Nanoparticles Developed for Targeted Brain Cancer Therapy
Researchers in Illinois, USA, have reported the development of the first bioconjugated nanoparticles that destroy brain cancer cells without damaging nearby healthy cells.
Elena Rozhkova of the Argonne National Laboratory and colleagues at the University of Chicago, used a platform of 5-nm titanium dioxide nanoparticles tethered through a 3,4-dihydroxyphenylacetic acid (DOPAC) linker to the antihuman-IL13 α2R. The team’s efforts could provide new hope in the development of novel therapy for glioblastoma multiforme (GBM), a form of primary cancer that frequently causes death within months of diagnosis.
Recent studies have demonstrated that titanium dioxide nanoparticles can destroy some cancer cells when exposed to UV light. However, progress has been stifled by difficulties in getting the nanoparticles – whose width is approximately one 50,000th that of a human hair – to target and enter cancer cells, while avoiding healthy cells.
The group’s approach was to link titanium dioxide nanoparticles to an antibody that recognizes and attaches to GBM cells. When exposed to cultured human GBM cells, the ‘nanobio hybrids’ destroyed up to 80% of the brain cells after 5 min of exposure to focused white light. Phototoxicity is mediated by a reactive oxygen species, mainly superoxide, which damages the cell membrane and initiates programed death of the cancer cell.
Speaking to Future Medicinal Chemistry about the significance of her team’s findings, Rozhkova said, “light-induced cytotoxicity of our nanobio hybrid material toward glioblastoma cells is pronounced and specific, without harmful effects to normal human astrocytes. Using modification of particles with organic molecules we are able to tune redox chemistry on the nanoparticles’ surface to enable absorption of a visible part of the solar spectrum by the 5-nm TiO2 particles.”
Commenting on the potential implications of the study, Rozhkova continued. “The advantages of nanotechnology-based therapies compared with classical therapeutics (in our case we can make a comparison with photodynamic therapy) are the result of a synergistic combination of the advanced physical properties of inorganic materials with the targeting abilities of biomolecules and the multiple functions of drugs and imaging payloads in one ‘ideal’ therapeutic system. Additionally, we demonstrated a proof of concept that can be applied for destruction of other types of cancers and pathogenic cells.”
Looking forward, the group plans to run animal studies and is currently working on detailed mechanistic studies of the photoreactivity of TiO2 nanoparticles and their application for cellular signal transduction.
Source: Rozhkova EA, Ulasov I, Lai B, Dimitrijevic NM, Lesniak MS, Rajh T. A high-performance nanobio photocatalyst for targeted brain cancer therapy. Nano Lett. 9(9), 3337–3342 (2009).
Lower Levels of Brain Dopamine Proteins Linked to Adhd
A recently published study suggests that symptoms of attention-deficit hyperactivity disorder (ADHD) may be due to a problem with the dopamine pathway in the brain, rather than environmental-based causes, as is believed by some.
Between 2001 and 2009, researchers at the Brookhaven National Laboratory, USA, scanned the brains of 55 patients with ADHD who were not receiving treatment and 44 healthy control patients. They focussed on imaging the dopamine reward pathway (mesoaccumbens pathway), in the midbrain and nucleus accumbens by taking PET scans of dopamine transporters and D2/D3 receptors. The dopamine transporters and D2/D3 receptors were traced using the radioligands [11C]cocaine and [11C]raclopride, respectively.
The results showed that ADHD patients had lower specific binding than the control group, suggesting that low levels of dopamine proteins correspond to higher levels of inattention and worsening ADHD symptoms.
“These deficits in the brain’s reward system may help explain clinical symptoms of ADHD, including inattention and reduced motivation, as well as the propensity for complications such as drug abuse and obesity among ADHD patients,” commented researcher Nora Volkow, who believes the study gives credence to the use of pharmacological medication, such as amphetamine methylphenidates, to treat disorders such as ADHD.
Sources: Nair J, Ehimare U, Beitman BD, Nair SS, Lavin A. Clinical review: evidence-based diagnosis and treatment of ADHD in children. Mol. Med. 103(6), 617–621 (2006); Volkow ND, Wang G-J, Kollins SH et al. Evaluating dopamine reward pathway in ADHD: clinical implications. JAMA 302(10), 1084–1091 (2009).
Peg-Based 3D Hydrogel Slide Shows Promise
Researchers at the University of Cambridge, UK, have developed a hydrogel slide for monitoring small molecule–protein interactions. The new technology could contribute to improving drug-discovery efforts.
A microarray is a multiplex lab-on-a-chip that comprises a solid substrate – such as a glass slide – that is used for high-throughput studies of molecular interactions. As part of efforts to identify new drug candidates, scientists have immobilized small molecules on 2D slides, before probing them with a fluorescently labeled target protein. However, such efforts have been hampered by difficulties in detecting the fluorescent signals as well as the small number of molecules that can be attached to slides.
In a recent study, David Spring and colleagues have outlined the development of a polyethylene glycol(PEG)-based 3D hydrogel slide, which, due to its greater surface area than previous 2D slides, can attach more molecules. The group decided to compare their newly developed slide with a commercially available 3D polymer-coated slide. The researchers functionalized both slides with biotin and employed fluorescently labeled avidin as the probe protein. Their results showed that the hydrogel slide had a loading capacity an order of magnitude greater than the commercial slide, improved signal sensitivity and spot morphology, as well as on average a sixfold higher fluorescent intensity.
