PTEN and glioblastoma: Among the down-hit compounds, paclitaxel—a microtubule-stabilizing agent that induces defects in mitotic spindle assembly and cell division—is already known to down-regulate miR-21 expression in human glioblastoma cells independent on the status of phosphatase and tensin homolog (PTEN), a target gene of miR-21, in a previous report18.