Many groups are working to discover new, safer ways to deliver drugs that fight cancer to the tumor without damaging healthy cells. Others are finding ways to boost the body’s own immune system to attack cancer cells. For the first time, researchers at Penn State have combined the two approaches by conjugating biodegradable polymer nanoparticles encapsulated with chosen cancer-fighting drugs into immune cells to create a smart, targeted system to attack cancers of specific types.
“The traditional way to deliver drugs to tumors is to put the drug inside some type of nanoparticle and inject those particles into the bloodstream,” said Jian Yang, professor of biomedical engineering, Penn State. “Because the particles are so small, if they happen to reach the tumor site they have a chance of penetrating through the blood vessel wall because the vasculature of tumors is usually leaky.”
The odds of interacting with cancer cells can be improved by coating the outside of the nanoparticles with antibodies or certain proteins or peptides that will lock onto the cancer cell when they make contact. However, this is still a passive drug delivery technology. If the particle does not go to the tumor, there is no chance for them to bind and deliver the drug.
Yang and Cheng Dong, department head and distinguished professor of biomedical engineering, wanted a more active method of targeting drugs to the cancer wherever it was located, whether circulating in the blood, or in the brain or in any of the other organs of the body.
“I have 10 years of working in immunology and cancer,” Dong said. “Jian is more a biomaterials scientist. He knows how to make the nanoparticles biodegradable. He knows how to modify the particles with surface chemistry, to decorate them with peptides or antibodies. His material is naturally fluorescent, so you can track the particles at the same time they are delivering the drug, a process called theranostics that combines therapy and diagnostics. On the other hand, I study the cancer microenvironment, and I have discovered that the microenvironment of the tumor generates kinds of inflammatory signals similar to what would happen if you had an infection.”
Immune cells, which were built to respond to inflammatory signals, will be naturally attracted to the tumor site. This makes immune cells a perfect active delivery system for Yang’s nanoparticles. The same technology is also likely to be effective for infectious or other diseases, as well as for tissue regeneration, Dong said.
In the first proof of their technology, the two research groups targeted circulating melanoma cells. In a paper published in the current online issue of the journal Small, titled “Immune Cell-Mediated Biodegradable Theranostic Nanoparticles for Melanoma Targeting,” the researchers report the use of a novel biodegradable and photoluminescent poly (lactic acid) (BPLP-PLA) nanoparticle, loaded with melanoma-specific drugs with immune cells as the nanoparticle carriers. They showed that the immune cells could bind to the melanoma cells under shear stress conditions similar to those in the bloodstream. These experiments were all performed outside the body. Next they intend to perform studies in animal models and in solid tumors.
“This is the first study and is just to show that the technology works,” Dong said. “This study is not about curing melanoma. There are probably other ways to do that. We used melanoma cells to validate the approach.”
A chance meeting between a spider expert and a chemist has led to the development of antibiotic synthetic spider silk.
After five years’ work an interdisciplinary team of scientists at The University of Nottingham has developed a technique to produce chemically functionalised spider silk that can be tailored to applications used in drug delivery, regenerative medicine and wound healing.
The Nottingham research team has shown for the first time how ‘click-chemistry’ can be used to attach molecules, such as antibiotics or fluorescent dyes, to artificially produced spider silk synthesised by E.coli bacteria. The research, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) has been published in the online journal Advanced Materials.
The chosen molecules can be ‘clicked’ into place in soluble silk protein before it has been turned into fibres, or after the fibres have been formed. This means that the process can be easily controlled and more than one type of molecule can be used to ‘decorate’ individual silk strands.
In a laboratory in the Centre of Biomolecular Sciences, Professor Neil Thomas from the School of Chemistry in collaboration with Dr Sara Goodacre from the School of Life Sciences, has led a team of BBSRC DTP-funded PhD students starting with David Harvey who was then joined by Victor Tudorica, Leah Ashley and Tom Coekin. They have developed and diversified this new approach to functionalising ‘recombinant’ — artificial — spider silk with a wide range of small molecules.
They have shown that when these ‘silk’ fibres are ‘decorated’ with the antibiotic levofloxacin it is slowly released from the silk, retaining its anti-bacterial activity for at least five days.
