This work was funded by a grant from the Faculty Research Council to K.S.H. (Office of Research and Grants, Azusa Pacific University-USA). A.N.G. and J.F.M. are recipients of the Scholarly Undergraduate Research Experience (SURE) Fellowship. S.K.M. and B.M.R. are recipients of the STEM Research Fellowship Grants (Center for Research in Science, Azusa Pacific University-USA). We are grateful to Dr. Matthew Berezuk and Dr. Philip Cox for guidance on the bioassays.

NOTE: Several chemicals and biological reagents used in this protocol are toxic and carcinogenic. Consult relevant material safety data sheets (MSDS) prior to use. Use appropriate personal protective gears (Occupational Safety and Health Administration-approved safety goggles, proper gloves, lab coats, full-length pants, and closed-toe shoes) prior to starting the experiment. In addition, adopt appropriate safety practices when performing synthesis and handling toxic chemicals and reagents (fume hood).
1. Solid phase synthesis of spirocyclic heterocycles 6 and 7
NOTE: Synthesis was based on previously published work11,12. The updated protocol reveals that the tetrabutylammonium fluoride-catalyzed ring opening of the tricyclic heterocycle was not needed, and thus its elimination shortens the synthetic procedure.
<ol>
	<li>Perform Michael addition of furfurylamine to the REM linker (duration: 25 min setup + 24 h reaction time).
	<ol>
		<li>Add 1 g (1 equivalents [equiv.]) of REM resin, 20 mL (20 equiv.) of dimethylformamide (DMF), and 2.4 mL of furfurylamine to a 25 mL solid-phase reaction vessel. Agitate the reaction vessel at room temperature for 24 h following the reaction initiation. 
		NOTE: Ensure thorough mixing so that the resin does not sit at the bottom of the vessel.</li>
		<li>Wash the resin with DMF 1x after the reaction is complete. Then, wash 4x, alternating between dichloromethane (DCM) and methanol. Dry the resin thoroughly in the reaction vessel following washes.</li>
	</ol>
	</li>
	<li>Perform tandem Michael addition/1,3-dipolar cycloaddition (duration: 25 min setup + 48 h reaction time).
	<ol>
		<li>To the dry resin, add 1.48 mL (5 equiv.) of triethylamine (TEA), 0.637 g (2 equiv.) of nitro-olefin, and 10 mL of dry toluene to the reaction vessel.</li>
		<li>Then, add 1.085 mL (4 equiv.) of trimethylsilyl chloride (TMSCl) to the reaction vessel in a well-ventilated fume hood. 
		NOTE: As this reaction produces HCl gas, do not cap the reaction vessel until the gas has been released under a fume hood.</li>
		<li>Securely cap the reaction vessel, and agitate at room temperature for 48 h. 
		NOTE: Ensure thorough mixing of the resin with the reagents.</li>
		<li>Use 5 mL of methanol to quench the reaction.</li>
		<li>Drain the vessel to remove the solution, and then wash 4x, alternating between DCM and methanol. Dry the resin thoroughly in the reaction vessel following washes.</li>
	</ol>
	</li>
	<li>Perform N-alkylation of the resin-bound heterocycle to form the quaternary amine (duration: 10 min setup + 24 h reaction time).
	<ol>
		<li>To the dry resin in the reaction vessel, add 5 mL of DMF and 10 equiv. of alkyl halide, and agitate at room temperature for 24 h. 
		NOTE: Ensure thorough mixing of the reagents with the resin.</li>
		<li>Wash the resin with DMF 1x after the reaction is complete. Then, use DCM and methanol alternately to wash 4x. Dry the resin in the reaction vessel following washes.</li>
	</ol>
	</li>
	<li>Perform &#946;-elimination of the quaternary amine for cleavage from the polymer support (duration: 15 min setup + 24 h reaction time).
	<ol>
		<li>To the dry resin in the reaction vessel, add 3 mL of DCM and 1.49 mL (5 equiv.) of TEA to cleave the heterocycle from the polymer support.</li>
		<li>Agitate the reaction mixture for 24 h to ensure thorough mixing of the resin with the solution. Wash 4x, alternating between DCM and methanol. Collect the elution from all the washes, and concentrate via rotatory evaporation.</li>
		<li>Triturate with methanol to purify the spirocyclic oxime. Dry the resin thoroughly in the reaction vessel following washes for reuse in future experiments.</li>
	</ol>
	</li>
</ol>
2. Cytotoxicity assay using MTT 14
<ol>
	<li>Prepare 20 mL of a 5 mg/mL MTT solution using sterile phosphate-buffered saline (PBS, 0.9% NaCl in water) as the diluent. Filter and store at -20 &#176;C. Then, prepare a 1:1 dilution of the MTT solution from step 2.1 in serum-free cell culture medium (DMEM).</li>
	<li>Prepare 1 mL each of stock solutions in 1.5 mL microcentrifuge tubes of 100 mM, 10 mM, 1 mM, 100 &#181;M, 10 &#181;M, 1 &#181;M, 0.1 &#181;M, and 0.01 &#181;M of test compounds in dimethyl sulfoxide (DMSO). Store at -20 &#176;C. Prepare 200 &#181;L per dose of the working solutions of test compounds by diluting stock concentrations 1:1000 in serum-free medium in 1.5 mL tubes.</li>
	<li>In the tissue culture hood, seed COS-7 cells (African green monkey kidney cells, Cercopithecus aethiops kidney) in complete medium [DMEM with 10% fetal bovine serum (FBS)] onto flat-bottom, tissue-culture-treated 96-well plates at a concentration of 4 &#215; 103 cells/200 &#181;L per well using a multi-channel pipettor. COS-7 cells were chosen because (1) these are commonly used cells for cytotoxicity assays and (2) these were already available in the institution.</li>
	<li>Incubate COS-7 cells for 24 h at 37 &#176;C in an atmosphere containing 5% CO2.</li>
	<li>Aspirate the supernatant from the wells using a glass Pasteur pipette attached to a vacuum pump. Dose the cells in triplicate with the test compounds using the working solutions prepared in step 2.2 (See Table 1). Incubate cells as described in step 2.4.</li>
	<li>Aspirate the supernatant from the wells. Add 200 &#181;L of MTT solution to each well. Incubate at 37 &#176;C in an atmosphere containing 5% CO2 for 4 h.</li>
	<li>Gently aspirate the supernatant from the wells without disturbing the purple formazan crystals. Add 200 &#181;L of DMSO to each well to dissolve the purple formazan crystals. Incubate at room temperature for 15 min.</li>
	<li>Measure absorbance at 590 nm14 or 600 nm for each well using a 96-well plate reader. Use wells with no cells as background and average the absorbance value. Subtract the averaged absorbance background value from the absorbance value of each treated well. Normalize the data as a percentage of the average zero dosage value (average the three zero-dose values). Plot data on the y-axis: linear (% relative cell viability); x-axis: log (concentration). Plot each series as an individual curve (e.g., triplicate data should have 3 curves)</li>
</ol>

