Nanomedicine Made Easy
Alan W. Shindel MD, Maurice M. Garcia MD, Tom F. Lue MD
Department of Urology,University of California, San Francisco
Nanomedicine and Nanotechnology
“Nanotechnology” is the study of methods by which to manipulate the sub-microscopic environment. It is a multi-disciplinary field that involves applied physics, materials science, interface science, supramolecular chemistry (non-covalent molecular bonding interactions), chemical/electrical/mechanical engineering, robotics, and the biological sciences. 1 “Nanomedicine” is the application of nanotechnology to the medical sciences.
A nanometer is 1 one-billionth of a meter, or 1 x 10-9 m. The prefix “nano” is often used to refer to anything of sub-microscopic dimensions. It is more precise to define “nanoscale” as referring to objects between 10 and 100 nanometers in length. For instance, a nanoparticle is a semicrystalline or amorphous zero-dimensional structure with at least one dimension between 10 and 100 nm and a relatively high surface-area to volume ratio.2
To convey a sense of scale, the relative proportion of a nanometer to a meter is comparable to that of a marble relative to the size of the earth. Carbon-carbon bond lengths are approximately 0.12 – 0.15 nm, and the diameter of the DNA double helix is about 2 nm. Bacteria of the genus Mycoplasma, the smallest free-living organisms, are approximately 200 nm in length.3
The unifying theme of nanotechnology is the control and manipulation of matter on the atomic and molecular scale. Certainly, many biological processes and therapeutics utilize components (proteins, genes, etc.) that exist and/or are manipulated on the nanoscale. Nanotechnology is distinct from these other processes/therapies because the component nano-materials are either man-made or their movement/function is controlled by man-made devices.
The fundamental concepts of what would later be termed “nanotechnology” were first described by the renowned physicist Richard Feynmann at the American Physical Society Meeting at the California Institute of Technology on December 29th, 1959. He described a future in which atoms and molecules could be directly manipulated using very precise tools. In Fenyman’s vision, a set of tools could be built to make and operate a series of exponentially smaller and more precise tools. This process could be repeated indefinitely, ultimately leading to tools that could manipulate atoms and molecules directly.
The determination to exert control over matter on the nanoscale gained momentum as scientific breakthroughs permitted characterization, measurement, and study of matter at the progressively smaller dimensions. As knowledge of the universe at the nanoscale increased, the myriad ways in which physical properties of matter change as dimensions decrease became readily apparent.2, 4 These unique properties may permit numerous novel applications in the near future.
Nanotechnology applications in Urology and Sexual Medicine
Many breakthroughs in nanotechnology may be applied to urological research and routine patient care in the near future. A complete review of nanotechnology applications within urology is beyond the scope of this paper. Interested readers are referred to the excellent review on applications of nanotechnology relevant to urology by Gommersall et al.5 Briefly, with respect to urology, nanotechnology may lead to improvements in radiographic imaging contrast agents 6-8, detection and ablation of urologic cancers 9, 10,11, 12, the engineering of artificial tissues13, 14 and bioartificial organs15,16, and the precision of new surgical devices.5, 17-19
With respect to sexual medicine, nanotechnology may play a number of important roles in tissue replacement for ED. The replacement of damaged tissues has long been a particular interest of materials scientists. Research directed at the replacement of tissues using stem cells (both embryonic and adult somatic) has blossomed recently due in large part to technical advances afforded by nanotechnology. Nanoscale scaffolds may be used as a matrix for stem cell delivery or as a site onto which stem cells can be seeded for growth at a selected delivery site. In addition to a potential role in producing scaffold materials, nanotechnology holds promise in fulfilling two key requisites for studies of stem cell-based therapy for ED: the growth and tracking of stem cells in-vivo.
Adult stem cell therapy for the treatment of erectile dysfunction (ED) in animal models
The integrity of the erectile tissues of the corpora cavernosa is critical to the maintenance of erectile function. Erectile dysfunction (ED) of organic etiology is commonly the result of metabolic damage to the cavernous nerves, endothelial cells and/or smooth muscle surrounding the sinusoids of the erectile tissue. While there has been great progress in the development of therapies to treat ED, there is currently no means by which to enhance in-situ repair of damaged cells and tissues. Tissue repair/replacement with newer and healthier cells would theoretically restore the function of damaged cells and reverse ED.
