Discovery and biological evaluation of phthalazines as novel non-kinase TGFβ pathway inhibitors

Area of Science:

• Biochemistry
• Molecular Biology
• Drug Discovery

Background:

• Transforming Growth Factor beta (TGFβ) is vital for tissue homeostasis and immune responses.
• Dysregulation of TGFβ is implicated in numerous diseases, with significant interest in its role in the tumor microenvironment.
• Current therapies targeting the TGFβ pathway, primarily via TGFβ receptor kinase inhibition, lack FDA approval.

Purpose of the Study:

• To identify novel non-receptor kinase inhibitors of the TGFβ pathway.
• To explore alternative mechanisms for modulating TGFβ signaling beyond direct TGFβ receptor inhibition.

Main Methods:

• Computational screening of an in-house chemical library to identify potential TGFβRI kinase inhibitors.
• Cell-based assays using a firefly luciferase reporter system to assess TGFβ-Smad signaling.
• Synthesis and evaluation of phthalazine-based compounds for potency and cytotoxicity.
• Western blot analysis to confirm Smad phosphorylation inhibition.

Main Results:

• A phthalazine-based molecule demonstrated moderate potency against TGFβ-Smad signaling.
• The lead compound (10p) showed high potency (IC50 = 0.11 μM) and a high selectivity index (~112-fold).
• Compound 10p reduced Smad phosphorylation without inhibiting the TGFβRI enzyme, indicating a non-receptor kinase mechanism.

Conclusions:

• A novel small-molecule scaffold based on phthalazine was identified.
• This scaffold targets the TGFβ pathway through a non-receptor kinase mechanism.
• Compound 10p represents a promising candidate for further development in TGFβ-related diseases.