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Nanoparticles, nanoshells, nanotubes: How tiny specks may provide powerful tools against cancer

17.11.2005


They’re but a tiny speck, existing in a variety of forms: particles, tubes, shells, even a soccerball-like shape. They also share a common prefix: "nano," connoting their size, a billionth of a meter or roughly 25-millionth of an inch.



Today, cancer researchers are exploring the potential of such nanostructures to exquisitely target cancer cells without harming surrounding tissue, and to image the formation of tumors long before they have a chance to become life-threatening.

While diagnostics and approved therapies are years away, several are nearing clinical studies, while a few already are being tested in patients. A press conference on "Advances in Nanotechnology for Cancer Diagnostics and Treatment" is being featured at the "Molecular Targets and Cancer Therapeutics" International Conference here.


Research highlights from this session include:

A nanotube, combined with monoclonal antibodies, is detecting cancer cells, offering a potential cost-effective way to diagnose whether cells are cancerous or not in a matter of minutes versus hour or days with current methods.

Nanoshells, filled with gold particles, are destroying tumor cells when heated with laser light. What’s more, these nanoshells interact with light in specific ways, and can be "tuned" to discrete destructive wavelengths by varying the size of the core and the shell.

A nanoparticle combined with a hormone and cell-killing peptide is being tested to image, target and destroy primary and metastatic breast cancer cells.

A novel kind of "nanocomplex" consisting of a microscopic, lipid-based liposome and an antibody along with gene therapy is entering clinical studies, in an approach that scientists hope will both detect and target metastatic cancer cells for destruction.

Single Wall Carbon Nanotubes with Adsorbed Monoclonal Antibodies Detect Breast Cancer Cells (Abstract 3126)

A biochemist and an engineer have used tiny carbon nanotubes and monoclonal antibodies to detect cancer cells in the laboratory dish. The work might lead to nanotube-based biosensors that can spot circulating cancer cells in the blood from a new cancer or from a treated tumor that has returned.

Balaji Panchapakesan, Ph.D., at the University of Delaware in Newark, and his co-workers coated the surface of microscopic carbon nanotubes with a monoclonal antibody. The antibodies – so-called guided missiles that home in on targets on the surface of cancer cells – were specific for insulin-like growth factor 1 receptor (IGF1R), which is commonly found on cancer cells.

When cancer cells and antibodies bind together, there is a measurable change in electric current, according to Panchapakesan. He and his group placed antibody-nanotube combinations between electrodes and compared the increase in electrical charge between two different types of breast cancer cells. One type, human BT474 breast cancer cells, had moderate IGF1R expression, while the other type, MCF7, had a higher expression of IGF1R.

The researchers found that the change in the conductance of the antibody-nanotube device was proportional to the number of receptors on the cancer cell surfaces. That is, the BT474 cancer cells, which had less IGF1R on their surfaces, had a three-fold increase in conductance. IGF1R-laden MCF7 cells showed an eight-fold rise in conductivity.

"When the antibody proteins – which are specific to the cell surface receptor (IGF1R) of the cancer cell and are attached to the nanotube – bind to the cancer cell surface, they produce a specific change in the electrical conductivity," Panchapakesan explains. The scientists found a "spike" in current with the MCF7 cells because it correlated with the greater IGF1R expression.

"The technique could be used for detection and it could be used for recurring circulating tumor cells or micrometastases remaining from the originally treated tumor," explains co-author Eric Wickstrom, Ph.D., of Jefferson Medical College of Thomas Jefferson University in Philadelphia.

"This could be cost-effective and could diagnose whether cells are cancerous or not in a matter of minutes versus hours or days with current methods of histology sectioning," says Dr. Panchapakesan. "It might also allow for large scale production methods to make thousands of sensors and have microarrays of these to detect cancer proteins."

The researchers plan to test the technique with additional breast cancer markers, as well as with markers for other cancers. They are also planning to perform animal studies, examining the sensitivity of the antibody-nanotube system in detecting cancer cells in the blood and in detecting specific types of cancer cells shed in the blood from tumors.

Immunonanoshells for Selective Photothermal Therapy (Abstract 3198) and Nanoshells for Combined Cancer Therapy and Imaging in vivo (Abstract 2711)

Researchers at Rice University are working on a novel and systematic approach to cancer treatment that involves the use of advanced technologies that are by themselves harmless − but appear to offer potent cancer-killing properties when used together.

