Targeted therapy resistance mechanisms and therapeutic implications in melanoma

Computational pharmacology profiling of borapetoside C against melanoma

Melanoma,also known as a 'black tumor', begins in the melanocytes when cells (that produce pigment) grows out of control. Immunological dysregulation, which raises the risk for multiple illnesses, including melanoma, may be influenced by stress tiggered through viral infection, long term effects of ultraviolet radiation, environmental pollutants etc. Borapetoside C is one of the phytoconstituents from Tinospora crispa, and its biological source has been reported for its antistress property. Network pharmacology and KEGG pathway analysis of borapetoside C-regulated proteins were conducted to identify the hub genes involved in melanoma development. Further, a molecular docking was performed between borapetoside C and targets involved in melanoma. Further, the top 3 complexes were selected based on the binding energy to conduct molecular dynamics simulations to evaluate the stability of ligand-protein complex followed by principal component analysis and dynamic cross-correlation matrix. In addition, borapetoside C was also screened for its pharmacokinetics and toxicity profile. Network Pharmacology studies and KEGG pathway analysis revealed 8 targets involved in melanoma. Molecular docking between borapetoside C and targets involved in melanoma identified 3 complexes with minimum binding i.e. borapetoside C- MAP2K1, MMP9, and EGFR. Further, molecular dynamics simulations showed a stable complex of borapetoside C with MMP9 and EGFR. The present study suggested that borapetoside C may target MMP9 and EGFR to possess an anti-melanoma property. This finding can be useful in developing a novel therapeutic agent against melanoma from a natural source.Communicated by Ramaswamy H. Sarma.

Exogenous Hydrogen Sulfide Induces A375 Melanoma Cell Apoptosis Through Overactivation of the Unfolded Protein Response

Purpose

Melanomas are highly malignant and rapidly develop drug resistance due to dysregulated apoptosis. Therefore, pro-apoptotic agents could be effective for the management of melanoma. Hydrogen sulfide is ubiquitous in the body, and exogenous hydrogen sulfide has been reported to show inhibitory and pro-apoptotic effects on cancer cells. However, whether high concentrations of exogenous hydrogen sulfide have pro-apoptotic effects on melanoma and its mechanisms remain unknown. Hence, this study aimed to explore the pro-apoptotic effects and mechanisms of exogenous hydrogen sulfide on the A375 melanoma cell line treated with a hydrogen sulfide donor (NaHS).

Methods

The cell proliferation test, flow cytometric analysis, Hoechst 33258 staining, and Western blotting of B-cell lymphoma 2 and cleaved caspase-3 were used to explore the pro-apoptotic effects of hydrogen sulfide on A375 cells. The transcriptional profile of NaHS-treated A375 cells was further explored via high-throughput sequencing. Western blotting of phosphorylated inositol-requiring enzyme 1α (p-IRE1α), phosphorylated protein kinase R-like ER kinase (p-PERK), phosphorylated eukaryotic translation initiation factor 2α (p-eIF2α), C/EBP homologous protein, glucose-regulating protein 78, IRE1α, PERK, and eIF2α was performed to verify the changes in the transcriptional profile.

Results

NaHS inhibited A375 melanoma cell proliferation and induced apoptosis. The endoplasmic reticulum stress unfolded protein response and apoptosis-associated gene expression was upregulated in NaHS-treated A375 melanoma cells. The overactivation of the unfolded protein response and increase in endoplasmic reticulum stress was verified at the protein level.

Conclusion

Treatment with NaHS increased endoplasmic reticulum stress, which triggered the overactivation of the unfolded protein response and ultimately lead to melanoma cell apoptosis. The pro-apoptotic effect of NaHS suggests that it can be explored as a potential therapeutic agent in melanoma.

