Work with Brazilian citrus greening genome could aid Florida industry

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An Asian citrus psyllid feeds on a citrus tree, leaving a bacteria that will starve the tree of nutrients and eventually kill it.

A University of Florida researcher has mapped the DNA genome of a new strain of citrus greening that could further threaten Florida's beleaguered $9 billion citrus industry. Knowing the genetic makeup of the various strains is critical to finding a cure.

Dean Gabriel, a plant bacteriology specialist with UF/IFAS, helped sequence and map the genome of the most prevalent form of the disease in Florida, and now he and colleagues have done the same for a new strain of the disease discovered in Brazil.

There is no cure for either strain, although researchers believe that knowing the genetic makeup of the disease is critical to finding one. Gabriel said by having that "roadmap" of the bacteria genome, they will be certain there are no surprises in the Brazilian species, which has now been found in Texas. In addition, the mapping should help guide them to improvements in control methods and toward more usable genes and treatments.

"What the genome does, it lets you know everything that the organism has and doesn't have in its artillery for offense and defense -- and it lets you design a strategy to control it," Gabriel said.

Researchers often liken having the genetic sequence for an organism to having its list of parts.

"Having all the genetic information is like having a detailed roadmap of the organism," said Jackie Burns, director of the UF/IFAS Citrus Research and Education Center in Lake Alfred.

Citrus greening was first discovered by farmers in China in 1911 and made its first appearance in Florida in 2005. It is spread by a tiny insect called the Asian citrus psyllid that feeds on the trees, leaving bacteria that starve the tree of nutrients. Infected trees produce fruits that are unsuitable for sale as fresh fruit or for juice and most die within a few years. The disease has already affected millions of citrus trees in North America.

Gabriel's team's work will be outlined in a research paper that will be published in February in the journal Molecular Plant-Microbe Interaction. The genome map is already available online, at GenBank.

To map the bacteria's DNA genome, Gabriel's Brazilian colleagues first diced up and crushed tissue from the veins of infected citrus trees where the organism was most highly concentrated. They used chemicals to extract DNA and purified it. The team had to separate the tree DNA from that of the bacterium.

DNA comprises four nucleotides, which fall into an order to encode genes specific to an organism. Gabriel likened it to examining beads on a necklace: The beads come in only four colors, and the color sequence determines each gene -- in this case, the DNA greening "necklace" held 1,195,201 beads, or 1,044 genes.

To obtain the nucleotide sequence from the purified bacterial DNA, they used state-of-the-art sequencing machines at the UF Interdisciplinary Center for Biotechnology Research.

The research was funded by the Citrus Research and Development Foundation Inc., an affiliate of UF's Institute of Food and Agricultural Sciences.

In the battle against greening, UF/IFAS researchers have tried everything from working on ways to eradicate the psyllid to grafting trees that show better resistance to greening.

Frederick Gmitter, a citrus breeder and faculty member at IFAS' Citrus REC, said his research team has found new experimental rootstocks that seem to be supporting healthier trees -- even ones with citrus greening. In addition, his team is studying "escape trees," which are trees that remain unscathed, even when surrounded by thousands of infected tress.

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Story Source:

The above story is based on materials provided by University of Florida Institute of Food and Agricultural Sciences. Note: Materials may be edited for content and length.

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Journal Reference:

1. Nelson Arno Wulff, Shujian Zhang, João C Setubal, Nalvo F Almeida, Elaine C Martins, Ricardo Harakava, Dibyendu Kumar, Luiz T Rangel, Xavier Foissac, Joseph Bove, Dean W GABRIEL. The complete genome sequence of Candidatus Liberibacter americanus, associated with citrus Huanglongbing.. Molecular Plant-Microbe Interactions, 2013; 131107142521009 DOI: 10.1094/MPMI-09-13-0292-R

On The High Seas, China Moves "Unilaterally"

 

 

Seeded on Sun May 11, 2014 1:37 AM

China has not been shy in recent years about making broad claims to control much of the South China Sea. But by installing an expensive drilling rig in disputed waters, it now appears more willing to act first and invite diplomacy later. It is in effect creating “facts” in the water that its regional rivals, and ultimately the United States, must either accept or fight.

