Activatable synthetic biomarker systems for gene- and cell-based cancer detection and theranostics
Abstract
Introduction: The ability to non-invasively detect cancer cells and other cell types within tumours has many valuable applications for early cancer diagnosis and grading, monitoring disease progression, and assessing treatment response. While technologies for detecting endogenous cancer biomarkers in bodily fluids or through imaging are being rapidly developed, they often face challenges that result in low sensitivity and/or specificity. To address these limitations, an emerging strategy involves building exogenously delivered tools that use reporter genes as synthetic biomarkers. Leveraging synthetic biology, reporter genes can be assembled into cancer-activatable gene circuits which link their expression to the presence of endogenous cancer molecules not readily assayed, generating synthetic biomarkers that serve as unambiguous signals for cancer. In this thesis, we describe the design and evaluation of cancer-activatable synthetic biomarker systems which are encoded upon both gene- and cell-vector platforms. Methods: We first outline the detection and grading of prostate cancer using survivin-driven, tumour-activatable DNA minicircles (MCs) which upon intratumoural injection produce detectable reporter levels in blood related to cancer aggressiveness. We subsequently built a theranostic MC system by combining urinary identification of aggressive prostate lesions with the ability to selectively treat them using a prodrug-activated gene therapy. Finally, we describe an activatable imaging system in T cells which allows immune-cancer cell communication to be visualized through multimodal reporter gene imaging. Results: Using diagnostic tumour-activatable MCs, we discriminated between aggressive and non-aggressive prostate cancers in mice by measuring the differing levels of an exogenous blood or urine reporter protein. Furthermore, we paired lesion detection with a therapeutic MC which specifically attenuated the growth of aggressive prostate lesions. Finally, we engineered T cells with a synthetic notch imaging system which targeted these cells to antigen-expressing tumours, inducing expression of imaging reporter genes in response to antigen binding. Notably, for the first time we observed in vivo antigen-dependent cell-cell communication using magnetic resonance imaging. Conclusion: The studies presented here contribute to the growing repertoire of synthetic biomarker systems, laying a foundation for activatable gene- and cell-based technologies for improved cancer detection, grading, and monitoring.