DDDR-02. NOVEL MDM4 INHIBITOR CEP-1347-BASED THERAPY FOR P53 WILD-TYPE MALIGNANT MENINGIOMA

Abstract BACKGROUND Although a significant proportion of meningiomas are clinically aggressive, there is currently no effective chemotherapy for them. An increasing number of studies have been conducted to develop targeted therapies, but none have focused on the p53 pathway as a potential target. In this study, we determined the in vitro and in vivo effects of CEP-1347, a novel small-molecule inhibitor of MDM4 with known safety in humans, on malignant meningioma cells, and also investigated the effects of CEP-1347 when combined with MDM2 inhibition. METHODS The effects of CEP-1347 and MDM4 knockdown on the p53 pathway in human meningioma cell lines with and without a p53 mutation were investigated using RT-PCR and Western blot analyses. The growth inhibitory effects of CEP-1347 were investigated in vitro and in a mouse xenograft model of meningioma. We also investigated the effects of CEP-1347 in combination with genetic or pharmacological inhibition of MDM2 in vitro. [Results] CEP-1347 at clinically relevant concentrations inhibited MDM4 expression, activated the p53 pathway in malignant meningioma cells with wild-type p53, and inhibited growth preferentially in cells expressing wild-type p53, which was mostly mimicked by MDM4 knockdown. CEP-1347 effectively inhibited the growth of malignant meningioma xenografts at a dose substantially lower than the maximum dose that could be safely administered to humans. The small-molecule MDM2 inhibitor RG7112 effectively cooperated with CEP-1347 to reduce MDM4 expression, activate the p53 pathway, and inhibit cell growth. [Conclusion] Our findings suggest that targeting the p53 pathway with CEP-1347 is a novel and viable approach to treating aggressive meningiomas, with even greater efficacy when combined with MDM2 inhibitors.