High-throughput Format Research Articles

Human CD34+ progenitor hematopoiesis in liquid culture for in vitro assessment of drug-induced myelotoxicity

Utilization of validated CFU-GM assays for myelotoxicity screening is hampered by its labor-intensive and low-throughput nature. Herein, we transformed the defined CFU-GM assay conditions and IC90 endpoint into a higher throughput format. Human CD34+ hematopoietic progenitors were cultured in a 96-well plate for 14days with the same cytokine (rhGM-CSF) used in the CFU-GM assay. Expansion and differentiation toward myeloid lineages were manifested by characteristic changes in nuclear and cytoplasmic morphology and by temporal expression patterns of CD34, CD11b and CD13 markers. Inhibition of CD34+ cell myelopoiesis by 12 anticancer drugs known to induce myelotoxicity in the clinic was quantifiable using either general cytotoxicity endpoints (cell growth area or total nucleus count) or lineage specific readouts (count of cells expressing CD11b and/or CD13). The IC50 and IC90 values derived from the concentration-response curves of 14-day drug exposure in CD34+ cell culture were highly correlated with those from the international validation study of the CFU-GM assay, demonstrating capability to assess general cytotoxicity, cell proliferation and myelopoiesis simultaneously. These results suggest that this human CD34+ hematopoietic progenitor cell assay can be used as a direct replacement for the validated, low throughput CFU-GM assay, and could expand application of in vitro myelotoxicity testing.

A mini-review on Sirtuin activity assays

Sirtuins belong to the class III histone deacetylase family with NAD-dependent protein lysine deacylase activities, which has been shown to play important roles in many physiological processes, including the regulation of transcription, DNA repair, metabolism and protein secretion. Small molecules that can modulate Sirtuin activity are important for fundamental studies of Sirtuin biology and drug development. High-throughput assays to screen for small molecule modulators of Sirtuins have been approved to be very useful tools for the development of therapeutics and research tools targeting Sirtuins. In this review, we will summarize the reported assays (during 2000–2015) for Sirtuins and discuss how these assays show different performances for the possibility of screening Sirtuin modulators and the application of high-throughput format screening.

Kinetic characterization of trans-proteolytic activity of Chikungunya virus capsid protease and development of a FRET-based HTS assay.

Chikungunya virus (CHIKV) capsid protein (CVCP) is a serine protease that possesses cis-proteolytic activity essential for the structural polyprotein processing and plays a key role in the virus life cycle. CHIKV being an emerging arthropod-borne pathogenic virus, is a public health concern worldwide. No vaccines or specific antiviral treatment is currently available for chikungunya disease. Thus, it is important to develop inhibitors against CHIKV enzymes to block key steps in viral reproduction. In view of this, CVCP was produced recombinantly and purified to homogeneity. A fluorescence resonance energy transfer (FRET)-based proteolytic assay was developed for high throughput screening (HTS). A FRET peptide substrate (DABCYL-GAEEWSLAIE-EDANS) derived from the cleavage site present in the structural polyprotein of CVCP was used. The assay with a Z’ factor of 0.64 and coefficient of variation (CV) is 8.68% can be adapted to high throughput format for automated screening of chemical libraries to identify CVCP specific protease inhibitors. Kinetic parameters Km and kcat/Km estimated using FRET assay were 1.26 ± 0.34 μM and 1.11 × 103 M−1 sec−1 respectively. The availability of active recombinant CVCP and cost effective fluorogenic peptide based in vitro FRET assay may serve as the basis for therapeutics development against CHIKV.

A Versatile Cell Death Screening Assay Using Dye-Stained Cells and Multivariate Image Analysis.

A novel dye-based method for measuring cell death in image-based screens is presented. Unlike conventional high- and medium-throughput cell death assays that measure only one form of cell death accurately, using multivariate analysis of micrographs of cells stained with the inexpensive mix, red dye nonyl acridine orange, and a nuclear stain, it was possible to quantify cell death induced by a variety of different agonists even without a positive control. Surprisingly, using a single known cytotoxic agent as a positive control for training a multivariate classifier allowed accurate quantification of cytotoxicity for mechanistically unrelated compounds enabling generation of dose–response curves. Comparison with low throughput biochemical methods suggested that cell death was accurately distinguished from cell stress induced by low concentrations of the bioactive compounds Tunicamycin and Brefeldin A. High-throughput image-based format analyses of more than 300 kinase inhibitors correctly identified 11 as cytotoxic with only 1 false positive. The simplicity and robustness of this dye-based assay makes it particularly suited to live cell screening for toxic compounds.

