Overcoming the leptomeningeal seeding of medulloblastoma by targeting HSP70.

Leptomeningeal seeding (LMS) via cerebrospinal fluid is a common and often fatal progression in medulloblastoma (MB), significantly worsening prognosis. However, its molecular drivers are poorly understood, and effective treatments remain limited. This study aimed to establish a physiologically relevant MB LMS model and identify novel therapeutic targets through detailed characterization of seeding cell biology. Using three rounds of serial orthotopic xenograft transplantation and in vivo selection, we isolated distinct seeding (S3) and non-seeding (N3) MB cell populations. Functional and transcriptomic analyses revealed unique phenotypes and differentially expressed genes (DEGs). Based on DEGs, we screened inhibitors and assessed the therapeutic efficacy of the HSP70 inhibitor VER155008, alone and with chemotherapeutics (ifosfamide or cisplatin), both in vitro and in a preclinical LMS mouse model established by cerebellar implantation of S3 cells. S3 cells showed slower proliferation, altered migration behavior, and increased adhesion to collagen IV versus N3 cells. Transcriptomic profiling identified HSP70 as the most upregulated gene in S3 cells, with strong enrichment in metabolic pathways. Among six candidate compounds, VER155008 most effectively suppressed S3 cell viability. In vitro, VER155008 combined with 4-hydroperoxycyclophosphamide (active ifosfamide metabolite) produced a synergistic antitumor effect. This synergy was confirmed in vivo, where VER155008 with ifosfamide significantly reduced spinal LMS. These findings highlight HSP70 as a promising therapeutic target for MB LMS. The observed synergy between VER155008 and ifosfamide supports a selective combination strategy, offering a novel therapeutic avenue to improve outcomes in patients with leptomeningeal dissemination of MB.