Neil Thomas, a Professor of Medicinal and Biological Chemistry, said: “Our technique allows the rapid generation of biocompatible, mono or multi-functionalised silk structures for use in a wide range of applications. These will be particularly useful in the fields of tissue engineering and biomedicine.”
Remarkable qualities of spider silk
Spider silk is strong, biocompatible and biodegradable. It is a protein-based material that does not appear to cause a strong immune, allergic or inflammatory reaction. With the recent development of recombinant spider silk, the race has been on to find ways of harnessing its remarkable qualities.
The Nottingham research team has shown that their technique can be used to create a biodegradable mesh which can do two jobs at once. It can replace the extra cellular matrix that our own cells generate, to accelerate growth of the new tissue. It can also be used for the slow release of antibiotics.
Professor Thomas said: “There is the possibility of using the silk in advanced dressings for the treatment of slow-healing wounds such as diabetic ulcers. Using our technique infection could be prevented over weeks or months by the controlled release of antibiotics. At the same time tissue regeneration is accelerated by silk fibres functioning as a temporary scaffold before being biodegraded.”
The medicinal properties of spider silk recognised for centuries.
The medicinal properties of spider silk have been recognised for centuries but not clearly understood. The Greeks and Romans treated wounded soldiers with spider webs to stop bleeding. It is said that soldiers would use a combination of honey and vinegar to clean deep wounds and then cover the whole thing with balled-up spider webs.
There is even a mention in Shakespeare’s Midsummer Night’s Dream: “I shall desire you of more acquaintance, good master cobweb,” the character ‘Bottom’ said. “If I cut my finger, I shall make bold of you.”
‘I think we could make that!’
The idea came together at a discipline bridging university ‘sandpit’ meeting five years ago. Dr Goodacre says her chance meeting at that event with Professor Thomas proved to be one of the most productive afternoons of her career.
Dr Goodacre, who heads up the SpiderLab in the School of Life Sciences, said: “I got up at that meeting and showed the audience a picture of some spider silk. I said ‘I want to understand how this silk works, and then make some.’
“At the end of the session Neil came up to me and said ‘I think my group could make that.’ He also suggested that there might be more interesting ‘tweaks’ one could make so that the silk could be ‘decorated’ with different, useful, compounds either permanently or which could be released over time due to a change in the acidity of the environment.”
The approach required the production of the silk proteins in a bacterium where an amino acid not normally found in proteins was included. This amino acid contained an azide group which is widely used in ‘click’ reactions that only occur at that position in the protein. It was an approach that no-one had used before with spider silk — but the big question was — would it work?
Dr Goodacre said: “It was the start of a fascinating adventure that saw a postdoc undertake a very preliminary study to construct the synthetic silks. He was a former SpiderLab PhD student who had previously worked with our tarantulas. Thanks to his ground work we showed we could produce the silk proteins in bacteria. We were then joined by David Harvey, a new PhD student, who not only made the silk fibres, incorporating the unusual amino acid, but also decorated it and demonstrated its antibiotic activity. He has since extended those first ideas far beyond what we had thought might be possible.”
David Harvey’s work is described in this paper but Professor Thomas and Dr Goodacre say this is just the start. There are other joint SpiderLab/Thomas lab students working on uses for this technology in the hope of developing it further.
David Harvey, the lead author on this their first paper, has just been awarded his PhD and is now a postdoctoral researcher on a BBSRC follow-on grant so is still at the heart of the research. His current work is focused on driving the functionalised spider silk technology towards commercial application in wound healing and tissue regeneration.
Where will we be in 5 years’ time?
Dr Goodacre said: “It is likely that this paper is just the start of a very exciting range of studies using the new spider silk material. Some of the future work will also be supported by other, neat ideas from the world of spiders and their silk, which the SpiderLab is currently trying to unravel.”
Tiny machines like nanorockets are ideal candidates for drug delivery in the human body. Chemists at Radboud University now demonstrate the first complete movement regulation of a nanorocket, by providing temperature responsive brakes. An interesting feature for practical applications, since temperature sensitivity enables the rocket to stop in diseased tissues where temperatures are higher.
