The human melanoma side population displays molecular and functional characteristics of enriched chemoresistance and tumorigenesis

An Investigation into the In Vitro Targeted Killing of CD44-Expressing Triple-Negative Breast Cancer Cells Using Recombinant Photoimmunotherapeutics Compared to Auristatin-F-Based Antibody-Drug Conjugates

Triple-negative breast cancer (TNBC) is the deadliest form of breast cancer with limited treatment options. The persistence of highly tumorigenic CD44-expressing subpopulation referred to as cancer stem cells (CSCs), endowed with the self-renewal capacity, has been associated with therapeutic resistance, hence clinical relapses. To mitigate these undesired events, targeted immunotherapies using antibody-photoconjugate (APC) or antibody-drug conjugate (ADC), were developed to specifically release cytotoxic payloads within targeted cells overexpressing cognate antigen receptors. Therefore, an αCD44(scFv)-SNAP-tag antibody fusion protein was engineered through genetic fusion of a single-chain antibody fragment (scFv) to a SNAPf-tag fusion protein, capable of self-conjugating with benzylguanine-modified light-sensitive near-infrared (NIR) phthalocyanine dye IRDye700DX (BG-IR700) or the small molecule toxin auristatin-F (BG-AURIF). Binding of the αCD44(scFv)-SNAPf-IR700 photoimmunoconjugate to antigen-positive cells was demonstrated by confocal microscopy and flow cytometry. By switching to NIR irradiation, CD44-expressing TNBC was selectively killed through induced phototoxic activities. Likewise, the αCD44(scFv)-SNAPf-AURIF immunoconjugate was able to selectively accumulate within targeted cells and significantly reduced cell viability through antimitotic activities at nano- to micromolar drug concentrations. This study provides an in vitro proof-of-concept for a future strategy to selectively destroy light-accessible superficial CD44-expressing TNBC tumors and their metastatic lesions which are inaccessible to therapeutic light.

The modulation of ion channels in cancer chemo-resistance

Ion channels modulate the flow of ions into and out of a cell or intracellular organelle, leading to generation of electrical or chemical signals and regulating ion homeostasis. The abundance of ion channels in the plasma and intracellular membranes are subject to physiological and pathological regulations. Abnormal and dysregulated expressions of many ion channels are found to be linked to cancer and cancer chemo-resistance. Here, we will summarize ion channels distribution in multiple tumors. And the involvement of ion channels in cancer chemo-resistance will be highlighted.

Persister state-directed transitioning and vulnerability in melanoma

Melanoma is a highly plastic tumor characterized by dynamic interconversion of different cell identities depending on the biological context. Melanoma cells with high expression of the H3K4 demethylase KDM5B (JARID1B) rest in a slow-cycling, yet reversible persister state. Over time, KDM5Bhigh cells can promote rapid tumor repopulation with equilibrated KDM5B expression heterogeneity. The cellular identity of KDM5Bhigh persister cells has not been studied so far, missing an important cell state-directed treatment opportunity in melanoma. Here, we have established a doxycycline-titratable system for genetic induction of permanent intratumor expression of KDM5B and screened for chemical agents that phenocopy this effect. Transcriptional profiling and cell functional assays confirmed that the dihydropyridine 2-phenoxyethyl 4-(2-fluorophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxylate (termed Cpd1) supports high KDM5B expression and directs melanoma cells towards differentiation along the melanocytic lineage and to cell cycle-arrest. The high KDM5B state additionally prevents cell proliferation through negative regulation of cytokinetic abscission. Moreover, treatment with Cpd1 promoted the expression of the melanocyte-specific tyrosinase gene specifically sensitizing melanoma cells for the tyrosinase-processed antifolate prodrug 3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin (TMECG). In summary, our study provides proof-of-concept for a dual hit strategy in melanoma, in which persister state-directed transitioning limits tumor plasticity and primes melanoma cells towards lineage-specific elimination.

Heme Oxygenase-1 Has a Greater Effect on Melanoma Stem Cell Properties Than the Expression of Melanoma-Initiating Cell Markers

Melanoma-initiating cells (MICs) contribute to the tumorigenicity and heterogeneity of melanoma. MICs are identified by surface and functional markers and have been shown to display cancer stem cell (CSC) properties. However, the existence of MICs that follow the hierarchical CSC model has been questioned by studies showing that single unselected melanoma cells are highly tumorigenic in xenotransplantation assays. Herein, we characterize cells expressing MIC markers (CD20, CD24, CD133, Sca-1, ABCB1, ABCB5, ALDH^high) in the B16-F10 murine melanoma cell line. We use flow cytometric phenotyping, single-cell sorting followed by in vitro clonogenic assays, and syngeneic in vivo serial transplantation assays to demonstrate that the expression of MIC markers does not select CSC-like cells in this cell line. Previously, our group showed that heme-degrading enzyme heme oxygenase-1 (HO-1) can be upregulated in melanoma and increase its aggressiveness. Here, we show that HO-1 activity is important for non-adherent growth of melanoma and HO-1 overexpression enhances the vasculogenic mimicry potential, which can be considered protumorigenic activity. However, HO-1 overexpression decreases clone formation in vitro and serial tumor initiation in vivo. Thus, HO-1 plays a dual role in melanoma, improving the progression of growing tumors but reducing the risk of melanoma initiation.

ABCB1 in dermatology: roles in skin diseases and their treatment

Adenosine triphosphate-binding cassette subfamily B member 1 (ABCB1), also known as permeability glycoprotein, multidrug-resistant protein 1, or cluster of differentiation 243 (CD243), is a crucial protein for purging foreign substances from cells. The functions of ABCB1 have been investigated extensively for their roles in cancer, stem cells, and drug resistance. Abundant pharmacogenetic studies have been conducted on ABCB1 and its association with treatment responsiveness to various agents, particularly chemotherapeutic and immunomodulatory agents. However, its functions in the skin and implications on dermatotherapeutics are far less reported. In this article, we reviewed the roles of ABCB1 in dermatology. ABCB1 is expressed in the skin and its appendages during drug delivery and transport. It is associated with treatment responsiveness to various agents, including topical steroids, methotrexate, cyclosporine, azathioprine, antihistamines, antifungal agents, colchicine, tacrolimus, ivermectin, tetracycline, retinoid acids, and biologic agents. Moreover, genetic variation in ABCB1 is associated with the pathogenesis of several dermatoses, including psoriasis, atopic dermatitis, melanoma, bullous pemphigoid, Behçet disease, and lichen planus. Further investigation is warranted to elucidate the roles of ABCB1 in dermatology and the possibility of enhancing therapeutic efficacy through ABCB1 manipulation.

