Novel Phosphorylated STAT3 Inhibitor Enhances T Cell Cytotoxicity against Melanoma through Inhibition of Regulatory T Cells

Scientists have made new findings in immunotherapy, particularly in the treatment of melanoma, through the discovery of a novel phosphorylated STAT3 inhibitor. According to a study, this inhibitor, WP1066, enhances T cell cytotoxicity against melanoma by inhibiting regulatory T cells (Tregs). The activation of STAT3 has been identified as a key mediator of melanoma malignancy, including immune suppression in patients. Increasing evidence suggests that Tregs play a crucial role in suppressing anti-tumor immunity and negating efficacious immunotherapy approaches.

Key Takeaways:

• The activation of STAT3 is a key mediator of melanoma malignancy, including immune suppression in patients.
• Regulatory T cells (Tregs) play a dominant role in suppressing anti-tumor immunity and negating efficacious immunotherapy approaches.
• WP1066, a novel phosphorylated STAT3 inhibitor, enhances T cell cytotoxicity against melanoma by inhibiting Tregs.
• The mean percentage of peripheral blood mononuclear cells expressing phosphorylated STAT3 (p-STAT3) was significantly elevated in samples from patients with melanoma brain metastases.
• The p-STAT3 inhibitor WP1066 enhanced CD3+ (which contained Tregs) but not CD8+ T cell cytotoxicity against human A375 melanoma cells.
• WP1066 inhibited FoxP3+ Treg induction in a dose-dependent manner, confirming its role in Treg inhibition.
• 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 its inhibition of Tregs.
• WP1066 does not directly activate CD8+ T cells, but rather enhances their cytotoxicity through the inhibition of Tregs.
• This study suggests that WP1066 can be a potential therapeutic agent for treating melanoma through its inhibition of Tregs.

Statistics:

• Mean percentage of peripheral blood mononuclear cells expressing phosphorylated STAT3 (p-STAT3) in patients with melanoma brain metastases: 16.13 [+ or -]2.48% (compared to 4.17 [+ or -]1.79% in healthy donors).
• WP1066 inhibited FoxP3+ Treg induction in a dose-dependent manner.

Sources:

• Cancer Immunology, Immunotherapy, 2009;58(7):1023-32.
• The University of Texas MD Anderson Cancer Center, Dept. of Neurosurgery, Unit 442, 1515 Holcombe Boulevard, Houston, TX 77030-4009 USA.
• Springer, 233 Spring Street, New York, NY 10013, USA.
• Cancer Weekly, 2009.