China signaled it would take unilateral steps last year, when it declared an air defense zone over parts of the East China Sea that includes islands at the center of a long-smoldering dispute with Japan. In the battle of wills with Vietnam, China has unleashed a new and potentially powerful tool in its battle for territory: its oil industry and the rigs a state oil-company official once called “our mobile national territory.”

Study validates air sampling techniques to fight bioterrorism

 

May 9, 2014

Saint Louis University

Air and surface sampling techniques currently used by the US government are effective in fighting bioterrorism and potentially saving lives, a former Department of Homeland Security medical officer finds. Air sampling has been readily accepted for similar uses such as measuring for particulate matter, however using it to detect bacteria in biological terrorism was a new concept instituted after the 9/11 attacks.

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Alexander Garza, M.D., MPH, is the associate dean for public health practice and associate professor of epidemiology at Saint Louis University College for Public Health and Social Justice.

Air and surface sampling techniques currently used by the US government are effective in fighting bioterrorism and potentially saving lives, a Saint Louis University researcher finds.

Results published in Biosecurity and Bioterrorism by Alexander Garza, M.D., MPH, former chief medical officer at the Department of Homeland Security and a team of researchers from Los Alamos National Lab reviewed the data from a series of experiments simulating a bioterrorism attack against the Pentagon. Garza is now the associate dean for public health practice and associate professor of epidemiology at Saint Louis University College for Public Health and Social Justice.

In 2005 and 2009, the Pentagon Force Protection Agency (PFPA) in order to simulate a deliberate attack, staged the release of a harmless bacteria that is biological similar to Bacillus anthracis, the bacteria that causes the disease anthrax. They then evaluated the local response procedures to such an attack. In conjunction with this exercise, the Department of Homeland Security ran its own experiments to test the efficacy of an air and surface sampling system known as BioWatch in detecting these biological agents in the environment.

In the experiments, multiple kilograms of benign material were released, which included a small portion of the anthrax simulant. The team collected samples of the air through several portable sampling units and had them analyzed at specialized laboratories.

"We were able to detect the biological organisms released several kilometers from where the agent was originally released," Garza said. "We were not entirely surprised by the results. Since all of the modeling that had been done to date showed that air samplers should be able to detect these types of attack, what was missing was empirical evidence showing that these systems would work in real world conditions. We now have that evidence."

"The traditional way to detect that someone has been exposed to a biological agent is to wait until a person becomes symptomatic and then hope that the clinician is able to correctly diagnose the patient," Garza said, "which is exactly what happened during the anthrax attacks in 2001."

Garza points out the problem with this approach is that once people become sick they are likely to die, which can potentially lead to significant casualties in a large-scale attack.

"This experiment confirmed that a biological attack could be detected earlier using air sampling which means public health would have more time to respond."

Air sampling has been readily accepted for similar uses such as measuring for particulate matter, however using it to detect bacteria in biological terrorism was a new concept instituted after the 9/11 attacks. This type of sampling is now part of a sophisticated system used by the Department of Homeland Security and the Department of Defense.

However, in order for the system to work more efficiently in the real world, Garza believes the detection cycle, which currently takes between 12-36 hours, would need to produce results in a shorter time frame.

"The current process is labor-intensive and time-consuming. It takes a lot of manual labor and time to do the laboratory work," he said.

Since it usually takes at least a couple of days for a person to show symptoms from a biological attack, Garza emphasizes the importance of an improved detecting system that would give officials more time to investigate and ramp up a medical response plan to save lives.

"If we can detect a dangerous pathogen in the environment at an earlier stage, we can quickly start planning the response procedure for it like distributing antibiotics," Garza said. "The sooner we pick up clues, the sooner we can act and save more lives."

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Story Source:

The above story is based on materials provided by Saint Louis University. The original article was written by Riya V. Anandwala. Note: Materials may be edited for content and length.

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Journal Reference:

1. Alexander G. Garza, Sheila M. Van Cuyk, Michael J. Brown, Kristin M. Omberg. Detection of the Urban Release of aBacillus anthracisSimulant by Air Sampling. Biosecurity and Bioterrorism: Biodefense Strategy, Practice, and Science, 2014; 12 (2): 66 DOI: 10.1089/bsp.2013.0086

Citrus greening affects roots before leaves

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Orange blossoms at the UF Research and Education Center in Lake Alfred.

