Macroporous hydrogel micropillars for quantifying Met kinase activity in cancer cell lysates

Overactive and overexpressed kinases have been implicated in the cause and progression of many cancers. Kinase inhibitors offer a targeted approach for treating cancers associated with increased or deregulated kinase activity. Often, however, cancer cells exhibit initial resistance to these inhibitors or evolve to develop resistance during treatment. Additionally, cancers of any one tissue type are typically heterogeneous in their oncogenesis mechanisms, and thus diagnosis of a particular type of cancer does not necessarily provide insight into what kinase therapies may be effective. For example, while some lung cancer cells that overexpress the epidermal growth factor receptor (EFGR) respond to treatment with EGFR kinase inhibitors, overexpression or hyperactivity of Met kinase correlates with resistance to EGFR kinase inhibitors. Here we describe a microfluidic-based assay for quantifying Met kinase activity in cancer cell lysates with the eventual goals of predicting cancer cell responsiveness to kinase inhibitors and monitoring development of resistance to these inhibitors. In this assay, we immobilized a phosphorylation substrate for Met kinase into macroporous hydrogel micropillars. We then exposed the micropillars to a cancer cell lysate and detected substrate phosphorylation using a fluorescently conjugated antibody. This assay is able to quantify Met kinase activity in whole cell lysate from as few as 150 cancer cells. It can also detect cells expressing overactive Met kinase in a background of up to 75% non-cancerous cells. Additionally, the assay can quantify kinase inhibition by the Met-specific kinase inhibitors SU11274 and PHA665752, suggesting predictive capability for cellular response to kinase inhibitors.     

Multiplexed tyrosine kinase activity detection in cancer cells using a hydrogel immobilized substrate

Kinases play a key role in cellular signaling, and the overactivation or overexpression of these kinases has been linked to a variety of cancers. Tyrosine kinase inhibitors treat the mechanism of these cancers by targeting the specific kinases that are overactive. Some patients, however, do not respond to these inhibitors or develop resistance to these inhibitors during treatment. Additionally, even within cancers of the same tissue type, different kinases may be overactive in different patients. For example, some lung cancers overexpress epidermal growth factor receptor (EGFR) and respond to EGFR inhibitors, whereas other lung cancers do not overexpress EGFR and receive no benefit from this treatment. Even among patients exhibiting EGFR overexpression, some do not respond to EGFR kinase inhibitors because other kinases, such as Met kinase, are also overactivated. Here we describe a quantitative and specific multiplexed microfluidic assay using a hydrogel immobilized substrate for measuring the kinase activity of Met and Abl kinase from cancer cells. We immobilized kinase-specific substrates on macroporous hydrogel micropillars in microchannels. These microchannels were incubated with 6 μl of a kinase reaction solution containing cancer cell lysate, and we measured kinase activity via fluorescence detection of a phosphotyrosine antibody. We showed that the assay can specifically measure the activity of both Met and Abl kinase within one microchannel and has the potential to measure the activity of as many as five kinases within one microchannel. The assay also detected Met kinase inhibition from lysates of cancer cells grown in the Met kinase inhibitor PHA665752.

An improved cell membrane chromatography method for the simultaneous screening of two epidermal growth factor receptor antagonists from radix scutellariae

A high‐expression epidermal growth factor receptor cell membrane chromatography using the silica gel with the average particle size of 3 μm as the stationary phase carrier coupled with high‐performance liquid chromatography and mass spectrometry was established for the online screening of epidermal growth factor receptor antagonists from Radix Scutellariae (Huang Qin in Chinese), a traditional Chinese medicine. In this study, the growth factor receptor cell membrane chromatography model using the smaller particle size carrier showed a higher efficiency for simultaneous screening baicalein, another one of the potential epidermal growth factor receptor antagonists from Radix Scutellariae extract besides wogonin, which was found in our previous work. The molecular docking result showed the occupancy site and binding mode of baicalein and wogonin with epidermal growth factor receptor tyrosine kinase were similar to gefitinib. The result of the assay for the in vitro inhibitory activity showed that baicalein and wogonin inhibited the growth of the high‐expression epidermal growth factor receptor cell in a dose‐dependent manner and even achieved a better inhibition effect than gifitinib in the low‐dosage range.     

