An MITF- and mTOR-dependent FLCN pathway suppresses TFE3-driven metastasis in melanoma.

Cancer cells have remarkable plasticity allowing them to acquire many biological states. Melanoma cells have the ability to switch from a proliferative melanocytic state to an invasive mesenchymal state and back again resulting in intratumoral heterogeneity. While microphthalmia-associated transcription factor (MITF) promotes the melanocytic phenotype, it is unclear what transcription factors drive the mesenchymal phenotype, and what mechanisms regulate the switch from the proliferative state to the mesenchymal state. We show that nuclear localization of the MITF paralog TFE3 correlates positively with metastatic potential in melanoma cell lines and tumors, and that deletion of TFE3 in MITF-low melanoma cell lines eliminates migration and metastatic ability. Further, we find that MITF suppresses the mesenchymal phenotype by activating expression of FNIP2, which encodes a component of an mTORC1-stimulated pathway promoting cytoplasmic retention and lysosomal degradation of TFE3. These findings point to the mTOR pathway and TFE3 as key regulators of melanoma plasticity.

The anti-cancer efficacy of a novel phenothiazine derivative is independent of dopamine and serotonin receptor inhibition.

Introduction: An attractive, yet unrealized, goal in cancer therapy is repurposing psychiatric drugs that can readily penetrate the blood-brain barrier for the treatment of primary brain tumors and brain metastases. Phenothiazines (PTZs) have demonstrated anti-cancer properties through a variety of mechanisms. However, it remains unclear whether these effects are entirely separate from their activity as dopamine and serotonin receptor (DR/5-HTR) antagonists. Methods: In this study, we evaluated the anti-cancer efficacy of a novel PTZ analog, CWHM-974, that was shown to be 100-1000-fold less potent against DR/5-HTR than its analog fluphenazine (FLU). Results: CWHM-974 was more potent than FLU against a panel of cancer cell lines, thus clearly demonstrating that its anti-cancer effects were independent of DR/5-HTR signaling. Our results further suggested that calmodulin (CaM) binding may be necessary, but not sufficient, to explain the anti-cancer effects of CWHM-974. While both FLU and CWHM-974 induced apoptosis, they induced distinct effects on the cell cycle (G0/G1 and mitotic arrest respectively) suggesting that they may have differential effects on CaM-binding proteins involved in cell cycle regulation. Discussion: Altogether, our findings indicated that the anti-cancer efficacy of the CWHM-974 is separable from DR/5-HTR antagonism. Thus, reducing the toxicity associated with phenothiazines related to DR/5-HTR antagonism may improve the potential to repurpose this class of drugs to treat brain tumors and/or brain metastasis.

Quantification of capture efficiency, purity, and single-cell isolation in the recovery of circulating melanoma cells from peripheral blood by dielectrophoresis.

This paper describes a dielectrophoretic method for selection of circulating melanoma cells (CMCs), which lack reliable identifying surface antigens and are extremely rare in blood. This platform captures CMCs individually by dielectrophoresis (DEP) at an array of wireless bipolar electrodes (BPEs) aligned to overlying nanoliter-scale chambers, which isolate each cell for subsequent on-chip single-cell analysis. To determine the best conditions to employ for CMC isolation in this DEP-BPE platform, the static and dynamic dielectrophoretic response of established melanoma cell lines, melanoma cells from patient-derived xenografts (PDX) and peripheral blood mononuclear cells (PBMCs) were evaluated as a function of frequency using two established DEP platforms. Further, PBMCs derived from patients with advanced melanoma were compared with those from healthy controls. The results of this evaluation reveal that each DEP method requires a distinct frequency to achieve capture of melanoma cells and that the distribution of dielectric properties of PBMCs is more broadly varied in and among patients versus healthy controls. Based on this evaluation, we conclude that 50 kHz provides the highest capture efficiency on our DEP-BPE platform while maintaining a low rate of capture of unwanted PBMCs. We further quantified the efficiency of single-cell capture on the DEP-BPE platform and found that the efficiency diminished beyond around 25% chamber occupancy, thereby informing the minimum array size that is required. Importantly, the capture efficiency of the DEP-BPE platform for melanoma cells when using optimized conditions matched the performance predicted by our analysis. Finally, isolation of melanoma cells from contrived (spike-in) and clinical samples on our platform using optimized conditions was demonstrated. The capture and individual isolation of CMCs, confirmed by post-capture labeling, from patient-derived samples suggests the potential of this platform for clinical application.