Human ES and iPS cells display less drug resistance than differentiated cells, and naïve-state induction further decreases drug resistance

Pluripotent stem cells (PSCs) possess unique characteristics that distinguish them from other cell types. Human embryonic stem (ES) cells are recently gaining attention as a powerful tool for human toxicity assessment without the use of experimental animals, and an embryonic stem cell test (EST) was introduced for this purpose. However, human PSCs have not been thoroughly investigated in terms of drug resistance or compared with other cell types or cell states, such as naïve state, to date. Aiming to close this gap in research knowledge, we assessed and compared several human PSC lines for their resistance to drug exposure. Firstly, we report that RIKEN-2A human induced pluripotent stem (iPS) cells possessed approximately the same sensitivity to selected drugs as KhES-3 human ES cells. Secondly, both ES and iPS cells were several times less resistant to drug exposure than other non-pluripotent cell types. Finally, we showed that iPS cells subjected to naïve-state induction procedures exhibited a sharp increase in drug sensitivity. Upon passage of these naïve-like cells in non-naïve PSC culture medium, their sensitivity to drug exposure decreased. We thus revealed differences in sensitivity to drug exposure among different types or states of PSCs and, importantly, indicated that naïve-state induction could increase this sensitivity.

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.

SOX2 upregulates side population cells and enhances their chemoresistant ability by transactivating ABCC1 expression contributing to intrinsic resistance to paclitaxel in melanoma

Paclitaxel is the last choice for the treatment of advanced melanoma as a second-line chemotherapeutic agent, but there are still many cases of intrinsic resistance to paclitaxel in melanoma and the reasons that cause paclitaxel resistance remain unclear. Here, we identified that high expression of SRY-box transcription factor 2 (SOX2) and high ratio of side population (SP) cells reduced the sensitivity to paclitaxel in melanoma cells. The knockout and the induction of SOX2 completely depleted and significantly upregulated the ratios of melanoma SP cells, respectively. These data suggest that SOX2, a pluripotent transcription factor for inducing cancer stem cells in melanoma, is also sufficient and necessary for the induction of melanoma SP cells. ATP-binding cassette (ABC) subfamily C member 1 (ABCC1) is one of ABC transporters which causes SP cells to be resistance to chemotherapeutic agents by efficiently pumping drugs out of cells. The knockout and the induction of ABCC1 significantly increased and decreased the sensitivity of melanoma cells to paclitaxel. High expression of ABCC1 was identified in melanoma cell lines with high expression of SOX2 and in their SP cells. SOX2 was identified to induce ABCC1 transcription. Taken together, SOX2 upregulates SP cells and enhances their chemoresistant ability by increasing ABCC1 expression, which contributes to intrinsic resistance to paclitaxel in melanoma. Our findings will lead to new insights into melanoma biology and therapy resistance, and eventually to new therapeutic targets.

Extracellular Vesicles Shedding Promotes Melanoma Growth in Response to Chemotherapy

Extracellular vesicles (EVs) are emerging as key players in intercellular communication. EVs can transfer biological macromolecules to recipient cells, modulating various physiological and pathological processes. It has been shown that tumor cells secrete large amounts of EVs that can be taken up by malignant and stromal cells, dictating tumor progression. In this study, we investigated whether EVs secreted by melanoma cells in response to chemotherapy modulate tumor response to alkylating drugs. Our findings showed that human and murine melanoma cells secrete more EVs after treatment with temozolomide and cisplatin. We observed that EVs shed by melanoma cells after temozolomide treatment modify macrophage phenotype by skewing macrophage activation towards the M2 phenotype through upregulation of M2-marker genes. Moreover, these EVs were able to favor melanoma re-growth in vivo, which was accompanied by an increase in Arginase 1 and IL10 gene expression levels by stromal cells and an increase in genes related to DNA repair, cell survival and stemness in tumor cells. Taken together, this study suggests that EVs shed by tumor cells in response to chemotherapy promote tumor repopulation and treatment failure through cellular reprogramming in melanoma cells.

Inhibition of Stearoyl-CoA desaturase 1 reverts BRAF and MEK inhibition-induced selection of cancer stem cells in BRAF-mutated melanoma

BACKGROUND

Combination therapy with BRAF and MEK inhibitors significantly improves survival in BRAF mutated melanoma patients but is unable to prevent disease recurrence due to the emergence of drug resistance. Cancer stem cells (CSCs) have been involved in these long-term treatment failures. We previously reported in lung cancer that CSCs maintenance is due to altered lipid metabolism and dependent upon Stearoyl-CoA-desaturase (SCD1)-mediated upregulation of YAP and TAZ. On this ground, we investigated the role of SCD1 in melanoma CSCs.

METHODS

SCD1 gene expression data of melanoma patients were downloaded from TCGA and correlated with disease progression by bioinformatics analysis and confirmed on patient's tissues by qRT-PCR and IHC analyses. The effects of combination of BRAF/MEKi and the SCD1 inhibitor MF-438 were monitored by spheroid-forming and proliferation assays on a panel of BRAF-mutated melanoma cell lines grown in 3D and 2D conditions, respectively. SCD1, YAP/TAZ and stemness markers were evaluated in melanoma cells and tissues by qRT-PCR, WB and Immunofluorescence.

RESULTS

We first observed that SCD1 expression increases during melanoma progression. BRAF-mutated melanoma 3D cultures enriched for CSCs overexpressed SCD1 and were more resistant than 2D differentiated cultures to BRAF and MEK inhibitors. We next showed that exposure of BRAF-mutated melanoma cells to MAPK pathway inhibitors enhanced stemness features by upregulating the expression of YAP/TAZ and downstream genes but surprisingly not SCD1. However, SCD1 pharmacological inhibition was able to downregulate YAP/TAZ and to revert at the same time CSC enrichment and resistance to MAPK inhibitors.