Synthesis of C-5 benzoyl and azido functionalized 2,2′-dithiobis-and 2,2′-diselenobis(1H-indoles)

Novel methods for the synthesis of C-5 benzoyl and azido analogues of 2,2′-dithiobis(1H-indole), 1, and 2,2′-diselenobis(1H-indole), 2, are described to further explore the structure activity relationships in this region of the molecule. Analogues 3-i displayed inhibitory activity (IC₅₀ = 0.45-2.03 μ) toward the catalytic domain of the epidermal growth factor receptor tyrosine kinase that was equivalent to or better than that of unsubstituted compounds 1 and 2. The regiochemistry of Friedel-Crafts benzoylation onto 1 was determined by X-ray crystallography. To test the potential for compounds of this class to interact with the epidermal growth factor receptor tyrosine kinase via a sulfhydryl exchange mechanism, reaction of a 2,2′-dithiobis(1H-indole) with glutathione was carried out and the product characterized.     

A short and unequivocal synthesis of 5-aminotetrazolo[1,5-a]-quinazoline as a tricyclic analogue of 4-(3-bromoanilino)-6,7-dimethoxyquinazoline (PD 153035)

The discovery of 4-(3-bromoanilino)-6,7-dimethoxyquinazoline (PD 153035) as an extremely potent inhibitor of the tyrosine kinase activity of the epidermal growth factor receptor led to the preparation of several fused tricyclic quinazoline analogues. The present paper reports a new tricyclic derivative: 5-(3-bromoanilino)-7,8-dimethoxytetrazolo[1,5-a]quinazoline. This compound was synthesized by two different pathways viaa 1,3-dipolar cycloaddition of an azide at carbon 2 of the quinazoline ring.     

Immobilization of antibodies and enzyme-labeled antibodies by radiation polymerization

Immobilization of antibodies and enzyme-labeled antibodies by radiation polymerization at low temperatures was studied. The antibody activity of antibody was not affected by irradiation at an irradiation dose of below 8 MR and low temperatures. Immobilization of peroxidase-labeled anti-rabbit IgG goat IgG, anti-peroxidase, peroxidase, and anti-alpha-fetoprotein was carried out with hydrophilic and hydrophobic monomers. The activity of the immobilized enzyme-labeled antibody membranes varied with the thickness of the membranes and increased with decreasing membrane thickness. The activity of the immobilized antibody particles was varied by particle size. Immobilized anti-alpha-fetoprotein particles and membranes can be used for the assay of alpha-fetoprotein by the antigen-antibody reaction, such as a solid-phase sandwich method with high sensitivity.     

Practical and efficient synthesis of gefitinib through selective O-alkylation: A novel concept for a transient protection group

A practical process that includes a simple four-step procedure for the preparation of gefitinib (1), a tyrosine kinase inhibitor that targets the epidermal growth factor receptor, is described. Dramatic improvements over previously reported conventional synthetic procedures were achieved. We found effective coupling conditions to minimize the inevitable production of an N-alkylated side product, N-(3-chloro-4-fluorophenyl)-7-methoxy-6-(3-morpholinopropoxy)-N-(3-morpholinopropyl)-quinazoline-4-amine (3) using a transient trimethylsilyl protecting group. We synthesized gefitinib in an 81.1% overall yield from a commercially available starting material on a multigram scale using a route that did not require work-up of any of the reaction steps.     