Stem cell therapy is a promising means by which to promote in-situ tissue healing and replacement of damaged cells with healthy populations of local cell types. Stem cells are defined as cells that may differentiate into many different lineages and have the capacity to self-renew, While cells derived from human embryos are a source of healthy multi- and pluri-potent stem cells,20-22 embryonic stem cell therapy has been hampered by ongoing ethical and governmental debates concerning the use cells harvested from early-stage embryos. More recently, adult mesenchymal stem cells have emerged as an alternative to embryonic stem cells. Adult stem cells have a number of advantages relative to embryonic stems cells; they fulfill many of the criteria of true stem cells, are more readily available than embryonic stem cells, and there is little ethical opposition to their use.
While much of the early work on adult stem cells was focused on bone marrow derived stem cells (BMSC), adipose tissue derived stem cells (ADSC) have recently been recognized as possessing comparable multi-lineage potential, capacity for self-renewal, in-vivo growth and differentiation plasticity, and ability to secrete of important trophic cytokines such as VEG-F and IGF.23, 24 Studies have established that ADSC are 5 to 50-fold more plentiful in a sample of adipose tissue compared to the concentration of BMSC in a comparable volume of bone marrow.11 Furthermore, adipose tissue is abundant, easy to harvest with little morbidity, and renewable. These advantages serve to make harvest of ADSC safer and more efficient than harvest of BMSC.
Animal model experiments
There is an abundance of promising research from various medical sub-disciplines that has shown, using animal models, that both BMSC and ADSC can promote wound healing and re-populate tissue injury sites with normal stem-cell derived blood vessels, smooth, skeletal, and cardiac muscle, nerves, and connective tissue. 20-22 Research on applications of ADSC for a multitude of human conditions is ongoing and will likely lead to many novel and exciting new therapies.
Challenges to cell-based translational science: translating animal model research to human therapies
While in-vitro and in-vivo animal model work has yielded very promising results, the process of translating such work to human clinical trials requires that key questions about the treatment be addressed.25 Any new therapy begins with Phase I clinical trials. The primary focus of Phase I clinical trials is safety. Therefore, the first questions that must be addressed are related to the fate of injected stems cells. It must be determined whether or not the injected survive, migrate, and/or degenerate into malignant cells. Cell tracking is also important in Phase II, III, and IV clinical trials, during which dosing and efficacy of an investigational therapy are systematically investigated.
It is abundantly clear that the fate and location of stem cells injected for treatment purposes must be defined at all times so that clinical outcomes, positive or negative, can be correlated to the presence of treatment cells. Unfortunately, it has been difficult to address concerns regarding stem cell fate in humans due to challenges in cell labeling. The ideal “cell label” must be safe, non-toxic, and durable over the long study periods favored by the FDA to conclude that the cell therapy is safe.
Non-invasive stem cell tracking: nanoparticles and Magnetic Resonance Imaging (MRI)
Song et al. recently reported successful tracking of human BMSC labeled with superparamagnetic iron oxide (SPIO) nanoparticles by magnetic resonance imaging (MRI) in an animal model 26. SPIO are normally used as an intravenous contrast agent for MRI imaging of the liver, spleen, and vascular system. SPIO-labeled BMSC were injected into the corpora-cavernosa of immune-suppressed rabbits and adult male rats. Over a period of 3 months, MRI was used to serially image the penis and to confirm the presence and retention of the labeled BMSC. In a similar study, Daldrup et al.27 demonstrated that autologous mouse BMSC can be tracked in-vivo using MRI and iron nanoparticlles, while Rice et al.28 demonstrated that mouse ADSC can be labeled with SPIO and tracked in-vivo.
Nano-engineered iron particles represent a potentially useful means by which to track stem cell fate in human trials of stem cell therapy. Iron is generally non-toxic, persists in cells for long duration, and may be a near ideal method by which to track stem cells in future studies.
Nanotechnology has the potential to contribute to numerous scientific disciplines. In turn, these contributions may serve to provide new technologies with which to refine and enhance diagnosis and treatment of human disease. Through advances in in-vivo cellular tracking imaging, nanotechnology is poised to help translate advances in stem cell science to the clinical arena. In-vivo cellular tracking will allow clinicians to correlate stem cell dose and dose-interval with clinical outcomes, in order to better define mechanisms of therapy, optimal dosing, and potential long term toxicities. Nanotechnology may play a critical role in making stem cell therapy for erectile dysfunction a reality. It is likely that novel and exciting applications and opportunities will continue to develop as nanotechnology progresses.
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