Tetralol derivative NNC-55-0396 targets hypoxic cells in the glioblastoma microenvironment: an organ-on-chip approach

Glioblastoma (GBM) is a highly malignant brain tumour characterised by limited treatment options and poor prognosis. The tumour microenvironment, particularly the central hypoxic region of the tumour, is known to play a pivotal role in GBM progression. Cells within this region adapt to hypoxia by stabilising transcription factor HIF1-α, which promotes cell proliferation, dedifferentiation and chemoresistance. In this study we sought to examine the effects of NNC-55-0396, a tetralol compound which overactivates the unfolded protein response inducing apoptosis, using the organ-on-chip technology. We identified an increased sensitivity of the hypoxic core of the chip to NNC, which correlates with decreasing levels of HIF1-α in vitro. Moreover, NNC blocks the macroautophagic process that is unleashed by hypoxia as revealed by increased levels of autophagosomal constituent LC3-II and autophagy chaperone p62/SQSTM1. The specific effects of NNC in the hypoxic microenvironment unveil additional anti-cancer abilities of this compound and further support investigations on its use in combined therapies against GBM.

T-type channels in cancer cells: Driving in reverse

In the strongly polarized membranes of excitable cells, activation of T-type Ca²⁺ channels (TTCCs) by weak depolarizing stimuli allows the influx of Ca²⁺ which further amplifies membrane depolarization, thus "recruiting" higher threshold voltage-gated channels to promote action potential firing. Nonetheless, TTCCs perform other functions in the plasma membrane of both excitable and non-excitable cells, in which they regulate a number of biochemical pathways relevant for cell cycle and cell fate. Furthermore, data obtained in the last 20 years have shown the involvement of TTCCs in tumor biology, designating them as promising chemotherapeutic targets. However, their activity in the steadily-depolarized membranes of cancer cells, in which most voltage-gated channels are in the inactivated (nonconducting) state, is counter-intuitive. Here we discuss that in cancer cells weak hyperpolarizing stimuli increase the fraction of open TTCCs which, in association with Ca²⁺-dependent K⁺ channels, may critically boost membrane hyperpolarization and driving force for Ca²⁺ entry through different voltage-independent Ca²⁺ channels. Available evidence also shows that TTCCs participate in positive feedback circuits with signaling effectors, which may warrant a switch-like activation of pro-proliferative and pro-survival pathways in spite of their low availability. Unravelling TTCC modus operandi in the context of non-excitable membranes may facilitate the development of novel anticancer approaches.

FAK Inhibition Induces Glioblastoma Cell Senescence-Like State through p62 and p27

Focal adhesion kinase (FAK) is a central component of focal adhesions that regulate cancer cell proliferation and migration. Here, we studied the effects of FAK inhibition in glioblastoma (GBM), a fast growing brain tumor that has a poor prognosis. Treating GBM cells with the FAK inhibitor PF-573228 induced a proliferative arrest and increased cell size. PF-573228 also reduced the growth of GBM neurospheres. These effects were associated with increased p27/CDKN1B levels and β-galactosidase activity, compatible with acquisition of senescence. Interestingly, FAK inhibition repressed the expression of the autophagy cargo receptor p62/SQSTM-1. Moreover, depleting p62 in GBM cells also induced a senescent-like phenotype through transcriptional upregulation of p27. Our results indicate that FAK inhibition arrests GBM cell proliferation, resulting in cell senescence, and pinpoint p62 as being key to this process. These findings highlight the possible therapeutic value of targeting FAK in GBM.

The rise of T-type channels in melanoma progression and chemotherapeutic resistance

Hyperactivation of the Mitogen Activated Protein Kinase (MAPK) pathway is prevalent in melanoma, principally due to mutations in the BRAF and NRAS genes. MAPK inhibitors are effective only short-term, and recurrence occurs due to functional redundancies or intertwined pathways. The remodeling of Ca²⁺ signaling is also common in melanoma cells, partly through the increased expression of T-type channels (TTCCs). Here we summarize current knowledge about the prognostic value and molecular targeting of TTCCs. Furthermore, we discuss recent evidence pointing to TTCCs as molecular switches for melanoma chemoresistance, which set the grounds for novel combined therapies against the advanced disease.

