass screw tube (for 20 mL), and 10 mL (14.9 g) of chloroform is taken. Dissolved in (degassed with nitrogen bubble) (10 g / L) and stored at −20 ° C. (partially precipitated but re-dissolved during use).
Next, as component (A), 1,2-linoleoyl-sn-glycero-3-phosphatidylcholine (hereinafter referred to as “DLOPC”) chloroform solution (stock solution) (manufactured by Avanti Polar Lipids) is used as a glass screw tube ( 20 ml), diluted with degassed chloroform to 10 g / L, and stored at −20 ° C.
Furthermore, as component (C), 100 mg of cholesterol (hereinafter referred to as “CHOL”) (manufactured by Wako Pure Chemical Industries, Ltd.) is accurately taken in a glass screw tube (for 20 mL) and 10 mL (14.9 g). (10 g / L) and stored at 4 ° C.
In addition, 3,3′-bis [N, N-bis (carbomethyl) aminomethyl] fluorescein (calcein) (hereinafter referred to as “calcein”) (made by Dojindo Laboratories Co., Ltd .: CAS No. 1461-15) −0) was dissolved in PBS (phosphate isotonic buffer: pH 7.4) previously deaerated with a nitrogen bubble to prepare a saturated solution of calcein (˜3 g / L). The concentration can be appropriately determined depending on the application. Moreover, when it was hard to melt | dissolve, it was made to melt | dissolve completely with an ultrasonic wave and a hot water bath.

(2) Preparation of lipid membrane First, for the components (A) to (C), the molar ratio (DLOPC: DSPC: CHOL) to be adjusted and the total number of moles of lipids are determined, and each component (A) having a volume corresponding thereto is determined. The lipid solution of component (C) was collected in an eggplant type flask (if the total lipid amount was about 30 μmol, it could be handled with a 50 mL flask). In addition, since the area of a lipid membrane will become small when the amount of solutions is extremely small, in that case, chloroform was further added.
Next, the flask containing these lipid solutions was set in a rotary evaporator (manufactured by IWAKI, product number: REN-1). The constant temperature layer of the rotary evaporator was set to about 30 ° C., and the chloroform solvent was carefully distilled off while paying attention to the liquid level in the flask. When the film was formed, it was left for several tens of minutes while drawing a vacuum. Furthermore, the inside of the evaporator was returned to normal pressure by nitrogen substitution, and the flask was removed. Next, nitrogen gas was blown onto the lipid membrane in the flask to remove the residual chloroform solvent.

(3) Preparation of Multilamellar Liposomes (MLV) To the lipid membrane prepared as described in (2) above, the drug (calcein) solution prepared in (1) above (if the lipid amount is about 30 μmol, ~ 2 mL (MLV is The minimum amount that can be made)) was added under a nitrogen stream. The flask was again set on a rotary evaporator and kept at 60 ° C. while rotating.
When the film was almost peeled off, the bottom of the flask was attached to an ultrasonic cleaner, and the remaining film was peeled off. Moreover, when it did not peel off easily, several glass beads (~ 3mmφ) were put and sonicated. When the membrane was completely peeled off, it was further sonicated for about 1 to 2 minutes to obtain a multilayer membrane liposome (MLV) suspension.

(4) Liposome sizing (preparation of ˜100 nmφ monolayer liposome)
The MLV suspension prepared in the above (3) is passed through a membrane filter having a pore size of 100 nm (eg, Whatman polycarbonate membrane filter) at 60 to 70 ° C. 10 times or more to obtain an MLV suspension having a particle size of 100 nm or less. Obtained. When Mini-Extruder Set (Catalog No. 610000: 100 nmφ pore size membrane filter) manufactured by Avanti Polar Lipids was used, 1 mL each could be prepared.
Subsequently, the particle size was measured with a particle size measuring device (manufactured by Otsuka Electronics, model number: ELS-Z), and it was confirmed that the particle size was 100 nm or less. This suspension was stored at 4 ° C. or at a low temperature at which the drug (calcein) did not precipitate.