CONCLUSIONS

Our data underscore the role of SCD1 as prognostic marker in melanoma and promote the use of SCD1 inhibitors in combination with MAPK inhibitors for the control of drug resistance.

1α, 25-Dihydroxyvitamin D3 alters ectonucleotidase expression and activity in human cutaneous melanoma cells

PURPOSE

We hypothesized that vitamin D decreases rates of adenosine formation in human cutaneous melanoma cells through the inhibition of extracellular adenosine 5'-triphosphate breakdown, thereby affecting tumor cell viability. Therefore, the objective of this study was to explore the mechanisms of action of 1α, 25-dihydroxyvitamin D3 (1,25(OH)₂ D3) on the activity and expression of ectonucleotidases in cutaneous melanoma cells.

METHODS

A human melanoma cell line, SK-Mel-28, was treated with 1 to 50 nM of the active vitamin D metabolite (1,25(OH)₂ D3) over 24 hours, followed by determination of NTPDase1/CD39 and ecto-5'-nucleotidase/CD73 activity and expression rates of the purinergic system-related NTPDASE1, NT5E and adenosine deaminase and vitamin D receptor. An 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay was used to evaluate cellular viability.

RESULTS

1,25(OH)₂ D3 decreased adenosine monophosphate hydrolysis via ecto-5'-nucleotidase/CD73 and expression of CD73, but did not change NTPDase1/CD39 activity; it increased the CD39 expression. We also observed an increase of cell viability at 1 nM, but this viability decreased as the concentrations of vitamin D active metabolite increased to 50 nM. There were no differences in gene expression levels.

CONCLUSION

To the best of our knowledge, we showed for the first time a mechanism of control of adenosine production via modulation of the purinergic system in cutaneous melanoma cells treated with the active metabolite of vitamin D. This study provides original information regarding mechanisms, in which vitamin D plays a key role in preventing tumor progression in human melanoma cells.

Poly(ethylene glycol) induces cell toxicity in melanoma cells by producing a hyperosmotic extracellular medium

Poly(ethylene glycol) is a polymer that is widely used as a biomaterial and has been approved in a host of applications. While generally viewed as inert, recent studies with poly(ethylene glycol) suggest that it may have some effects on cells and tissues, making it potentially attractive as a therapeutic agent. In this study, the effect of poly(ethylene glycol) on the cell viability, membrane transport and apoptotic markers of metastatic melanoma cells was examined. The data were combined with observed effects of the polymer on the cell media, including osmolality and viscosity, in order to elucidate any structure-function relationship between the polymer and cells. It was observed that poly(ethylene glycol) reduced the cellular viability of A375 cells, and that the effect was dependent on poly(ethylene glycol) molecular weight and concentration. The mechanism was highly correlated with changes in the osmolality of the cell medium, which is determined by the inherent structure of poly(ethylene glycol), and in particular the ethylene oxide units. This mechanism was specific to poly(ethylene glycol) and was not observed with the similar linear, hydrophilic polymer poly(vinyl pyrrolidone). Overall, the data suggest that poly(ethylene glycol) and poly(ethylene glycol)-like compounds have a distinct effect on cellular activity, presumably mediated in part by their osmotic effects, supporting the further investigation of these polymers as pharmaceutically active compounds.

Apoptosis induced by 9,11‑dehydroergosterol peroxide from Ganoderma Lucidum mycelium in human malignant melanoma cells is Mcl‑1 dependent

9,11-Dehydroergosterol peroxide [9(11)-DHEP] is an important steroid from medicinal mushroom, which has been reported to exert antitumor activity in several tumor types. However, the role of 9(11)-DHEP toward the malignant melanoma cells has not been investigated. In the present study, the steroid from Ganoderma lucidum was purified on a submerged culture, and its antitumor mechanisms on A375 human malignant melanoma cells was investigated by MTT, flow cytometry and western blotting. The studies demonstrated that apoptotic mechanisms of the steroid were caspase-dependent and mediated via the mitochondrial pathway. The steroid did not cause significant changes in the expression levels of B-cell lymphoma 2 (Bcl-2) family proteins, Bcl-2-like protein 11, p53 upregulated modulator of apoptosis, Bcl-2-associated X protein, BH3 interacting-domain death agonist, Bcl-2-associated death promoter and Bcl-2, but it significantly downregulated induced myeloid leukemia cell differentiation protein Mcl-1 (Mcl-1) in melanoma cells, suggesting the key role of Mcl-1 in regulating apoptosis of melanoma cells induced by the steroid. These properties of 9(11)-DHEP advocate its usage as supplements in human malignant melanoma chemoprevention. The present study also suggests that mycelium of G. lucidum has a potential for producing bioactive substances and extracts with applications in medicine.

Mapping heterogeneity in patient-derived melanoma cultures by single-cell RNA-seq

Recent technological advances in single-cell genomics make it possible to analyze cellular heterogeneity of tumor samples. Here, we applied single-cell RNA-seq to measure the transcriptomes of 307 single cells cultured from three biopsies of three different patients with a BRAF/NRAS wild type, BRAF mutant/NRAS wild type and BRAF wild type/NRAS mutant melanoma metastasis, respectively. Analysis based on self-organizing maps identified sub-populations defined by multiple gene expression modules involved in proliferation, oxidative phosphorylation, pigmentation and cellular stroma. Gene expression modules had prognostic relevance when compared with gene expression data from published melanoma samples and patient survival data. We surveyed kinome expression patterns across sub-populations of the BRAF/NRAS wild type sample and found that CDK4 and CDK2 were consistently highly expressed in the majority of cells, suggesting that these kinases might be involved in melanoma progression. Treatment of cells with the CDK4 inhibitor palbociclib restricted cell proliferation to a similar, and in some cases greater, extent than MAPK inhibitors. Finally, we identified a low abundant sub-population in this sample that highly expressed a module containing ABC transporter ABCB5, surface markers CD271 and CD133, and multiple aldehyde dehydrogenases (ALDHs). Patient-derived cultures of the BRAF mutant/NRAS wild type and BRAF wild type/NRAS mutant metastases showed more homogeneous single-cell gene expression patterns with gene expression modules for proliferation and ABC transporters. Taken together, our results describe an intertumor and intratumor heterogeneity in melanoma short-term cultures which might be relevant for patient survival, and suggest promising targets for new treatment approaches in melanoma therapy.

