Switch type I to type II TRK inhibitors for combating clinical resistance induced by xDFG mutation for cancer therapy

Area of Science:

• Medicinal Chemistry
• Oncology
• Molecular Biology

Background:

• Acquired resistance to first-generation TRK inhibitors (larotrectinib, entrectinib) due to TRK xDFG mutations is a significant clinical challenge.
• Development of next-generation TRK inhibitors is crucial for treating resistant TRK-driven cancers.

Purpose of the Study:

• To design and synthesize novel selective type II TRK inhibitors.
• To evaluate the efficacy of these inhibitors against wild-type and resistant TRK fusion proteins.

Main Methods:

• Hybridization strategy using 6-(pyrrolidin-1-yl)imidazo[1,2-b]pyridazine scaffold.
• In vitro kinase inhibition assays (IC50 determination) against TRKA, TRKB, TRKC, and specific mutants (TRKA^G667C).
• Cell proliferation assays using Ba/F3 cells engineered with various TRK fusion proteins (wild-type, xDFG, solvent-front mutants).

Main Results:

• Compound 12d demonstrated potent inhibition of TRKA/B/C (IC50s 3.3-6.4 nM) and TRKA^G667C (IC50 9.4 nM).
• 12d effectively suppressed proliferation in Ba/F3 cells harboring wild-type and resistant TRK fusion proteins.
• 12d exhibited superior activity against CD74-TRKA^G667C and ETV6-TRKC^G696C compared to existing inhibitors, with IC50s of 2.6 nM and 6.1 nM, respectively.
• 12d also showed potent antiproliferative effects against TRKC^G623R and TRKC^G623E mutants (IC50s 28.2-31.0 nM).

Conclusions:

• A novel series of type II TRK inhibitors based on the imidazo[1,2-b]pyridazine scaffold was successfully developed.
• Compound 12d represents a promising lead candidate for overcoming acquired resistance in TRK-driven cancers.
• Further investigation of 12d is warranted for its potential therapeutic application in resistant TRK fusion-positive malignancies.