Synthesis of Novel Benzoxazinone Compounds as Epidermal Growth Factor Receptor (EGFR) Tyrosine Kinase Inhibitors

Two benzoxazinone compounds as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors were synthesized and characterized by NMR and high-resolution mass spectrometry (HRMS). An efficient chlorination method was introduced in the synthesis of 4-chloro-2-oxo-2H-benzoxazinone-6-yl acetate. The inhibition activities of the target compounds and the important intermediates for EGFR tyrosine kinase activity in vitro were determined.     

Novel enzyme-linked immunosorbent assay for determination of fluvastatin in plasma at picogram level

For the first time, an enzyme-linked immunosorbent assay (ELISA) has been developed and validated for the determination of fluvastatin (FLV) in plasma samples at picogram level. The assay employed a polyclonal antibody that specifically recognizes FLV with high affinity, and FLV conjugate of bovine serum albumin (FLV-BSA) immobilized onto microplate wells as a solid-phase. The assay involved a competitive binding reaction between FLV, in plasma sample, and the immobilized FLV-BSA for the binding sites on a limited amount of the anti-FLV antibody. The bound anti-FLV antibody was quantified with horseradish peroxidase-labeled second anti-rabbit IgG antibody (HRP-IgG) and 3,3′,5,5′-tetramethylbenzidine (TMB) as a substrate for the peroxidase enzyme. The concentration of FLV in the sample was quantified by its ability to inhibit the binding of the anti-FLV antibody to the immobilized FLV-BSA and subsequently the color intensity in the assay wells. The conditions for the proposed ELISA were investigated and the optimum conditions were employed in the determination of FLV in plasma samples. The assay limit of detection was 10 pg mL⁻¹ and the effective working range at relative standard deviations (RSD) of ≤5% was 20-1000 pg mL⁻¹. Analytical recovery of FLV from spiked plasma was 97.1-102.7 ± 2.85-6.25%. The precision of the assay was satisfactory; RSD was 2.46-5.37 and 3.19-6.64% for the intra- and inter-assay precision, respectively. The analytical procedure is convenient, and one can analyze ∼200 samples per working day, facilitating the processing of large-number batch of samples. The proposed ELISA has a great value in routine analysis of FLV for its therapeutic monitoring and pharmacokinetic studies.     

Design and Synthesis of Novel EGFR Inhibitors with L‐Rhamnose–Benzoxazinone Hybrids

Four L ‐rhamnose–benzoxazinone compounds as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors were designed and synthesized. All structures of the compounds were characterized by ¹H‐NMR, ¹³C‐NMR, and high‐resolution mass spectrometry. The inhibition activities of the target compounds for the EGFR tyrosine kinase activity in vitro were determined. Compounds 6a , 6b , 6c , 6d displayed moderate activity in targeting EGFR.     

Quantitative analysis of 17beta-estradiol in river water by fluorometric enzyme immunoassay using biotinylated estradiol.

A sensitive and simple immunoassay to determine 17beta-estradiol (E2) in fresh water was developed. The method is based on a solid-phase avidin-biotin binding assay and solid phase extraction. The binding event of E2 to the antibody is detected indirectly by the competitive reaction between E2 and biotinylated estradiol (BE) as a tracer for the limited binding sites of antibodies immobilized onto the wall of a microtiter plate. Namely, E2 concentrations are determined from the strong interaction between BE and avidin conjugated with horseradish peroxidase (avidin-HRP). In order to achieve a sensitive measurement for the binding of BE to the antibody immobilized on the microtiter plate substrate, QuantaBlu fluorogenic peroxidase substrate (QFPS) was employed. The detection limit and the linear range of E2 determination were 27 pM and 27 - 7480 pM, respectively. The relative standard deviations (RSD) for the E2 assay were between 0.3 and 12.0% (n = 3). The cross-reactivities of several other estrogens in this assay system were also investigated. No serious influences from any cross-reaction caused by other estrogens tested in this experiment were observed. The determination of E2 in water samples from eight rivers and a marsh in Hokkaido was performed by the immunoassay combined with solid phase extraction. It was found that the concentration of E2 was in the range between 0.06 and 67 pM.     