(5) Purification of Liposome Suspension The liposome suspension prepared in (4) above was transferred to a tube for ultracentrifugation (manufactured by Beckman Coulter, Inc., product number: No. 349622) and about 5 times as much. Chloroform solvent (degassed) was added to fill the tube.
Subsequently, ultracentrifugation (50000 rpm, 2 hours) was performed at 10 ° C. using an ultracentrifugation apparatus (manufactured by Beckman Coulter, Inc .: model number: Optima (trademark) Max Ultracentrifuge). Next, the supernatant was gently removed, a small amount of solvent was added to the precipitated liposomes, and the suspension was resuspended to fill the solvent up to the top of the tube. The operation from ultracentrifugation to resuspension was performed 3 to 4 times in total. Finally, an appropriate amount of solvent was added and the volume was measured (liposome suspension stock solution). The resulting liposome suspension stock solution was transferred to a glass screw tube, purged with nitrogen, and stored at 4 ° C. or at a low temperature at which the drug did not precipitate.

The following various evaluations were performed on the properties of the liposomes using the above-mentioned liposome suspension stock solution.
(Ionizing radiodegradability of DLOPC-DSPC-CHOL liposome)
1. Lipid composition dependence First, the lipid composition dependence of liposomes was evaluated.

(1) Preparation of X-ray irradiation liposome sample and X-ray irradiation First, calcein-encapsulated DLOPC-DSPC-CHOL liposome was adjusted to 30 mM (total lipid concentration). PBS that had not been degassed was used for dilution.
Next, 20 μL each of the sample solution obtained above is put into three 0.5 mL microtubes, and 130 μL of PBS to which Triton X-100 (manufactured by Nacalai Tesque Co., Ltd.) is added at 1% as a surfactant is added. It was bathed in a hot water at 80 ° C. or higher for 1 minute to decompose the liposomes and take out the inclusions to make positive controls.
Next, 200 μL each of the sample solution was put into two 1.5 mL type microtubes (ultrafiltration microtube, molecular weight cut off 10,000). One of them at 37 ° C
Using a soft X-ray irradiation apparatus (manufactured by softex, M-150WE type), the following conditions, that is, 33.5 ± 1 Gy / min at the position of the suspension surface, total 150 minutes (total 5 kGy) Were irradiated with X-rays. The other was kept at 37 ° C. without irradiation. After irradiation with the above X-rays, these two liposome samples were lightly stirred, then 20 μL was sampled from each of them at a predetermined time, and transferred to an ultrafiltration tube. The liposome sample was always kept at 37 ° C. 130 μL of PBS was added to the ultrafiltration microtube to which the liposome sample had been transferred, and immediately centrifuged (operation) at 4 ° C. and 6000 g for 90 minutes. The fluorescence intensity of the filtrate obtained by centrifugation was measured using a fluorescence microplate reader (Spectra Fluoro Plus manufactured by TECAN) or a fluorescence spectrophotometer (RF-1500 manufactured by Shimadzu Corporation).
The release rate (% E) was calculated from the fluorescence intensity of the positive control and the fluorescence intensity of the sample.

(2) Evaluation of ionizing radiation sensitivity The release rate (% E) calculated in the above item (1) is applied to the following formula (1) to perform a linear regression to calculate the release rate constant k, and k _irrad / k _cont (Ionizing Radiation Sensitivity Constant: IRSI (Ionizing Radiation Sensitivity Index) was determined, where k _irrad is irradiation and k _cont is the release rate constant of non-irradiated liposomes.
In [100 / (100-% E)] = kt (1)
Here, t represents the elapsed time after the start of irradiation.
The relationship between the lipid composition and the IRSI value is shown in FIG.

