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Research team at the University of Delaware has developed technology to program strands of DNA into switches that turn proteins on and off. DNA is essentially a code with four components- the nucleotides guanine, adenine, cytosine, and thymine. In cells, the arrangement of these four nucleotides determines the proteins made by DNA. Scientists have repurposed the DNA code to design logic-gated DNA circuits.
The custom sequence designed DNA strands were ordered from a manufacturer while the proteins were made and purified in the lab. Next, the protein was attached to the DNA to make protein-DNA conjugates. The group then tested the DNA circuits on E. coli bacteria and human cells. The target proteins organized, assembled, and disassembled in accordance with their design.
Researchers demonstrated that DNA-logic devices could activate a non-toxic cancer prodrug, 5-fluorocytosine, into its toxic chemotherapeutic form, 5-fluorouracil. Cancer prodrugs are inactive until they are metabolized into their therapeutic form. Scientists designed DNA circuits that controlled the activity of a protein that was responsible for conversion of the prodrug into its active form. The DNA circuit and protein activity was turned “on” by specific RNA/DNA sequence inputs, while in the absence of said inputs the system stayed “off.”
Scientists based their sequence inputs on microRNA, small RNA molecules that regulate cellular gene expression. MicroRNA in cancer cells contains anomalies that would not be found in healthy cells-some microRNA are present in cancer cells but absent in healthy cells. The group calculated how nucleotides should be arranged to activate the cancer prodrug in the presence of cancer microRNA, but stay inactive and non-toxic in a non-cancerous environment where the microRNA are missing.
When the cancer microRNAs were present and able to turn the DNA circuit on, cells were unable to grow. When the circuit was turned off, cells grew normally. Using the newly developed technology could make it possible for researchers to target the DNA sequence.
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