Mek inhibition results in marked antitumor activity against metastatic melanoma patient-derived melanospheres and in melanosphere-generated xenografts

Unveiling the Dynamic Interplay between Cancer Stem Cells and the Tumor Microenvironment in Melanoma: Implications for Novel Therapeutic Strategies

Cutaneous melanoma still represents a significant health burden worldwide, being responsible for the majority of skin cancer deaths. Key advances in therapeutic strategies have significantly improved patient outcomes; however, most patients experience drug resistance and tumor relapse. Cancer stem cells (CSCs) are a small subpopulation of cells in different tumors, including melanoma, endowed with distinctive capacities of self-renewal and differentiation into bulk tumor cells. Melanoma CSCs are characterized by the expression of specific biomarkers and intracellular pathways; moreover, they play a pivotal role in tumor onset, progression and drug resistance. In recent years, great efforts have been made to dissect the molecular mechanisms underlying the protumor activities of melanoma CSCs to provide the basis for novel CSC-targeted therapies. Herein, we highlight the intricate crosstalk between melanoma CSCs and bystander cells in the tumor microenvironment (TME), including immune cells, endothelial cells and cancer-associated fibroblasts (CAFs), and its role in melanoma progression. Specifically, we discuss the peculiar capacities of melanoma CSCs to escape the host immune surveillance, to recruit immunosuppressive cells and to educate immune cells toward an immunosuppressive and protumor phenotype. We also address currently investigated CSC-targeted strategies that could pave the way for new promising therapeutic approaches for melanoma care.

Onychocolone A produced by the fungus Onychocola sp. targets cancer stem cells and stops pancreatic cancer progression by inhibiting MEK2-dependent cell signaling

Pancreatic cancer (PC) shows a high fatality rate that can only be faced with a combination of surgery and chemotherapy or palliative treatment in the case of advanced patients. Besides, PC tumors are enriched with subpopulations of cancer stem cells (CSCs) that are resistant to the existing chemotherapeutic agents, which raises an important need for the identification of new drugs. To fill this gap, we have tested the anti-tumoral activity of microbial extracts, which chemical diversity offers a broad spectrum of potential new bioactive compounds. Extracts derived from the fungus Onychocola sp. CF-107644 were assayed via high throughput screening followed by bioassay-guided fractionation and resulted in the identification and isolation of six benzophenone derivatives with antitumoral activity: onychocolones A-F (#1-6). The structures of the compounds were established by spectroscopic methods, including ESI-TOF MS, 1D and 2D NMR analyses and X-ray diffraction. Compounds #1-4 significantly inhibited the growth of the pancreas tumoral cell lines, with low-micromolar Median Effective Doses (ED50s). Compound #1 (onychocolone A) was prioritized for further profiling due to its pro-apoptotic effect, which was further validated on 3D spheroids and pancreatic CSCs. Protein expression assays showed that the effect was mechanistically linked to the inhibition of MEK onco-signaling pathway. The efficacy of onychocolone A was also demonstrated in vivo by the reduction of tumor growth in a pancreatic xenograft mouse model generated by CSCs. Altogether, the data support that onychocolone A is a promising new small molecule for hit-to-lead development of a new treatment for PC.

Targeting CD20-expressing malignant melanoma cells augments BRAF inhibitor killing

BACKGROUND

Mutant BRAF targeted therapies remain a standard of care for the treatment of metastatic malignant melanoma (MM); however, high initial response rates are tempered by the persistence of residual MM cells that eventually lead to disease recurrence and mortality. As MM recurrence during targeted therapy can present with the simultaneous occurrence of multiple tumour nodules at the original body sites, we hypothesized the presence of an intrinsically resistant MM cell subpopulation.

OBJECTIVES

To identify an MM cell subpopulation that is intrinsically resistant to targeted therapy and possibly responsible for MM recurrence.

METHODS

Using melanoma cell lines, we defined culture conditions for the reproducible three-dimensional growth of melanospheres to investigate putative cancer stem cell populations. We undertook RNA sequencing and bioinformatic analysis to characterize cell populations between adherent and nonadherent culture, and cells expressing or not expressing CD20. Furthermore, we defined an in vitro assay to evaluate the killing of melanoma cancer stem cells as a therapeutic test using combination therapies targeting driver mutation and CD20.

