Neddylation is a posttranslational modification that regulates protein stability, activity, and subcellular localization. Here, we describe a new tool for exploring the neddylation cycle of cullin1 (Cul1) directly in a cellular context. This assay utilizes the NanoLuc® Binary Technology (NanoBiT) to monitor the covalent neddylation status of Cul1. A stable clonal cell line derived from HEK293 was developed that expressed a C-terminus LgBiT tagged-Cul1 and N-terminus SmBiT tagged-Nedd8. Using this cell line, we screened inhibitors that are known to disrupt Nedd8 biology and demonstrated that both inhibitors of Nedd8-activating enzyme (NAE) and Constitutive photomorphogenesis 9 signalosome (CSN) complex produce concentration and time dependent signal decreases and increases, respectively. The kinetics of both responses could be monitored in real time and demonstrated that modulation of the Nedd8 pathway occurs rapidly. Further characterization of the cellular components of this cell line was performed in order to quantify the various levels of Cul1, Nedd8 and NAE and determined to be near endogenous levels. There was no difference between control and stably transfected cell lines in viability studies of NAE and CSN inhibitors. Taken together, these results suggest that the NanoBiT assay can be used to monitor Cul1 neddylation specifically and in real time.

A new technology from Quanterix called SiMoA (single molecule array) which employs a fully automated system capable of ultrasensitive sandwich based ELISA detection was explored. Our studies focused upon the inhibition of the autophagy initiating kinase ULK1 by measuring the both total Atg13 and the phosphorylation of Atg13(pSer318) from control and following compound treatment in either overexpressing or wild type tissue culture samples. The results show linear protein concentration dependence over two orders of magnitude and provide an assay window of 8- to 100-fold signal to background for inhibition of phosphorylation for both wild type and overexpressed samples, respectively. Moreover, overexpressed samples displayed 17-fold pSer318-Atg13 above wild type levels of with no apparent differences in compound potency. Lastly, the inhibition of ULK1 from mouse derived wild type xenografts also demonstrated loss of pSer318-Atg13 upon ULK1 inhibitor treatment that compared favorably to Western blot. These results show that the SiMoA technology can detect quantitatively low levels of endogenous biomarkers with the ability to detect the loss of pSer318-Atg13 upon ULK1 inhibition.

Cellular effects of a Nedd8-activating enzyme (NAE) inhibitor, MLN4924, using the AlphaScreen format were explored. MLN4924 acts as a substrate-assisted inhibitor of NAE by forming a tight binding Nedd8–MLN4924 adduct. The inhibited enzyme can no longer transfer Nedd8 downstream to modify and activate the E3 cullin–RING ligases. This results in the stabilization of proteins regulated by the proteasome, leading to cell death. These studies monitored the endogenous cellular changes to NAE∼Nedd8 thioester, the formation of the Nedd8–MLN4924 adduct, and the reduction in the Cul1–Nedd8. Lysates derived from MLN4924-treated HCT116 cells showed that whereas the β-subunit of NAE remained constant, reductions of both NAE∼Nedd8 thioester and Cul1–Nedd8 levels occurred with a concomitant rise of the adduct. Moreover, the formation of the Nedd8–MLN4924 adduct was approximately stoichiometric with the concentration of NAEβ. Higher density 384-well cell-based assays illustrated the kinetics of enzyme inactivation across a wider range of MLN4924 concentrations, showing a rapid loss of NAE∼Nedd8 thioester and Cul1–Nedd8. The reduction of NAE∼Nedd8 thioester precedes the loss of Cul1–Nedd8 at twice the rate. Finally, these results clearly demonstrate the utility of the homogeneous assay for quantitative assessment of these endogenous cellular components in a 384-well plate in response to inhibition of NAE by MLN4924.

Pharmacodynamic responses to drug treatment are often used to confirm drug-on-target biological responses. Methods ranging from mass spectrometry to immunohistochemistry exist for such analyses. By far, the most extensively used methodologies employ antigen-specific antibodies for detection (at a minimum) and, in some cases, target quantitation as well. Using a novel frequency-modulating technology from BioScale called acoustic micro magnetic particle (AMMP) detection, two pathway biomarkers were chosen for pharmacodynamic analysis and compared with either AlphaScreen or LI-COR Western blot assays. For these studies, pharmacodynamic biomarkers for both proteasome and phosphoinositol 3-kinase inhibition were used. Our results show clearly that the BioScale technology is a robust and rapid method for measuring recombinant standards or endogenously derived proteins from both tissue culture and mouse xenograft tumor lysates. Moreover, the sensitivity obtained with the BioScale platform compares favorably with LI-COR Western blot and AlphaScreen technologies. Furthermore, the use of the ViBE Bioanalyzer eliminates the labor-intensive effort of Western blot analysis and is devoid of the optical and other endogenous interfering substances derived from lysates of xenograft tumors typically observed with AlphaScreen.