Although citrus greening enters trees through their leaves, University of Florida researchers have discovered that the deadly disease attacks roots long before the leaves show signs of damage -- a finding that may help growers better care for trees while scientists work to find a cure.

"The role of root infection by insect-carried bacterial pathogens has been greatly underestimated," said Evan Johnson, a research assistant scientist with UF's Institute of Food and Agricultural Sciences.

Hundreds of researchers throughout the world are rushing to find a viable treatment for citrus greening, which is devastating Florida's $9 billion citrus industry and has affected citrus production throughout North America.

Johnson was the lead author of a scientific paper outlining the research published in the April issue of the journal Plant Pathology. He and his fellow team members -- Jian Wu, a graduate student in soil and water science, researcher Diane Bright and Jim Graham, a professor of soil microbiology -- are based at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

Citrus greening first enters the tree via a tiny insect, the Asian citrus psyllid, which sucks on leaf sap and leaves behind bacteria that spread through the tree. Johnson said the bacteria travel quickly to the roots, where they replicate, damage the root system and spread to the rest of the host tree's canopy. The disease starves the tree of nutrients, leaving fruits that are green and misshapen, unsuitable for sale as fresh fruit or juice. Most infected trees die within a few years.

It was originally thought that the leaves and fruit were affected first, but the team's research found that greening causes a loss of 30 to 50 percent of trees' fibrous roots before symptoms are visible above ground.

"This early root loss means that the health of a citrus tree is severely compromised before the grower even knows it is infected," Johnson said.

Experts say this research is significant in the fight against greening.

"Based on the work of Dr. Johnson and his colleagues, we now know how important roots are in the development of greening disease," said Jackie Burns, director of the CREC. "We hope further investigations on the role of roots in this disease will lead to future management solutions that help growers remain productive until a permanent solution can be found."

To battle greening, UF/IFAS researchers have attempted everything from trying to eradicate the psyllid to breeding trees that show better greening resistance. While Johnson's research is not a cure, it may help more trees survive as scientists continue their search.

"We are still trying to determine how the bacteria are killing the roots," Johnson said. "This finding suggests that growers should focus more effort on maintaining the health of the root system in relation to other soilborne pests and overall soil quality to maintain as much of the root system as possible."

Johnson suggested that growers increase the acidity levels of irrigation water and soil to match the optimum pH for the rootstock (preliminary results show that this improves root density compared to untreated groves) and water more frequently for shorter periods. Those treatments are being studied by UF researchers in Lake Alfred and at the Southwest Florida Research and Education Center in Immokalee.

He added that while psyllid control is essential, growers should make careful decisions on how many resources to devote to any management strategy for greening-infected trees, based on their economic means, until field trials have been completed.

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Story Source:

The above story is based on materials provided by University of Florida Institute of Food and Agricultural Sciences. The original article was written by Kimberly Moore Wilmoth. Note: Materials may be edited for content and length.

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Journal Reference:

1. E. G. Johnson, J. Wu, D. B. Bright, J. H. Graham. Association of ‘CandidatusLiberibacter asiaticus’ root infection, but not phloem plugging with root loss on huanglongbing-affected trees prior to appearance of foliar symptoms. Plant Pathology, 2014; 63 (2): 290 DOI: 10.1111/ppa.12109

Making it big: Metamaterial applications a step closer to reality

 

May 9, 2014

The Agency for Science, Technology and Research (A*STAR)

The use of a fabrication technique borrowed from the semiconductor industry brings metamaterial applications a step closer to reality. Artificial materials engineered to have properties not found in nature, such as a negative refractive index are engineered to interact with light and sound waves in ways that natural materials cannot. They thus have the potential to be used in exciting new applications, such as invisibility cloaks, high-resolution lenses, efficient and compact antennas, and highly sensitive sensors.

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Metamaterials are engineered to interact with light and sound waves in ways that natural materials cannot. They thus have the potential to be used in exciting new applications, such as invisibility cloaks, high-resolution lenses, efficient and compact antennas, and highly sensitive sensors.

