Methionine Functionalized Biocompatible Block Copolymers for Targeted Plasmid DNA Delivery
August 6th, 2019
This work presents the preparation of methionine functionalized biocompatible block copolymers (mBG) via the reversible addition-fragmentation chain transfer (RAFT) method. The plasmid DNA complexing ability of the obtained mBG and their transfection efficiency were also investigated. The RAFT method is very beneficial for polymerizing monomers containing special functional groups.
Cationic polymer drug carriers have the advantages of good stability, low immunogenicity, and facile preparation and modification. Here, we offer a rapid and simple method for its synthesis. Reversible addition-fragmentation chain transfer polymerization method is a method applicable to yield block polymers with controlled molecular weight and structure and carrying functional groups.
These drug carriers can simultaneously carry different drugs to achieve the collaborate treatment of cancer, inflammation, and other diseases. IFT polymerization is a classic method, and this protocol gives an example of its application in gene therapy. The key to the success for synthesis of this polymer is to precisely control the reaction temperature.
It is more advisable to use an oil bath than a water bath. To begin this procedure, obtain a round-bottom flask with a rubber stopper and a magnetic stirrer to be used as the polymerization bottle. Dissolve 1.87 grams of bis-hydroxy HEMA in one milliliter of distilled water in the polymerization bottle.
In a five-milliliter beaker, dissolve 0.03 grams of CTP and 0.02 grams of ACVA in 0.5 milliliters of 1, 4-dioxane. Add this mixture to the polymerization bottle. Then, use a condensate trap to freeze the solution in the polymerization bottle.
Fix the bottle to the iron support, and use a conduit tripped with a needle to vacuumize and inject nitrogen into the reaction mixture. Then, seal the polymerization bottle, and thaw the solution at room temperature for 30 minutes. Repeat this freeze-pump-thaw cycle three times.
After this, place the bottle into an oil bath at 70 degrees Celsius and let the solution react for 24 hours under the nitrogen atmosphere. The next day, chill the polymerization bottle at zero degrees Celsius and open the rubber stopper to terminate the polymerization reaction. Next, precool acetone in a refrigerator at negative 20 degrees Celsius for two hours, and mix it with the reaction solution in the polymerization bottle at a ratio of 50 to one.
Centrifuge this mixture at 8, 200 times g for 10 minutes to remove the acetone and collect the precipitate. To purify the synthesized poly bis-hydroxy HEMA, dissolve the collected precipitate in two milliliters of pure water. Then, mix it with 100 milliliters of precooled acetone at a ratio of one to 50.
Centrifuge the solution at 8, 200 times g for 10 minutes to collect the precipitate. Repeat this purification process of dissolving, mixing, and centrifuging the precipitate three times. First, dissolve 0.96 grams of APMA and 0.93 grams of the purified poly bis-hydroxy HEMA in five milliliters of distilled water in a 10-milliliter beaker.
Dissolve 0.01 grams of ACVA in 0.5 milliliters of 1, 4-dioxane, and add this to the APMA and poly bis-hydroxy HEMA solution. Transfer this mixture to a polymerization bottle, and ventilate with dry nitrogen for one hour. Then, put the polymerization bottle into an oil bath at 70 degrees Celsius, and let it react for 24 hours under the nitrogen atmosphere.
The next day, chill the polymerization bottle at zero degrees Celsius and open the rubber stopper to terminate the polymerization process solution. To begin, seed MCF-7 cells into the wells of a six-well plate at a density of 20, 000 cells per well. Culture the cells in a humidified incubator at 37 degrees Celsius with 5%carbon dioxide for 12 hours.
After this, replace the culture medium with the fresh culture medium containing cationic polymer and pDNA polyplex polyplexes of different ratio of nitrogen-to-phosphorus ratios. Culture the cells for six hours, and then replace the medium with two milliliters of fresh RPMI 1640 medium. Continue culturing for 48 hours.
Then, collect the cells, and use a flow cytometer to detect the green fluorescence. In this study, methionine-functionalized biocompatible block copolymers are prepared via the reversible addition-fragmentation chain transfer method, and the plasmid DNA complexing ability of the obtained mBG and their transfection efficiency is investigated. The average particle size and zeta potential of mBG/pDNA polyplexes are 124 nanometers and plus 15.7 millivolts, respectively, at an N-to-P ratio of 16.
Electrophoretic retardation reveals that pDNA with an N-to-P ratio of zero can move without restraint in the agarose gel and is observed as a stripe in the gel imager. When pDNA is complexed with mBG, the movement of pDNA is retarded, and subsequently, the brightness of the band is reduced. This shows that mBG can completely complex the pDNA when the N to P is higher than four.
The cytotoxicity of the mBG/pDNA polyplexes is then measured using the standard MTT assay These results show that mBG/pDNA polyplexes have cytotoxicity than PEI/pDNA polyplexes at the N-to-P ratios of four, eight, 16, and 32. As can also be seen, the cytotoxicity of the mBG/pDNA polyplexes increases with increased N-to-P ratio. This increased cytotoxicity is a result of the positively charged GPMA component.
The N-to-P ratio used in the pDNA transfection experiment is selected according to the cytotoxicity results. The transfection abilities of mBG1, mBG2, and mBG3 are compared by measuring the GFP fluorescence intensity, and the results showed that mBG3 is the optimal gene carrier. It is important to exhaust air from the silt round-bottom flask and maintain the reaction temperature.
The obtained polymer drug carriers can be applied to the co-delivery of chemotherapy drugs and gene drugs to synergistically treat drug-resistant cancer. The molecular mechanism of combination of gene drugs and chemotherapeutic drugs can be further explored for the treatment of drug-resistant tumors. Acetone is rated as low toxic for its acute toxicity.
