A novel phosphorylated STAT3 inhibitor enhances T cell cytotoxicity against melanoma through inhibition of regulatory T cells

Abstract

The activation of signal transducer and activator of transcription 3 (STAT3) has been identified as a key mediator that drives the fundamental components of melanoma malignancy, including immune suppression in melanoma patients. Increasing evidence also suggests that regulatory T cells (Tregs) are important in suppressing anti-tumor immunity and play a dominant role in negating efficacious immunotherapy approaches. We hypothesized that WP1066, a novel inhibitor of STAT3 signaling, reverses immune suppression through the inhibition of Tregs and that this contributes to the antitumor activity of these agents against melanoma brain metastases. We found that the mean percentage of peripheral blood mononuclear cells expressing phosphorylated STAT3 (p-STAT3) was significantly elevated in samples from patients with melanoma brain metastases compared to healthy donors, 16.13% ± 2.48% vs 4.17% ± 1.79%. The p-STAT3 inhibitor WP1066 enhanced CD3+ (which contained Tregs) but not CD8+ T cell cytotoxicity against human A375 melanoma cells, indicating that this p-STAT3 blockade agent did not directly activate CD8+ T cells. Furthermore, the p-STAT3 inhibitor did not enhance the cytotoxicity of CD3+CD25-T cells (from which Tregs were excluded), indicating that the enhanced cytotoxicity of WP1066 is secondary to its inhibition of Tregs. This was confirmed by demonstrating that WP1066 inhibited FoxP3+ Treg induction in a dose-dependent manner. Moreover, CD3+ T cells exhibited markedly enhanced levels of phosphorylated ZAP-70, a critical proximal signal in T cell activation, after exposure to WP1066. Similar effects were not observed in Treg-depleted CD3+CD25-T cell populations, confirming that the T cell activation by WP compounds is secondary to their inhibition of the Tregs. These results suggest that WP1066 enhances T cell cytotoxicity against melanoma through inhibition of Tregs.

Bcr-Abl ubiquitination and Usp9x inhibition block kinase signaling and promote CML cell apoptosis

“…Jak2 ubiquitination also explains the reported Jak/Stat-inhibitory activity of WP1130 (V.K., N.J.D., manuscript in preparation) and less-active derivatives such as WP1066 and WP1034. [38][39][40][41] Based on the activities reported here and on previous observations, WP1130 initiates a series of events that results in the ubiquitination of proteins such as Bcr-Abl with K63-linked polymers. This form of protein modification typically signals for proteins to traffic or transfer to organelles, and, in the case of Bcr-Abl, the aggresome appears to be the main site for transfer.…”

Naringenin reduces lung metastasis in a breast cancer resection model

“…The purified CD4 + T cells were cultured with anti-CD3 antibody (3 μg/mL), anti-CD28 antibody (1 μg/mL) and TGF-β1 (5 ng/mL) to induce regulatory T cells (Kong et al, 2009). Naringenin was supplemented to the culture at concentrations of 0 and 100 μmol/L for 72 h. Cells treated with neither TGF-β1 nor naringenin were used as normal controls.…”

STAT3 Inhibition Enhances the Therapeutic Efficacy of Immunogenic Chemotherapy by Stimulating Type 1 Interferon Production by Cancer Cells

“…In TH17 cells, STAT3 activation stimulates the expression of the ectonucleotidases CD39 and CD73, hence augmenting their immunosuppressive actions (13). In Tregs, STAT3 functionally and physically interacts with FOXP3 (14), which might explain why STAT3 enhances the function of FOXP3 þ Tregs (15). STAT3 can be activated in distinct myeloid cell types, including tumor-associated macrophages and myeloidderived suppress cells, stimulating their immunosuppressive function (16,17).…”