To engineer stem cells as gene delivery vehicles for cancer therapy, they are transfected ex-vivo with transgenes (non-integrating) to transiently express the therapeutics of interest. Integrating vectors (e.g. lentiviral) are potentially oncogenc and not suitable for stem cell based cancer therapy. The vector that is used for stem cell transfection needs to be highly efficient because the methods to rapidly produce unlimited quantities of undifferentiated stem cells have not yet perfected. Moreover, stem cells in cell culture change/mutate over time (usually after eight passages), thereby providing a limited window of opportunity for processing. In addition to efficiency, transfection vectors need to be non-oncogenic to stem cells because they could potentially transform normal stem cells into cancer initiating cells and result in tumor formation. Therefore, high levels of safety are expecte from vectors that are used in stem cell engineering. Unfortunately, for demonstration of safety many non-integrating vectors have been simply evaluated for their impact on metabolic activity of stem cells and there has been no comprehensive study that has closely looked at vectors' potential for genotoxicity, upgregulation of oncogenes and other detrimental effects. While metabolic activity (proliferation) assay is one important tool to evaluate toxicity but it does not tell the whole story. More in depth toxicity analysis is required to evaluate the true toxicity especially when the intension is to use stem cells as a means for treating cancer. Therefore, it is essential to ensure that the engineered stem cells don't become tumorigenic during the transfection process. The proposed research intends to address two significant deficiencies that currently exist: 1) low efficiency of non-viral vectors in stem cell transfection, and 2) insufficint toxicity data (e.g., cell viability, membrane integrity, micronuclei formation, tumorigenicity and upregulation of oncogenes) related to the use of non-viral gene delivery systems in stem cell engineering. The objective of this research is to develop a non-genotoxic/non-oncogenic vector that could transfect stem cells with high efficiency (>80%) while preserving their viability and tumor tropism. Currently, there is no non- integrating viral or non-viral vector available that can transfect stem cells with high efficiency (>50%) while maintaining low toxicity. To achieve the objective, two types of recombinant vectors will be engineered: targeted and non-targeted. The targeted vectors are equipped with peptides that bind to Vascular Endothelial Growth Factor Receptor (VEGFR) for cellular entry. This receptor is highly expressed on the membrane of stem cells and a safe route for cellular entry. The non-targeted vectors are equipped with efficient non-cationic cell penetrating peptides which are able to enter the stem cells through the cell wall. The structures of proposed recombinant fusion vectors are novel and never been designed before. These vectors are designed to contain all the major motifs necessary for efficient stem cell transfection. Concurrently, the proposed vectors can maintain low toxicity because of their non-cationic characteristics and biodegradability.
Stem cell-mediated gene delivery is emerging as a strategy to improve the efficacy and minimize the toxicity of current gene therapy approaches. To engineer stem cells as gene delivery vehicles for disease therapy, they are transfected ex-vivo with transgenes to express the therapeutic of interest. The goal of this research is to develop a non-oncogenic vector that can safely and efficiently transfect stem cells with potential application in various stem cell-based therapy protocols.
