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Updated: Jul 2, 2025
A Multiplexed Luciferase-based Screening Platform for Interrogating Cancer-associated Signal Transduction in Cultured Cells
Published on: July 3, 2013
Reporter cell lines to screen for inhibitors or regulators of the KRAS-RAF-MEK1/2-ERK1/2 pathway
Laura Weatherdon1, Kate Stuart1,2, Megan Cassidy1
1Signalling Programme, The Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT, U.K.
Abstract:
The RAS-regulated RAF-MEK1/2-ERK1/2 signalling pathway is activated in cancer due to mutations in RAS proteins (especially KRAS), BRAF, CRAF, MEK1 and MEK2. Whilst inhibitors of KRASG12C (lung adenocarcinoma) and BRAF and MEK1/2 (melanoma and colorectal cancer) are clinically approved, acquired resistance remains a problem. Consequently, the search for new inhibitors (especially of RAS proteins), new inhibitor modalities and regulators of this pathway, which may be new drug targets, continues and increasingly involves cell-based screens with small molecules or genetic screens such as RNAi, CRISPR or protein interference. Here we describe cell lines that exhibit doxycycline-dependent expression KRASG12V or BRAFV600E and harbour a stably integrated EGR1:EmGFP reporter gene that can be detected by flow cytometry, high-content microscopy or immunoblotting. KRASG12V or BRAFV600E-driven EmGFP expression is inhibited by MEK1/2 or ERK1/2 inhibitors (MEKi and ERKi). BRAFi inhibit BRAFV600E-driven EmGFP expression but enhance the response to KRASG12V, recapitulating paradoxical activation of wild type RAF proteins. In addition to small molecules, expression of iDab6, encoding a RAS-specific antibody fragment inhibited KRASG12V- but not BRAFV600E-driven EmGFP expression. Finally, substitution of EmGFP for a bacterial nitroreductase gene allowed KRASG12V or BRAFV600E to drive cell death in the presence of a pro-drug, which may allow selection of pathway inhibitors that promote survival. These cell lines should prove useful for cell-based screens to identify new regulators of KRAS- or BRAF-dependent ERK1/2 signalling (drug target discovery) as well as screening or triaging 'hits' from drug discovery screens.
Insights
New cell lines enable screening for drugs targeting cancer-driving RAS-RAF-MEK-ERK signaling. These tools help identify novel drug targets and screen potential inhibitors for KRAS and BRAF mutations, addressing treatment resistance.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- The RAS-RAF-MEK-ERK signaling pathway is frequently activated in various cancers due to mutations in key proteins like KRAS and BRAF.
- While inhibitors for KRASG12C, BRAF, and MEK1/2 exist, acquired resistance necessitates the development of new therapeutic strategies and drug targets.
- Cell-based screening methods, including genetic and small molecule screens, are crucial for discovering novel regulators and inhibitors of this pathway.
Purpose of the Study:
- To develop novel doxycycline-inducible cell lines for studying RAS-RAF-MEK-ERK pathway activation in cancer.
- To create reporter cell lines for high-throughput screening of small molecules and genetic modifiers targeting KRAS and BRAF mutations.
- To establish a cell-based system for identifying new drug targets and evaluating potential inhibitors, including antibody fragments.
Main Methods:
- Generation of cell lines with doxycycline-dependent expression of KRASG12V or BRAFV600E.
- Integration of a stably expressed EGR1:EmGFP reporter gene for pathway activity monitoring via flow cytometry, microscopy, or immunoblotting.
- Utilized MEK/ERK inhibitors, BRAF inhibitors, and a RAS-specific antibody fragment (iDab6) to validate pathway modulation.
- Incorporated a bacterial nitroreductase gene for pro-drug mediated cell killing to select for pathway inhibitors promoting survival.
Main Results:
- Doxycycline-inducible KRASG12V and BRAFV600E expression successfully activated the EGR1:EmGFP reporter.
- MEK/ERK inhibitors suppressed reporter gene expression, while BRAF inhibitors selectively affected BRAFV600E but showed paradoxical activation with KRASG12V.
- The RAS-specific antibody fragment iDab6 inhibited KRASG12V-driven reporter expression but not BRAFV600E.
- The nitroreductase system enabled selection of compounds that promote cell survival under pathway activation.
Conclusions:
- The developed cell lines provide a robust platform for drug discovery targeting the RAS-RAF-MEK-ERK pathway.
- These tools facilitate the identification of novel drug targets and the screening/triaging of potential therapeutic agents against KRAS and BRAF-driven cancers.
- The system effectively models pathway dynamics, including paradoxical activation, and allows for selection-based screening of survival-promoting inhibitors.
