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Efflux of chemotherapy drugs by P‐glycoprotein (P‐gp) at the plasma membrane is thought to be a major cause of cancer multidrug resistance. In this report, we show by flow cytometry that P‐gp also concentrates large amounts of 2 different drugs, Hoechst 33342 and daunorubicin, within a cytoplasmic compartment of multidrug resistant CHRC5 cells. A quantitative assay of Hoechst 33342 revealed that cytoplasmic sequestration by P‐gp in CHRC5 cells accounted for about half of the amount of Hoechst 33342 accumulated by the drug‐sensitive parental Aux B1 cells. Daunorubicin sequestered in the cytoplasm of CHRC5 cells could be released by inhibiting P‐gp function with cyclosporin A, resulting in cell death. A likely site of drug sequestration is P‐gp‐containing cytoplasmic vesicles, in which the P‐gp is oriented so that drugs are transported and concentrated in the interior of the vesicles. P‐gp was detected in the membranes of cytoplasmic vesicles of CHRC5 cells by confocal immunofluorescence microscopy and immunoelectron microscopy with anti‐P‐gp monoclonal antibodies (MAbs). Vesicular localization of daunorubicin was observed by epifluorescence microscopy. The origin and nature of the P‐gp‐containing vesicles are unknown, but they do not correspond to endocytic vesicles. Our results directly demonstrate that chemosensitizer‐induced release of drugs sequestered in cytoplasmic vesicles by P‐gp can be used to overcome multidrug resistance. Int. J. Cancer 76:857–864, 1998.© 1998 Wiley‐Liss, Inc.

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Diffuse gliomas are primary brain tumors associated with a poor prognosis. Cellular and molecular mechanisms driving the invasive growth patterns and therapeutic resistance are incompletely understood. The emerging field of cancer neuroscience offers a novel approach to study these brain tumors in the context of their intricate interactions with the nervous system employing and combining methodological toolsets from neuroscience and oncology. Increasing evidence has shown how neurodevelopmental and neuronal-like mechanisms are hijacked leading to the discovery of multicellular brain tumor networks. Here, we review how gap junction-coupled tumor-tumor-astrocyte networks, as well as synaptic and paracrine neuron-tumor networks drive glioma progression. Molecular mechanisms of these malignant, homo- and heterotypic networks, and their complex interplay are reviewed. Lastly, potential clinical-translational implications and resulting therapeutic strategies are discussed.

Incurable gliomas are characterized by their infiltration into the whole brain. Recently, we described tumor microtubes as a novel structure contributing to glioma cell invasion and uncovered synaptic contacts on glioma cells that drive brain tumour progression. However, the exact effects of neuronal activity on glioma cell motility are yet unclear. Here, we show how a recently described neuronal-like cellular transcription state of glioblastoma cells is correlated to glioma cell invasion in vivo. To unravel the details of neuronal features of glioma invasion in space and time, we established a novel approach of intravital imaging for brain tumor cells with a membrane-bound GFP combined with deep learning algorithms that are used to track glioma cell processes with a high temporal resolution over several hours. This approach uncovers how invading tumor microtubes use Levy-like movement patterns indicative of efficient search patterns often employed by animal predators searching for scarce resources such as food. Neuronal activity is able to accelerate the tumor microtube dynamics, accelerate the Levy-like movement patterns and increase the overall invasion speed of glioma cells. These processes are mediated by local calcium transients in glioma cell somata and tumor microtubes. In accordance, genetic manipulation and pharmacological perturbation of AMPA receptors reduces tumor microtube length, number and branching points by interfering with intracellular calcium transients. All in all, the work here uncovers novel neuronal activity-mediated mechanisms of glioma cell invasion, a hallmark of this yet fatal disease.

BACKGROUND Gliomas are incurable brain tumors characterized by their infiltrative growth which makes them a whole-brain disease. Previously we described membrane protrusions called tumor microtubes (TMs), and glutamatergic synapses between neurons and glioma cells, as mechanisms contributing to glioma cell invasion and tumor progression. However, the interrelation of the two, and the exact mechanisms of glioma cell dynamics over time was unknown. Therefore, we investigate neuronal synaptic input on TM-associated glioma cell motility. MATERIAL AND METHODS Here we established a novel workflow for analyzing single glioma cell dynamics over several hours with in-vivo two-photon microscopy. First, a membranous fluorescent marking of patient-derived glioma cells was established to reliably track membrane changes. Secondly, augmented microscopy based on deep- and machine-learning algorithms was used to track glioma cells. Neuronal activity was manipulated with different doses of isoflurane anesthesia, and used to study its effects on glioma cell dynamics. RESULTS This novel method revealed that motility of glioma cells can be described by the displacement of whole glioma cell somata (somatokinesis) and TM dynamics. TM motility in turn could be sub-categorized into protrusion, retraction and branching. Next, we describe three different invasion modes, all with similarities to different cell types involved in CNS development. Lastly, the effects of neuronal activity on glioma cell invasion were investigated. With the application of high anesthesia and subsequently reduced neuronal activity, TM turnover, branching events and as a result glioma cell invasion were inhibited, but in a heterogeneous manner. CONCLUSION The novel workflow allowed to comprehensively characterize glioma cell invasion over several hours. Its application demonstrates novel, hitherto unknown cellular mechanisms of glioma cell invasion, and provides a link between TM biology and neuron-glioma communication. Finally, neuronal input drives distinct subtypes of glioma cell motility patterns.All in all, this work presents an important first step in understanding mechanisms that lead to the whole- brain colonization of glioma cells making these brain tumors incurable. A further characterization of the exact molecular mechanisms that drive neuronal activity-dependent glioma cell motility is warranted.

As one of the most aggressive incurable primary brain tumors, glioblastomas show a high invasivity and therapeutic resistance caused by their cellular and molecular heterogeneity. In previous studies, we showed that glioma cells interconnect using membrane protrusions called tumor microtubes to form a therapy-resistant malignant network. Here, we extend the concept of tumor networks to heterogeneous connectivity with the glial microenvironment. Using high-resolution light microscopy, ultrastructural tissue imaging, patch-clamp electrophysiology, intravital structural and functional microscopy, we characterize tumor-astrocyte connectivity. First, we used high-resolution light microscopy with immunohistochemistry and ultrastructural imaging to discover and characterize gap junctional connections between tumor cells and astrocytes. Next, we probed functional, heterotypic connections using dye filling with patch-clamp electrophysiology. Employing calcium imaging, we could demonstrate bidirectional communication patterns between tumor cells and astrocytes. We further characterized the stability of these astrocyte-glioma networks by using longitudinal imaging of single cells over several weeks in patient-derived xenograft models. For this, we used sulforhodamine 101 (SR101) as a marker for astrocyte-glioma connectivity to simultaneously visualize tumor cells and their glial microenvironment. The percentage of SR101 uptake in glioma cells increases over time, showing an increasing integration of tumor cells into the tumor-and astrocyte network during tumor evolution. Tumor cells, which are unconnected to other tumor cells or astrocytes, are the main drivers of invasion while a subgroup of glioma cells with stable astrocyte connectivity stay in place over several weeks. Lastly, we showed how these functional, heterotypic connections contribute to therapeutic resistance in the context of radiotherapy. In conclusion, we investigated multicellular networks between glioblastoma cells and astrocytes, their plasticity and role for therapeutic resistance.