Intrinsic fluorescence of the clinically approved multikinase inhibitor nintedanib reveals lysosomal sequestration as resistance mechanism in FGFR-driven lung cancer

Background

Studying the intracellular distribution of pharmacological agents, including anticancer compounds, is of central importance in biomedical research. It constitutes a prerequisite for a better understanding of the molecular mechanisms underlying drug action and resistance development. Hyperactivated fibroblast growth factor receptors (FGFRs) constitute a promising therapy target in several types of malignancies including lung cancer. The clinically approved small-molecule FGFR inhibitor nintedanib exerts strong cytotoxicity in FGFR-driven lung cancer cells. However, subcellular pharmacokinetics of this compound and its impact on therapeutic efficacy remain obscure.

Methods

3-dimensional fluorescence spectroscopy was conducted to asses cell-free nintedanib fluorescence properties. MTT assay was used to determine the impact of the lysosome-targeting agents bafilomycin A1 and chloroquine combined with nintedanib on lung cancer cell viability. Flow cytometry and live cell as well as confocal microscopy were performed to analyze uptake kinetics as well as subcellular distribution of nintedanib. Western blot was conducted to investigate protein expression. Cryosections of subcutaneous tumor allografts were generated to detect intratumoral nintedanib in mice after oral drug administration.

Results

Here, we report for the first time drug-intrinsic fluorescence properties of nintedanib in living and fixed cancer cells as well as in cryosections derived from allograft tumors of orally treated mice. Using this feature in conjunction with flow cytometry and confocal microscopy allowed to determine cellular drug accumulation levels, impact of the ABCB1 efflux pump and to uncover nintedanib trapping into lysosomes. Lysosomal sequestration - resulting in an organelle-specific and pH-dependent nintedanib fluorescence - was identified as an intrinsic resistance mechanism in FGFR-driven lung cancer cells. Accordingly, combination of nintedanib with agents compromising lysosomal acidification (bafilomycin A1, chloroquine) exerted distinctly synergistic growth inhibitory effects.

Conclusion

Our findings provide a powerful tool to dissect molecular factors impacting organismal and intracellular pharmacokinetics of nintedanib. Regarding clinical application, prevention of lysosomal trapping via lysosome-alkalization might represent a promising strategy to circumvent cancer cell-intrinsic nintedanib resistance.

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0592-3) contains supplementary material, which is available to authorized users.

Histone Deacetylase Inhibitor Treatment Increases the Expression of the Plasma Membrane Ca2+ Pump PMCA4b and Inhibits the Migration of Melanoma Cells Independent of ERK

Several new therapeutic options emerged recently to treat metastatic melanoma; however, the high frequency of intrinsic and acquired resistance among patients shows a need for new therapeutic options. Previously, we identified the plasma membrane Ca²⁺ ATPase 4b (PMCA4b) as a metastasis suppressor in BRAF-mutant melanomas and found that mutant BRAF inhibition increased the expression of the pump, which then inhibited the migratory and metastatic capability of the cells. Earlier it was also demonstrated that histone deacetylase inhibitors (HDACis) upregulated PMCA4b expression in gastric, colon, and breast cancer cells. In this study, we treated one BRAF wild-type and two BRAF-mutant melanoma cell lines with the HDACis, SAHA and valproic acid, either alone, or in combination with the BRAF inhibitor, vemurafenib. We found that HDACi treatment strongly increased the expression of PMCA4b in all cell lines irrespective of their BRAF mutational status, and this effect was independent of ERK activity. Furthermore, HDAC inhibition also enhanced the abundance of the housekeeping isoform PMCA1. Combination of HDACis with vemurafenib, however, did not have any additive effects on either PMCA isoform. We demonstrated that the HDACi-induced increase in PMCA abundance was coupled to an enhanced [Ca²⁺]_i clearance rate and also strongly inhibited both the random and directional movements of A375 cells. The primary role of PMCA4b in these characteristic changes was demonstrated by treatment with the PMCA4-specific inhibitor, caloxin 1c2, which was able to restore the slower Ca²⁺ clearance rate and higher motility of the cells. While HDAC treatment inhibited cell motility, it decreased only modestly the ratio of proliferative cells and cell viability. Our results show that in melanoma cells the expression of both PMCA4b and PMCA1 is under epigenetic control and the elevation of PMCA4b expression either by HDACi treatment or by the decreased activation of the BRAF-MEK-ERK pathway can inhibit the migratory capacity of the highly motile A375 cells.

