Sorafenib increases tumor treating fields-induced cell death in glioblastoma by inhibiting STAT3

A newly diagnosed or recurrent Glioblastoma multiforme (GBM) can be treated with Tumor-treating fields (TTFields), an emerging type of alternative electric field-based therapy using low-intensity electric fields. TTFields have a penchant to arrest mitosis, eventually leading to apoptosis. Therefore, it is regarded as a potential anticancer therapy. However, in this study, we confirmed the combined efficacy of sorafenib and TTFields to improve the treatment efficiency of malignant GBM. Experimentation revealed the ability of sorafenib to decrease the signal transducer and activator of transcription 3 (STAT3) and this inhibition increased the sensitivity of TTFields in preventing tumor expansion. It was found that both combinatorial as well as monotherapy aimed to inhibit or reduce the level of STAT3, but the extent was different and based upon the reaction conditions. This drug is also capable of arresting multiple kinase pathways along with STAT3-related proteins (Mcl-1 and Survivin). STAT3 silencing can also be accomplished by RNA interference and can increase the TTFields-sensitizing effect of sorafenib. If the effects are reversed and gene regulating STAT3 is expressed more, it annihilates the effects of treatment. Moreover, sorafenib plus TTFields significantly inhibited xenograft tumor growth and combinatorial treatment reduced STAT3 expression more effectively in vivo. These in vitro and in vivo results indicate that sorafenib tends to sensitize GBM cells to TTFields-induced apoptosis by inhibiting STAT3.