Abemaciclib Inhibits Retinoblastoma Tumor Growth by Targeting CDK1/2

Purpose: This study aimed to investigate the antitumor efficacy and molecular mechanisms of abemaciclib in retinoblastoma beyond its canonical role as a cyclin-dependent kinase (CDK) 4/6 inhibitor. Methods: Transcriptomic differences between retinoblastoma and healthy retinal tissues were analyzed using multiple Gene Expression Omnibus (GEO) datasets. Candidate gene was validated by immunohistochemistry in patient specimens and by Western blotting and quantitative real-time PCR in retinoblastoma cell lines. Cell viability and proliferation were evaluated by CCK-8, EdU incorporation, and soft agar colony formation assays. Flow cytometry was performed to analyze cell cycle distribution and apoptosis rates. RNA sequencing and Western blotting were performed to investigate the antitumor mechanisms of abemaciclib in retinoblastoma. DNA damage was specifically detected using γ-H2AX immunofluorescence staining. Additionally, subcutaneous patient-derived xenograft (PDX) and orthotopic cell line-derived xenograft (CDX) models of retinoblastoma were established in immunodeficient mice to evaluate the in vivo therapeutic efficacy. Results: Integrated analysis of five GEO datasets revealed that, among the CDK family members, only CDK1 and CDK2 were consistently overexpressed in retinoblastoma, a finding validated in clinical specimens and cell lines. Abemaciclib significantly inhibited retinoblastoma cell proliferation in vitro and effectively suppressed tumor growth in both PDX and orthotopic CDX models. Mechanistically, abemaciclib reduced phosphorylation of CDK1 and CDK2, resulting in G2/M cell-cycle arrest. It also increased reactive oxygen species (ROS) production, caused DNA damage, inhibited DNA damage repair, activated the p53/p21 pathway, and ultimately induced apoptosis. Conclusions: These findings provide preclinical evidence that establishes abemaciclib as a promising novel treatment strategy for retinoblastoma.