Engineering multifunctional nucleic acid probes/nanomaterials for cancer studies

Essential cancer research studies include diagnosis of early-stage cancer and elucidation of the disease processes, with the hope of finding efficient anti-cancer therapy systems. Among the various types of molecular tools, multifunctional nucleic acid probes serve versatile roles via rational selection and construction processes (e.g., use as sensors, catalytic enzymes, drugs, and aptamers). My doctoral research has focused exclusively on the sensor and aptamer functions, in particular the engineering of multifunctional nucleic acid probes or nanomaterials for detection and analysis of cancer cells.;My most recent work has involved the construction of an aptamer-micelle as an efficient detection and delivery vehicle toward cancer cells. An aptamer, which can specifically bind to a broad spectrum of targets, including small molecules, proteins, and even disease cells, is a single-stranded DNA or RNA molecule isolated from combinational libraries by a process termed SELEX (Systematic Evolution of Ligands by Exponential enrichment). The Tan research group has developed a whole-cell-SELEX strategy to generate a panel of aptamers for specific diseased cells without any prior knowledge about the target molecules. Although aptamers have shown great promise in molecular recognition toward specific cancer cells, the relatively weak binding affinities of some aptamers at physiological temperatures has hampered cell targeting and applications to targeted therapy. To solve this problem, an aptamer-micelle strategy was implemented by attaching lipid tails onto the ends of low-affinity aptamers. This resulted in several beneficial and innovative properties, such as greatly enhanced binding ability, extremely low dissociation rates, additional internalization pathways, as well as sensitive and rapid cancer detection.;Cancer originates from mutations in human genes and genetic alterations which cause molecular changes to cell structure that ultimately result in morphological and physiological abnormalities. Consequentially, my research has also focused on designing molecular sensors to detect such changes via intracellular mRNA monitoring. The monitoring of oncogene expression or spatial localization allows cellular events and disease pathogenesis to be more accurately understood. Besides serving as genetic information housekeepers, nucleic acids can also be built into various sensors based on Watson-Crick base-pairing and diverse signal transduction mechanisms. However, the complex nature of living cells poses challenges to the design of such sensors by the susceptibility of nucleic acids to enzyme digestion and inefficient self-delivery into the cells. Two methods were tested to address these limitations: introduction of locked nucleic acid bases into the sensor design and modification of sensors with single-walled carbon nanotubes. These two methodologies have yielded robust probes, thus permitting more reliable intracellular gene studies at the single-cell level.;Results of my doctoral research demonstrate that multifunctional nucleic acids can be utilized as key building blocks to fulfill the various goals in cancer research.