In the figure, X _DLOPC , X _DSPC , and X _CHOL represent mole fractions of DLOPC, DSPC, and COOL, respectively. The size (diameter) of the circle is proportional to IRSI. That is, generally _{X DLOPC} is IRSI becomes maximum at around _0.1, where _{X CHOL} small, is not stable particle size, for example less than 0.2 mol. Further, CHOL is _{X CHOL} becomes impossible to form a 0.65 larger liposomes. In order to produce stable liposomes having a large IRSI, the composition of the liposomes within the range shown in FIG. 1, that is, within the range _where the molar ratio of X _DLOPC is small, particularly when X _DLOPC is 0.1 or more and 0.2 or less. Can be determined. X _DLOPC may have a lower limit value of 0.05 or more, and an upper limit value of 0.5 or less, or 0.3 or less, depending on the purpose. On the other hand, when utilizing the difference in IRSI _{is, X CHOL} is limited to the range of 0.3 ≦ _{X CHOL} ≦ _0.6, may be changed to _{X DLOPC.} That is, within this range, when preparing liposomes with a large IRSI, X _DLOPC is as small as above, for example, when the molar ratio is 0.1 or more and 0.2 or less, and liposomes with a small IRSI are prepared. X _DLOPC may be set to a molar ratio exceeding 0.2, for example. The upper limit value of X _DLOPC may be 0.5 or less, and further 0.3 or less.
Thus, with _respect to X _DLOPC , X _DSPC , and X _CHOL in particular, by _specifying the molar ratio of X _DLOPC to be in the above range of 0.1 to 0.2, the IRSI is high, that is, the dose of ionizing radiation with a small dose Liposomes that can be decomposed by irradiation to release the drug as the contents can be produced. Furthermore, by defining the molar ratio of cholesterol (X _{CHO L} ) as 0.3 ≦ X _CHO ≦ 0.6, liposomes having a more stable particle size can be formed. Furthermore, by varying, for example, increasing the molar ratio of X _DLOPC to the above range (within the range of these cholesterols), liposomes that have a small IRSI, that is, can be controlled more precisely by the dose of ionizing radiation. It can be.

2. Lipid concentration dependency Next, the lipid concentration dependency of liposomes was evaluated.

(1) Preparation of liposome sample for X-ray irradiation and X-ray irradiation First, prepared in the section of preparation of chloroform solution and drug solution (model drug calcein solution) of each of the above (1) (A) component to (C) component Using each of the prepared solutions, liposomes of DLOPC-DSPC-CHOL (molar ratio = 2: 2: 6) encapsulating the model drug calcein were prepared according to the procedure in the above section, and 30 and 30 using PBS. Adjusted to 4 mM (total lipid concentration). PBS that was not degassed was used.
Next, 20 μL each of two types of sample solutions having different lipid concentrations are put into three 0.5 mL microtubes, and 130 μL of PBS with 1% Triton X-100 added as a surfactant is added. Bathing in water for a minute, the liposomes were decomposed and the inclusions were taken out to make a positive control.
Next, 200 μL each of the above two kinds of sample solutions was put into two 1.5 mL type microtubes. Each one of them at 37 ° C., using the same soft X-ray irradiation apparatus as above, under the following conditions, that is, 33.5 ± 1 Gy / min at the position of the suspension surface for a total of 15 minutes (total X-rays were irradiated at 500 Gy). Each remaining one was kept at 37 ° C. without irradiation.
After irradiation with the above X-rays, these two liposome samples were lightly stirred, then 20 μL was sampled from each of them at a predetermined time, and transferred to an ultrafiltration tube. The liposome sample was always kept at 37 ° C. 130 μL of PBS was added to the ultrafiltration microtube to which the liposome sample had been transferred, and immediately centrifuged (operation) at 4 ° C. and 6000 g for 90 minutes. The fluorescence intensity of the filtrate obtained by centrifugation was measured using the above-mentioned fluorescence microplate reader or fluorescence spectrophotometer.
The release rate (% E) was calculated in time series from the fluorescence intensity of the positive control and the fluorescence intensity of the sample. The result is shown in FIG.

  As can be seen from FIG. 2, it was confirmed that the release rate was improved at any time in time series when the total lipid concentration was lower (lipid concentration 4 mM).