This tactic focuses on two main ingredients: structures called "nanoshells," which are microscopic balls consisting of a silica core coated with a thin layer of gold and, secondly, near infrared light (NIR). Used alone, nanoshells are non-toxic and can be excreted with no ill effect because gold is biologically compatible. Near-infrared light delivered by a laser has minimal interaction with components found in tissue, and so also does not harm the body.

But when nanoshells are injected into an experimental animal with cancer, they accumulate in the tumor; the addition of NIR laser light heats up their gold shell, causing the particles to destroy tumor cells. Furthermore, because of their size − a few nanometers, or billionths of a meter, in diameter − these nanoshells interact with light in specific ways, and can be "tuned" to discrete destructive wavelengths by varying the size of the core and the shell.

Two new studies advance the use of this technology. One, reported by bioengineering graduate student Andre Gobin, is the first to demonstrate how nanoshells and imaging can be used together to treat tumors in animal models. Gobin and a team of Rice researchers injected nanoshells into the blood stream of mice implanted with colon cancer knowing, based on previous experiments, that the nanoshells would preferentially accumulate in the tumors. This occurs because blood vessels that develop in fast-growing solid tumors are ill-formed and permeable, and nanoshells traveling through blood end up spilling out of these leaky vessels into tumor tissue. Once there, the tumor only slowly excretes them as waste. The nanoshells are also hidden from the immune system because they are "shielded" by a protective polymer coating, poly-(ethylene glycol) or PEG. This does not change the properties of the nanoshells but renders them "invisible" to the body’s natural defense mechanism.

Twenty hours after the nanoshells were injected, the researchers imaged their presence in the tumor by using a small hand-held optical coherence tomography (OCT) probe similar to that which dermatologists can use to find skin cancers. According to Gobin, the researchers hope that these probes, already commercially available, can be adapted to both image nanoshells in tumors with higher resolution, and then therapeutically heat them up with a secondary laser coupled to the probe, making nanoshell-assisted therapy user friendly.

In this study, however, a different laser source was used to irradiate the tumors in the experimental group of mice. At the end of the study, 82 percent of the mice survived in the experimental group, but all mice in the control group that did not receive nanoshells and laser therapy had to be sacrificed because of their large tumors.

The second Rice University study aims to improve the method of delivery of nanoshells to a tumor. Although the leaky blood vessel strategy can passively dump nanoshells into tumors, it cannot "find" tiny cancers that have metastasized and have not yet "recruited" a substantial system of blood vessels to feed them. To counteract that, researchers have fused a nanoshell to an antibody; the idea behind such "immunonanoshells" is to have a targeted nanoshell that can find a specific type of cancer wherever it may hide, says study author, bioengineering graduate student Amanda Lowery

In the study that Lowery reports, the researchers hooked "Y"-shaped anti-HER2 antibodies to nanoshells, and the antibody bound to HER2 over-expressing breast cancers. They then applied these immunonanoshells to the top of laboratory breast cancer cells, and used laser light to heat the agent. Researchers then stained the cells to see which lived and found that only HER2-expressing cells which had bound nanoshells and were exposed to the near infrared laser, died. Cells that were not exposed to laser light also survived, suggesting that the antibody-nanoshell treatment effectively destroyed HER2 over-expressing cancer cells. The research team is now planning to test this strategy in animal models.

According to Gobin, Lowery, and the Rice University faculty they work with, nanotechnology to treat cancer takes advantage of much of the biology already known about the disease, and marries it to a suite of techniques based on next era technology.

Targeting Breast Cancer and Metastases with a Combination of LHRH and Lytic Peptide, Hecate, bound to Iron Oxide Nanoparticles (Abstract 3280)

Researchers have combined a hormone, a cell-killing peptide and nanoparticles to both target and kill breast cancer cells.

The scientists, led by Carola Leuschner, Ph.D., at the Pennington Biomedical Research Center in Baton Rouge, were hoping to come up with an efficient means by which they could image, target and destroy primary and metastatic breast cancer cells, while leaving normal cells alone.

They took advantage of the abundance of receptors for luteinizing hormone releasing hormone (LHRH) on breast cancer cell surfaces and created a molecular complex, combining LHRH with a 10 nm nanoparticle – superparamagnetic ironoxide – and a cell-killing peptide drug, Hecate.

