A nanoscale calcium sulfite-based drug delivery carrier and a preparation method and application thereof

Abstract

The application relates to the technical field of pharmaceutical preparations, and discloses a nanoscale calcium sulfite-based drug delivery carrier as well as a preparation method and application thereof. The preparation method comprises the following steps: respectively preparing a calcium salt aqueous solution, a sulfite aqueous solution and a polyacrylic acid aqueous solution; adding an alkali liquor to the polyacrylic acid aqueous solution to adjust the pH to alkaline, then adding a precipitant, and stirring uniformly to obtain a polyacrylic acid template suspension; slowly adding the calcium salt aqueous solution into the polyacrylic acid template suspension and stirring; then slowly adding the sulfite aqueous solution into the polyacrylic acid template suspension and stirring to obtain a complex suspension; and performing separation, washing and drying on the complex suspension, and the obtained solid is the calcium sulfite-based drug delivery carrier. The nanoscale calcium sulfite-based drug delivery carrier has a size of 10-200 nanometers, a uniform size distribution and a regular appearance, is suitable for the medical field, can load chemotherapeutic drugs, and can be used as a drug for tumor chemotherapy combined with SO2 gas treatment.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical formulation technology, specifically to a nanoscale calcium sulfite-based drug delivery carrier, its preparation method, and its application. Background Technology

[0002] Calcium-based biomaterials, such as calcium phosphate and calcium carbonate, possess excellent biocompatibility and biodegradability, and are commonly used as drug carriers in the biomedical field. Compared to commonly used calcium phosphate and calcium carbonate nanocarriers, calcium sulfite not only exhibits pH-responsive degradation characteristics, but its degradation product, sulfur dioxide gas, can react with hydrogen peroxide gas highly expressed in tumors to generate toxic free radicals and deplete the intracellular antioxidant glutathione, enhancing oxidative stress in tumor cells. This makes it suitable for sulfur dioxide gas therapy in tumor treatment. Using calcium sulfite nanomaterials as drug delivery carriers not only enables pH-responsive drug release but also allows for the combined use of chemotherapy and sulfur dioxide gas therapy in tumor treatment. Therefore, calcium sulfite nanomaterials are an ideal drug delivery carrier with enormous application potential in the field of nanomedicine.

[0003] Currently, the application of calcium sulfite in nanomedicine is relatively limited, mainly because nanomedicine places high demands on the size, dispersibility, and stability of materials. Conventional synthesis methods, such as flue gas desulfurization and desulfurized gypsum methods, produce calcium sulfite with relatively large sizes, unsuitable for nanomedicine. Patent CN101712484A provides columnar calcium sulfite particles with a diameter of 0.5–8 mm and numerous micropores on their surface, allowing for better contact with water; however, their large diameter makes them unsuitable for nanomedicine. Patent CN107188213B discloses a method for preparing amorphous calcium sulfite microparticles with a particle size of 600–800 nm and uniform distribution; however, the introduction of lime slurry in the preparation process not only increases the complexity of subsequent processing but also reduces the biocompatibility of the material.

[0004] Developing a controllable synthesis method for calcium sulfite nanocarriers with small size, uniform particle size, good dispersion, and colloidal stability will be of great significance for expanding the application of calcium sulfite in the biomedical field. Summary of the Invention

[0005] This application provides a nanoscale calcium sulfite-based drug delivery carrier, its preparation method, and its application, aiming to solve the technical problems of existing calcium sulfite carriers, such as large size, uneven particle size, and low biocompatibility.

[0006] To achieve the above objectives, the present application adopts the following technical solution.

[0007] A first aspect of this application provides a method for preparing a nanoscale calcium sulfite-based drug delivery carrier, comprising:

[0008] Prepare aqueous solutions of calcium salts, sulfites, and polyacrylic acid separately;

[0009] Alkaline solution was added to an aqueous solution of polyacrylic acid to adjust the pH to alkaline, then a precipitant was added and stirred until homogeneous to obtain a polyacrylic acid template suspension.

[0010] A calcium salt aqueous solution was slowly added to the polyacrylic acid template suspension and stirred; then a sulfite aqueous solution was slowly added to the polyacrylic acid template suspension and stirred to obtain a composite suspension.

[0011] The complex suspension is separated, washed, and dried to obtain a solid, which is the calcium sulfite-based drug delivery carrier.

[0012] In some embodiments, the calcium salt includes any one or a mixture of calcium chloride or its hydrate, calcium nitrate or its hydrate, or calcium bicarbonate or its hydrate.