The soft nanosystems that the bio-organic chemists at Radboud University work with self assemble, which means that they spontaneously form functional units. This allows the nanorockets to change shape, making them ideal candidates for containing cargo like medicine. ‘Our biggest challenge is to provide our nanorockets with various functionalities’, says Daniela Wilson, head of Radboud University’s Bio-organic chemistry department and Nanomedicine theme leader ‘We now demonstrate the first molecularly built brake system, enabling the rockets to start and stop at desired locations.’
Temperature responsive brakes
The brakes consist of brushes made of polymers – long chains of responsive units – that grow onto the surface of the nanorockets. These brushes swell or collapse in response to the environmental temperature and in this way regulate fuel access to the rocket; in this case H2O2, hydrogen peroxide. Their sensitivity is high, as is shown by the fact that the brushes immediately collapse at a temperature of 35 degrees Celsius or higher, making the machine stop. ‘This all happens without affecting the catalytic activity or the shape of the nanorocket’, explains Wilson. ‘Therefore, nanorockets equipped with this valve system are able to move with great efficiency in water, even at low concentrations of fuel.’
Figure 1. Left side: in temperatures below 35 degrees Celsius, the brushes swell, opening up the valve, allowing fuel inside and propelling the nanorocket forward. Right side: when the temperature rises above 35 degrees Celsius, the brushes collapse, closing off the valve and stopping the supply of fuel, and thus the movement (copyright: Nature Chemistry).
Magnetic field acts as steering wheel
In another publication in Advanced Materials, Wilson and colleagues show how low
magnetic fields can act as a steering wheel for the nanorockets. By growing magnetic metallic nickel into the core of the rockets, magnetic field can be used to guide and steer the rockets into desired directions.
But, there’s always room for improvement. Wilson: ‘What would be even more interesting than temperature responsive brakes, is a system that responds to light. This would allow us to start or stop a nanorocket by shining a laser light on it. Furthermore, even though our nanorockets are not toxic to living cells, they are not completely biodegradable yet. And of course that is one of the prerequisites for their use as medicine carriers in the body. These are only some examples of the next challenges for our group!’
Scientists from the University of Utah and University of Washington have developed blueprints that instruct human cells to assemble a virus-like delivery system that can transport custom cargo from one cell to another. As reported online in Nature on Nov. 30, the research is a step toward a nature-inspired means for delivering therapeutics directly to specific cell types within the body.
“We’re shifting our perception from viruses as pathogens, to viruses as inspiration for new tools,” says Wesley Sundquist, Ph.D., co-chair of the Department of Biochemistry at the University of Utah School of Medicine. He is also co-senior author on the study with Neil King, Ph.D., an assistant professor at the Institute for Protein Design at the University of Washington.
The carefully designed instructions set forth a series of self-propelled events that mimic how some viruses transfer their infectious contents from one cell to the next.
From the blueprints tumbled out self-assembling, soccer ball-shaped “nanocages”, the structure of which was reported previously. Adding on specific pieces of genetic code from viruses caused the nanocages to be packaged within cell membranes, and then exported from cells. Like a shuttle leaving Earth to bring goods to a space station, the tiny capsules undocked from one cell, traveled to another and docked there, emptying its contents upon arrival.
In this case, the protective nanocages carried cargo that the scientists used like homing beacons to track the vessels’ journeys. Next steps are to design nanocages that hold drugs or other small molecules.
“We are now able to accurately and consistently design new proteins with tailor-made structures,” says King. “Given the remarkably sophisticated and varied functions that natural proteins perform, it’s exciting to consider the possibilities that are open to us.”
The researchers’ decision to model the microscopic shipping system after viruses was no accident. Viruses have honed their skills to effectively spread their infectious wares to large numbers of cells. Decades of research, including in-depth investigations of the human immunodeficiency virus (HIV) by Sundquist’s team, have led to an understanding of how the pathogens accomplish this goal with such efficiency.
A test of whether you truly understand something is to build it yourself. And that’s what Sundquist and King’s teams have done here. “The success of our system is the first formal proof that this is how virus budding works,” remarks Sundquist.
Viruses taught them that such a delivery system must include three essential properties: an ability to grasp membranes, self-assemble, and to be released from cells. Introducing coding errors into any one of those steps brought shipments to a halt.
