Targeting RET Solvent-Front Mutants with Alkynyl Nicotinamide-Based Inhibitors

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• Selpercatinib and pralsetinib are approved RET inhibitors for RET-altered cancers.
• Acquired RET mutations can lead to resistance against these therapies.
• The precise resistance profile of all RET G810 mutants to current inhibitors was not fully characterized.

Purpose of the Study:

• To comprehensively profile selpercatinib and pralsetinib activity against all six RET G810 solvent-front mutants.
• To develop novel next-generation RET inhibitors targeting selpercatinib/pralsetinib-resistant mutants.
• To evaluate the efficacy of novel inhibitors in preclinical models.

Main Methods:

• In vitro kinase assays and cell-based assays were used to assess inhibitor activity against RET G810 mutants.
• Synthesis and characterization of novel alkynyl nicotinamide-based RET inhibitors.
• Pharmacokinetic studies and in vivo efficacy assessments in xenograft tumor models.

Main Results:

• RET G810V was surprisingly sensitive to selpercatinib and pralsetinib, while G810D conferred resistance alongside G810C/R/S.
• Novel alkynyl nicotinamide compounds (HSN608, HSL476, HSL468) demonstrated potent inhibition of all tested G810 mutants and the V804M gatekeeper mutant.
• HSN608 showed favorable pharmacokinetics and significant tumor regression in a selpercatinib-resistant G810C xenograft model.

Conclusions:

• This study elucidates the differential sensitivity of RET G810 mutants to current TKIs.
• Novel alkynyl nicotinamide-based RET inhibitors are effective against resistant mutants.
• These findings support the development of new therapeutic strategies for RET-driven cancers.