Novel solid-phase refolding method for preparation of scFv-immobilized polystyrene plates with high-antigen-binding activity

In the present study, we demonstrated site-specific immobilization and solid-phase refolding of single-chain Fv antibodies on hydrophilic polystyrene (phi-PS) plates that was mediated by novel polystyrene binding peptides (PS-tags: RIIIRRIRR), which were originally isolated and optimized in previous studies. Three PS-tag-fused scFvs, namely scFv-PS, scFv-(PS), and scFv-PSII, which were over-expressed in the insoluble fraction of Escherichia coli cells were denatured and site-specifically immobilized onto hydrophilic PS plates in the presence of 0.5~4 M urea and 0.1% Tween 20. The antigen-binding activity of the scFvs was efficiently recovered by washing the surface of the plate with PBS that contained 0.1% Tween 20 (PBST). The solid-phase refolding mediated by PS-tag was successfully applied to several scFvs such as mouse anti-CRP antibodies and an anti-RNase antibody, although further investigation of the versatility of scFv-PSII is needed. The maximal density of PS-tag-fused scFvs was increased more than 15-fold compared with a whole monoclonal antibody (mAb) immobilized on Maxisorp™ and, consequently, the sensitivity of PS-tag-fused scFvs for CRP in a sandwich ELISA was increased 25-fold. Thus, the novel, solid-phase, refolding method mediated by a PS-tag will be very useful for preparation of solid supports coated with recombinant antibody fragments, which can be used in immunoassays and immuno-separation.     

Facile Synthesis of Novel Perfluorocarbon‐Modulated 4‐Anilinoquinazoline Analogues

4‐Anilinoquinazoline analogues stand out among many kinds of small molecules that inhibit the tyrosine kinase activities of epidermal growth factor receptor (EGFR ), thus serving as significant molecular targets for anticancer drug design. Herein, a series of novel perfluorocarbon (PFC ) modulated 4‐anilinoquinazolines were designed and prepared straightforwardly by nucleophilic substitution reaction of various anilinoquinazolines and PFC ‐derived methanesulfonate. In the presence of base, the reaction proceeded smoothly to afford a wide range of 4‐anilinoquinazolines with different substituents on aniline moiety in good to high yields. Furthermore, the PFC ‐modified analogues of gefitinib and erlotinib were also obtained in 93% and 90% respectively, which may have potential for developing new inhibitors of the epidermal growth factor receptor (EGFR ) tyrosine kinase and fluorinated contrast agents (CA ) for ¹⁹F MRI .     

Non-isotopic receptor assay for benzodiazepines using a biotin-labeled ligand and biotin-immobilized microtiter plate.

A non-isotopic receptor assay for benzodiazepine drugs was developed using a biotin-labeled ligand, biotin-1012S. Biotinylated bovine serum albumin (biotin-BSA) was immobilized onto the wall of microtiter plate wells by simple adsorption. Avidin peroxidase conjugate could be extracted from solution owing to its strong interaction with biotin. The amount of avidin peroxidase taken up on the wall was then determined by measuring the enzyme activity. The competition between immobilized biotin on the wall and free biotin for avidin provided the basis for a solid-phase avidin-biotin binding assay. By this binding assay, not only biotin but also biotin-1012S could be measured sensitively. Because 1012S is a ligand with high affinity to benzodiazepine receptors, biotin-1012S could be utilized as a probe ligand for a non-isotopic receptor assay. Based upon the competition between biotin-1012S and various benzodiazepine drugs for the receptor binding sites, a non-isotopic receptor assay was demonstrated.     