<ol>
	<li>Shangary, S., Wang, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Small-molecule+inhibitors+of+the+MDM2-p53+protein-protein+interaction+to+reactivate+p53+function:+a+novel+approach+for+cancer+therapy.">Small-molecule inhibitors of the MDM2-p53 protein-protein interaction to reactivate p53 function: a novel approach for cancer therapy.</a> Annual Review of Pharmacology and Toxicology. 49, 223-241 (2009).</li><li>Zhao, Y., Aguilar, A., Bernard, D., Wang, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Small-molecule+inhibitors+of+the+MDM2-p53+protein-protein+interaction+(MDM2+inhibitors)+in+clinical+trials+for+cancer+treatment.">Small-molecule inhibitors of the MDM2-p53 protein-protein interaction (MDM2 inhibitors) in clinical trials for cancer treatment.</a> Journal of Medicinal Chemistry. 58 (3), 1038-1052 (2015).</li><li>Paolo, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+effective+virtual+screening+protocol+to+identify+promising+p53-MDM2+inhibitors.">An effective virtual screening protocol to identify promising p53-MDM2 inhibitors.</a> Journal of Chemical Information and Modeling. 56 (6), 1216-1227 (2016).</li><li>Shieh, S. Y., Ikeda, M., Taya, Y., Prives, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+damage-induced+phosphorylation+of+p53+alleviates+inhibition+by+MDM2.">DNA damage-induced phosphorylation of p53 alleviates inhibition by MDM2.</a> Cell. 91 (3), 325-334 (1997).</li><li>Hwang, B. J., Ford, J. M., Hanawalt, P. C., Chu, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+the+p48+xeroderma+pigmentosum+gene+is+p53+dependent+and+is+involved+in+global+genomic+repair.">Expression of the p48 xeroderma pigmentosum gene is p53 dependent and is involved in global genomic repair.</a> Proceedings of the National Academy of Sciences of the United States of America. 96 (2), 424-428 (1999).</li><li>Oliner, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oncoprotein+MDM2+conceals+the+activation+domain+of+tumor+suppressor+p53.">Oncoprotein MDM2 conceals the activation domain of tumor suppressor p53.</a> Nature. 362, 857-860 (1993).</li><li>Nag, S., Qin, J., Srivenugopal, K. S., Wang, M., Zhang, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+MDM2-p53+pathway+revisited.">The MDM2-p53 pathway revisited.</a> Journal of Biomedical Research. 27 (4), 254-271 (2013).</li><li>Bond, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single+nucleotide+polymorphism+in+the+MDM2+promoter+attenuates+the+p53+tumor+suppressor+pathway+and+accelerates+tumor+formation+in+humans.">A single nucleotide polymorphism in the MDM2 promoter attenuates the p53 tumor suppressor pathway and accelerates tumor formation in humans.</a> Cell. 119 (5), 591-602 (2004).</li><li>Isobe, M., Emanuel, B. S., Givol, D., Oren, M., Croce, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+gene+for+human+p53+tumor+antigen+to+band+17p13.">Localization of gene for human p53 tumor antigen to band 17p13.</a> Nature. 320 (6057), 84-85 (1986).</li><li>Gupta, A. K., Bharadwaj, M., Kumar, A., Mehrotra, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spiro-oxindoles+as+a+promising+class+of+small+molecules+inhibitors+of+p53-MDM2+interaction+useful+in+targeted+cancer+therapy.">Spiro-oxindoles as a promising class of small molecules inhibitors of p53-MDM2 interaction useful in targeted cancer therapy.</a> Topics in Current Chemistry. 375 (1), 1-25 (2017).</li><li>Griffin, S. A., Drisko, C. R., Huang, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tricyclic+heterocycles+as+precursors+to+functionalized+spirocyclic+oximes.">Tricyclic heterocycles as precursors to functionalized spirocyclic oximes.</a> Tetrahedron Letters. 58, 4551-4553 (2017).</li><li>Drisko, C. R., Griffin, S. A., Huang, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solid-phase+synthesis+of+[4.4]spirocyclic+oximes.">Solid-phase synthesis of [4.4]spirocyclic oximes.</a> Journal of Visualized Experiments. (144), e58508 (2019).</li><li>Lawrence, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Linked+parallel+synthesis+and+MTT+bioassay+screening+of+substituted+chalcones.">Linked parallel synthesis and MTT bioassay screening of substituted chalcones.</a> Journal of Combinatorial Chemistry. 3 (5), 421-426 (2001).</li><li>. MTT assay protocol Available from: <a target="_blank" href="https://www.abcam.com/kits/mtt-assay-protocol">https://www.abcam.com/kits/mtt-assay-protocol</a> (2020)</li></ol>

The authors have nothing to disclose.

