Singapore - Nanomedicine: Bringing brighter light into living bodies

Fluorescence image of breast cancer cells incubated with dye-loaded BSA nanoparticles showing that the nanoparticles have entered the cell cytoplasms (red) but not the nuclei (blue)

Fluorescent dyes with aggregation-induced emission provide new probes for cancer diagnosis and therapy

Fluorescent nanoparticles loaded with organic light-emitting dyes are expected to transform live-animal imaging technologies. Compared to inorganic quantum dots, these optically stable materials are non-toxic and can easily be modified with functional groups, making them ideal when targeting specific tissues in the body. Unfortunately, traditional dyes have been known to aggregate and lose their emission intensity when incorporated in nanoparticles at high concentration. To overcome this problem, a team of researchers led by Bin Liu and Ben Zhong Tang at the A*STAR Institute of Materials Research and Engineering have now designed a family of dyes with enhanced fluorescence upon aggregation1.

At the heart of the traditional dyes is a planar chromophore called triphenylamine-modified dicyanomethylene, which emits red light in dilute solutions but fluoresces weakly when aggregated. “The close vicinity of the chromophores induces fluorescence quenching due to non-radiative pathways,” says Liu.

Liu, Tang and their team reversed this phenomenon by attaching propeller-shaped tetraphenylethene pendants to each extremity of the chromophore. Contrary to planar compounds, the shape of the propellers prevents strong stacking interactions between chromophores, blocking the aggregation-caused quenching process. In addition, the physical confinement prevents these propellers from rotating freely, enabling light emission.

The team formulated the dyes using a bovine serum albumin (BSA) matrix — a biocompatible and clinically used polymer — and evaluated their performance as probes. Experimental characterization showed that the wavelength of the emission maximum of the nanoparticles remained unchanged upon encapsulation and that the intensity of the emitted light increased with the dye loading.

Live imaging of breast cancer cells revealed that the nanoparticles displayed more intense and homogeneously distributed red fluorescence in the cytoplasms (see image) than free aggregates, suggesting that BSA boosted the cellular uptake of the dyes. The team also found that the nanoparticles were optically stable in biological media and displayed good biocompatibility.

The researchers intravenously injected the nanoparticles in liver-tumor-bearing mice for in vivo imaging studies. They found that unlike free aggregates, the nanoparticles selectively accumulated in the tumor, clearly highlighting the cancerous tissue in the animals. “This demonstration underscores new research opportunities to explore similar diagnostic probes with potential clinical applications,” says Liu.

The team is currently investigating near-infrared emissive biological probes for targeted in vivo tumor imaging applications. The nanoparticles can also be utilized to understand cancer metastasis or the fate of transplanted stem cells. “These probes are promising in multimodal imaging applications through integration with magnetic resonance imaging or nuclear imaging reagents,” says Liu.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering

References

1. Qin, W. et al. Biocompatible nanoparticles with aggregation-induced emission characteristics as far-red/near-infrared fluorescent bioprobes for in vitro and in vivo imaging applications. Advanced Functional Materials 22, 771–779 (2012). | article

USA - Novel nanotherapeutic delivers clot-busting drugs directly to obstructed blood vessels

The shear-activated nanotherapeutic breaks apart and releases its drug when it encounters regions of vascular narrowing. Credit: Wyss Institute

Researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University have developed a novel biomimetic strategy that delivers life-saving nanotherapeutics directly to obstructed blood vessels, dissolving blood clots before they cause serious damage or even death. This new approach enables thrombus dissolution while using only a fraction of the drug dose normally required, thereby minimizing bleeding side effects that currently limit widespread use of clot-busting drugs.

The research findings, which were published online today in the journalScience, have significant implications for treating major causes of death, such as heart attack, stroke, and pulmonary embolism, that are caused by acute vascular blockage by blood thrombi.

The inspiration for the targeted vascular nanotherapeutic approach came from the way in which normal blood platelets rapidly adhere to the lining of narrowed vessels, contributing to the development of atherosclerotic plaques. When vessels narrow, high shear stresses provide a physical cue for circulating platelets to stick to the vessel wall selectively in these regions. The vascular nanotherapeutic is similarly about the size of a platelet, but it is an aggregate of biodegradable nanoparticles that have been coated with the clot-busting drug, tissue plasminogen activator (tPA).

Much like when a wet ball of sand breaks up into individual grains when it is sheared between two hands, the aggregates selectively dissociate and release tPA-coated nanoparticles that bind to clots and degrade them when they sense high shear stress in regions of vascular narrowing, such as caused by blood clot formation.

