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Published on: November 9, 2020
Identification of a Highly Cooperative PROTAC Degrader Targeting GTP-Loaded KRAS(On) Alleles
Vesna Vetma1,2, Ilaria Puoti1, Natalia K Karolak1
1Centre for Targeted Protein Degradation, School of Life Sciences, University of Dundee, 1 James Lindsay Place, DD1 5JJ Dundee, Scotland, U.K.
Abstract:
Kirsten rat sarcoma viral oncogene homologue (KRAS) is a frequently mutated oncogene in multiple types of cancer and is a high priority target for oncology drug development. There are many different KRAS mutations, including mutations that favor the GTP-loaded hydrolysis-incompetent "active" state of KRAS, KRAS(on), that can lead to tumorigenesis. However, small molecule interventions thus far have predominantly targeted single mutations of "inactive" GDP-loaded KRAS, KRAS(off), such as KRASG12C. Here, we address this gap through the development of heterobifunctional VHL-based PROTACs capable of engaging and degrading KRAS(on), thus addressing a wider range of KRAS mutations. By studying ternary complex affinity, stability, and binding modes using SPR and X-ray cocrystal structures, we identified PROTACs that exhibit high positive cooperativity in forming ternary complexes with VHL and GCP-loaded KRAS as representative of KRAS(on) variants. Degrader activity profiling in relevant cancer cells supported the discovery of ACBI4, a PROTAC which forms a highly stable and cooperative ternary complex between VHL and GTP-bound KRAS and which potently degrades KRASG12R, leading to antiproliferative effect in KRAS mutant-driven cancer cells. ACBI4 provides a new chemical tool for studying the impact of degrading KRAS(on) mutants, which is not possible with current pan-KRAS inhibitors or degraders.
Insights
Researchers developed novel PROTACs targeting the active KRAS(on) state, a key driver in many cancers. One PROTAC, ACBI4, effectively degrades KRASG12R, offering a new tool for cancer research.
Area of Science:
- Oncology
- Molecular Biology
- Drug Discovery
Background:
- Kirsten rat sarcoma viral oncogene homologue (KRAS) is a critical oncogene in cancer development.
- KRAS mutations, particularly the active GTP-bound state (KRAS(on)), drive tumorigenesis.
- Current therapies often target inactive KRAS (KRAS(off)) forms like KRASG12C, leaving other mutations unaddressed.
Purpose of the Study:
- To develop novel heterobifunctional VHL-based Proteolysis Targeting Chimeras (PROTACs) capable of engaging and degrading KRAS(on) variants.
- To address the unmet need for targeting a broader range of KRAS mutations beyond KRASG12C.
- To identify PROTACs with high affinity and stability in ternary complexes with VHL and GTP-loaded KRAS.
Main Methods:
- Development of VHL-based PROTACs.
- Surface Plasmon Resonance (SPR) to study ternary complex affinity and stability.
- X-ray cocrystallography to determine binding modes.
- Degrader activity profiling in cancer cell lines.
Main Results:
- Identified PROTACs exhibiting high positive cooperativity in ternary complex formation with VHL and GTP-loaded KRAS.
- Discovered ACBI4, a PROTAC forming a stable ternary complex with VHL and GTP-bound KRAS.
- ACBI4 potently degrades KRASG12R, inducing antiproliferative effects in KRAS-mutant cancer cells.
Conclusions:
- ACBI4 represents a promising new chemical tool for targeting KRAS(on) mutations.
- This PROTAC enables the study of KRAS(on) degradation, which is not achievable with existing pan-KRAS inhibitors or degraders.
- The findings open new avenues for developing targeted therapies against a wider spectrum of KRAS-driven cancers.
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