A Novel Small Molecule Inhibitor of Signal Transducers and Activators of Transcription 3 Reverses Immune Tolerance in Malignant Glioma Patients

Abstract

Overcoming the profound immunosuppression in patients with solid cancers has impeded efficacious immunotherapy. Signal transducers and activators of transcription 3 (STAT3) has recently emerged as a potential target for effective immunotherapy, and in this study, we describe a novel small molecule inhibitor of STAT3 that can penetrate the central nervous system (CNS) in mice and in physiologically relevant doses in vitro and reverse tolerance in immune cells isolated from glioblastoma multiforme (GBM) patients. Specifically, it induces the expression of costimulatory molecules on peripheral macrophages and tumor-infiltrating microglia, stimulates the production of the immune-stimulatory cytokines interleukin 2 (IL-2), IL-4, IL-12, and IL-15, and induces proliferation of effector T cells from GBM patients that are refractory to CD3 stimulation. We show that the functional enhancement of immune responses after STAT3 inhibition is accompanied by up-regulation of several key intracellular signaling molecules that critically regulate T-cell and monocyte activation. Specifically, the phosphorylation of Syk (Tyr 352 ) in monocytes and ZAP-70 (Tyr 319 ) in T cells are enhanced by the STAT-3 inhibitor in marked contrast to toll-like receptor and T-cell receptor agonists, respectively. This novel small molecule STAT3 inhibitor has tremendous potential for clinical applications with its penetration into the CNS, easy parental administration, direct tumor cytotoxicity, and potent immune adjuvant responses in immunosuppressed cancer patients.

Signal Transducer and Activator of Transcription-3: A Molecular Hub for Signaling Pathways in Gliomas

“…One route to reversing immune tolerance is by targeting CD8 + CD25 À T cells themselves. When STAT-3 activity in monocytes from glioma patients was inhibited, the expression of costimulatory molecules such as CD80 and CD86 was up-regulated, an event that presumably enhanced Tcell activation and is a critical step in reversing immune evasion (39). These data show that inhibiting STAT-3 affects the activation of glioma-infiltrating CD8 + T cells, which serve as one of many potential targets in overcoming immune suppression.…”

“…Preliminary in vivo studies showed that WP1066 successfully crossed the bloodbrain barrier, a key feature in drug design for glioma patients (39), and that it significantly inhibited the growth of glioma xenografts compared with untreated controls (49). Importantly, the effects of WP1066 are tumor specific.…”

“…WP1066 also reversed immune tolerance in glioblastoma patients, presumably by blocking STAT-3 -mediated immune suppression and tolerogenesis. WP1066-stimulated proliferation of T cells from glioblastoma patients and enhanced immunogenic responses in glioma-infiltrating microglia, macrophages, and peripheral blood monocytes (39). WP1066 also promoted immunogenic responses by up-regulating the costimulatory molecules CD80 and CD86 and the T-cell effector cytokines IL-2, IL-4, IL-12, and IL-15 (39).…”

Efficacy and pharmacodynamic effects of bosutinib (SKI-606), a Src/Abl inhibitor, in freshly generated human pancreas cancer xenografts

“…This may be particularly important with Src inhibitors, where a nonmetastatic subcutaneous model may not pick up important anti-invasive or antimetastatic properties of a drug. Finally, the altered immunologic environment of a nude mouse obscures immunologic properties of these compounds, which may be important for Src inhibitors because STAT signaling regulates immune tolerance in animal models (34). Although the model can be used as a platform to screen novel drugs for therapeutic potential and evaluate biomarkers of response/resistance preclinically, it is also being evaluated as a way to select drugs for specific patients in an ongoing clinical protocol at Johns Hopkins (35).…”

Synthesis of Novel Cannabinoid Ligands and Their Use as Anti-Glioma and Anti-Inflammatory Agents

“…The decline in pSTAT3 is of particular interest due its role in tumorigenesis, i.e. proliferation, angiogenesis, and inhibition of apoptosis, 113 the proposed role in immune tolerance in glioblastoma patients, 114 and provides a novel target in cancer therapy. 113,115 This suggests that cannabinoid receptors may be a novel target for the regulation of STAT3 function via CB1 or CB2 regulation of G αo -c-Src 116 or via a GPR55 regulated G α12/13 -RhoA-ERK-STAT3 pathway.…”