RESULTS

We described the culture conditions that promote MM cells to form melanospheres with a reproducible colony-forming efficiency rate of 0.3-1.3%. RNA sequencing of melanosphere vs. conventional MM cell cultures (n = 6), irrespective of the BRAF mutation status, showed that melanosphere formation was associated with growth and differentiation transcriptional signatures resembling MM tumours. Importantly, melanosphere formation also led to the emergence of a CD20+ MM cell subpopulation, similar to that observed in primary human MM tumours. CD20+ MM cells were resistant to BRAF inhibitor therapy and, consistent with this finding, demonstrated a Forkhead box protein M1 transcriptomic profile (n = 6). Combining BRAF inhibitor and anti-CD20 antibody treatment led to the additional killing of previously resistant CD20+  BRAF mutant MM cells.

CONCLUSIONS

In patients with MM that harbour a CD20+ subpopulation, combined therapy with BRAF inhibitor and anti-CD20 antibody could potentially kill residual MM cells and prevent disease recurrence.

Advanced Cellular Models for Preclinical Drug Testing: From 2D Cultures to Organ-On-A-Chip Technology

Simple Summary

Novel strategies that aim at personalizing cancer therapy are in rapid evolution. In the past decade, new methods to test for the efficacy of either standard-of-care medicines or novel targeted compounds have been implemented. In this review, we introduce the reader to experimental studies that employ patient-derived material to produce spheroids, organoids, or organs-on-a-chip as platforms that allow a more accurate representation of cancer complexity compared to bidimensional cell cultures. We discuss on the versatility and reliability of these model systems, provide evidence of their usage in drug screenings, and describe potential downfalls. The open question is whether or not tumor mimicry in vitro will be, in the near future, advanced enough to prospectively inform about treatment outcome on a certain patient.

Abstract

Cancer is a complex disease arising from a homeostatic imbalance of cell-intrinsic and microenvironment-related mechanisms. A multimodal approach to treat cancer that includes surgery, chemotherapy, and radiation therapy often fails in achieving tumor remission and produces unbearable side effects including secondary malignancies. Novel strategies have been implemented in the past decades in order to replace conventional chemotherapeutics with targeted, less toxic drugs. Up to now, scientists have relied on results achieved in animal research before proceeding to clinical trials. However, the high failure rate of targeted drugs in early phase trials leaves no doubt about the inadequacy of those models. In compliance with the need of reducing, and possibly replacing, animal research, studies have been conducted in vitro with advanced cellular models that more and more mimic the tumor in vivo. We will here review those methods that allow for the 3D reconstitution of the tumor and its microenvironment and the implementation of the organ-on-a-chip technology to study minimal organ units in disease progression. We will make specific reference to the usability of these systems as predictive cancer models and report on recent applications in high-throughput screenings of innovative and targeted drug compounds.

Targeting Melanoma-Initiating Cells by Caffeine: In Silico and In Vitro Approaches

The beneficial effects of coffee on human diseases are well documented, but the molecular mechanisms of its bioactive compounds on cancer are not completely elucidated. This is likely due to the large heterogeneity of coffee preparations and different coffee-based beverages, but also to the choice of experimental models where proliferation, differentiation and immune responses are differently affected. The aim of the present study was to investigate the effects of one of the most interesting bioactive compounds in coffee, i.e., caffeine, using a cellular model of melanoma at a defined differentiation level. A preliminary in silico analysis carried out on public gene-expression databases identified genes potentially involved in caffeine’s effects and suggested some specific molecular targets, including tyrosinase. Proliferation was investigated in vitro on human melanoma initiating cells (MICs) and cytokine expression was measured in conditioned media. Tyrosinase was revealed as a key player in caffeine’s mechanisms of action, suggesting a crucial role in immunomodulation through the reduction in IL-1β, IP-10, MIP-1α, MIP-1β and RANTES secretion onto MICs conditioned media. The potent antiproliferative effects of caffeine on MICs are likely to occur by promoting melanin production and reducing inflammatory signals’ secretion. These data suggest tyrosinase as a key player mediating the effects of caffeine on melanoma.

