Parthenolide reduces the frequency of ABCB5-positive cells and clonogenic capacity of melanoma cells from anchorage independent melanospheres

Mechanisms of Melanoma Progression and Treatment Resistance: Role of Cancer Stem-like Cells

Melanoma is the third most common type of skin cancer, characterized by its heterogeneity and propensity to metastasize to distant organs. Melanoma is a heterogeneous tumor, composed of genetically divergent subpopulations, including a small fraction of melanoma-initiating cancer stem-like cells (CSCs) and many non-cancer stem cells (non-CSCs). CSCs are characterized by their unique surface proteins associated with aberrant signaling pathways with a causal or consequential relationship with tumor progression, drug resistance, and recurrence. Melanomas also harbor significant alterations in functional genes (BRAF, CDKN2A, NRAS, TP53, and NF1). Of these, the most common are the BRAF and NRAS oncogenes, with 50% of melanomas demonstrating the BRAF mutation (BRAFV600E). While the successful targeting of BRAFV600E does improve overall survival, the long-term efficacy of available therapeutic options is limited due to adverse side effects and reduced clinical efficacy. Additionally, drug resistance develops rapidly via mechanisms involving fast feedback re-activation of MAPK signaling pathways. This article updates information relevant to the mechanisms of melanoma progression and resistance and particularly the mechanistic role of CSCs in melanoma progression, drug resistance, and recurrence.

Micropropagation of Feverfew (Tanacetum parthenium) and Quantification of Parthenolide Content in Its Micropropagated and Conventionally Grown Plants

Feverfew (Tanacetum parthenium) is a well-known multi-functional plant with anti-inflammatory, cardiotonic, antiangiogenic, and anticancer effects. The therapeutic value of this plant is due to its phytochemical constitutes, especially parthenolide. Tissue culture techniques have been applied to improve the bioactive components of many herbal plants. Hence, this study, was carried out to establish a protocol for micropropagation of the feverfew plant and to quantify parthenolide content in its micropropagated and conventionally grown plants. To establish an aseptic culture, different concentrations of sodium hypochlorite (NaOCl) were investigated for seed surface sterilization. Besides, the effects of plant growth regulators (PGRs) on the callus induction, shoot organogenesis from callus and in vitro rooting were evaluated. Additionally, the parthenolide yield of the micropropagated and conventionally grown plants was determined by using high-performance liquid chromatography (HPLC). The results showed that surface sterilization of feverfew seeds with 6% NaOCl for 15 min obtained 65.00 ± 2.69% aseptic seeds. Murashige and Skoog (MS) medium supplemented with 0.4 mg/L thidiazuron (TDZ) and 2 mg/L 2,4-dichlorophenoxy acetic acid (2,4-D) resulted in 86.00 ± 1.72% callus induction. The highest number of shoots (5.00 ± 0.15) per explant was obtained in the treatment of MS medium supplemented with 5 mg/L zeatin. MS medium fortified with 3 mg/L indole-3-butyric acid (IBA) produced the maximum number of roots per plantlet (8.90 ± 0.35). A total of 90% of the micropropagated plantlets survived when planted in perlite + peat moss (1:1 v/v); the micropropagated plantlets were successfully established in the ex vitro conditions. According to parthenolide analysis, its level was significantly higher in the micropropagated plants than conventionally grown plants. Among different solvents, ethanolic extraction obtained the highest parthenolide content of the feverfew plant. Hence, it can be concluded that micropropagation of feverfew could be applied to produce disease-free planting materials and to improve the parthenolide content of the feverfew plant.

Cannabidiol Induces Cell Death in Human Lung Cancer Cells and Cancer Stem Cells

Currently, there is no effective therapy against lung cancer due to the development of resistance. Resistance contributes to disease progression, recurrence, and mortality. The presence of so-called cancer stem cells could explain the ineffectiveness of conventional treatment, and the development of successful cancer treatment depends on the targeting also of cancer stem cells. Cannabidiol (CBD) is a cannabinoid with anti-tumor properties. However, the effects on cancer stem cells are not well understood. The effects of CBD were evaluated in spheres enriched in lung cancer stem cells and adherent lung cancer cells. We found that CBD decreased viability and induced cell death in both cell populations. Furthermore, we found that CBD activated the effector caspases 3/7, increased the expression of pro-apoptotic proteins, increased the levels of reactive oxygen species, as well as a leading to a loss of mitochondrial membrane potential in both populations. We also found that CBD decreased self-renewal, a hallmark of cancer stem cells. Overall, our results suggest that CBD is effective against the otherwise treatment-resistant cancer stem cells and joins a growing list of compounds effective against cancer stem cells. The effects and mechanisms of CBD in cancer stem cells should be further explored to find their Achilles heel.

USP47 maintains the stemness of colorectal cancer cells and is inhibited by parthenolide

Colorectal cancer stem cells (CCSCs) are implicated in colorectal tumor initiation, invasion, recurrence and treatment resistance, so elucidation of the mechanism underlying the cancer stem cells induction and development of drugs targeting CCSCs are vital for cancer treatment. Growing evidence shows that dysregulated deubiquitinase (DUBs) expression is frequently associated with stemness and maintenance of cancer stem cells (CSCs). In the current study, we found that upregulation of USP47 is associated with tumorigenesis and poor prognosis in clinical patients with colorectal cancer (CRC). Besides, USP47 was highly expressed in CCSCs enriched by serum-free culture. Further investigation showed that USP47 is closely involved in the maintenance of the stemness of CCSCs. USP47 silencing reduces proliferation and migration of colorectal cancer cells and suppresses the self-renewal of CCSCs by downregulating the expression of cancer stem cell markers, including CD44, CD133, CD166, OCT4 and NANOG. Furthermore, we identified Parthenolide (PTL), a natural sesquiterpene lactone, as a novel USP47 inhibitor. PTL diminishes CCSCs self-renewal and induces apoptosis of CCSCs. Taken together, our findings highlighted a novel DUB involved in the modulation of CCSCs stemness and the potential of PTL in the CRC treatment by targeting CCSCs as the USP47 inhibitor.

