STAT3 PHOSPHORYLATION INHIBITORS WITH PYRIMETHAMINE AND PIOGLITAZONE PHARMACOPHORES: AN IN SILICO AND IN VITRO APPROACH FOR DRUG REPURPOSING

The activated phosphorylated form of the signal transducer and activator of transcription 3 (pSTAT3) is upregulated in neurological diseases as well as in numerous cancers and inflammatory conditions. STAT3 activity can be inhibited either directly, by blocking phosphorylation at Tyr705 within the SH2 domain or by preventing DNA binding, or indirectly, by targeting upstream cytokine or growth factor receptors and Janus kinases. In this study, we aimed to identify FDA-approved drugs capable of directly inhibiting STAT3 phosphorylation at Tyr705. Pharmacophores derived from two known STAT3 inhibitors, pyrimethamine and pioglitazone, were used to query the DrugBank database. This approach identified 40 approved compounds, of which 32 shared the pyrimethamine pharmacophore. Molecular docking analyses targeting Tyr705, using phospho-L-tyrosine as a control, revealed 15 compounds with stronger predicted binding affinities than the control. The three top-ranked candidates anticancer drugs imatinib, pazopanib, and nilotinib were further evaluated in HeLa and BV2 cells by Western blot. Pazopanib significantly reduced pSTAT3 levels in both cell lines, whereas nilotinib increased pSTAT3 levels in BV2 cells. Although pyrimethamine exhibited a lower predicted binding affinity than phospho-L-tyrosine, it effectively reduced pSTAT3 levels in HeLa cells and showed a trend toward inhibition in BV2 cells. Collectively, these results indicate that pyrimethamine and other FDA-approved drugs sharing its pharmacophore may be repurposed as inhibitors of STAT3 Tyr705 phosphorylation.
Acknowledgment: This work was supported by PRISMA grant 4242 of the Science Foundation Republic of Serbia.