Andrographolide derivatives inhibit guanine nucleotide exchange and abrogate oncogenic Ras function

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• Aberrant signaling by oncogenic mutant rat sarcoma (Ras) proteins is implicated in approximately 15% of human tumors.
• Direct inhibition of Ras proteins by small molecules has been a significant challenge in cancer therapy.
• Existing small-molecule ligands bind Ras and inhibit function by interfering with exchange factor binding, but their efficacy against oncogenic mutants is unclear.

Purpose of the Study:

• To investigate andrographolide (AGP) and its derivatives as potential inhibitors of Ras signaling.
• To determine if AGP derivatives can effectively target oncogenic mutant Ras proteins.
• To validate the inhibition of GDP-GTP exchange as a therapeutic strategy against mutant Ras.

Main Methods:

• Utilized a dynamics-based pocket identification scheme and ensemble docking.
• Employed innovative cell-based assays to evaluate the effects of AGP derivatives.
• Measured GTP loading and mitogen-activated protein kinase (MAPK) activation in response to EGF stimulation.

Main Results:

• Andrographolide (AGP) and its benzylidene derivatives bind to transient pockets on Kirsten-Ras (K-Ras).
• AGP derivatives inhibit GDP-GTP exchange, reducing GTP loading of wild-type K-Ras upon EGF stimulation.
• Prolonged treatment with AGP derivatives reduced GTP loading and signal transmission of oncogenic K-RasG12V.

Conclusions:

• AGP derivatives directly bind Ras and block GDP-GTP exchange.
• These compounds inhibit signaling pathways mediated by both wild-type and oncogenic K-Ras.
• Inhibiting nucleotide exchange factors is a viable strategy to abrogate oncogenic mutant Ras function.