Scientific Resources

Proof of drug-target engagement in physiologically-relevant contexts is a key pillar of successful therapeutic target validation. We developed two orthogonal technologies,the cellular thermal shift assay (CETSA) and a covalent chemical probe reporter approach (harnessing sulfonyl fluoride tyrosine labeling and subsequent click chemistry) to measure the occupancy of the mRNA-decapping scavenger enzyme DcpS by a small molecule inhibitor in live cells. Enzyme affinity determined using isothermal dose response fingerprinting (ITDRFCETSA) and the concentration required to occupy 50% of the enzyme (OC50) using the chemical probe reporter assay were very similar. In this case,the chemical probe method worked well due to the long offset kinetics of the reversible inhibitor (determined using a fluorescent dye-tagged probe). This work suggests that CETSA could become the first choice assay to determine in-cell target engagement due to its simplicity. View Publication

We present a simple microfluidic system that generates water-in-water,aqueous two phase system (ATPS) droplets,by passive flow focusing. ATPS droplet formation is achieved by applying weak hydrostatic pressures,with liquid-filled pipette tips as fluid columns at the inlets,to introduce low speed flows to the flow focusing junction. To control the size of the droplets,we systematically vary the interfacial tension and viscosity of the ATPS fluids and adjust the fluid column height at the fluid inlets. The size of the droplets scales with a power law of the ratio of viscous stresses in the two ATPS phases. Overall,we find a drop size coefficient of variation (CV; i.e.,polydispersity) of about 10%. We also find that when drops form very close to the flow focusing junction,the drops have a CV of less than 1%. Our droplet generation method is easily scalable: we demonstrate a parallel system that generates droplets simultaneously and improves the droplet production rate by up to one order of magnitude. Finally,we show the potential application of our system for encapsulating cells in water-in-water emulsions by encapsulating microparticles and cells. To the best of our knowledge,our microfluidic technique is the first that forms low interfacial tension ATPS droplets without applying external perturbations. We anticipate that this simple approach will find utility in drug and cell delivery applications because of the all-biocompatible nature of the water-in-water ATPS environment. View Publication

Identification of agents that target human leukemia stem cells is an important consideration for the development of new therapies. The present study demonstrates that rocaglamide and silvestrol,closely related natural products from the flavagline class of compounds,are able to preferentially kill functionally defined leukemia stem cells,while sparing normal stem and progenitor cells. In addition to efficacy as single agents,flavaglines sensitize leukemia cells to several anticancer compounds,including front-line chemotherapeutic drugs used to treat leukemia patients. Mechanistic studies indicate that flavaglines strongly inhibit protein synthesis,leading to the reduction of short-lived antiapoptotic proteins. Notably though,treatment with flavaglines,alone or in combination with other drugs,yields a much stronger cytotoxic activity toward leukemia cells than the translational inhibitor temsirolimus. These results indicate that the underlying cell death mechanism of flavaglines is more complex than simply inhibiting general protein translation. Global gene expression profiling and cell biological assays identified Myc inhibition and the disruption of mitochondrial integrity to be features of flavaglines,which we propose contribute to their efficacy in targeting leukemia cells. Taken together,these findings indicate that rocaglamide and silvestrol are distinct from clinically available translational inhibitors and represent promising candidates for the treatment of leukemia. View Publication

Mast cells are unique hematopoietic cells that are richly distributed in the skin and mucosal surfaces of the respiratory and gastrointestinal tract. They play a key role in allergic inflammation by releasing a cocktail of granular constituents,including histamine,serine proteases,and various eicosanoids and cytokines. As such,a number of drugs target either inhibition of mast cell degranulation or the products of degranulation. To identify potential novel drugs and mechanisms in mast cell biology,assays were developed to identify inhibitors of mast cell degranulation and activation in a phenotypic screen. Due to the challenges associated with obtaining primary mast cells,cord blood-derived mononuclear cells were reproducibly differentiated to mast cells and assays developed to monitor tryptase release and prostaglandin D2 generation. The tryptase assay was particularly sensitive,requiring only 500 cells per data point,which permitted a set of approximately 12,000 compounds to be screened robustly and cost-effectively. Active compounds were tested for concomitant inhibition of prostaglandin D2 generation. This study demonstrates the robustness and effectiveness of this approach in the identification of potential novel compounds and mechanisms targeting mast cell-driven inflammation,to enable innovative drug discovery efforts to be prosecuted. View Publication

In the United States alone,there are approximately 500,000 burn injuries that require medical treatment every year. Limitations of current treatments necessitate the development of new methods that can be applied quicker,result in faster wound regeneration,and yield skin that is cosmetically similar to undamaged skin. The development of new hydrogel biomaterials and bioprinting deposition technologies has provided a platform to address this need. Herein we evaluated characteristics of twelve hydrogels to determine their suitability for bioprinting applications. We chose hydrogels that are either commercially available,or are commonly used for research purposes. We evaluated specific hydrogel properties relevant to bioprinting applications,specifically; gelation time,swelling or contraction,stability,biocompatibility and printability. Further,we described regulatory,commercial and financial aspects of each of the hydrogels. While many of the hydrogels screened may exhibit characteristics suitable for other applications,UV-crosslinked Extracel,a hyaluronic acid-based hydrogel,had many of the desired properties for our bioprinting application. Taken together with commercial availability,shelf life,potential for regulatory approval and ease of use,these materials hold the potential to be further developed into fast and effective wound healing treatments. View Publication