Desensitization of metastatic melanoma cells to therapeutic treatment through repeated exposure to dacarbazine

Aberrant anti-cancer drug efflux mediated by membrane protein ABC transporters (ABCB5 and ABCG2) is thought to characterize melanoma heterogeneous chemoresistant populations, presumed to have unlimited proliferative and self-renewal abilities. Therefore, this study primarily aimed to investigate whether continuous exposure of melanoma cells to dacarbazine (DTIC) chemotherapeutic drug enriches cultures with therapy resistant cells. Thereafter, we sought to determine whether combining the genotoxic activity of DTIC with the oxidative insults of hypericin activated photodynamic therapy (HYP-PDT) could synergized to kill heterogenous chemoresistant melanoma populations. This study revealed that DTIC resistant (UCT Mel-1DTICR2) melanoma cells were less sensitive to all therapies than parental melanoma cells (UCT Mel-1), yet combination therapy was the most efficient. At the exception of DTIC treatment, both HYP-PDT and the combination therapy were effective in significantly reducing the Hoechst non-effluxing dye melanoma main populations (MP) compared to their side population (SP) counterparts. Likewise, HYP-PDT and combination therapy significantly reduced self-renewal capacity, increased expression of ABCB5 and ABCG2 transporters and differentially induced cell cycle arrest and cell death (apoptosis or necrosis) depending on the melanoma MP cell type. Collectively, combination therapy could synergistically reduce melanoma proliferative and clonogenic potential. However, further research is needed to decipher the cellular mechanisms underlying this resistance which would enable combination therapy to reach therapeutic fruition.

Nano magnetic liposomes-encapsulated parthenolide and glucose oxidase for ultra-efficient synergistic antitumor therapy

Multifunctional nanoplatforms yield extremely high synergistic therapeutic effects on the basis of low biological toxicity. Based on the unique tumor microenvironment (TME), a liposomes (Lips)-based multifunctional antitumor drug delivery system known as GOD-PTL-Lips@MNPs was synthesized for chemotherapy, chemodynamic therapy (CDT), starvation therapy, and magnetic targeting synergistic therapy. Evidence has suggested that parthenolide (PTL) can induce apoptosis and consume excessive glutathione (GSH), thereby increasing the efficacy of chemodynamic therapy. On the other hand, glucose oxidase (GOD) can consume intratumoral glucose, lower pH and increase the level of H₂O₂ in the tumor tissue. Integrated Fe₃O₄ magnetic nanoparticles (MNPs) containing Fe²⁺ and Fe³⁺ effectively catalyzes H₂O₂ to a highly toxic hydroxyl radical (•OH) and provide magnetic targeting. During the course of in vitro and in vivo experiments, GOD-PTL-Lips@MNPs demonstrated remarkable synergistic antitumor efficacy. In particular, in mice receiving a 14 day treatment of GOD-PTL-Lips@MNPs, tumor growth was significantly inhibited, as compared with the control group. Moreover, toxicology study and histological examination demonstrated low biotoxicity of this novel therapeutic approach. In summary, our data suggests great antitumor potential for GOD-PTL-Lips@MNPs which could provide an alternative means of further improving the efficacy of anticancer therapies.

Parthenolide as Cooperating Agent for Anti-Cancer Treatment of Various Malignancies

Primary and acquired resistance of cancer to therapy is often associated with activation of nuclear factor kappa B (NF-κB). Parthenolide (PN) has been shown to inhibit NF-κB signaling and other pro-survival signaling pathways, induce apoptosis and reduce a subpopulation of cancer stem-like cells in several cancers. Multimodal therapies that include PN or its derivatives seem to be promising approaches enhancing sensitivity of cancer cells to therapy and diminishing development of resistance. A number of studies have demonstrated that several drugs with various targets and mechanisms of action can cooperate with PN to eliminate cancer cells or inhibit their proliferation. This review summarizes the current state of knowledge on PN activity and its potential utility as complementary therapy against different cancers.

Nanomagnetic liposome-encapsulated parthenolide and indocyanine green for targeting and chemo-photothermal antitumor therapy

Aim: To synthesize a drug-delivery system with chemo-photothermal function and magnetic targeting, to validate its antitumor effect. Materials & methods: Parthenolide (PTL), employing chemotherapy and indocyanine green (ICG) providing phototherapy, were encased separately in the lipid and aqueous phases of liposomes (Lips). The Fe₃O₄ nanoparticles (MNPs), endowing magnetic targeting, were modified on the surface of Lips. The antitumor effects were investigated in vitro and in vivo. Results: ICG-PTL-Lips@MNPs showed outstanding synergistic antitumor efficacy in vitro and in vivo. Especially, after 14-day treatment, the tumor volumes decreased significantly and the biotoxicity was very low. Conclusion: The designed ICG-PTL-Lips@MNPs possess synergistic effects of chemotherapy, photothermal and targeting therapy, which are expected to provide an alternative way to further improve antitumor efficacy.