A graphene oxide-based fluorescent scheme for the determination of the activity of the β-site amyloid precursor protein (BACE1) and its inhibitors

The enzyme cleaving the beta-site amyloid precursor protein (BACE1) is a prime therapeutic target for treatment of Alzheimer’s disease (AD). Hence, improved high-throughput methods for probing the activity of BACE1 are crucial with respect to the discovery of novel drugs for treatment and prevention of AD. We describe a graphene oxide (GO)-based fluorescent platform for the determination of BACE1 activity and screening of its inhibitors. It is found that covalent linkage of the fluorescein isothiocyanate (FITC)-labeled enzyme substrate (of sequence GTEEISEVNLDAEFRHDSGYKK) to GO results in quenching of the FITC fluorescence, but that on peptide cleavage by BACE1, FITC is released from the GO surface and fluorescence is restored. In contrast to other fluorescent assays, the method presented here shows much higher quenching efficiency and sensitivity, and it can be used at pH value of 4.5 where BACE1 exhibits higher activity. The inhibition of BACE1 activity by a potential inhibitor results in retarded fluorescence recovery. The half-maximum inhibition value of a well-known BACE1 inhibitor was found to be 82.7 nM, which is in agreement with the value reported earlier. In our perception, this method represents a valuable tool for screening of BACE1 inhibitors and discovery of AD drugs in a high-throughput screening format using microplate readers.

Leveraging high‐throughput technology to accelerate the time to clinic: A case study of a mAb

Acceleration of development timelines to support material production for early‐phase clinical trials has been a continuous goal within the life sciences industry, driven largely by the need to advance an ever increasing number of novel therapeutics into the clinic. This has challenged cell culture and purification development groups to become more efficient, realized in part by leveraging a platform process in the case of mAbs, adopting high‐throughput (HT) technologies, and scaling‐up directly from the HT formats to pilot and clinical scales for toxicology and clinical production. The work presented herein focuses on a case study where a mammalian cell culture process producing mAb A was developed almost exclusively utilizing HT technology. The study describes how HT systems such as microbioreactors for cell culture development and minicolumns driven by robotics for purification development were integrated to rapidly develop a robust production process that was then directly scaled‐up nearly 17 000‐fold for cell culture and 5200‐fold for purification steps to generate material for investigational new drug‐enabling toxicology studies at the 250 L bioreactor scale, followed by another rapid scale‐up to 1000 L for clinical production. Performance comparability across scales demonstrates the effectiveness of HT process development for accelerating the time to clinic.

In situ patterned micro 3D liver constructs for parallel toxicology testing in a fluidic device

3D tissue models are increasingly being implemented for drug and toxicology testing. However, the creation of tissue-engineered constructs for this purpose often relies on complex biofabrication techniques that are time consuming, expensive, and difficult to scale up. Here, we describe a strategy for realizing multiple tissue constructs in a parallel microfluidic platform using an approach that is simple and can be easily scaled for high-throughput formats. Liver cells mixed with a UV-crosslinkable hydrogel solution are introduced into parallel channels of a sealed microfluidic device and photopatterned to produce stable tissue constructs in situ. The remaining uncrosslinked material is washed away, leaving the structures in place. By using a hydrogel that specifically mimics the properties of the natural extracellular matrix, we closely emulate native tissue, resulting in constructs that remain stable and functional in the device during a 7-day culture time course under recirculating media flow. As proof of principle for toxicology analysis, we expose the constructs to ethyl alcohol (0–500 mM) and show that the cell viability and the secretion of urea and albumin decrease with increasing alcohol exposure, while markers for cell damage increase.

High-throughput sample-to-answer detection of DNA/RNA in crude samples within functionalized micro-pipette tips.

