Biotechnology 21
thumbnail-sized substrate containing thousands of work to see that useful new products actually make it to
microscopic spots of oligonucleotides (stretches of DNA market.”
about 20 base pairs in length) laid out in a grid. Meanwhile, researchers at Temple University’s School
Often referred to as ‘gene chips’, DNA microarray of Pharmacy in Philadelphia, US, are using DNA to
assays and their RNA counterparts have become one of customise prescriptions in order to prevent adverse drug
the most powerful tools for gene-expression profiling, reactions before a single dose is taken (Fig. 1).
the identification of mutations, and the detection of According to the US Department of Health and Human
multiple pathogens in patients afflicted either by multiple Services, more than 770 000 people are killed or injured
diseases or drug-resistant strains of diseases. Aside from each year in the US by such reactions. At the top of
their potential future role in personalised medicine, the the list of problem drugs is Warfarin, the most widely
widespread use of DNA microarray assay devices could prescribed anticoagulant. That is why Evgeny Krynetskiy,
have an immediate and profound impact on the treatment associate professor and director of the Jayne Haines
of diseases today. Center for Pharmacogenomics and Drug Safety, has
In a typical experiment, a microarray is prepared and focused research on that drug. “Prescribing this medicine
mounted in a well chamber and the DNA is hybridised is like trial and error in finding the right dosage that
(a standard technique in which complementary single works best for you,” says Krynetskiy. “Five milligrams is
strands of DNA bind to form double-stranded DNA a typical dose, but a little less or a little more could have
‘hybrids’). A suspension of negatively-charged silica dramatic consequences or no benefit at all.”
microspheres is then dispersed through gravitational Doctors call this optimal dosage the therapeutic
sedimentation over the microarray surface, a process window, and Krynetskiy is trying to find it through
which takes about 20 minutes. pharmacogenomics, the study of a person’s response to
Because the substrate or background surface of the drugs based on their genetic makeup. It’s a collaboration
microassay is positively charged, the silica microspheres that crosses campuses and includes Krynetskiy and fellow
will spread across clinical faculty
the entire surface at the School of
and adhere to it.
“One of the most amazing things about our
Pharmacy, clinicians
However, on surface
electrostatic detection method is that it requires
at Temple University
areas containing
nothing more than the naked eye to read out
Hospital and
double-stranded Jeannes Hospital.
DNA, which is highly
results that currently require chemical labelling
The researchers are
negatively charged,
and confocal laser scanners…”
studying why people
and on areas process the same
containing single- drug differently. In
stranded DNA, also negatively charged but to a lesser this case, they’re trying to find the correlation between
degree than double-stranded DNA, the microspheres genotypes, or a person’s inner code of DNA, and the
will levitate above the substrate surface, stacking up correct dosage of Warfarin. By collecting saliva samples
in “equilibrium heights” that are dictated by a balance and extracting DNA from 77 participants already on the
between gravitational and electrostatic forces. drug, the researchers can look for variances, genetic
These electrostatic interactions on the microarray clues, which make people metabolise the same drug in
surface result in charge-density contrasts that are readily very different ways.
observed. Surface areas containing DNA segments “Our findings have confirmed there is a genetic
take on a frosted or translucent appearance, and can variance of certain genotypes that correlate to how these
be correlated to specific hybridisations that reveal the participants respond to this drug,” says co-investigator
presence of genes, mutations and pathogens. Nima Patel, associate professor in the School of Pharmacy.
“Our technique is essentially a millionfold parallel “So, if you have this genotype, we can conclude what
version of the classic experiment used by Robert Millikan your risks may be, based on your DNA.”
almost 100 years ago, when he determined the charge of That would allow doctors to prescribe the correct
a single electron by observing the positions of oil droplets dosage of Warfarin and decrease the risk of adverse
levitated above a charged plate,” said Groves. drug reactions: too low a dose can increase the risk of
There are a number of short-term ‘next steps” for this dangerous blood clots, while too large can cause
research, Groves said, including testing its application in life-threatening bleeding. What may be equally
high-density arrays and pushing its resolution limits. noteworthy about Krynetskiy’s and Patel’s research is
“Since the resolution of electrostatic-based imaging is that more than half the participants are either African
determined by the number of particle-observations rather American or Hispanic, two groups underrepresented in
than by the diffraction limit of light, our readouts could clinical trials. So finding their therapeutic window, the
serve as a form of ultramicroscopy,” he said. “The real place where they will safely get the maximum benefit
grand challenge for this technology, however, will be for of a drug, is particularly important in this personalised
us to find suitable industrial partners with whom we can medicine quest. u
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