Carotenoids from Marine Microalgae as Antimelanoma Agents

Melanoma cells are highly invasive and metastatic tumor cells and commonly express molecular alterations that contribute to multidrug resistance (e.g., BRAF^V600E mutation). Conventional treatment is not effective in a long term, requiring an exhaustive search for new alternatives. Recently, carotenoids from microalgae have been investigated as adjuvant in antimelanoma therapy due to their safety and acceptable clinical tolerability. Many of them are currently used as food supplements. In this review, we have compiled several studies that show microalgal carotenoids inhibit cell proliferation, cell migration and invasion, as well as induced cell cycle arrest and apoptosis in various melanoma cell lines. MAPK and NF-ĸB pathway, MMP and apoptotic factors are frequently affected after exposure to microalgal carotenoids. Fucoxanthin, astaxanthin and zeaxanthin are the main carotenoids investigated, in both in vitro and in vivo experimental models. Preclinical data indicate these compounds exhibit direct antimelanoma effect but are also capable of restoring melanoma cells sensitivity to conventional chemotherapy (e.g., vemurafenib and dacarbazine).

Overcoming chemoresistance to b-raf inhibitor in melanoma via targeted inhibition of phosphoenolpyruvate carboxykinase1 using 3-mercaptopropionic acid

The resistance of melanoma to BRAF inhibitors remains a tough clinical challenge. In order to explore the underlying mechanism of drug resistance in melanoma, we established the resistant cell line to vemurafenib, and assessed the changes of drug-resistant cells on proliferation, apoptosis, oxidative stress and tumor stemness. Our results suggest that phosphoenolpyruvate carboxykinase1 (PCK1) is activated and inhibits the oxidative stress caused by vemurafenib in drug-resistant cells. Long term treatment of vemurafenib increases the expression of PCK1 which reduces the production of reactive oxygen species (ROS) by activating PI3K/Akt pathway. After the inhibition of PCK1 by 3-mercaptopropionic acid (3-MPA), the therapeutic sensitivity of vemurafenib is restored. In conclusion, this study disclosed that drug-resistant cells appeared to regulate their own proliferation, oxidative stress and tumor dryness by activating Akt/PCK1/ROS pathway, and shed new insights into acquiring drug resistance in melanoma.

ADT-OH, a hydrogen sulfide-releasing donor, induces apoptosis and inhibits the development of melanoma in vivo by upregulating FADD

Hydrogen sulfide (H₂S) is now widely considered the third endogenous gasotransmitter and plays critical roles in cancer biological processes. In this study, we demonstrate that 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADT-OH), the most widely used moiety for synthesising slow-releasing H₂S donors, induces melanoma cell death in vitro and in vivo. Consistent with previous reports, ADT-OH inhibited IκBɑ degradation, resulting in reduced NF-κB activation and subsequent downregulation of the NF-κB-targeted anti-apoptotic proteins XIAP and Bcl-2. More importantly, we found that ADT-OH suppressed the ubiquitin-induced degradation of FADD by downregulating the expression of MKRN1, an E3 ubiquitin ligase of FADD. In addition, ADT-OH had no significant therapeutic effect on FADD-knockout B16F0 cells or FADD-knockdown A375 cells. Based on these findings, we evaluated the combined effects of ADT-OH treatment and FADD overexpression on melanoma cell death in vivo using a mouse xenograft model. As expected, tumour-specific delivery of FADD through a recombinant Salmonella strain, VNP-FADD, combined with low-dose ADT-OH treatment significantly inhibited tumour growth and induced cancer cell apoptosis. Taken together, our data suggest that ADT-OH is a promising cancer therapeutic drug that warrants further investigation into its potential clinical applications.