The effect of micro-sized titanium dioxide on WM-266-4 metastatic melanoma cell line

Titanium dioxide (TiO2) is widely used as an inorganic UV-filter in cosmetic products; however, it has been classified as possibly carcinogenic to humans. While numerous studies demonstrated cytotoxic and genotoxic effects of nano-sized TiO2 in different cell lines, including human skin cells, studies investigating the effects of micro-TiO2 on human keratinocytes and melanocytes, in healthy and cancer cells, are scarce. Adenosine triphosphate (ATP) binding cassette subfamily B member 5 (ABCB5) is a plasma membrane protein known for its role in the tumorigenicity, progression, and recurrence of melanoma. Here, we investigated the effect of micro-TiO2 (average particle size ≤5 µm) on the metabolic activity, cytotoxicity and ABCB5 mRNA expression in metastatic melanoma cells. Metastatic melanoma cell line WM-266-4 was treated with different concentrations of micro-TiO2 for different incubation times to obtain dose- and time-dependent responses. Untreated WM-266-4 cells, cultured under the same conditions, were used as control. The cell metabolic activity was determined by MTT assay. Cytotoxicity of micro-TiO2 was analyzed by lactate dehydrogenase (LDH) cytotoxicity assay. The ABCB5 mRNA expression in melanoma cells was analyzed using quantitative reverse transcription polymerase chain reaction (RT-qPCR). After 120 hours of exposure to micro-TiO2 the metabolic activity of melanoma cells decreased, especially at the two highest micro-TiO2 concentrations. Comparably, the cytotoxicity of micro-TiO2 on melanoma cells increased after 48 and 120 hours of exposure, in a time-dependent manner. The ABCB5 mRNA expression in micro-TiO2-treated melanoma cells also decreased significantly after 24 and 48 hours, in a time-dependent manner. Overall, our results suggest inhibitory effects of micro-TiO2 on the metabolic activity and ABCB5 mRNA expression in metastatic melanoma cells, indicating its potential use as an anticancer agent.

The plant sesquiterpene lactone parthenolide inhibits Wnt/β-catenin signaling by blocking synthesis of the transcriptional regulators TCF4/LEF1

The Wnt/β-catenin pathway is essential for embryonic development and homeostasis, but excessive activation of this pathway is frequently observed in various human diseases, including cancer. Current therapeutic drugs targeting the Wnt pathway often lack sufficient efficacy, and new compounds targeting this pathway are therefore greatly needed. Here we report that the plant-derived natural product parthenolide (PTL), a sesquiterpene lactone, inhibits Wnt signaling. We found that PTL dose-dependently inhibits Wnt3a- and CHIR99021-induced transcriptional activity assessed with the T-cell factor (TCF)/lymphoid enhancer factor (LEF) firefly luciferase (TOPFlash) assay in HEK293 cells. Further investigations revealed that PTL decreases the levels of the transcription factors TCF4/LEF1 without affecting β-catenin stability or subcellular distribution. Moreover, this effect of PTL on TCF4/LEF1 was related to protein synthesis rather than to proteasome-mediated degradation. Of note, siRNA-mediated knockdown of RPL10, a ribosome protein PTL binds, substantially decreased TCF4/LEF1 protein levels and also Wnt3a-induced TOPFlash activities, suggesting a potential mechanism by which PTL may repress Wnt/β-catenin signaling. In summary, PTL binds RPL10 and thereby potently inhibits the Wnt/β-catenin pathway.

Salmonella VNP20009-mediated RNA interference of ABCB5 moderated chemoresistance of melanoma stem cell and suppressed tumor growth more potently

Drug resistance remains an obstacle hindering the success of chemotherapy. Cancer stem cells (CSCs) have been recently found to confer resistance to chemotherapy. Therefore functional markers of CSCs should be discovered and specific therapies targeting these cells should be developed. In our investigation, a small population of B16F10 cells which was positive for ATP-binding cassette sub-family B member 5 (ABCB5) was isolated. This population displayed characteristics similar to those of CSCs and ABCB5 was identified to confer tumor growth and drug resistance in B16F10 cell line. Although targeting ABCB5 by small short interfering RNA delivered by VNP20009 failed to inhibit tumor growth, the combined treatment of VNP-shABCB5 and chemotherapy can act synergistically to delay tumor growth and enhance survival time in a primary B16F10 mice model. Results suggest that the combined treatment of VNP-shABCB5 and chemotherapy can improve the efficacy of chemotherapeutic drugs. Therefore, this combination therapy is of potential significance for melanoma treatment.

Exogenous growth factors bFGF, EGF and HGF do not influence viability and phenotype of V600EBRAF melanoma cells and their response to vemurafenib and trametinib in vitro

It has been shown that the response of ^V600EBRAF melanoma cells to targeted therapeutics is affected by growth factors. We have investigated the influence of three different growth factors, bFGF, EGF and HGF used either alone or in combination, on the response of ^V600EBRAF melanoma cell populations established from surgical specimens to vemurafenib and trametinib, targeting ^V600EBRAF and MEK1/2, respectively.

We report that proliferation and phenotype of ^V600EBRAF melanoma cell populations were not detectably influenced by exogenous growth factors. Neither cell distribution in cell cycle and CCND1 expression nor activity of signaling pathways crucial for melanoma development and maintenance, including the RAF/MEK/ERK pathway, WNT/β-catenin pathway and NF-κB signaling, were affected by the presence of different growth factors. We furthermore show that vemurafenib and trametinib abrogated the activity of ERK1/2, arrested cells in G₀/G₁ cell cycle phase, triggered apoptosis, induced changes in the expression of CXCL8, CCND1 and CTGF and the frequency of Ki-67^high and CD271^high cells. These effects were, however, similar in the presence of different growth factors. Interestingly, comparable results were also obtained for melanoma cells grown without exogenous growth factors bFGF, EGF and HGF for a period as long as 4 months prior the drug treatment.