Leuschner and her co-workers tested two different versions of the complex to see which might be the best way to treat and image tumors and metastases in breast cancer. In one version, the nanoparticle’s surface was covered with alternating "sun rays" of LHRH and Hecate. In the other, the nanoparticle was bound directly to LHRH-Hecate.

They first tested the two versions in the laboratory dish in two different breast cancer cell lines and in a mouse cell control. In a proof of concept study, they found evidence that the alternating LHRH and lytic peptide on the ironoxide particle was effective at killing cancer cells, suggesting that the cell-killing peptide worked best when it came in direct contact with the cell membrane. "It is possible that if the lytic peptide has no interaction with the membrane it is targeting, it cannot kill," Leuschner says.

The research group next looked at nude mice – mice lacking immune systems – that carried xenografts of human breast cancer. In another proof-of-concept study, they found that if a nanoparticle-Hecate combination is injected the drug can’t kill the tumor cells because it essentially couldn’t find them. When LHRH is injected prior to the three-headed combination or the LHRH-drug combination, the LHRH receptors on the tumor cells were blocked. These findings suggest a receptor-mediated process.

"The take home message is that you need to have a targeted entity to kill the cancer cells," Dr. Leuschner says. "Without the LHRH targeting moiety, the nanoparticle-drug construct doesn’t kill the cancer cells and it’s like a generally systemic chemotherapy drug."

Again, the LHRH-ironoxide-Hecate combination worked best in targeting and killing breast cancer cells, including metastatic cells.

According to Leuschner, the approach using nanoparticles has promising applications for both imaging and treatment at the same time, and might also be used to monitor treatment responses in breast cancer patients. The approach might be useful for other cancers, such as colon, lung, and ovarian, as well as for melanoma and non-Hodgkin’s lymphoma.

The next step is to design a more efficient complex. "Right now we saturated the nanoparticle, and it may not be necessary to use that much of the drug," she says. "It might help us optimize doses for tumor cell destruction and image quality, and cut costs too."

Tumor-Targeting Nanodelivery Systems: Expanding the Potential for Cancer Therapy and Diagnosis (Abstract 3891)

Getting drugs to reach cancer cells once they have spread from the original site of the tumor in the body has continually frustrated physicians and researchers. But now, scientists are combining a novel kind of "nanocomplex" consisting of a microscopic, lipid-based liposome and an antibody along with gene therapy in an approach they hope will both detect and target metastatic cancer cells for destruction.

Esther H. Chang, Ph.D., at Georgetown University Medical Center’s Lombardi Comprehensive Cancer Center in Washington, D.C., and her co-workers have created a liposome nanoparticle roughly one millionth of an inch across with antibodies peppering the surface that can home in on tumor cells wherever they spread in the body. The liposome encapsulates the p53 gene, which makes a protein that helps initiate a self-destruct process called apoptosis in cells with genetic damage. The liposome-antibody complex finds the cancer cell by binding to the transferrin receptor, which is present on the cancer cell surface in high numbers. When this happens, the p53 "payload" moves into the tumor cell.

"If we are going to have an effective cancer therapy, we have to be able to treat metastatic lesions," says Chang. "The problem is tumor-specific delivery, and the key is to deliver this nanocomplex systemically. We’ve been using a synthetic system to deliver genes because viral vectors aren’t reliable."

More than one-half of cancers have mutations in the p53 gene, which has been called the "guardian of the genome" because of its ability to get rid of genetically damaged cells. The researchers thought that getting a working version into the cancer cells would increase the effectiveness of chemotherapy and radiation, which cause such damage in the course of treatment.

In preclinical work, Chang and her group found that the nanoparticle-p53 therapy enhanced chemotherapy and radiation treatment for cancer, pushing damaged cancer cells to die. They have also demonstrated that the nanocomplex goes only to cancer cells, leaving normal tissue alone, and have used this approach in testing several other therapeutic genes in animals as well.

"The gene therapy using p53 targets tumors and metastases is going into the clinic as a prototype of gene delivery strategy for this technology," she notes. "It’s a platform technology." A phase I study of the strategy has already begun at Georgetown University Medical Center and will enroll 20 patients with advanced solid tumors, including head and neck, prostate, pancreatic, breast, bladder, colon, cervical, brain, melanoma and lung cancers.

Since the nanocomplex systemically targets both primary tumors and metastases, this technology can also deliver contrast agents directly to the tumor to improve detection, as well as tumor resolution and definition.

Warren R. Froelich | EurekAlert!
Further information:
http://www.aacr.org

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