Disruption of normal blood flow to the heart, lung, and brain due to thrombosis is one of the leading causes of death and long-term adult disability in the developing world. Today, patients with pulmonary embolism, strokes, heart attacks, and other types of acute thrombosis leading to near-complete vascular occlusion, are most frequently treated in an acute care hospital setting using systemic dosages of powerful clot-dissolving drugs. Because these drugs can cause severe and often fatal bleeding as they circulate freely throughout the body, the size of the dosage given to any patient is limited because efficacy must be balanced against risk.

The new shear-activated nanotherapeutic has the potential to overcome these efficacy limitations. By targeting and concentrating drug at the precise site of the blood vessel obstruction, the Wyss team has been able to achieve improved survival in mice with occluded lung vessels with less than 1/50th of the normal therapeutic dose, which should translate into fewer side effects and greater safety. This raises the possibility that, in the future, an emergency technician might be able immediately administer this nanotherapeutic to anyone suspected of having a life-threatening blood clot in a vital organ before the patient even reached the hospital.

The inter-disciplinary and inter-institutional collaborative research team, which was led by Wyss Founding Director Donald Ingber M.D., Ph.D., and Wyss Technology Development Fellow Netanel Korin, Ph.D., also included Wyss postdoctoral Fellow Mathumai Kanapathipillai, Ph.D., as well as Benjamin D. Matthews, Marilena Crescente, Alexander Brill, Tadanori Mammoto, Kaustabh Ghosh, Samuel Jurek, Sidi A. Bencherif, Deen Bhatta, Ahmet U. Coskun, Charles L. Feldman, and Denisa D. Wagner from Brigham and Women's Hospital, Children's Hospital Boston, Harvard Medical School, the Harvard School of Engineering and Applied Sciences, and Northeastern University. Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and Children's Hospital Boston, and Professor of Bioengineering at Harvard's School of Engineering and Applied Sciences.

Commenting on the work, Ingber noted that "the vascular nanotherapeutic we developed that selectively becomes activated in regions of high shear stress, much like living platelets do, is a wonderful example of how we at the Wyss Institute take inspiration from biology, and how biomimetic strategies can lead to new and unexpected solutions to age-old problems that existing technologies can't address."

More information: "Shear-Activated Nanotherapeutics for Drug Targeting to Obstructed Blood Vessels," by N. Korin et al., Science, 2012.

Journal reference: Science   

Provided by Harvard University

http://medicalxpress.com/

Australia – S Korea - Fighting Food Allergies Through A Korean-Australian Collaboration

Food scientists in Australia and Korea are working together to develop innovative processing techniques that alter the properties of allergenic proteins in milk and food products.

Food scientists in Australia and South Korea are minimizing the adverse health effects of allergens in milk and other food products by developing innovative processing techniques that alter the properties of allergenic proteins.

A new memorandum of understanding signed today between the University of New South Wales (UNSW) School of Chemical Engineering and Korea’s National Institute of Animal Science (NIAS) will explore the potential benefits of this and other innovative food safety technologies.

The food allergy research group at UNSW, led by Dr. Alice Lee, aims to develop nano-sensors that can better detect allergens such as those found in animal milk, which can cross a spectrum and in severe cases can result in potentially life threatening anaphylaxis.

They are also working to understand how these allergens change after harvest and during food processing, and how this affects the resulting human reaction.

“Food allergy has been an emerging food safety concern especially in developed countries,” said Lee. “The current collaborative research project we have with the National Institute of Animal Science is focused on reducing the health risks of milk allergens by a means of high pressure processing.”

Under the new agreement, a researcher from the NIAS has been seconded to UNSW to work in the Food Science and Technology group, which is also looking at microbiological risks such as E. coli and salmonella, and chemical risks posed by traces of antibiotics, hormones, and pesticides.

Antibiotics are often administered to livestock in very low doses to fend off bacteria growth, but leftover residues can sometimes be present in meat, says Lee, resulting in negative health impacts when humans are exposed.

Korea’s Rural Development Administration Department is comparable to Australia’s Department of Agriculture, Fisheries and Forestry, says Lee, so it has a broad research focus, with a range of possibilities for future research collaborations in the areas of food safety.

“Korea and Australia share a common interest in food security, global food availability, and food safety – especially around livestock hygiene,” said Professor Rob Burford, head of the School of Chemical Engineering. “This is an exciting partnership for UNSW.”

Source: UNSW.