We develop a micro-pipette tip-based nucleic acid test (MTNT) for high-throughput sample-to-answer detection of both DNA and RNA from crude samples including cells, bacteria, and solid plants, without the need of sample pretreatment and complex operation. MTNT consists of micro-pipette tips and embedded solid phase nucleic acid extraction membranes, and fully integrates the functions of nucleic acid extraction from crude samples, loop-mediated isothermal amplification (LAMP) of nucleic acids, and visual readout of assays. The total assaying time for DNA or RNA from a variety of crude samples ranges from 90 to 160 min. The limit of detection (LOD) of MTNT is 2 copies of plasmids containing the target nucleic acid fragments of Ebola virus, and 8 CFU of Escherichia coli carrying Ebola virus-derived plasmids. MTNT can also detect CK-19 mRNA from as few as 2 cancer cells without complicated procedures such as RNA extraction and purification. We further demonstrate MTNT in a high-throughput format using an eight-channel pipette and a homemade mini-heater, with a maximum throughput of 40 samples. Compared with other point-of-care (POC) nucleic acid tests (NAT), MTNT could assay both DNA and RNA directly from liquid (cells/bacteria/blood) or solid (plant) samples in a straightforward, sensitive, high-throughput, and containment-free manner, suggesting a considerable promise for low-cost and POC NAT in remote areas.

Abstract 311: High-throughput spheroid formation in a 384-well format using magnetic 3D bioprinting

Abstract Technical limitations in the rapid and reproducible formation of multicellular tumor spheroids prevent their widespread use in high-throughput screening for cancer research and drug development. Existing systems for spheroid formation require lengthy processing times, and make simple tasks like media exchange and sample retention challenging. An ideal 3D cell culture system would print spheroids rapidly, while being easy to handle and process for high-throughput applications. To address this unmet need, we use magnetic 3D bioprinting for high-throughput spheroid formation. Magnetic 3D bioprinting is based on the principle of magnetizing cells using a magnetic nanoparticle assembly. Once magnetized, these cells can be directed and aggregated using magnetic forces; specifically, magnetized cells can be aggregated into spheroids in 384-well plates. These spheroids can be cultured long-term, and, as they are magnetic, the spheroids can be held down or transferred out of the well, avoiding the technical issues of other 3D systems to retain samples. Moreover, the magnetic nanoparticles have no effect on cell behavior and do not interfere with fluorescence. We demonstrated this method by printing spheroids of HepG2, HCT-116, A549, and PANC-1 cancer cells in 384-well plates. We printed spheroids rapidly (15 min) and reproducibly, with cell numbers as small as 100 cells. We assayed the spheroids by using their contraction over time as an endpoint, which we validated as a toxicity endpoint correlating with cell migration, proliferation, and viability. In running these experiments we also demonstrated that these spheroids are amenable to high-content testing, with multiple experiments being performed on the same spheroid to yield more data per test. Thus, this study introduces magnetic 3D bioprinting for high-throughput spheroid formation, where multicellular tumor spheroids that represent native tumor environments can be rapidly and easily printed for cancer research and compound screening. Citation Format: Hubert Tseng, Jacob A. Gage, William L. Haisler, Glauco R. Souza. High-throughput spheroid formation in a 384-well format using magnetic 3D bioprinting. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 311. doi:10.1158/1538-7445.AM2015-311

A Cell-Based Internalization and Degradation Assay with an Activatable Fluorescence–Quencher Probe as a Tool for Functional Antibody Screening

For the development of therapeutically potent anti-cancer antibody drugs, it is often important to identify antibodies that internalize into cells efficiently, rather than just binding to antigens on the cell surface. Such antibodies can mediate receptor endocytosis, resulting in receptor downregulation on the cell surface and potentially inhibiting receptor function and tumor growth. Also, efficient antibody internalization is a prerequisite for the delivery of cytotoxic drugs into target cells and is critical for the development of antibody–drug conjugates. Here we describe a novel activatable fluorescence–quencher pair to quantify the extent of antibody internalization and degradation in the target cells. In this assay, candidate antibodies were labeled with a fluorescent dye and a quencher. Fluorescence is inhibited outside and on the surface of cells, but activated upon endocytosis and degradation of the antibody. This assay enabled the development of a process for rapid characterization of candidate antibodies potentially in a high-throughput format. By employing an activatable secondary antibody, primary antibodies in purified form or in culture supernatants can be screened for internalization and degradation. Because purification of candidate antibodies is not required, this method represents a direct functional screen to identify antibodies that internalize efficiently early in the discovery process.