Heme oxygenase promotes B-Raf-dependent melanosphere formation

Biosynthesis and degradation of heme, an iron-bound protoporphyrin molecule utilized by a wide variety of metabolic processes, are tightly regulated. Two closely related enzymes, heme oxygenase 1 (HMOX1) and heme oxygenase 2 (HMOX2), degrade free heme to produce carbon monoxide, Fe²⁺ , and biliverdin. HMOX1 expression is controlled via the transcriptional activator, NFE2L2, and the transcriptional repressor, Bach1. Transcription of HMOX1 and other NFE2L2-dependent genes is increased in response to electrophilic and reactive oxygen species. Many tumor-derived cell lines have elevated levels of NFE2L2. Elevated expression of NFE2L2-dependent genes contributes to tumor growth and acquired resistance to therapies. Here, we report a novel role for heme oxygenase activity in melanosphere formation by human melanoma-derived cell lines. Transcriptional induction of HMOX1 through derepression of Bach1 or transcriptional activation of HMOX2 by oncogenic B-Raf^V600E results in increased melanosphere formation. Genetic ablation of HMOX1 diminishes melanosphere formation. Further, inhibition of heme oxygenase activity with tin protoporphyrin markedly reduces melanosphere formation driven by either Bach1 derepression or B-Raf^V600E expression. Global transcriptome analyses implicate genes involved in focal adhesion and extracellular matrix interactions in melanosphere formation.

A novel oral micellar fenretinide formulation with enhanced bioavailability and antitumour activity against multiple tumours from cancer stem cells

Background

An increasing number of anticancer agents has been proposed in recent years with the attempt to overcome treatment-resistant cancer cells and particularly cancer stem cells (CSC), the major culprits for tumour resistance and recurrence. However, a huge obstacle to treatment success is the ineffective delivery of drugs within the tumour environment due to limited solubility, short circulation time or inconsistent stability of compounds that, together with concomitant dose-limiting systemic toxicity, contribute to hamper the achievement of therapeutic drug concentrations. The synthetic retinoid Fenretinide (4-hydroxy (phenyl)retinamide; 4-HPR) formerly emerged as a promising anticancer agent based on pre-clinical and clinical studies. However, a major limitation of fenretinide is traditionally represented by its poor aqueous solubility/bioavailability due to its hydrophobic nature, that undermined the clinical success of previous clinical trials.

Methods

Here, we developed a novel nano-micellar fenretinide formulation called bionanofenretinide (Bio-nFeR), based on drug encapsulation in an ion-pair stabilized lipid matrix, with the aim to raise fenretinide bioavailability and antitumour efficacy.

Results

Bio-nFeR displayed marked antitumour activity against lung, colon and melanoma CSC both in vitro and in tumour xenografts, in absence of mice toxicity. Bio-nFeR is suitable for oral administration, reaching therapeutic concentrations within tumours and an unprecedented therapeutic activity in vivo as single agent.

Conclusion

Altogether, our results indicate Bio-nFeR as a novel anticancer agent with low toxicity and high activity against tumourigenic cells, potentially useful for the treatment of solid tumours of multiple origin.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1383-9) contains supplementary material, which is available to authorized users.

Theophylline induces differentiation and modulates cytoskeleton dynamics and cytokines secretion in human melanoma-initiating cells

AIMS

Cutaneous melanoma is the most aggressive skin cancer, derived from neoplastic transformation of melanocytes. Since several evidences highlighted the importance of a hierarchical model of differentiation among cancer cells, closely related to resistance mechanisms and tumor relapse, we investigated the effects of theophylline (Theo), a methylxanthine commonly used in treatment of respiratory diseases, on melanoma cells with different degree of differentiation, including patient-derived melanoma-initiating cells.

MATERIALS AND METHODS

The antiproliferative and antimetastatic effects of Theo was demonstrated by cell counting, adhesion and migration assays on A375 and SK-MEL-30 cells. Further, Theo ability to reduce cell growth was highly significant in A375-derived spheroids and in two patient-derived melanoma-initiating cells (MICs). In order to identify pathways potentially involved in the antineoplastic properties of Theo, a comparative mass spectrometry proteomic analysis was used. Then, melanin content, tyrosinase and tissue transglutaminase activities as differentiation markers and actin re-organization through confocal microscopy were evaluated. Furthermore, a secretome profile of MICs after Theo treatments was performed by multiplex immunoassay.

KEY FINDINGS

Obtained results demonstrate inhibitory effects of Theo on melanoma cell proliferation and migration, mainly in MICs, together with the induction of differentiation parameters. Moreover, our data indicate that the known anti-melanoma effect of Theo is due also to its ability to interfere with cytoskeleton dynamics and to induce the secretion of inflammatory molecules involved in recruitment of immunosuppressive cells in tumor microenvironment.