The synthesis of the spirocyclic compounds was based on previous research conducted by this laboratory, but with some modifications (Figure 1)11,12. The progress of each reaction step was monitored by IR spectroscopy. Michael addition of the REM linker&#160;1&#160;with furfurylamine afforded polymer-bound&#160;2&#160;(IR 1722 cm-1&#160;&#8594; 1731 cm-1). From the previous report, ISOC of&#160;2&#160;produced the tricyclic heterocyclic compound&#160;3, as confirmed by the detection of the TMS group (IR 1214 cm-1). This is a critical step of the synthesis as ISOC provided the necessary regio- and stereoselectivity of the products. A hydroxyl group stretching frequency of 3500 cm-1&#160;was observed instead of the frequency of the TMS functional group. This may be because the tricyclic compound is a transient intermediate that leads to the spirocyclic system.
Different types of REM resin were found to limit the synthesis. High-loading polymer (1.00 mmol/g) prevented the synthesis of spirocyclic compounds containing bulky R2&#160;side chains. Due to the similarities in the functional groups in resins&#160;4&#160;and&#160;5, the results of IR were inconclusive. The success of this step could only be determined by attempting to regenerate the REM linker (5&#160;&#8594;&#160;1). Regeneration did not occur in instances when a bulky R2&#160;group was added. Low-loading resins (0.5 mmol/g or lower) are recommended for successful synthesis. This synthesis method is consistent with procedures described in the literature.
As a preliminary test, a protocol was developed for a cytotoxicity assay using MTT. Over the course of several trials, critical steps and limitations were discovered. For the results to be normalized across all wells, cells had to be evenly seeded across wells, necessitating the measurement of the cell concentration prior to seeding. The assay required plates with flat-bottomed wells, as the absorbance could not be accurately read from round-bottomed wells. Additionally, excess MTT that remained after incubation had to be removed to prevent interference in the readings without disturbing the insoluble formazan.
The absorbance of the dissolved formazan should be read at 590 nm. However, current instrumentation in the lab necessitated taking readings at 600 nm instead. Storage at 0 &#176;C was found to be important for the chemicals used in the assay (cisplatin, spirocyclic molecules, furfurylamine). DMSO-a chemical with known cytotoxicity-was used as the solvent for the test compounds and was used to make dilutions for the assay. The MTT reagent itself had to be prepared, as it was stored as a powder that needed to be dissolved and filtered, as insoluble particles interfered with readings.
Overall, the results for this assay are intended to be preliminary, as only a small number of molecules were tested. An exhaustive test with a battery of molecules is planned, and a full manuscript will be forthcoming. In addition, the synthesis might be applicable for amines derived from pyrrole-2-carbaldehyde. In this case, spirocyclic pyrrolidines can be synthesized and tested for cytotoxic effects on cancer cell lines.

