PP-121 is a multi-targeted inhibitor of PDGFR, Hck, mTOR, VEGFR2, Src and Abl with IC50 of 2 nM, 8 nM, 10 nM, 12 nM, 14 nM and 18 nM, also inhibits DNA-PK with IC50 of 60 nM.

PP-121 selectivity interacts within a hydrophobic pocket that is conserved between both tyrosine kinases and PI3Ks, not serine-threonine kinases. PP-121 makes a hydrogen bond to Glu310 in Src, effectively substituting for the structural role of the catalytic lysine and resulting in the ordering of helix C and stabilization of an active conformation. PP-121 also inhibits other PI3Ks including p110α and DNA-PK with IC50 of 52 nM and 60 nM, respectively. PP-121 potently and dose-dependently blocks the phosphorylation of Akt, p70S6K and S6 in two glioblastoma cell lines, U87 and LN229. PP-121 potently inhibits the proliferation of a subset of the tumor cell lines by direct inhibition of PI3Ks and mTOR. PP-121 induces a G0/G1 arrest in LN220, U87 and Seg1 cells. PP-121 also blocks tyrosine phosphorylation induced by v-Src in NIH3T3 cells transformed with v-Src(Thr338). PP-121 could restore actin stress fiber staining in NIH3T3 cells transformed with v-Src(Thr338). PP-121 at a low concentration of 40 nM inhibits Ret autophosphorylation in TT thyroid carcinoma cells that express the C634W oncogenic Ret mutant35. PP-121 inhibits cell proliferation with IC50 of 50 nM in TT thyroid carcinoma cells. PP-121 inhibits cell proliferating stimulated only with VEGF with IC50 of 41 nM in human umbilical vein endothelial cells (HUVECs). PP-121 directly inhibits Bcr-Abl induced tyrosine phosphorylation, resulting in drug-induced apoptosis in K562 cells and a combination of apoptosis and cell cycle arrest in Bcr-Abl expressing BaF3 cells.