From 2012.igem.org

pDAWN of A New Era: Engineering Bacterial Theraputics

Historically, medical treatments have typically employed purely chemical or mechanical means, such as the realignment of fractured bones, or antibiotic treatment. The use of bacteria as a platform for medical treatments is a relatively new idea, and one that we have expanded upon in two ways.

Firstly, we are engineering E. coli bacteria which may enable highly targeted eradication of human epidermal growth factor receptor 2 (HER2) overexpressing cancer cells. Although technical advances for the imaging and detection of tumors have progressed rapidly, current treatments such as chemotherapy and radiotherapy are not targeted exclusively to tumor cells. These treatments are toxic towards surrounding healthy tissue and result in significant adverse effects during treatment. However, our bacteria display on their surface the Designed Ankyrin Repeat Protein (DARPin) H10-2-G3 which binds to HER2 with picomolar affinity. Surface display of the DARPin was achieved by fusion of H10-2-G3 to the C-terminus of an ice nucleation protein (INPNC) lacking internal repeat domains. Upon binding to HER2 overexpressing cells, bacterial cytotoxicity can be triggered with spatial and temporal precision by illumination with blue light, which activates overexpression and secretion of Cytolysin A (ClyA) under the control of the pDawn transcriptional module.

Furthermore, we also investigated the feasibility of engineering bacterial biofilms that can act as antimicrobial surfaces. Hospital acquired infections (HAI) are a major concern for hospital staff, and can drastically increase the morbidity and mortality of any patient receiving care in a hospital. A significant number of HAIs arise as a result of bacterial biofilms contaminating hospital surfaces, especially those found on urinary catheters. Current antimicrobial surfaces rely on chemical compounds that slowly leach out over time, and are not suitable for use on surfaces such as urinary catheters, which are placed inside the body of the patient. We are engineering E. coli. bacteria to form non-pathogenic biofilms that express bacteriolytic proteins capable of inhibiting the formation of pathogenic biofilms that are potential sources of HAI. These bacteria express luxS, a key enzyme in the synthesis of a small quorum signalling molecule, Autoinducer-2 (AI-2). The production of AI-2 in E. coli. is thought to enhance E. coli. biofilm formation. These cells will also carry the lysostaphin (lss) gene, which encodes an enzyme that selectively destroys the cell walls of Streptococcus bacteria, a common pathogen in many hospital settings.