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

TL;DR

This study shows that a drug targeting the STAT3 pathway can kill HPV-related cancer cells and boost immune responses in mice.

Contribution

The study demonstrates that CPA-7, a STAT3 inhibitor, effectively targets HPV16+ tumors by inducing cell death and enhancing T-cell activity.

Findings

CPA-7 inhibited STAT3 signaling and caused significant cell death in HPV16+ C3.43 cells in vitro.

In vivo, CPA-7 eradicated early-stage tumors and increased tumor-specific CD8 T-cells in late-stage tumor-bearing mice.

Targeting STAT3 reduced tumor progression and enhanced the anti-tumor immune response in HPV16+ cancers.

Abstract

Standard treatment for human papillomavirus positive (HPV+) cancer includes surgical resection combined with chemo and/or radiation therapy. These can impair fertility, speech, or quality of life. This highlights the immediate need for better and less invasive treatment of HPV-driven cancers. The two viral proteins that put patients with an HPV infection at risk for cancer are able to suppress the immune-mediated clearance of HPV+ cells. Here we describe the efficacy of CPA-7, a drug that shuts down the STAT3 signaling pathway partially responsible for this immune suppression in HPV-driven tumors. This drug rescued the HPV-specific immune response in mice bearing HPV+ tumors and directly killed the cancer cells. Combined, these effects empowered CPA-7 to cure a significant percentage of mice bearing late-stage HPV+ tumors, highlighting the therapeutic efficacy of targeting STAT3 in HPV-driven disease.

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.

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