Small-molecule inhibition of the interaction of E3 ubiquitin-ligase mouse double minute 2 homolog (MDM2) with p53 is known to restore p53-mediated induction of tumor cell apoptosis1,2,3. MDM2 is a negative regulator of the p53 pathway and is often overexpressed in cancer cells4,5,6,7,8,9. Recent crystallographic and biochemical studies have revealed that small molecules containing a spirocyclic framework can effectively inhibit MDM2-p53 interactions10. The spirocyclic framework (Figure 1, shaded in blue) is considered a privileged motif as derivatization of this rigid orthogonal ring system has led to the discovery of novel therapeutic drugs. Accessing this interesting architecture poses a challenge when using traditional organic synthesis techniques. Although the therapeutic effects of spirocyclic molecules in biological systems have been investigated, synthesis of these molecules is still a cumbersome process. Unwanted side products, using harsh conditions, and hazardous transition metals are often problematic.
The potential use of the spirocyclic motif in drug development led to the development of a protocol utilizing solid-phase synthesis to generate a library of molecules with the motif in addition to other interchangeable functional groups11,12. The separation of products and reactants between steps could be achieved by simply utilizing an REM linker attached to a resin bead and a solid-phase filter vessel. This would cut down steps and potentially increase yields. This synthetic approach could produce a large array of potential drug candidates. However, the effectiveness of these molecules in a biological system would require further investigation.
To determine the cytotoxicity of these spirocyclic compounds, the MTT assay13,14 was employed. This method measures cell viability and can be used to indirectly determine cell cytotoxicity. Different concentrations of the inhibitors were added to cultured cells in a 96-well plate, and the proportion of living cells was measured by colorimetric analysis of the extent of reduction of yellow MTT by mitochondrial dehydrogenases to the purple formazan compound (Figure 2). The activity is most often reported as an IC50 value-the concentration at which cell growth is inhibited by 50% relative to an untreated control. This paper describes the protocol for the MTT assay and the preliminary results of these novel spirocyclic molecules.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>CELLS</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>COS-7 cells (ATCC CRL-1651)</td>
			<td>ATCC</td>
			<td>CRL-1651</td>
			<td>African green monkey kidney cells</td>
		</tr>
		<tr>
			<td>CHEMICALS</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1-Bromooctane</td>
			<td>Sigma-Aldrich</td>
			<td>152951</td>
			<td>Alkyl-halide</td>
		</tr>
		<tr>
			<td>Allylbromide</td>
			<td>Sigma-Aldrich</td>
			<td>337528</td>
			<td>Alkyl-halide</td>
		</tr>
		<tr>
			<td>Benzylbromide</td>
			<td>Sigma-Aldrich</td>
			<td>B17905</td>
			<td>Alkyl-halide</td>
		</tr>
		<tr>
			<td>Cisplatin</td>
			<td>Cayman Chemical</td>
			<td>13119</td>
			<td>Cytotoxicity control</td>
		</tr>
		<tr>
			<td>Dichloromethane (DCM)</td>
			<td>Sigma-Aldrich</td>
			<td>270997</td>
			<td>Solvent</td>
		</tr>
		<tr>
			<td>Dimethylformamide (DMF)</td>
			<td>Sigma-Aldrich</td>
			<td>227056</td>
			<td>Solvent</td>
		</tr>
		<tr>
			<td>Dimethylsulfoxide (DMSO)</td>
			<td>Sigma-Aldrich</td>
			<td>276855</td>
			<td>Solvent</td>
		</tr>
		<tr>
			<td>DMEM, high glucose, with L-glutamine</td>
			<td>Genesee Scientific</td>
			<td>25-500</td>
			<td>Cell culture media</td>
		</tr>
		<tr>
			<td>FBS (Fetal bovine serum)</td>
			<td>Sigma-Aldrich</td>
			<td>F4135</td>
			<td>Cell culture media</td>
		</tr>
		<tr>
			<td>Furfurylamine</td>
			<td>Acros Organics</td>
			<td>119800050</td>
			<td>reagent&#160;</td>
		</tr>
		<tr>
			<td>Iodomethane</td>
			<td>Sigma-Aldrich</td>
			<td>289566</td>
			<td>Alkyl-halide</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Sigma-Aldrich</td>
			<td>34860</td>
			<td>Solvent</td>
		</tr>
		<tr>
			<td>MTT ((3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide)</td>
			<td>EMD Millipore</td>
			<td>Calbiochem 475989-1GM</td>
			<td>Reagent</td>
		</tr>
		<tr>
			<td>Phosphate-buffered Saline (PBS)</td>
			<td>Genesee Scientific</td>
			<td>25-507</td>
			<td>Cell culture media</td>
		</tr>
		<tr>
			<td>REM Resin</td>
			<td>Nova Biochem</td>
			<td>8551010005</td>
			<td>Polymer support; 0.500 mmol/g loading</td>
		</tr>
		<tr>
			<td>trans-&#946;-nitrostyrene</td>
			<td>Sigma-Aldrich</td>
			<td>N26806</td>
			<td>Nitro-olefin reagent</td>
		</tr>
		<tr>
			<td>Toluene</td>
			<td>Sigma-Aldrich</td>
			<td>244511</td>
			<td>Solvent</td>
		</tr>
		<tr>
			<td>Triethylamine (TEA)</td>
			<td>Sigma-Aldrich</td>
			<td>T0886</td>
			<td>Reagent for beta-elimination</td>
		</tr>
		<tr>
			<td>Trimethylsilyl chloride (TMSCl)</td>
			<td>Sigma-Aldrich</td>
			<td>386529</td>
			<td>Reagent; CAUTION - highly volatile; creates HCl gas</td>
		</tr>
		<tr>
			<td>GLASSWARE/INSTRUMENTATION</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>25 mL solid-phase reaction vessel</td>
			<td>Chemglass</td>
			<td>CG-1861-02</td>
			<td>Glassware with filter</td>
		</tr>
		<tr>
			<td>96 Well plate reader</td>
			<td>Promega (Turner Biosystems)</td>
			<td>9310-011</td>
			<td>Instrument</td>
		</tr>
		<tr>
			<td>AVANCE III NMR Spectrometer</td>
			<td>Bruker</td>
			<td>N/A</td>
			<td>Instrument; 300 MHz; Solvents: CDCl3 and CD3OH</td>
		</tr>
		<tr>
			<td>Thermo Scientific Nicole iS5</td>
			<td>Thermo Scientific</td>
			<td>IQLAADGAAGFAHDMAZA</td>
			<td>Instrument</td>
		</tr>
		<tr>
			<td>Wrist-Action Shaker</td>
			<td>Burrell Scientific</td>
			<td>757950819</td>
			<td>Instrument</td>
		</tr>
	</tbody>
</table>

functionalized spirocyclic heterocycle synthesis and cytotoxicity assay

Spirocyclic heterocycles have recently been reported in literature to be potential drugs for cancer therapy. The synthesis of these novel orthogonal ring systems is challenging. An efficient methodology to synthesize these compounds was recently published that described the solid phase synthesis in four steps rather than the previously reported five steps. The advantage of this shorter synthesis is the elimination of the use of toxic reagents. Low-loading Regenerating Michael (REM) linker-based resin was found to be crucial in the synthesis as high-loading versions prevented the addition of reagents containing bulky phenyl and aromatic side chains. The colorimetric 3-(4&#8242;,5&#8242;-dimethylthiazol-2&#8242;-yl)-2,5- diphenyltetrazolium bromide (MTT) assay was used to examine the cytotoxicity of micromolar concentrations of these novel spirocyclic molecules in vitro. MTT is readily available commercially and produces relatively fast, reliable results, making this assay ideal for these spirocyclic heterocycles. Orthogonal ring structures as well as furfurylamine (a precursor in the synthesis method containing a similar 5-member ring motif) were tested.