“I was sure that this would need fine-tuning but it was clean from the very beginning,” says lead author Jörg Votteler, Ph.D., a postdoctoral fellow in biochemistry at the University of Utah. When electron microscopist David Belnap, Ph.D. saw that images of the cages aligned closely with computer models, he knew they had made what they set out to design. “When it’s right, you know it,” he says.
The system could be modified as long as the three basic tenets were left intact. For example, the scientists could swap in differently shaped cages, or cause another type of membranes to surround them. Modularity means the vessels can be customized for various applications.
This study is proof of principle that the systems works, but more needs to be done before it can be applied therapeutically. Researchers will need to determine whether the capsules can navigate long journeys within living animals, for instance, and whether they can deliver medicines in sufficient quantities.
“As long as we keep pushing knowledge forward we can guarantee there will be good outcomes, though we can’t guarantee what or when,” says Sundquist.
Performing chemical reactions inside tiny droplets can help manufacturers develop greener processes for coating drugs
An A*STAR-led discovery could lead to improvements in the way drugs are delivered to the right parts of the body by uncovering the mechanisms that help oil, water, and free radicals mix in tiny droplets1,2.
Emulsion polymerization is an emerging technology used to produce enormous chain-like molecules called polymers inside oil-filled drops suspended in water. This approach enables producers of goods such as latex paints to do away with traditional oil-based solvents, which helps them meet stricter environmental controls. Recently, researchers have discovered that ‘mini-emulsions’, in which droplets are shrunk to nanoscale sizes using powerful blenders and stabilized with fatty molecules, can produce nanoparticles for applications including controlled drug release.
Alex van Herk from the A*STAR Institute of Chemical and Engineering Sciences explains that in mini-emulsions, each droplet can be regarded as a ‘nanoreactor’ — a segregated system where all the ingredients for polymerization are present in one spot. Once a highly reactive free radicalenters the drop, the small molecules inside link into chains. “The nanoreactors grow completely independently, and we can achieve very high reaction rates,” he says.
This polymerization only works when one free radical enters a nanoreactor. However, the molecules that generate free radicals, known as initiators, generally produce them in pairs. To better understand these radical movements, van Herk and colleagues from the Netherlands and the United Kingdom investigated the effects of using initiators that either repelled or attracted water molecules.
Typical initiators are water-soluble and researchers propose that they create pairs of free radicals in water where one of the free radicals enters the nanoreactor and starts the polymerization. However, when the initiator is a water-repelling molecule, such as lauroyl peroxide, theory predicts the chemical reaction will be hindered because the two radicals in a confined space would easily recombine and the polymerization process would not start.
Surprisingly, the A*STAR-led team found mini-emulsion polymerization proceeded rapidly and completely using lauroyl peroxide initiators. To explain this discrepancy, the team deduced that a free radical must leave by an alternative mechanism, known as chain transfer, which transforms one of the water molecules surrounding the nanoreactor into a hydroxyl radical compound. The remaining radical produces latex nanoparticles that correspond one-to-one with the initial droplet size — a benefit for manufacturers seeking to predict morphologies with exact specifications.
“Industry is only modestly adopting mini-emulsion polymerization, partly because its mechanism is not fully understood and controllable yet,” says van Herk. “These findings give us a better edge to design and produce special nanoparticle morphologies such as low-cost nanocapsules.”
The team of researchers at Saarland University, led by Professor of Condensed Matter Physics Karin Jacobs, initially had something quite different in mind. Originally, the team set out to research and describe the characteristics of hydrophobins – a group of naturally occurring proteins. ‘We noticed that the hydrophobins form colonies when they are placed in water. They immediately arrange themselves into tightly packed structures at the interface between water and glass or between water and air,’ explains Karin Jacobs. ‘There must therefore be an attractive force acting between the individual hydrophobin molecules, otherwise they would not organize themselves into colonies.’ But Professor Jacobs, research scientist Dr Hendrik Hähl and their team did not know how strong this force was.
