Chemical Education Today
Reports from Other Journals
Research Advances by Angela G. King
Ingenious New Delivery System for Antioxidant SOD Scientists in Georgia report successful lab tests of new polymer microparticles that show promise of being a longsought way of delivering drugs directly into the cell structures that are responsible for inflammation. Those immune system structures—macrophages—devour and destroy foreign substances such as invading bacteria and cellular debris. However, they also release so-called reactive oxygen species (ROS) that help cause arthritis, acute liver failure, and other inflammatory diseases. Georgia Tech’s Niren Murthy and colleagues at the Emory University School of Medicine have successfully conducted cell culture experiments with microparticles encapsulating the enzyme superoxide dismutase (SOD). SOD is getting wide attention as a potential treatment for inflammatory diseases because it scavenges reactive oxygen species. However one roadblock to clinical use of SOD is the lack of a delivery system. SOD is membrane impermeable and therefore needs a delivery vehicle to be able to enter the macrophage. Researchers explored the use of liposome-based delivery vehicles but were hindered by their short shelf lives. Polymer-based microparticles are also being explored. Polyester-based microparticles have a long shelf-life but their well-known and acidic degradation products can cause inflammation, which would counteract SOD treatment. Acid-degradable polymers, such as polyacetals, react in the acidic lysosomes and phagosomes of bacteria and have been shown effective for intracellular drug delivery. Now
Murthy’s research team has demonstrated that polyketals, a new family of acid-degradable polymers made from a chain of ketal linkages, could be effective in delivering SOD into bacterial cells. The ketals hydrolyze 1000 times more quickly in the acidic phagosome (pH 4.5) compared to blood’s pH 7.4. The resulting degradation products are neutral and may not cause the inflammation seen with polyesters. Additionally, polyketals that degrade in the phagosome could osmotically destabilize it. Only one polyketal, poly(1,4-phenyleneacetone dimethyl ketal), had previously been a candidate for drug discovery, and upon degradation it produces the potential toxin, benzene dimethanol. Poly(cyclohexane-1,4-diyl acetone dimethylene ketal), or PCADK for short, is a new polyketal developed for drug delivery by the Georgia Tech team (Figure 1). PCADK is synthesized on a multigram scale via an acetal exchange reaction between 1,4-cyclohexanedimethanol and 2,2-dimethoxypropane. The resulting polymer, with an approximate molar mass of 6000, degrades into acetone, which is on the FDA’s Generally Recognized as Safe (GRAS) list, and 1,4cyclohexanedimethanol, which displays a very low toxicity (LD50 3200 mg/kg). 1,4-cyclohexanedimethanol is approved for food packaging and as an indirect food additive. Most of the 1,4-cyclohexanedimethanol dosed orally by rats is excreted intact. Hydrolysis kinetic studies were performed to estimate PCADK behavior in blood (pH 7.4) and the phagosome (pH 4.5). The hydrolysis is pH sensitive, with the polyketal
Figure 1. PCADK, a new polymer for drug delivery. (A) Synthesis of PCADK from 1,4-cyclohexanedimethanol (CDM) and 2,2-dimethoxypropane (DMP), and acid hydrolysis of PCADK into CDM and acetone. (B) Formulation of SOD loaded microparticles by w/o/w double emulsion. Microparticles degrade after phagocytosis, in the acidic environment of the phagosome. Reprinted with permission from Bioconjugate Chem. 2007, 18, 4–7. Copyright 2007 American Chemical Society.
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Chemical Education Today
Reports from Other Journals
Figure 2. SEM images of SOD-PCADK microparticles: (A) 6000x magnification, (B) 1000x magnification. Reprinted with permission from Bioconjugate Chem. 2007, 18, 4–7. Copyright 2007 American Chemical Society.
