An SPR investigation into the therapeutic drug monitoring of the anticancer drug imatinib with selective aptamers operating in human plasma.

The anticancer drug imatinib is often involved in therapeutic drug monitoring (TDM) studies aimed at improving the treatment of several forms of leukemia and gastrointestinal stromal tumors (GIST). To further implement the TDM of imatinib in clinical practice, we developed a detection assay by using an ssDNA aptamer, which demonstrated excellent selectivity and was not affected by interference from the components of human plasma samples. The efficient binding of imatinib to the aptamer was demonstrated by means of surface plasmon resonance (SPR) analysis, which allowed the development of a quantitative assay in the concentration range between 400 and 6000 ng mL-1 (0.7-10 µM), where a lower limit of quantification (LLOQ) of 400 ng mL-1 was achieved. The precision of the assay was found to be within 12.0%, whereas the accuracy was in a range between 97.1 and 101.5%. The sample preparation procedure displayed a recovery in the range of 48.8-52.8%. Solid validation data were collected according to the regulatory guidelines and the method was compared with standard analytical techniques, leading to the development of a feasible aptasensor for the TDM of patients administered with imatinib.

Enzyme-Based Electrochemical Biosensor for Therapeutic Drug Monitoring of Anticancer Drug Irinotecan.

Therapeutic drug monitoring (TDM) is the clinical practice of measuring pharmaceutical drug concentrations in patients' biofluids at designated intervals, thus allowing a close and timely control of their dosage. To date, TDM in oncology can only be performed by trained personnel in centralized laboratories and core facilities employing conventional analytical techniques (e.g., MS). CPT-11 is an antineoplastic drug that inhibits topoisomerase type I, causing cell death, and is widely used in the treatment of colorectal cancer. CPT-11 was also found to directly inhibit acetylcholine esterase (AChE), an enzyme involved in neuromuscular junction. In this work, we describe an enzymatic biosensor, based on AChE and choline oxidase (ChOx), which can quantify CPT-11. ACh (acetylcholine) substrate is converted to choline, which is subsequently metabolized by ChOx to give betaine aldehyde and hydrogen peroxide. The latter one is then oxidized at a suitably polarized platinum electrode, providing a current transient proportional to the amount of ACh. Such an enzymatic process is hampered by CPT-11. The biosensor showed a ∼60% maximal inhibition toward AChE activity in the clinically relevant concentration range 10-10 000 ng/mL of CPT-11 in both simple (phosphate buffer) and complex (fetal bovine serum) matrixes, while its metabolites showed negligible effects. These findings could open new routes toward a real-time TDM in oncology, thus improving the therapeutic treatments and lowering the related costs.

Label-free efficient and accurate detection of cystic fibrosis causing mutations using an azimuthally rotated GC-SPR platform.

Plasmonic nanosensors are candidates for the development of new sensors with low detection limits, high sensitivity, and specificity for target detection: these characteristics are of critical importance in the screening of mutations responsible for inherited diseases. In this work, we focused our study on the detection of some of the most frequent mutations responsible for cystic fibrosis (CF) among the Italian population. For the detection of the CF mutations we adopted a recently developed and highly sensitive Grating Coupled-Surface Plasmon Resonance (GC-SPR) enhanced spectroscopy method for label-free molecular identification exploiting a conical illumination configuration. Gold sinusoidal gratings functionalized with heterobifunctional PEG were used as sensing surfaces, and the specific biodetection was achieved through the coupling with DNA hairpin probes designed for single nucleotide discrimination. Such substrates were used to test unlabeled PCR amplified homozygous wild type (wt) and heterozygous samples, deriving from clinical samples, for the screened mutations. Hybridization conditions were optimized to obtain the maximum discrimination ratio (DR) between the homozygous wild type and the heterozygous samples. SPR signals obtained from hybridizing wild type and heterozygous samples show DRs able to identify univocally the correct genotypes, as confirmed by fluorescence microarray experiments run in parallel. Furthermore, SPR genotyping was not impaired in samples containing unrelated DNA, allowing the platform to be used for the concomitant discrimination of several alleles also scalable for a high throughput screening setting.

Development of a multiplex sandwich aptamer microarray for the detection of VEGF165 and thrombin.

