Challenging the "Undruggable"─Targeting STAT3 but Identifying Potent TrkA-Targeted Inhibitors

Area of Science:

• Oncology
• Pharmacology
• Biochemistry

Background:

• Signal transducer and activator of transcription 3 (STAT3) is a challenging anticancer target due to complex signaling and poor druggability.
• Developing effective STAT3 inhibitors requires innovative screening and optimization strategies.
• Target engagement is crucial for validating drug candidates early in the discovery pipeline.

Purpose of the Study:

• To establish a target engagement-focused screening and optimization pipeline for discovering novel STAT3 inhibitors.
• To identify and characterize compounds with high affinity and selectivity for TrkA, a related kinase.
• To demonstrate the efficacy of identified inhibitors in cellular cancer models.

Main Methods:

• Differential scanning fluorimetry (DSF) high-throughput screening to identify STAT3 stabilizers.
• Cellular thermal shift assays (CETSA) for target engagement validation.
• Orthogonal biochemical and cellular assays to assess inhibitor affinity and selectivity for TrkA.
• In vitro and cellular assays to evaluate compound efficacy in cancer models.

Main Results:

• Initial screening identified compounds that stabilized STAT3 but also showed high affinity for TrkA.
• Optimization refined inhibitor selectivity towards TrkA, leading to potent TrkA inhibition.
• The lead compound, PI-15, demonstrated robust target engagement and TrkA inhibition in cellular assays.
• PI-15 showed efficacy in cellular TrkA cancer models.

Conclusions:

• A target engagement-focused approach is vital for early-stage drug discovery, particularly for challenging targets like STAT3.
• This pipeline successfully identified PI-15, a potent TrkA inhibitor with demonstrated cellular efficacy.
• Prioritizing rigorous target engagement validation accelerates the discovery of promising drug candidates for cancer therapy.