Using Magenetic Nanoparticles to Combat Cancer

Scientists at Georgia Tech have developed a potential new treatment against cancer that attaches magnetic nanoparticles to cancer cells, allowing them to be captured and carried out of the body. The treatment, which has been tested in the laboratory and will now be looked at in survival studies, is detailed online in the Journal of the American Chemical Society.

Magnetic Nanoparticles Capture Ovarian Cancer Cells
FLV = 1.77 MB

"We've been able to use magnetic nanoparticles to capture free-floating cancer cells and then take them out of the body,” said John McDonald, chair of the School of Biology at Georgia Tech and chief research scientist at the Ovarian Cancer Institute. “This technology may be of special importance in the treatment of ovarian cancer where the malignancy is typically spread by free-floating cancer cells released from the primary tumor into the abdominal cavity.”

The idea came to the research team from the work of Ken Scarberry, a Ph.D. student in Tech’s School of Chemistry and Biochemistry. Scarberry originally conceived of the idea as a means of extracting viruses and virally infected cells when his advisor, Chemistry professor John Zhang, had another idea. He asked if the technology could be applied to cancer. Scarberry suggested it might be an effective means of preventing cancer cells from spreading.

They began by testing the therapy on mice. After giving the cancer cells in the mice a fluorescent green tag and staining the magnetic nanoparticles red, they were able to apply a magnet and move the green cancer cells to the abdominal region.
“If the therapy is able to pass further tests that show it can prevent the cancer from spreading from the original tumor,” Scarberry said, “it could be an important tool in cancer treatment.”
This technology holds more promise than solely using antibodies to fight cancer because there seems to be less potential for the body to develop an immune response due to the unique peptide-targeting strategy, and the composition of the magnetic nanoparticles.

"If you modify the nanoparticle and target it directly to the tumor cells using a small peptide, you are less likely to generate an undesirable immune response and more accurately target the cells of interest,” said Research Scientist Erin Dickerson.

In addition to testing magnetic nanoparticles, the research team is collaborating with other groups at Georgia Tech to determine how peptide-directed gold nanoparticles and nanohydrogels might also be used in fighting cancer.

Cell Press : How cell's master transcribing machine achieves near perfection

One of the most critical processes in biology is the transcription of genetic information from DNA to messenger RNA (mRNA), which provides the blueprint for the proteins that form the machinery of life. Now, researchers have discovered new details of how the cell's major transcriptional machinery, RNA polymerase II (Pol II), functions with such exquisite precision. With almost unerring accuracy, Pol II can select the correct molecular puzzle piece, called a nucleosidetriphosphate (NTP), to add to the growing mRNA chain, although these puzzle pieces can be highly similar molecules.
Two papers in the June 6, 2008, issue of the journal Molecular Cell, published by Cell Press, describe advances in understanding Pol II copying fidelity. The papers are by Craig Kaplan of Stanford University and his colleagues; and Mikhail Kashlev of the National Cancer Institute Center for Cancer Research and his colleagues.
The researchers said their findings not only offer unprecedented details about the fidelity mechanism of Pol II, but likely about fidelity in all cellular genetic copying machines. They said their discoveries also offer understanding of how defective Pol II can generate errors in transcribing mRNA—errors that can promote cancer formation. Both groups concentrated on the function of the Pol II "active site" region, where the enzyme captures an RNA component, called a nucleosidetriphosphate (NTP), and chemically attaches it to the RNA chain. Although Pol II uses the DNA genetic sequence as a template to specify the RNA sequence, another largely unknown fidelity mechanism exists by which Pol II discriminates against incorrect NTPs. This fidelity mechanism is extremely precise; it can distinguish the NTPs that make up RNA from the deoxyNTPs used in DNA—although the two molecules differ only in one small chemical group.
In their paper, Kaplan and colleagues explored a key component of the active site known as the "trigger loop." This small bit of protein is highly mobile, and although researchers have believed that it plays a critical function in discriminating the correct NTP, that function was poorly understood.
In studies with yeast, Kaplan and his colleagues produced a mutant form of Pol II with a subtly crippled trigger loop. This mutation substituted one amino acid with another in what was believed to be a key position in the trigger loop, His 1085, for interacting with incoming NTPs to discriminate the correct one. The researchers compared the detailed molecular function of normal and His 1085 mutant Pol II enzymes during the encounter with both correct and incorrect NTPs. They also compared the behavior of the mutant with the action of the mushroom toxin alpha-amanitin, which is theorized to block Pol II by interfering with the trigger loop. The researchers' studies of the mutant and alpha-amanitin revealed crucial details showing how the trigger loop determines fidelity, said Kaplan.
"We found that the amanitin-treated wild-type enzyme behaved very similar to our mutant enzyme," said Kaplan. In fact, he said, the experiments, as well as structural information on the active site, indicated that alpha-amanitin targets the same His 1085 position in the trigger loop as does their mutation. Kaplan concluded that the findings reveal a specific and critical role for the trigger loop.
"These findings reveal what is called a 'kinetic selection' mechanism for Pol II, which is like many polymerases," he said. "That is, the active site in one condition has a similar affinity for both correct and incorrect NTPs. However, because of motion within the active site—in this case the action of the trigger loop—catalytic activity in the active site proceeds much faster with the correct NTP than with the incorrect NTP. The trigger loop is mobile, and only when it is positioned properly in response to a correct substrate can it really function.
"We think this mode of substrate recognition is a general theme for systems that have to select the right molecule out of a giant pool of the wrong molecules," said Kaplan. An example, he said, is when the protein-making ribosomal machinery must select the correct transfer RNA from among similar-but-incorrect transfer RNAs.
Besides Kaplan, other co-authors on the paper were Karl-Magnus Larsson and Roger Kornberg.
In the other Molecular Cell paper, Kashlev and colleagues used a different yeast mutant to explore the function of the Pol II active site. In their screen for Pol II mutants, they identified one, E1103G, that shows a several-fold increase in error rate over the normal, wild-type Pol II.
Importantly, said Kashlev, the researchers could precisely measure the transcription error rate using a new assay, called a retrotransposition assay, developed by co-author Jeffrey Strathern.
The researchers' analysis of the effects of E1103G yielded significant insights into the function of the trigger loop, said Kashlev.
"Normally, when an NTP diffuses into the active site of the polymerase, the trigger loop closes behind it like a door, long enough for the polymerase to perform the chemistry to add the NTP to the end of the RNA chain," he said. "If the NTP is incorrect, there is a tendency for this door to stay open for a longer time, which means that the NTP has a chance to diffuse out of the active site before the polymerase can proceed to chemistry.
"Our mutation occupies a strategic position important for keeping the loop open, like a latch," said Kashlev. "So, in the mutant, the door wants to stay in the closed state for a longer time, which means if an incorrect NTP migrates into the active site, there is time for the polymerase to add this incorrect NTP to the RNA chain."
Kashlev said the motivation for their studies of Pol II transcription fidelity is to understand the effects of Pol II errors on genome stability. Specifically, error-prone Pol II could generate mRNA that produces aberrant versions of the critical enzyme DNA polymerase. As DNA polymerase is responsible for gene replication, the result of its malfunction could be a burst of gene mutation causing an "error catastrophe" that could lead to genome instability and cancer formation.
###
Besides Kashlev and Strathern, other co-authors of the paper were Maria Kireeva, Yuri Nedialkov, Gina Cremona, Yuri Purtov, Lucyna Lubkowska, Francisco Malagon and Zachary Burton.