The effect of timing of stereotactic radiosurgery treatment of melanoma brain metastases treated with ipilimumab

OBJECTIVE

Melanoma represents the third most common cause of CNS metastases. Immunotherapy has evolved as a treatment option for patients with Stage IV melanoma. Stereotactic radiosurgery (SRS) also elicits an immune response within the brain and may interact with immunotherapy. The authors report on a cohort of patients treated for brain metastases with immunotherapy and evaluate the effect of SRS timing on the intracranial response.

METHODS

All consecutively treated melanoma patients receiving ipilimumab and SRS for treatment of brain metastases at the University of Virginia between 2009 and 2014 were included in this retrospective analysis; data from 46 patients harboring 232 brain metastases were reviewed. The median duration of clinical follow-up was 7.9 months (range 3–42.6 months). The median age of the patients was 63 years (range 24.3–83.6 years). Thirty-two patients received SRS before or during ipilimumab cycles (Group A), whereas 14 patients received SRS after ipilimumab treatment (Group B). Radiographic and clinical responses were assessed at approximately 3-month intervals after SRS.

RESULTS

The 2 cohorts were comparable in pertinent baseline characteristics with the exception of SRS timing relative to ipilimumab. Local recurrence–free duration (LRFD) was significantly longer in Group A (median 19.6 months, range 1.1–34.7 months) than in Group B patients (median 3 months, range 0.4–20.4 months) (p = 0.002). Post-SRS perilesional edema was more significant in Group A.

CONCLUSIONS

The effect of SRS and ipilimumab on LRFD seems greater when SRS is performed before or during ipilimumab treatments. The timing of immunotherapy and SRS may affect LRFD and postradiosurgical edema. The interactions between immunotherapy and SRS warrant further investigation so as to optimize the therapeutic benefits and mitigate the risks associated with multimodality, targeted therapy.

Intratumor and Intertumor Heterogeneity in Melanoma

Melanoma is a cancer that exhibits one of the most aggressive and heterogeneous features. The incidence rate escalates. A high number of clones harboring various mutations contribute to an exceptional level of intratumor heterogeneity of melanoma. It also refers to metastases which may originate from different subclones of primary lesion. Such component of the neoplasm biology is termed intertumor and intratumor heterogeneity. These levels of tumor heterogeneity hinder accurate diagnosis and effective treatment. The increasing number of research on the topic reflects the need for understanding limitation or failure of contemporary therapies. Majority of analyses concentrate on mutations in cancer-related genes. Novel high-throughput techniques reveal even higher degree of variations within a lesion. Consolidation of theories and researches indicates new routes for treatment options such as targets for immunotherapy. The demand for personalized approach in melanoma treatment requires extensive knowledge on intratumor and intertumor heterogeneity on the level of genome, transcriptome/proteome, and epigenome. Thus, achievements in exploration of melanoma variety are described in details. Particularly, the issue of tumor heterogeneity or homogeneity given BRAF mutations is discussed.

Basil polysaccharide attenuates hepatocellular carcinoma metastasis in rat by suppressing H3K9me2 histone methylation under hepatic artery ligation-induced hypoxia

Hepatocellular carcinoma (HCC) is one of the most common and fatal cancers in the world. Tumor metastasis is an important factor of poor prognosis in patients with HCC. Tumor hypoxia can promote tumor cell metastasis in HCC. Epigenetic modification is closely related to tumor hypoxia and metastasis. In our previous research, we found that basil polysaccharide suppressed migration and invasion of HCC cell by inhibiting hypoxia induced histone methylation in vitro. In the present study, we investigated the effect of basil polysaccharide on the walker 256 carcinoma cell metastasis in rat. We established an intratumoral hypoxic model in rat by hepatic artery ligation (HAL). Then rats were treated with basil polysaccharide (75, 150 and 300mg/kg). The results showed that HAL could promote tumor metastasis by aggravating tumor hypoxia. However, basil polysaccharide could inhibit tumor metastasis in intratumoral hypoxia. Further, we demonstrated that basil polysaccharide could down-regulate the expression of HIF-1α, G9a, LSD1, JMJD1A, JMJD2B, JARID1B and H3K9me2. Synchronously, basil polysaccharide could increase E-cadherin and VMP1 expression, and decrease N-cadherin, vimentin and β-catenin expression. The results indicated that histone modifying enzymes might be a new therapeutic target of basil polysaccharide on hepatocellular carcinoma metastasis.

Hide-and-seek: the interplay between cancer stem cells and the immune system

The enhanced ability of cancer stem cells (CSCs) to give rise to new tumors suggests that these cells may also have an advantage in evading immune detection and elimination. This tumor-forming ability, combined with the known plasticity of the immune system, which can play both protumorigenic and antitumorigenic roles, has motivated investigations into the interaction between CSCs and the immune system. Herein, we review the interplay between host immunity and CSCs by examining the immune-related mechanisms that favor CSCs and the CSC-mediated expansion of protumorigenic immune cells. Furthermore, we discuss immune cells, such as natural killer cells, that preferentially target CSCs and the strategies used by CSCs to evade immune detection and destruction. An increased understanding of these interactions and the pathways that regulate them may allow us to harness immune system components to create new adjuvant therapies that eradicate CSCs and improve patient survival.

