Mocetinostat Shows Network-Inhibitory Effects on Glioblastoma Cells, Enhancing Radiotherapy Efficacy

Abstract Purpose Glioblastoma cells use neurite-like extensions, called tumor microtubes (TMs), as intercellular connections to integrate into a communicating network that contributes to glioblastoma’s high therapy resistance. Understanding the biological functions of tumor cell connectivity and overcoming network resistance has emerged as a new therapeutic opportunity. We tested histone deacetylase inhibitors (HDACi) regarding their potential to overcome TM-mediated connectivity and resistance to therapy in glioblastoma. Methods To investigate HDACi, we applied a recently established drug testing pipeline consisting of mono- and co-culture of primary glioblastoma cells in vitro with simplified brain organoids readouts of TM parameters and tumor cell viability. Next, the effect of the class I HDACi mocetinostat in our in vivo two-photon microscopy model with radiotherapy as cytotoxic co-treatment was investigated. To understand underlaying molecular mechanisms, bulk RNA sequencing was performed. Results Mocetinostat showed dose-dependent anti-TM effects in vitro , in contrast to other classes of HDACi in monoculture. In a co-culture of glioblastoma cells with cortical spheroids from human induced pluripotent stem cells, mocetinostat treatment led to a dose- and time-dependent antiproliferative effect. Co-treatment of mocetinostat with radiation increased radiotherapy efficacy in co-cultures as well as in vivo. Potential genes associated with suppressed TM formation as well as radiosensitization were found through bulk RNA sequencing. Conclusions With this drug testing and development pipeline, the HDACi mocetinostat was found to exhibit anti-TM effects in vitro and in vivo . Increased radiotherapy efficacy under mocetinostat support the concept of therapeutic tumor cell network disconnection, strengthening this avenue for novel neuroscience-instructed cancer therapies.