Irinotecan Upregulates Fibroblast Growth Factor Receptor 3 Expression in Colorectal Cancer Cells, Which Mitigates Irinotecan-Induced Apoptosis

BACKGROUND: Irinotecan (IRI) is an integral part of colorectal cancer (CRC) therapy, but response rates are unsatisfactory and resistance mechanisms are still insufficiently understood. As fibroblast growth factor receptor 3 (FGFR3) mediates essential survival signals in CRC, it is a candidate gene for causing intrinsic resistance to IRI. METHODS: We have used cell line models overexpressing FGFR3 to study the receptor's impact on IRI response. For pathway blockade, a dominant-negative receptor mutant and a small molecule kinase inhibitor were employed. RESULTS: IRI exposure induced expression of FGFR3 as well as its ligands FGF8 and FGF18 both in cell cultures and in xenograft tumors. As overexpression of FGFR3 mitigated IRI-induced apoptosis in CRC cell models, this suggests that the drug itself activated a survival response. On the cellular level, the antiapoptotic protein bcl-xl was upregulated and caspase 3 activation was inhibited. Targeting FGFR3 signaling using a dominant-negative receptor mutant sensitized cells for IRI. In addition, the FGFR inhibitor PD173074 acted synergistically with the chemotherapeutic drug and significantly enhanced IRI-induced caspase 3 activity in vitro. In vivo, PD173074 strongly inhibited growth of IRI-treated tumors. CONCLUSION: Together, our results indicate that targeting FGFR3 can be a promising strategy to enhance IRI response in CRC patients.

Trabectedin Is Active against Malignant Pleural Mesothelioma Cell and Xenograft Models and Synergizes with Chemotherapy and Bcl-2 Inhibition In Vitro

Malignant pleural mesothelioma (MPM) is characterized by widespread resistance to systemic therapy. Trabectedin is an antineoplastic agent targeting both the malignant cells and the tumor microenvironment that has been approved for the treatment of advanced soft tissue sarcoma and ovarian cancer. In this preclinical study, we evaluated the antineoplastic potential of trabectedin as a single agent and in drug combination approaches in human MPM. Therefore, we utilized an extended panel of MPM cell lines (n = 6) and primary cell cultures from surgical MPM specimens (n = 13), as well as nonmalignant pleural tissue samples (n = 2). Trabectedin exerted a dose-dependent cytotoxic effect in all MPM cell cultures in vitro when growing as adherent monolayers or nonadherent spheroids with IC₅₀ values ≤ 2.6 nmol/L. Nonmalignant mesothelial cells were significantly less responsive. The strong antimesothelioma activity was based on cell-cycle perturbation and apoptosis induction. The activity of trabectedin against MPM cells was synergistically enhanced by coadministration of cisplatin, a drug routinely used for systemic MPM treatment. Comparison of gene expression signatures indicated an inverse correlation between trabectedin response and bcl-2 expression. Accordingly, bcl-2 inhibitors (Obatoclax, ABT-199) markedly synergized with trabectedin paralleled by deregulated expression of the bcl-2 family members bcl-2, bim, bax, Mcl-1, and bcl-x_L as a consequence of trabectedin exposure. In addition, trabectedin exerted significant antitumor activity against an intraperitoneal MPM xenograft model. Together, these data suggest that trabectedin exerts strong activity in MPM and synergizes with chemotherapy and experimental bcl-2 inhibitors in vitro Thus, it represents a promising new therapeutic option for MPM. Mol Cancer Ther; 15(10); 2357-69. ©2016 AACR.

