Abstract
STAT3 N-terminal domain is a promising molecular target for cancer treatment and modulation of
immune responses. However, STAT3 is localized in the cytoplasm, mitochondria, and nuclei, and thus, is
inaccessible to therapeutic antibodies. Its N-terminal domain lacks deep pockets on the surface and
represents a typical "non-druggable" protein. In order to successfully identify potent and selective
inhibitors of the domain, we have used virtual screening of billion structure-sized virtual libraries of
make-on-demand screening samples. The results suggest that the expansion of accessible chemical space
by cutting-edge ultra-large virtual compound databases can lead to successful development of small
molecule drugs for hard-to-target intracellular proteins.