High-throughput nanogap formation by field-emission-induced electromigration

High-throughput nanogap formation is reported for simultaneous fabrication of integrated nanogap arrays. Ten series-connected nanogaps with butterfly and bottle shapes were integrated by using electromigration induced by a field emission current (“activation”). Initially, ten series-connected butterfly-shaped nickel (Ni) nanogaps were fabricated with electron-beam lithography and lift-off processes. Activation with a preset current of 300 nA reduced the separation of the gaps to <10 nm. Similar results for bottle-shaped nanogaps indicated that integration of nanogaps using activation is not dependent on nanogap shape. The activation method was also used for the mass production of 30 identical nanogaps. Overall, the distance between the Ni nanogap electrodes was completely controlled by activation.

Non-specific adsorption of serum and cell lysate on 3D biosensor platforms: A comparative study based on SPRi

Comparative study for non-specific adsorption of cell lysate and serum on recently developed biosensor surfaces is reported. Different surface chemistries including, polyethylene glycol (PEG), α-cyclodextrin (CD), hydrogel dextran and surface initiated polymerization (SIP) based gold surfaces were taken into account for this study. Various techniques including, surface plasmon resonance imaging (SPRi) and matrix-assisted laser desorption ionization tandem time-of-flight mass spectrometry (MALDI−TOF/TOF MS) technique to evaluate the surfaces with Fourier transform infrared spectroscopy (FTIR) for the confirmation of surface fabrication were used. A high non-specific adsorption response of cell lysate and serum was observed on these so-called non-fouling surfaces. The obtained results from this comparative study provided some hope to explore SIP and dextran surface as a universal platform for biosensor applications. SIP produced best result and showed high sensitivity and minimum non-specific adsorption. We believe that this comparative study will surely help the researchers to further upgrade these surfaces and especially SIP to make it more universal for biosensor microarray applications including biomarker discovery in high throughput format.

Screening Pools of Compounds against Multiple Endogenously Expressed Targets in a Chemoproteomics Binding Assay.

Chemoproteomics-based competition-binding assays allow the screening of compounds against endogenous proteins in cell or tissue extracts, but these assays are hampered by low throughput and high cost. Using compound pools rather than single compounds in a screening campaign holds the promise of increased efficiency and substantial cost reduction. Previous attempts to screen compounds in pools often fell short due to complex data tracking, deconvolution issues, compound interferences, and automation problems. The desire to screen compounds in a high-throughput chemoproteomics format sparked a reassessment of compound pooling. Through the integration of acoustic dispensing, we enabled a flexible pooling process, allowing mixture creation by combining randomized or specific samples to create defined pools. Automation enabled end-to-end tracking, using barcode scan check points and output files to track data and ensure integrity during the mixture creation process. The compound pooling approach proved to be highly compatible with the chemoproteomics assay technology. Pools of 10 compounds in a single well did not show compound interference effects or increased false-positive/negative rates. In the present study, four targets, TBK1, PI3Kδ, PI3Kγ, and mTOR, were screened using a chemoproteomics approach against pools of 10 compounds per well, resulting in robust hit identification.

High-Throughput Cancer Cell Sphere Formation for Characterizing the Efficacy of Photo Dynamic Therapy in 3D Cell Cultures.

Photodynamic therapy (PDT), wherein light sensitive non-toxic agents are locally and selectively activated using light, has emerged as an appealing alternative to traditional cancer chemotherapy. Yet to date, PDT efficacy has been mostly characterized using 2D cultures. Compared to 2D cultures, 3D sphere culture generates unique spatial distributions of nutrients and oxygen for the cells that better mimics the in-vivo conditions. Using a novel polyHEMA (non-adherent polymer) fabrication process, we developed a microfluidic sphere formation platform that can (1) generate 1,024 uniform (size variation <10%) cancer spheres within a 2 cm by 2 cm core area, (2) culture spheres for more than 2 weeks, and (3) allow the retrieval of spheres. Using the presented platform, we have successfully characterized the different responses in 2D and 3D cell culture to PDT. Furthermore, we investigated the treatment resistance effect in cancer cells induced by tumor associated fibroblasts (CAF). Although the CAFs can enhance the resistance to traditional chemotherapy agents, no significant difference in PDT was observed. The preliminary results suggest that the PDT can be an attractive alternative cancer therapy, which is less affected by the therapeutic resistance induced by cancer associated cells.