3. Dose rate dependency Furthermore, the dose rate dependency of liposomes was evaluated.

(1) Preparation of liposome sample for X-ray irradiation and X-ray irradiation First, prepared in the section of preparation of chloroform solution and drug solution (model drug calcein solution) of each of the above (1) (A) component to (C) component Using each of the prepared solutions, a DLOPC-DSPC-CHOL (molar ratio = 2: 2: 6) liposome encapsulating the model drug calcein was prepared according to the procedure in the above section, and 4 mM (4 mM) using PBS. Total lipid concentration). PBS that was not degassed was used.
Next, 20 μL of the above sample solution is placed in three 0.5 mL microtubes, 130 μL of PBS with 1% Triton X-100 added as a surfactant is added, and further bathed at 80 ° C. or higher for 1 minute. The liposomes were decomposed and the inclusions were taken out to make positive controls.
Next, 200 μL each of the above sample solution was put into two 1.5 mL type microtubes. One of them was irradiated with X-rays at 37 ° C. under the following conditions using the same soft X-ray irradiation apparatus as described above. That is, at a suspension surface position of about 3.4 Gy / min, a total of 500 Gy (150 minutes), 200 Gy (60 minutes), 100 Gy (30 minutes), or about 0.34 Gy / min, a total of 100 Gy (300 Min), 50 Gy (150 min), 20 Gy (60 min), and 10 Gy (30 min). Each remaining one was kept at 37 ° C. without irradiation.
After irradiation with the above X-rays, both of these liposome samples were lightly stirred, and then 20 μL was sampled from each of them at a predetermined time, and transferred to an ultrafiltration tube. The liposome sample was always kept at 37 ° C. 130 μL of PBS was added to the ultrafiltration microtube to which the liposome sample had been transferred, and immediately centrifuged (operation) at 4 ° C. and 6000 g for 90 minutes. The fluorescence intensity of the filtrate obtained by centrifugation was measured using the above-mentioned fluorescence microplate reader or fluorescence spectrophotometer.
The release rate (% E) was calculated over time from the fluorescence intensity of the above positive control and the fluorescence intensity of the above sample. The results at each dose are shown in FIGS.

  As can be understood from FIG. 3, it was confirmed that a good release rate can be achieved with irradiation of a total of 500 Gy at a dose rate (3.4 Gy / min). Also in FIG. 4, it was confirmed that a good release rate can be achieved by irradiation with a total of 100 Gy at a dose rate (0.34 Gy / min). 3 and 4, when the same dose (100 kGy), the dose rate (dose emitted per unit time) is smaller (FIG. 4), the better emission rate is obtained, that is, X-rays It was confirmed that sensitivity increased.

4). Comparison of unsaturated phospholipid types First, the types of unsaturated phospholipids were compared.

(1) Preparation of liposome sample for X-ray irradiation and X-ray irradiation First, the above 2. Lipid concentration-dependent (1) Preparation of liposome sample for X-ray irradiation and lipid used in the section of X-ray irradiation, as component (A), dioleoylphosphatidylcholine (DOPC) (AVANTI) instead of DLOPC Product name: 1,2-dioleoyl-sn-glycero-3-phosphocholine), dilinolenoyl phosphatidylcholine (DLNPC) (AVANTI POLAR LIPIDS, product name: 1,2-dinolenoyl-sn-gly 3-phosphocholine), or diarachidonyl phosphatidylcholine (DAPC) (manufactured by AVANTI POLAR LIPIDS, trade name: 1,2-arachidonoyl-sn-glycero-3-p liposomes (liposome composition ratio, unsaturated phospholipids: DSPC: CHOL = 2: 2: 6) were prepared in the same manner except that the total lipid concentration was 10 mM, and the following irradiation conditions were used. The release rate was measured by irradiating the line.
X-ray irradiation conditions: 0.33 Gy / min, total 100 Gy (total 300 minutes), 37 ° C.
The result is shown in FIG.

  As a result, the emissivity 5 hours after the start of irradiation is ˜0% for DOPC, 25% for DLOPC, 5% for DLNPC (same as non-irradiation), and DAPC In the case of 2% (lower than non-irradiated (5%)). Therefore, it was confirmed that the release rate was the best in the case of DLOPC.

5. Comparison of types of saturated phospholipids Next, the types of saturated phospholipids were compared.

(1) Preparation of liposome sample for X-ray irradiation and X-ray irradiation First, the above 2. Lipid concentration-dependent (1) Preparation of liposome sample for X-ray irradiation and lipid used in the section of X-ray irradiation, as component (B), instead of DSPC, dipalmitoylphosphatidylcholine (DPPC) (Nippon Yushi) Product name: COATSOME MC-6060), dimyristoylphosphatidylcholine (DMPC) (manufactured by NOF Corporation, product name: MC-4040), or dilauroylphosphatidylcholine (DLPC) (manufactured by NOF Corporation, trade name) : MC-2020), and the liposome (liposome composition ratio, saturated phospholipid: DLOPC: CHOL = 2: 2: 6) was prepared in the same manner except that the total lipid concentration was 10 mM. The release rate was measured by irradiation with X-rays.
X-ray irradiation conditions: 0.33 Gy / min, total 100 Gy (total 300 minutes), 37 ° C.
The result is shown in FIG.