Journal of Clinical Investigation : Finding the source: Cells that initiate a common infant tumor identified

Infantile hemangiomas, exemplified by the strawberry-like patches that appear on the skin of infants soon after birth, are benign tumors that develop in 5%-10% of Caucasian infants and usually disappear by the age of 9 without treatment. Joyce Bischoff and colleagues, at Children's Hospital Boston, have now identified the cells that give rise to these tumors and used them to develop a new mouse model of this disease.
Cells expressing the protein CD133 were isolated from infantile hemangioma tissue and individual cells were grown separately in culture. After each cell had been grown long enough for it to have given rise to a large population of cells, the cells were transplanted into immunodeficient mice, where they generated human blood vessels. Overtime, the number of blood vessels decreased and fat cells became evident. As these observations recapitulate those made in individuals with infantile hemangioma — where blood vessels form and then disappear leaving behind fat cells — the authors conclude that a single cell can give rise to infantile hemangioma and that their new model of these tumors will help identify therapeutic targets.
###
TITLE: Multipotential stem cells recapitulate human infantile hemangioma in immunodeficient mice
AUTHOR CONTACT: Joyce Bischoff Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts, USA. Phone: (617) 919-2192; Fax: (617) 730-0231; E-mail: joyce.bischoff@childrens.harvard.edu.

Wiley-Blackwell : Talking to Cells

Sweet nothings: Artificial vesicles and bacterial cells communicate by way of sugar components

For an organism to develop and function, the individual cells must exchange information, or communicate, with each other. Is it possible to learn their language and “talk to” the cells? Yes it is: Cameron Alexander and George Pasparakis at the University of Nottingham (UK) have been able to facilitate a conversation between bacterial cells and artificial polymer vesicles. In the journal Angewandte Chemie they report that this first communication occurred by way of sugar groups on the vesicle surface. The vesicles subsequently transfer information to the cells—in the form of dye molecules.

Complex structures made of many sugar components on the surfaces of cells are the “language” used for processes such as cell recognition, for example, in the differentiation of tissues or the identification of endogenous cells and foreign invaders. Scientists would like to be able to use this glycocode to “address” target cells and to intervene directly in cellular processes to treat diseases or to guide regeneration of damaged tissues.
The British scientists took an interesting route to learn more about the “language” of cells: they constructed vesicles, tiny capsules whose outer shell is made of special polymer building blocks. Their special trick: the polymer chains are equipped with side chains bearing glucose units that wind up being exposed on the vesicle surface.
The researchers brought the vesicles together with bacteria that have glucose-binding proteins on their surface. The behavior of the bacteria varies depending on the polymer’s composition and the size of the vesicles. Among the bacteria were some individuals that enter into very strong bonds with large vesicles. These associated bacteria are then in a position to receive molecular “information” from the vesicles: dye molecules that were previously placed in the vesicles transferred specifically into the interior of these bacteria.
“Our vesicles can be viewed as simple replicas of living cells,” says Alexander, “that can communicate with real cells by way of the glycocode as well as through signal molecules inside the vesicles.” Possible applications include drug transporters that deliver their cargo to specific target cells, or antibiotic transporters that deliver their toxic load exclusively to infectious agents.