having a half-life of 24.1 days at pH 4.5 and more than four years at pH 7.4. A double emulsion procedure encapsulated SOD into PCADK-based microparticles. Essentially, an aqueous solution of SOD was homogenized into methylene chloride. The resulting emulsion was then dripped into an aqueous polyvinylalcohol solution and again subjected to homogenization. The new emulsion was poured into a pH 7.4 buffer before the methylene chloride was evaporated. The particles that resulted were collected by centrifugation and freeze-dried. The SOD–PCADK microparticles produced in this manner range in size from 3–15 m in diameter as measured by scanning electron microscopy (Figure 2). Cell cultures were used to investigate the ability of the SOD–PCADK microparticles to scavenge superoxide from macrophages. Macrophages were incubated for 2 h with either SOD–PCADK microparticles, free SOD, or empty PCADK microparticles. The superoxide production from each type of macrophage was then measured with an established cytochrome c-based assay. Free SOD caused very little decrease in superoxide production, while the SOD–PCADK microparticles caused a 60% decrease. The researchers state that the new polymer microparticles have several advantages over other potential delivery systems. The particles remain intact until reaching acid environments such as the phagosomes—literal death chambers—that form after macrophages engulf bacteria and other particles. Then the polymers break down, releasing their SOD directly at the site where inflammation begins, a great breakthrough in the treatment of inflammation-based disease. More Information 1. Lee, Sungmun; Yang, Stephen C.; Heffernan, Michael J.; Taylor, W. Robert; Murthy, Niren. Polyketal Microparticles: A New Delivery Vehicle for Superoxide Dismutase. Bioconjugate Chem. 2007, 18, 4–7. 2. This Journal has published a discussion, tested demonstration, and laboratory on SOD. See J. Chem. Educ. 1985, 62, 990; 1991, 68, 57; 1983, 60, 1082, respectively. 3. Niren Murthy’s research Web page is available at http://www. bme.gatech.edu/groups/murthylab/; an online report of this research
Figure 3. Illustration of a possible mechanism accounting for FePt@ CoS2 yolk–shell nanocrystals killing HeLa Cells. After cellular uptake, FePt nanoparticles were oxidized to give Fe3 (omitted for clarity) and Pt2 ions (yellow). The Pt2 ions enter into the nucleus (and mitochondria), bind to DNA, and lead to apoptosis of the HeLa cell. Reprinted with permission from J. Am. Chem. Soc. 2007, 129, 1428–1433. Copyright 2007 American Chemical Society.
project can be found at http://www.gatech.edu/news-room/release. php?id=914 (both sites accessed Apr 2007). 4. Details of the FDA GRAS list can be found at http://vm.cfsan. fda.gov/~dms/eafus.html (accessed Apr 2007).
Toward Development of an Anticancer “Egg” Scientists in Hong Kong are reporting synthesis and early laboratory tests of a new nanostructure that they believe may lead to the design of an anticancer nanomedicine. Bing Xu and colleagues describe the structure as an eggshell nanocrystal. Like a chicken’s egg, the structure has an outer shell that encloses a “yolk” that can be released from the shell. The hollow nanocrystals form through the Kirkendall effect, which causes metal atoms to diffuse toward the outer layer, generating a hollow core and causing pores to form in the shell. Xu’s team wanted a nanostructure with a yolk consisting of iron and platinum, the metal responsible for the activity of the widely used chemotherapeutic drug, cisplatin. In their experiments, the researchers obtained FePt nanoparticles through standard thermal decomposition protocols, converted the nanoparticles to FePt@Co core-shell intermediates, and then obtained FePt@CoS2 by injecting a solution of S2. Transmission electron microscopy (TEM) revealed the desired FePt@CoS2 yolk–shell nanocrystals. The nanocrystals dispersed well in water after brief ultrasonic treatment,
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Reports from Other Journals which demonstrates the hydrophilicity of the shell surface and indicates that they will interact with water-based biological systems. Cultures of human cancer cells took up the nano structures, and the nanostructures released their yolks. This proved to have “exceptionally high toxicity” for the cancer cells (Figure 3). The number of dead HeLa cells increased dramatically with the length of time the cells were incubated with the nanocrystals. The IC50 of the nanocrystals was approximately 1.5 g/mL, which corresponds to 35.5 ng of Pt/mL, much lower than cisplatin’s 230 ng of Pt/mL. After three days of incubation with HeLa cells, the FePt@CoS2 nanocrystals could be observed by TEM in organelles such as mitochondria, confirming cellular uptake. “This type of yolk–shell nanostructure may lead to novel nanomedicine for treating cancers,” the researchers state, describing nanostructures that may be coated with antibodies that specifically target cancer cells and thus reduce body-wide side effects that occur with traditional chemotherapeutic drugs. The high cytotoxicity of the FePt@CoS2 yolk–shell nano crystals was credited to the FePt core, and this was confirmed by measuring the low cytotoxicity of CoS2 hollow nanospheres and cysteine-coated FePt nanoparticles. More Information 1. Gao, Jinhao; Liang, Gaolin; Zhang, Bei; Kuang, Yi; Zhang, Xixiang; Xu, Bing. FePt@CoS2 Yolk–Shell Nanocrystals as a Potent Agent to Kill HeLa Cells. J. Am. Chem. Soc. 2007, 129, 1428– 1433. 2. This Journal has published numerous articles on nano technology. See J. Chem. Educ. 2006, 83, 1516; 2005, 82, 1625; and 2005, 82, 1274 for examples. 3. General information on nanocrystals and research exploring their applications can be found online at http://www.lbl.gov/ScienceArticles/Research-Review/Magazine/2001/Fall/features/02Nanocrystals. html and http://nanocrystal.pa.msu.edu/ (both sites accessed Apr 2007). 4. Additional information on the Kirkendall effect can be found in Science 2004, 304, 711.