Asian Scientist Newsroom | Academia

USA - Size matters in drug delivery

Tumor study reveals size limitations for new drugs

A new study shows that combining angiogenesis inhibitors and nanomedicines only improves cancer treatment when the nanomedicines are at the small end of a size range. Top panels show the control setups. Bottom panels show mammary tumor tissue after normalization of blood vessels. Few of the large nanoparticles are visible in the bottom left panel, while the smaller nanoparticles have penetrated well, as seen in the bottom right panel.

Combining two strategies that are designed to improve the results of cancer treatment — angiogenesis inhibitors and nanomedicines — may only be successful if the smallest nanomedicines are used.

A new study led by researchers at the Harvard School of Engineering and Applied Sciences (SEAS) and Massachusetts General Hospital (MGH) has found that normalizing blood vessels within tumors, which improves the delivery of standard chemotherapy drugs, can actually block the delivery of larger nanotherapy molecules.

“We found that vascular normalization only increases the delivery of the smallest nanomedicines to cancer cells,” says lead author Vikash P. Chauhan, a graduate student in bioengineering at SEAS. “We also showed that the smallest nanomedicines are inherently better than larger nanomedicines at penetrating tumors, suggesting that smaller nanomedicines may be ideal for cancer therapy.”

The results have been published in Nature Nanotechnology.

Angiogenesis, the tumor-driven creation of new blood vessels, provides growing cancers with a food source — but it also provides a potential channel for drug delivery.

The problem is that the vessels supplying tumors tend to be disorganized, oversized, and leaky. These abnormalities prevent the delivery of chemotherapy drugs to cells that are not close to the tumor vessels.

The leakage of plasma out of blood vessels also increases pressure within the tumor, further reducing the drugs’ ability to penetrate the tissue. Fortunately, drugs that inhibit angiogenesis can reduce some of these problems in a process called vascular normalization.

“Anti-angiogenic agents are prescribed to a large number of cancer patients in combination with conventional therapeutics,” explains principal investigator Rakesh K. Jain, Cook Professor of Radiation Oncology (Tumor Biology) at Harvard Medical School and director of the Steele Laboratory of Tumor Biology at MGH. Jain is also Chauhan’s Ph.D. adviser.

The combination of standard chemotherapy drugs and normalization therapy has previously been shown to improve the effectiveness of treatment on some types of cancer.

New nanomedicines, on the other hand, are designed to exploit the abnormality of tumor vessels.

Nanomedicines, despite the name, are actually about 10 to 100 times larger than standard chemotherapy drugs — too large to penetrate the pores of blood vessels in normal tissues, but still small enough to pass through the oversized pores of tumor vessels. Because nanomedicines generally cannot penetrate normal tissues, they are expected to cause fewer side effects.

The question in the Harvard-MGH study was whether vascular normalization would help or hinder the delivery of nanomedicines to tumors. The researchers found, through both theory and in vivo experimentation, that it depends on the size of the nanomedicines.

Their mathematical model predicted that inhibiting angiogenesis would simultaneously reduce the size of the pores in the blood vessels and relieve pressure in the tumor, allowing small particles to penetrate.

Confirming this experimentally in a mouse model of breast cancer, the investigators showed that vascular normalization (using an antibody called DC101) improved the penetration of 12-nanometer particles but not of 60- or 125-nanometer particles.

They treated mice with implanted breast tumors either with DC101 and Doxil, a 100-nanometer version of the chemotherapy drug doxorubicin, or with DC101 and Abraxane, a 10-nanometer version of paclitaxel.  Although treatment with both chemotherapeutics delayed tumor growth, vascular normalization with DC101 improved the effectiveness only of Abraxane and had no effect on Doxil treatment.

“A variety of anti-cancer nanomedicines are currently in use or in clinical trials,” says Chauhan, who completed the work at MGH.  “Our findings suggest that combining smaller nanomedicines with anti-angiogenic therapies may have a synergistic effect and that smaller nanomedicines should inherently penetrate tumors faster than larger nanomedicines, due to the physical principles that govern drug penetration. While it looks like future development of nanomedicines should focus on making them small — around 12 nanometers in size — we also need to investigate ways to improve delivery of the larger nanomedicines that are currently in use.”

Additional co-authors of the Nature Nanotechnology report are Triantafyllos Stylianopoulos, John Martin, Walid Kamoun, and Dai Fukumura of MGH; and Zoran Popovic, Ou Chen, and Moungi Bawendi of the Massachusetts Institute of Technology (MIT).

The work benefited from a long-term collaboration between Harvard, MGH, and MIT that explores the use of quantum dots as a biocompatible fluorescent marker in medical studies.

Support for the study included grants from the National Institutes of Healthand the Department of Defense.

Adapted from an earlier release by Sue McGreevey, Massachusetts General Hospital.

news.harvard.edu