In this work we have developed a multiplex microarray system capable of detecting VEGF165 and thrombin. We recently described a Sandwich Aptamer Microarray (SAM) for thrombin detection feasible for use in multiplex microarrays; here we describe a new aptasensor for VEGF165 detection employing Vap7 and VEa5, two DNA aptamers recognizing different sites of the protein. The aptamers were modified to be adapted to the solid phase platform of SAM and their capability to simultaneously recognize VEGF165 by forming a ternary complex was analyzed in solution. Having so defined the best tandem arrangement of modified aptamers, we set up the aptasensor for VEGF165, and finally analyzed the multiplex system with the two aptasensors for the simultaneous detection of VEGF165 and thrombin. The results indicate that each sandwich is specific, even when the two proteins are mixed. The system performance is consistent with the behavior evidenced by the biochemical analysis, which proves to be valuable to drive the evaluation and refinement of aptamers prior to or along the development of a detection platform. Since thrombin upregulates VEGF expression, the simultaneous recognition of these two proteins could be useful in the analysis of biomarkers in pathologies characterized by neo-angiogenesis.

Human thrombin detection through a sandwich aptamer microarray: interaction analysis in solution and in solid phase.

We have developed an aptamer-based microarray for human thrombin detection exploiting two non-overlapping DNA thrombin aptamers recognizing different exosites of the target protein. The 15-mer aptamer (TBA1) binds the fibrinogen-binding site, whereas the 29-mer aptamer (TBA2) binds the heparin binding domain. Extensive analysis on the complex formation between human thrombin and modified aptamers was performed by Electrophoresis Mobility Shift Assay (EMSA), in order to verify in solution whether the chemical modifications introduced would affect aptamers/protein recognition. The validated system was then applied to the aptamer microarray, using the solid phase system devised by the solution studies. Finally, the best procedure for Sandwich Aptamer Microarray (SAM) and the specificity of the sandwich formation for the developed aptasensor for human thrombin were optimized.

ELISA assay employing epitope-specific monoclonal antibodies to quantify circulating HER2 with potential application in monitoring cancer patients undergoing therapy with trastuzumab.

Circulating HER2 extracellular domain (HER2 ECD) levels were proposed as a surrogate for HER2 tissue expression to monitor breast cancer patients for early relapse or responses to standard or HER2-targeted therapies, such as the monoclonal antibody (mAb) trastuzumab. Currently, available commercial ELISA assays for HER2 ECD rely on antibodies recognizing undisclosed or unknown epitopes. In this work, two ELISA assays employing MGR2 and MGR3 epitope-specific mAbs for HER2 ECD were developed and validated, showing good assay precision and linearity of the dose-response signal within the dynamic range of 0.19-12.50 ng mL-1 and detection limits of 0.76 and 0.75 ng mL-1 for the MGR2 and MGR3 assays, respectively. The developed assay showed a good agreement with two widely used commercial kits for HER2 ECD quantification in serum samples from breast cancer patients. A complete characterization of mAb-HER2 ECD interaction was performed by means of surface plasmon resonance using trastuzumab as control for both epitope mapping and kinetics analysis. The epitopes recognized by the two mAbs showed no overlap with trastuzumab, which was confirmed by trastuzumab interference analysis in serum samples. The method showed to be a practical approach to determine HER2 ECD with a high degree of sensitivity, reliability and recovery in samples containing mAbs-based therapies.

Biosensing Technologies for Therapeutic Drug Monitoring.

BACKGROUND AND RATIONALE: Therapeutic drug monitoring (TDM) is the clinical practice of measuring pharmaceutical drug concentrations in patients' biofluids at designated intervals to allow a close and timely control of their dosage. This practice allows for rapid medical intervention in case of toxicity-related issues and/or adjustment of dosage to better fit the therapeutic demand. Currently, TDM is performed in centralized laboratories employing instruments, such as immunoassay analyzers and mass spectrometers that can be run only by trained personnel. However, the time required for the preparation, samples analysis, and data processing, together with the related financial cost, severely affects the application of TDM in medical practices. Therefore, a new generation of analytical tools is necessary to respond to the timely need of drug administration or reduction aiming at effectively treating oncologic patients. AIM OF THE REVIEW: State-of-the-Art Technologies for TDM: Technological advances in the field of nanosciences and biosensors offer the unique opportunity to address such issues. The interest for the so-called nanobiosensors is considerably increasing, particularly in drug discovery and clinical chemistry, even though there are only few examples reporting their use for TDM. The techniques employing nanobiosensors are mainly based on electrochemical, optical, and mass detection systems. CONCLUSIONS: In this review, we described the most promising methodologies that, in our opinion, will bring TDM towards the next stage of clinical practice in the future.