SIGNIFICANCE

Data strongly suggest that Theo supplement, either as drug or as dietary supply, may represent a potent additional weapon against melanoma.

TNF-alpha and metalloproteases as key players in melanoma cells aggressiveness

Background

Melanoma aggressiveness determines its growth and metastatic potential. This study aimed at identifying new molecular pathways controlling melanoma cell malignancy.

Methods

Ten metastatic melanoma cell lines were characterized by their proliferation, migration and invasion capabilities. The most representative cells were also characterized by spheroid formation assay, gene- and protein- expression profiling as well as cytokines secretion and the most relevant pathways identified through bioinformatic analysis were tested by in silico transcriptomic validation on datasets generated from biopsies specimens of melanoma patients. Further, matrix metalloproteases (MMPs) activity was tested by zymography assays and TNF-alpha role was validated by anti-TNF cell-treatment.

Results

An aggressiveness score (here named Melanoma AGgressiveness Score: MAGS) was calculated by measuring proliferation, migration, invasion and cell-doubling time in10human melanoma cell lines which were clustered in two distinct groups, according to the corresponding MAGS. SK-MEL-28 and A375 cell lines were selected as representative models for the less and the most aggressive phenotype, respectively. Gene-expression and protein expression data were collected for SK-MEL-28 and A375 cells by Illumina-, multiplex x-MAP-and mass-spectrometry technology. The collected data were subjected to an integrated Ingenuity Pathway Analysis, which highlighted that cytokine/chemokine secretion, as well as Cell-To-Cell Signaling and Interaction functions as well as matrix metalloproteases activity were significantly different in these two cell types. The key role of these pathways was then confirmed by functional validation. TNF role was confirmed by exposing cells to the anti-TNF Infliximab antibody. Upon such treatment melanoma cells aggressiveness was strongly reduced. Metalloproteases activity was assayed, and their role was confirmed by comparing transcriptomic data from cutaneous melanoma patients (n = 45) and benign nevi (n = 18).

Conclusions

Inflammatory signals such as TNF and MMP-2 activity are key intrinsic players to determine melanoma cells aggressiveness suggesting new venue sin the identification of novel molecular targets with potential therapeutic relevance.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0982-1) contains supplementary material, which is available to authorized users.

Lipid Storage and Autophagy in Melanoma Cancer Cells

Cancer stem cells (CSC) represent a key cellular subpopulation controlling biological features such as cancer progression in all cancer types. By using melanospheres established from human melanoma patients, we compared less differentiated melanosphere-derived CSC to differentiating melanosphere-derived cells. Increased lipid uptake was found in melanosphere-derived CSC vs. differentiating melanosphere-derived cells, paralleled by strong expression of lipogenic factors Sterol Regulatory Element-Binding Protein-1 (SREBP-1) and Peroxisome Proliferator-Activated Receptor-γ (PPAR-γ). An inverse relation between lipid-storing phenotype and autophagy was also found, since microtubule-associated protein 1A/1B-Light Chain 3 (LC3) lipidation is reduced in melanosphere-derived CSC. To investigate upstream autophagy regulators, Phospho-AMP activated Protein Kinase (P-AMPK) and Phospho-mammalian Target of Rapamycin (P-mTOR) were analyzed; lower P-AMPK and higher P-mTOR expression in melanosphere-derived CSC were found, thus explaining, at least in part, their lower autophagic activity. In addition, co-localization of LC3-stained autophagosome spots and perilipin-stained lipid droplets was demonstrated mainly in differentiating melanosphere-derived cells, further supporting the role of autophagy in lipid droplets clearance. The present manuscript demonstrates an inverse relationship between lipid-storing phenotype and melanoma stem cells differentiation, providing novel indications involving autophagy in melanoma stem cells biology.