We conclude that the composition or lack of exogenous growth factors bFGF, EGF and HGF do not markedly influence viability and phenotype of ^V600EBRAF melanoma cells and their response to vemurafenib and trametinib in vitro. Our results question the necessity of these growth factors in the medium that is used for culturing ^V600EBRAF melanoma cells.

Parthenolide induces MITF-M downregulation and senescence in patient-derived MITF-M(high) melanoma cell populations

The activity of the M isoform of microphthalmia-associated transcription factor (MITF-M) has been attributed to regulation of differentiation, proliferation, survival and senescence of melanoma cells. MITF expression was shown to be antagonized by the activation of transcription factor NF-κB. Parthenolide, an inhibitor of NF-κB, has not been yet reported to affect MITF-M expression. Our results obtained in patient-derived melanoma cell populations indicate that parthenolide efficiently decreases the MITF-M level. This is neither dependent on p65/NF-κB signaling nor RAF/MEK/ERK pathway activity as inhibition of MEK by GSK1120212 (trametinib) and induction of ERK1/2 activity by parthenolide itself do not interfere with parthenolide-triggered depletion of MITF-M in both wild-type BRAF and BRAF^V600E melanoma populations. Parthenolide activity is not prevented by inhibitors of caspases, proteasomal and lysosomal pathways. As parthenolide reduces MITF-M transcript level and HDAC1 protein level, parthenolide-activated depletion of MITF-M protein may be considered as a result of transcriptional regulation, however, the influence of parthenolide on other elements of a dynamic control over MITF-M cannot be ruled out. Parthenolide induces diverse effects in melanoma cells, from death to senescence. The mode of the response to parthenolide is bound to the molecular characteristics of melanoma cells, particularly to the basal MITF-M expression level but other cell-autonomous differences such as NF-κB activity and MCL-1 level might also contribute. Our data suggest that parthenolide can be developed as a drug used in combination therapy against melanoma when simultaneous inhibition of MITF-M, NF-κB and HDAC1 is needed.

A combination of photodynamic therapy and chemotherapy displays a differential cytotoxic effect on human metastatic melanoma cells

BACKGROUND

Cutaneous melanoma represents the most lethal form of skin cancer and remains refractory to current therapies. Failure of treatment has been attributed to the over-expression of ABC transporters which efflux the drugs, below their cytotoxic threshold within cells. Therefore, this study set to investigate; the efficacy of a combinatorial approach comprising chemotherapy (Dacarbazine) and photodynamic therapy (PDT) to overcome resistance in pigmented and unpigmented metastatic melanoma and potentially identify resistant mechanisms.

METHODS

The cytotoxic effect of the chemotherapy, PDT and combination therapy treatment (Dacarbazine+PDT) was determined using a cell viability XTT assay. Thereafter, melanoma cells morphology, self-renewal capacity and ABCG2 protein expression, were determined using fluorescence microscopy, clonogenic assay, western blot and flow cytometry. All results were analyzed by t-test and ANOVA, followed by individual comparisons with post-tests.

RESULTS

This study describes possible synergism of PDT+DTIC in reducing melanoma cell viability in vitro. At 24h post-treatment, only the unpigmented melanomas were sensitive to DTIC treatment (20-25% death at 1.25mM). At 48h, a lethal dose of 50% was reached in these cells in contrast to the pigmented melanoma (20% at 48h). The same trend was observed with the combination therapy (DTIC+PDT) at both time points. Furthermore, complete morphological disruption could be observed upon PDT only and PDT+DTIC treatments. Moreover, PDT and DTIC+PDT suppressed the self-renewal capacity of both melanoma cell lines. No significant differences in ABCG2 protein expression was found at 24h post-treatment.

CONCLUSION

Overall, these results suggest that human melanomas remain heterogeneous in their phenotypes. Moreover, in our metastatic melanoma cells, ABCG2 transporters did not seem to be involved in resistance to therapies. Significantly though, a combinatorial approach of PDT and chemotherapy significantly decreases the self-renewal capacity of metastatic melanoma cells and could be a suggested adjunctive approach to post-resection treatment regimes.

Inflammatory regulation of stem-like cells in melanoma

The link between inflammation, immunity and cancer is well established. In the last decade, there has been considerable excitement over cancer stem cells, believed to be a subset of tumour cells responsible for their initiation, propagation and resistance to conventional chemoradiotherapy. In this review, we discuss the characterization of cancer stem cells and describe their modulation by inflammation with a focus on melanoma.

Pentoxifylline Inhibits WNT Signalling in β-Cateninhigh Patient-Derived Melanoma Cell Populations

Background

The heterogeneity of melanoma needs to be addressed and combination therapies seem to be necessary to overcome intrinsic and acquired resistance to newly developed immunotherapies and targeted therapies. Although the role of WNT/β-catenin pathway in melanoma was early demonstrated, its contribution to the lack of the melanoma patient response to treatment was only recently recognized. Using patient-derived melanoma cell populations, we investigated the influence of pentoxifylline on melanoma cells with either high or low expression of β-catenin.

