SLAS2016 continued
reported her experience in moving from 384 to 1536 wells/plate for phe- notypic assays. Until recently, limitations in liquid handling, including washing and media exchange, precluded the use of 1536-well plates. But she was attracted to the higher-density plates due to lower reagent cost and expected higher throughput.
The washing issue was addressed by the BlueWasher from Blue Cat Bio (Toronto, Canada). The device uses centrifugation for noncontact, contamination-free removal of liquids from all plate formats, including 1536-well, and achieves near-zero residual volume in each well after wash- ing. Users can add up to four separate wash solutions, which are often required for some complex phenotypic assays.
Dr. Plant’s bridging study successfully compared EC50 data generated in Figure 2 – VIAFLO ASSIST from INTEGRA Biosciences.
High-throughput screening gets faster and faster Over the last 10 years, high-throughput screening (HTS) has been con-
ducted at ever-increasing speeds, reducing per-well dispense time from a few minutes to a few seconds to a well per second, as reported by Dr. Melanie Leveridge of GlaxoSmithKline (Brentford, U.K.). The biggest factor in HTS time improvements came from replacing chromatography with higher-speed matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) with multiple reaction monitoring. These instruments have the specificity needed to identify fragment peaks. Smaller wells, which increase well-to-plate ratios, contribute to the method’s speed. The small wells require handling nanoliter volumes of liquids. Dr. Leveridge reported use of 1536-well plates and some runs with 6144-well plates, while other lecturers select 384 wells as more practical, given the abilities of contemporary liquid-handling modules.
Replacing the LC step with laser desorption is also economically favor- able. According to one author, replacing a five-minute UHPLC run with MALDI-TOF reduced assay costs from about $540/sample to less than $1.00/sample. Other presenters corroborated crossing the dollar/well threshold with MALDI-TOF.
A poster by E. Hall of LabCyte and colleagues at AstraZeneca (Macclesfield, U.K.) and IonSense, Inc. (Saugus, Mass.) described one system. In the ex- ample, a modified Echo liquid handler ejects 2.5-nL drops of sample from a 384-well plate onto IonSense’s Vapur gold substrate mesh. Excited helium from the DART (Direct Analysis in Real Time)-MS interface from IonSense impinges on the gold mesh, which vaporizes and ionizes the sample. Throughput is three samples per second. The interface was evaluated using an assay of caffeine in water in a 384-well plate. CV for the plates was less than 15% using single-ion monitoring. The authors went on to use the system in a 1000-compound screen.
The move to 1536 and 6144 wells There seemed to be a clear acceptance that 1536-well plates held a place
in the mainstream. A lecture by Dr. Helen Plant of AstraZeneca (London) AMERICAN LABORATORY 18
both 384- and 1536-well formats. Then, for further confirmation, drug master screens of a 43K library were run in 1536-well plates, which required only two weeks. Required number of cells was reduced 25%, reagent cost/ assay was now deemed affordable for screenings at scale, and there was a fourfold reduction in the campaign time. During post-lecture Q&A, Plant was asked if she expected to eventually use 6144-well plates. She replied that evaporation is so rapid at 1536 that higher open-well densities may not be practical and microfluidic tubes will replace wells.
Trueness replaces accuracy Dr. George Rodrigues of Artel (Westbrook, Maine) discussed recent up-
dates to international standards for liquid handling. The most significant change from his working group recognized that the term “accuracy” is ambiguous, and so “trueness” was chosen as a substitute. Precision will still measure scatter of assay results, and “trueness” will measure the difference between the measured value and the true value.
Notable new products SLAS organizers recognize that innovative new products often originate
in small firms that cannot afford or even staff a regular booth. These firms (such as SiO2
Medical Products and Click Bio, below) were given an
opportunity to engage the scientific community through the AveNEW section on the exhibition floor. It consisted of a 20 × 20-sq.-ft. booth in the middle of the hall.
SiO2 Medical Products (Auburn, Ala.) exhibited plasticware incorporat-
ing an inert silica layer that is bonded using plasma-enhanced chemical vapor deposition to items such as polyolefin or polystyrene plastic vials or multiple-well plates to improve storage stability, as required in source plates for compound libraries. Vapor of hexamethyldisiloxane is swept into the plastic well and destroyed with oxygen plasma. A thin layer of silica is deposited onto the plastic surface. Surprisingly, the silica is very flexible and resistant to cracking or spalling. The silica film stops the migration of oxygen and water through the plastic. If a hydrophobic surface is desired, the silica can be reacted with silanes, which makes a polar surface nonpolar.
More than half of the instruments in the exhibition were designed to process plates manufactured to ANSI SLAS 1-2004 standards. Click Bio (Reno, Nev.) introduced the Click plate, which facilitates designing and assembling various reservoirs and vials that fit into the 1–2004 format. The
APRIL 2016
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