Author, reporter, Curator: Tilda Barliya PhD
Dr. Ritu Saxena’s exciting report on the fascinating work of Dr. Apostolia M. Tsimberidou “personalized medicine gearing up to tackle cancer”, inspired me to go back and review this topic and see how nanotechnology can be applied in personalized medicine.
To read the Dr. Saxena’s post, please see https://pharmaceuticalintelligence.com/2013/01/07/personalized-medicine-gearing-up-to-tackle-cancer/
It is based on an interview with Dr. A. M. Tsimberidou based on her paper:
Personalized medicine in a phase I clinical trials program: the MD Anderson Cancer Center initiative.
In March 2011 Nature Reviews issued a special issue features discussions of the advances, challenges and progress in the field of personalized cancer medicine by key opinion leaders who presented at the Worldwide Innovative Networking (WIN) symposium (**).
So what is personalized medicine?
Personalized medicine is a huge movement in the modern medical world. It aims to move away from the traditional practice of prescribing standard doses of standard drugs for a condition to every patient, and shifts the focus onto targeting the precise drug and dose required according to the patient’s physiology.
This is achieved by detecting and tracking molecular biomarkers, which indicate the presence and level of activity of a particular biological system in a patient’s body, whether inherent or foreign.
Another major part of the emerging field of personalized medicine is pharmacogenomics – analyzing the genetic makeup of the patient to determine whether a particular medication will be successful, or if it will have any adverse effects. (1). This is particularly important in cancer treatment, where the chemotherapy drugs used can be very damaging to healthy cells as well as cancerous ones, and the exact genetics of the tumor cells can vary widely between patients, and even between locations in one patient’s body.
Personalized medicine involves:
- Detection (DNA polymorphism, RNA and protein expression, metabolits, Lipids etc)
- Diagnosis (imaging)
- Prognosis and
- Treatment (targeted-therapy)
Given the size symmetry, nanomaterials offer unprecedented sensitivity, capable of sensing biological markers and processes at the single-molecule or single-cell level either in vitro or in vivo. Techniques are being developed for high-throughput DNA sequencing using nanopores, to obtain genetic information from a patient so that targeted medication can be selected as rapidly as possible.
Cancer, a very complex disease, is propagated by various types of molecular aberrations which drive the development and progression of malignancies. Large-scale screenings of multiple types of molecular aberrations (e.g., mutations, copy number variations, DNA methylations, gene expressions) become increasingly important in the prognosis and study of cancer. Consequently, a computational model integrating multiple types of information is essential for the analysis of the comprehensive data.
One of the greatest promises of near-term nanotechnoloogy is cheaper DNA sequencing to speed the development of personalized medicine. (3)
Nanotechnology and DNA sequencing
Tumors are known to be highly heterogenetic, due to the many acquired aberration in the cancer cells. Therefore, there are not only genetic differences between different patients, but also genetic differences within the same patient; for example from different locations in the same patient, that can greatly affect the success of a therapy. Therefore, sensitive and extensive yet inexpensive whole-genome sequencing is of major medical need to enable the application personalized medicine. A review of the potential of this emerging nanotechnology “Nanopore sensors for nucleic acid analysis ” was published recently in Nature Nanotechnology (4).
The growing need for cheaper and faster genome sequencing has prompted the development of new technologies that surpass conventional Sanger chain-termination methods in terms of speed and cost. These second- and third-generation sequencing technologies — inspired by the $1,000 genome challenge proposed by the National Institutes of Health in 2004 (ref. 5) — are expected to revolutionize genomic medicine. Nanopore sensors are one of a number of DNA sequencing technologies that are currently poised to meet this challenge.
Nanopore-based sensing is attractive for DNA sequencing applications because it is a
- requires low reagent volumes
approach that can be scaled for high-throughput DNA analysis.
This approach can be scaled up for high-throughput DNA analysis, it typically requires low reagent volumes, benefits from
relatively low cost and supports long read lengths, so it could potentially enable de novo sequencing and long-range haplotype mapping. Although, nanopore technology is not conceptually new and raised many skeptical opinions it has made major progress in the past few years and are thus worth sharing.
