External ID: PRPC_INH_TRFRET_1536_1X%INH PRUN
Protocol:
Assay Overview:
The purpose of this assay is to identify compounds that act as inhibitors of PRPc cell surface expression. This assay detects PrPc on the surface of living LD9 fibroblast cells using two PRPC-specific antibodies which carry donor and acceptor fluorophores, respectively.
In this assay, the antibodies are directed against distinct, non-overlapping PrPc epitopes. Antibody occupancy of both epitopes of a PrPc molecule results in FRET signal emission. Free antibody or single antibody occupancy is not detected. The assay employs long half-life lanthanide donors (Europium or Terbium cryptate) and acceptor fluorophores XL665 or d2: SAF32 (aa53-93) and D18 (aa133-157) labeled with the donor and acceptor fluorophores, respectively. Ratios of 665 nm to 620 nm measurements are calculated, to take into account non-specific absorption of 620 nm light by the assay matrix. Compounds are tested in singlicate at a final nominal concentration of 13.8 microM.
Protocol Summary:
The LD9 cell line (subclone of L929, which is a mouse fibroblast cell line) was routinely cultured in T-175 sq cm flasks at 37 C and 95% relative humidity (RH). The growth media consisted of Opti-MEM I Reduced Serum Medium (no phenol red) supplemented with 5% v/v Bovine Growth Serum Supplemented Calf and 1X Penicillin-Streptomycin.
The day before the assay, 3 uL of cell growth media was dispensed into the first two columns of 1536 well microtiter plates and 1500 cells in 3 uL of cell growth media were seeded into the remaining wells. Next, 42 nL of test compound in DMSO, Brefeldin A (58 uM final concentration) in DMSO, or DMSO alone (1.38% final concentration) were dispensed to the appropriate wells. The plates were then incubated for 21 hours at 37 C, 5% CO2, and 95 % RH.
The assay was started by adding 1 uL of SAF32-Tb at a final concentration of 0.072ug/mL and 1ul of D18-d2 at a final concentration of 0.66ug/mL to all wells, respectively. Labeled Antibodies were prepared in 1X PBS. Plates were centrifuged and after 3 hours of incubation at room temperature, well TRFRET was read on a ViewLux microplate reader (Perkin Elmer, Turku, Finland). Measurements were performed by exciting the plates at 340 nM, and monitoring well fluorescence at 618 nm (Tb) and 671 nm (d2) with the ViewLux microplate reader.
To normalize data, values measured from both fluorescence emission wavelengths were used to calculate a ratio for each well, according to the following mathematical expression:
Ratio = I671nm / I618nm
Where:
I represents the measured fluorescence emission intensity at the enumerated wavelength in nm.
The percent inhibition was calculated from the median ratio as follows:
%_Inhibition = 100 * ( ( Ratio_Test_Compound - Median_Ratio_Low_Control ) / ( Median_Ratio_High_Control - Median_Ratio_Low_Control ) ) )
Where:
Test_Compound is defined as wells containing cells, test compounds and DMSO.
High_Control is defined as wells containing cells, Brefeldin A and DMSO.
Low_Control is defined as the median of the wells containing test compounds.
PubChem Activity Outcome and Score:
A mathematical algorithm was used to determine nominally inhibiting compounds in the primary screen. Two values were calculated: (1) the average percent inhibition of all compounds tested, and (2) three times their standard deviation. The sum of these two values was used as a cutoff parameter, i.e. any compound that exhibited greater % inhibition than the cutoff parameter was declared active.
The reported PubChem Activity Score has been normalized to 100% observed primary inhibition. Negative % inhibition values are reported as activity score zero.
The PubChem Activity Score range for active compounds is 100-18, and for inactive compounds 18-0.
List of Reagents:
LD9 cells (supplied by Assay Provider)
Opti-MEM Reduced Serum Medium (Life Technologies, part 11058-021)
Bovine Growth Serum Supplemented Calf (Hyclone, part SH30541.03)
Penicillin-Streptomycin (100X) (Life Technologies, part 15140-122)
Brefeldin A (Control, Sigma, part B7651)
SAF32-Tb (Cisbio, custom labeled antibody)
D18-d2 (Cisbio, custom labeled antibody)
PBS (Life Technologies, part 10010-031)
Detachin Cell Detachment Reagent (Genlantis, part T100100)
T-175 Flasks (Nunc, part 159910)
1536-well plates (Corning, part 7298)
Comment:
Due to the increasing size of the MLPCN compound library, this assay may have been run as two or more separate campaigns, each campaign testing a unique set of compounds. All data reported were normalized on a per-plate basis. Possible artifacts of this assay can include, but are not limited to: dust or lint located in or on wells of the microtiter plate, and compounds that modulate well fluorescence. All test compound concentrations reported above and below are nominal; the specific test concentration(s) for a particular compound may vary based upon the actual sample provided by the MLSMR.