A High‐Throughput Screening Process for the Discovery of Melanoma Chemotherapeu cs Targeted at the ErbB4 Receptor Tyrosine Kinase 1
1
2
Richard L. Cullum , Ram B. Gupta and David J. Riese, II
1
2
Departments of Chemical Engineering and Drug Discovery and Development , Auburn University, Auburn, AL 36849 Methods
Background
RTK Pathway
MTT
TMB Substrate HRP
Signal Molecules
Receptor Tyrosine Kinase
Color
an ‐Phosphotyrosine Detec on An body
Extracellular
Intracellular
Tyrosine Kinase Domain
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
ATP
S mulated Kinase
ADP
P
Tyr
Tyr
P
P
Tyr
Tyr
P
P
Tyr
Tyr
P
P
Tyr
Tyr
P
P
Tyr
Tyr
P
P
Tyr
Tyr
P
P
Tyr
Tyr
P
P
Tyr
Tyr
P
ACTIVE
Phosphorylated Tyrosines
NADH
Phosphorylated ErbB4
Cellular Response
ACTIVE
Mo va on
A small molecule library containing 10,000 molecules was screened using a proprietary (DiscoveRx) cell‐based system that detects s mula on of ErbB4 tyrosine phosphoryla on by measuring the binding of a modified SH2 domain to a site of ErbB4 tyrosine phosphoryla on.5 The 23 hits that emerged from this screen were then assayed for s mula on of ErbB4 tyrosine phosphoryla on using the sandwich ELISA. The results for 7 of the most promising hits from the sandwich ELISA are shown here.
Formazan
Mean
Median
SD
K3
4.28
5.13
4.34
0.02
8.53
L3
4.27
3.42
5.91
‐1.52
10.06
M3
7.31
5.70
4.23
3.16
11.45
N3
6.44
6.49
1.97
4.51
8.37
O3
4.95
4.98
3.53
1.49
8.42
P3
7.16
6.75
2.92
4.30
10.03
A4
4.92
4.69
1.42
3.52
6.31
2
Results
Crystal structure of the ErbB4 RTK
4
Dose Response for Ligand S mula on of ErbB4
In effort to minimize background noise and maximize signal, every parameter involved in the comple on of the assay needed to be op mized. The following table represents the op mized condi on for some of the key parameters in this par cular ELISA.
Parameter
Conclusions
Optimized Condition
Capture Antibody
R&D Systems anti‐ErbB4 (100 ng/well)
Blocking Agent
1% BSA, 0.05% NaN3 in PBS
Molecules that s
Incubation time for blocking
2 hours
The ELISA is sensi
Evaporation control
Plate sealer; humid environment
22 compounds can be screened per plate
Number of plate washings
5 in between each step
Lysate concentration
107 cells/mL
A
Detection method
HRP‐conjugated anti‐phosphotyrosine (1:1200)
Substrate
TMB (100 L/well)
Average Absorbance vs. Lysate Sample 4.50
3.75
3.00
Absorbance
Cells were treated with 3 nM NRG2 in the presence of increasing concentra ons of NRG2/Q43L.3
2.25
1.50
Objec ve
0.75
Signal/Noise Trial 2 2/Q43L 1 6.002 2.529 2 6.375 2.544 3 4.746 2.173 4 5.357 2.093 5 6.135 2.306 6 7.150 2.528 7 5.518 2.084 8 6.030 2.076 Mean 5.914 2.292 SD 0.721 0.214
Trial 1 2 3 4 5 6 7 8 Mean SD
2/Q43L 0.693 0.706 0.614 0.642 0.853 0.737 0.396 0.670 0.664 0.130
0.00 Mock
Develop a high‐throughput screening process that can iden fy molecules that s mulate ErbB4 tyrosine phosphoryla on, fail to s mulate ErbB4 coupling, and inhibit agonist induced ErbB4 coupling.
NRG2B
NRG2B/Q43L
Lysate Sample
The figure above represents the average absorbance readings from eight separate trials.
