Discovery of novel STAT3 DNA binding domain inhibitors.

Background: STAT3 is a pro-oncogenic transcription factor. Pyrimethamine (PYM) is a STAT3 inhibitor that suppresses the proliferation of some cancer cells through downregulation of STAT3 target proteins. Methodology & Results: We have used structure-based tools to design novel PYM-based compounds. Intracellular target validation studies revealed that representative compounds 11b-d and 15a downregulate STAT3 downstream proteins and inhibit STAT3 DNA binding domain (DBD). Relative to PYM, a cohort of these compounds are >100-fold more cytotoxic to cancer cells with constitutively active (high pSTAT3) and basal (low pSTAT3) STAT3 signaling, suggesting that STAT3 DBD inhibition is deleterious to the proliferation of cancer cells with low and high pSTAT3 levels. Conclusion: These are promising leads for further preclinical evaluation as therapeutic agents for STAT3-dependent cancers.