Findings

Our results indicate that pentoxifylline inhibits the activity of the canonical WNT pathway in melanoma cell populations with high basal activity of this signalling. This is supported by lowered overall activity of transcription factors TCF/LEF and reduced nuclear localisation of active β-catenin. Moreover, treatment of β-catenin^high melanoma cell populations with pentoxifylline induces downregulation of genes that are targets of the WNT/β-catenin pathway including connective tissue growth factor (CTGF) and microphthalmia-associated transcription factor (MITF-M), a melanocyte- and melanoma cell-specific regulator.

Conclusions

These results suggest that pentoxifylline, a drug approved by the FDA in the treatment of peripheral arterial disease, might be tested in a subset of melanoma patients with elevated activity of β-catenin. This pharmaceutical might be tested as an adjuvant drug in combination therapies when the response to immunotherapy is prevented by high activity of the WNT/β-catenin pathway.

Notch4+ cancer stem-like cells promote the metastatic and invasive ability of melanoma

Sphere formation in conditioned serum‐free culture medium supplemented with epidermal growth factor and basic fibroblast growth factor (tumorospheres) is considered useful for the enrichment of cancer stem‐like cells, also known as tumor‐initiating cells. We used a gene expression microarray to investigate the gene expression profile of melanoma cancer stem‐like cells (MCSLCs). The results showed that MCSLCs highly expressed the following Notch signaling pathway molecules: Notch3 (NM_008716), Notch4 (NM_010929), Dtx4 (NM_172442), and JAG2 (NM_010588). Immunofluorescence staining showed tumorosphere cells highly expressed Notch4. Notch4^high B16F10 cells were isolated by FACS, and Western blotting showed that high Notch4 expression is related to the expression of epithelial–mesenchymal transition (EMT)‐associated proteins. Reduced invasive and migratory properties concomitant with the downregulation of the EMT markers Twist1, vimentin, and VE‐cadherin and the overexpression of E‐cadherin was observed in human melanoma A375 and MUM‐2B cells. In these cells, Notch4 was also downregulated, both by Notch4 gene knockdown and by application of the γ‐secretase inhibitor, DAPT. Mechanistically, the re‐overexpression of Twist1 by the transfection of cells with a Twist1 expression plasmid led to an increase in VE‐cadherin expression and a decrease in E‐cadherin expression. Immunohistochemical analysis of 120 human melanoma tissues revealed a significant correlation between the high expression of Notch4 and the metastasis of melanoma. Taken together, our findings indicate that Notch4+ MCSLCs trigger EMT and promote the metastasis of melanoma cells.

Cyclic AMP efflux inhibitors as potential therapeutic agents for leukemia

Apoptotic evasion is a hallmark of cancer. We propose that some cancers may evade cell death by regulating 3'-5'-cyclic adenosine monophosphate (cAMP), which is associated with pro-apoptotic signaling. We hypothesize that leukemic cells possess mechanisms that efflux cAMP from the cytoplasm, thus protecting them from apoptosis. Accordingly, cAMP efflux inhibition should result in: cAMP accumulation, activation of cAMP-dependent downstream signaling, viability loss, and apoptosis. We developed a novel assay to assess cAMP efflux and performed screens to identify inhibitors. In an acute myeloid leukemia (AML) model, several identified compounds reduced cAMP efflux, appropriately modulated pathways that are responsive to cAMP elevation (cAMP-responsive element-binding protein phosphorylation, and deactivation of Very Late Antigen-4 integrin), and induced mitochondrial depolarization and caspase activation. Blocking adenylyl cyclase activity was sufficient to reduce effects of the most potent compounds. These compounds also decreased cAMP efflux and viability of B-lineage acute lymphoblastic leukemia (B-ALL) cell lines and primary patient samples, but not of normal primary peripheral blood mononuclear cells. Our data suggest that cAMP efflux is a functional feature that could be therapeutically targeted in leukemia. Furthermore, because some of the identified drugs are currently used for treating other illnesses, this work creates an opportunity for repurposing.

Diminution of miR-340-5p levels is responsible for increased expression of ABCB5 in melanoma cells under oxygen-deprived conditions

Melanoma is usually highly refractory to chemotherapy. This resistance to treatment is mainly due to high heterogeneity and plasticity of melanoma cells strictly connected to changes in tumor microenvironment. Hypoxia can drastically alter cancer biology. Solid tumor cells under hypoxia gain stem-like features, they are more invasive and drug-resistant than their normoxic counterparts. These effects could be mediated by changes in miRNA expression under hypoxia. MiRNAs are small non-coding RNA molecules that can negatively control gene expression. In the present study using microarray technology we evaluated the expression of miRNAs in melanoma cells derived from nodular melanoma and grown under normoxic and hypoxic conditions. Using R environment for statistical analysis we found that 70 miRNAs were differentially-expressed, and 16 of them were significantly down-regulated in melanoma cells grown in hypoxic conditions compared to cells grown in normoxia. We intended to find transcripts whose expression is increased due to down-regulation of selected miRNAs. Bioinformatics analysis revealed that increased levels of HIF-2α, ABCB5, OCT4, SOX2 and ZEB1 in different melanoma populations under hypoxia could be a result of significant down-regulation of miR-340-5p. Inhibition of miR-340-5p confirmed that this miRNA negatively influences the expression of ABCB5. This is the first study showing the relationship between miR-340-5p and expression of ABCB5, a transmembrane transporter involved in drug resistance considered as a marker of melanoma stem-like cells.