An autophagy-driven pathway of ATP secretion supports the aggressive phenotype of BRAFV600E inhibitor-resistant metastatic melanoma cells

The ingrained capacity of melanoma cells to rapidly evolve toward an aggressive phenotype is manifested by their increased ability to develop drug-resistance, evident in the case of vemurafenib, a therapeutic-agent targeting BRAF^V600E. Previous studies indicated a tight correlation between heightened melanoma-associated macroautophagy/autophagy and acquired Vemurafenib resistance. However, how this vesicular trafficking pathway supports Vemurafenib resistance remains unclear. Here, using isogenic human and murine melanoma cell lines of Vemurafenib-resistant and patient-derived melanoma cells with primary resistance to the BRAF^V600E inhibitor, we found that the enhanced migration and invasion of the resistant melanoma cells correlated with an enhanced autophagic capacity and autophagosome-mediated secretion of ATP. Extracellular ATP (eATP) was instrumental for the invasive phenotype and the expansion of a subset of Vemurafenib-resistant melanoma cells. Compromising the heightened autophagy in these BRAF^V600E inhibitor-resistant melanoma cells through the knockdown of different autophagy genes (ATG5, ATG7, ULK1), reduced their invasive and eATP-secreting capacity. Furthermore, eATP promoted the aggressive nature of the BRAF^V600E inhibitor-resistant melanoma cells by signaling through the purinergic receptor P2RX7. This autophagy-propelled eATP-dependent autocrine-paracrine pathway supported the maintenance and expansion of a drug-resistant melanoma phenotype. In conclusion, we have identified an autophagy-driven response that relies on the secretion of ATP to drive P2RX7-based migration and expansion of the Vemurafenib-resistant phenotype. This emphasizes the potential of targeting autophagy in the treatment and management of metastatic melanoma.

Comprehensive DNA methylation study identifies novel progression-related and prognostic markers for cutaneous melanoma

BACKGROUND

Cutaneous melanoma is the deadliest skin cancer, with an increasing incidence and mortality rate. Currently, staging of patients with primary melanoma is performed using histological biomarkers such as tumor thickness and ulceration. As disruption of the epigenomic landscape is recognized as a widespread feature inherent in tumor development and progression, we aimed to identify novel biomarkers providing additional clinical information over current factors using unbiased genome-wide DNA methylation analyses.

METHODS

We performed a comprehensive DNA methylation analysis during all progression stages of melanoma using Infinium HumanMethylation450 BeadChips on a discovery cohort of benign nevi (n = 14) and malignant melanoma from both primary (n = 33) and metastatic (n = 28) sites, integrating the DNA methylome with gene expression data. We validated the discovered biomarkers in three independent validation cohorts by pyrosequencing and immunohistochemistry.

RESULTS

We identified and validated biomarkers for, and pathways involved in, melanoma development (e.g., HOXA9 DNA methylation) and tumor progression (e.g., TBC1D16 DNA methylation). In addition, we determined a prognostic signature with potential clinical applicability and validated PON3 DNA methylation and OVOL1 protein expression as biomarkers with prognostic information independent of tumor thickness and ulceration.

CONCLUSIONS

Our data underscores the importance of epigenomic regulation in triggering metastatic dissemination through the inactivation of central cancer-related pathways. Inactivation of cell-adhesion and differentiation unleashes dissemination, and subsequent activation of inflammatory and immune system programs impairs anti-tumoral defense pathways. Moreover, we identify several markers of tumor development and progression previously unrelated to melanoma, and determined a prognostic signature with potential clinical utility.

Growth Hormone Receptor Knockdown Sensitizes Human Melanoma Cells to Chemotherapy by Attenuating Expression of ABC Drug Efflux Pumps

Melanoma remains one of the most therapy-resistant forms of human cancer despite recent introductions of highly efficacious targeted therapies. The intrinsic therapy resistance of human melanoma is largely due to abundant expression of a repertoire of xenobiotic efflux pumps of the ATP-binding cassette (ABC) transporter family. Here, we report that GH action is a key mediator of chemotherapeutic resistance in human melanoma cells. We investigated multiple ABC efflux pumps (ABCB1, ABCB5, ABCB8, ABCC1, ABCC2, ABCG1, and ABCG2) reportedly associated with melanoma drug resistance in different human melanoma cells and tested the efficacy of five different anti-cancer compounds (cisplatin, doxorubicin, oridonin, paclitaxel, vemurafenib) with decreased GH action. We found that GH treatment of human melanoma cells upregulates expression of multiple ABC transporters and increases the EC50 of melanoma drug vemurafenib. Also, vemurafenib-resistant melanoma cells had upregulated levels of GH receptor (GHR) expression as well as ABC efflux pumps. GHR knockdown (KD) using siRNA in human melanoma cells treated with sub-EC50 doses of anti-tumor compounds resulted in significantly increased drug retention, decreased cell proliferation and increased drug efficacy, compared to mock-transfected controls. Our set of findings identify an unknown mechanism of GH regulation in mediating melanoma drug resistance and validates GHR as a unique therapeutic target for sensitizing highly therapy-resistant human melanoma cells to lower doses of anti-cancer drugs.

HERV-K activation is strictly required to sustain CD133+ melanoma cells with stemness features

BACKGROUND

Melanoma is a heterogeneous tumor in which phenotype-switching and CD133 marker have been associated with metastasis promotion and chemotherapy resistance. CD133 positive (CD133+) subpopulation has also been suggested as putative cancer stem cell (CSC) of melanoma tumor. Human endogenous retrovirus type K (HERV-K) has been described to be aberrantly activated during melanoma progression and implicated in the etiopathogenesis of disease. Earlier, we reported that stress-induced HERV-K activation promotes cell malignant transformation and reduces the immunogenicity of melanoma cells. Herein, we investigated the correlation between HERV-K and the CD133+ melanoma cells during microenvironmental modifications.

METHODS

TVM-A12 cell line, isolated in our laboratory from a primary human melanoma lesion, and other commercial melanoma cell lines (G-361, WM-115, WM-266-4 and A375) were grown and maintained in the standard and stem cell media. RNA interference, Real-time PCR, flow cytometry analysis, self-renewal and migration/invasion assays were performed to characterize cell behavior and HERV-K expression.

