Computer-aided lead optimization derives a unique, orally bioavailable inhibitor of the signal transducer and activator of transcription (Stat)3 Src homology 2 domain. BP-1-102 binds Stat3 with an affinity (K_D) of 504 nM, blocks Stat3–phospho-tyrosine (pTyr) peptide interactions and Stat3 activation at 4–6.8 μM, and selectively inhibits growth, survival, migration, and invasion of Stat3-dependent tumor cells. BP-1-102–mediated inhibition of aberrantly active Stat3 in tumor cells suppresses the expression of c-Myc, Cyclin D1, Bcl-xL, Survivin, VEGF, and Krüppel-like factor 8, which is identified as a Stat3 target gene that promotes Stat3-mediated breast tumor cell migration and invasion. Treatment of breast cancer cells with BP-1-102 further blocks Stat3–NF-κB cross-talk, the release of granulocyte colony-stimulating factor, soluble intercellular adhesion molecule 1, macrophage migration-inhibitory factor/glycosylation-inhibiting factor, interleukin 1 receptor antagonist, and serine protease inhibitor protein 1, and the phosphorylation of focal adhesion kinase and paxillin, while enhancing E-cadherin expression. Intravenous or oral gavage delivery of BP-1-102 furnishes micromolar or microgram levels in tumor tissues and inhibits growth of human breast and lung tumor xenografts.

We present evidence that the cisplatin-resistant human ovarian cancer lines, A2780S/CP1 (S/CP1), A2780S/CP3 (S/CP3) and A2780S/CP5 (S/CP5), derived by subjecting the sensitive A2780S ovarian cancer line to multiple rounds of cisplatin treatments followed by recovery and are resistant to 1, 3 and 5 μM cisplatin, respectively, have increased colony-forming ability and altered morphology that is consistent with enhanced motility, migration and invasiveness in vitro. The malignant phenotype progresses with increasing resistance and is associated with hyperactive epidermal growth factor receptor (EGFR)/extracellular signal-regulated kinase (Erk)1/2 and janus kinases (Jaks), aberrant signal transducer and activator of transcription (Stat) 3 activation promoted by EGFR and Jaks, and epithelial-mesenchymal transition (EMT) in vitro. Survivin and FLIP anti-apoptotic factors, vascular endothelial growth factor (VEGF) and matrix metalloproteinase activities are also elevated in the resistant cells. Accordingly, the ectopic expression of constitutively-active Stat3C in the sensitive A2780S cells diminished cisplatin sensitivity. The inhibition of EGFR or Stat3 activity repressed Survivin, VEGF and Vimentin expression and the colony-forming potential, viability, motility and migration of the resistant cells, and sensitized them to cisplatin. Analysis of human ovarian cancer patients’ tumor tissues shows aberrantly-active EGFR and Stat3 that in certain cases correlate with Vimentin over-expression. Intra-peritoneal mouse xenograft studies revealed, compared with the sensitive A2780S line that had low tumor incidence restricted to the ovary, a high tumor incidence for the resistant S/CP3 and S/CP5 lines that formed tumor nodules at several locations on the small intestine and colon, and which responded poorly to cisplatin, but were sensitive to concurrent treatment with cisplatin and EGFR or Stat3 inhibitor. Hyperactive EGFR signaling through Stat3 and the Jak-Stat3 activity together promote ovarian cancer progression to cisplatin resistance and therefore represent targets for preventing the development of cisplatin resistance and the recurrent disease during cisplatin therapy in ovarian cancer.

STAT3 offers an attractive target for cancer therapy, but small-molecule inhibitors with appealing pharmacologic properties have been elusive. Here, we report hydroxamic acid–based and benzoic acid–based inhibitors (SH5-07 and SH4-54, respectively) with robust bioactivity. Both inhibitors blocked STAT3 DNA-binding activity in vitro and in human glioma, breast, and prostate cancer cells and in v-Src–transformed murine fibroblasts. STAT3-dependent gene transcription was blocked along with Bcl-2, Bcl-xL, Mcl-1, cyclin D1, c-Myc, and survivin expression. Nuclear magnetic resonance analysis of STAT3-inhibitor complexes defined interactions with the SH2 and DNA-binding domains of STAT3. Ectopic expression of the SH2 domain in cells was sufficient to counter the STAT3-inhibitory effects of SH4-54. Neither compound appreciably affected STAT1 or STAT5 DNA-binding activities, STAT3-independent gene transcription, or activation of a panel of oncogenic kinases in malignant cells. Each compound decreased the proliferation and viability of glioma, breast, and prostate cancer cells and v-Src–transformed murine fibroblasts harboring constitutively active STAT3. Further, in mouse xenograft models of glioma and breast cancer, administration of SH5-07 or SH4-54 effectively inhibited tumor growth. Our results offer preclinical proof of concept for SH5-07 and SH4-54 as candidates for further development as cancer therapeutics. Cancer Res; 76(3); 652–63. ©2015 AACR.

(E)-4-(3,5-dimethoxystyryl)phenyl acetate (Cmpd1) is a resveratrol analog that preferentially inhibits glioma, breast, and pancreatic cancer cell growth, with IC₅₀ values of 6–19 μM. Notably, the human U251MG glioblastoma tumor line is the most sensitive, with an IC₅₀ of 6.7 μM, compared with normal fibroblasts, which have an IC₅₀ > 20 μM. Treatment of U251MG cells that harbor aberrantly active signal transducer and activator of transcription (Stat) 3 with Cmpd1 suppresses Stat3 tyrosine705 phosphorylation in a dose-dependent manner in parallel with the induction of pserine727 Stat3 and extracellular signal-regulated kinase/mitogen-activated protein kinase 1/2 (pErk1/2^MAPK). Inhibition of pErk1/2^MAPK induction by the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] blocked both the pserine727 Stat3 induction and ptyrosine705 Stat3 suppression by Cmpd1, indicating dependency on the mitogen-activated protein/extracellular signal-regulated kinase kinase–Erk1/2^MAPK pathway for Cmpd1-induced modulation of Stat3 signaling. Cmpd1 also blocked epidermal growth factor–stimulated pStat1 induction, whereas upregulating pSrc, pAkt, p-p38, pHeat shock protein 27, and pmammalian target of rapamycin levels. However, pJanus kinase 2 and pEpidermal growth factor receptor levels were not significantly altered. Treatment of U251MG cells with Cmpd1 reduced in vitro colony formation, induced cell cycle arrest in the G2/M phase and cleavage of caspases 3, 8, and 9 and poly(ADP ribose) polymerase, and suppressed survivin, myeloid cell leukemia 1, Bcl-xL, cyclin D1, and cyclin B1 expression. Taken together, these data identify a novel mechanism for the inhibition of Stat3 signaling by a resveratrol analog and suggest that the preferential growth inhibitory effects of Cmp1 occur in part by Erk1/2^MAPK-dependent modulation of constitutively active Stat3.