Epigenetic mechanisms involved in melanoma pathogenesis and chemoresistance

The discovery of highly recurrent mutations in melanoma, such as BRAF(V600E), completely changed the clinical management including therapy of melanoma patients. In the era of Personalized Medicine targeted melanoma therapies showed high response rates, currently evidenced by BRAF inhibitors or immune-stimulating therapies. In addition to genetic biomarkers, epigenetic knowledge in melanoma has undergone a major step forward in recent years. In particular, epigenetics is unveiling new perspectives to fight this disease, providing an encouraging number of DNA methylation based biomarkers that will likely improve patient stratification for prognosis and treatment. In this regard, putative targetable biomarkers or those with predictive value for the outcome of currently applied therapies are promising tools for future precision oncology strategies. In addition, the progress made in genetic and epigenetic profiling technologies and their reconfiguration to real-time clinical screening approaches makes personalized medicine in melanoma an achievable objective in upcoming years.

MCL-1, BCL-XL and MITF Are Diversely Employed in Adaptive Response of Melanoma Cells to Changes in Microenvironment

Melanoma cells can switch their phenotypes in response to microenvironmental insults. Heterogeneous melanoma populations characterized by long-term growth and a high self-renewal capacity can be obtained in vitro in EGF(+)bFGF(+) medium whilst invasive potential of melanoma cells is increased in serum-containing cultures. In the present study, we have shown that originally these patient-derived melanoma populations exhibit variable expression of pro-survival genes from the BCL-2 family and inhibitors of apoptosis (IAPs), and differ in the baseline MCL-1 transcript stability as well. While being transferred to serum-containing medium, melanoma cells are well protected from death. Immediate adaptive response of melanoma cells selectively involves a temporary MCL-1 increase, both at mRNA and protein levels, and BCL-X_L can complement MCL-1, especially in MITF_low populations. Thus, the extent of MCL-1 and BCL-XL contributions seems to be cell context-dependent. An increase in MCL-1 level results from a transiently enhanced stability of its transcript, but not from altered protein turnover. Inhibition of MCL-1 preceding transfer to serum-containing medium caused the induction of cell death in a subset of melanoma cells, which confirms the involvement of MCL-1 in melanoma cell survival during the rapid alteration of growth conditions. Additionally, immediate response to serum involves the transient increase in MITF expression and inhibition of ERK-1/2 activity. Uncovering the mechanisms of adaptive response to rapid changes in microenvironment may extend our knowledge on melanoma biology, especially at the stage of dissemination.

Phenotypic diversity of patient-derived melanoma populations in stem cell medium

Melanomas are highly heterogeneous tumors and there is no treatment effective at achieving long-term remission for metastatic melanoma patients. Thus, an appropriate model system for studying melanoma biology and response to drugs is necessary. It has been shown that composition of the medium is a critical factor in preserving the complexity of the tumor in in vitro settings, and melanospheres maintained in stem cell medium are a good model in this respect. In the present study, we observed that not all nodular melanoma patient-derived cell populations grown in stem cell medium were capable of forming melanospheres, and cell aggregates and anchorage-independent single-cell cultures emerged instead. Self-renewing capacity and unlimited growth potential indicated the presence of cells with stem-like properties in all patient-derived populations but immunophenotype and MITF expression exhibited variability. Enhanced MITF expression and activity was observed in melanospheres in comparison with cell aggregates and single-cell culture, and hypoxic-like conditions that increased the ability of single-cell population to form melanospheres enhanced MITF expression and cell pigmentation as well. Thus, MITF seems to be a critical transcription factor for formation of both patient-derived and hypoxia-induced melanospheres. After 2 years of continuous culturing, melanospheres progressively underwent transition into cell aggregates that was accompanied by changes in expression of several MITF-dependent genes associated with melanogenesis and survival and alterations in the composition of subpopulations but not in the frequency of ABCB5-positive cells. Several biological properties of parent tumor are well preserved in patient-derived melanospheres, but during prolonged culturing the heterogeneity is substantially lost when the melanospheres are substituted by cell aggregates. This should be considered when cell aggregates instead of melanospheres are used in the study of melanoma biology and cell response to drugs.

Parthenolide inhibits cancer stem-like side population of nasopharyngeal carcinoma cells via suppression of the NF-κB/COX-2 pathway

Cancer stem cells play a central role in the pathogenesis of nasopharyngeal carcinoma and contribute to both disease initiation and relapse. In this study, cyclooxygenase-2 (COX-2) was found to regulate cancer stem-like side population cells of nasopharyngeal carcinoma cells and enhance cancer stem-like cells' characteristics such as higher colony formation efficiency and overexpression of stemness-associated genes. The regulatory effect of COX-2 on cancer stem-like characteristics may be mediated by ABCG2. COX-2 overexpression by a gain-of-function experiment increased the proportion of side population cells and their cancer stemness properties. The present study also demonstrated that in contrast to the classical chemotherapy drug 5-fluorouracil, which increased the proportion of side population cells and upregulated the expression of COX-2, parthenolide, a naturally occurring small molecule, preferentially targeted the side population cells of nasopharyngeal carcinoma cells and downregulated COX-2. Moreover, we found that the cancer stem-like cells' phenotype was suppressed by using COX-2 inhibitors NS-398 and CAY10404 or knocking down COX-2 with siRNA and shRNA. These findings suggest that COX-2 inhibition is the mechanism by which parthenolide induces cell death in the cancer stem-like cells of nasopharyngeal carcinoma. In addition, parthenolide exhibited an inhibitory effect on nuclear factor-kappa B (NF-κB) nucler translocation by suppressing both the phosphorylation of IκB kinase complex and IκBα degradation. Taken together, these results suggest that parthenolide may exert its cancer stem cell-targeted chemotherapy through the NF-κB/COX-2 pathway.