Countering TRAIL Resistance in Melanoma

Melanoma of the skin has become a prime example for demonstrating the success of targeted cancer therapy. Nevertheless, high mortality has remained, mainly related to tumor heterogeneity and inducible therapy resistance. But the development of new therapeutic strategies and combinations has raised hope of finally defeating this deadly disease. TNF-related apoptosis-inducing ligand (TRAIL) represents a promising antitumor strategy. The principal sensitivity of melanoma cells for TRAIL was demonstrated in previous studies; however, inducible resistance appeared as a major problem. To address this issue, combination strategies were tested, and survival pathway inhibitors were shown to sensitize melanoma cells for TRAIL-induced apoptosis. Finally, cell cycle inhibition was identified as a common principle of TRAIL sensitization in melanoma cells. Mitochondrial apoptosis pathways, pro- and antiapoptotic Bcl-2 proteins as well as the rheostat consisted of Smac (Second mitochondria-derived activator of caspase) and XIAP (X-linked inhibitor of apoptosis protein) appeared to be of particular importance. Furthermore, the role of reactive oxygen species (ROS) was recognized in this setting. Inducible TRAIL resistance in melanoma can be explained by (i) high levels of antiapoptotic Bcl-2 proteins, (ii) high levels of XIAP, and (iii) suppressed Bax activity. These hurdles have to be overcome to enable the use of TRAIL in melanoma therapy. Several strategies appear as particularly promising, including new TRAIL receptor agonists, Smac and BH3 mimetics, as well as selective kinase inhibitors.

Crucial role of reactive oxygen species (ROS) for the proapoptotic effects of indirubin derivative DKP-073 in melanoma cells

Melanoma represents a prime example demonstrating the success of targeted therapy in cancer. Nevertheless, it remained a deadly disease until now, and the identification of new, independent strategies as well as the understanding of their molecular mechanisms may help to finally overcome the high mortality. Both indirubins and TNF-related apoptosis-inducing ligand (TRAIL) represent promising candidates. Here, the indirubin derivative DKP-073 is shown to trigger apoptosis in melanoma cells, which is enhanced by the combination with TRAIL and is accompanied by complete loss of cell viability. Addressing the signaling cascade, characteristic molecular steps were identified as caspase-3 activation, downregulation of XIAP, upregulation of p53 and TRAIL receptor 2, loss of mitochondrial membrane potential, and STAT-3 dephosphorylation. The decisive step, however, turned out to be the early production of ROS already at 1 h. This was proven by antioxidant pretreatment, which completely abolished apoptosis induction and loss of cell viability as well as abrogated all signaling effects listed above. Thus, ROS appeared as upstream of all proapoptotic signaling. The data indicate a dominant role of ROS in apoptosis regulation, and the new pathway may expose a possible Achilleś heel of melanoma.

AXL/AKT axis mediated-resistance to BRAF inhibitor depends on PTEN status in melanoma

Multiple genetic mutations within melanoma not only cause lesion-specific responses to targeted therapy but also alter the molecular route of resistance to that therapy. Inactivation of PTEN occurs in up to 30% of melanomas, frequently with a concurrent activating BRAF mutation. PTEN loss regulates both acquired and intrinsic drug resistance. Here we show that AXL/AKT axis mediated-resistance to BRAF inhibitor (BRAFi) depends upon PTEN status in melanoma. Hyperactivation of both ERK and AKT pathways was associated with BRAFi resistance in melanoma with wildtype PTEN. The PTEN-impaired melanoma cells required only the ERK resistance mechanism. Moreover, we identified AXL as a key upstream effector of AKT pathway-associated resistance to BRAFi in melanoma with wildtype PTEN, but not in melanoma with impaired PTEN. Notably, we confirmed that blocking AXL by shRNA and a small molecular inhibitor could rescue the sensitivity of resistant melanoma cells with wildtype PTEN to BRAFi and inhibit their growth in vitro and in vivo. Our study has uncovered a mechanism by which PTEN status contributes to acquired resistance to BRAFi and offers a rational strategy to guide clinical testing in pre-identified subsets of patients who relapse during treatment with BRAFi. The identified protein AXL represents a promising therapeutic target for BRAF mutant melanoma patients with wildtype PTEN.