While the theory of this interaction is relatively well understood, it has been challenging to fabricate metamaterials that are large enough to be practical. Now, Yi Zhou and colleagues at the A*STAR Data Storage Institute in Singapore have demonstrated a promising new fabrication technique that can produce large areas of an important class of metamaterial, known as fishnet metamaterials1.

Most optical metamaterials consist of tiny repeated metallic structures. When light of a particular frequency falls on them, it establishes oscillating fields inside each structure. These fields can resonate with each other and thereby produce desirable collective behavior. Fishnet metamaterials usually have several vertically stacked repeat units spread out over much larger lateral dimensions. Because they are structured both vertically and laterally, they are called three-dimensional materials.

Fishnet metamaterials are usually made in one of two ways. They can be fabricated by carefully patterning individual films and then stacking these films on top of each other. However, this multilayer process is difficult, as it requires careful alignment of the films.

The second approach is to pattern a sacrificial substrate and then deposit repeated layers onto it. This 'pattern-first' process suffers from its own difficulties, the most important of which is that the total thickness of the final fishnet material is typically limited to tens of nanometers or less. This restricts the kind of resonances that can be achieved and, in turn, the functionality of the final film.

Zhou and colleagues were able to increase the total thickness of pattern-first fishnet films to around 300 nanometers, allowing five bilayers of film to be deposited and resulting in a strong characteristic resonance and pronounced metamaterial behavior. To achieve this, they adopted a technique called trilayer lift-off, which is commonly used in industry but seldom applied in research laboratories. It involves patterning a sacrificial layer of a photoresist resting on a layer of silicon dioxide under which lies a second photoresist layer.

By alternating the patterning and etching steps, the A*STAR team could achieve a film thickness greatly exceeding the size of the lateral patterns etched into the film. "This technique will help researchers design large-area three-dimensional nanodevices more easily," says Zhou, "and help bring the science of metamaterials to reality."

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Story Source:

The above story is based on materials provided by The Agency for Science, Technology and Research (A*STAR). Note: Materials may be edited for content and length.

Conducting polymer films decorated with biomolecules for cell research use

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This is an image of stamp and substrate.

The ability to create conducting polymer films in a variety of shapes, thicknesses and surface properties rapidly and inexpensively will make growing and testing cells easier and more flexible, according to a team of Penn State bioengineers.

"The ultimate goal of this collaborative project is to be able to create a substrate for growth and manipulation of cells," said Sheereen Majd, assistant professor of bioengineering. "Cells on a surface need to recognize biomolecules like extracellular matrix proteins to be able to adhere and grow. We ultimately would like to be able to use these polymer films to manipulate adhesion, growth, proliferation and migration of cells." Majd and her team are creating patterned films of conducting polymers on gold substrates by electrodeposition through hydrogel stamps. They report their results today (May 9) in Advanced Materials.

The researchers create their hydrogel stamps from agarose -- a sugar extracted from seaweed -- poured into molds. While most of the current experiments use arrays of dots, because the researchers use molded stamps, a wide variety of shapes -- dots, squares, lines -- are possible. The stamp is dipped in a solution of monomer and a dopant and placed on the gold surface. An electrical current through the hydrogel and gold polymerizes the monomer and dopant at the surface. If a biomolecule of interest is also included in the stamping solution, it becomes embedded in the polymer film as well.

Because the presence of dopant is important for the electrical conductivity of these polymers, only areas where monomer and dopant exist together form conductive films of polymer. The process takes from one to two minutes and the longer the current is applied, the thicker the film.

The researchers were able to produce a series of films using the same monomer but different dopants and biomolecules by altering the solution on various parts of the stamp. In this way researchers can change the surface properties and functionality of the films. The stamp can also be used multiple times before re-inking becomes necessary, simplifying and speeding up the process.

Creating arrays of different biomolecules and different shapes in conducting polymers is especially important when studying excitable cells like neurons or muscle cells because they react to electricity.

Conducting polymer arrays will allow manipulation of cells using chemical and electrical signals, expanding the ways cells can be treated. Varying films laid down on one substrate can put multiple experiments all in one

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Story Source:

The above story is based on materials provided by Penn State. The original article was written by A'ndrea Elyse Messer. Note: Materials may be edited for content and length.

Epigenetic mechanisms distinguishing stem cell function, blood cancer decoded

 

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Researchers at Dartmouth's Norris Cotton Cancer Center have published results from a study in Cell Reports that discovers a new mechanism that distinguishes normal blood stem cells from blood cancers.