The Hard-To-Close Window of T-Type Calcium Channels

T-Type calcium channels (TTCCs) are key regulators of membrane excitability, which is the reason why TTCC pharmacology is subject to intensive research in the neurological and cardiovascular fields. TTCCs also play a role in cancer physiology, and pharmacological blockers such as tetralols and dihydroquinazolines (DHQs) reduce the viability of cancer cells in vitro and slow tumor growth in murine xenografts. However, the available compounds are better suited to blocking TTCCs in excitable membranes rather than TTCCs contributing window currents at steady potentials. Consistently, tetralols and dihydroquinazolines exhibit cytostatic/cytotoxic activities at higher concentrations than those required for TTCC blockade, which may involve off-target effects. Gene silencing experiments highlight the targetability of TTCCs, but further pharmacological research is required for TTCC blockade to become a chemotherapeutic option.

T-Type Cav3.1 Channels Mediate Progression and Chemotherapeutic Resistance in Glioblastoma

T-type Ca²⁺ channels (TTCC) have been identified as key regulators of cancer cell cycle and survival. In vivo studies in glioblastoma (GBM) murine xenografts have shown that drugs able to block TTCC in vitro (such as tetralol derivatives mibefradil/NNC-55-096, or different 3,4-dihydroquinazolines) slow tumor progression. However, currently available TTCC pharmacologic blockers have limited selectivity for TTCC and are unable to distinguish between TTCC isoforms. Here we analyzed the expression of TTCC transcripts in human GBM cells and show a prevalence of Cacna1g/Ca_v3.1 mRNAs. Infection of GBM cells with lentiviral particles carrying short hairpin RNA against Ca_v3.1 resulted in GBM cell death by apoptosis. We generated a murine GBM xenograft via subcutaneous injection of U87-MG GBM cells and found that tumor size was reduced when Ca_v3.1 expression was silenced. Furthermore, we developed an in vitro model of temozolomide-resistant GBM that showed increased expression of Ca_v3.1 accompanied by the activation of macroautophagy. We confirmed a positive correlation between Ca_v3.1 and autophagic markers in both GBM cultures and biopsies. Of note, Ca_v3.1 knockdown resulted in transcriptional downregulation of p62/SQSTM1 and deficient autophagy. Together, these data identify Ca_v3.1 channels as potential targets for slowing GBM progression and recurrence based on their role in regulating autophagy. SIGNIFICANCE: These findings identify Ca_v3.1 calcium channels as a molecular target to regulate autophagy and prevent progression and chemotherapeutic resistance in glioblastoma.

Inhibition of WNT-CTNNB1 signaling upregulates SQSTM1 and sensitizes glioblastoma cells to autophagy blockers

WNT-CTNN1B signaling promotes cancer cell proliferation and stemness. Furthermore, recent evidence indicates that macroautophagy/autophagy regulates WNT signaling. Here we investigated the impact of inhibiting WNT signaling on autophagy in glioblastoma (GBM), a devastating brain tumor. Inhibiting TCF, or silencing TCF4 or CTNNB1/β-catenin upregulated SQSTM1/p62 in GBM at transcriptional and protein levels and, in turn, autophagy. DKK1/Dickkopf1, a canonical WNT receptor antagonist, also induced autophagic flux. Importantly, TCF inhibition regulated autophagy through MTOR inhibition and dephosphorylation, and nuclear translocation of TFEB, a master regulator of lysosomal biogenesis and autophagy. TCF inhibition or silencing additionally affected GBM cell proliferation and migration. Autophagy induction followed by its blockade can promote cancer cell death. In agreement with this notion, halting both TCF-CTNNB1 and autophagy pathways decreased cell viability and induced apoptosis of GBM cells through a SQSTM1-dependent mechanism involving CASP8 (caspase 8). In vivo experiments further underline the therapeutic potential of such dual targeting in GBM.