Spirocyclic oximes 6 and 7 were synthesized using a modified protocol (Figure 1). Michael addition of furfurylamine to an REM linker 1b afforded polymer-bound resin 2. The progress of the reaction was monitored by infrared (IR) spectroscopy by detecting the disappearance of the &#945;,&#946;-unsaturated ester at 1722 cm-1&#160;(Figure 3). Spirocyclic-bound resin 4 was formed from 2 via a transient intermediate 3. Methanolic hydrolysis of 4 produced 3-[(3E)-(2S, 4R)-2-phenyl-3-hydroxyimino 4-hydroxymethyl-pyrrolidin-1-yl]-propionic acid methyl ester 7, while alkylation followed by &#946;-elimination afforded (3E)-(2S, 4R)-4-hydroxymethyl-1-methyl-2-phenyl-3-pyrrolidine oxime 6. The identity of the spirocyclic oximes was determined by&#160;1H and&#160;13C nuclear magnetic resonance spectroscopic analysis and the purity by mass spectroscopy based on our previous results11.
The MTT assay is a well-known colorimetric assay for determining cell viability12. As seen in&#160;Figure 2, mitochondrial reductases present in living cells convert the yellow tetrazolium of MTT to an insoluble purple formazan solid. Using a spectrophotometer, the formazan formation is quantified by measuring the absorbance at 600 nm. Cisplatin, which is known to induce cell death at high concentrations, was used as a positive control (Figure 4). As expected, the higher the concentration of cisplatin, the lower&#160;the cell viability. Next, the MTT assay was used to test the spirocyclic compounds 6 and 7 and furfurylamine. Furfurylamine was used to determine the effect of the furan ring alone compared to the spirocyclic framework. As depicted in&#160;Figure 5, furfurylamine and spirocyclic oxime 6 showed similar cytotoxicity. However, the toxicity of spirocyclic compound 7 was noticeably greater than that of furfurylamine and 6. A library of spirocyclic oximes will be synthesized to fully investigate the cytotoxicity as well as the other anticancer effects of these heterocycles.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61950/61950fig1.jpg" /> 
Figure 1: Construction of spirocyclic compounds using an updated solid phase synthesis. The orthogonal spirocycic framework is shaded in blue. Note that step (c) is not needed, which avoids using the toxic reagent TBAF. The reaction conditions are as follows: (a) furfurylamine, DMF, (b) &#946;-nitrostyrene, TMSCl, TEA, toluene, (c) TBAF, (d) alkyl halide, DMF, and (e) TEA, DCM. Abbreviations: TBAF = tetrabutylammonium fluoride; DMF = dimethylformamide; TMSCl = trimethylsilyl chloride; TEA = triethylamine; DCM = dichloromethane; ISOC = intramolecular silyoxy olefin cycloaddition. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61950/61950fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61950/61950fig2.jpg" /> 
Figure 2: Mechanism of the MTT assay. Visibly yellow tetrazolium salt of MTT is reduced by mitochondrial reductases in living COS-7 cells to form purple insoluble formazan. Abbreviation: MTT = 3-(4&#8242;,5&#8242;-dimethylthiazol-2&#8242;-yl)-2,5- diphenyltetrazolium bromide. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61950/61950fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61950/61950fig3.jpg" /> 
Figure 3: Monitoring the progress of each solid phase reaction step by infrared spectroscopy. The stretching frequency at 1717 cm-1&#160;indicated the presence of an unsaturated ester, 1733 cm-1&#160;depicted a saturated ester, and signal around 3300-3500 cm-1&#160;indicated the presence of a hydroxyl group. Detectable stretching frequencies for polystyrene are also shown. Abbreviations: REM = Regenerating Michael; ISOC = intramolecular silyoxy olefin cycloaddition. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61950/61950fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61950/61950fig4.jpg" /> 
Figure 4: Effects of cisplatin on COS-7 cell viability in a modified MTT assay. Concentrations of cisplatin ranged from 0 &#181;M to 60 &#181;M. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61950/61950fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61950/61950fig5.jpg" /> 
Figure 5: Effects of test compounds on COS-7 cell viability in a modified MTT assay. Concentrations ranged from 0 &#181;M to 100 &#181;M and were plotted on a log scale. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61950/61950fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Table 1" src="/files/ftp_upload/61950/61950table1.jpg" /> 
Table 1: Layout of the 96-well plate. All test data rows were in triplicate. Wells containing only COS-7 cells and medium were used as controls. To ensure that DMSO was not the cause of cytotoxicity in the cisplatin-dosed cells, wells containing only DMSO were used as solvent controls. Wells containing COS-7 cells are highlighted. Abbreviations: DMSO = dimethylsulfoxide; PBS = phosphate-buffered saline. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61950/61950table1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Functionalized Spirocyclic Heterocycle Synthesis and Cytotoxicity Assay at JoVE.com

Functionalized Spirocyclic Heterocycle Synthesis and Cytotoxicity Assay

Here, we describe a bioassay using 3-(4&#8242;,5&#8242;-dimethylthiazol-2&#8242;-yl)-2,5- diphenyltetrazolium bromide (MTT) to test previously synthesized spirocyclic oximes.

Spirocyclic heterocycles have recently been reported in literature to be potential drugs for cancer therapy. The synthesis of these novel orthogonal ring ...

functionalized-spirocyclic-heterocycle-synthesis-cytotoxicity

Nanyang Technological University

Research

JoVE Journal

Biology

1.4K Views.  Azusa Pacific University. Here, we describe a bioassay using 3-(4′,5′-dimethylthiazol-2′-yl)-2,5- diphenyltetrazolium bromide (MTT) to test previously synthesized spirocyclic oximes.

