Targeting STAT3 promotes cell death and enhances T-cell activity in HPV-associated cancer

Human papillomavirus oncoproteins early (E)6 and E7 are crucial for sustaining chronic infection and driving malignant transformation in stratified epithelia when the immune system fails to clear the virus. In addition to impairing the cellular surveillance systems that maintain genomic integrity and promoting cell cycle progression, these oncoproteins increase interleukin-23 (IL-23) production by tumor-associated macrophages in HPV⁺ cancers, leading to suppression of local tumor-specific T-cell immunity. IL-23 signaling through the IL-23 receptor (IL-23R) on HPV-specific CD8⁺ T cells reduces their cytotoxicity and proliferative capacity. Downstream, IL-23R activates signal transducer and activator of transcription 3 (STAT3), a transcription factor known to drive multiple cancer hallmarks. To investigate how STAT3 signaling affects both the progression of HPV+ tumors and specifically the T-cell response against its E6 and E7 proteins, we employed the C3.43 syngeneic murine tumor model, which expresses the full length HPV16 genome under its native promoters, and used the cisplatin derived small molecule inhibitor CPA-7 to inhibit STAT3. IL-23R signaling induces phosphorylation of STAT3 monomers (pSTAT3), leading to their dimerization and subsequent nuclear translocation, where they bind DNA. CPA-7 prevents dimerized STAT3 from binding DNA and functionally reduces overall pSTAT3 levels. In vitro treatment of HPV⁺ C3.43 tumor cells with CPA-7 revealed that STAT3 inhibition induces tumor cell death. In vivo, mice challenged with C3.43 tumor cells and treated with CPA-7 completely eradicated their tumors, with 4 of 10 mice demonstrating durable immune memory upon tumor re-challenge. Remarkably, even established, late-stage HPV⁺ tumors were fully eradicated upon CPA-7 treatment. Full eradication required an intact adaptive immune system, as CPA-7 treatment failed to eliminate HPV⁺ tumors in mice lacking both CD4⁺ and CD8⁺ T cells. Together, these data demonstrate that STAT3 promotes HPV⁺ tumor cell survival and suppresses the adaptive, tumor-specific T-cell immune response. Targeting STAT3 may therefore represent a promising strategy to induce tumor cell death and counteract IL-23-induced, STAT3-mediated immune suppression in HPV-associated cancers.