The Development of a Genetic Circuit in E. coli BL21 (DE3) for the Targeted Killing of PD-L1 Expressing Thyroid Cancer Cells Via the Delivery of Colicin A

Cancer is defined as a group of diseases that can occur when cells of various parts grow uncontrollably, resulting in a tumor, and tissue or organ invasion. Each year, thyroid cancer occurs in 33,000 women, and 12,000 men globally. In Oman alone, thyroid cancer was ranked the second most common cancer among the 2,307 cases in 2019. There are four main types of thyroid cancer, and they are follicular, papillary, medullary, and anaplastic thyroid cancer. Despite their slow growth, follicular and Papillary cancer are the most common types, followed by medullary and anaplastic thyroid cancer. Anaplastic thyroid cancer, however, is among the most aggressive types. Despite the good prognosis of early-stage thyroid cancer, recurrence is common in 10-15% of patients, whereas bone and lung metastasis are common in 5% of patients. Moreover, the prognosis and survival of patients with advanced thyroid cancer suggests a lack of effective therapies. This research proposal suggests the use of bacteria in targeted thyroid cancer therapy. There are many benefits of utilizing bacteria in cancer therapy, including their motility, which allows them to reach the hypoxic tumor core and proliferate at the tumor microenvironment. Additionally, genetically engineered bacteria can target specific biomarkers on cancer cells, and even produce and deliver therapeutic molecules to the tumor site, thus limiting the treatment?s side effects. The suggested methodology for this proposal involves using genetically engineered nonpathogenic bacteria to bind to a biomarker specific to thyroid cancer cells, such as PD-L1, and deliver therapeutic molecules to them. PD-L1 is the target chosen for this proposal is programmed death-ligand 1 (PD-L1), which is expressed on various cells including antigen presenting cells and tumor cells. PD-L1 is the main ligand for the immune-checkpoint receptor, programmed death-1 (PD-1), which is expressed on macrophages, T-cells, natural killer cells, dendritic cells, and monocytes. The interaction between PD-1 and PD-L1 inhibits T-cell activation and proliferation; promotes apoptosis in cytotoxic T-cells; promotes differentiation in regulatory T-cells; and suppresses the secretion of cytokines, such as interleukin-2 and interferon-?, hence protecting tumor cells from the body?s immune response. Moreover, tumors with increased PD-L1 expression have exhibited poor prognosis in various studies and a study suggested that elevated expression levels of PD-L1 in papillary thyroid cancer (PTC) was correlated with a higher risk of recurrence. The expression levels of PD-L1 in thyroid cancer vary based on the subtype and progression level. that papillary, follicular, and anaplastic thyroid carcinomas (ATC) all expressed PD-L1 in various levels (between 6.1% - 22.2%), with follicular and anaplastic thyroid carcinomas exhibiting a strong intensity of immunohistochemistry (IHC) staining, and PTC exhibiting a weak staining intensity. The overall expression of PD-L1 in thyroid cancer cells is positive, suggesting its use as a potential biomarker for therapeutic bacterial cells to bind to. This proposal suggests the potential of using genetically engineered bacteria to target PD-L1, a specific biomarker commonly expressed in thyroid cancer cells, enabling the delivery of therapeutic molecules to the tumor microenvironment. The project aims to genetically engineer bacteria to express a protein targeting PD-L1.