Targeting STAT3 Promotes Tumor Cell Death and Enhances T-Cell Activity in HPV16-Positive Cancer

Background/Objectives: Human papillomavirus (HPV) oncoproteins early (E)6 and E7 cause upregulation of the IL-6 and IL-23 cytokines in HPV16+ cancers, contributing to tumor progression through enhanced tumor cell proliferation and suppression of the tumor specific adaptive CD8 T-cell response. The IL-6 and IL-23 receptors signal through signal transducer and activator of transcription 3 (STAT3) in the tumor microenvironment. Methods: To better understand how HPV-induced STAT3 signaling contributes to tumor progression and explore its therapeutic potential, we used the platinum (IV) compound CPA-7, a specific STAT3 inhibitor. CPA-7 was tested in vitro for its ability to inhibit STAT3 signaling, alter proliferation, and cause cell death in HPV16+ C3.43 tumor cells. In vivo, CPA-7 was tested for its ability to affect the HPV specific T-cell response, tumor growth, and survival in C3.43 tumor bearing mice. Results: In vitro, CPA-7 inhibited STAT3 signaling, reduced proliferation, and caused significant cell death to HPV16+ C3.43 cells. In vivo, CPA-7 eradicated early-stage HPV16+ tumors, while therapeutic treatment of late-stage tumors led to a systemically increased presence of tumor-specific CD8 T-cells and halted tumor progression. Conclusions: These results suggest that targeting STAT3 signaling downregulates tumor cell proliferation and induces tumor cell death. In addition, targeting STAT3 increases the HPV-specific anti-tumor adaptive immune response. Combined, this results in significantly reduced late-stage HPV16+ tumor progression.