New Biosensors Precisely Monitor Drug Levels in Serum

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Researchers have created biosensors that can accurately measure levels of cancer, arthritis, and organ transplant drugs in blood samples.

“Our biosensor technology will enable tests like therapeutic drug monitoring on less sophisticated equipment,” said senior author Professor Kirill Alexandrov, of the QUT Centre for Genomics and Personalised Health. He believes these new biosensors could disrupt the $70 billion global diagnostic market by allowing more personalized treatment on cheaper lab equipment and new point-of-care devices.

The paper appeared this month in Nature Communications and the studies were conducted by researchers from the CSIRO-QUT Synthetic Biology Alliance in collaboration with Clarkson University in the US and Pathology Queensland.

This report describes artificial small molecule:protein complexes that act as chemically induced dimerization (CID) systems. These CID’s produce measurable responses and are controlled by drugs. In two separate studies, such systems were adapted to accurately measure immunosuppressant drugs cyclosporine A, tacrolimus and rapamycin, and anticancer drug methotrexate, which requires close monitoring to reduce toxicity and organ damage.

“Proteins are at the core of a US$70-billion-dollar global diagnostic market that relies heavily on central lab processing,” Alexandrov said.

“With further development, the biosensor technology could lead to a fingerstick test that potentially provides doctors with patient results in 3-5 minutes during a standard consultation,” he added.

Biological systems contain many soluble and membrane receptors that gain or lose biochemical activity in response to small molecule binding. Most of these represent allosteric systems where ligand binding controls conformation or dynamics of the proteins.

According to this team, biophysical and structural analysis of their methotrexate-controlled CID system reveals the critical role played by drug-induced conformational change. Using several starting points, they created CID systems controlled by methotrexate.

They tested their biosensor by constructing electrochemical biosensors of methotrexate which enabled quantification of the drug in human serum. In addition, using the methotrexate and a functionally related biosensor of rapamycin, the researchers developed a multiplexed bioelectronic system that can perform repeated measurements of multiple analytes.

Protein complexity and fragility made construction and use of protein biosensors difficult, Alexandrov said, but the modular design could be adapted to potentially target any small molecule – not just therapeutic drugs.

The new proteins were produced by engineered bacteria then altered using recombinant DNA technology to produce artificial switch molecules that were tailored to recognize a particular drug.

“The protein biosensors are ‘switched off’– like an electrical circuit with a missing piece. Only the targeted biochemical in human fluids like blood or saliva can complete the circuit and ’switch on’ a signal proportional to the amount of biomarker detected,” Alexandrov said.

When activated, the different protein biosensors produce either a change of color for hue-based readings, or electrochemical current.

The team experimented with applications using common glucometer technology to develop a cheap, portable, and accurate device.

“Activated electrochemical biosensors broke down glucose and generated electrons as by-products to produce electrical current proportional to the amount of captured target molecule,” he said.

The Clarkson team also demonstrated the feasibility of multiplexing this technology to detect two different biomarkers at the same time.

The technology is use-specific, however, Alexandrov said.  Researchers will need to re-engineer devices and manufacturing processes for new clinical uses.

“There are a huge number of parameters to reconcile when building a medical device. It’s incredibly hard and that’s why new diagnostic technologies come to the market very slowly,” he said.

Alexandrov was the lead author in another biosensor study that appeared recently in Angewandte Chemie (11 October 2021).

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