Team:Penn/LightActivatedOverview

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<div style="text-align:center;font-size:34px;color:white;"><b>Light-Activated Cytotoxic Drug Delivery </b></div>
 
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<div style="text-align:center;font-size:34px;color:white;"><b>Light-Activated Cell Lysis </b></div>
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<b><div class="name" align="center">Objectives</div></b><br>
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<div align="center"><img src="https://static.igem.org/mediawiki/2012/f/fc/Lightdispschematic.gif" height="525" width="700" /></div>
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<b><div style="color:black">Problems With Current Targeted Therapies</div></b>
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<p style="color:black;text-indent:30px;">In order to develop a module for light activated cell lysis, we had to implement two elements:
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Current therapies generally rely on either spatial targeting (targeting within a physical area) or cellular targeting (targeting to a specific antigen or biomarker).  
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<ol style="font-size:15px"><li><b>Construct a light-activation system that can express a downstream gene of interest.</b></li>
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<li><b>Express a cytolytic protein that can be expressed as our therapeutic drug to lyse cancer cells.</b></li>
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<b><div class="name" align="center">Objective 1: Light-Activated Sensor</div></b><br><br>
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<b><div class="name" align="center" style="font-size:16px;">Selection of YF1/FixJ Blue Light Sensor</div></b><br>
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<p style="color:black;text-indent:30px;">After reading many papers to select an appropriate light-sensing system to use, we selected the YF1/FixJ blue light system. We had also considered the red light sensor Cph8 but ultimately decided on YF1/FixJ because of its high on/off ratio of gene expression and also because of its availability to us (we were fortunate enough to come across the YF1/FixJ system in the form of the pDawn plasmid from the Moglich lab in Germany).</p><br>
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<b><div class="name" align="center" style="font-size:16px;">YF1/FixJ System (pDawn)</div></b>
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<p style="color:black;text-indent:30px;">As shown below in Figure 1, the YF1/FixJ system works through a "repress the repressor" concept. Upon 480 nm blue light illumination, YF1 (a fusion of a LOV protein domain and a histidine kinase) phosphorylates a FixJ response regulator that activates the pFixK2 promoter. The activation of pFixK2, promotes expression of the cI repressor that, in turn, represses the lambda promoter pR. The net result is activation of the gene in the downstream MCS. </p><br>
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<div align="center"><img src="https://static.igem.org/mediawiki/2012/7/74/PDAWN.gif" />
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<div style="text-align:center"><b>Figure 1</b><br /></div>
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<b><div class="name" align="center">Objective 2: Expression of a Cytolytic Protein</div></b><br>
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<b><div class="name" align="center">Cytolysin A (ClyA)</div></b><br>
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ClyA is a protein native to E. coli, Shigella flexneri, and Salmonella typhi that is capable of forming 13-mer pore complexes in a redox-independent manner. Expression of clyA in the absence of other hemolytic toxins is sufficient to induce hemolysis experimentally, and is therefore considered to be a potent cytolytic agent. Unlike a similar protein, HlyA, ClyA is not synthesized as a protoxin, which requires further posttranslational modifications to become active. ClyA is functional immediately following translation of mRNA to protein.
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ClyA is a 34kDa protein that is composed primarily of α-helical bundles that form a rod-shaped molecule. The membrane insertion domain is known as a β tongue (shown in yellow in Figure 2) and is critical for hemolytic activity. If the β tongue is mutated, the hemolytic activity of clyA is abrogated. </p>
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<p style="color:black;text-indent:30px;">Current therapies generally rely on either spatial targeting (targeting within a physical area) or cellular targeting (targeting to a specific antigen or biomarker). </p>
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<br><b>Figure 2</b></div>Figure 2: ClyA forms a 13-mer pore complex that consists of hydrophobic beta tongues (yellow) on the head domains of individual monomer units that play an important role in influencing its cytolytic functions.
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<b>Spatial Targeting:</b> Surgeons excise a tumor manually, without </p><p style="color:black">regard for cellular heterogeneity within and around the tumor area.</p>
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<p style="color:black"><b>Cellular Targeting:</b> Monoclonal antibodies identify antigens on certain cells or viruses. Monoclonal antibodies are often coupled with therapeutic agents.</p><p style="color:black"> However, if the antigen is present in healthy tissue outside the diseased area, it will be targeted as well.</p>
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<b><div class="name" align="center">Mechanism of Action</div></b>
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<p style="color:black;text-indent:30px;">These targeting mechanisms are imperfect on their own because they also target healthy tissue. Furthermore, the majority of therapies employ no targeting mechanisms at all (e.g. pharmacologic therapies). Even when diseases are clearly localized in specific areas and specific cells (such as cancer), current therapies such as chemotherapy attack the entire body and result in significant adverse effects. Patients who undergo chemotherapy suffer significant damage to fast-dividing cells throughout the entire body, which can result in immune system depression, hair loss, pain, and organ damage.</p>
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<h1><b>A Novel Therapeutic Platform</b></h1>
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<p style="color:black;text-indent:30px;">What if you could combine spatial targeting and cellular targeting into the same therapeutic? This idea is unprecedented but would allow for precise targeting of specific cells within a specific area, leaving healthy tissue intact and keeping side effects to a minimum.</p>
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<p style="color:black;text-indent:30px;">We selected ClyA as our cytolytic protein because of its unique mechanism of action that makes it especially potent. ClyA is secreted from bacteria in outer membrane vesicles (OMV's), within which it forms pore assemblies. As shown below in Figure 3, these pore assemblies allow ClyA to latch on to the cell wall of other cells and through the use of its encapsulating pore assembly lyse the cell wall. </p><br>
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<p style="color:black;text-indent:30px;">The 2012 Penn iGEM team has engineered a novel platform for targeted therapeutics which employs simultaneous spatial and cellular targeting. We have achieved spatial (and temporal) targeting with a blue light-switchable transgene expression system, and cellular targeting through display of an antibody-mimetic protein on the surface of E. coli for the first time.</p>
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<p style="color:black;text-indent:30px;">As a proof of concept, we applied our system to the treatment of cancer, a disease in which spatial and cellular targeting are of utmost importance. We displayed a high-affinity antibody-mimetic protein which targets Human Epidermal Growth Factor Receptor 2 (HER2), a protein commonly overexpressed in cancer cells. We combined this cellular targeting with a light-activated cytotoxic protein delivery system to successfully target and kill breast cancer cells.</p>
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<p style="color:black;text-indent:30px;">Upon conception of this project, we realized that although hundreds of academic research projects and iGEM projects have been conducted in the realm of Health and Medicine, almost no engineered bacterial therapeutics have been brought to the clinic. We analyzed the hurdles and road ahead for bacterial synthetic biology-enabled therapeutics, compiling a thorough report with specific actions which iGEM teams in Health/Medicine can take to make their therapies more clinically tractable. This project directly informed our wet lab work, causing us to port our therapeutic system into a non-pathogenic, probiotic bacterial strain which is already used in human therapies today.</p>
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<p style="color:black;text-indent:30px;">We hope our targeted therapeutic platform will allow other scientists and iGEM teams to target any cells they choose. In the near term, we are planning to test our cancer cell targeting/killing bacterial system in a mouse model and make a real impact on cancer research and therapy.</p>
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<div class="fig"><div align="center"><img src="https://static.igem.org/mediawiki/2012/6/6c/ClyA-Pore-Assembly.jpg" /><br>
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<br><b>Figure 3</b></div>Figure 3: Shown above in the first image are pore assemblies containing 13-mers of ClyA interacting with the surface of the target membrane. The second image below shows the ClyA assembly lysing the cell membrane through pore formation. (Wallace et. al 2000)
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Latest revision as of 03:32, 27 October 2012

