The FOXM1 Inhibitor, RCM-1, Enhances Venetoclax Mediated Apoptosis Through the Downregulation of ATP2B4 in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children. Intensifying chemotherapy has failed to improve survival rates for metastatic or relapsed RMS cases, and survivors often suffer from significant long-term toxicities. New therapies are critically needed to improve treatment effectiveness and reduce side effects in RMS. FOXM1 is an oncogenic transcription factor highly overexpressed in RMS and associated with poor survival outcomes. Since FOXM1 inhibits apoptosis, in this study, we explored the combination of RCM-1, a specific FOXM1 inhibitor, with venetoclax, an antiapoptotic BCL2 inhibitor. This combination therapy effectively reduced tumor cell viability in vitro, induced tumor cell apoptosis in vivo, and was safe in a mouse model of RMS. Using RNA sequencing, we demonstrated that the combination therapy decreased ATP2B4, a plasma membrane calcium channel protein. Furthermore, we showed that RCM-1, rather than venetoclax, treatment reduced ATP2B4 expression and enhanced RMS cells' sensitivity to apoptosis. We subsequently confirmed that FOXM1 transcriptionally regulated the expression of ATP2B4, as shown by the luciferase assay. Using publicly available datasets, we found that ATP2B4 is overexpressed in RMS compared to normal muscle cells. Additionally, the knockdown of ATP2B4 inhibited cell proliferation, colony formation, and cell migration. In sum, combining RCM-1 with venetoclax sensitizes RMS to apoptosis by decreasing ATP2B4. These findings suggest that ATP2B4 plays a key role in regulating intracellular calcium levels, cell growth, and migration. This makes ATP2B4 a promising therapeutic target for RMS and supports studying this combination therapy in early-stage human clinical trials.