[0013] The sulfite includes any one or a mixture of potassium sulfite or its hydrate, sodium sulfite or its hydrate, or ammonium sulfite or its hydrate.

[0014] In some embodiments, the precipitant is one or more of methanol, ethanol, n-propanol, isopropanol, and butanol.

[0015] In some embodiments, the molar ratio of calcium salt, sulfite and polyacrylic acid is 1:1:(0.0025-0.145); the volume ratio of the polyacrylic acid aqueous solution to the precipitant is (0.01-2):1.

[0016] In some embodiments, the drying is freeze-drying.

[0017] A second aspect of this application provides a nanoscale calcium sulfite-based drug delivery carrier prepared by the above-described preparation method.

[0018] A third aspect of this application provides a drug delivery system comprising the aforementioned nanoscale calcium sulfite-based drug delivery carrier and an effective dose of drug loaded on the nanoscale calcium sulfite-based drug delivery carrier.

[0019] In some embodiments, the drug delivery system is coated with a liposome layer.

[0020] The raw materials for the liposome layer include sodium 1,2-dipalmitoyl-sn-glycerol-3-phosphate (DOPA), 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), and polyethylene glycol phosphate (DSPE-PEG). 2000) and cholesterol.

[0021] In some implementations, the drug is a chemotherapy drug.

[0022] A fourth aspect of this application provides the use of the above-mentioned drug delivery system in a drug for tumor chemotherapy combined with sulfur dioxide gas therapy.

[0023] Compared with the prior art, the beneficial effects of this application are as follows:

[0024] This application uses polyacrylic acid as a template to prepare nanoscale calcium sulfite-based drug delivery carriers via coprecipitation. The carriers have a size of 10–200 nanometers, with uniform size distribution and regular morphology, making them suitable for the medical field.

[0025] The calcium sulfite-based drug delivery carrier of this application exhibits good biodegradability. The chemotherapeutic drugs loaded onto it can be released in a pH-responsive manner within the weakly acidic tumor microenvironment, thereby treating the tumor. Simultaneously, the calcium sulfite-based drug delivery carrier degrades to release Ca... 2+ Ions and SO2 gas, in which Ca 2+ Ions have no toxic side effects and good biocompatibility; SO2 gas can react with H2O2 highly expressed in tumors to generate toxic free radicals and consume the intracellular antioxidant glutathione (GSH), thus enabling SO2 gas therapy for tumors.

[0026] The calcium sulfite-based drug delivery system of this application can be used as a drug in combination with SO2 gas therapy for tumor chemotherapy. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 SEM image of the calcium sulfite-based drug delivery carrier prepared in Example 1;

[0029] Figure 2 SEM image of the calcium sulfite-based drug delivery system prepared in Example 4;

[0030] Figure 3 TEM and elemental surface scans of the calcium sulfite-based drug delivery system with a liposome-encapsulated layer prepared in Example 5. Detailed Implementation

[0031] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0032] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0033] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0035] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0036] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0037] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] In a first aspect, this application provides a method for preparing a nanoscale calcium sulfite-based drug delivery carrier, comprising:

[0040] Prepare aqueous solutions of calcium salts, sulfites, and polyacrylic acid separately;

[0041] Alkaline solution was added to an aqueous solution of polyacrylic acid to adjust the pH to alkaline, then a precipitant was added and stirred until homogeneous to obtain a polyacrylic acid template suspension.

[0042] A calcium salt aqueous solution was slowly added to the polyacrylic acid template suspension and stirred; then a sulfite aqueous solution was slowly added to the polyacrylic acid template suspension and stirred to obtain a composite suspension.

[0043] The complex suspension is separated, washed, and dried to obtain a solid, which is the calcium sulfite-based drug delivery carrier.

[0044] In the embodiments of this application, the calcium salt is a water-soluble calcium salt used to provide calcium ions; it includes, but is not limited to, any one or more mixtures of calcium chloride or its hydrate, calcium nitrate or its hydrate, or calcium bicarbonate or its hydrate.

[0045] In the embodiments of this application, the sulfite is a water-soluble sulfite used to provide sulfite ions; it includes, but is not limited to, any one or more mixtures of potassium sulfite or its hydrate, sodium sulfite or its hydrate, or ammonium sulfite or its hydrate.