RMEL3, a novel BRAFV600E-associated long noncoding RNA, is required for MAPK and PI3K signaling in melanoma

Previous work identified RMEL3 as a lncRNA with enriched expression in melanoma. Analysis of The Cancer Genome Atlas (TCGA) data confirmed RMEL3 enriched expression in melanoma and demonstrated its association with the presence of BRAF^V600E. RMEL3 siRNA-mediated silencing markedly reduced (95%) colony formation in different BRAF^V600E melanoma cell lines. Multiple genes of the MAPK and PI3K pathways found to be correlated with RMEL3 in TCGA samples were experimentally confirmed. RMEL3 knockdown led to downregulation of activators or effectors of these pathways, including FGF2, FGF3, DUSP6, ITGB3 and GNG2. RMEL3 knockdown induces gain of protein levels of tumor suppressor PTEN and the G1/S cyclin-Cdk inhibitors p21 and p27, as well as a decrease of pAKT (T308), BRAF, pRB (S807, S811) and cyclin B1. Consistently, knockdown resulted in an accumulation of cells in G1 phase and subG0/G1 in an asynchronously growing population. Thus, TCGA data and functional experiments demonstrate that RMEL3 is required for MAPK and PI3K signaling, and its knockdown decrease BRAF^V600E melanoma cell survival and proliferation.

Transient receptor potential cation 3 channel regulates melanoma proliferation and migration

Melanoma has an extremely poor prognosis due to its rapidly progressive and highly metastatic nature. Several therapeutic drugs have recently become available, but are effective only against melanoma with specific BRAF gene mutation. Thus, there is a need to identify other target molecules. We show here that Transient receptor potential, canonical 3 (TRPC3) is widely expressed in human melanoma. We found that pharmacological inhibition of TRPC3 with a pyrazole compound, Pyr3, decreased melanoma cell proliferation and migration. Similar inhibition was observed when the TRPC3 gene was silenced with short-hairpin RNA (shRNA). Pyr3 induced dephosphorylation of signal transducer and activator of transcription (STAT) 5 and Akt. Administration of Pyr3 (0.05 mg/kg) to mice implanted with human melanoma cells (C8161) significantly inhibited tumor growth. Our findings indicate that TRPC3 plays an important role in melanoma growth, and may be a novel target for treating melanoma in patients.

Critical role of reactive oxygen species (ROS) for synergistic enhancement of apoptosis by vemurafenib and the potassium channel inhibitor TRAM-34 in melanoma cells

Inhibition of MAP kinase pathways by selective BRAF inhibitors, such as vemurafenib and dabrafenib, have evolved as key therapies of BRAF-mutated melanoma. However, tumor relapse and therapy resistance have remained as major problems, which may be addressed by combination with other pathway inhibitors. Here we identified the potassium channel inhibitor TRAM-34 as highly effective in combination with vemurafenib. Thus apoptosis was significantly enhanced and cell viability was decreased. The combination vemurafenib/TRAM-34 was also effective in vemurafenib-resistant cells, suggesting that acquired resistance may be overcome. Vemurafenib decreased ERK phosphorylation, suppressed antiapoptotic Mcl-1 and enhanced proapoptotic Puma and Bim. The combination resulted in enhancement of proapoptotic pathways as caspase-3 and loss of mitochondrial membrane potential. Indicating a special mechanism of vemurafenib-induced apoptosis, we found strong enhancement of intracellular ROS levels already at 1 h of treatment. The critical role of ROS was demonstrated by the antioxidant vitamin E (α-tocopherol), which decreased intracellular ROS as well as apoptosis. Also caspase activation and loss of mitochondrial membrane potential were suppressed, proving ROS as an upstream effect. Thus ROS represents an initial and independent apoptosis pathway in melanoma cells that is of particular importance for vemurafenib and its combination with TRAM-34.

Combinatorial drug screening and molecular profiling reveal diverse mechanisms of intrinsic and adaptive resistance to BRAF inhibition in V600E BRAF mutant melanomas