Practical fluorimetric assay for the detection of anticancer drug SN-38 in human plasma.

The implementation of therapeutic drug monitoring in the routine clinical practice in oncology is mainly limited by the lack of therapeutic indexes for the majority of the anticancer drugs, and by the absence of suitable analytical tools, which can accurately quantify in real time the concentration of the administered drugs and their relevant metabolites in biological fluids. In this work, a simple and efficient fluorimetric determination of SN-38, the active metabolite of the anticancer drug irinotecan, was developed and applied to human plasma samples. The intrinsic fluorescence of SN-38 allowed its quantification in the range 10-500 ng mL-1 with a LOQ of 5.0 ng mL-1 and a LOD of 1.5 ng mL-1. Low interferences due to main metabolites of irinotecan and comedications, commonly associated with administration of irinotecan, were observed. A validation study, according to FDA and EMA guidelines for bioanalytical method validation, was carried out and, finally, blind samples were analyzed in parallel with a HPLC-MS method obtaining an excellent agreement between the two techniques.

Sensitive detection of Ochratoxin A in food and drinks using metal-enhanced fluorescence.

Easy, sensitive, rapid and low cost ochratoxin biosensors are strongly demanded in food analysis since Ochratoxin A (OTA) is a widely diffused food contaminant, highly detrimental for human health. In this work, a novel plasmonic based optical biosensor prototype for ochratoxin A is described. It exploits the metal-enhanced fluorescence phenomenon due to the silver film over nanosphere plasmonic substrate. Since ochratoxin A could be present in different food commodities, sensor performances have been tested on three different matrices (dried milk, juices, and wheat mix). Firstly, a common OTA extraction solvent and a labeling and detection protocol were defined for the analyzed matrices. Then, the efficiency of the Ag-FON surfaces in signal amplification for the detection of low ochratoxin A concentrations was defined. Using samples spiked with OTA-AF 647 or with unlabeled OTA we were able to detect the mycotoxin at concentrations lower than E.U. specifications of 0.5 µg/kg in wheat, milk and apple juice. The test performances are comparable to those of ELISA kits but the platform presented here, once optimized, present some perspective advantages, such as: low cost and time consuming, versatility of the protocol for the investigation of different matrices, employment also in non-qualified laboratories, small dimensions that allow its integration in a compact device for OTA on-site detection.

Development and Optimization of a Thrombin Sandwich Aptamer Microarray.

A sandwich microarray employing two distinct aptamers for human thrombin has been optimized for the detection of subnanomolar concentrations of the protein. The aptamer microarray demonstrates high specificity for thrombin, proving that a two-site binding assay with the TBA1 aptamer as capture layer and the TBA2 aptamer as detection layer can ensure great specificity at times and conditions compatible with standard routine analysis of biological samples. Aptamer microarray sensitivity was evaluated directly by fluorescent analysis employing Cy5-labeled TBA2 and indirectly by the use of TBA2-biotin followed by detection with fluorescent streptavidin. Sub-nanomolar LODs were reached in all cases and in the presence of serum, demonstrating that the optimized aptamer microarray can identify thrombin by a low-cost, sensitive and specific method.

Signal enhancement in DNA microarray using dye doped silica nanoparticles: application to human papilloma virus (HPV) detection.

DNA microarray is a powerful tool for the parallel of nucleic acids and other biologically significant molecules. In this communication we report an easy and cheap synthesis route for incorporating organic dyes into monodisperse inorganic silica nanoparticles and their application on the detection of carcinogenic risky Human Papilloma Virus using DNA microarray technology. We correlate our system with conventional direct dyes and commercial quantum dots, with a promising increase in optical signal, and a related decrease of the limit of detection, thus giving a remarkable improvement in this technique towards early diagnosis of diseases and trace level detection of dangerous biological contaminants.