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

TGF beta is crucial for the homeostasis of epithelial and neural tissues, wound repair, and regulating immune responses. Its dysregulation is associated with a vast number of diseases, of which modifying the tumor microenvironment is one of vital clinical interest. Despite various attempts, there is still no FDA-approved therapy to inhibit the TGF beta pathway. Major mainstream approaches involve impairment of the TGF beta pathway via inhibition of the TGF beta RI kinase. With the purpose to identify non-receptor kinase-based inhibitors to impair TGF beta signaling, an in-house chemical library was enriched, through a computational study, to eliminate TGF beta RI kinase activity. Selected compounds were screened against a cell line engineered with a firefly luciferase gene under TGF beta-Smad-dependent transcriptional control. Results indicated moderate potency for a molecule with phthalazine core against TGF beta-Smad signaling. A series of phthalazine compounds were synthesized and evaluated for potency. The most promising compound (10p) exhibited an IC50 of 0.11 +/- 0.02 mu M and was confirmed to be non-cytotoxic up to 12 mu M, with a selectivity index of approximately 112-fold. Simultaneously, 10p was confirmed to reduce the Smad phosphorylation using Western blot without exhibiting inhibition on the TGF beta RI enzyme. This study identified a novel small-molecule scaffold that targets the TGF beta pathway via a non-receptor-kinase mechanism. (C) 2021 Published by Elsevier Masson SAS.

Automated summary

TGF beta plays a crucial role in maintaining the homeostasis of epithelial and neural tissues, wound repair, and immune responses. Dysregulation of TGF beta is associated with various diseases, with modifying the tumor microenvironment being of significant clinical interest. Despite efforts, there is currently no FDA-approved therapy to inhibit the TGF beta pathway, but targeting TGF beta RI kinase remains a major approach.