This is where the neighbouring research group led by Professor Ralf Seemann got involved. One of Seemann’s research teams, which is headed by Dr Jean-Baptiste Fleury, studies processes that occur at the interfaces between two liquids. The research team set up a minute experimental arrangement with four tiny intersecting flow channels, like a crossroads, and allowed a stream of oil to flow continuously from one side of the crossing to the other. From the other two side channels they injected ‘fingers’ of water which protruded into the crossing zone. As the hydrophobins tended to gather at the interface of the carrier medium, they were in this case arranged at the water-oil interface at the front of the fingers. The physicists then ‘pushed’ the two fingers closer and closer together in order to see when the attractive force took effect. ‘At some point the two aqueous fingers suddenly coalesced to form a single stable interface consisting of two layers,’ says Ralph Seemann. ‘The weird thing is that it also functions the other way around, that is, when we use oil fingers to interrupt a continuous flow of water,’ he explains. This finding is quite new, as up until now other molecules have only exhibited this sort of behaviour in the one or the other scenario. Normally proteins will orient themselves so that either their hydrophilic (‘water loving’) sides are in contact with the aqueous medium, or their hydrophobic (‘water fearing’) side is in contact with an oily medium. That a type of molecule can form stable bilayers in both environments is something wholly new.
Encouraged by these findings, the researchers decided to undertake a third phase of experiments to find out whether the stable bilayer could be reconfigured to form a small membrane-bound transport sac – a vesicle. They attempted to inflate the stable membrane bilayer in a manner similar to creating a soap bubble, but using water rather than air. The experiment worked. The cell-like sphere with the outer bilayer of natural proteins was stable. ‘That’s something no one else has achieved,’ says Jean-Baptiste Fleury, who carried out the successful experiments. Up until now it had only been possible to create monolayer membranes or vesicles from specially synthesized macromolecules. Vesicles made from a bilayer of naturally occurring proteins that can also be tailored for use in an aqueous or an oil-based environment are something quite new.
In subsequent work, the research scientists have also demonstrated that ion channels can be incorporated into these vesicles, allowing charged particles (ions) to be transported through the bilayer of hydrophobins in a manner identical to the way ions pass through the lipid bilayers of natural cells.
As a result, the physicists now have a basis for further research work, such as examining the means of achieving more precisely targeted drug delivery. In one potential scenario, the vesicles could be used to transport water-soluble molecules through an aqueous milieu or fat-soluble molecules through an oily environment. Dr Hendrik Hähl describes the method as follows: ‘Essentially we are throwing a vesicle “cape” over the drug molecule. And because the “cape” is composed of naturally occurring molecules, vesicles such as these have the potential to be used in the human body.’
The results of this research work were a surprise. Originally, the goal was simply to measure the energy associated with the agglomeration of the hydrophobin molecules when they form colonies. But the discovery that hydrophobin bilayers could be formed in both orientations, opened the door to experiments designed to see whether vesicles could be formed. That one thing would lead to another in this way, offers an excellent example of the benefits of this type of basic, curiosity-driven research. ‘The “discovery” of these vesicles is archetypal of this kind of fundamental research. Or to put it another way, if someone had said to us at the beginning: “Create these structures from a natural bilayer,” we very probably wouldn’t have succeeded,’ says Professor Karin Jacobs in summary.
Researchers funded in part by NIBIB have recently shown that magnetic bacteria are a promising vehicle for more efficiently delivering tumor-fighting drugs. They reported their results in the August 2016 issue of Nature Nanotechnology.
One of the biggest challenges in cancer therapy is being able to sufficiently deliver chemotherapy drugs to tumors without exposing healthy tissues to their toxic effects. One way researchers have attempted to overcome this is by developing nanocarriers—extremely small particles packed with drugs. The nanocarriers are designed so they’re only taken up by cancer cells, thereby preventing the drugs from being absorbed by healthy tissues as they travel through the body’s circulation.
Yet while nanocarriers do a good job protecting healthy tissues, the amount of drug successfully delivered to tumors remains low. The main reasons for this shortcoming are that nanocarriers rely on the circulation system to carry them to the tumor, so a large percentage are filtered out of the body before ever reaching their destination. In addition, differences in pressure between the tumor and its surrounding tissue prevent nanocarriers from penetrating deep inside the tumor. As a result, nanocarriers aren’t able to reach the tumor’s hypoxic zones, which are regions of active cell division that are characterized by low oxygen content.
