Exploiting the polypharmacology of alectinib for synergistic RNA splicing disruption with RBM39 degraders

Precise control of pre-mRNA splicing is critical for transcriptome integrity, and its disruption is increasingly recognised as a vulnerability in cancer. Here, we identify a functional interplay between two key splicing regulators, RBM39 and serine/arginine protein kinase 1 (SRPK1), and show that dual targeting of these factors severely compromises splicing fidelity in high-risk neuroblastoma. We use the molecular glue indisulam to degrade RBM39 and repurpose the clinical ALK inhibitor alectinib which potently inhibits SRPK1. Co-treatment with indisulam and alectinib inhibited cell proliferation, induced apoptosis, and caused G2/M arrest in multiple cancer cell lines, including MYCN -amplified neuroblastoma. RNA sequencing revealed enhanced splicing defects preferentially in DNA repair and genome maintenance related genes following combination treatment, leading to R-loop accumulation and increased DNA damage. In the Th-MYCN/ALK ^F1174L neuroblastoma mouse model, combination therapy induced complete tumour regression and significantly improved survival rates compared with monotherapies. These findings demonstrate that combining indisulam and alectinib is a promising approach to treat aggressive malignancies such as high-risk neuroblastoma, exploiting the previously untapped polypharmacology of alectinib as a clinical RNA splicing inhibitor and supporting the therapeutic value of co-targeting interdependent splicing factors for synergistic benefit.