  As a result, the emissivity 4 hours after the start of irradiation is 15% for DSPC, 3% for DPPC (same as non-irradiation), 11% for DMPC, and DLPC The case was 2% (same as non-irradiation). Therefore, it was confirmed that the release rate was the best in the case of DSPC.

(Preparation of ¹⁰ B-containing compound-encapsulated liposome)
¹⁰ B-containing compound-encapsulated liposomes were prepared according to the method described in the above section (Preparation of ionizing radiation-sensitive liposomes).

( Preparation example of ¹⁰ B-containing compound (BSSB) )
^{First, 10} B a cluster ^{(10 B-enriched sodium mercaptododecaptododecaborate:} BSH :( Ltd.) Katchem Ltd.) 63 mg (0.3 mmol) by dissolving in water of 3 mL ¹⁰ B a cluster solution (0.1 mol / L) 3 mL Prepared. To this solution, 30% hydrogen peroxide water was added so as to be 1.2 mol with respect to 2 mol of ¹⁰ B cluster, and an appropriate amount of 5 mol / L sodium hydroxide was added to adjust the pH to about 11. The solution was kept at 50 ° C. and subjected to an oxidation reaction for 6 hours. Three hours after the start of the reaction, an appropriate amount of a 5 mol / L aqueous sodium hydroxide solution was added to adjust the pH (the pH decreased as the reaction progressed), and the pH was returned to about 11. To supplement the hydrogen peroxide consumed by the generation of oxygen gas, 30% hydrogen peroxide was added in the same amount as the first time. As a result, 60 mg (0.15 mmol) of BSSB compound from which hydrogen was eliminated from BSH was obtained.

( Preparation of BSSB and carboplatin mixed solution )
100 mg of carboplatin (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 10 mL of physiological saline (0.9% NaCl solution) to obtain 10 mL of a 10 g / L carboplatin / physiological saline (0.9% NaCl) solution. .
The BSSB 200 mg obtained above was completely dissolved in 1 mL of a 10 g / L carboplatin / saline solution (0.9% NaCl) to prepare a BSSB and carboplatin mixed solution.

( Preparation of liposomes encapsulating BSSB and carboplatin )
In the same manner as above, the DLOPC: DSPC: CHOL molar ratio = 2: 2: 6, and the lipid membrane obtained by adjusting the total lipid molar amount to 10 micromolar, the obtained BSSB and carboplatin 2 mL of a mixed solution was added under a nitrogen stream to obtain multilamellar liposomes (MLV). Further, in the same manner as above, (4) liposome sizing and (5) liposome suspension purification were performed to obtain a BSSB and carboplatin-encapsulated liposome suspension (diameter of about 100 nm) (lipid concentration in the suspension: 10 mM). The content of BSSB in the obtained liposome suspension was 4% by weight as ¹⁰ B per liposome membrane (100% by weight), and the content of carboplatin was 0.3% by weight per liposome membrane.

( Evaluation of thermal neutron irradiation and liposome membrane degradation )
100 μL each of the sample solution obtained above is put into two 0.5 mL microtubes and diluted 10-fold with 0.9% NaCl solution to which 1% Triton X-100 (manufactured by Nacalai Tesque) is added as a surfactant. Then, it was set as positive control.
Next, 400 μL each of the above sample solution was put into two 0.5 mL type microtubes (ultrafiltration microtube, molecular weight cut off 10,000). One of them, using a thermal neutron beam generator (Japan Atomic Energy Agency: Research Reactor JRR-4), irradiation conditions: thermal neutron flux: 1.6 × 10 ⁹ n / cm ² / s, 4 hours, 37 ° C. And irradiated with thermal neutrons. The other was kept at 37 ° C. without irradiation. After irradiation with the above thermal neutron beam, these two liposome samples were lightly stirred and then 100 μL was sampled from each of them at a predetermined time, transferred to an ultrafiltration tube, and centrifuged at 10 ° C. and 6000 g for 90 minutes ( Operation). The filtrate obtained by centrifugation was diluted 10-fold with physiological saline (0.9% NaCl). This solution was measured using a high-frequency induction plasma emission spectrometer (ICP-AES) (manufactured by Seiko Instruments Inc.), and the release rate of carboplatin (anticancer agent) was determined based on the Pt concentration contained in carboplatin. The result is shown in FIG.
From the results of FIG. 8, it can be seen that the liposome itself is somewhat unstable due to the inclusion of BSSB, but carboplatin is released at a time by irradiation with thermal neutrons. On the other hand, no release of carboplatin was observed from liposomes not encapsulating BSSB.

