The goal of personalized medicine is to precisely tailor treatment to the individual. To this end, the ability to measure drugs in the body rapidly and in real time would hold the promise to revolutionalise healthcare by delivering the right drug, at the right dose, and at the right time. The development of such technologies including immunoassays or HPLC-MS, however, faces significant challenges such as:

  • Lower sensitivity and selectivity
  • Lengthy sample preparation
  • Batch processing and addition of exogenous reagents
  • Single time-point measurement
  • Stability issues for extended period of time

Continuous and real time monitoring of the drugs could facilitate administration of a therapeutic dose that is continuously optimized for maximal efficacy and minimal side effects for a specific diseased patient.

Aptamer based electrochemical sensors (E-AB) have shown to address these challenges and have demonstrated their promise as a tool for real time drug monitoring. E-AB employs an electrode-bound, redox-reporter-modified aptamer as their recognition element. Binding of the target molecule to this aptamer induces a conformational change that produces an easily measured electrochemical output, without needing reagent additions or wash steps (Figure 1).

Figure 1. Overview of E-AB sensor consisting of redox – reporter modified aptamer covalently attached to a gold electrode via alkane – thiol self-assembled monolayer that undergoes a conformational change upon binding to the target drug resulting in enhanced signal (Adapted from Idili et al., 2019).

To this end, following researchers developed a real time E-AB’s capable of continuously tracking a wide range of circulating drugs in living subjects.

Real-time, aptamer-based tracking of doxorubicin in vivo

Ferguson et al., 2013 developed a real time microfluidic E-AB for measuring therapeutic in vivo concentrations of doxorubicin (DOX, a chemotherapeutic drug) in live rats and human whole blood for several hours with high sensitivity and specificity at sub-minute temporal resolution. Upon binding to the target molecule, the aptamer probe underwent a conformational change that modulated the redox current and generated an electrochemical signal (Figure 2). The signal gain provided a direct measurement of DOX concentration with LOD of 10 nM in buffer.

Figure 2. Sensor overview and real time quantitative measurement of specific molecules in the blood of living animals using aptamer based electrochemical sensor (top image).  Continuous real time measurement of DOX in vitro in human whole blood (green) relative to actual concentrations (purple) over the course of 4 hours (center image). Real time measurement of drugs in the blood of live rats (bottom image).

Real time DOX measurement in live rats with a lowest dose of 0.1 mg/m2, showed observable signal change resulting in a peak concentration of 0.13 uM – a therapeutically relevant range for human dosing. Importantly, the sensor did not respond to ifosfamide (Ifex), mesna, mitomycin-C (MTC), dacarbazine (DTIC), or cisplatin (CDDP) – agents commonly administered with DOX. The sensor required no exogenous reagents, operated at room temperature and could be reconfigured to measure different target molecules by exchanging probes in a modular manner.

Real time, aptamer-based biosensor for tenofovir detection in vivo

Aliakbarinodehi et al., 2017 developed a highly selective and sensitive aptamer based biosensor (AptaFET) for detection of tenofovir (TFV), an anti-retroviral small molecule drug approved for the treatment of HIV and Hepatitis B. This biosensor was based on the combination of aptamers for target recognition and 6-mercapto-1-hexanol (MCH) field effect transistors for the transduction of the drug-probe interaction to an electric signal (Figure 3). The sensor was selective for TFV in both buffer and plasma and showed a linear detection range of 1 nM to 100 nM, compared with clinical range of 20 nM to 860 nM, indicating sufficient sensitivity for clinical application.

Figure 3. (A) Schematic representation of the sensing interface consisting of TFV aptamer and MCH as sensing surface of biosensor. (B) Dose response curve of AptaFET biosensor and responses related to non-specific drugs. (C) AptaFET response comparison of TFV and other non-specific drugs in buffer and plasma. (D) Real time monitoring of the real part of the impedance at 10 Hz for an electrode modified with TFV aptamer upon injection of TFV as the specific target (blue) and Abi as non-specific target (red).

Overall, the performance of such E-AB in terms of LOD and linear range is better or comparable to other biosensors that are suitable for point of care (POC) analytical applications. This proves the capability of the E-AB to be utilized for continuous monitoring of a wide range of small molecules in human plasma, improving the overall efficacy and safety of treatment.

At Aptamer Group Ltd, we are involved in continuous development of similar aptamer-based biosensors for therapeutic small molecule targets and even protein biomarkers using our high affinity aptamers. We have successfully developed aptamers against various chemotherapeutic drugs including irinotecan and imatinib, which are now available for purchase. If you would like more information on such platforms, please contact us using the form below.

References:

Aliakbarinodehi N, Jolly P, Bhalla N, et al. Aptamer-based Field-Effect Biosensor for Tenofovir Detection. Sci Rep. 2017;7:44409. Published 2017 Mar 15. doi:10.1038/srep44409.

Idili A, Arroyo-Currás N, Ploense KL, et al. Seconds-resolved pharmacokinetic measurements of the chemotherapeutic irinotecan in situ in the living body. Chem Sci. 2019;10(35):8164‐8170. Published 2019 Jul 22. doi:10.1039/c9sc01495k

Ferguson BS, Hoggarth DA, Maliniak D, et al. Real-time, aptamer-based tracking of circulating therapeutic agents in living animals. Sci Transl Med. 2013;5(213):213ra165. doi:10.1126/scitranslmed.3007095.

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