Delivery of Bacterial Therapeutics to Solid Tumors

Duke University, Durham NC

Investigators

Abstract

CBET-0828630 Yuan Bacteria have been engineered recently as vectors for gene delivery. Compared to other vectors, they have several unique advantages, such as being capable of producing therapeutic agents without infecting host cells and active transport in tissues that may overcome physiological barriers to gene delivery. However, several key issues remain to be addressed in order to improve efficacy of bacterium-mediated gene therapy. For bacterial vectors delivered locally via intratumoral infusion, the first issue is bacterial dissemination from tumor to normal organs. It may significantly reduce gene delivery to tumor cells and cause adverse effects in normal tissues. Therefore, the Specific Aim 1 in the proposal is to investigate mechanisms of the dissemination using non-pathogenic Escherichia coli (E. coli). The study will quantify biodistribution of E. coli in mice after intratumoral infusion and use the data to determine kinetics and pathways of bacterial dissemination. Based on these results, the Specific Aim 2 is to develop novel strategies for blocking bacterial dissemination. A thermally sensitive polymer solution will be used to block the dissemination through tumor microvessels during intratumoral infusion and a novel synthetic gene circuit will be implemented into the E. coli for eliminating chronically disseminated bacteria at a few days after the infusion. The second issue is hindrance to bacterial transport in solid tumors, which may prohibit homogenous gene delivery. To improve the transport, the Specific Aim 3 is to genetically engineer E. coli to constitutively express invasin that can bind to several integrin receptors on tumor cells to facilitate transcellular transport. The study will quantify bacterial transport through transcellular and interstitial pathways in vitro, using both monolayer and multicellular layer (MCL) tumor models. Results from the study may provide important information on mechanisms of bacterial transport that can be used to improve bacterial delivery in vivo. The objective of the proposed research is to address key issues in bacterium-mediated gene delivery. The study is innovative since systemic dissemination of bacteria has never been characterized in previous studies although intratumoral infusion has been a routine method for administration of all gene vectors. The proposed study will quantitatively investigate the dissemination and develop methods to block it. In addition, the study will explore synthetic biology, an emerging multidisciplinary field, for improving gene delivery. These innovative approaches to gene delivery are based on previous studies of the PI and Co-PI, funded by NSF and other agencies for improving delivery of macromolecules and viral vectors in solid tumors and developing novel synthetic gene circuits in bacteria. Results from the proposed study may reveal mechanisms of bacterium transport in tumors and facilitate discovery of novel design principles for bacterial vectors, which will likely be applicable to not only the E. coli used in this study but also other engineered bacteria. Gene delivery is one of the main challenges in gene therapy. It has limited therapeutic efficacy in target tissues and caused adverse effects in normal organs. Results from the proposed research may be used to improve efficiency of gene delivery and safety in cancer gene therapy. In addition, the proposed research represents an important step in extending basic concepts and design methods in synthetic biology to address a pressing issue in cancer treatment. To further broaden the impact, the research projects will be integrated with biomedical engineering (BME) education at Duke University. Specifically, results from the research projects will be incorporated into three BME courses, which are currently taught by the PI and Co-PI. In addition, the research projects will involve undergraduate students through independent studies and the Pratt Research Fellow program at Duke University. Smaller research projects will also be developed for summer students recruited through an existing outreach program for underrepresented students and those with disabilities. These educational activities may stimulate students interests in science and engineering and encourage them to pursue careers in these fields. Finally, results from the proposed research will be presented at national and international conferences and published in scientific journals.