STAT3 has been shown to interact with:
* AR, 
* ELP2, 
* EP300, 
* EGFR, 
* HIF1A, 
* JAK1, 
* JUN 
* KHDRBS1, 
* mTOR, 
* MYOD1, 
* NDUFA13, 
* NFKB1, 
* NR3C1, 
* NCOA1, 
* PML,
* RAC1, 
* RELA, 
* RET, 
* RPA2, 
* STAT1, 
* Stathmin,
* Src,  and
* TRIP10. 
* KPNA4. 
Niclosamide seems to inhibit the STAT3 signalling pathway.
Nicotinamide (a type of vitamin B) naturally inhibits STAT3. However NAC (Acetylcysteine) inhibits STAT3 inhibitors.