A Novel Small Molecule, LLL12, Inhibits STAT3 Phosphorylation and Activities and Exhibits Potent Growth-Suppressive Activity in Human Cancer Cells

Abstract

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) signaling is frequently detected in cancer, promoting its emergence as a promising target for cancer treatment. Inhibiting constitutive STAT3 signaling represents a potential therapeutic approach. We used structure-based design to develop a nonpeptide, cell-permeable, small molecule, termed as LLL12, which targets STAT3. LLL12 was found to inhibit STAT3 phosphorylation (tyrosine 705) and induce apoptosis as indicated by the increases of cleaved caspase-3 and poly (ADP-ribose) polymerase in various breast, pancreatic, and glioblastoma cancer cell lines expressing elevated levels of STAT3 phosphorylation. LLL12 could also inhibit STAT3 phosphorylation induced by interleukin-6 in MDA-MB-453 breast cancer cells. The inhibition of STAT3 by LLL12 was confirmed by the inhibition of STAT3 DNA binding activity and STAT3-dependent transcriptional luciferase activity. Downstream targets of STAT3, cyclin D1, Bcl-2, and survivin were also downregulated by LLL12 at both protein and messenger RNA levels. LLL12 is a potent inhibitor of cell viability, with half-maximal inhibitory concentrations values ranging between 0.16 and 3.09 microM, which are lower than the reported JAK2 inhibitor WP1066 and STAT3 inhibitor S3I-201 in six cancer cell lines expressing elevated levels of STAT3 phosphorylation. In addition, LLL12 inhibits colony formation and cell migration and works synergistically with doxorubicin and gemcitabine. Furthermore, LLL12 demonstrated a potent inhibitory activity on breast and glioblastoma tumor growth in a mouse xenograft model. Our results indicate that LLL12 may be a potential therapeutic agent for human cancer cells expressing constitutive STAT3 signaling.

STAT3 Serine 727 Phosphorylation: A Relevant Target to Radiosensitize Human Glioblastoma

“…Those dimers translocate into the nucleus where they regulate expression of target-genes (5). pSTAT3-Y705 inhibits apoptosis through upregulation of Survivin (38),…”

Inhibition of STAT3 enhances the radiosensitizing effect of temozolomide in glioblastoma cells in vitro and in vivo

“…Thus, STAT3 is a convergence point of many signaling pathways and plays a major role in oncogenesis. Efforts are ongoing to develop anticancer drugs that target STAT3 (14)(15)(16). In malignant gliomas, a number of potential drugs inhibiting STAT3 activity have been investigated (17)(18)(19)(20)(21)(22)(23).…”

Two small molecule compounds, LLL12 and FLLL32, exhibit potent inhibitory activity on STAT3 in human rhabdomyosarcoma cells

“…For simulated binding energies to STAT3, LLL12 is 10-fold better than LLL3 and is predicted to be more potent than LLL3 in inhibiting constitutive STAT3 pathway. Recently, we reported the potent inhibition of STAT3 phosphorylation and growthsuppression of LLL12 in human breast cancer and glioblastoma cells (21).…”

“…The simulated binding energies of LLL12 to STAT3 predict it to be a potent inhibitor of the constitutive STAT3 pathway. The detail of LLL12 synthesis was described in our previous report (21).…”