RESULTS

Melanoma cells, exposed to stem cell media, undergo phenotype-switching and expansion of CD133+ melanoma cells, concomitantly promoted by HERV-K activation. Notably, the sorted CD133+ subpopulation showed stemness features, characterized by higher self-renewal ability, embryonic genes expression, migration and invasion capacities compared to the parental cell line. RNA interference-mediated downregulation experiments showed that HERV-K has a decisive role to expand and maintain the CD133+ melanoma subpopulation during microenvironmental modifications. Similarly, non nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz and nevirapine were effective to restrain the activation of HERV-K in melanoma cells, to antagonize CD133+ subpopulation expansion and to induce selective high level apoptosis in CD133+ cells.

CONCLUSIONS

HERV-K activation promotes melanoma cells phenotype-switching and is strictly required to expand and maintain the CD133+ melanoma cells with stemness features in response to microenvironmental modifications.

The Stem Cell Connection of Pituitary Tumors

Tumors in the pituitary gland are typically benign but cause serious morbidity due to compression of neighboring structures and hormonal disruptions. Overall, therapy efficiency remains suboptimal with negative impact on health and comfort of life, including considerable risk of therapy resistance and tumor recurrence. To date, little is known on the pathogenesis of pituitary tumors. Stem cells may represent important forces in this process. The pituitary tumors may contain a driving tumor stem cell population while the resident tissue stem cells may be directly or indirectly linked to tumor development and growth. Here, we will briefly summarize recent studies that afforded a glance behind the scenes of this stem cell connection. A better knowledge of the mechanisms underlying pituitary tumorigenesis is essential to identify more efficacious treatment modalities and improve clinical management.

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.

Downregulated expression of miRNA-149 promotes apoptosis in side population cells sorted from the TSU prostate cancer cell line

The objective of the present study was to identify prostate cancer stem cells and determine the effects of modulating specific miRNAs on prostate CSC proliferation and apoptosis. We applied flow cytometry sorting of side population cells to cultures of prostate cancer cell lines (TSU, DU145, PC-3 and LNCaP). The proportion of SP cells in the TSU line was 1.60±0.40% (mean ± SD), while that of the DU145, PC-3 and LNCaP lines was 0.60±0.05, 0.80±0.05 and 0.60±0.20%, respectively. Because the proportion of SP cells derived from TSU cells is greater, these cells were selected to sort side population cells and non-side population cells. The stem-like properties of SP cells had been identified by in vivo and in vitro experiments, and the related study was published. RNA was extracted from the SP cells and non-SP cells and analyzed using miRNA microarray technology. Fifty-three miRNAs with significant differences in their expression were detected in total. Furthermore, 20 of these miRNAs were validated by qPCR. We found that hsa-miR‑149 expression in SP cells and non-SP cells was significantly different; hsa-miR-149 was significantly upregulated in SP cells. By constructing a vector for lentiviral infection, we found that the downregulation of hsa-miR-149 leads to a reduction in proliferation, an increase in apoptosis, and a significant reduction in the colony formation potential, thus, inhibiting tumor growth in vivo of SP cells from the TSU cell line. The present study will provide new avenues toward understanding the function of prostate cancer stem cells (PCSCs) in tumorigenicity and metastasis.

Roles of different IRES-dependent FGF2 isoforms in the acquisition of the major aggressive features of human metastatic melanoma

Fibroblast growth factor 2 (FGF2) is involved in many physiological and pathological processes. Fgf2 deregulation contributes to the acquisition of malignant features of melanoma and other cancers. FGF2 is an alternative translation product expressed as five isoforms, a low-molecular-weight (18 KDa) and four high-molecular-weight (22, 22.5, 24, 34 KDa) isoforms, with different subcellular distributions. An internal ribosomal entry site (IRES) in its mRNA controls the translation of all the isoforms with the exception for the cap-dependent 34 KDa. The 18-KDa isoform has been extensively studied, while very few is known about the roles of high molecular weight isoforms. FGF2 is known to promote melanoma development and progression. To disclose the differential contribution of FGF2 isoforms in melanoma, we forced the expression of IRES-dependent low-molecular-weight (LMW, 18 KDa) and high-molecular-weight (HMW, 22, 22.5, 24 KDa) isoforms in a human metastatic melanoma cell line. This comparative study highlights that, while LMW isoform confers stem-like features to melanoma cells and promotes angiogenesis, HMW isoforms induce higher migratory ability and contribute to tumor perfusion by promoting vasculogenic mimicry (VM) when endothelial cell-driven angiogenesis is lacking. To conclude, FGF2 isoforms mainly behave in specific, antithetical manners, but can cooperate in different steps of tumor progression, providing melanoma cells with major malignant features.

KEY MESSAGE

FGF2 is an alternative translation product expressed as different isoforms termed LMW and HMW. FGF2 is involved in melanoma development and progression. HMW FGF2 isoforms enhance in vitro motility of melanoma cells. LMW FGF2 confers stem-like features and increases in vivo metastasization. LMW FGF2 promotes angiogenesis while HMW FGF2 induces vasculogenic mimicry.

The cancer stem-cell signaling network and resistance to therapy

The study of cancer stem cells (CSCs) has shown that tumors are driven by a subpopulation of self-renewing CSCs that retain the capacity to engender the various differentiated cell populations that form tumors. The characterization of CSCs has indicated that CSCs are remarkably resistant to conventional radio- and chemo-therapy. Clinically, the remaining populations of CSC are responsible for metastasis and recurrence in patients with cancer, which can lead to the disease becoming chronic and incurable. Therefore, the elimination of CSCs is an important goal of cancer treatments. Furthermore, CSCs are subject to strong regulation by the surrounding microenvironment, which also impacts tumor responses. In this review, we discuss the mechanisms by which pathways that are defective in CSCs influence ultimately therapeutic and clinical outcomes.

Solamargine triggers cellular necrosis selectively in different types of human melanoma cancer cells through extrinsic lysosomal mitochondrial death pathway

BACKGROUND

Previous reports showed that the Steroidal Glycoalkaloid Solamargine inhibited proliferation of non-melanoma skin cancer cells. However, Solamargine was not tested systematically on different types of melanoma cells and was not simultaneously tested on normal cells either. In this study we aimed to investigate the effect of Solamargine and the mechanism involved in inhibiting the growth of different types of melanoma cells.