The utility of antibody reagents for the detection of specific cellular targets for both research and diagnostic applications is widespread and continually expanding. Often it is useful to develop specific antibodies as reagent pairs that distinguish different epitopes of the target such that sandwich enzyme-linked immunosorbent assay can be used for selective and specific detection. However, the identification of pairing antibodies is often cumbersome and labor-intensive even with the use of designed peptide-specific epitopes as antigens. We have developed a robust and high-throughput method for identifying pairing complementary antibodies derived either from commercial sources or during a rabbit hybridoma monoclonal screening and selection process using protein A capture with the AlphaScreen bead-based assay format. We demonstrate the value and effectiveness of this assay with three protein targets: Akt2, ATF3, and NAEβ (the β-subunit of the neddylation activation enzyme).

237 Aurora A kinase regulates the activity of a number of proteins essential to the proper execution of mitosis. Perturbation of Aurora A results in aberrant mitoses leading to cell death. We have developed a selective Aurora A kinase inhibitor, MLN8237; to be used for the therapeutic intervention of human cancers. MLN8237 displays potent activity against Aurora A in both enzymes and cell assays. In cells, MLN8237 proved to be more than 200 fold more selective for Aurora A than the structurally related kinase Aurora B. Treatment of cultured human tumor cells with MLN8237 results in mitotic spindle abnormalities, mitotic accumulation, inhibition of cell proliferation and apoptosis. MLN8237 is orally bioavailable and has a favorable pharmacokinetic profile. A single oral administration of MLN8237 to nude mice bearing subcutaneous human tumor xenografts resulted in a time dependent accumulation of mitotic cells, consistent with the pharmacological effect being mediated through Aurora A inhibition. Repeat oral administration of MLN8237 at well tolerated doses to nude mice bearing subcutaneous human tumor xenografts resulted in dramatic tumor growth inhibition in all models evaluated. In these models, MLN8237 induced mitotic accumulation and apoptosis. MLN8237 did not appreciably inhibit Aurora B at efficacious concentrations, as indicated by measuring phosphorylated histone H3 Ser10 staining. MLN8237 is currently in Phase I clinical trials in patients with advanced malignancies.

Adenine phosphoribosyltransferase plays a role in purine salvage by catalyzing the direct conversion of adenine to adenosine monophosphate. The involvement of the purine salvage pathway in tumor proliferation and angiogenesis makes adenine phosphoribosyltransferase a potential target for oncology drug discovery. We have expressed and characterized recombinant, N-terminally Histagged human adenine phosphoribosyltransferase. Two assay formats were assessed for use in a high throughput screen: a spectrophotometric-based enzyme-coupled assay system and a radiometric ionic capture scintillation proximity bead assay format. Ultimately, the scintillation proximity assay format was chosen because of automated screening compatibility limitations of the coupled assay. We describe here the biochemical characterization of adenine phosphoribosyltransferase and the development of a robust, homogeneous, 384-well assay suitable for high throughput screening.

This chapter contains sections titled: General Considerations for Biochemical High-throughput Screening Expression and Purification of Recombinant Enzymes Design of Expression Constructs Expression Assessment and Optimization Purification Peptidases Application of Fluorogenic Substrates to Configure Peptidase Screens The Value of Continuous Assays Oxidoreductases NAD(P)-dependent Oxidoreductases Non-NAD(P) Cofactor-dependent Oxidoreductases Oxidases or Oxygen-utilizing Oxidoreductases General Considerations Transferases, Synthetases and Lipid-modifying Enzymes Streptavidin–Biotin Capture Ionic Capture Hydrophobic Capture Kinases Streptavidin–Biotin Capture Homogeneous Time-resolved Fluorescence (HTRF) Pyruvate Kinase–Lactate Dehydrogenase Assay System Pitfalls and Reasons for Assay Development Failures