Identifying requirements for RSK2 specific inhibitors.

Area of Science:

• Biochemistry
• Molecular Biology
• Drug Discovery

Background:

• Kinase inhibitors often lack specificity, especially for closely related family members like ribosomal S6 kinases (RSK).
• RSK isoforms (RSK1-4) are downstream effectors of ERK1/2 with distinct physiological roles, necessitating isoform-specific targeting.
• The natural product SL0101, a flavonoid glycoside, exhibits binding to RSK1/2 via a unique conformational change in the N-terminal kinase domain (NTKD).

Purpose of the Study:

• To investigate the structural basis for SL0101 binding to RSK isoforms.
• To identify modifications of SL0101 that enhance binding stability and isoform specificity.
• To develop a tool compound for selective RSK2 inhibition.

Main Methods:

• Molecular modeling to predict binding interactions and identify resistance mutations.
• Kinetic analysis to characterize inhibitor binding to RSK2.
• Synthesis and evaluation of SL0101 derivatives with modifications on the rhamnose moiety.

Main Results:

• A single amino acid difference in RSK3/4 likely prevents the conformational rearrangement required for SL0101 binding.
• Kinetic studies revealed that regions outside the RSK NTKD are crucial for stable inhibitor binding.
• A novel SL0101 analogue with an n-propyl-carbamate modification demonstrated highly stable binding to RSK2 but not RSK1.

Conclusions:

• The identified SL0101 modification provides a basis for developing RSK2-specific inhibitors.
• Understanding the structural determinants of SL0101 binding facilitates the design of targeted kinase therapies.
• This work advances the potential for selective modulation of RSK signaling pathways.