"These findings constitute a significant advance toward the goal of killing leukemia cells without harming the body's normal blood stem cells which are often damaged by chemotherapy," said Patricia Ernst, PhD, co-director of the Cancer Mechanisms Program of the Norris Cotton Cancer Center and an associate professor in Genetics at the Geisel School of Medicine.

The study focused on a pathway regulated by a gene called MLL1 (for Mixed Lineage Leukemia). Ernst served as principal investigator; Bibhu Mishra, PhD, as lead author.

When the MLL1 gene is damaged, it can cause leukemia, which is a cancer of the blood, often occurring in very young patients. Researchers found that the normal version of the gene controls many other genes in a manner that maintains the production of blood cells.

"This control becomes chaotic when the gene is damaged or 'broken' and that causes the normal blood cells to turn into leukemia," said Ernst.

The researchers showed that the normal gene acts with a partner gene called MOF that adds small "acetyl" chemical modification around the genes that it controls. The acetyl modification acts as a switch to turn genes on. When this function is disrupted, MLL1 cannot maintain normal blood stem cells.

The researchers also found that a gene called Sirtuin1 (more commonly known for controlling longevity) works against MLL1 to keep the proper amount of "acetyl" modifications on important stem cell genes. Blood cancers involving MLL1, in contrast, do not have this MOF-Sirtuin balance and place a different chemical modification on genes that result in leukemia.

Blood stem cells also represent an important therapy for patients whose own stem cells are destroyed by chemotherapy. This study also reveals a new way to treat blood stem cells from donors that would expand their numbers.

"These finding suggest that drugs that block Sirtuin1 may be combined with MLL1 blocking drugs in certain leukemia to both preserve stem cells that make normal blood at the same time as killing leukemia cells," said Ernst.

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Story Source:

The above story is based on materials provided by The Geisel School of Medicine at Dartmouth. Note: Materials may be edited for content and length.

Intestinal enzyme maintains microbial balance: Study shows how

 

May 9, 2014

Massachusetts General Hospital

The mechanism by which an enzyme produced in the intestinal lining helps to maintain a healthy population of gastrointestinal microbes has been identified by researchers. The research team describes finding that intestinal alkaline phosphatase promotes the growth of beneficial bacteria by blocking the growth-inhibiting action of adenosine triphosphate -- an action first described in this paper -- within the intestine.

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Massachusetts General Hospital (MGH) investigators have identified the mechanism by which an enzyme produced in the intestinal lining helps to maintain a healthy population of gastrointestinal microbes. In their report in American Journal of Physiology -- Gastrointestinal and Liver Physiology, the research team describes finding that intestinal alkaline phosphatase (IAP) promotes the growth of beneficial bacteria by blocking the growth-inhibiting action of adenosine triphosphate (ATP) -- an action first described in this paper -- within the intestine.

"We found that ATP is a natural inhibitor of bacteria in our intestines and that IAP promotes the growth of 'good' bacteria by blocking ATP," says Richard Hodin, MD, of the MGH Department of Surgery, senior author of the report which has been released online. "By helping to keep these healthy bacteria happy, IAP protects us against dangerous pathogens that can get the upper hand when the balance is disrupted."

The beneficial bacteria and other microbes that normally populate the human digestive system contribute to the digestive process and also prevent the proliferation of any disease-causing bacteria that may be present. A drop in the number of beneficial species -- which may be caused by antibiotic treatment, poor nutrition or other health conditions -- can allow the population of harmful bacteria to rise, contributing to serious medical problems including chronic diarrhea from pathogenic species such as C. difficile, inflammatory bowel disease, and metabolic syndrome.

Previous research by Hodin's team found that IAP keeps pathogenic bacteria in the gastrointestinal tract from passing through the intestinal wall, and a 2010 study in mice revealed that the enzyme plays an important role in maintaining levels of beneficial bacteria, including restoring levels reduced by antibiotic treatment. However, that study also showed that IAP does not directly promote bacterial growth, leaving exactly how the enzyme helps maintain the microbial population an open question that the current study was designed to investigate.