PTEN status is a crucial determinant of the functional outcome of combined MEK and mTOR inhibition in cancer

Combined MAPK/PI3K pathway inhibition represents an attractive, albeit toxic, therapeutic strategy in oncology. Since PTEN lies at the intersection of these two pathways, we investigated whether PTEN status determines the functional response to combined pathway inhibition. PTEN (gene, mRNA, and protein) status was extensively characterized in a panel of cancer cell lines and combined MEK/mTOR inhibition displayed highly synergistic pharmacologic interactions almost exclusively in PTEN-loss models. Genetic manipulation of PTEN status confirmed a mechanistic role for PTEN in determining the functional outcome of combined pathway blockade. Proteomic analysis showed greater phosphoproteomic profile modification(s) in response to combined MEK/mTOR inhibition in PTEN-loss contexts and identified JAK1/STAT3 activation as a potential mediator of synergistic interactions. Overall, our results show that PTEN-loss is a crucial determinant of synergistic interactions between MAPK and PI3K pathway inhibitors, potentially exploitable for the selection of cancer patients at the highest chance of benefit from combined therapeutic strategies.

Targeted inhibition of MEK1 by cobimetinib leads to differentiation and apoptosis in neuroblastoma cells

Background

Neuroblastoma (NB) is one of the most common childhood malignancies. Currently, high risk NB carries a poor outcome and significant treatment related toxicities and, thus has been a focus for new therapeutics research in pediatric oncology. In this study, we evaluated the effects of the MEK inhibitor cobimetinib, as a single agent and in combinations, on the growth, survival and differentiation properties against a molecularly representative panel of NB cell lines.

Methods

In vitro anti-proliferative activity of cobimetinib alone or in combination was investigated by cell viability assays and its target modulatory activity was evaluated using phospho-kinases antibody arrays and western blot analysis. To determine the effect of combination with cis-RA on differentiation and resulting enhanced cellular cytotoxicity, the expression of glial fibrillary acidic protein (GFAP) and microtubule-associated protein 2 (MAP2) expression levels were examined by immuno-fluorescence.

Results

Our findings show that cobimetinib alone induced a concentration-dependent loss of cell viability in all NB cell lines. In addition, cobimetinib showed feedback activation of MEK1/2, and the dephosphorylation of extracellular signal-regulated kinases (ERK1/2) and c-RAF, providing information on the biological correlates of MEK inhibition in NB. Combined treatment with cis-RA, led to differentiation and enhanced sensitization of NB cells lines to cobimetinib.

Conclusion

Collectively, our results provide evidence that cobimetinib, in combination with cis-RA, represents a feasible option to develop novel treatment strategies for refractory NB.

Tyr1068-phosphorylated epidermal growth factor receptor (EGFR) predicts cancer stem cell targeting by erlotinib in preclinical models of wild-type EGFR lung cancer

Tyrosine kinase inhibitors (TKIs) have shown strong activity against non-small-cell lung cancer (NSCLC) patients harboring activating epidermal growth factor receptor (EGFR) mutations. However, a fraction of EGFR wild-type (WT) patients may have an improvement in terms of response rate and progression-free survival when treated with erlotinib, suggesting that factors other than EGFR mutation may lead to TKI sensitivity. However, at present, no sufficiently robust clinical or biological parameters have been defined to identify WT-EGFR patients with greater chances of response. Therapeutics validation has necessarily to focus on lung cancer stem cells (LCSCs) as they are more difficult to eradicate and represent the tumor-maintaining cell population. Here, we investigated erlotinib response of lung CSCs with WT-EGFR and identified EGFR phosphorylation at tyrosine1068 (EGFRtyr1068) as a powerful biomarker associated with erlotinib sensitivity both in vitro and in preclinical CSC-generated xenografts. In contrast to the preferential cytotoxicity of chemotherapy against the more differentiated cells, in EGFRtyr1068 cells, erlotinib was even more active against the LCSCs compared with their differentiated counterpart, acquiring potential value as CSC-directed therapeutics in the context of WT-EGFR lung cancer. Although tumor growth was inhibited to a similar extent during erlotinib or chemotherapy administration to responsive tumors, erlotinib proved superior to chemotherapy in terms of higher tolerability and reduced tumor aggressiveness after treatment suspension, substantiating the possibility of preferential LCSC targeting, both in adenocarcinoma (ADC) and squamous cell carcinoma (SCC) tumors. We conclude that EGFRtyr1068 may represent a potential candidate biomarker predicting erlotinib response at CSC-level in EGFR-WT lung cancer patients. Finally, besides its invariable association with erlotinib sensitivity in EGFR-WT lung CSCs, EGFRtyr1068 was associated with EGFR-sensitizing mutations in cell lines and patient tumors, with relevant diagnostic, clinical and therapeutic implications.