The principle of nanopore sensing is analogous to that of a Coulter counter. A nanoscale aperture (the nanopore) is formed in an insulating membrane separating two chambers filled with conductive electrolyte. Charged molecules (A,G,C,T) are driven through the pore under an applied electric potential (a process known as electrophoresis), thereby modulating the ionic current through the nanopore. This current reveals useful information about the structure and dynamic motion of the molecule.
Here’s an example for a nanopore-based sequencing device is a Graphene- chip that is used as trans-electrode membrane (5).
Electrical measurements on graphene membranes in which a single nanopore has been drilled show that the membrane’s effective insulating thickness is less than one nanometer. This small effective thickness makes graphene an ideal substrate for very high-resolution, high throughput nanopore-based single molecule detectors. The sensitivity of graphene’s in-plane electronic conductivity to its immediate surface environment, as influenced by trans-electrode potential, will offer new insights into atomic surface processes and sensor development opportunities. (4-6).
A nanopore-based diagnostic tool could offer various advantages:
- it could detect target molecules at very low concentrations from very small sample volumes;
- it could simultaneously screen panels of biomarkers or genes (which is important in disease diagnosis,
- monitoring progression and prognosis);
- it could provide rapid analysis at relatively low cost; and
- it could eliminate cumbersome amplification and conversion steps such as PCR, bisulphite conversion and Sanger sequencing
Nanopores are likely to have an increasing role in medical diagnostics and DNA sequencing in years to come, but they will face competition from a number of other techniques. These include
- single-molecule evanescent field detection of sequencing-by-synthesis in arrays of nanochambers (Pacific Biosciences),
- sequencing by ligation on self-assembled DNA nanoarrays (Complete Genomics), and the
- detection of H+ ions released during sequencing-by-synthesis on silicon field-effect transistors from multiple polymerase-template reactions (Ion Torrent).
However, the possibility of using nanopore-based sensors to perform long base reads on unlabelled ssDNA molecules in a rapid and costeffective manner could revolutionize genomics and personalized medicine.
Current trends suggest that many challenges in sequencing with biological nanopores
- the high translocation velocity and the
- lack of nucleotide specificity
have been resolved. Similarly, given the progress with solid-state nanopores, if the
- translocation velocity could be reduced to a single nucleotide (which is ~3Å long) per millisecond, and if
- nucleotides could be identified uniquely with an electronic signature (an area of intense research),
it would be possible to sequence a molecule containing one million bases in less than 20 minutes. Furthermore, if this technology could be scaled to an array of 100,000 individually addressed nanopores operating in parallel, it would be possible to sequence an entire human genome (some three billion base pairs) with 50-fold coverage in less than one hour.
Although, none of the nanopore-solid base sequencing technique have been used as a tool in a clinical trial, one UK-based biotechnology company has its way, nanopore sequencing may soon be available to the public. Earlier this year 2012 Oxford Nanopore Technologies (ONT) announced that it was on the verge of manufacturing a commercial nanopore sensor. [The company said that by year’s end it would release a $900 handheld model, which it claims can sequence a virus genome 48 000 bases long, and a larger, scalable model that could decode a human genome in as little as 15 minutes. In contrast, conventional systems cost upward of $500 000 and take weeks to sequence a human genome (7).]
2. G.E. Marchant. Small is Beautiful: What Can Nanotechnology Do for Personalized Medicine?. Current Pharmacogenomics and Personalized Medicine, 2009, 7, 231-237. http://www.benthamscience.com/cppm/Sample/cppm7-4/002AF.pdf
4. Venkatesan BM and Bashi R. Nanopore sensors for nucleic acid analysis. Nature Nanotechnology 2011; 18: http://libna.mntl.illinois.edu/pdf/publications/127_venkatesan.pdf
5. Garaj S., Hubbard W., Reina A., King J., Branton D and Golovchenko JA. Graphene as a sub-nanometer trans-electrode membrane. Nature 2010 (9) 467(7312): 190-193. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2956266/
6. Min SK., Kim WY., Cho Y and Kim KS. Fast DNA sequencing with a graphene-based nanochannel device. Nature Nanotechnology 2011; 6: 162-165. http://biophy.nju.edu.cn/lablog/wp-content/uploads/2011/10/Fast-DNA-sequencing-with-a-graphene-based.pdf
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