METHODS

Solamargine effect was tested on normal cells and on another three melanoma cell lines. Vertical growth phase metastatic and primary melanoma cell lines WM239 and WM115, respectively and the radial growth phase benign melanoma cells WM35 were used. The half inhibitory concentration IC50 of Solamargine was determined using Alamarblue assay. The cellular and subcellular changes were assessed using light and Transmission Electron Microscope, respectively. The percentage of cells undergoing apoptosis and necrosis were measured using Flow cytometry. The different protein expression was detected and measured using western blotting. The efficacy of Solamargine was determined by performing the clonogenic assay. The data collected was analyzed statistically on the means of the triplicate of at least three independent repeated experiments using one-way ANOVA test for parametric data and Kruskal-Wallis for non-parametric data. Differences were considered significant when the P values were less than 0.05.

RESULTS

Hereby, we demonstrate that Solamargine rapidly, selectively and effectively inhibited the growth of metastatic and primary melanoma cells WM239 and WM115 respectively, with minimum effect on normal and benign WM35 cells. Solamargine caused cellular necrosis to the two malignant melanoma cell lines (WM115, WM239), by rapid induction of lysosomal membrane permeabilization as confirmed by cathepsin B upregulation which triggered the extrinsic mitochondrial death pathway represented by the release of cytochrome c and upregulation of TNFR1. Solamargine disrupted the intrinsic apoptosis pathway as revealed by the down regulation of hILP/XIAP, resulting in caspase-3 cleavage, upregulation of Bcl-xL, and Bcl2, and down regulation of Apaf-1 and Bax in WM115 and WM239 cells only. Solamargine showed high efficacy in vitro particularly against the vertical growth phase melanoma cells.

CONCLUSION

Our findings suggest that Solamargine is a promising anti-malignant melanoma drug which warrants further attention.

Understanding melanoma stem cells

Tumors are incredibly diverse and contain many different subpopulations of cells. The cancer stem cell (CSC) subpopulation is responsible for many aspects of tumorigenesis and has been shown to play an important role in melanoma development, progression, drug resistance and metastasis. However, it is becoming clear that tumor cell populations are dynamic and can be influenced by many factors, such as signals from the tumor microenvironment and somatic evolution. This review will present the current understanding of CSCs and the challenges of identifying and characterizing this dynamic cell population. The known characteristics and functions of melanoma stem cells, and the potential for therapeutic targeting of these cells in melanoma, will be discussed.

Stereotactic radiosurgery and immunotherapy for metastatic spinal melanoma

The management of metastatic spinal melanoma involves maximizing local control, preventing recurrence, and minimizing treatment-associated toxicity and spinal cord damage. Additionally, therapeutic measures should promote mechanical stability, facilitate rehabilitation, and promote quality of life. These objectives prove difficult to achieve given melanoma's elusive nature, radioresistant and chemoresistant histology, vascular character, and tendency for rapid and early metastasis. Different therapeutic modalities exist for metastatic spinal melanoma treatment, including resection (definitive, debulking, or stabilization procedures), stereotactic radiosurgery, and immunotherapeutic techniques, but no single treatment modality has proven fully effective. The authors present a conceptual overview and critique of these techniques, assessing their effectiveness, separately and combined, in the treatment of metastatic spinal melanoma. They provide an up-to-date guide for multidisciplinary treatment strategies. Protocols that incorporate specific, goal-defined surgery, immunotherapy, and stereotactic radiosurgery would be beneficial in efforts to maximize local control and minimize toxicity.

Histone Modifications, Modifiers and Readers in Melanoma Resistance to Targeted and Immune Therapy

The treatment of melanoma has been revolutionized by new therapies targeting MAPK signaling or the immune system. Unfortunately these therapies are hindered by either primary resistance or the development of acquired resistance. Resistance mechanisms involving somatic mutations in genes associated with resistance have been identified in some cases of melanoma, however, the cause of resistance remains largely unexplained in other cases. The importance of epigenetic factors targeting histones and histone modifiers in driving the behavior of melanoma is only starting to be unraveled and provides significant opportunity to combat the problems of therapy resistance. There is also an increasing ability to target these epigenetic changes with new drugs that inhibit these modifications to either prevent or overcome resistance to both MAPK inhibitors and immunotherapy. This review focuses on changes in histones, histone reader proteins and histone positioning, which can mediate resistance to new therapeutics and that can be targeted for future therapies.

Nanoparticle-mediated drug delivery for treating melanoma

Melanoma originated from melanocytes is the most aggressive type of skin cancer with limited treatment options. New targeted therapeutic options with the discovery of BRAF and MEK inhibitors have shown significant survival benefits. Despite the recent progress, development of chemoresistance and systemic toxicity remains a challenge for treating metastatic melanoma. While the response from the first line of treatment against melanoma using dacarbazine remains only 5-10%, the prolonged use of targeted therapy against mutated oncogene BRAF develops chemoresistance. In this review, we will discuss the nanoparticle-based strategies for encapsulation and conjugation of drugs to the polymer for maximizing their tumor distribution through enhanced permeability and retention effect. We will also highlight photodynamic therapy and design of melanoma-targeted nanoparticles.

Apoptosis induced by Ginkgo biloba (EGb761) in melanoma cells is Mcl-1-dependent

Melanoma is an aggressive skin cancer. Unfortunately, there is currently no chemotherapeutic agent available to significantly prolong the survival of the most patients with metastatic melanomas. Here we report that the Ginkgo biloba extract (EGb761), one of the most widely sold herbal supplements in the world, potently induces apoptosis in human melanoma cells by disturbing the balance between pro- and anti-apoptosis Bcl-2 family proteins. Treatment with EGb761 induced varying degrees of apoptosis in melanoma cell lines but not in melanocytes. Induction of apoptosis was caspase-dependent and appeared to be mediated by the mitochondrial pathway, in that it was associated with reduction in mitochondrial membrane potential and activation of Bax and Bak. Although EGb761 did not cause significant change in the expression levels of the BH3-only Bcl-2 family proteins Bim, Puma, Noxa, and Bad, it significantly downregulated Mcl-1 in sensitive but not resistant melanoma cells, suggesting a major role of Mcl-1 in regulating apoptosis of melanoma cells induced by EGb761. Indeed, siRNA knockdown of Mcl-1 enhanced EGb761-induced apoptosis, which was associated with increased activation of Bax and Bak. Taken together, these results demonstrate that EGb761 kills melanoma cells through the mitochondrial apoptotic pathway, and that Mcl-1 is a major regulator of sensitivity of melanoma cells to apoptosis induced by EGb761. Therefore, EGb761 with or without in combination with targeting Mcl-1 may be a useful strategy in the treatment of melanoma.