Penn 2012 iGEM Wiki

Image Map

Light-Activated Cell Lysis

Objectives


In order to develop a module for light activated cell lysis, we had to implement two elements:

  1. Construct a light-activation system that can express a downstream gene of interest.
  2. Express a cytolytic protein that can be expressed as our therapeutic drug to lyse cancer cells.
Objective 1: Light-Activated Sensor


Selection of YF1/FixJ Blue Light Sensor

After reading many papers to select an appropriate light-sensing system to use, we selected the YF1/FixJ blue light system. We had also considered the red light sensor Cph8 but ultimately decided on YF1/FixJ because of its high on/off ratio of gene expression and also because of its availability to us (we were fortunate enough to come across the YF1/FixJ system in the form of the pDawn plasmid from the Moglich lab in Germany).


YF1/FixJ System (pDawn)

As shown below in Figure 1, the YF1/FixJ system works through a "repress the repressor" concept. Upon 480 nm blue light illumination, YF1 (a fusion of a LOV protein domain and a histidine kinase) phosphorylates a FixJ response regulator that activates the pFixK2 promoter. The activation of pFixK2, promotes expression of the cI repressor that, in turn, represses the lambda promoter pR. The net result is activation of the gene in the downstream MCS.



Figure 1
Objective 2: Expression of a Cytolytic Protein

Cytolysin A (ClyA)

ClyA is a protein native to E. coli, Shigella flexneri, and Salmonella typhi that is capable of forming 13-mer pore complexes in a redox-independent manner. Expression of clyA in the absence of other hemolytic toxins is sufficient to induce hemolysis experimentally, and is therefore considered to be a potent cytolytic agent. Unlike a similar protein, HlyA, ClyA is not synthesized as a protoxin, which requires further posttranslational modifications to become active. ClyA is functional immediately following translation of mRNA to protein. ClyA is a 34kDa protein that is composed primarily of α-helical bundles that form a rod-shaped molecule. The membrane insertion domain is known as a β tongue (shown in yellow in Figure 2) and is critical for hemolytic activity. If the β tongue is mutated, the hemolytic activity of clyA is abrogated.




Figure 2
Figure 2: ClyA forms a 13-mer pore complex that consists of hydrophobic beta tongues (yellow) on the head domains of individual monomer units that play an important role in influencing its cytolytic functions.

Mechanism of Action

We selected ClyA as our cytolytic protein because of its unique mechanism of action that makes it especially potent. ClyA is secreted from bacteria in outer membrane vesicles (OMV's), within which it forms pore assemblies. As shown below in Figure 3, these pore assemblies allow ClyA to latch on to the cell wall of other cells and through the use of its encapsulating pore assembly lyse the cell wall.




Figure 3
Figure 3: Shown above in the first image are pore assemblies containing 13-mers of ClyA interacting with the surface of the target membrane. The second image below shows the ClyA assembly lysing the cell membrane through pore formation. (Wallace et. al 2000)