Speaking to Future Medicinal Chemistry about his group’s work, Spring said, “[Our results are] very significant because, as a result of the higher loading capacity, our 3D slides displayed an approximate sixfold increase in signal intensity and also a higher than average signal-to-noise ratio when compared against a leading commercial slide and comparative 2D slide. The discovery of small molecule–protein interactions is important in terms of the discovery of potential drug leads and biological probes, but these interactions are often much weaker than traditional interactions detected using microarrays. The use of a PEG-based microarray with increased loading capacity and signal-to-noise-ratio will facilitate their detection, which might be beyond traditional microarray platforms.”
Small-molecule microarrays represent one of the least developed areas of microarray research. As a result, current immobilization platforms have not been developed with them in mind. We describe the first 3D hydrogel microarray platform focused solely at detecting small molecule–protein interactions.”
Looking forward, the team suggests that the surface of the hydrogel slide could be modified by introducing other functional groups, allowing the targeting of different molecule–protein interactions.
Source: Marsden DM, Nicholson RL, Ladlow M, Spring DR. 3D small-molecule microarrays. Chem. Commun. DOI: 10.1039/b913665g (2009) (Epub ahead of print).
The Backdoor Approach: Novel Binding Mechanism of Pak Inhibitor Elucidated
Researchers from the Fox Chase Cancer Centre, USA, have published a report on the mechanism of action of a novel inhibitor of the p21-activated kinase 1 (PAK1), a development that could provide new insights into combination cancer therapies.
The scientists demonstrated that 1,1‘-disulfanediyldinaphthalen-2-ol (IPA-3), a small-molecule inhibitor of PAK1, covalently binds to the regulatory domain of the enzyme rather than the active site like traditional kinase inhibitors.
IPA-3, which was discovered by the same team of researchers from approximately 33,000 drug candidates, is an allosteric inhibitor that the team found to be more selective than traditionally used inhibitors, which target kinase active sites and have the potential to bind to non-targeted enzymes, resulting in drug toxicity. IPA-3 was also shown to prevent PAK binding to Cdc42, a protein implicated in cell cycle regulation.
“By targeting PAK1’s specific regulatory domain, IPA-3 is a highly selective molecule that takes a more-or-less backdoor approach to shutting down a kinase, which means that it is less likely it will also turn off other kinases unintentionally,” commented co-author Jeffery Peterson. “If we can create drugs that take advantage of this mechanism, we could create new combination therapies that will allow doctors to kill what might otherwise be drug-resistant cells.”
Cancer therapies based on nonactive site-targeting kinase inhibitors are already on the market – Gleevec® being a prime example – and, although IPA-3 may cause other unwanted effects in humans, the team believes that molecules similar to IPA-3, which target the regulatory domain, could represent a new avenue of research for drug discovery.
Source: Viaud J, Peterson JR. An allosteric kinase inhibitor binds the p21-activated kinase autoregulatory domain covalently. Mol. Cancer Ther. 8(9), 1–7 (2009).
Hiv Drug Patent Over-Ruled by Indian Authorities
The antiretroviral drug tenofovir can be manufactured in Indian franchises and sold to middle-income countries such as Brazil and China, following a ruling by the Delhi patent office overturning the patent.
Tenofovir was developed by Gilead Sciences and sold in the USA as Viread®. It inhibits the enzyme reverse transcriptase, is implicated in HIV and is one of the most prolific antiretroviral drugs on sale.
Gilead Sciences’ patent allowed Indian franchises to manufacture the drug and sell it to low-income countries but protected Gilead Sciences’ right to sell the drug exclusively in middle-income countries, including Brazil and China.
Further Indian patent restrictions meant that the sale of low-cost tenofovir was not a viable business venture for Indian manufacturers of generic drugs. The ruling, which is expected to be challenged by Gilead, will allow Indian companies to sell low-cost versions of the drug to developing countries.
Cipla, whose appeal against the patent was upheld, says that the ruling will lead to greater access to the drug at lower costs by HIV patients around the world. The company had been manufacturing tenofovir against the terms of the patent but faced a lack of interest from developing countries that were concerned that if the patent were upheld, their supply of tenofovir would cease.
Source: India overturns HIV drug patents. Financial Times Online:www.ft.com/cms/s/0/d06440c6-97e2-11de-8d3d-00144feabdc0.html?nclick_check=1
Canadian Team Creates Protein-Production Factory
Researchers at the University of British Columbia, Canada, have reported successfully adapting a single protein on the surface of the bacterium Caulobacter crescentus to turn it into a protein-production factory.
The findings, presented recently at the Society for General Microbiology’s meeting at Heriot-Watt University, Edinburgh, UK, suggest that the proteins produced could be useful in developing vaccines and drugs.
C. crescentus is a harmless bacterium that has a single protein layer on its surface. John Smit and colleagues modified the system that secretes proteins, and which assembles into a structure known as the ‘S-layer’, to secrete numerous other proteins that could be useful for therapeutic applications.
They also demonstrated that, by keeping the S-layer protein intact while inserting new entities inside, they could produce a dense selection of proteins on the cell surface, potentially allowing the whole bacterium to be used for therapeutic applications.
“This S-layer system is very efficient at producing and secreting proteins – we can make the bacterium into a protein pump, secreting over half of all the protein it makes as engineered S-layer protein,” said Smit. “Applications of S-layer display that we are currently developing include anticancer vaccines, an HIV infection blocker and agents to treat Crohn’s and colitis, and diarrhea in malnourished populations”.
Bacteria are frequently used in biotechnology to produce useful proteins. If the bacteria secrete the protein rather than keep it contained within the cell, purification costs can be substantially lowered. The British Columbia researchers have developed a commercially available kit based on their new technology that could see application in developing countries where it might be used to manufacture HIV-blocking agents cost effectively.
Source: Making bacteria make useful proteins: www.eurekalert.org/pub_releases/2009-09/sfgm-mbm090209.php