By: Rachel Berlin, Marketing Manager

List Labs is proud to be exhibiting at ASM Biothreats February 12-14th. The conference will be held in Baltimore, Maryland at the Hilton Hotel.

Thought leaders in academia, industry and government will gather to present and discuss the latest developments in the emerging field of biothreats. This year’s conference has an expanded program to include tracks on high consequence pathogen research, biological threat reduction, product development, and policy.

List Labs will be exhibiting in booth #29 and Nancy Shine will be presenting her poster on Sensitive Detection of Anthrax Lethal Factor in Plasma Using a Specific Biotinylated Fluorogenic Substrate during poster session 1 on Wednesday, February 14th from 10:30 AM- 11:30 AM in space #020. Come learn about our products that assist in the biological threat reduction such Botulinum Neurotoxins, Anthrax Lethal Factor, FRET Peptides, Shiga Toxins, Tetanus Toxins, and more! All of our research reagents are available for purchase on our website.

Visit Nancy and Karen in the List Labs booth #29, or contact us to schedule a time to meet with them at the show.  Click here for more information or to register for this conference.

By: Suzanne Canada, Ph.D.
Tanager Medical Writing

An exciting report was released in October about a new class of targeted anti-tumor drugs, in which genetically engineered stem cells were used to deliver cytotoxins to brain tumors.¹ Brain cancers known as glioblastomas (GBM) are notoriously difficult to treat because the tumors often re-grow after surgery and because most standard cancer therapies cannot pass the blood-brain barrier. Those cancer therapies that can reach the tumors must be delivered at high doses which can be toxic to the entire body, without specifically targeting the GBM tumor. In this case, a research team at Massachusetts General Hospital (MGH) in Boston used stem cells, added to mouse brain tumors after surgery, to deliver Pseudomonas exotoxin directly at the site of the tumor itself. ²

Although this research is cutting-edge and an exciting development for GBM patients, the idea of using toxins attached to targeting molecules such as antibodies or specific ligands has long been explored as a way of fighting diseases, especially cancer. One popular approach has been to use antibodies linked to toxins to aid in targeting the therapy. (See Chari 2008 and Goldmacher 2011 for reviews).^{3, 4} An example is the approach taken by group of researchers looking for ways to increase the effectiveness of Herceptin®, a monoclonal antibody that is best known for targeting HER-overexpressing malignant breast cancer tumors. Antibody was coupled to both diphtheria toxin and multi-walled carbon nanotubes. They found that both conjugates were more effective in specifically killing HER-2 expressing cells than Herceptin® alone.⁵

An elegant approach to targeting toxins is to activate the toxin by cleavage at the site of therapy. This is precisely the approach used by Schafer and colleagues.⁶ Their model system exploited the fact that metalloproteinases are commonly overexpressed on the surface of squamous cell cancers. Anthrax toxin was engineered to be activated by cleavage by urokinase plasminogen activator (uPA) on the cell surface and metalloproteinases. This approach seemed to work on xenografted human head and neck squamous cell carcinoma (HNSCC) cell lines by inducing apoptotic and necrotic tumor cell death. However, cultured cancer cell lines were found to be insensitive to the engineered toxin, so the researchers concluded that the regulation of two-fold activation was not straightforward as anticipated.

Shiga toxin– produced by an organism responsible for bacterial dysentery – has properties that could be harnessed for cancer research⁷. A group of researchers took advantage of the binding of the Shiga toxin B pentamer to the glycosphingolipid globotriaosylceramide (Gb3) on the cell surface. After binding, the Shiga toxin complex is internalized by eukaryotic cells where the Shiga toxin A moiety can exert its toxic effect. Gb3 is reportedly over-expressed in throat, gastric, and ovarian cancers—and researchers hope that this overexpression pattern could be used to attain more targeted therapy. Specific binding of GB3 by the Shiga toxin B pentamer could also be exploited for imaging of these tumors and for delivering a genetically engineer Shiga toxin A chimera that would only be activated in cancer cells.

In their quest for new and more effective therapies, researchers have noted that bacterial toxins are examples of highly toxic, but also targeted and regulated systems that have co-evolved with the eukaryotic hosts (humans).^{8, 9} In the words of Fabbri et al., “Knowledge of their properties could be used for medical purposes.”  List Biological Laboratories, Inc. provides purified bacterial toxins for research purposes, including Anthrax toxins (Product # 169, 172, & 176), Shiga toxins (Product # 161 & 162), Diphtheria toxins (Product # 149, 150, & 151), and others.