[0046] In the embodiments of this application, polyacrylic acid with a molecular weight of 1000-50000 is preferred; the preferred precipitant is methanol, ethanol, n-propanol, isopropanol, or butanol, or a mixture of two or more of methanol, ethanol, n-propanol, isopropanol, or butanol. Controlling the solubility and structure of the polyacrylic acid template using a water-alcohol mixed solvent is beneficial for the room-temperature mineralization synthesis of calcium sulfite-based drug delivery carriers.

[0047] In the embodiments of this application, when preparing the calcium salt aqueous solution, sulfite aqueous solution, and polyacrylic acid aqueous solution, the concentration of the calcium salt aqueous solution is preferably 0.01-1 mol / L; the concentration of the sulfite aqueous solution is preferably 0.01-1 mol / L; and the concentration of the polyacrylic acid aqueous solution is preferably 1-11 mg / ml. In the step of preparing the polyacrylic acid template suspension, the volume ratio of the polyacrylic acid aqueous solution to the precipitant is (0.01-2):1. In the step of preparing the composite suspension, the molar ratio of calcium salt, sulfite, and polyacrylic acid is preferably 1:1:(0.0025-0.145). Through the preparation and ratio setting of the above solutions, the embodiments of this application can prepare nanoscale calcium sulfite-based drug delivery carriers with uniform size and regular morphology, with a size of 10-200 nanometers.

[0048] Secondly, this application provides a nanoscale calcium sulfite-based drug delivery carrier prepared by the above-described method. The nanoscale calcium sulfite-based drug delivery carrier comprises nanoscale calcium sulfite particles with a size of 10-200 nm, exhibiting uniform size distribution and regular morphology, making it suitable for the medical field.

[0049] This application uses polyacrylic acid as a template to prepare calcium sulfite nanoparticles via a co-precipitation method. These nanoparticles exhibit good biodegradability and can undergo pH-responsive degradation in the weakly acidic microenvironment of tumors, generating Ca2+. 2+ Ions and SO2 gas, in which Ca 2+ Ions have no toxic side effects on organisms and have good biocompatibility; SO2 gas can react with H2O2 highly expressed in tumors to generate toxic free radicals and consume the intracellular antioxidant glutathione (GSH), thus enabling SO2 gas therapy for tumors.

[0050] When the nanoscale calcium sulfite-based drug delivery carrier of this application loads a drug, the drug can be released in a controlled manner through pH response in the weakly acidic microenvironment of the tumor, thereby performing chemotherapy on the tumor and simultaneously treating the tumor with SO2 gas.

[0051] Thirdly, this application provides a drug delivery system, including an effective dose of drug and a nanoscale calcium sulfite-based drug delivery carrier loaded with said drug.

[0052] Specifically, the drug is preferably a chemotherapeutic agent, such as hydroxycamptothecin. The drug delivery system of this application can be used as a drug for tumor chemotherapy combined with SO2 gas therapy. The drug delivery system is prepared by the following method:

[0053] Prepare aqueous solutions of calcium salts, sulfites, and polyacrylic acid separately;

[0054] Hydroxycamptothecin was dissolved in an aqueous solution of polyacrylic acid, and the pH was adjusted to alkaline by adding alkali solution. Then, a precipitant was added and the mixture was stirred until homogeneous to obtain a drug-loaded polyacrylic acid template suspension.

[0055] A calcium salt aqueous solution was slowly added to the drug-loaded polyacrylic acid template suspension and stirred; then a sulfite aqueous solution was slowly added to the drug-loaded polyacrylic acid template suspension and stirred to obtain a composite suspension.

[0056] The drug-loaded complex suspension is separated, washed, and dried to obtain a solid, which is a nanoscale calcium sulfite-based drug delivery system.

[0057] As a preferred embodiment of this application, a liposome layer is coated on the surface of a nanoscale calcium sulfite-based drug delivery system using liposome encapsulation technology to increase its stability and dispersibility, thereby further improving drug delivery and therapeutic efficacy.

[0058] The raw materials for the liposome layer include sodium 1,2-dipalmitoyl-sn-glycerol-3-phosphate (DOPA), 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), and polyethylene glycol phosphate (DSPE-PEG). 2000 ) and cholesterol.

[0059] The specific method is as follows:

[0060] The nanoscale calcium sulfite-based drug delivery system was dispersed in anhydrous ethanol, a chloroform solution of DOPA was added, and the mixture was ultrasonically mixed for 20 min. Then, the free DOPA was removed by centrifugation, and the solid phase was collected.

[0061] The solid phase was redispersed into a mixture containing DPPC, cholesterol, and DSPE-PEG. 2000 The liposomes were stirred overnight at room temperature in a chloroform solution, and then removed by rotary evaporation at 50°C. Finally, ultrapure water was added and the liposomes were rehydrated under ultrasonic assistance to obtain a nanoscale calcium sulfite-based drug delivery system encapsulating a liposome layer.