Dual‐enzyme,co‐immobilized capillary microreactor combined with substrate recycling for high‐sensitive glutamate determination based on CE

A new method for high‐sensitive determination of glutamate was developed and evaluated based on CE by using dual‐enzyme co‐immobilized capillary microreactor combined with substrate recycling. The capillary microreactor was prepared by covalently co‐immobilizing glutamate dehydrogenase (GDH) and glutamic pyruvic transaminase (GPT) on the inner surface of a capillary and was characterized by SEM, ultraviolet‐visible spectroscopy, and fluorescence spectroscopy. The GDH‐GPT co‐immobilized capillary microreactor showed great stability and reproducibility. The apparent K_m for glutamate with GDH‐GPT coupled reaction was determined to be 0.61±0.06 mM but 2.56±0.24 mM when only GDH was immobilized. Glutamate determination was based on on‐column monitoring UV absorption at 340 nm of the reaction product reduced nicotinamide adenine dinucleotide, of which peak area was directly related to the glutamate concentration. The response of the present co‐immobilized GDH‐GPT assay for glutamate is greatly enhanced over single enzyme system, and a 15.7‐fold improvement in sensitivity was obtained. The detection limit of the proposed method is 0.15 μM glutamate (S/N=3). Selectivity for glutamate is good over most of the 20 amino acids. Finally, this method was successfully applied to determine the glutamate content in rat plasma and serum samples.     

Inhibition effects of 5-S-glutathionyl-N-beta-alanyl-L-dopa analogues against Src protein tyrosine kinase.

Twelve analogues of the antibacterial phenolic peptide 5-S-glutathionyl-N-beta-alanyl-L-dopa (5-S-GA-L-D, 1) were synthesized via orthoquinone using tyrosinase. Several synthesized compounds inhibited the v-Src autophosphorylation tyrosine kinase reaction with an IC50 value comparable to that of herbimycin A. The inhibition of c-Src substrate phosphorylation was much less active than v-Src autophosphorylation inhibition. 5-S-GA-L-D (1) and its analogous competed with peptide substrate and non-compared with ATP. The analogues showed no effects on substrate phosphorylation by epidermal growth factor receptor (EGFR), and this selectivity is the most characteristic feature of the 5-S-GA-L-D and its analogues (1-12).     

Homogeneous single-label tyrosine kinase activity assay for high throughput screening

Protein post-translational modifications (PTMs) are regulatory mechanisms carried out by different enzymes in a cell. Kinase catalyzed phosphorylation is one of the most important PTM affecting the protein activity and function. We have developed a single-label quenching resonance energy transfer (QRET) assay to monitor tyrosine phosphorylation in a homogeneous high throughput compatible format. Epidermal growth factor receptor (EGFR) induced phosphorylation was monitored using Eu³⁺-chelate labeled peptide and label-free phosphotyrosine specific antibody in presence of a soluble quencher molecule. In the QRET kinase assay, antibody binding to phosphorylated Eu³⁺-peptide protects the Eu³⁺-chelate from luminescence quenching, monitoring high time-resolved luminescence (TRL) signals. In the presence of specific kinase inhibitor, antibody recognition and Eu³⁺-chelate protection is prevented, allowing an efficient luminescence quenching. The assay functionality was demonstrated with a panel of EGFR inhibitors (AG-1478, compound 56, erlotinib, PD174265, and staurosporine). The monitored IC₅₀ values ranged from 0.08 to 155.3 nM and were comparable to those found in the literature. EGFR activity and inhibition assays were performed using low nanomolar enzyme and antibody concentration in a 384-well plate format, demonstrating its compatibility for high throughput screening (HTS).     

Using measurements of anchoring energies of liquid crystals on surfaces to quantify proteins captured by immobilized ligands