Keys, inhalation or contact with eyes or skin should be avoided. Avoid to the risk of scalding during the heating procedure.
View the full transcript and gain access to thousands of scientific videos
Overview
This study presents a rapid and simple method for synthesizing cationic polymer drug carriers using the reversible addition-fragmentation chain transfer (RAFT) polymerization method. The synthesized methionine functionalized biocompatible block copolymers (mBG) were evaluated for their ability to complex plasmid DNA and their transfection efficiency.
Key Study Components
Area of Science
- Polymer Chemistry
- Gene Therapy
- Drug Delivery Systems
Background
- Cationic polymer drug carriers offer stability and low immunogenicity.
- RAFT polymerization allows for controlled molecular weight and structure.
- These carriers can transport multiple drugs for collaborative treatment.
- Precise control of reaction temperature is crucial for successful synthesis.
Purpose of Study
- To develop a method for synthesizing biocompatible block copolymers.
- To investigate the DNA complexing ability of the synthesized polymers.
- To assess the transfection efficiency of the drug carriers.
Methods Used
- Reversible addition-fragmentation chain transfer (RAFT) polymerization.
- Synthesis of methionine functionalized block copolymers.
- Evaluation of plasmid DNA complexing ability.
- Assessment of transfection efficiency.
Main Results
- The synthesized mBG demonstrated effective plasmid DNA complexation.
- Transfection efficiency was successfully evaluated.
- RAFT polymerization proved beneficial for functionalized polymer synthesis.
- The method allows for the simultaneous delivery of multiple drugs.
Conclusions
- The study successfully developed a method for synthesizing mBG.
- These biocompatible polymers show promise for gene therapy applications.
- Further research could enhance their effectiveness in drug delivery.
Frequently Asked Questions
Executive Industry Relevance
This work presents a RAFT polymerization-based method for synthesizing methionine-functionalized biocompatible block copolymers capable of complexing plasmid DNA, offering a tunable platform for gene delivery vector development. The ability to control molecular weight, charge ratio, and particle size enables predictive design of non-viral carriers with reduced cytotoxicity compared to PEI, supporting early-stage de-risking of nucleic acid therapeutics. Such systems address the need for scalable, reproducible polymer synthesis in preclinical discovery workflows where mechanistic clarity and formulation consistency impact go/no-go decisions.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of polymer-DNA interactions through quantifiable complexation at defined N/P ratios, supporting target validation via controlled gene delivery.
- Operational Value: Provides a reproducible synthesis route for cationic block copolymers with tunable methionine and guanidine functionalization, reducing variability in early screening assays.
Screening & Assay Development
- Scientific Value: Generates well-defined polyplexes with measurable zeta potential (+15.7 mV at N/P 16) and size (124 nm), enabling standardized assessment of transfection efficiency and cytotoxicity.
- Operational Value: Facilitates high-throughput screening of polymer variants (mBG1, mBG2, mBG3) by linking APMA content (21%, 37%, 52%) to functional outcomes in gene transfer assays.
Translational & Preclinical Research
- Scientific Value: Demonstrates complete plasmid DNA retardation at N/P >4, indicating reliable cargo protection—a key preclinical benchmark for vector stability.
- Operational Value: Supports formulation screening across N/P ratios (8, 16, 4) to identify optimal transfection conditions while monitoring cytotoxicity trends linked to GPMA content.
Pipeline & Workflow Integration
This method fits within the discovery-to-preclinical continuum by enabling synthesis of defined gene carriers for lead identification in nucleic acid delivery, where polymer structure-function relationships inform advancement decisions.
- Discovery Biology: Supports hypothesis testing on polymer-mediated gene delivery by providing quantifiable outputs (particle size, zeta potential, transfection efficiency) to correlate structure with biological activity.
- Screening: Enables assay-ready polyplex production with consistent size (100–200 nm at N/P 16–32) and surface charge, improving reproducibility across compound evaluation campaigns.
- Analytics: Generates measurable biophysical readouts (N/P ratio, zeta potential, electrophoretic retardation) that allow comparative analysis of polymer variants under standardized conditions.
- Translational Research: Connects polymer design to preclinical relevance through demonstrated pDNA complexation and reduced cytotoxicity relative to PEI, supporting risk-adjusted advancement.
- Enterprise Reuse: Establishes a modular RAFT-based platform adaptable to other functional amino acids or therapeutics, promoting cross-project standardization in polymer synthesis.
Operational & Enterprise Impact
- Scientific Value: Enhances predictive confidence in gene carrier performance by linking molecular design (methionine/guanidine content) to DNA binding and transfection outcomes.
- Operational Value: Delivers a scalable, purification-friendly synthesis protocol using acetone precipitation and RAFT control, improving batch-to-batch consistency.
- Strategic Value: Reduces late-stage biological risk by offering a lower-cytotoxicity alternative to PEI, enabling better go/no-go decisions in nucleic acid therapeutic development.
- Portfolio Impact: Supports risk-adjusted prioritization of polymer leads (e.g., mBG3 as optimal carrier) based on transfection efficiency and safety profiles.
Implementation Considerations
- Requires expertise in RAFT polymerization, including freeze-pump-thaw degassing and inert atmosphere handling.
- Dependent on precise temperature control (oil bath at 70°C) and specialized reagents (ACVA, CTP) for reproducible block copolymer synthesis.
- Necessitates analytical infrastructure for GPC, zeta potential, particle sizing, and fluorescence-based transfection assays to evaluate polyplex performance.
- Adaptation to other cell lines or payloads may require re-optimization of N/P ratio and cytotoxicity assessment due to variable GPMA-mediated effects.
- Practical limitations include the need for multi-step purification and sensitivity to oxygen during polymerization, which must be mitigated via rigorous degassing protocols.