[0062] The present application will be further illustrated by the following examples.

[0063] Example 1

[0064] This embodiment provides a method for preparing a nanoscale calcium sulfite-based drug delivery carrier, including:

[0065] At room temperature, a calcium chloride solution with a concentration of 1 mol / L, a sodium sulfite solution with a concentration of 1 mol / L, and a polyacrylic acid solution with a concentration of 10.29 mg / mL were prepared respectively; wherein the number average molecular weight of polyacrylic acid was 2000.

[0066] Take 7 mL of polyacrylic acid solution, add sodium hydroxide solution until the pH is alkaline, then add 40 mL of anhydrous ethanol, stir at room temperature for 10 minutes to obtain an emulsion; add 0.5 mL of calcium chloride solution dropwise to the emulsion, stirring continuously for 10 minutes; then add 0.5 mL of sodium sulfite solution dropwise to obtain a suspension; stir continuously for 4 hours, centrifuge the suspension at 8000 rpm for 10 minutes, wash the solid phase three times with anhydrous ethanol to obtain a nanoscale calcium sulfite-based drug delivery carrier.

[0067] Example 2

[0068] This embodiment provides a method for preparing a nanoscale calcium sulfite-based drug delivery carrier, including:

[0069] At room temperature, a calcium chloride solution with a concentration of 1 mol / L, a sodium sulfite solution with a concentration of 1 mol / L, and a polyacrylic acid solution with a concentration of 10.29 mg / mL were prepared respectively; wherein the number average molecular weight of polyacrylic acid was 1000.

[0070] Take 7 mL of polyacrylic acid solution, add sodium hydroxide solution until the pH is alkaline, then add 40 mL of anhydrous ethanol, stir at room temperature for 10 minutes to obtain an emulsion; add 0.5 mL of calcium chloride solution dropwise to the emulsion, stirring continuously for 10 minutes; then add 0.5 mL of sodium sulfite solution dropwise to obtain a suspension; stir continuously for 4 hours, centrifuge the suspension at 8000 rpm for 10 minutes, wash the solid phase three times with anhydrous ethanol to obtain a nanoscale calcium sulfite-based drug delivery carrier.

[0071] Example 3

[0072] This embodiment provides a method for preparing a nanoscale calcium sulfite-based drug delivery carrier, including:

[0073] At room temperature, a calcium chloride solution with a concentration of 1 mol / L, a sodium sulfite solution with a concentration of 1 mol / L, and a polyacrylic acid solution with a concentration of 10.29 mg / mL were prepared respectively; wherein the number average molecular weight of polyacrylic acid was 50,000.

[0074] Take 7 mL of polyacrylic acid solution, add sodium hydroxide solution until the pH is alkaline, then add 100 mL of anhydrous ethanol, stir at room temperature for 10 minutes to obtain an emulsion; add 0.5 mL of calcium chloride solution dropwise to the emulsion, stirring continuously for 10 minutes; then add 0.5 mL of sodium sulfite solution dropwise to obtain a suspension; stir continuously for 4 hours, centrifuge the suspension at 8000 rpm for 10 minutes, wash the solid phase three times with anhydrous ethanol to obtain a nanoscale calcium sulfite-based drug delivery carrier.

[0075] Example 4

[0076] This embodiment provides a method for preparing a calcium sulfite-based drug delivery system, including:

[0077] At room temperature, a calcium chloride solution with a concentration of 1 mol / L, a sodium sulfite solution with a concentration of 1 mol / L, and a polyacrylic acid solution with a concentration of 10.29 mg / mL were prepared respectively; wherein the number average molecular weight of polyacrylic acid was 2000.

[0078] Take 7 mL of polyacrylic acid solution, add 5 mg of hydroxycamptothecin, and then add sodium hydroxide solution until the pH is alkaline; then add 40 mL of anhydrous ethanol, stir at room temperature for 10 minutes to obtain an emulsion; add 0.5 mL of calcium chloride solution dropwise to the emulsion, and stir continuously for 10 minutes; then add 0.5 mL of sodium sulfite solution dropwise to obtain a suspension; stir continuously for 4 hours, centrifuge the suspension at 8000 rpm for 10 minutes, wash the solid phase three times with anhydrous ethanol to obtain a calcium sulfite-based drug delivery system.

