Inhibition of melanoma cell directional migration in vitro via different cellular targets

Medicinal applications and molecular targets of dequalinium chloride

For more than 60 years dequalinium chloride (DQ) has been used as anti-infective drug, mainly to treat local infections. It is a standard drug to treat bacterial vaginosis and an active ingredient of sore-throat lozenges. As a lipophilic bis-quaternary ammonium molecule, the drug displays membrane effects and selectively targets mitochondria to deplete DNA and to block energy production in cells. But beyond its mitochondriotropic property, DQ can interfere with the correct functioning of diverse proteins. A dozen of DQ protein targets have been identified and their implication in the antibacterial, antiviral, antifungal, antiparasitic and anticancer properties of the drug is discussed here. The anticancer effects of DQ combine a mitochondrial action, a selective inhibition of kinases (PKC-α/β, Cdc7/Dbf4), and a modulation of Ca²⁺-activated K⁺ channels. At the bacterial level, DQ interacts with different multidrug transporters (QacR, AcrB, EmrE) and with the transcriptional regulator RamR. Other proteins implicated in the antiviral (MPER domain of gp41 HIV-1) and antiparasitic (chitinase A from Vibrio harveyi) activities have been identified. DQ also targets α -synuclein oligomers to restrict protofibrils formation implicated in some neurodegenerative disorders. In addition, DQ is a typical bolaamphiphile molecule, well suited to form liposomes and nanoparticules useful for drug entrapment and delivery (DQAsomes and others). Altogether, the review highlights the many pharmacological properties and therapeutic benefits of this old 'multi-talented' drug, which may be exploited further. Its multiple sites of actions in cells should be kept in mind when using DQ in experimental research.

The Role of Calmodulin in Tumor Cell Migration, Invasiveness, and Metastasis

Calmodulin (CaM) is the principal Ca²⁺ sensor protein in all eukaryotic cells, that upon binding to target proteins transduces signals encoded by global or subcellular-specific changes of Ca²⁺ concentration within the cell. The Ca²⁺/CaM complex as well as Ca²⁺-free CaM modulate the activity of a vast number of enzymes, channels, signaling, adaptor and structural proteins, and hence the functionality of implicated signaling pathways, which control multiple cellular functions. A basic and important cellular function controlled by CaM in various ways is cell motility. Here we discuss the role of CaM-dependent systems involved in cell migration, tumor cell invasiveness, and metastasis development. Emphasis is given to phosphorylation/dephosphorylation events catalyzed by myosin light-chain kinase, CaM-dependent kinase-II, as well as other CaM-dependent kinases, and the CaM-dependent phosphatase calcineurin. In addition, the role of the CaM-regulated small GTPases Rac1 and Cdc42 (cell division cycle protein 42) as well as CaM-binding adaptor/scaffold proteins such as Grb7 (growth factor receptor bound protein 7), IQGAP (IQ motif containing GTPase activating protein) and AKAP12 (A kinase anchoring protein 12) will be reviewed. CaM-regulated mechanisms in cancer cells responsible for their greater migratory capacity compared to non-malignant cells, invasion of adjacent normal tissues and their systemic dissemination will be discussed, including closely linked processes such as the epithelial–mesenchymal transition and the activation of metalloproteases. This review covers as well the role of CaM in establishing metastatic foci in distant organs. Finally, the use of CaM antagonists and other blocking techniques to downregulate CaM-dependent systems aimed at preventing cancer cell invasiveness and metastasis development will be outlined.

Voltage-gated sodium channel as a target for metastatic risk reduction with re-purposed drugs

Objective: To determine the exact role of sodium channel proteins in migration, invasion and metastasis and understand the possible anti-invasion and anti-metastatic activity of repurposed drugs with voltage gated sodium channel blocking properties.

Material and methods: A review of the published medical literature was performed searching for pharmaceuticals used in daily practice, with inhibitory activity on voltage gated sodium channels. For every drug found, the literature was reviewed in order to define if it may act against cancer cells as an anti-invasion and anti-metastatic agent and if it was tested with this purpose in the experimental and clinical settings.

Results: The following pharmaceuticals that fulfill the above mentioned effects, were found: phenytoin, carbamazepine, valproate, lamotrigine, ranolazine, resveratrol, ropivacaine, lidocaine, mexiletine, flunarizine, and riluzole. Each of them are independently described and analyzed.

Conclusions: The above mentioned pharmaceuticals have shown anti-metastatic and anti-invasion activity and many of them deserve to be tested in well-planned clinical trials as adjunct therapies for solid tumors and as anti-metastatic agents. Antiepileptic drugs like phenytoin, carbamazepine and valproate and the vasodilator flunarizine emerged as particularly useful for anti-metastatic purposes.