Over half of BRAFV600E melanomas display intrinsic resistance to BRAF inhibitors, in part due to adaptive signaling responses. In this communication we ask whether BRAFV600E melanomas share common adaptive responses to BRAF inhibition that can provide clinically relevant targets for drug combinations. We screened a panel of 12 treatment-naïve BRAFV600E melanoma cell lines with MAP Kinase pathway inhibitors in pairwise combination with 58 signaling inhibitors, assaying for synergistic cytotoxicity. We found enormous diversity in the drug combinations that showed synergy, with no two cell lines having an identical profile. Although the 6 lines most resistant to BRAF inhibition showed synergistic benefit from combination with lapatinib, the signaling mechanisms by which this combination generated synergistic cytotoxicity differed between the cell lines. We conclude that adaptive responses to inhibition of the primary oncogenic driver (BRAFV600E) are determined not only by the primary oncogenic driver but also by diverse secondary genetic and epigenetic changes ("back-seat drivers") and hence optimal drug combinations will be variable. Because upregulation of receptor tyrosine kinases is a major source of drug resistance arising from diverse adaptive responses, we propose that inhibitors of these receptors may have substantial clinical utility in combination with inhibitors of the MAP Kinase pathway.

Novel Treatments in Development for Melanoma

The past several years can be considered a renaissance era in the treatment of metastatic melanoma. Following a 30-year stretch in which oncologists barely put a dent in a very grim overall survival (OS) rate for these patients, things have rapidly changed course with the recent approval of three new melanoma drugs by the FDA. Both oncogene-targeted therapy and immune checkpoint blockade approaches have shown remarkable efficacy in a subset of melanoma patients and have clearly been game-changers in terms of clinical impact. However, most patients still succumb to their disease, and thus, there remains an urgent need to improve upon current therapies. Fortunately, innovations in molecular medicine have led to many silent gains that have greatly increased our understanding of the nature of cancer biology as well as the complex interactions between tumors and the immune system. They have also allowed for the first time a detailed understanding of an individual patient's cancer at the genomic and proteomic level. This information is now starting to be employed at all stages of cancer treatment, including diagnosis, choice of drug therapy, treatment monitoring, and analysis of resistance mechanisms upon recurrence. This new era of personalized medicine will foreseeably lead to paradigm shifts in immunotherapeutic treatment approaches such as individualized cancer vaccines and adoptive transfer of genetically modified T cells. Advances in xenograft technology will also allow for the testing of drug combinations using in vivo models, a truly necessary development as the number of new drugs needing to be tested is predicted to skyrocket in the coming years. This chapter will provide an overview of recent technological developments in cancer research, and how they are expected to impact future diagnosis, monitoring, and development of novel treatments for metastatic melanoma.

[Molecular and pathomorphological prognostic markers for melanoma: Current approaches and prospects]

The incidence of melanoma demonstrates a persistent increasing tendency, which justifies the need to study and identify new prognostic markers for the development and course of this disease. The given paper shows current approaches to melanoma staging, including those to applying pathomorphological prognostic criteria, and discusses prospects for using the results of genomic and epigenomic studies of the carcinoma in clinical practice.

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

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

Exploiting cannabinoid-induced cytotoxic autophagy to drive melanoma cell death

Although the global incidence of cutaneous melanoma is increasing, survival rates for patients with metastatic disease remain <10%. Novel treatment strategies are therefore urgently required, particularly for patients bearing BRAF/NRAS wild-type tumors. Targeting autophagy is a means to promote cancer cell death in chemotherapy-resistant tumors, and the aim of this study was to test the hypothesis that cannabinoids promote autophagy-dependent apoptosis in melanoma. Treatment with Δ(9)-Tetrahydrocannabinol (THC) resulted in the activation of autophagy, loss of cell viability, and activation of apoptosis, whereas cotreatment with chloroquine or knockdown of Atg7, but not Beclin-1 or Ambra1, prevented THC-induced autophagy and cell death in vitro. Administration of Sativex-like (a laboratory preparation comprising equal amounts of THC and cannabidiol (CBD)) to mice bearing BRAF wild-type melanoma xenografts substantially inhibited melanoma viability, proliferation, and tumor growth paralleled by an increase in autophagy and apoptosis compared with standard single-agent temozolomide. Collectively, our findings suggest that THC activates noncanonical autophagy-mediated apoptosis of melanoma cells, suggesting that cytotoxic autophagy induction with Sativex warrants clinical evaluation for metastatic disease.