Abstract 1883: Treatment with histone deacetylase (HDAC) and BRAF inhibitors upregulates the expression of the plasma membrane Ca2+ pump, PMCA4b and alters intracellular Ca2+ handling in BRAF mutant melanoma cells

The aim of our study was to test the effects of histone deacetylase (HDAC) and BRAF inhibitors on the expression and activity of the plasma membrane Ca2+ pump isoform 4b (PMCA4b) in BRAF mutant melanoma cell lines. Remodeling of Ca2+ homeostasis during malignancy is caused by the rearrangement of the Ca2+ signaling machinery, including Ca2+ pumps, Na+/Ca2+ exchangers and channels. Plasma membrane calcium ATPases (ATP2B - or PMCA) maintain the resting low intracellular calcium concentration by pumping out excess calcium from the cytosol. Changes in PMCA expression during malignant transformation have been described previously in colorectal and breast cancer cells, and most recently by our group in melanomas. We found that in BRAF mutant melanoma cells the PMCA 4b protein level was markedly elevated by BRAF inhibitor treatment. Overexpression of PMCA4b suppressed motility and metastatic potential. Previously, it was shown that HDAC inhibitors-induced differentiation up-regulated PMCA4b expression in gastric, colon and breast cancer cells. In the present study we treated BRAF mutant and BRAF wild type melanoma cells with HDAC inhibitors (SAHA (suberanilohydroxamic acid) or valproic acid) and tested the changes in abundance, localization and function of PMCA4b. Expression levels of the PMCA proteins were analyzed by qRT-PCR and Western Blotting. Subcellular localization of the PMCAs and the effects of treatments on cytosolic Ca2+ signaling were analyzed by confocal microscopy. We found that treatment with the HDAC inhibitors increased the level of PMCA4b expression at both mRNA and protein levels in both BRAF wild type and BRAF mutant cell types. The increased PMCA4b level was coupled with enhanced plasma membrane localization and with a faster Ca2+ clearance after stimulation. Our results show that in melanoma cells the expression of PMCA4b is under epigenetic control and HDAC inhibitors efficiently enhanced PMCA4b expression independent of the BRAF status of cells.

Citation Format: Luca Hegedus, Tamas Garay, Eszter Molnar, Karolina Varga, Rita Padanyi, Katalin Paszty, Balazs Hegedus, Mathias Wolf, Michael Grusch, Eniko Kallay, Agnes Enyedi. Treatment with histone deacetylase (HDAC) and BRAF inhibitors upregulates the expression of the plasma membrane Ca2+ pump, PMCA4b and alters intracellular Ca2+ handling in BRAF mutant melanoma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1883.

Abstract B01: Multilevel interference with receptor-PI3K-mTORC1 signaling is key mechanism for anticancer activity of fatty acid synthase inhibitors

The metabolic oncogene fatty acid synthase (FASN) is overexpressed in 80% of ovarian cancers (OC) and indicates poor prognosis. Exposure of OC to inhibitors of FASN elicits a complex stress response that interferes with receptor-PI3K-mTORC1 signaling (briefly designated ‘PI3K pathway’). Here we demonstrate that FASN inhibitors capitalize on multiple mechanisms to interfere with the PI3K pathway, and that silencing this cascade is crucial for the anticancer action of the drugs. Data were obtained using thin-layer chromatography, ELISA, Western blotting, quantitative micropatterning and growth assays, respectively. Exposure of OC cells (SKOV3, OVCAR-3) to FASN inhibitors (C75, G28UCM) causes lipid redistribution toward storage lipids, whereas membrane lipid rafts and signaling lipids are diminished, which significantly impairs EGF receptor/ErbB/HER function and expression. A severe depletion of phosphatidylinositol (3,4,5) trisphosphate (PIP3), which represents the crucial product of PI3K action, is associated with drug-dependent silencing of AKT. Moreover, FASN blockers rapidly stimulate expression of the stress response gene REDD1 (RTP801/Dig2/DDIT4) followed by slow activation of the energy sensor AMPK. Induction of these mTORC1 upstream repressors has been found to block downstream phosphorylation of ribosomal S6 protein. Moreover, long-term stress imposed by persistent FASN blockade leads to accelerated degradation of signaling proteins. Interestingly, concurrent targeting of the PI3K pathway using the dual PI3K/mTOR blocker NVP-BEZ235 does not aggravate the FASN anticancer drug effects. However, forced expression of constitutive active AKT counteracts FASN inhibitor-mediated mTORC1 silencing and abrogates growth arrest. Our data thus suggest that FASN inhibitors by themselves can efficiently eliminate PI3K downstream activity. This mechanism appears crucial for the anticancer effect, which cannot be augmented by co-exposure to drugs that target the very same pathway. On the other hand, silencing PI3K signaling by FASN inhibitors was found to release a negative feedback loop toward MAPK. Thus, FASN drug-mediated PI3K silencing is associated with cross-activation of ERK1/2. Accordingly, co-treatment with the MEK inhibitor selumetinib (AZD6244) significantly improves the anticancer action of FASN inhibitors, whereas introduction of constitutive active MEK does not alter FASN drug-induced growth inhibition. Collectively these data demonstrate that FASN inhibitors utilize a whole panel of different mechanisms to abrogate receptor-PI3K-mTORC1 signaling, which represents at least one of the crucial mechanisms of anticancer action of these compounds.