 

1. Paddock C., (2014) Stem cells that release cancer-killing toxins offer new brain tumor treatment. Last accessed: 06 January 2015.
2. Stuckey DW, Hingtgen SD, Karakas N, Rich BE, Shah K (2015) Engineering toxin-resistant therapeutic stem cells to treat brain tumors Stem Cells 33(2):589-600. doi: 10.1002/stem.1874. PMID: 25346520
3. Chari RV (2008) Targeted cancer therapy: conferring specificity to cytotoxic drugs. Acc Chem Res 41(1):98-107. PMID: 17705444
4. Goldmacher VS, Kovtun YV (2011) Antibody-drug conjugates: using monoclonal antibodies for delivery of cytotoxic payloads to cancer cells Ther Deliv 2(3):397-416. PMID: 22834009
5. Oraki KM, Mirzaie S, Zeinali M, Amin M, Said HM, Jalaili A, Mosaveri N, Jamalan M (2014) Ablation of breast cancer cells using trastuzumab-functionalized multi-walled carbon nanotubes and trastuzumab-diphtheria toxin conjugate Chem Biol Drug Des 83(3):259-65. PMID: 24118702
6. Schafer JM, Peters DE, Morley T, Liu S, Molinolo AA, Leppla SH, Bugge TH (2011) Efficient Targeting of Head and Neck Squamous Cell Carcinoma by Systemic Administration of a Dual uPA and MMP-Activated Engineered Anthrax Toxin. PLoS ONE 6(5): e20532. PMID: 21655226 
7. Engedal N, Skotland T, Torgersen ML, Sandvig K (2011) Shiga toxin and its use in targeted cancer therapy and imaging Microb Biotechnol 4(1):32-46. PMID: 21255370
8. Barth H, Aktories K, Popoff MR, Stiles BG (2004) Binary bacterial toxins: biochemistry, biology, and applications of common Clostridium and Bacillus proteins Microbiol Mol Biol Rev 68(3):373-402.
   PMID: 15353562
9. Fabbri A, Travaglione S, Falzano L, Fiorentini C (2008) Bacterial protein toxins: current and potential clinical use Curr Med Chem 15(11):1116-25. PMID: 18473807

Shiga Toxins May be Purchased without Government Approval

The CDC has removed Shiga toxins (Stx1 and Stx2) from the list of materials requiring oversight.  As a result, Shiga Toxins are no longer classified as select agents and may be purchased without government approval for your research and investigative needs.   While Shiga toxins carry fewer restrictions, the interest in them and their value for research has never been higher.

Usage of Shiga Toxins in Research

As tools, these cytotoxins are valuable in studying intracellular transport within the Golgi apparatus.  They can be used to eliminate mammalian cell types with Gb3 receptors. Shiga toxins are potent virulence factors, important in human health.  They are implicated in many cases of food borne illness, estimated to affect 76 million people and cause 5,000 deaths every year in the United States alone.  Shiga toxin producing bacteria, usually Escherichia coli O157, enter the food chain through contamination, infect the gastrointestinal tract and cause diarrheal illness.  The bacteria infect the large intestine and produce Shiga toxin which crosses the gastrointestinal epithelium entering the blood stream; ultimately the toxins are responsible for organ damage.  These potent virulence factors are important targets for the development of therapies and for the detection of contamination.

Shiga toxins function by inhibiting eukaryotic protein synthesis by cleaving a specific adenine from the 28S RNA of the 60S subunit of the ribosome.  Although Shiga toxin 1 and Shiga toxin 2 share only 56% amino acid homology, making them immunologically distinct, activities of these two forms of toxin, binding affinity to Gb3 and N-glycosidase activity, appear to be identical.  In spite of these similarities, Shiga toxin 2 is more closely associated with human disease.  Although endothelial cells are the primary cell type vulnerable to shiga toxin, several other types express Gb3 receptors and are therefore potential targets.

Get Shiga Toxins for Research from ListLabs

Both Shiga 1 and Shiga 2 and mouse antibodies to the toxins are available from List Labs. You can read more about them here. At this time we are evaluating polyclonal and monoclonal antibodies that recognize all seven subtypes of Stx2 and monoclonals that recognize all subtypes of Stx1.  Look for these antibodies to appear in our future offerings.