Aurora kinase B inhibition reduces the proliferation of metastatic melanoma cells and enhances the response to chemotherapy

BACKGROUND

The poor response to chemotherapy and the brief response to vemurafenib in metastatic melanoma patients, make the identification of new therapeutic approaches an urgent need. Interestingly the increased expression and activity of the Aurora kinase B during melanoma progression suggests it as a promising therapeutic target.

METHODS

The efficacy of the Aurora B kinase inhibitor barasertib-HQPA was evaluated in BRAF mutated cells, sensitive and made resistant to vemurafenib after chronic exposure to the drug, and in BRAF wild type cells. The drug effectiveness has been evaluated as cell growth inhibition, cell cycle progression and cell migration. In addition, cellular effectors of drug resistance and response were investigated.

RESULTS

The characterization of the effectors responsible for the resistance to vemurafenib evidenced the increased expression of MITF or the activation of Erk1/2 and p-38 kinases in the newly established cell lines with a phenotype resistant to vemurafenib. The sensitivity of cells to barasertib-HQPA was irrespective of BRAF mutational status. Barasertib-HQPA induced the mitotic catastrophe, ultimately causing apoptosis and necrosis of cells, inhibited cell migration and strongly affected the glycolytic metabolism of cells inducing the release of lactate. In association i) with vemurafenib the gain in effectiveness was found only in BRAF(V600K) cells while ii) with nab-paclitaxel, the combination was more effective than each drug alone in all cells.

CONCLUSIONS

These findings suggest barasertib as a new therapeutic agent and as enhancer of chemotherapy in metastatic melanoma treatment.

MITF in melanoma: mechanisms behind its expression and activity

MITF (microphthalmia-associated transcription factor) represents a melanocytic lineage-specific transcription factor whose role is profoundly extended in malignant melanoma. Over the last few years, the function of MITF has been tightly connected to plasticity of melanoma cells. MITF participates in executing diverse melanoma phenotypes defined by distinct gene expression profiles. Mutation-dependent alterations in MITF expression and activity have been found in a relatively small subset of melanomas. MITF activity is rather modulated by its upstream activators and suppressors operating on transcriptional, post-transcriptional and post-translational levels. These regulatory mechanisms also include epigenetic and microenvironmental signals. Several transcription factors and signaling pathways involved in the regulation of MITF expression and/or activity such as the Wnt/β-catenin pathway are broadly utilized by various types of tumors, whereas others, e.g., BRAF^V600E/ERK1/2 are more specific for melanoma. Furthermore, the MITF activity can be affected by the availability of transcriptional co-partners that are often redirected by MITF from their own canonical signaling pathways. In this review, we discuss the complexity of a multilevel regulation of MITF expression and activity that underlies distinct context-related phenotypes of melanoma and might explain diverse responses of melanoma patients to currently used therapeutics.

Universal screening test based on analysis of circulating organ-enriched microRNAs: a novel approach to diagnostic screening

Early disease detection leads to more effective and cost-efficient treatment. It is especially important for cancer and neurodegenerative diseases, because progression of these pathologies leads to significant and frequently irreversible changes in underlying pathophysiological processes. At the same time, the development of specific screening tests for detection of each of the hundreds of human pathologies in asymptomatic stage may be impractical. Here, we discuss a recently proposed concept: the development of minimally invasive Universal Screening Test (UST) based on analysis of organ-enriched microRNAs in plasma and other bodily fluids. The UST is designed to detect the presence of a pathology in particular organ systems, organs, tissues or cell types without diagnosing a specific disease. Once the pathology is detected, more specific, and if necessary invasive and expensive, tests can be administered to precisely define the nature of the disease. Here, we discuss recent studies and analyze the data supporting the UST approach.

Future perspectives in melanoma research: meeting report from the "Melanoma Bridge", Napoli, December 5th-8th 2013

The fourth "Melanoma Bridge Meeting" took place in Naples, December 5 to 8th, 2013. The four topics discussed at this meeting were: Diagnosis and New Procedures, Molecular Advances and Combination Therapies, News in Immunotherapy, and Tumor Microenvironment and Biomarkers.