Vegetable Soup Chemical Reactions A new study suggests that chemists working on tight budgets in developing countries may be able to substitute
extracts of potatoes, celery, eggplant, carrot, cassava, horseradish, or an array of other inexpensive and locally available vegetable products for the costly reagents traditionally needed for chemical reactions. Geoffrey A. Cordell at the University of Illinois at Chicago and colleagues in Brazil explain that the high cost of imported reagents is a major problem for academic, chemical industry, and pharmaceutical laboratories in developing countries. Their report describes how some of the more than 7,000 vegetable crops grown throughout the world can be used in laboratory work as environmentally and economically sound substitutes for commercial reagents. The authors have summarized the use of more than 30 plants—ranging from ginger root to pumpkin and Boston fern—cited in literature as chemical reagents for reactions that include chiral reduction of ketones, oxidation of alcohols, and deracemization of alcohols and esters. “The evaluation of locally available vegetables, fruits, common plants, and natural waste products for a selection of standard organic chemical reactions of commercial significance could prove to be a very valuable economic endeavor,” the report notes. “It may well offer new opportunities to expand the role of natural products as sustainable chemical reagents where high-cost, nonrenewable reagents are presently used.” Using plant-based reagents also affords an economical and safe way for instructors to expose their students to the realm of synthetic chemistry. More Information 1. Cordell, Geoffrey A.; Lemos, Telma L. G.; Monte, Francisco J. Q.; De Mattos, Marcos C. Vegetables as Chemical Reagents. J. Nat. Prod. 2007, 70, 478–492. 2. This Journal has published numerous articles on the use of microbial and plant biocatalysts. See J. Chem. Educ. 2000, 77, 344; 2004, 81, 1048; 2005, 82, 1049 for examples. 3. Additional discussion of ref 1 is available online at http:// www.intute.ac.uk/sciences/spotlight/issue46/Chemistry_veggie.html (accessed Apr 2007). 4. Cordell’s research Web page can be found at http://www. uic.edu/pharmacy/depts/pmch/faculty_sites/Cordell.htm (accessed Apr 2007).
Angela G. King is Senior Lecturer in Chemistry at Wake Forest University, P. O. Box 7486, Winston-Salem, NC 27109;
[email protected].
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Summary of the Use of Foods and Vegetables as Chemical Reagentsa food/vegetable botanical name common name
Allium shoenoprasum Armoracia lapatifolia Apium graveolens var. rapaceum Arctium lappa Arracacia xanthorrhiza Artemisia vulgaris Beta vulgaris Brassica rapa Colocasia esculenta Coriandrum sativum Cucurbita pepo Cyrtomium falcatum Daucus carota Dendrobium phalenopsis Dioscorea alata Helianthus tuberosus Hordeum vulgare Ipomeoa batatas Ipomeoa batatas Malus sylvestris Manihot dulcis Manihot esculenta Nelumbo nucifera Nephrolepis cordifolia Nephrolepis exaltata Phaseolus aureus Polymnia sonchifolia Raphanus sativus Solanum melongena Solanum tuberosum Spirodela punctata Triticum aestivum Undaria pinnatifida Zingiber officinale
reaction(s) effectedb
chive bulb horseradish
BFKc CDFcK
celery root burdock root arracacha root wormwood beet root turnip root taro root coriander root pumpkin Japanese holly fern carrot root orchid yam tuber artichoke wheat sweet white potato tuber sweet red potato tuber apple sweet cassava manioc root lotus root fishbone fern Boston fern green grams, dal yacon root radish root eggplant, aubergine potato tuber duckweed wheat wakame seaweed ginger root
BCDFK BcFcK BFK B BFK BFcKc BFK BcFK B D B;CDFc;HJKLK D BFK CDFK B BcFKc; K BcFcKc D; CDFc KGEDL BcFKGEDL Kc D D GIJK BKc BFKc K BCDFKc; D CD B B BFKc
a Whole plant preparations only. Please see the original paper for references to procedures. b Reactions. B: Deracemization of an alcohol; C: Deracemization of esters; D: Ester hydrolysis; E: Reduction of an aldehyde to a primary alcohol; F: Oxidation of an alcohol to a carbonyl; G: Reduction of an a,b-unsaturated ketone to an allylic alcohol; H: Reduction of an azidoketone; I: Reduction of a double bond; J: Chiral reduction of a ketone; K: Chiral reduction of an aromatic ketone; L: Chiral reduction of a ketone carbonyl of a b-ketoester. c Attempted; poor result.
Table reprinted with permission from J. Nat. Prod. 2007, 70, 478–492. Copyright 2007 American Chemical Society.
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