RAS mutation-specific signaling dynamics in response to paralog- and state- selective RAS inhibitors

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• A high therapeutic index (TI) is critical for effective cancer therapies, balancing target inhibition in tumor cells with minimal effects on normal cells.
• RAS-targeting inhibitors, including mutant-specific, paralog-selective, and state-selective types, have advanced cancer treatment.
• The Signaling Inhibition Index (SII), representing differential inhibition between RAS-mutant (RAS(MUT)) and normal cells, is poorly defined for these inhibitors.

Purpose of the Study:

• To evaluate the SII of state- and paralog-selective RAS inhibitors across diverse RAS-mutant (RAS(MUT)) and RAS-wild-type (RAS(WT)) models.
• To define the differential inhibition of oncogenic signaling achieved by various RAS-targeting strategies.
• To inform the design and clinical application of RAS-targeted therapies by understanding SII variability.

Main Methods:

• Assessment of SII for panRAS-GEF(OFF), panKRAS(OFF), and panRAS(ON) inhibitors in various RAS(MUT) and RAS(WT) models.
• Evaluation of MAPK suppression in mutant versus wild-type cells.
• Analysis of inhibitor efficacy in models with specific RAS mutations (e.g., KRAS(G12X), KRAS(G13D), RAS(Q61X)) and genetic contexts (e.g., NF1 loss).

Main Results:

• PanRAS-GEF(OFF) inhibitors demonstrated neutral or negative SII, with comparable or reduced MAPK suppression in RAS(MUT) cells versus RAS(WT) cells.
• PanKRAS(OFF) inhibitors showed a higher SII than panRAS-GEF(OFF) inhibitors, indicating better tumor-versus-normal cell selectivity.
• PanRAS(ON) inhibitors exhibited broader activity but a relatively narrow SII.
• RAS(Q61X) models were resistant to SHP2+MEK inhibitor combinations due to NRAS reactivation and impaired SHP2 binding.
• All tested RAS inhibitors (mutant-specific, state-, and paralog-selective) were active in the same subset of RAS(MUT) models, with the majority of RAS(MUT) cell lines being insensitive to all.

Conclusions:

• Significant SII variability exists among RAS-targeted inhibitors, dependent on the specific RAS driver mutation and cellular context.
• PanRAS-GEF(OFF) inhibitors generally exhibited the lowest SII.
• Most RAS-mutant tumors may be insensitive to any single RAS-targeted inhibitor.
• Integrating SII considerations into the development and clinical application of RAS-targeted therapies is crucial for improving therapeutic outcomes.