Aloe-emodin exerts a potent anticancer and immunomodulatory activity on BRAF-mutated human melanoma cells

Aim of this study was to extend the knowledge on the antineoplastic effect of aloe-emodin (AE), a natural hydroxyanthraquinone compound, both in metastatic human melanoma cell lines and in primary stem-like cells (melanospheres). Treatment with AE caused reduction of cell proliferation and induction of SK-MEL-28 and A375 cells differentiation, characterized by a marked increase of transamidating activity of transglutaminase whose expression remained unmodified. In vitro antimetastatic property of AE was evaluated by adhesion and Boyden chamber invasion assays. The effect of AE on melanoma cytokines/chemokines production was determined by a multiplex assay: interestingly AE showed an immunomodulatory activity through GM-CSF and IFN-γ production. We report also that AE significantly reduced the proliferation, stemness and invasive potential of melanospheres. Moreover, AE treatment significantly enhanced dabrafenib (a BRAF inhibitor) antiproliferative activity in BRAF mutant cell lines. Our results confirm that AE possesses remarkable antineoplastic properties against melanoma cells, indicating this anthraquinone as a promising agent for differentiation therapy of cancer, or as adjuvant in chemotherapy and targeted therapy. Further, its mechanisms of action support a potential efficacy of AE treatment to counteract resistance of BRAF-mutated melanoma cells to target therapy.

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.

PTEN expression and function in adult cancer stem cells and prospects for therapeutic targeting

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a non-redundant lipid phosphatase that restrains and fine tunes the phosphatidylinositol-3-kinase (PI3K) signaling pathway. PTEN is involved in inherited syndromes, which predispose to different types of cancers and is among the most frequently inactivated tumor suppressor genes in sporadic cancers. Indeed, loss of PTEN function occurs in a wide spectrum of human cancers through a variety of mechanisms, including mutations, deletions, transcriptional silencing, or protein instability. PTEN prevents tumorigenesis through multiple mechanisms and regulates a plethora of cellular processes, including survival, proliferation, energy metabolism and cellular architecture. Moreover, recent studies have demonstrated that PTEN is able to exit, exist, and function outside the cell, allowing for inhibition of the PI3K pathway in neighboring cells in a paracrine fashion. Most recently, studies have shown that PTEN is also critical for stem cell maintenance and that PTEN loss can lead to the emergence and proliferation of cancer stem cell (CSC) clones. Depending on the cellular and tissue context of origin, PTEN deletion may result in increased self-renewal capacity or normal stem cell exhaustion and PTEN-defìcient stem and progenitor cells have been reported in prostate, lung, intestinal, and pancreatic tissues before tumor formation; moreover, reversible or irreversible PTEN loss is frequently observed in CSC from a variety of solid and hematologic malignancies, where it may contribute to the functional phenotype of CSC. In this review, we will focus on the role of PTEN expression and function and downstream pathway activation in cancer stem cell biology and regulation of the tumorigenic potential; the emerging role of PTEN in mediating the crosstalk between the PI3K and MAPK pathways will also be discussed, together with prospects for the therapeutic targeting of tumors lacking PTEN expression.

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.

Research on tumorigenicity of cinnamaldehyde in melanoma cell lines and its mechanism

Melanoma is a highly malignant tumor originating from melanocytes. This disease is characterized by inconspicuous onset, high malignancy, and poor prognosis. The aim of this study is to explore the effect of cinnamaldehyde on melanoma tumorigenicity and its mechanism. Melanoma cells were subcutaneously injected into a nude mouse to establish the tumour model. A comparison was made for the difference in formation and growth of melanoma cell tumor between normal saline and cinnamaldehyde. A comparison was also made for the number of new vessels between the normal saline group (the control group) and the cinnamaldehyde group (the experimental group) through immumohistochemical staining. The western blot was used to detect the difference in expression levels of vascularization related proteins. The results indicated that the volume of tumors formed and the number of new vessels in melanoma cells of the cinnamaldehyde group decreased significantly compared with those in the cells of the normal saline group. A further study indicated that the expression of hypoxia-inducible factor-a (HIF-α) and vascular endothelial growth factor (VEGF) in the melanoma of the cinnamaldehyde group decreased significantly. In conclusion, cinnamaldehyde plays a certain role in inhibiting the occurrence and progression of melanoma and its action mechanism may be manifested by inhibiting expression of VEGF and HIF-α, thus blood vessel simulation and formation of new blood vessels of melanoma cells, and growth of tumors accordingly.