FOXM1 targeting alters AURKB activity and reshapes antitumor immunity to curb the progression of small cell lung cancer.

Background: Small cell lung cancer (SCLC) is a lethal lung malignancy and patients are often diagnosed with distant metastasis. Nearly all patients suffer from disease relapsing with inherent chemoresistance. Lack of targeted SCLC therapies further worsens disease outcomes, making it highly desirable to identify novel and effective therapeutic targets.

Methods: To search for potential therapeutic targets in SCLC, we analyzed publicly available single-cell and bulk RNA-sequencing (RNA-seq) data from normal, lung adenocarcinoma, and SCLC tumor tissues. To assess the targeting potential of FOXM1, we developed various in vitro models, including DOX-On-shFOXM1 (Tet-ON) inducible stable knockdown systems. Cisplatin resistant human and murine SCLC cell lines were generated to assess the role of FOXM1 in chemotherapy resistance. Immunoblotting, immunohistochemistry (IHC), and immuno-fluorescence were used to analyze the expression of FOXM1 and target proteins. ChIP-assay was used to study protein-gene interactions. Further, multicolor flow cytometry was employed to study the effect of FOXM1 inhibition on human T cells activation and differentiation. Subcutaneous xenograft and SCLC spontaneous (RPM: RB ^fl/fl ;TP53 ^fl/fl ;LSL-MYC ^T58A ) mouse models were used to evaluate the efficacy of FOXM1 inhibitors.

Results: Single-cell as well as bulk RNA-seq data revealed that FOXM1, an oncogenic transcription factor, is overexpressed in SCLC, and it was recapitulated in human and murine SCLC tissues and cell lines. Interestingly, chemo-resistant (CR) SCLC showed a substantially higher FOXM1 expression than naïve SCLC. Silencing FOXM1 genetically or pharmacologically by FOXM1 inhibitors revealed a marked reduction in cell viability, colony formation, migration and sphere formation in naïve and CR SCLC cells. Moreover, FOXM1 inhibition induced apoptosis and cell cycle arrest in SCLC cells. Furthermore, FOXM1 inhibition in combination with first-line platinum-based chemotherapy showed synergistic anticancer effects in both xenograft and RPM mouse models of SCLC. Our RNA-seq analysis revealed that FOXM1 inhibition altered the Aurora Kinase B (AURKB) signaling pathway, which is dysregulated in SCLC. Moreover, we found FOXM1 inhibition enhanced T cell activation and supported the differentiation of CD8 + cytotoxic T cells, and T cell-mediated killing of cancer cells.

Conclusions: Our study demonstrates that FOXM1 targeting using small molecule inhibitors has the potential to be a novel therapeutic strategy to combat SCLC progression including chemotherapeutic resistance and reshaping the anti-tumor immune response.