Supported by Medical Scientific Fund of the Mayor of the City of Vienna & ‘Initiative Krebsforschung’ of the Medical University Vienna, Austria.

Citation Format: Renate Wagner, Katharina Pröstling, Daniel Veigel, Gerald Stübiger, Michael Grusch, Julian Weghuber, Christian Singer, Heidrun Karlic, Ramón Colomer, Bellinda Benhamú, María Luz López-Rodríguez, Fausto Hegardt, Jordi García, Dolors Serra, Peter Valent, Thomas Grunt. Multilevel interference with receptor-PI3K-mTORC1 signaling is key mechanism for anticancer activity of fatty acid synthase inhibitors. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B01.

Fibroblast growth factor receptor 3 isoforms: Novel therapeutic targets for hepatocellular carcinoma?

Fibroblast growth factor receptors (FGFRs) are frequently up-regulated in subsets of hepatocellular carcinoma (HCC). Here, we provide mechanistic insight that FGFR3 splice variants IIIb and IIIc impact considerably on the malignant phenotype of HCC cells. The occurrence of FGFR3 variants was analyzed in human HCC samples. In hepatoma/hepatocarcinoma cell lines, FGFR3 isoforms were overexpressed by lentiviral constructs or down-modulated by small interfering RNA (siRNA; affecting FGFR3-IIIb and -IIIc) or an adenoviral kinase-dead FGFR3-IIIc construct (kdFGFR3). Elevated levels of FGFR3-IIIb and/or -IIIc were found in 53% of HCC cases. FGFR3-IIIb overexpression occurred significantly more often in primary tumors of large (pT2-4) than of small size (pT1). Furthermore, one or both isoforms were enhanced mostly in cases with early tumor infiltration and/or recurrence at the time of surgery or follow-up examinations. In hepatoma/hepatocarcinoma cells, up-regulated FGFR3-IIIb conferred an enhanced capability for proliferation. Both FGFR3-IIIb and FGFR3-IIIc suppressed apoptotic activity, enhanced clonogenic growth, and induced disintegration of the blood/lymph endothelium. The tumorigenicity of cells in severe combined immunodeficiency mice was augmented to a larger degree by variant IIIb than by IIIc. Conversely, siRNA targeting FGFR3 and kdFGFR3 reduced clonogenicity, anchorage-independent growth, and disintegration of the blood/lymph endothelium in vitro. Furthermore, kdFGFR3 strongly attenuated tumor formation in vivo.

CONCLUSIONS

Deregulated FGFR3 variants exhibit specific effects in the malignant progression of HCC cells. Accordingly, blockade of FGFR3-mediated signaling may be a promising therapeutic approach to antagonize growth and malignant behavior of HCC cells.

Is fibroblast growth factor receptor 4 a suitable target of cancer therapy?

Fibroblast growth factors (FGF) and their tyrosine kinase receptors (FGFR) support cell proliferation, survival and migration during embryonic development, organogenesis and tissue maintenance and their deregulation is frequently observed in cancer development and progression. Consequently, increasing efforts are focusing on the development of strategies to target FGF/FGFR signaling for cancer therapy. Among the FGFRs the family member FGFR4 is least well understood and differs from FGFRs1-3 in several aspects. Importantly, FGFR4 deletion does not lead to an embryonic lethal phenotype suggesting the possibility that its inhibition in cancer therapy might not cause grave adverse effects. In addition, the FGFR4 kinase domain differs sufficiently from those of FGFRs1-3 to permit development of highly specific inhibitors. The oncogenic impact of FGFR4, however, is not undisputed, as the FGFR4-mediated hormonal effects of several FGF ligands may also constitute a tissue-protective tumor suppressor activity especially in the liver. Therefore it is the purpose of this review to summarize all relevant aspects of FGFR4 physiology and pathophysiology and discuss the options of targeting this receptor for cancer therapy.