“Only a very small proportion of drugs reach the hypoxic zones, which are believed to be the source of metastasis. Therefore, targeting the low-oxygen regions will most likely decrease the rate of metastasis while maximizing the effect of a therapy,” says Sylvain Martel, Ph.D., Director of the Polytechnique Montréal NanoRobotics Laboratory and lead researcher of the study.
Martel and his research team were attempting to develop robotic nanocarriers that would travel to hypoxic zones when they realized nature may have already created one in the form of a bacteria called magnetococcus marinus or MC-1. MC-1 cells thrive in deep waters where oxygen is sparse. In order to find these areas, the bacteria rely on a two-part navigation system. The first part involves a chain of magnetic nanocrystals within MC-1 that acts like a compass needle and causes the bacteria to swim in a north direction when in the Northern Hemisphere. The second part consists of sensors that allow the bacteria to detect changes in oxygen levels. This unique navigation system helps the bacteria migrate to and maintain their position at areas of low oxygen.
With funding support from NIBIB and others, Martel’s research team conducted a series of experiments to show that the bacteria’s unique navigation system could be exploited to more efficiently deliver drugs to tumors.
In an initial experiment, mice that had been given human colorectal tumors were injected with either live MC-1 cells, dead MC-1 cells, or as a control group, non-magnetic beads (roughly the same size as the bacteria). The injection was made into the tissue directly adjacent to the tumors after which the mice were exposed to a computer-programmed magnetic field, meant to direct the cells or beads into the tumor. Upon examination of the tumors, the researchers found minimal penetration of the dead bacterial cells and the beads into the tumor, whereas the live bacterial cells were found deep within the tumor and especially in regions with low oxygen content.
“When they get inside the tumor, we switch off the magnetic field and the bacteria automatically rely on the oxygen sensors to seek out the hypoxic areas,” says Martel. “We constrain them to the tumor and then let nature do the rest.”
Next, the researchers wanted to see whether attaching vesicles loaded with drugs to the cells would affect their movement into the tumors. They attached approximately 70 drug-containing vesicles to each bacterial cell. The cells were then injected into another set of mice with colorectal tumors and exposed to the magnet. After examining the tumors of those mice, the researchers estimated that on average, 55% of the injected bacterial cells with attached vesicles made it into the tumor. For comparison, some researchers estimate that only approximately 2% of drugs delivered via current nanocarriers make it into tumors.
“This proof-of-concept work shows the potential to tap into the intricate and optimized cell machinery of single celled organisms such as bacteria,” said Richard Conroy, Ph.D., director of the Division of Applied Sciences and Technology at NIBIB. “The ability to actively and precisely target drug delivery to a tumor will help reduce side effects and potentially improve the efficacy of treatments.”
The next step for Martel’s team is to determine the effects of the drug-loaded bacterial cells on reducing tumor size. They would also like to test whether the bacteria can be used to deliver other types of cancer-killing medicines such as molecules that instruct the immune system to attack tumors.
In addition, the team is working to expand the types of tumors the bacteria could be used for. Currently, the bacteria have to be injected very close to the tumor because, if injected into arteries, the excessive blood flow and the distance needed to travel would impact the number of bacteria that reach the tumor. This limits the drug delivery approach to cancers that are easily accessible such as colorectal, prostate, and potentially breast cancer. However, Martel’s team has shown in animals that they can transport the bacteria through arteries and sufficiently close to the tumor by first encapsulating them in magnetic carriers and propelling them by the magnetic field of an MRI scanner. The bacteria can then be released from the carriers, like torpedoes from a submarine, once close to the tumor. This multi-step approach could potentially open the door for using the bacteria to deliver drugs to tumors deeper in the body.
Martel says that preliminary test results of the bacteria in mice and rats and the fact that the bacteria die within 30 minutes of being injected, suggest that they could potentially be safe in humans.
“These bacteria are really the perfect machine. They replicate, they’re cheap, and we can inject hundreds of millions or more at a time,” says Martel.
Beads, disks, bowls and rods: scientists at Radboud University have demonstrated the first methodological approach to control the shapes of nanovesicles. This opens doors for the use of nanovesicles in biomedical applications, such as drug delivery in the body.