Targeting apoptosis pathways in cancer and perspectives with natural compounds from mother nature

Although the incidences are increasing day after day, scientists and researchers taken individually or by research group are trying to fight against cancer by several ways and also by different approaches and techniques. Sesquiterpenes, flavonoids, alkaloids, diterpenoids, and polyphenolic represent a large and diverse group of naturally occurring compounds found in a variety of fruits, vegetables, and medicinal plants with various anticancer properties. In this review, our aim is to give our perspective on the current status of the natural compounds belonging to these groups and discuss their natural sources, their anticancer activity, their molecular targets, and their mechanism of actions with specific emphasis on apoptosis pathways, which may help the further design and conduct of preclinical and clinical trials. Unlike pharmaceutical drugs, the selected natural compounds induce apoptosis by targeting multiple cellular signaling pathways including transcription factors, growth factors, tumor cell survival factors, inflammatory cytokines, protein kinases, and angiogenesis that are frequently deregulated in cancers and suggest that their simultaneous targeting by these compounds could result in efficacious and selective killing of cancer cells. This review suggests that they provide a novel opportunity for treatment of cancer, but clinical trials are still required to further validate them in cancer chemotherapy.

Gene expression profiling identifies microphthalmia-associated transcription factor (MITF) and Dickkopf-1 (DKK1) as regulators of microenvironment-driven alterations in melanoma phenotype

BACKGROUND

The diversity of functional phenotypes observed within a tumor does not exclusively result from intratumoral genetic heterogeneity but also from the response of cancer cells to the microenvironment. We have previously demonstrated that the morphological and functional phenotypes of melanoma can be dynamically altered upon external stimuli.

FINDINGS

In the present study, transcriptome profiles were generated to explore the molecules governing phenotypes of melanospheres grown in the bFGF(+)EGF(+) serum-free cultures and monolayers maintained in the serum-containing medium. Higher expression levels of MITF-dependent genes that are responsible for differentiation, e.g., TYR and MLANA, and stemness-related genes, e.g., ALDH1A1, were detected in melanospheres. These results were supported by the observation that the melanospheres contained more pigmented cells and cells exerting the self-renewal capacity than the monolayers. In addition, the expression of the anti-apoptotic, MITF-dependent genes e.g., BCL2A1 was also higher in the melanospheres. The enhanced activity of MITF in melanospheres, as illustrated by the increased expression of 74 MITF-dependent genes, identified MITF as a central transcriptional regulator in melanospheres. Importantly, several genes including MITF-dependent ones were expressed in melanospheres and original tumors at similar levels. The reduced MITF level in monolayers might be partially explained by suppression of the Wnt/β-catenin pathway, and DKK1, a secreted inhibitor of this pathway, was highly up-regulated in monolayers in comparison to melanospheres and original tumors. Furthermore, the silencing of DKK1 in monolayers increased the percentage of cells with self-renewing capacity.

CONCLUSIONS

Our study indicates that melanospheres can be used to unravel the molecular pathways that sustain intratumoral phenotypic heterogeneity. Melanospheres directly derived from tumor specimens more accurately mirrored the morphology and gene expression profiles of the original tumors compared to monolayers. Therefore, melanospheres represent a relevant preclinical tool to study new anticancer treatment strategies.

Natural compounds' activity against cancer stem-like or fast-cycling melanoma cells

Background

Accumulating evidence supports the concept that melanoma is highly heterogeneous and sustained by a small subpopulation of melanoma stem-like cells. Those cells are considered as responsible for tumor resistance to therapies. Moreover, melanoma cells are characterized by their high phenotypic plasticity. Consequently, both melanoma stem-like cells and their more differentiated progeny must be eradicated to achieve durable cure. By reevaluating compounds in heterogeneous melanoma populations, it might be possible to select compounds with activity not only against fast-cycling cells but also against cancer stem-like cells. Natural compounds were the focus of the present study.

Methods

We analyzed 120 compounds from The Natural Products Set II to identify compounds active against melanoma populations grown in an anchorage-independent manner and enriched with cells exerting self-renewing capacity. Cell viability, cell cycle arrest, apoptosis, gene expression, clonogenic survival and label-retention were analyzed.

Findings

Several compounds efficiently eradicated cells with clonogenic capacity and nanaomycin A, streptonigrin and toyocamycin were effective at 0.1 µM. Other anti-clonogenic but not highly cytotoxic compounds such as bryostatin 1, siomycin A, illudin M, michellamine B and pentoxifylline markedly reduced the frequency of ABCB5 (ATP-binding cassette, sub-family B, member 5)-positive cells. On the contrary, treatment with maytansine and colchicine selected for cells expressing this transporter. Maytansine, streptonigrin, toyocamycin and colchicine, even if highly cytotoxic, left a small subpopulation of slow-dividing cells unaffected. Compounds selected in the present study differentially altered the expression of melanocyte/melanoma specific microphthalmia-associated transcription factor (MITF) and proto-oncogene c-MYC.

Conclusion

Selected anti-clonogenic compounds might be further investigated as potential adjuvants targeting melanoma stem-like cells in the combined anti-melanoma therapy, whereas selected cytotoxic but not anti-clonogenic compounds, which increased the frequency of ABCB5-positive cells and remained slow-cycling cells unaffected, might be considered as a tool to enrich cultures with cells exhibiting melanoma stem cell characteristics.

Melanoma stem cells and metastasis: mimicking hematopoietic cell trafficking?