Abstract 1671: Fibroblast growth factor receptor 3 enhances progression of hepatocellular carcinoma

Purpose of the study. To provide mechanistic evidence that fibroblast growth factor receptor 3 (FGFR3) and its two splice variants, FGFR3-IIIb and -IIIc, impact considerably on the malignant phenotype of hepatocellular carcinoma (HCC).

Experimental procedures. The occurrence of FGFR3 and its two isoforms was analyzed in human HCC samples by qRT-PCR and immunostaining. In hepatoma/hepatocarcinoma cell lines FGFR3-isoforms were overexpressed by lentiviral constructs or were down-modulated by siRNA or an adenoviral kinase-dead FGFR3 (kdFGFR3) construct. Cell lines were tested for anchorage-independent growth, proliferation at low-densities and their cell-cycle distribution, as well as their ability to form tumors after subcutaneous injection into the flanks of SCID-mice.

Results. Upregulated FGFR3 was found in almost 50% of HCC patients, which was often due to the enhanced expression of FGFR3-IIIb. Furthermore, patients with FGFR3-IIIb overexpression showed early tumor recurrence indicating that this isoform may be a major player in tumor progression. In hepatoma/hepatocarcinoma cells, upregulated FGFR3-IIIb or FGFR3-IIIc conferred an enhanced capability for proliferation and tumor growth. Both isoforms enhanced downstream signaling and increased the cells’ ability to grow at low densities. The tumorigenicity of cells in SCID-mice was augmented more by variant IIIb than by IIIc. This stronger impact of FGFR-IIIb on cell proliferation could also be seen in analysis of the cell cycle distribution, which was shifted to the S-phase. Conversely, siFGFR3 and kdFGFR3 affected both receptor-variants and strongly reduced clonogenic growth at low density and anchorage-independent growth. Furthermore, kdFGFR3 arrested the cells in G2/M and strongly attenuated tumor formation in vivo.

Conclusions: Upregulated FGFR3 is associated with development and progression of hepatocellular carcinoma. Accordingly, blockade of FGFR3-mediated signaling may be a promising therapeutic approach to antagonize growth and malignant behavior of HCC cells.

Citation Format: Jakob Paur, Lisa Nika, Christiane Maier, Julia Kostka, Petra Heffeter, Sonja Kappel, Daniela Kandioler, Klaus Holzmann, Brigitte Marian, Walter Berger, Michael Grusch, Bettina Grasl-Kraupp. Fibroblast growth factor receptor 3 enhances progression of hepatocellular carcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1671. doi:10.1158/1538-7445.AM2015-1671

Epigenetic down-regulation of integrin α7 increases migratory potential and confers poor prognosis in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a devastating malignancy characterized by invasive growth and rapid recurrence. The identification and inhibition of molecular components leading to this migratory and invasive phenotype are thus essential. Accordingly, a genome-wide expression array analysis was performed on MPM cell lines and a set of 139 genes was identified as differentially expressed in cells with high versus low migratory activity. Reduced expression of the novel tumour suppressor integrin α7 (ITGA7) was found in highly motile cells. A significant negative correlation was observed between ITGA7 transcript levels and average displacement of cells. Forced overexpression of ITGA7 in MPM cells with low endogenous ITGA7 expression inhibited cell motility, providing direct evidence for the regulatory role of ITGA7 in MPM cell migration. MPM cells showed decreased ITGA7 expressions at both transcription and protein levels when compared to non-malignant mesothelial cells. The majority of MPM cell cultures displayed hypermethylation of the ITGA7 promoter when compared to mesothelial cultures. A statistically significant negative correlation between ITGA7 methylation and ITGA7 expression was also observed in MPM cells. While normal human pleura samples unambiguously expressed ITGA7, a varying level of expression was found in a panel of 200 human MPM samples. In multivariate analysis, ITGA7 expression was found to be an independent prognostic factor. Although there was no correlation between histological subtypes and ITGA7 expression, importantly, patients with high tumour cell ITGA7 expression had an increased median overall survival compared to the low- or no-expression groups (463 versus 278 days). In conclusion, our data suggest that ITGA7 is an epigenetically regulated tumour suppressor gene and a prognostic factor in human MPM.

