Presenting Author:
Principal Investigator:
Department:
Neurological Surgery
Keywords:
Glioblastoma Multiforme, Therapeutic Resistance, Cancer Stem Cell, Novel Therapeutics, Recurrence
Location:
Third Floor, Feinberg Pavilion, Northwestern Memorial Hospital
B88 - Basic Science
Dopamine signaling and therapeutic resistance in glioblastoma multiforme
Glioblastoma multiforme (GBM), the most common primary brain tumor in adults, is characterized by aggressive recurrence after initial treatment. It has been postulated that recurrence is driven by highly therapy resistance subpopulation of tumor cells known as glioma stem cells (GSCs). While clonal selection has been posited as the main driver of therapy resistance, recent studies from our laboratory and others have shown a high degree of plasticity in GBM cells, which enables differentiated GBM cells to gain a GSC state. Termed conversion, this molecular process increases the frequency of GSCs and may promotes recurrence. Therefore, we have developed a plasticity-based high-throughput drug screening method for preventing conversion. Our initial screening has identified several novel compounds that act as antagonists of neurotransmitter receptors. Further investigation revealed that treatment of patient-derived xenograft (PDX) GBM lines with temozolomide (TMZ) led to the formation of a population of cells that express both CD133, a marker of GSCs, and dopamine receptors 2 and 3 (DRDs) (control: 19.7%, TMZ: 83.8%, p<.001). PDX cells treated with a dopamine receptor agonist exhibited increased expression of SOX2, OCT4 and c-Myc—well-established GSC-markers. Further, treatment with this agonist was sufficient to increase the self-renewal capacity of PDX cells (GBM6 p<.05, GBM39 p<.01, GBM5 p<.05). We next utilized electrophysiology to determine if DRD receptors induced by TMZ respond differently in GSC and non GSC-cells. We treated glioma cells expressing a GSC-reporter, enabling real-time monitoring of GSCs, with dopamine agonists while monitoring with patch-clamping; GSCs show a 3-fold increase in hyperpolarization relative to non-GSCs (p<.001). We next probed the ability of chlorpromazine (CPM), an anti-psychotic, to alter stemness. CPM treatment reduced sphere-forming capacity both alone and in combination with dopamine receptor agonist (GBM6 p<.001, GBM 39 p<.0001). To identify the possible downstream target of dopamine signaling in gliomagenesis, we analyzed clinical data from TCGA and performed pathway enrichment analysis. This analysis identified 4 pathways that had a statistically significant positive correlation with DRD2 signaling, including two master transcription factors HIF1α and HIF2α (HIF2α P=.027 and HIF1α P=.024). A DRD2 agonist induced expression of both HIF1α and HIF2α in PDX GBM; cells with HIF1α knocked down by shRNA treated with DRD agonists are unable to induce the expression of stemness marker c-Myc. These data suggest that dopamine’s influence on GSC states represents a novel activation of the HIF pathway. Overall, we hypothesize that dopamine receptors are a unique therapeutic target for blocking recurrence in GBM. Targeting these receptors represents a strategy by which specific molecular changes induces by chemotherapeutic agents can be inhibited to prevent the induction of resistance in recurrent tumor cells.