A method to investigate the anti-metabolic activity of anti-cancer agents on ovarian cancer cells cultured in a 96-well high throughput format.

BackgroundAn early step of advanced ovarian cancer begins when floating cancerous cells as single cells or small clusters grow on the peritoneal surface. This surface is rich in extracellular matrix (ECM) proteins, which have profound effects on cellular behaviour and can facilitate cancer progression. Subsequently, this ECM may alter cellular metabolism making cancer cells susceptible to chemotherapeutic agents differently. Therefore, generating a cell culture tool in vitro that includes the interaction between ECM and cancer cells will facilitate our understanding of how cancer cells behave during cancer treatment. There is some evidence to suggest that in an in vitro model that includes ECM components such as collagens will provide a better predictive tool for drug evaluation than a traditional cell monolayer (2D) culture model.FindingsAs a proof -of- concept, we made a collagen gel in a 96-well plate format and utilised this to evaluate the efficacy of clinical cytotoxic drugs, a targeted drug, and food compounds in single and combination treatments. The primary endpoints were to measure the reduction of cellular metabolism and secretion of vascular endothelial growth factor (VEGF). The invasive capacity of cancer cells was observed in collagen gels and it was cell line-dependent. The responses to drugs were prominently observed in collagen gels, but they had little effect on 2D cell monolayers. These responses were cell line- and type of drug-dependent.ConclusionsThe collagen gel in a 96 well plate format was easy to set up and could have potential to identify drug sensitivity in the clinical management of women with platinum resistant ovarian cancer.

Cell-Based High-Throughput Screening for Aromatase Inhibitors in the Tox21 10K Library.

Multiple mechanisms exist for endocrine disruption; one nonreceptor-mediated mechanism is via effects on aromatase, an enzyme critical for maintaining the normal invivo balance of androgens and estrogens. We adapted the AroER tri-screen 96-well assay to 1536-well format to identify potential aromatase inhibitors (AIs) in the U.S. Tox21 10K compound library. In this assay, screening with compound alone identifies estrogen receptor alpha (ERα) agonists, screening in the presence of testosterone (T) identifies AIs and/or ERα antagonists, and screening in the presence of 17β-estradiol (E2) identifies ERα antagonists. Screening the Tox-21 library in the presence of T resulted in finding 302 potential AIs. These compounds, along with 31 known AI actives and inactives, were rescreened using all 3 assay formats. Of the 333 compounds tested, 113 (34%; 63 actives, 50 marginal actives) were considered to be potential AIs independent of cytotoxicity and ER antagonism activity. Structure-activity analysis suggested the presence of both conventional (eg, 1, 2, 4, - triazole class) and novel AI structures. Due to their novel structures, 14 of the 63 potential AI actives, including both drugs and fungicides, were selected for confirmation in the biochemical tritiated water-release aromatase assay. Ten compounds were active in the assay; the remaining 4 were only active in high-throughput screen assay, but with low efficacy. To further characterize these 10 novel AIs, we investigated their binding characteristics. The AroER tri-screen, in high-throughput format, accurately and efficiently identified chemicals in a large and diverse chemical library that selectively interact with aromatase.

Development of a fluorescence anisotropy-based assay for Dop, the first enzyme in the pupylation pathway

The Pup-proteasome system (PPS) carries out regulated tagging and degradation of proteins in bacterial species belonging to the phyla Actinobacteria and Nitrospira. In the pathogen Mycobacterium tuberculosis, where this proteolytic pathway was initially discovered, PPS enzymes are essential for full virulence and persistence in the mammalian host. As such, PPS enzymes are potential targets for development of antituberculosis therapeutics. Such development often requires sensitive and robust assays for measurements of enzymatic activities and the effect of examined inhibitors. Here, we describe the development of an in vitro activity assay for Dop, the first enzyme in the PPS. Based on fluorescence anisotropy measurements, this assay is simple, sensitive, and compatible with a high-throughput format for screening purposes. We demonstrate how this assay can also be reliably and conveniently used for detailed kinetic measurements of Dop activity. As such, this assay is of value for basic research into Dop and the PPS. Finally, we show that the assay developed here primarily for the mycobacterial Dop can be readily employed with other Dop enzymes, using the same simple protocol.