Targeting histone lysine methylation in cancer

Within the vast landscape of histone modifications lysine methylation has gained increasing attention because of its profound regulatory potential. The methylation of lysine residues on histone proteins modulates chromatin structure and thereby contributes to the regulation of DNA-based nuclear processes such as transcription, replication and repair. Protein families with opposing catalytic activities, lysine methyltransferases (KMTs) and demethylases (KDMs), dynamically control levels of histone lysine methylation and individual enzymes within these families have become candidate oncology targets in recent years. A number of high quality small molecule inhibitors of these enzymes have been identified. Several of these compounds elicit selective cancer cell killing in vitro and robust efficacy in vivo, suggesting that targeting 'histone lysine methylation pathways' may be a relevant, emerging cancer therapeutic strategy. Here, we discuss individual histone lysine methylation pathway targets, the properties of currently available small molecule inhibitors and their application in the context of cancer.

Side population

The side population (SP) assay has been utilized as a method for isolation and characterization of normal and cancer stem cells from a variety of tissues. However, the SP phenotype may not be a common property of all stem cells. This chapter reviews the principle and potential pitfalls of the SP assay with an emphasis on mammary gland SP cell analysis.

Staurosporine analogs promote distinct patterns of process outgrowth and polyploidy in small cell lung carcinoma cells

We have recently shown that staurosporine mediates the conversion of small cell lung carcinoma (SCLC) cells into a neuron-like process-bearing phenotype. Here, we have extended these studies to the staurosporine analogs K252a, lestaurtinib, PKC412, stauprimide, and UCN-01 and analyzed their influence on process extension, cell cycle distribution, and induction of polyploidy in four SCLC cell lines. In GLC-2 cells, all compounds provoked extensive process formation with the exception of PKC412 that showed no response. In H1184 cells, process formation was predominantly induced by staurosporine and, to lesser extent, in lestaurtinib-, stauprimide-, and UCN-01-treated cells. In the presence of K252a or PKC412, cells became bipolar and spindle shaped or showed pronounced cell flattening. In GLC-36 and SCLC-24H cells, only cell flattening was detectable. Process formation was reversible upon drug removal as shown for GLC-2 and H1184 cells. Fluorescence-activated cell sorting (FACS) and fluorescence in situ hybridization (FISH) analysis indicated the induction of polyploidy in all staurosporine and in two out of four stauprimide-treated SCLC cell lines. For other staurosporine analogs, polyploidy was observed only in UCN-01-treated GLC-36 cells and in K252a-treated H1184 and GLC-36 cells. The presence of staurosporine or its analogs did not alter the constitutive activation pattern of the canonical Akt/PI3K or MEK/extracellular signal-regulated kinase (ERK)1/2 signaling pathways nor could we detect an influence of stauprimide application on the expression level of the c-Myc oncogene. These data demonstrate that in SCLC cells, albeit a higher substrate specificity, staurosporine analogs can induce staurosporine-comparable effects.

Differential chemosensitivity to antifolate drugs between RAS and BRAF melanoma cells

BACKGROUND

The importance of the genetic background of cancer cells for the individual susceptibility to cancer treatments is increasingly apparent. In melanoma, the existence of a BRAF mutation is a main predictor for successful BRAF-targeted therapy. However, despite initial successes with these therapies, patients relapse within a year and have to move on to other therapies. Moreover, patients harbouring a wild type BRAF gene (including 25% with NRAS mutations) still require alternative treatment such as chemotherapy. Multiple genetic parameters have been associated with response to chemotherapy, but despite their high frequency in melanoma nothing is known about the impact of BRAF or NRAS mutations on the response to chemotherapeutic agents.

METHODS

Using cell proliferation and DNA methylation assays, FACS analysis and quantitative-RT-PCR we have characterised the response of a panel of NRAS and BRAF mutant melanoma cell lines to various chemotherapy drugs, amongst them dacarbazine (DTIC) and temozolomide (TMZ) and DNA synthesis inhibitors.

RESULTS

Although both, DTIC and TMZ act as alkylating agents through the same intermediate, NRAS and BRAF mutant cells responded differentially only to DTIC. Further analysis revealed that the growth-inhibitory effects mediated by DTIC were rather due to interference with nucleotide salvaging, and that NRAS mutant melanoma cells exhibit higher activity of the nucleotide synthesis enzymes IMPDH and TK1. Importantly, the enhanced ability of RAS mutant cells to use nucleotide salvaging resulted in resistance to DHFR inhibitors.

CONCLUSION

In summary, our data suggest that the genetic background in melanoma cells influences the response to inhibitors blocking de novo DNA synthesis, and that defining the RAS mutation status could be used to stratify patients for the use of antifolate drugs.

The roles of Jumonji-type oxygenases in human disease

The iron- and 2-oxoglutarate-dependent oxygenases constitute a phylogenetically conserved class of enzymes that catalyze hydroxylation reactions in humans by acting on various types of substrates, including metabolic intermediates, amino acid residues in different proteins and various types of nucleic acids. The discovery of jumonji (Jmj), the founding member of a class of Jmj-type chromatin modifying enzymes and transcriptional regulators, has culminated in the discovery of several branches of histone lysine demethylases, with essential functions in regulating the epigenetic landscape of the chromatin environment. This work has now been considerably expanded into other aspects of epigenetic biology and includes the discovery of enzymatic steps required for methyl-cytosine demethylation as well as modification of RNA and ribosomal proteins. This overview aims to summarize the current knowledge on the human Jmj-type enzymes and their involvement in human pathological processes, including development, cancer, inflammation and metabolic diseases.