Video: Functionalized Spirocyclic Heterocycle Synthesis and Cytotoxicity Assay

Optimization of the Ugi Reaction Using Parallel Synthesis and Automated Liquid Handling

The optimization of a Ugi reaction involving the mixing of furfurylamine, benzaldehyde, boc-glycine and t-butylisocyanide is described. Triplicate runs of 48 parallel experiments are reported, varying concentration, solvent and the excess of some of the reagents. The isolation of the product was achieved by a simple filtration and wash procedure. The highest yield obtained was 66% from 0.4 M methanol with 1.2 eq. of imine. This is significantly above the 49% yield obtained from the initial reaction under equimolar concentration at 0.4 M in methanol. Methanol solutions with reagent concentrations of 0.4M or 0.2M gave superior yields while all solvent systems at 0.07M performed poorly. At 0.2M, methanol and ethanol/methanol (60/40) mixtures were statistically equally good while THF/methanol (60/40) was poor and acetonitrile/methanol (60/40) was intermediate. Good reproducibility of the precipitate yields was obtained in these replicate experiments, allowing for subtle interaction effects to be positively identified.

The Ugi reaction has proved to be a convenient way to quickly create diverse libraries of compounds. It involves the reaction of an amine, an aldehyde, a carboxylic acid and an isonitrile typically in methanol at room temperature. In this video, we utilize a 48-slot Mettler-Toledo MiniBlock equipped with filtration tubes and a Mettler-Toledo MiniMapper automated liquid handler was used to deliver the reagents and solvent. The parameters of interest were the concentration, the solvent composition and the excess of some of the reagents.

The optimization of a Ugi reaction involving the mixing of furfurylamine, benzaldehyde, boc-glycine and t-butylisocyanide is described.  Triplicate runs ...

RNA Isolation from Embryonic Zebrafish and cDNA Synthesis for Gene Expression Analysis

Many important and complex laboratory procedures require an input of high quality, intact RNA.  A degraded sample or the presence of impurities can lead to disastrous results in downstream experimental applications.  It is therefore, of utmost importance to use solid techniques with numerous safeguards and quality control checks to ensure a superior sample.  Herein, we detail a protocol to isolate total RNA from whole zebrafish embryos using a commercially available chemical denaturant and subsequent cleanup to remove traces of DNA and impurities using a commercial RNA isolation kit. As RNA is relatively unstable and easily prone to cleavage by RNAses, most protocols assay gene expression using a cDNA product that is directly synthesized from an RNA template. We detail a procedure to convert RNA into the more stable cDNA product using a commercially available kit. Throughout these procedures there are numerous quality control checks to ensure that the sample is not degraded or contaminated.  The end product of these protocols is cDNA that is suitable for microarray analysis, RT-PCR or long-term storage.    

The isolation of high quality, intact RNA is an essential step in many laboratory protocols. Here, we demonstrate RNA extraction from whole zebrafish embryos and cDNA synthesis for subsequent application in various experimental procedures including gene expression microarray analysis.

Many important and complex laboratory procedures require an input of high quality, intact RNA.  A degraded sample or the presence of impurities can lead ...

Synthesis and Calibration of Phosphorescent Nanoprobes for Oxygen Imaging in Biological Systems

Oxygen measurement by phosphorescence quenching [1, 2] consists of the following steps: 1) the probe is delivered into the medium of interest (e.g. blood or interstitial fluid); 2) the object is illuminated with light of appropriate wavelength in order to excite the probe into its triplet state; 3) the emitted phosphorescence is collected, and its time course is analyzed to yield the phosphorescence lifetime, which is converted into the oxygen concentration (or partial pressure, pO2). The probe must not interact with the biological environment and in some cases to be 4) excreted from the medium upon the measurement completion. Each of these steps imposes requirements on the molecular design of the phosphorescent probes, which constitute the only invasive component of the measurement protocol. Here we review the design of dendritic phosphorescent nanosensors for oxygen measurements in biological systems. The probes consist of Pt or Pd porphyrin-based polyarylglycine (AG) dendrimers, modified peripherally with polyethylene glycol (PEG's) residues. For effective two-photon excitation, termini of the dendrimers may be modified with two-photon antenna chromophores, which capture the excitation energy and channel it to the triplet cores of the probes via intramolecular FRET (F&ouml;rster Resonance Energy Transfer). We describe the key photophysical properties of the probes and present detailed calibration protocols.

We present principles of oxygen measurements by phosphorescence quenching and review design of porphyrin-based dendritic nanosensors for oxygen imaging in biological systems.

Oxygen measurement by phosphorescence quenching [1, 2] consists of the following steps: 1) the probe is delivered into the medium of interest (e.g. blood ...

Microwave-assisted One-pot Synthesis of N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB)