A eudesmane-type sesquiterpene isolated from Pluchea odorata (L.) Cass. combats three hallmarks of cancer cells: Unrestricted proliferation, escape from apoptosis and early metastatic outgrowth in vitro

Pluchea odorata is ethno pharmaceutically used to treat inflammation-associated disorders. The dichloromethane extract (DME) was tested in the carrageenan-induced rat paw oedema assay investigating its effect on inflammation that was inhibited by 37%. Also an in vitro anti-neoplastic potential was reported. However, rather limited information about the bio-activity of purified compounds and their cellular mechanisms are available. Therefore, two of the most abundant eudesmanes in P. odorata were isolated and their anti-neoplastic and anti-intravasative activities were studied. HL-60 cells were treated with P. odorata compounds and metabolic activity, cell number reduction, cell cycle progression and apoptosis induction were correlated with relevant protein expression. Tumour cell intravasation through lymph endothelial monolayers was measured and potential causal mechanisms were analyzed by Western blotting. Compound PO-1 decreased the metabolic activity of HL-60 cells (IC50 = 8.9 μM after 72 h) and 10 μM PO-1 induced apoptosis, while PO-2 showed just weak anti-neoplastic activities at concentrations beyond 100 μM. PO-1 arrested the cell cycle in G1 and this correlated with induction of JunB expression. Independent of this mechanism 25 μM PO-1 decreased MCF-7 spheroid intravasation through the lymph endothelial barrier. Hence, PO-1 inhibits an early step of metastasis, impairs unrestricted proliferation and induces apoptosis at low micromolar concentrations. These results warrant further testing in vivo to challenge the potential of PO-1 as novel lead compound.

Apelin promotes lymphangiogenesis and lymph node metastasis

Whereas the role of the G-protein-coupled APJ receptor and its ligand, apelin, in angiogenesis has been well documented, the ability of the apelin/APJ system to induce lymphangiogenesis and lymphatic metastasis has been largely unexplored. To this end, we first show that APJ is expressed in lymphatic endothelial cells (LECs) and, moreover, that it responds to apelin by activating the apelinergic signaling cascade. We find that although apelin treatment does not influence the proliferation of LECs in vitro, it enhances their migration, protects them against UV irradiation-induced apoptosis, increases their spheroid numbers in 3D culture, stimulates their in vitro capillary-like tube formation and, furthermore, promotes the invasive growth of lymphatic microvessels in vivo in the matrigel plug assay. We also demonstrate that apelin overexpression in malignant cells is associated with accelerated in vivo tumor growth and with increased intratumoral lymphangiogenesis and lymph node metastasis. These results indicate that apelin induces lymphangiogenesis and, accordingly, plays an important role in lymphatic tumor progression. Our study does not only reveal apelin as a novel lymphangiogenic factor but might also open the door for the development of novel anticancer therapies targeting lymphangiogenesis.

Sensitivity of Melanoma Cells to EGFR and FGFR Activation but Not Inhibition is Influenced by Oncogenic BRAF and NRAS Mutations

BRAF and NRAS are the two most frequent oncogenic driver mutations in melanoma and are pivotal components of both the EGF and FGF signaling network. Accordingly, we investigated the effect of BRAF and NRAS oncogenic mutation on the response to the stimulation and inhibition of epidermal and fibroblast growth factor receptors in melanoma cells. In the three BRAF mutant, two NRAS mutant and two double wild-type cell lines growth factor receptor expression had been verified by qRT-PCR. Cell proliferation and migration were determined by the analysis of 3-days-long time-lapse videomicroscopic recordings. Of note, a more profound response was found in motility as compared to proliferation and double wild-type cells displayed a higher sensitivity to EGF and FGF2 treatment when compared to mutant cells. Both baseline and induced activation of the growth factor signaling was assessed by immunoblot analysis of the phosphorylation of the downstream effectors Erk1/2. Low baseline and higher inducibility of the signaling pathway was characteristic in double wild-type cells. In contrast, oncogenic BRAF or NRAS mutation did not influence the response to EGF or FGF receptor inhibitors in vitro. Our findings demonstrate that the oncogenic mutations in melanoma have a profound impact on the motogenic effect of the activation of growth factor receptor signaling. Since emerging molecularly targeted therapies aim at the growth factor receptor signaling, the appropriate mutational analysis of individual melanoma cases is essential in both preclinical studies and in the clinical trials and practice.

