Anthrax

“Natural epidemics can be extremely large. Intentionally caused epidemics, bioterrorism, would be the largest of all....It doesn't take much biology expertise nowadays to assemble a virus....It's just unbounded if you are not there to stop the spread of it." - Bill Gates, Munich Security Conference 2017  "Five Americans were killed and 17 were sickened in the worst biological attacks in US history. " - FBI, Report on 2001 Anthrax Attacks

** Anthrax **and its potential treatment, Raxibacumab = = = Motivation and Background =

Why should I be scared?
In 2001, just one week after the September 11 attacks, seven letters were mailed to news media and senate offices [1]. Five of these letters contained inside a brown granular material, and the other two contained a fine powder [1]. The letters contained anthrax, an infectious disease caused by Bacillus anthracis. Five people died and 17 were injured. The CDC now considers anthrax to be a Category A agent, posing a risk to //national security//.

So what is it really?
Historically, anthrax, or woolsorter’s disease, was a common disease in livestock, and thus affected many workers in the tanning and wool industries [3]. The mechanism behind anthrax was first discovered by Robert Koch, who identified the underlying microbe //B.// anthracis in 1875 [2]. In his experiment, he isolated the bacterium, in endospore form, from infected cows and injected it into mice, killing them. This was the first time that a microbe was conclusively determined to cause disease.

Are people still affected today?
In the modern day, anthrax still infects many in African and Southern Asia. Around 2,000 cases are reported each year, and about two cases a year occur in the United States [2]. Anthrax infections are categorized by the way it enters the body: cutaneous anthrax results from spores entering through cuts in the skin, inhalational anthrax from spores entering the lungs, and gastrointestinal anthrax from spores that are consumed [2]. Once infected, the disease is not contagious.

What will it do to me?
Cutaneous anthrax, the least deadly and most common form of anthrax, is easily identified by the formation of a black, painless skin lesion at the site of the infection within two to five days of exposure. This is typically caused by handling tainted animals or animal products [2]. This type of anthrax is rarely fatal if treated. Inhalational anthrax is much rarer in humans and causes flu-like symptoms for several days followed by pneumonia and respiratory collapse. The fatality rate for inhalational anthrax is around 40% [2]. The most dangerous and rare form of the disease is gastrointestinal (GI) anthrax, which arises from consuming infected meat. Symptoms include vomiting of blood, severe diarrhea, and lesions throughout the gastrointestinal tract. GI anthrax has a mortality rate of 60% [2].

That sounds awful!
You're absolutely right. And in the wrong hands, anthrax can be easily deployed on a global scale to quickly and effortlessly incapacitate entire populations. This is why we must create and stockpile an effective treatment and prevention for all forms of anthrax. This will cost, of course, exactly one billion dollars. = = = Target Information =

What really causes anthrax?
Anthrax is deadly in humans and animals because of the unique nature of //B.// anthracis. Once infected, the bacterium enters the lymphatic system where it multiplies until it kills the host. Specifically, spores are picked up by macrophages, which then bring them into the lymph nodes [3]. There the spores germinate and the resulting bacilli multiply rapidly, destroying the macrophages and releasing the bacilli into the bloodstream [3]. Once in the bloodstream, the bacilli release three proteins called lethal factor, protective antigen, and edema factor [5]. While not dangerous individually, the combination of these three proteins into anthrax toxin leads to the destruction of tissue, bleeding, and ultimately death [2].

Can you expand on that, but with more scientific jargon?
As previously mentioned, anthrax toxin is a three-protein exotoxin composed of three parts: a cell binding protein called protective antigen (PA), and two enzymes called lethal factor (LF) and edema factor EF). For cell death to occur, PA first binds to an anthrax toxin receptor, either tumor endothelium marker-8 or capillary morphogenesis protein 2, on the cell surface [6]. PA is then cleaved into PA63 and PA20, of which PA20 dissociates. PA63 then assembles into seven cluster rings, which then bind to three LF and EF molecules [6]. The cell then ingests the toxin via endocytosis and it travels into the cytosol. Once in the cytosol, EF impairs cell-signaling pathways by increasing the level of cAMP in the cell, and LF alters cell-signaling pathways by destroying MAPKK to cause apoptosis [6]. The most effective treatment for anthrax toxin is to neutralize PA in some way before it allows EF and LF into the cell.

[[image:PA Anthrax.png width="458" height="347"]]
Figure 1: Protective antigen (PA, left) and the associated PA63 seven cluster ring (right) [6].

** What are the technical details? **
<span style="font-family: Arial,Helvetica,sans-serif;">Size: 82.8kDa = 82,800 g/mol <span style="font-family: Arial,Helvetica,sans-serif;">Location: Bloodstream <span style="font-family: Arial,Helvetica,sans-serif;">Function in a normal cell: None, it is introduced when B. anthracis<span style="font-family: Arial,Helvetica,sans-serif;"> invades the bloodstream. = = = Drug Information =

So what's the magic cure?
<span style="font-family: Arial,Helvetica,sans-serif;">In 2009, a drug called raxibacumab (trade name: ABthrax) began development for the treatment of inhalational anthrax at the request of the US Department of Health and Human Services in response to the 2001 anthrax attacks [4]. Human Genome Sciences, in conjunction with Cambridge Antibody Technology, began screening for potential antibodies that could neutralize PA binding to anthrax toxin receptors or inhibit the formation of the PA63 seven cluster ring [4]. Raxibacumab was identified, a monoclonal antibody that inhibits the formation of anthrax toxin by binding to the domain IV epitope of protective antigen (PA), which then prevents the binding of PA to cell receptors and thus EF and LF from entering cells [5].