A series of experiments first confirmed that mice lacking intestinal IAP had significant reductions in populations of several important bacterial species. Hypothesizing that IAP may act by blocking a growth-inhibiting activity of one of its target molecules, the researchers tested how well bacteria in stool samples would grow in the presence of four known IAP targets. Among the tested targets, only ATP significantly reduced bacterial growth; and ATP's inhibitory effects were reversed by application of IAP. Best known as the primary energy supply within cells, ATP also acts as a signaling molecule both inside and outside of cells, and this study is the first to identify such an activity for ATP within the gastrointestinal system.

Experiments in living mice revealed that IAP knockout animals had 10 times the normal level of ATP within their intestines and that fasting animals, in which IAP levels would be expected to drop, also had elevated intestinal ATP. Adding ATP to the intestines of mice in which IAP activity had been inhibited reduced levels of beneficial E.coli bacteria in the animals' digestive systems. Altogether the results show that ATP inhibits the growth of intestinal bacteria in mice and that IAP's growth-promoting effects result from the enzyme's inactivation of ATP and possibly of related molecules.

"Now we need to find out whether IAP also promotes the growth of beneficial intestinal bacteria in humans," says Hodin, who is a professor of Surgery at Harvard Medical School. "If it does, IAP-based therapies could offer a simple and safe approach to treating the millions of patients who suffer serious health problems caused by disruptions to intestinal microbial balance."

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Story Source:

The above story is based on materials provided by Massachusetts General Hospital. Note: Materials may be edited for content and length.

Toxicologists outline key health and environmental concerns associated with hydraulic fracturing

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Since the rise in the use of hydraulic fracturing of shale to produce natural gas and oil, scientists, politicians, industrialists, and others have debated the merits and detractions of the practice. In a newly published paper in Toxicological Sciences, members of the Society of Toxicology (SOT), alongside other experts, outline how toxicological sciences can be used to determine what risks may or may not be associated with hydraulic fracturing.

"Toxicology is the study of the effects of chemical, physical, or biological agents on living organisms and the environment. As such, toxicologists should be at the forefront of discussions of hydraulic fracturing," says Society of Toxicology President Norbert E. Kaminski, PhD. "We can provide information on the potential toxicity of the chemical and physical agents associated with the process, individually and in combination."

In "The Role of Toxicological Science in Meeting the Challenges and Opportunities of Hydraulic Fracturing" Bernard D. Goldstein, et al, identify a series of potential pathways of contamination and toxicological effects associated with hydraulic fracturing that should and are being explored by researchers:

• Water pollution: There is a potential for surface or groundwater contamination by hydraulic fracturing fluids and their constituents. The authors found that there are few confirmed cases of groundwater contamination, but that there is little research available on the chemical baselines of drinking and surface waters prior to hydraulic fracturing practices to determine contamination with toxicologically significant levels of chemicals as a result of routine hydraulic fracturing.
• Air Pollution: The authors write, "A single hydraulic fracturing site is unlikely to produce significant increments of ozone precursors. However, there is concern that in aggregate hydraulic fracturing activities in regions with thousands of wells, and which already have ozone levels close to the allowable health-based standard, such as the Northeast, may be tipped into nonattainment of the standard." Potential contaminants that are being studied include methane gas, diesel emissions, volatile organic compounds, and benzene, among others.
• Occupational Exposure: Workers at hydraulic fracturing sites are exposed to a series of potential hazards to their health. These potential hazards range from inhalation of gases and particulate matter to dermal exposure to these same elements. Evaluating exposure amounts, types of exposure, and lengths of exposure to various individual chemicals and the chemicals in combination is necessary to determine potential risks to hydraulic fracturing workers.

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Story Source:

The above story is based on materials provided by Society of Toxicology. Note: Materials may be edited for content and length.

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Journal Reference:

1. B. D. Goldstein, B. W. Brooks, S. D. Cohen, A. E. Gates, M. E. Honeycutt, J. B. Morris, J. Orme-Zavaleta, T. M. Penning, J. Snawder. The Role of Toxicological Science in Meeting the Challenges and Opportunities of Hydraulic Fracturing. Toxicological Sciences, 2014; 139 (2): 271 DOI: 10.1093/toxsci/kfu061

Chemotherapy timing is key to success, research shows

 

In studies with mice, the research team showed that this one-two punch, which relies on a nanoparticle that carries two drugs and releases them at different times, dramatically shrinks lung and breast tumors. The MIT team, led by Michael Yaffe, the David H. Koch Professor in Science, and Paula Hammond, the David H. Koch Professor in Engineering, describe the findings in the May 8 online edition of Science Signaling.