σp, σn = standard devia on of posi ve and nega ve control respec vely μp, μn = mean of posi ve and nega ve control respec vely
ve enough to yield an average Z‐factor of 0.664 with an ErbB4 par al agonist
er capture an body coa ng and blocking, the ELISA takes about 4.5 hours
The MTT Prolifera Agonis
Z‐Factor 2 0.693 0.750 0.656 0.521 0.953 0.728 0.851 0.687 0.730 0.130
mulate ErbB4 tyrosine phosphoryla on can be screened via ELISA in 96‐well format
These experiments can be performed at room temperature
Agonist and Par al Agonist Induced ErbB4 Tyrosine Phosphoryla on
CEM/ErbB4 cells were starved and s mulated with satura ng concentra ons of either NRG2b (10 nM) or NRG2b/Q43L (300 nM). Immunoprecipita on (IP) and immunoblo ng (IB) were used to assess ErbB4 tyrosine phosphoryla on.
Change in agonist Agonist Activity Z‐Factor (Z') concentration Reduction 10 nM → 2 nM 80% 0.246 10 nM → 0 nM 100% 0.236
ELISA Parameter Op miza on
NRG2/Q43L
NRG2
Mock
Western Blot for ErbB4 Tyrosine Phosphoryla on
95% C. I. Lower Upper
Compound ID
on mutants are found in a significant frac on of melanoma cell
lines. Ligands that antagonize agonist s mula on of ErbB4 could be used to treat ErbB4‐dependent tumors. The Q43L mutant of the naturally‐occurring ErbB4 agonist Neuregulin 2beta (NRG2) func ons as a par al agonist at ErbB4.3 NRG2/Q43L s mulates ErbB4 tyrosine phosphoryla on, but does not s mulate ErbB4 coupling to cell prolifera on and compe vely antagonizes agonist s mula on of ErbB4 coupling to cell prolifera on. Current methods for analyzing ErbB4 ligands (Western Blots and cell staining) are me consuming processes, and they cannot be scaled easily in order to screen large libraries of candidate ligands.
MTT Prolifera on Assay Results
Net s mula on of ErbB4 tyrosine phosphoryla on by each puta ve small molecule ErbB4 agonist was calculated by subtrac ng the effect of mock s mula on from each of the experimental sample values. The effect of each puta ve small molecule ErbB4 agonist was normalized against the effect of 10 nM NRG1β.
NAD+
an ‐ErbB4 Capture An body
Preliminary Results of Small Molecule Screening
Viable Cell
Intracellular Proteins
INACTIVE
Gain‐of‐func
MTT Prolifera on Assay for detec ng ErbB4 coupling to cell prolifera on
Sandwich ELISA for ErbB4 Tyrosine Phosphoryla on Detec on
Receptor tyrosine kinases (RTKs) are high affinity cell surface receptors. Once ac vated, they catalyze the phosphoryla on of tyrosine residues which promotes further intracellular responses. Although RTKs are regulators of normal cell processes, they are also known to be involved in the development and progression of many types of human malignancies. This has led to RTKs becoming proven targets for oncology drug discovery.1
Results
on Assay does iden fy molecules that s mulate ErbB4 coupling to cell prolifera on
c ac vity needs to be reduced by at least 80% in order to achieve a Z‐factor of 0.246
Future Direc ons In order to completely screen for par al agonists the following items need to be addressed: U
liza on of automated liquid handling system (robot) Cell s mula on and lysis in 96‐well format to allow for rapid transfer of lysate to ELISA plates Development of MTT Prolifera on Assay for antagonists
References (1) Riese, D. J. Expert Opin. Drug Discov. 2011, 6, 185–193. (2) Flaherty, K. T.; Hodi, F. S.; Bastian, B. C. Curr Opin Oncol 2010, 22, 178–183. (3) Wilson, K. J.; Mill, C. P.; Gallo, R. M.; Cameron, E. M.; VanBrocklin, H.; Settleman, J.; Riese, D. J. Biochem. J. 2012, 443, 133–144. (4) Qiu, C.; Tarrant, M. K.; Choi, S. H.; Sathyamurthy, A.; Bose, R.; Banjade, S.; Pal, A.; Bornmann, W. G.; Lemmon, M. A.; Cole, P. A.; Leahy, D. J. Structure 2008, 16, 460–467. (5) h p://www.discoverx.com/product‐data‐sheets‐3‐tab/93‐0465c3