In the present invention, the membrane component comprises (A) an unsaturated phospholipid or derivative thereof in which the acyl group is a linoleic acid residue, (B) a saturated phospholipid or derivative thereof in which the acyl group is a stearic acid residue, and ( C) Since a liposome comprising cholesterol or a derivative thereof and the membrane formed from the membrane component is at least partially degraded by exposure to ionizing radiation, it is included in the liposome. The release control of the applied drug can be performed with higher accuracy. Therefore, the liposome of the present invention can be used as a drug carrier capable of more accurately controlling the release of a drug to a site requiring treatment, and can be used as a liposome preparation by including a drug. it can.
Furthermore, according to the liposome preparation comprising a ¹⁰ B-containing compound in the liposome membrane of the present invention, the liposome membrane can be decomposed by irradiation with low energy thermal neutron rays, and the control of the release of the active agent can be improved.

It is a figure which shows the relationship between an ionizing radiation sensitivity (IRSI) of an ionizing radiolytic liposome, and a lipid composition. It is a figure which shows the relationship between the ionizing radiation sensitivity of a liposome, and a liposome suspension density | concentration (lipid amount conversion). It is a figure which shows the relationship between the ionizing radiation sensitivity of a liposome, and a dose (dose rate: 3.4 Gy / min). It is a figure which shows the relationship between the ionizing radiation sensitivity of a liposome, and a dose (dose rate: 0.34 Gy / min). It is a figure which shows the release rate according to the kind of unsaturated phospholipid of a liposome. It is a figure which shows the discharge | release rate according to the kind of saturated phospholipid of a liposome. It is a figure which shows the synthesis example (preparation example) of a boron containing compound. It is a figure which shows discharge | release of carboplatin from a liposome by boron neutron capture reaction.

Claims (8)

The membrane component is (A) an unsaturated phospholipid or derivative thereof in which the acyl group is a linoleic acid residue, (B) a saturated phospholipid or derivative thereof in which the acyl group is a stearic acid residue, and (C) cholesterol or a derivative thereof The component (A) has a mole fraction of 0.05 to 0.5, the component (C) has a mole fraction of 0.3 to 0.6, and the balance is the component (B). and liposomes film formed from the film component, characterized in that it is at least partially degraded by exposure to ionizing radiation. The membrane component is (A) an unsaturated phospholipid or derivative thereof in which the acyl group is a linoleic acid residue, (B) a saturated phospholipid or derivative thereof in which the acyl group is a stearic acid residue, and (C) cholesterol or a derivative thereof The component (A) has a mole fraction of 0.05 to 0.5, the component (C) has a mole fraction of 0.3 to 0.6, and the balance is the component (B). And a membrane formed from the membrane component is at least partially decomposed by exposure to ionizing radiation, and further comprises a ¹⁰ B-containing compound in the membrane. The component (A) is dilinoleoyl phosphatidylcholine (DLOPC), the component (B) is distearoyl phosphatidylcholine (DSPC), and the component (C) is cholesterol. The liposome described. The liposome according to any one of claims 1 to 3, wherein the total lipid molar concentration of the liposome is 0.01 to 10 mM. The liposome according to any one of claims 1 to 4, wherein a dose rate of the ionizing radiation is 0.01 to 1 Gy / min. A liposome preparation comprising a drug in the liposome according to any one of claims 1 to 5. The liposome preparation according to claim 6, wherein the drug is an anticancer drug. The molar ratio of the component (A) is adjusted in the range of 0.05 to 0.5, the molar ratio of the component (C) is adjusted in the range of 0.3 to 0.6, and the balance is the component (B). claims 1 to methods made regulating liposomes according to any one of 3, characterized in that a.

Images