Some Background

Cancer is a global scourge; it strikes without regard to age, race, gender, ethnicity, and socioeconomic class. Fortunately, such treatment options as radiation therapy and chemotherapy have dramatically improved patient outcomes, prolonging life in most patients and offering a cure to others. While radiotherapy has achieved sub-millimeter1 precision in targeting solid tumor cancers, chemotherapy is administered systemically, resulting in off-target effects in healthy dividing cells, often with considerable disruption to quality of life. Loss of white blood cell progenitors leads to a broken immune system. Death of cells lining the digestive tract causes vomiting and diarrhea. Damage to cells of the hair follicle brings baldness and the immense toll on one’s body image.

Our Project

SilenshR is a synthetic biology solution that leverages the innate capacity of bacteria to colonize the hypoxic and immune-privileged cores of tumors, conferring specificity to a systemic therapeutic approach. Once the SilenshR E. coli reach a cell density of 2*10 ¹¹ colony forming units (cfu) per milliliter within the tumor, genetic circuits are activated allowing SilenshR recombinants to invade cancer cells and release a short hairpin RNA (shRNA) targeting an expressed oncogene thereby halting the unchecked cellular proliferation of cancer. By circumventing the need for systemic delivery of chemotherapy and the inevitable off-target cytotoxicity, SilenshR keeps the immune system intact, spares the digestive epithelial lining from damage and relieves anxiety surrounding hair loss.

Our invasiveness circuit is mediated by diffusion of the small molecule AHL, or acylhomoserine lactone, produced by AHL synthase. The presence of the AHL autoregulator in our bacteria promotes transcription at the lux promoter, regulating AHL synthase in a positive feedback loop as well as the genes invasin and hlyA from Yersinia and Listeria, respectively. Invasin interacts with surface B1-integrin receptors on the cancer cell membrane, resulting in phagocytosis of the SilenshR bacteria. Within the phagosome, the HlyA protein, diffusible across membranes, inserts pores, compromising the SilenshR’s containment within the vesicle.

SilenshR is not just one recombinant bacterial strain or one sequence of DNA: SilenshR is a revised approach to cancer treatment with greater specificity and less discomfort. Just as different chemotherapeutics might be prescribed depending on the affected organ, the therapeutically active component of SilenshR, the shRNA sequence, can be altered depending on the particular gene promoting tumor growth. For example, while EGFR (Epidermal Growth Factor Receptor) overexpression contributes to tumor malignancy in lung cancer and c-MYC drives cell proliferation in breast cancer, SilenshR recombinants can be used to treat both kinds of cancer with a simple restriction digest and swap of a 63 base pair stretch of DNA encoding shRNA. In the cytosol, the shRNA is cleaved at the hairpin by the Dicer complex and the resulting siRNA is complementary to a sequence in the mRNA of targeted protein product. Degradation of the mRNA by the RNA-Induced Silencing Complex, or RISC, results in an inhibition of translation of the targeted gene.