"I think it's a harbinger of what nanomedicine can do for us in the future," says Hammond, who is a member of MIT's Koch Institute for Integrative Cancer Research. "We're moving from the simplest model of the nanoparticle -- just getting the drug in there and targeting it -- to having smart nanoparticles that deliver drug combinations in the way that you need to really attack the tumor."

Doctors routinely give cancer patients two or more different chemotherapy drugs in hopes that a multipronged attack will be more successful than a single drug. While many studies have identified drugs that work well together, a 2012 paper from Yaffe's lab was the first to show that the timing of drug administration can dramatically influence the outcome.

In that study, Yaffe and former MIT postdoc Michael Lee found they could weaken cancer cells by administering the drug erlotinib, which shuts down one of the pathways that promote uncontrolled tumor growth. These pretreated tumor cells were much more susceptible to treatment with a DNA-damaging drug called doxorubicin than cells given the two drugs simultaneously.

"It's like rewiring a circuit," says Yaffe, who is also a member of the Koch Institute. "When you give the first drug, the wires' connections get switched around so that the second drug works in a much more effective way."

Erlotinib, which targets a protein called the epidermal growth factor (EGF) receptor, found on tumor cell surfaces, has been approved by the Food and Drug Administration to treat pancreatic cancer and some types of lung cancer. Doxorubicin is used to treat many cancers, including leukemia, lymphoma, and bladder, breast, lung, and ovarian tumors.

Staggering these drugs proved particularly powerful against a type of breast cancer cell known as triple-negative, which doesn't have overactive estrogen, progesterone, or HER2 receptors. Triple-negative tumors, which account for about 16 percent of breast cancer cases, are much more aggressive than other types and tend to strike younger women.

That was an exciting finding, Yaffe says. "The problem was," he adds, "how do you translate that into something you can actually give a cancer patient?"

From lab result to drug delivery

To approach this problem, Yaffe teamed up with Hammond, a chemical engineer who has previously designed several types of nanoparticles that can carry two drugs at once. For this project, Hammond and her graduate student, Stephen Morton, devised dozens of candidate particles. The most effective were a type of particle called liposomes -- spherical droplets surrounded by a fatty outer shell.

The MIT team designed their liposomes to carry doxorubicin inside the particle's core, with erlotinib embedded in the outer layer. The particles are coated with a polymer called PEG, which protects them from being broken down in the body or filtered out by the liver and kidneys. Another tag, folate, helps direct the particles to tumor cells, which express high quantities of folate receptors.

Once the particles reach a tumor and are taken up by cells, the particles start to break down. Erlotinib, carried in the outer shell, is released first, but doxorubicin release is delayed and takes more time to seep into cells, giving erlotinib time to weaken the cells' defenses. "There's a lag of somewhere between four and 24 hours between when erlotinib peaks in its effectiveness and the doxorubicin peaks in its effectiveness," Yaffe says.

The researchers tested the particles in mice implanted with two types of human tumors: triple-negative breast tumors and non-small-cell lung tumors. Both types shrank significantly. Furthermore, packaging the two drugs in liposome nanoparticles made them much more effective than the traditional forms of the drugs, even when those drugs were given in a time-staggered order.

As a next step before possible clinical trials in human patients, the researchers are now testing the particles in mice that are genetically programmed to develop tumors on their own, instead of having human tumor cells implanted in them.

The researchers believe that time-staggered delivery could also improve other types of chemotherapy. They have devised several combinations involving cisplatin, a commonly used DNA-damaging drug, and are working on other combinations to treat prostate, head and neck, and ovarian cancers. At the same time, Hammond's lab is working on more complex nanoparticles that would allow for more precise loading of the drugs and fine-tuning of their staggered release.

"With a nanoparticle delivery platform that allows us to control the relative rates of release and the relative amounts of loading, we can put these systems together in a smart way that allows them to be as effective as possible," Hammond says.