[0079] Example 5

[0080] This embodiment provides a method for preparing a calcium sulfite-based drug delivery system encapsulating a liposome layer, comprising:

[0081] Take 20 mg of the calcium sulfite-based drug delivery system prepared in Example 4, disperse it in 5 mg of anhydrous ethanol, add 1 mL of chloroform solution of DOPA (DOPA concentration of 4 mg / mL), sonicate and mix for 20 minutes, then centrifuge to remove free DOPA and collect the solid phase.

[0082] The solid phase was redispersed in 2 mL of a solution containing 15 mg of DPPC, 5 mg of cholesterol, and 5 mg of DSPE-PEG. 2000 The liposomes were stirred overnight at room temperature in a chloroform solution, and then removed by rotary evaporation at 50°C. Finally, 2 mL of ultrapure water was added and the liposomes were rehydrated under ultrasonic assistance to obtain a calcium sulfite-based drug delivery system encapsulating the liposome layer.

[0083] The calcium sulfite-based drug delivery carrier prepared in Example 1 was subjected to SEM testing, and its SEM spectrum is shown below. Figure 1 As shown, the calcium sulfite-based drug delivery carrier consists of spherical calcium sulfite particles with uniform size and regular morphology, with a size distribution of approximately 100 nm.

[0084] The calcium sulfite-based drug delivery system prepared in Example 4 was subjected to SEM testing, and its SEM spectrum is shown below. Figure 2 As shown. From Figure 2It can be seen that the size difference between the nano-calcium sulfite particles before and after drug loading is not significant, and they still maintain good size uniformity. Moreover, their size is mainly distributed at around 100nm, which can meet the size requirements for tumor treatment.

[0085] The calcium sulfite-based drug delivery system with a liposome-encapsulated layer prepared in Example 5 was subjected to TEM testing and elemental surface scanning. The results are as follows: Figure 3 As shown. Figure 3 In the image, a is the TEM spectrum, and b is the elemental surface scan spectrum. (From...) Figure 3 It can be seen that the calcium sulfite-based drug delivery system encapsulating the liposome layer has uniform size and good distribution. Furthermore, the presence of P and N elements unique to liposomes in the elemental scan proves that the liposome encapsulation was successful.

[0086] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A method of preparing a nanoscale calcium subsulfide-based drug delivery carrier, characterized by, The preparation method comprises the following steps: respectively preparing a calcium salt aqueous solution, a sulfite aqueous solution and a polyacrylic acid aqueous solution; adding a lye to the polyacrylic acid aqueous solution to adjust the pH to alkaline, and then adding a precipitant, and stirring uniformly to obtain a polyacrylic acid template suspension; wherein the precipitant is one or more of methanol, ethanol, n-propanol, isopropanol and butanol; slowly adding the calcium salt aqueous solution into the polyacrylic acid template suspension and stirring; then slowly adding the sulfite aqueous solution into the polyacrylic acid template suspension and stirring to obtain a composite suspension; separating, washing and drying the composite suspension, and the obtained solid is a calcium sulfite-based drug delivery carrier; wherein the molar ratio of the calcium salt, the sulfite and the polyacrylic acid is 1:1:(0.0025-0.145); the volume ratio of the polyacrylic acid aqueous solution to the precipitant is (0.01-2):

1.

2. The method of claim 1, wherein the method is characterized by, The calcium salt comprises any one or more of a mixture of calcium chloride or a hydrate thereof, calcium nitrate or a hydrate thereof, or calcium bicarbonate or a hydrate thereof; The sulfite comprises any one or more of a mixture of potassium sulfite or a hydrate thereof, sodium sulfite or a hydrate thereof, or ammonium sulfite or a hydrate thereof.

3. The method of claim 1, wherein the method is characterized by, The drying is freeze-drying.

4. A nano-sized calcium sulfite-based drug delivery carrier prepared by the preparation method in any one of claims 1-3.

5. A drug delivery system, characterized by The preparation method comprises the following steps:

6. The drug delivery system of claim 5, wherein, The drug delivery system is coated with a liposome layer on the surface; The raw materials of the liposome layer include 1,2-dipalmitoyl-sn-glycero-3-phosphate sodium salt (DOPA), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), phosphate ester polyethylene glycol (DSPE-PEG 2000 ), and cholesterol.

7. The drug delivery system according to claim 5 or 6, characterized in that The drug is a chemotherapeutic drug.

8. The use of the drug delivery system in claim 7 in the preparation of a drug for the treatment of tumors by combining chemotherapy with sulfur dioxide gas.

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