Biomolecules, including peptides,1-9 proteins,10,11 and antibodies and their engineered fragments,12-14 are gaining importance as both potential therapeutics and molecular imaging agents. Notably, when labeled with positron-emitting radioisotopes (e.g., Cu-64, Ga-68, or F-18), they can be used as probes for targeted imaging of many physiological and pathological processes.15-18 Therefore, significant effort has devoted to the synthesis and exploration of 18F-labeled biomolecules. Although there are elegant examples of the direct 18F-labeling of peptides,19-22 the harsh reaction conditions (i.e., organic solvent, extreme pH, high temperature) associated with direct radiofluorination are usually incompatible with fragile protein samples. To date, therefore, the incorporation of radiolabeled prosthetic groups into biomolecules remains the method of choice.23,24
N-Succinimidyl-4-[18F]fluorobenzoate ([18F]SFB),25-37 a Bolton-Hunter type reagent that reacts with the primary amino groups of biomolecules, is a very versatile prosthetic group for the 18F-labeling of a wide spectrum of biological entities, in terms of its evident in vivo stability and high radiolabeling yield. After labeling with [18F]SFB, the resulting [18F]fluorobenzoylated biomolecules could be explored as potential PET tracers for in vivo imaging studies.1 Most [18F]SFB radiosyntheses described in the current literatures require two or even three reactors and multiple purifications by using either solid phase extraction (SPE) or high-performance liquid chromatography (HPLC). Such lengthy processes hamper its routine production and widespread applications in the radiolabeling of biomolecules. Although several module-assisted [18F]SFB syntheses have been reported,29-32, 41-42 they are mainly based on complicated and lengthy procedures using costly commercially-available radiochemistry boxes (Table 1). Therefore, further simplification of the radiosynthesis of [18F]SFB using a low-cost setup would be very beneficial for its adaption to an automated process.
Herein, we report a concise preparation of [18F]SFB, based on a simplified one-pot microwave-assisted synthesis (Figure 1). Our approach does not require purification between steps or any aqueous reagents. In addition, microwave irradiation, which has been used in the syntheses of several PET tracers,38-41 can gives higher RCYs and better selectivity than the corresponding thermal reactions or they provide similar yields in shorter reaction times.38 Most importantly, when labeling biomolecules, the time saved could be diverted to subsequent bioconjugation or PET imaging step.28,43 The novelty of our improved [18F]SFB synthesis is two-fold: (1) the anhydrous deprotection strategy requires no purification of intermediate(s) between each step and (2) the microwave-assisted radiochemical transformations enable the rapid, reliable production of [18F]SFB.

Microwave-assisted One-pot Synthesis of N-succinimidyl-4-[18F]fluorobenzoate [18F]SFB

A facile, one-pot synthesis of N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) was developed based on a non-aqueous, three-step radiochemical process. Using microwave heating, the entire procedure can be completed in less than 30 min, or 60 min with further purification by preparative HPLC. The decay-corrected radiochemical yields (RCYs) were 35-5% (n > 30).

Biomolecules, including peptides,1-9 proteins,10,11 and antibodies and their engineered fragments,12-14 are gaining importance as both potential ...

Synthesis of Nine-atom Deltahedral Zintl Ions of Germanium and their Functionalization with Organic Groups

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later.1,2 Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9n- (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry.3-6 Notable milestones are the oxidative coupling of Ge94- clusters to oligomers and infinite chains,7-19 their metallation,14-16,20-25 capping by transition-metal organometallic fragments,26-34 insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization,35-47 addition of main-group organometallic fragments as exo-bonded substituents,48-50 and functionalization with various organic residues by reactions with organic halides and alkynes.51-58 
This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge94- clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC&equiv;CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2]2-. For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2)2]&bull;en which were characterized by single-crystal X-ray diffraction. 
The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large.

We present the high-temperature synthesis of intermetallic precursors K4Ge9, their dissolution in ethylenediamine to form Ge94- deltahedral Zintl ions, and the reaction of the clusters with alkynes to form organo-Zintl ions. The latter are characterized by electrospray mass spectrometry in solutions and by single-crystal X-ray diffraction in the solid state.

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later.1,2 ...

Intracellular Refolding Assay

This protocol describes a method to measure the enzymatic activity of molecular chaperones in a cell-based system and the possible effects of compounds with inhibitory/stimulating activity. Molecular chaperones are proteins involved in regulation of protein folding1 and have a crucial role in promoting cell survival upon stress insults like heat shock2, nutrient starvation and exposure to chemicals/poisons3. For this reason chaperones are found to be involved in events like tumor development, chemioresistance of cancer cells4 as well as neurodegeneration5. Design of small molecules able to inhibit or stimulate the activity of these enzymes is therefore one of the most studied strategies for cancer therapy7 and neurodegenerative disorders9. The assay here described offers the possibility to measure the refolding activity of a particular molecular chaperone and to study the effect of compounds on its activity. In this method the gene of the molecular chaperone investigated is transfected together with an expression vector encoding for the firefly luciferase gene. It has been already described that denaturated firefly luciferase can be refolded by molecular chaperones10,11. As normalizing transfection control, a vector encoding for the renilla luciferase gene is transfected. All transfections described in this protocol are performed with X-treme Gene 11 (Roche) in HEK-293 cells. In the first step, protein synthesis is inhibited by treating the cells with cycloheximide. Thereafter protein unfolding is induced by heat shock at 45&deg;C for 30 minutes. Upon recovery at 37&deg;C, proteins are re-folded into their active conformation and the activity of the firefly luciferase is used as read-out: the more light will be produced, the more protein will have re-gained the original conformation. Non-heat shocked cells are set as reference (100% of refolded luciferase).

In this protocol a method to measure intracellular protein refolding after heat shock is described. This method can be used to study foldases like molecular chaperones and their co-factors or compounds able to influence their activity. Firefly luciferase activity is used as reporter to measure chaperone refolding activity.

This protocol describes a method to measure the enzymatic activity of molecular chaperones in a cell-based system and the possible effects of compounds ...