We describe a simple optical method that employs measurement of the interaction energy of a liquid crystal (LC) with a surface (the so-called anchoring energy) to report proteins captured on surfaces through specific interactions with immobilized binding groups. To define the sensitivity and dynamic range of the response of the LC, we covalently immobilized a tyrosine-containing, 13-residue peptide sequence (Y1173) from the epidermal growth factor receptor/kinase (EGFR) at which autophosphorylation takes place and to which the adapter protein Shc binds. We determined that, on peptide-decorated (Y1173 or pY1173, where pY1173 is the corresponding phosphopeptide) surfaces incubated against anti-phosphotyrosine antibody, the anchoring energy of the LC decreased systematically from 4.4 to 1.4 microJ/m2 (with SEM=0.3 microJ/m2 for n=5) as the antibody concentration increased from 10 pM to 100 nM. Over the same range of antibody concentrations in solution and densities of immobilized peptides, independent ellipsometric measurements were not sufficiently sensitive to report the captured antibody (ellipsometric thicknesses were <0.1 nm). These results, when combined with control experiments reported in this article, provide the first demonstration of the use of anchoring energy measurements of LCs to report proteins captured by immobilized ligands on surfaces. The sensitivity and dynamic range of the methodology suggest that it may offer the basis of a simple yet broadly useful principle for reporting the interactions between proteins and other biomolecules that underlie complex and poorly understood chemical and biological events.     

Application of solid-phase extraction on anion-exchange cartridges to quantify 5'-nucleotidase activity.

The enzyme 5'-nucleotidase (5'-ribonucleotide phosphohydrolase, EC 3.1.3.5) catalyzes a critical reaction in intermediary metabolism, the phosphohydrolysis of nucleoside 5'-monophosphates to their corresponding nucleosides. We have evaluated solid-phase extraction on pre-packed anion-exchange cartridges as a chromatographic technique with which 5'-nucleotidase activity may be detected and quantified. Chromatographic conditions were established whereby substrate nucleotide was rapidly and completely separated from its corresponding nucleoside by solid-phase extraction. Both analytes were recovered quantitatively, without loss or degradation. This chromatographic system was integrated into a discontinuous radiochemical assay for 5'-nucleotidase which enabled both substrate utilization and product formation to be assessed simultaneously. Enzyme reaction samples could be analyzed directly for 5'-nucleotidase activity without any pre-chromatography preparation. The high capacity of the solid-phase cartridges and the inability of 5'-nucleotidase to enter the packing bed during analyte elution facilitated termination of the enzyme reaction by applying the entire reaction mixture to the cartridge. Loaded cartridges could then be stored at 4 degrees C prior to chromatography and subsequently batch-eluted. The excellent resolution between substrate and product in solid-phase extraction and the sensitivity of radioisotopic counting enabled detection/quantification of low tissue levels of 5'-nucleotidase in conjunction with ancillary assays for secondary enzyme reactions with the potential to elicit the artifactual loss of 5'-nucleotidase substrate/product when crude biological preparations are examined for 5'-nucleotidase activity. Our results demonstrate that solid-phase extraction on anion-exchange cartridges with elution solvents of appropriate pH offers several unique advantages for 5'-nucleotidase determination.     

High temporal resolution monitoring of enzyme reaction and inhibition using optically gated vacancy capillary electrophoresis and immobilized enzyme

A novel method for monitoring of enzyme reaction and inhibition with high temporal resolution was developed by using optically gated vacancy capillary electrophoresis (OGVCE) with laser-induced fluorescence (LIF) detection and immobilized enzyme. Trypsin cleavage reaction and inhibition were investigated by the presented OGVCE-LIF assay, using carboxyfluorescein (FAM) end-labeled Angiotensin as the substrate and commercially available immobilized trypsin. The substrate and the product were continuously loaded into the capillary by the electroosmotic flow while the immobilized enzyme remained in the sample vial. Substrate consumption and product formation were monitored simultaneously at 5 s interval during the whole reaction time. The enzymatic reaction rates obtained from the substrate and the product were highly consistent. The enzyme activity and the Michaelis constants of trypsin cleavage reaction, as well as the inhibition constant (for reversible competitive inhibitor) and the inhibition fraction (for irreversible inhibitor), were obtained. It was showed that the reported OGVCE-LIF method can perform fast, accurate, sensitive and reproducible CE enzyme assay with high temporal resolution, thus has great potential in application of the enzyme-substrate systems with fast reaction rate and the fluorescent substrate and products.