Discovery of a New CaMKII-Targeted Synthetic Lethal Therapy against Glioblastoma Stem-like Cells

SIMPLE SUMMARY: The poor prognoses of patients with glioblastoma multiforme (GBM) are attributed to glioblastoma stem-like cells (GSCs), which induce drug resistance and rapid tumor recurrence. Accordingly, the discovery of promising therapies targeting GSCs is important for the treatment of GBM. The purpose of this study is to explore a novel synthetic lethal therapy targeting calcium/calmodulin-dependent protein kinase II (CaMKII), an emerging target for combating GSCs. Through high-throughput drug combination screening using CaMKII inhibitors and a library of bioactive compounds in GSCs, we find that the combined treatment with CaMKII and neurokinin 1 receptor (NK1R) inhibitors exhibit chemical synthetic lethal effects both in vitro and in vivo. Further analyses at the molecular level demonstrate that NK1R is a potential synthetic lethal partner of CaMKIIγ in its role in eradicating GSCs. Therefore, we propose a novel CaMKII-targeted combination therapy for the effective treatment of GBM. ABSTRACT: Glioblastoma stem-like cells (GSCs) drive tumor initiation, cancer invasion, immune evasion, and therapeutic resistance and are thus a key therapeutic target for improving treatment for glioblastoma multiforme (GBM). We previously identified calcium/calmodulin-dependent protein kinase II (CaMKII) as an emerging molecular target for eliminating GSCs. In this study, we aim to explore a new CaMKII-targeted synthetic lethal therapy for GSCs. Through high-throughput drug combination screening using CaMKII inhibitors and a bioactive compound library in GSCs, neurokinin 1 receptor (NK1R) inhibitors such as SR 140333 and aprepitant are found to be potential anticancer agents that exhibit chemical synthetic lethal interactions with CaMKII inhibitors, including hydrazinobenzoylcurcumin (HBC), berbamine, and KN93. Combined treatment with NK1R and CaMKII inhibitors markedly suppresses the viability and neurosphere formation of U87MG- and U373MG-derived GSCs. In addition, the combination of HBC and NK1R inhibitors significantly inhibits U87MG GSC tumor growth in a chick embryo chorioallantoic membrane (CAM) model. Furthermore, the synthetic lethal interaction is validated using RNA interference of CaMKIIγ and NK1R. Notably, the synthetic lethal effects in GSCs are associated with the activation of caspase-mediated apoptosis by inducing p53 expression and reactive oxygen species generation, as well as the suppression of stemness marker expression by reducing nuclear factor-kappa B (NF-κB) activity. This follows the downregulation of phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling and a decrease in intracellular calcium concentration. Moreover, NK1R affects CaMKIIγ activation. These findings demonstrate that NK1R is a potential synthetic lethal partner of CaMKII that is involved in eradicating GSCs, and they suggest a new CaMKII-targeted combination therapy for treating GBM.