The shape of nanovesicles – called ‘polymersomes’ in jargon – in a solution varies at different compositions of that solution, scientist Roger Rikken and his colleagues at Radboud University discovered. “Besides the spherical shapes, we can create disks, rods, and bowl shaped stomatocytes by varying the ratio of the solvent. This regulates the osmotic pressure and permeability of the vesicles, controlling their deflation and subsequent re-inflation,” Rikken explains.
For the first time, the shape of the nanovesicles is now fully controllable and predictable. This offers possibilities to transform and mould the vesicles into nanocontainers or nanorockets, which are highly desirable, e.g. for drug delivery in the body. The shape of the polymersomes also affects their flow properties, as is also believed to be the case for red blood cells. It is therefore of great importance to obtain full control over shape transformations to utilise vesicles in drug transport via the blood stream.
By using the magnets of the High Field Magnet Laboratory, Rikken was able to determine the exact shape of the vesicles at every solvent ratio. Subsequently, he studied the variety of shapes with electron microscopy and described them mathematically. In this way, he discovered that the shape transformation follows the path of the lowest energy. “Nature is always trying to stay in balance. The four shapes that we found turn out to be located exactly at the energy minima in an existing model. The basic idea behind our discovery is actually very logical, but it was never described before.”
Viruses are able to redirect the functioning of cells in order to infect them. Inspired by their mode of action, scientists from the CNRS and Université de Strasbourg have designed a “chemical virus” that can cross the double lipid layer that surrounds cells, and then disintegrate in the intracellular medium in order to release active compounds.
To achieve this, the team used two polymers they had designed, which notably can self-assemble or dissociate, depending on the conditions. This work, the result of collaborative efforts by chemists, biologists and biophysicists, is published in the 1st September issue of Angewandte Chemie International Edition.
Biotechnological advances have offered access to a wealth of compounds with therapeutic potential. Many of these compounds are only active inside human cells but remain unusable because the lipid membrane surrounding these cells is a barrier they cannot cross. The challenge is therefore to find transfer solutions that can cross this barrier.
By imitating the ability of viruses to penetrate into cells, chemists in the Laboratoire de Conception et Application de Molécules Bioactives (CNRS/Université de Strasbourg) sought to design particles capable of releasing macromolecules that are only active inside cells. To achieve this, these particles must comply with several, often contradictory, constraints. They must remain stable in the extracellular medium, they must be able to bind to the cells so that they be internalized, but they must be more fragile inside the cells so that they can release their content.
Using two polymers designed by the team, the scientists succeeded in creating a “chemical virus” that meets the conditions necessary for the direct delivery of active proteins into cells.
In practice, the first polymer (pGi-Ni2+) serves as a substrate for the proteins that bind to it. The second, recently patented polymer (?PEI), encapsulates this assembly thanks to its positive charges, which bind to the negative charges of pGi-Ni2+. The particles obtained (30-40 nanometers in diameter) are able to recognize the cell membrane and bind to it. This binding activates a cellular response: the nanoparticle is surrounded by a membrane fragment and enters the intracellular compartment, called the endosome. Although they remain stable outside the cell, the assemblies are attacked by the acidity that prevails within this new environment. Furthermore, this drop in pH allows the ?PEI to burst the endosome, releasing its content of active compounds.
Thanks to this assembly, the scientists were able to concentrate enough active proteins within the cells to achieve a notable biological effect. Thus by delivering a protein called caspase 3 into cancer cell lines, they succeeded in inducing 80% cell death1.
The in vitro results are encouraging, particularly since this “chemical virus” only becomes toxic at a dose ten times higher than that used during the study. Furthermore, preliminary results in the mouse have not revealed any excess mortality. However, elimination by the body of the two polymers remains an open question. The next stage will consist in testing this method in-depth and in vivo, in animals. In the short term, this system will serve as a research tool to vectorize2 recombinant and/or chemically modified proteins into cells. In the longer term, this work could make it possible to apply pharmaceutical proteins to intracellular targets and contribute to the development of innovative drugs.
Read more: Imitating viruses to deliver drugs to cells