gms | German Medical Science

Objective: Chemotherapeutic treatment of high-grade glioma (HGG) aims to damage the DNA during mitosis, leading to mitotic catastrophe and cell death. Vincristine, in combination with Procarbazine and CCNU (PCV-treatment regimen), is established for the treatment of HGG, but its efficacy is often limited due to its severe neurotoxic side effects. Vincristine is an antimitotic agent, preventing spindle fiber attachment to chromatids. This attachment, as chromosomal segregation, is controlled by the spindle assembly checkpoint (SAC), which allows repair of chemotherapy-based damage. A gatekeeper of the SAC is the kinase Monopolar Spindle 1 (MPS1). Influencing the SAC by MPS1-inhibition might lead to an improved effect of Vincristine.

Method: mRNA expression of MPS1 was analyzed by sqRT-PCR in glioblastoma (GBM) cell lines and patients’ tumor samples. Immunohistochemistry was used to detect MPS1 protein expression in matched samples of 24 astrocytomas WHO grade II and 24 GBM. Tumor grade was correlated with protein expression. Cell cycle arrest under a MPS1-inhibitor (MPS1-IN-3) and/or Vincristine treatment were analyzed by FACS in the GBM cell line U251. Cell nucleus anomalies were detected by fluorescence microscopy. The effect of MPS1-IN-3 in combination with Vincristine was assessed in orthotopic GBM mouse models (n=3–7 mice/group).

Results: MPS1 was overexpressed by tumor tissue and corresponded positively to the tumor grade. The combination of Vincristine and MPS1-IN-3 in comparison to monotherapy with either substance led to significantly less cell cycle arrest of U251 cells (45% versus 14%) and resulted in drastic nuclear aberrancies, including lobed nuclei, multinucleated cells and micronuclei, reflecting gross chromosome segregation defects. In orthotopic mouse models, only the combination of MPS1-IN-3 and Vincristine treatment led to almost complete tumor shrinkage and prolonged survival, while 100% of the monotherapeutically treated mice died.

Conclusions: MPS1 may serve as a prognostic marker, as its expression level corresponded significantly to tumor grading. More importantly, it may also serve as a new therapeutic target, whose selective inhibition sensitizes GBM cells to the effects of antimitotic drugs. Regarding the synergistic effect of Vincristine and MPS1-IN-3 to tumor shrinkage, MPS1-inhibition might be an essential supplement to the PCV-treatment regimen. In future, a MPS1-targeted treatment may influence tumor control rates in HGG positively.