RNAi-mediated knockdown of protein kinase C-alpha inhibits cell migration in MM-RU human metastatic melanoma cell line

Protein kinase C (PKC) is a multigene family of serine/threonine protein kinases involved in cell signaling pathways of proliferation and motility. PKC interacts with Rho GTPases in the regulation of the actin cytoskeleton. The PKC-alpha isozyme binds the Rho GTPase cdc42, and both are coordinated with the Rac-phosphatidylinositol-3 kinase (PI3K) signaling pathway in melanoma cell invasion and migration on extracellular matrix proteins. To further define the role of PKC-alpha in melanoma cell migration, we tested the effect of PDBu and Ca dependent activation of PKC-alpha as well as treatment with the PKC-alpha inhibitors calphostin C and Go6976. Furthermore, we transfected siRNA targeted against PKC-alpha into human melanoma cells and performed time-lapse analysis of cell migration followed by western immunoblotting. We found that significant enhancement of cell migration at 0.5 h after PDBu treatment directly correlated with Ca dependent activation of PKC-alpha and was inhibited by the PKC-alpha inhibitor calphostin C. PKC-alpha siRNA transfection nearly abrogated PKC-alpha expression and significantly reduced melanoma cell migration compared with siRNA controls. These findings provide further evidence that PKC-alpha plays an important role in melanoma cell migration and may have implications in therapies designed to disrupt melanoma cell motility by alteration of PKC-alpha signaling.

Detecting PKC phosphorylation as part of the Wnt/calcium pathway in cutaneous melanoma

Signaling networks play crucial roles in the changes leading to malignancy. In melanoma, increased Wnt5A expression increases melanoma cell motility via activation of protein kinase C (PKC). PKC isoforms comprise a family ofserine/threonine kinases that are involved in the transduction of signals for cell proliferation, differentiation, and metastasis. The important role of PKC in processes leading to carcinogenesis and tumor cell invasion would render PKC a suitable target for cancer therapy, if not for its ubiquitous nature. Thus, targeting pathways leading to PKC activation that are more tumor specific, such as the non-canonical Wnt pathway, may prove to be the key to targeting PKC in cancer. Here we summarize the current understanding of the Wnt/calcium pathway and discuss methods of detecting activated/phosphorylated PKC as a result of Wnt signaling in malignant melanoma. We have shown that overexpression of Wnt5A results in the activation of PKC, while inhibition of Wnt5A via small interfering RNA (siRNA) treatment results in its inactivation. In addition, the use of PKC activators and inhibitors has allowed us to study Wnt5A effects on downstream genes that may prove to be key targets for molecular therapy.

The Wnt5A/protein kinase C pathway mediates motility in melanoma cells via the inhibition of metastasis suppressors and initiation of an epithelial to mesenchymal transition

We have shown that Wnt5A increases the motility of melanoma cells. To explore cellular pathways involving Wnt5A, we compared gain-of-function (WNT5A stable transfectants) versus loss-of-function (siRNA knockdown) of WNT5A by microarray analysis. Increasing WNT5A suppressed the expression of several genes, which were re-expressed after small interference RNA-mediated knockdown of WNT5A. Genes affected by WNT5A include KISS-1, a metastasis suppressor, and CD44, involved in tumor cell homing during metastasis. This could be validated at the protein level using both small interference RNA and recombinant Wnt5A (rWnt5A). Among the genes up-regulated by WNT5A was the gene vimentin, associated with an epithelial to mesenchymal transition (EMT), which involves decreases in E-cadherin, due to up-regulation of the transcriptional repressor, Snail. rWnt5A treatment increases Snail and vimentin expression, and decreases E-cadherin, even in the presence of dominant-negativeTCF4, suggesting that this activation is independent of Wnt/beta-catenin signaling. Because Wnt5A can signal via protein kinase C (PKC), the role of PKC in Wnt5A-mediated motility and EMT was also assessed using PKC inhibition and activation studies. Treating cells expressing low levels of Wnt5A with phorbol ester increased Snail expression inhibiting PKC in cells expressing high levels of Wnt5A decreased Snail. Furthermore, inhibition of PKC before Wnt5A treatment blocked Snail expression, implying that Wnt5A can potentiate melanoma metastasis via the induction of EMT in a PKC-dependent manner.

