Targeting MYCN Degradation by HLB-0532259 Induces Senescence in Retinoblastoma

Purpose: Amplification of MYCN is a primary driver of aggressive retinoblastoma (RB), yet it remains a challenging therapeutic target. This study aimed to evaluate the therapeutic potential of the PROTAC molecule HLB-0532259 in degrading MYCN and suppressing RB growth. Methods: Y79 and WERI-Rb1 RB cell lines were treated with HLB-0532259, and MYCN protein degradation, cell viability, and time-dependent transcriptional changes were assessed by Western blotting, cell viability assays, RNA-seq, and proteomics. The therapeutic potential was further validated in an orthotopic Y79 xenograft mouse model through intravitreal administration, with tumor burden evaluated by histology and immunohistochemistry. Results: HLB-0532259 induced dose-dependent degradation of MYCN in both cell lines, with Y79 cells showing higher sensitivity. Transcriptomic and proteomic analyses revealed rapid activation of the p53-p21 pathway, downregulation of DNA repair and epigenetic regulators, and accumulation of DNA damage. Proteomic profiling confirmed upregulation of senescence-associated secretory phenotype factors and downregulation of MYCN-dependent effectors, including HMGA1 and TRAF6. In orthotopic xenografts, intravitreal administration of HLB-0532259 reduced intraocular tumor burden, decreased Ki-67 and MYCN-positive cells, and activated p53, p21, and NF-κB signaling. Conclusions: Targeted MYCN degradation by HLB-0532259 effectively inhibits RB growth and induces a DNA damage-associated senescence program, highlighting targeted MYCN degradation as a promising therapeutic strategy for MYCN-driven RB.