Precise control of pre‑mRNA splicing is vital for transcriptome integrity, and its disruption is an emerging cancer vulnerability. Here, we use indisulam to degrade RBM39 and show that the clinical ALK inhibitor alectinib can be repurposed to inhibit SRPK1. Co-treatment of indisulam and alectinib inhibited cell proliferation, induced apoptosis, and caused cell cycle arrest in multiple cancer cell lines, including MYCN-amplified neuroblastoma. RNA sequencing revealed enhanced splicing defects preferentially in DNA repair-related genes following combination treatment, leading to R-loop accumulation and increased DNA damage. In the Th-MYCN/ALKF1174L 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 untapped polypharmacology of alectinib as an RNA splicing inhibitor and supporting the therapeutic value of co-targeting interdependent splicing factors for synergistic benefit.