Mining Text with the Prototype-Matching Method

Text documents are the most common means for exchanging formal knowledge among people. Text is a rich medium that can contain a vast range of information, but text can be difficult to decipher automatically. Many organizations have vast repositories of textual data but with few means of automatically mining that text. Text mining methods seek to use an understanding of natural language text to extract information relevant to user needs. This article evaluates a new text mining methodology: prototype-matching for text clustering, developed by the authors’ research group. The methodology was applied to four applications: clustering documents based on their abstracts, analyzing financial data, distinguishing authorship, and evaluating multiple translation similarity. The results are discussed in terms of common business applications and possible future research.

Contextual clustering for analysis of functional MRI data

We present a contextual clustering procedure for statistical parametric maps (SPM) calculated from time varying three-dimensional images. The algorithm can be used for the detection of neural activations from functional magnetic resonance images (fMRI). An important characteristic of SPM is that the intensity distribution of background (nonactive area) is known whereas the distributions of activation areas are not. The developed contextual clustering algorithm divides an SPM into background and activation areas so that the probability of detecting false activations by chance is controlled, i.e., hypothesis testing is performed. Unlike the much used voxel-by-voxel testing, neighborhood information is utilized, an important difference. This is achieved by using a Markov random field prior and iterated conditional modes (ICM) algorithm. However, unlike in the conventional use of ICM algorithm, the classification is based only on the distribution of background. The results from our simulations and human fMRI experiments using visual stimulation demonstrate that a better sensitivity is achieved with a given specificity in comparison to the voxel-by-voxel thresholding technique. The algorithm is computationally efficient and can be used to detect and delineate objects from a noisy background in other applications.

Reproducibility of fMRI: effect of the use of contextual information

We studied the effect of use of contextual information on the reproducibility of the results in analysis of fMRI data. We used data from a repeated simple motor fMRI experiment. In the first approach, statistical parametric maps were computed from a spatially unsmoothed data and thresholded using a Bonferroni corrected threshold. In the second approach, the maps were computed from a spatially unsmoothed data but were segmented into nonactive and active regions using a spatial contextual clustering method. In the third approach, the statistical parametric maps were computed from spatially smoothed data and thresholded, using, optionally, a spatial extent threshold. The variation in the classification was largest in the Bonferroni thresholded statistical parametric maps. There were no significant differences in variation between statistical parametric maps generated with all the other methods. In addition to reproducibility, the detection rates of weak simulated activations in the presence of measured scanner and physiological noise were investigated. Contextual clustering method was the most sensitive method, while the least sensitive method was the Bonferroni corrected thresholding. Using simulated data, we demonstrated that the contextual clustering method preserves the shapes of activation regions better than the method using spatial smoothing of the data.

Accuracy of a registration procedure for brain SPET and MRI: phantom and simulation studies

Phantom experiments and simulations were performed to evaluate the significance of different error sources in a clinical registration procedure for brain SPET and MRI based on external markers. The results from the phantom experiments were used to adjust the error model for simulations. In the phantom experiments, 13-14 external markers were attached to the surface of a three-dimensional brain phantom for computing registration. Three internal test markers were used to estimate the accuracy of registration. The phantom was imaged with two different SPET and MRI devices. The mean root-mean-squared (RMS) residual of the locations of the test markers after registration using different combinations of four external markers varied from 3.5 +/- 1.0 to 5.2 +/- 1.3 mm depending on the imaging equipment and parameters used. The accuracy improved with an increasing number of external markers, from 3.2 +/- 0.5 to 4.9 +/- 0.5 mm for 6 markers and from 3.1 +/- 0.1 to 4.7 +/- 0.1 mm for 13 markers. In simulations, the external markers had an error comparable to the corresponding error in the phantom experiments. The error in the test markers was varied independently of that of the external markers. When the locating error of the test markers was removed, about 2 mm of the residuals of the test markers were found to come from this source. When an error comparable to the resolution of the original images (7-10 mm for SPET, 2 mm for MRI) was included in the test markers, the largest mean RMS residual after registration was smaller than the resolution error (8.8 +/- 1.1 mm). This was due to the accuracy of localization of the external markers and the fact that the direction of the error was random for each marker. The size of the registration error of an image volume was site-dependent, being minimal near the centre of mass of the external markers. When comparing the error with the spatial resolution of SPET, it was concluded that the accuracy of registration is not the limiting factor in region-of-interest analysis of registered images, provided that the design and attachment of the marker system are appropriate.