Frequency detection of imidacloprid resistance allele in Aphis gossypii field populations by real-time PCR amplification of specific-allele (rtPASA)

The Aphis gossypii Glover (Hemiptera: Aphididae) is one of the most serious pests worldwide, and imidacloprid has been widely used to control this insect pest. Just like other classes of insecticides, the resistance to imidacloprid has been found in A. gossypii. An amino acid mutation (R81T) in the nicotinic acetylcholine receptor (nAChR) beta1 subunit was detected in the imidacloprid-resistant A. gossypii collected from Langfang (LF) and Dezhou (DZ) cities. To estimate the R81T mutation frequency of A. gossypii field populations, a simple, rapid and accurate rtPASA (real-time PCR amplification of specific allele) protocol was developed. The performance of the rtPASA protocol was evaluated by comparing with the data generated by a cPASA (competitive PCR amplification of specific allele) method from 50 individual genotypes. The R81T allele frequencies of the LF population (34.7%±1.3%) and DZ population (45.2%±5.2%) estimated by the rtPASA protocol matched the frequencies (LF 38.1%, DZ 48.2%) deduced by the cPASA method in specimens. The results indicated that the rtPASA format was applicable for the detection of mutation associated with imidacloprid resistance and will allow rapid and efficient monitoring of A. gossypii resistance in field populations in a high throughput format.

High-throughput process development of purification alternatives for the protein avidin.

With an increased number of applications in the field of the avidin-biotin technology, the resulting demand for highly-purified protein avidin has drawn our attention to the purification process of avidin that naturally occurs in chicken egg white. The high-throughput process development (HTPD) methodology was exploited, in order to evaluate purification process alternatives to commonly used ion-exchange chromatography. In a high-throughput format, process parameters for aqueous two-phase extraction, selective precipitation with salts and polyethylene glycol, and hydrophobic interaction and mixed-mode column chromatography experiments were performed. The HTPD strategy was complemented by a high-throughput tandem high-performance liquid chromatography assay for protein quantification. Suitable conditions for the separation of avidin from the major impurities ovalbumin, ovomucoid, ovotransferrin, and lysozyme were identified in the screening experiments. By combination of polyethylene glycol precipitation with subsequent resolubilization and separation in a polyethylene glycol/sulfate/sodium chloride two-phase system an avidin purity of 77% was obtained with a yield >90% while at the same time achieving a significant reduction of the process volume. The two-phase extraction and precipitation results were largely confirmed in larger scale with scale-up factors of 230 and 133, respectively. Seamless processing of the avidin enriched bottom phase was found feasible by using mixed-mode chromatography. By gradient elution a final avidin purity of at least 97% and yield >90% was obtained in the elution pool. The presented identification of a new and beneficial alternative for the purification of the high value protein thus represents a successful implementation of HTPD for an industrially relevant purification task.

High-throughput screening system for inhibitors of human Heat Shock Factor 2.

Development of novel anti-cancer drug leads that target regulators of protein homeostasis is a formidable task in modern pharmacology. Finding specific inhibitors of human Heat Shock Factor 1 (hHSF1) has proven to be a challenging task, while screening for inhibitors of human Heat Shock Factor 2 (hHSF2) has never been described. We report the development of a novel system based on an in vivo cell growth restoration assay designed to identify specific inhibitors of human HSF2 in a high-throughput format. This system utilizes a humanized yeast strain in which the master regulator of molecular chaperone genes, yeast HSF, has been replaced with hHSF2 with no detrimental effect on cell growth. This replacement preserves the general regulatory patterns of genes encoding major molecular chaperones including Hsp70 and Hsp90. The controlled overexpression of hHSF2 creates a slow-growth phenotype, which is the basis of the growth restoration assay used for high-throughput screening. The phenotype is most robust when cells are cultured at 25 °C, while incubation at temperatures greater than 30 °C leads to compensation of the phenotype. Overexpression of hHSF2 causes overexpression of molecular chaperones which is a likely cause of the slowed growth. Our assay is characterized by two unique advantages. First, screening takes place in physiologically relevant, in vivo conditions. Second, hits in our screen will be of medically relevant potency, as compounds that completely inhibit hHSF2 function will further inhibit cell growth and therefore will not be scored as hits. This caveat biases our screening system for compounds capable of restoring hHSF2 activity to a physiologically normal level without completely inhibiting this essential system.