Solid Phase Synthesis of a Functionalized Bis-Peptide Using "Safety Catch" Methodology

In 1962, R.B. Merrifield published the first procedure using solid-phase peptide synthesis as a novel route to efficiently synthesize peptides. This technique quickly proved advantageous over its solution-phase predecessor in both time and labor. Improvements concerning the nature of solid support, the protecting groups employed and the coupling methods employed over the last five decades have only increased the usefulness of Merrifield's original system. Today, use of a Boc-based protection and base/nucleophile cleavable resin strategy or Fmoc-based protection and acidic cleavable resin strategy, pioneered by R.C. Sheppard, are most commonly used for the synthesis of peptides1.
Inspired by Merrifield's solid supported strategy, we have developed a Boc/tert-butyl solid-phase synthesis strategy for the assembly of functionalized bis-peptides2, which is described herein. The use of solid-phase synthesis compared to solution-phase methodology is not only advantageous in both time and labor as described by Merrifield1, but also allows greater ease in the synthesis of bis-peptide libraries. The synthesis that we demonstrate here incorporates a final cleavage stage that uses a two-step "safety catch" mechanism to release the functionalized bis-peptide from the resin by diketopiperazine formation.
Bis-peptides are rigid, spiro-ladder oligomers of bis-amino acids that are able to position functionality in a predictable and designable way, controlled by the type and stereochemistry of the monomeric units and the connectivity between each monomer. Each bis-amino acid is a stereochemically pure, cyclic scaffold that contains two amino acids (a carboxylic acid with an &alpha;-amine)3,4. Our laboratory is currently investigating the potential of functional bis-peptides across a wide variety of fields including catalysis, protein-protein interactions and nanomaterials.

The efficient solid-phase peptide synthesis of a functionalized bis-peptide trimer utilizing a "safety catch" cleavage procedure from HMBA resin is described.

In 1962, R.B. Merrifield published the first procedure using solid-phase peptide synthesis as a novel route to efficiently synthesize peptides. This ...

Autonomously Bioluminescent Mammalian Cells for Continuous and Real-time Monitoring of Cytotoxicity

Mammalian cell-based in vitro assays have been widely employed as alternatives to animal testing for toxicological studies but have been limited due to the high monetary and time costs of parallel sample preparation that are necessitated due to the destructive nature of firefly luciferase-based screening methods. This video describes the utilization of autonomously bioluminescent mammalian cells, which do not require the destructive addition of a luciferin substrate, as an inexpensive and facile method for monitoring the cytotoxic effects of a compound of interest. Mammalian cells stably expressing the full bacterial bioluminescence (luxCDABEfrp) gene cassette autonomously produce an optical signal that peaks at 490 nm without the addition of an expensive and possibly interfering luciferin substrate, excitation by an external energy source, or destruction of the sample that is traditionally performed during optical imaging procedures. This independence from external stimulation places the burden for maintaining the bioluminescent reaction solely on the cell, meaning that the resultant signal is only detected during active metabolism. This characteristic makes the lux-expressing cell line an excellent candidate for use as a biosentinel against cytotoxic effects because changes in bioluminescent production are indicative of adverse effects on cellular growth and metabolism. Similarly, the autonomous nature and lack of required sample destruction permits repeated imaging of the same sample in real-time throughout the period of toxicant exposure and can be performed across multiple samples using existing imaging equipment in an automated fashion.

Mammalian cells expressing the bacterial bioluminescence gene cassette (lux) produce light autonomously. The resulting bioluminescent dynamics upon chemical exposure have been demonstrated to reflect the treatment effects on cellular growth and metabolism, making these cells an inexpensive, continuous, real-time toxicity screening tool that can easily be adapted for high-throughput automation.

Mammalian  cell-based in vitro assays have been  widely employed as alternatives to animal testing for toxicological studies but  have been limited due to ...

Rapid Synthesis and Screening of Chemically Activated Transcription Factors with GFP-based Reporters

Synthetic biology aims to rationally design and build synthetic circuits with desired quantitative properties, as well as provide tools to interrogate the structure of native control circuits. In both cases, the ability to program gene expression in a rapid and tunable fashion, with no off-target effects, can be useful. We have constructed yeast strains containing the ACT1 promoter upstream of a URA3 cassette followed by the ligand-binding domain of the human estrogen receptor and VP16. By transforming this strain with a linear PCR product containing a DNA binding domain and selecting against the presence of URA3, a constitutively expressed artificial transcription factor (ATF) can be generated by homologous recombination. ATFs engineered in this fashion can activate a unique target gene in the presence of inducer, thereby eliminating both the off-target activation and nonphysiological growth conditions found with commonly used conditional gene expression systems. A simple method for the rapid construction of GFP reporter plasmids that respond specifically to a native or artificial transcription factor of interest is also provided.

This protocol describes an experimental procedure for the rapid construction of artificial transcription factors (ATFs) with cognate GFP reporters&#160;and quantification of the ATFs ability to stimulate GFP expression via flow cytometry.

Synthetic biology aims to rationally design and build synthetic circuits with desired quantitative properties, as well as provide tools to interrogate the ...

Analysis of Global RNA Synthesis at the Single Cell Level following Hypoxia

Hypoxia or lowering of the oxygen availability is involved in many physiological and pathological processes. At the molecular level, cells initiate a particular transcriptional program in order to mount an appropriate and coordinated cellular response. The cell possesses several oxygen sensor enzymes that require molecular oxygen as cofactor for their activity. These range from prolyl-hydroxylases to histone demethylases. The majority of studies analyzing cellular responses to hypoxia are based on cellular populations and average studies, and as such single cell analysis of hypoxic cells are seldom performed. Here we describe a method of analysis of global RNA synthesis at the single cell level in hypoxia by using Click-iT RNA imaging kits in an oxygen controlled workstation, followed by microscopy analysis and quantification.&nbsp; Using cancer cells exposed to hypoxia for different lengths of time, RNA is labeled and measured in each cell. This analysis allows the visualization of temporal and cell-to-cell changes in global RNA synthesis following hypoxic stress.

We describe a technique for analysis of global RNA synthesis in hypoxia using imaging. Click-chemistry labeling of RNA has not previously been performed under hypoxia and allows visualization of global RNA changes at the single cell level. This approach complements the existing averaged RNA techniques, allowing direct visualization of cell-to-cell changes in global RNA synthesis.

Hypoxia or lowering of the oxygen availability is involved in many physiological and pathological processes. At the molecular level, cells initiate a ...