Epigallocatechin gallate, ellagic acid, and rosmarinic acid perturb dNTP pools and inhibit de novo DNA synthesis and proliferation of human HL-60 promyelocytic leukemia cells: Synergism with arabinofuranosylcytosine

Epigallocatechin gallate (EGCG), ellagic acid (EA) and rosmarinic acid (RA) are natural polyphenols exerting cancer chemopreventive effects. Ribonucleotide reductase (RR; EC 1.17.4.1) converts ribonucleoside diphosphates into deoxyribonucleoside diphosphates being essential for DNA replication, which is why the enzyme is considered an excellent target for anticancer therapy. EGCG, EA, and RA dose-dependently inhibited the growth of human HL-60 promyelocytic leukemia cells, exerted strong free radical scavenging potential, and significantly imbalanced nuclear deoxyribonucleoside triphosphate (dNTP) concentrations without distinctly affecting the protein levels of RR subunits (R1, R2, p53R2). Incorporation of (14)C-cytidine into nascent DNA of tumor cells was also significantly lowered, being equivalent to an inhibition of DNA synthesis. Consequently, treatment with EGCG and RA attenuated cells in the G0/G1 phase of the cell cycle, finally resulting in a pronounced induction of apoptosis. Sequential combination of EA and RA with the first-line antileukemic agent arabinofuranosylcytosine (AraC) synergistically potentiated the antiproliferative effect of AraC, whereas EGCG plus AraC yielded additive effects. Taken together, we show for the first time that EGCG, EA, and RA perturbed dNTP levels and inhibited cell proliferation in human HL-60 promyelocytic leukemia cells, with EGCG and RA causing a pronounced induction of apoptosis. Due to these effects and synergism with AraC, these food ingredients deserve further preclinical and in vivo testing as inhibitors of leukemic cell proliferation.

Lobatin B inhibits NPM/ALK and NF-κB attenuating anaplastic-large-cell-lymphomagenesis and lymphendothelial tumour intravasation

An apolar extract of the traditional medicinal plant Neurolaena lobata inhibited the expression of the NPM/ALK chimera, which is causal for the majority of anaplastic large cell lymphomas (ALCLs). Therefore, an active principle of the extract, the furanoheliangolide sesquiterpene lactone lobatin B, was isolated and tested regarding the inhibition of ALCL expansion and tumour cell intravasation through the lymphendothelium. ALCL cell lines, HL-60 cells and PBMCs were treated with plant compounds and the ALK inhibitor TAE-684 to measure mitochondrial activity, proliferation and cell cycle progression and to correlate the results with protein- and mRNA-expression of selected gene products. Several endpoints indicative for cell death were analysed after lobatin B treatment. Tumour cell intravasation through lymphendothelial monolayers was measured and potential causal mechanisms were investigated analysing NF-κB- and cytochrome P450 activity, and 12(S)-HETE production. Lobatin B inhibited the expression of NPM/ALK, JunB and PDGF-Rβ, and attenuated proliferation of ALCL cells by arresting them in late M phase. Mitochondrial activity remained largely unaffected upon lobatin B treatment. Nevertheless, caspase 3 became activated in ALCL cells. Also HL-60 cell proliferation was attenuated whereas PBMCs of healthy donors were not affected by lobatin B. Additionally, tumour cell intravasation, which partly depends on NF-κB, was significantly suppressed by lobatin B most likely due to its NF-κB-inhibitory property. Lobatin B, which was isolated from a plant used in ethnomedicine, targets malignant cells by at least two properties: I) inhibition of NPM/ALK, thereby providing high specificity in combating this most prevalent fusion protein occurring in ALCL; II) inhibition of NF-κB, thereby not affecting normal cells with low constitutive NF-κB activity. This property also inhibits tumour cell intravasation into the lymphatic system and may provide an option to manage this early step of metastatic progression.

The optogenetic promise for oncology: Episode I

As light-based control of fundamental signaling pathways is becoming a reality, the field of optogenetics is rapidly moving beyond neuroscience. We have recently developed receptor tyrosine kinases that are activated by light and control cell proliferation, epithelial–mesenchymal transition, and angiogenic sprouting—cell behaviors central to cancer progression.