<span style="font-family: Arial,Helvetica,sans-serif;">What does Raxibacumab look like?
Figure 2: Raxibacumab shown as cartoon and ribbons. [7]

**How does Raxibacumab inhibit PA?**
<span style="font-family: Arial,Helvetica,sans-serif;">Figure 3: Process for Raxibacumab inhibition of protective antigen (PA). [4]

<span style="font-family: Arial,Helvetica,sans-serif;">What are the technical details?
<span style="font-family: Arial,Helvetica,sans-serif;">Formula: C6320H9794N1702O1998S42 <span style="font-family: Arial,Helvetica,sans-serif;">Molecular weight: 142.96 kg/mol <span style="font-family: Arial,Helvetica,sans-serif;">CAS Number: 565451-13-0 <span style="font-family: Arial,Helvetica,sans-serif;">Other names: ABthrax <span style="font-family: Arial,Helvetica,sans-serif;">Maker or company: GlaxoSmithKline (formerly Human Genome Sciences) <span style="font-family: Arial,Helvetica,sans-serif;">Is it patented? Information was not found.

<span style="font-family: Arial,Helvetica,sans-serif;">What are the clinical details?
<span style="font-family: Arial,Helvetica,sans-serif;">Delivery method: Intravaneous<span style="font-family: Arial,Helvetica,sans-serif;"> injection <span style="font-family: Arial,Helvetica,sans-serif;">Side effects: Itchy skin, pain in limbs, and nausea

<span style="font-family: Arial,Helvetica,sans-serif;">You can't test anthrax in humans! How did this get past clinical trials?
<span style="font-family: Arial,Helvetica,sans-serif; font-size: 11pt;">Due to the urgent nature of its development, the FDA granted raxibacumab fast track designation and priority review. Since anthrax testing in humans would be unethical, the Animal Efficacy Rule was also applied [5]. This allows for the development of drugs on based on animal studies alone. The first animal studies were done on rabbits, which then progressed to cynomolgus macaques. 64% of the monkeys and 44% of the rabbits survived inhalational anthrax with raxibacumab, while //none// of the placebo groups survived [5]. The drug then went on to human trails, with four studies conducted to assess safety with 326 human volunteers [5]. = = = Origin =

<span style="font-family: Arial,Helvetica,sans-serif;">How was it discovered?
<span style="font-family: Arial,Helvetica,sans-serif;">As previously stated, Human Genome Sciences, in conjunction with Cambridge Antibody Technology, screened for potential antibodies that could neutralize PA binding to anthrax toxin receptors or inhibit the formation of the PA63 seven cluster ring [4]. Raxibacumab was then discovered.

<span style="font-family: Arial,Helvetica,sans-serif;">Are there any alternatives to Raxibacumab?
<span style="font-family: Arial,Helvetica,sans-serif;">Traditional methods of treatment of anthrax included large doses of antibiotics such as penicillin, ciprofloxacin, or doxycycline [3]. However, this merely destroys the B. anthracis<span style="font-family: Arial,Helvetica,sans-serif;"> bacilli (and only the non-resistant ones) and not the excreted toxins. If there is widespread infection, antitoxins such as Raxibacumab must be used in conjunction with antibiotics.

<span style="font-family: Arial,Helvetica,sans-serif;">Can Raxibacumab be used to treat other diseases?
<span style="font-family: Arial,Helvetica,sans-serif;">No. Raxibacumab was designed to specifically target protective antigen, so unless PA causes another disease, Raxibacumab use is quite limited.

= = = References =

= =

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[1] Federal Bureau of Investigation. Anthrax Investigation. []. (accessed Feb. 3, 2017) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[2] Centers for Disease Control. National Center for Emerging and Zoonotic Infectious Diseases: Anthrax. [] (Accessed Feb. 3, 2017) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[3] Dixon, Terry; Meselson, Matthew, Anthrax, New England Journal of Medicine, 1999, 341 (11): 815-826 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[4] Kummerfeldt, Carlos E, Raxibacumab: potential role in the treatment of inhalational anthrax, Infection and Drug Resistance, 2014, 7: 101-109 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[5] Mazumdar, Sohini, Raxibacumab, mAbs, 2009, 1, (6): 531-538 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[6] Research Collaboratory for Structural Bioinformatics. Molecule of the Month: Anthrax Toxin. [] (Accessed Feb. 3, 2017) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[7] SciFinder Substance Identifier. Raximacumab. [] (Accessed Feb. 3, 2017)

= <span style="font-family: Arial,Helvetica,sans-serif;">External Links =

For more information on Bill Gates and bioterrorism: http://www.telegraph.co.uk/news/2017/02/17/biological-terrorism-could-kill-people-nuclear-attacks-bill/

Created by: Tiger You VDS Spring 2017