Protein kinase C in melanoma

Protein kinase C (PKC) is activated by diacylglycerol generated by receptor-mediated hydrolysis of membrane phospholipids to mediate signals for cell growth and plays as a target of tumor-promoting phorbol esters in malignant transformation. PKC is a family of enzymes and their expression profiles have been examined in the normal melanocytes and melanoma cells, and studies have been carried out on the functions of PKC isoforms in proliferation, transformation, and metastasis of melanoma cells. Here, we summarize current knowledge of the expression and possible roles of the PKC family in melanoma in comparison with those of normal melanocytes.

Identification of Channels Promoting Calcium Spikes and Waves in HT1080 Tumor Cells

Intracellular Ca(2+) signals have been associated with cell polarization and locomotion. As cell motility underlies metastasis, we have sought to better characterize the Ca(2+) signaling events in HT1080 fibrosarcoma cells. We have tested the hypothesis that low voltage-activated (LVA) and nonvoltage-gated (NVG) channels of HT1080 cells participate in dynamic Ca(2+)-signaling events leading to cell migration and invasion. Immunofluorescence microscopy has shown that HT1080 cells express LVA T-type Ca(2+) channels uniformly about the cell periphery, whereas the transient receptor potential-1 (a NVG cation channel) protein appears as punctate spots about a cell's periphery. HT1080 cells exhibit periodic intracellular Ca(2+) spikes. High-speed imaging revealed that the Ca(2+) spikes were composed of a single Ca(2+) wave traveling unidirectionally about the periphery of the cytoplasm in a clockwise fashion (as viewed from basal to apical surfaces). The T-type Ca(2+) channel blocker mibefradil inhibited Ca(2+) spikes and waves on cells and, in parallel, inhibited cell motility and invasion in a dose-dependent manner. Similar changes were noted with the NVG cation channel blockers Gd(3+) and carboxyamido-triazole. The combination of LVA and NVG blockers further reduced Matrigel invasiveness. However, the Ca(2+) channel blockers nicardipine, SKF96365, diltiazem, and verapamil had no effect at appropriate doses. These results indicate that certain LVA and NVG channels regulate HT1080 cell motility. In addition to providing novel information regarding cancer cell motility, we suggest that it may be possible to design drugs that inhibit a key Ca(2+) wave, thereby enhancing the efficacy of emerging therapeutic protocols.

Photo-induced inactivation of protein kinase calpha by dequalinium inhibits motility of murine melanoma cells

Dequalinium (DECA) is a potent antitumor agent and inhibitor of protein kinase C (PKC). Previously it was shown that PKCalpha activity in vitro could be irreversibly inhibited when treated with DECA at low micromolar concentrations and irradiated with 366 nm of light. This approach was used to probe the role of intracellular PKC activity in the motility of metastatic murine melanoma B16 F10 cells and as a target for DECA analogs with increasing PKC inhibitory potencies. Pretreatment of a monolayer of B16 F10 cells with 250 nM of a DECA analog in the presence of UV irradiation for 5 min resulted in 1) complete inhibition of cell motility for up to 4 h in a time-lapse motility assay and 40 to 60% inhibition of cell migration in a Boyden chamber, and 2) inhibition by 40 to 60% of intracellular phosphatidylserine/Ca(2+)-dependent PKC catalytic activity, signifying inactivation of a conventional PKC isoform. Because PKCalpha is the only conventional PKC isoform detected in B16 F10 cells, a stably transfected clone expressing a kinase-defective mutant of PKCalpha was developed that exhibited a substantial loss of adhesion and motility and was refractory to further inhibition by DECA. These findings identify PKCalpha catalytic activity both as a mechanistic component of cell motility and adhesion and as a critical intracellular target of DECA. These studies further suggest that the combined use of UV with nanomolar concentrations of DECA offers an effective chemotherapeutic approach to inhibit metastatic behavior of melanoma cells.

Suppression of polarity, locomotion and F-actin levels of Walker carcinosarcoma cells by the inhibitor CI-959

Locomotor activity of tumor cells is an important factor for the capacity for invasion and metastasis. Therefore, inhibitors interfering with cellular mechanisms regulating spontaneous cell locomotion are of particular interest for cancer therapy. CI-959, a new benzothiophene cell activation inhibitor, has the capacity to suppress spontaneous polarity and locomotion of Walker carcinosarcoma cells. Suppression of polarity and locomotion was closely associated with a reduction in the relative amount of F-actin. The mechanisms involved in suppression of motility are Ca2(+)-independent and not related to cell-substratum adhesion. Walker carcinosarcoma cells appear to be able to locomote at very low (nM) levels of free [Ca2+]i.