Bioengineering
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Preparation and Characterization of Lipophilic Doxorubicin Pro-drug Micelles
Chapters
Summary August 2nd, 2016
A protocol for the preparation and characterization of lipophilic doxorubicin pro-drug loaded 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG) micelles is described.
Transcript
The overall goal of this protocol is to describe procedures for preparing and characterizing lipophilic doxorubicin prodrug loaded micell formulations. This method provides a simple and reliable approach for micell formulation. The synthesis of lipophilic prodrug of doxorubicin can enhance drug loading and stability, thus addressing a significant challenge in developing micell formulation.
The micell formulation can enhance drug targeting into tumors and therefore can reduce toxicities of cancer treatment. In addition to the application described in this project, this technical can also be used to prepare the nanomedicine for the agents. To synthesize lipophilic doxorubicin prodrug DOX-PA, weigh 390 milligrams of doxorubicin and 243 milligrams of palmitic acid hydrozide, and transfer them to a round bottom flask.
Add 150 milliliters of anhydrous methanol to the flask with a glass syringe. Then add 39 microliters of trifluoroacetic acid, or TFA, with a pipette. Using a magnetic stirrer, stir the reaction mixture for 18 hours at room temperature in the dark.
To purify DOX-PA using a silica gel column, first remove the solvent in the reaction mixture with a rotary evaporator. Add three grams of silica gel after the volume of the mixture is reduced to around 20 milliliters. Continue rotary evaporation to yield dry powders and to allow the absorption of products onto the silica gel.
Keep the sample under a vacuum for an additional 30 minutes after the dry powders are formed. Pack 50 grams of silica gel into a column using dichloromethane as a solvent. Carefully add the silica gel sample containing absorbed product to the column.
Elute the column with a mixture of dichloromethane and methanol while gradually increasing the percentage of methanol, thereby increasing solvent polarity. Collect fractions of elluent in test tubes at 25 milliliters per tube, and monitor the progress by thin layer chromatography, or TLC. Combine all fractions containing pure DOX-PA and remove the solvent using a rotary evaporator until dry powder is formed.
Further dry the product under a vacuum overnight. To prepare micelles, dissolve 40 milligrams of DSPE-PEG and four milligrams of DOX-PA with two milliliters of methanol in a 10 milliliter glass vial. Remove the organic solvent under a vacuum using a rotary evaporator, until a thin film forms in the vial.
Next, transfer two milliliters of Dulbecco's phosphate buffered saline, pH 7.4 to the glass vial. Select an ultrasonic bath that can generate enough ultrasonic power to disperse the thin polymer drug film. The output power of the ultrasonic bath used in this protocol is 110 watts.
Place the vial in an ultrasonic bath for three minutes at room temperate to generate micelles. Keep micelles at four degrees Celsius for short term storage, and minus 20 degrees celsius for long term storage. Once micelles are prepared, perform various characterizations to determine drug concentration in micelles, particle sizes, and in vitro anticancer activities.
To determine the DOX-PA concentration and drug encapsulation efficiency, dilute 25 microliters of drug loaded micelles with 500 microliters of DMSO. Measure the absorption at 490 nanometers with a UV-VIS spectrometer, and calculate drug concentrations and encapsulation efficiency as described in the text protocol. To evaluate in vitro anticancer activity, add the diluted cell suspensions into a 96 well cell culture plate at 100 microliters per well.
Incubate the cells in a cell culture incubator for 18 hours to allow cell attachment. Next, dilute a DOX DMSO solution and a DOX-PA DMSO solution with cell culture medium to obtain final drug concentrations. Keep the final DMSO concentration in all samples at 0.5%Then dilute DOX-PA micelles with cell culture medium to obtain final drug concentrations.
Use the blank cell culture medium as a control. Remove the 96 well cell culture plate from the incubator and replace the cell culture medium with 100 microliters of medium containing different treatment agents. Incubate the cells in the cell culture incubator for an additional 72 hours.
Next, aspirate the medium and add 100 microliters of medium containing 0.5 milligrams per milliliter of MTT. Incubate the cells in the cell culture incubator for an additional two hours. Carefully remove the medium and add 100 microliters of DMSO to dissolve formazan crystals.
Measure absorbence with the microplate spectrophotometer at a wavelength of 570 nanometers and a reference wavelength of 670 nanometers. Finally, calculate the cell viability as described in the text protocol. The synthesis scheme of DOX-PA is shown here.
Palmitic acid is conjugated to doxorubicin through a pH sensitive hydrozine linker. The structure of DOX-PA was further confirmed with a proton NMR spectrum. Characteristic NMR peaks from both doxorubicin and palmitic acid are observed.
Letters indicate peaks, and their corresponding moiety within the structure. Blank DSPE-PEG micelles without drug appear as a transparent liquid, whereas DOX-PA DSPE-PEG micelles appear as a red liquid, which is due to the DOX-PA loaded in the micelles. The mean particle size for blank DSPE-PEG micelles is around 17.0 nanometers.
The loading of DOX-PA increased micell particle size slightly, with a mean particle size for DOX-PA DSPE-PEG micelles of around 25.7 nanometers. A concentration dependent reduction in cell viability was achieved by treating DU145 cells with free doxorubicin, free DOX-PA, or DOX-PA micelles. Although free doxorubicin is more effective than free DOX-PA or DOX-PA micelles at lower concentrations, DOX-PA groups showed greater reduction in cell viability than free doxorubicin at higher concentrations.
Also, there appear to be no significant difference between DOX-PA and DOX-PA micelles at both higher and lower concentrations. After watching this video, you should have a good understanding of how to prepare the micell formulations with a film dispersion method. It's important to remember that the method described can be used to prepare micell with different drugs and carrier materials.
The design of carrier material is critical to improve the formulation performance. Following this procedure, the micell formulation can be further evaluated in vivo with animal tumor models to test the anticancer activity.
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