Malignant melanoma is a highly metastatic cancer that bears responsibility for the majority of skin cancer-related deaths. Amidst the research efforts to better understand melanoma progression, there has been increasing evidence that hints at a role for a subpopulation of virulent cancer cells, termed malignant melanoma stem or initiating cells (MMICs), in metastasis formation. MMICs are characterized by their preferential ability to initiate and propagate tumor growth and their selective capacity for self-renewal and differentiation into less tumorigenic melanoma cells. The frequency of MMICs has been shown to correlate with poor clinical prognosis in melanoma. In addition, MMICs are enriched among circulating tumor cells in the peripheral blood of cancer patients, suggesting that MMICs may be a critical factor in the metastatic cascade. Although these links exist between MMICs and metastatic disease, the mechanisms by which MMICs may advance metastatic progression are only beginning to be elucidated. Recent studies have shown that MMICs express molecules critical for hematopoietic cell maintenance and trafficking, providing a possible explanation for how circulating MMICs could drive melanoma dissemination. We therefore propose that MMICs might fuel melanoma metastasis by exploiting homing mechanisms commonly utilized by hematopoietic cells. Here we review the biological properties of MMICs and the existing literature on their metastatic potential. We will discuss possible mechanisms by which MMICs might initiate metastases in the context of established knowledge of cancer stem cells in other cancers and of hematopoietic homing molecules, with a particular focus on selectins, integrins, chemokines and chemokine receptors known to be expressed by melanoma cells. Biological understanding of how these molecules might be utilized by MMICs to propel the metastatic cascade could critically impact the development of more effective therapies for advanced disease.

Can nanomedicines kill cancer stem cells?

Most tumors are heterogeneous and many cancers contain small population of highly tumorigenic and intrinsically drug resistant cancer stem cells (CSCs). Like normal stem cell, CSCs have the ability to self-renew and differentiate to other tumor cell types. They are believed to be a source for drug resistance, tumor recurrence and metastasis. CSCs often overexpress drug efflux transporters, spend most of their time in non-dividing G0 cell cycle state, and therefore, can escape the conventional chemotherapies. Thus, targeting CSCs is essential for developing novel therapies to prevent cancer relapse and emerging of drug resistance. Nanocarrier-based therapeutic agents (nanomedicines) have been used to achieve longer circulation times, better stability and bioavailability over current therapeutics. Recently, some groups have successfully applied nanomedicines to target CSCs to eliminate the tumor and prevent its recurrence. These approaches include 1) delivery of therapeutic agents (small molecules, siRNA, antibodies) that affect embryonic signaling pathways implicated in self-renewal and differentiation in CSCs, 2) inhibiting drug efflux transporters in an attempt to sensitize CSCs to therapy, 3) targeting metabolism in CSCs through nanoformulated chemicals and field-responsive magnetic nanoparticles and carbon nanotubes, and 4) disruption of multiple pathways in drug resistant cells using combination of chemotherapeutic drugs with amphiphilic Pluronic block copolymers. Despite clear progress of these studies the challenges of targeting CSCs by nanomedicines still exist and leave plenty of room for improvement and development. This review summarizes biological processes that are related to CSCs, overviews the current state of anti-CSCs therapies, and discusses state-of-the-art nanomedicine approaches developed to kill CSCs.

Parthenolide enhances dacarbazine activity against melanoma cells

Dacarbazine induces a clinical response only in 15% of melanoma patients. New treatment strategies may involve combinations of drugs with different modes of action to target the tumor heterogeneity. We aimed to determine whether the combined treatment of heterogeneous melanoma cell populations in vitro with the alkylating agent dacarbazine and the nuclear factor-κB inhibitor parthenolide could be more effective than either drug alone. A panel of melanoma cell lines, including highly heterogeneous populations derived from surgical specimens, was treated with dacarbazine and parthenolide. The effect of drugs on the viable cell number was examined using an acid phosphatase activity assay, and the combination effect was determined by median-effect analysis. Cell death and cell-cycle arrest were assessed by flow cytometry. Gene expression was measured by real-time PCR and changes in the protein levels were evaluated by western blotting. Secretion of vascular endothelial growth factor and interleukin-8 was determined using an enzyme-linked immunosorbent assay. The self-renewing capacity was assessed using a clonogenic assay. Dacarbazine was less effective in heterogeneous melanoma populations than in the A375 cell line. Parthenolide and dacarbazine synergistically reduced the viable cell numbers. Both drugs induced cell-cycle arrest and apoptotic cell death. Importantly, parthenolide abrogated the baseline and dacarbazine-induced vascular endothelial growth factor secretion from melanoma cells in heterogeneous populations, whereas interleukin-8 secretion was not significantly affected by either drug. Parthenolide eradicated melanoma cells with self-renewing capacity also in cultures simultaneously treated with dacarbazine. The combination of parthenolide and dacarbazine might be considered as a new therapeutic modality against metastatic melanoma.

Parthenolide: from plant shoots to cancer roots

Parthenolide (PTL), a sesquiterpene lactone (SL) originally purified from the shoots of feverfew (Tanacetum parthenium), has shown potent anticancer and anti-inflammatory activities. It is currently being tested in cancer clinical trials. Structure-activity relationship (SAR) studies of parthenolide revealed key chemical properties required for biological activities and epigenetic mechanisms, and led to the derivatization of an orally bioavailable analog, dimethylamino-parthenolide (DMAPT). Parthenolide is the first small molecule found to be selective against cancer stem cells (CSC), which it achieves by targeting specific signaling pathways and killing cancer from its roots. In this review, we highlight the exciting journey of parthenolide, from plant shoots to cancer roots.