SRC-RAC1 signaling drives drug resistance to BRAF inhibition in de-differentiated cutaneous melanomas.

Rare gain-of-function mutations in RAC1 drive drug resistance to targeted BRAF inhibition in cutaneous melanoma. Here, we show that wildtype RAC1 is a critical driver of growth and drug resistance, but only in a subset of melanomas with elevated markers of de-differentiation. Similarly, SRC inhibition also selectively sensitized de-differentiated melanomas to BRAF inhibition. One possible mechanism may be the suppression of the de-differentiated state, as SRC and RAC1 maintained markers of de-differentiation in human melanoma cells. The functional differences between melanoma subtypes suggest that the clinical management of cutaneous melanoma can be enhanced by the knowledge of differentiation status. To simplify the task of classification, we developed a binary classification strategy based on a small set of ten genes. Using this gene set, we reliably determined the differentiation status previously defined by hundreds of genes. Overall, our study informs strategies that enhance the precision of BRAFi by discovering unique vulnerabilities of the de-differentiated cutaneous melanoma subtype and creating a practical method to resolve differentiation status.

Melanoma Brain Metastases in the Era of Targeted Therapy and Checkpoint Inhibitor Therapy.

Brain metastases commonly develop in melanoma and are associated with poor overall survival of about five to nine months. Fortunately, new therapies, including immune checkpoint inhibitors and BRAF/MEK inhibitors, have been developed. The aim of this study was to identify outcomes of different treatment strategies in patients with melanoma brain metastases in the era of checkpoint inhibitors. Patients with brain metastases secondary to melanoma were identified at a single institution. Univariate and multivariable analyses were performed to identify baseline and treatment factors, which correlated with progression-free and overall survival. A total of 209 patients with melanoma brain metastases were identified. The median overall survival of the cohort was 5.3 months. On multivariable analysis, the presence of non-cranial metastatic disease, poor performance status (ECOG 2-4), whole-brain radiation therapy, and older age at diagnosis of brain metastasis were associated with poorer overall survival. Craniotomy (HR 0.66, 95% CI 0.45-0.97) and treatment with a CTLA-4 checkpoint inhibitor (HR 0.55, 95% CI 0.32-0.94) were the only interventions associated with improved overall survival. Further studies with novel agents are needed to extend lifespan in patients with brain metastases in melanoma.

Locally invasive, castrate-resistant prostate cancer in a Pten/Trp53 double knockout mouse model of prostate cancer monitored with non-invasive bioluminescent imaging.

Here we have improved an existing mouse model of prostate cancer based on prostate-specific deletion of Pten and Trp53 by incorporating a Cre-activatable luciferase reporter. By coupling the deletion of those genes to the activation of a luciferase reporter, we were able to monitor tumor burden non-invasively over time. We show that, consistent with previous reports, deletion of both Pten and Trp53 on a C57BL/6 background accelerates tumor growth and results in both the loss of androgen receptor expression and castrate resistant tumors as compared with loss of Pten alone. Loss of Trp53 results in the development of sarcomatoid histology and the expression of markers of epithelial-to-mesenchymal transition Zeb1 and vimentin, with kinetics and penetrance dependent on whether one or both alleles of Trp53 were deleted. Homozygous deletion of Trp53 and Pten resulted in uniformly lethal disease by 25 weeks. While we were able to detect locally invasive disease in the peritoneal cavity in aggressive tumors from the double knockout mice, we were unable to detect lymphatic or hematogenous metastatic disease in lymph nodes or at distant sites.

Functional Genomic Screening Independently Identifies CUL3 as a Mediator of Vemurafenib Resistance via Src-Rac1 Signaling Axis.

Patients with malignant melanoma have a 5-year survival rate of only 15-20% once the tumor has metastasized to distant tissues. While MAP kinase pathway inhibitors (MAPKi) are initially effective for the majority of patients with melanoma harboring BRAFV600E mutation, over 90% of patients relapse within 2 years. Thus, there is a critical need for understanding MAPKi resistance mechanisms. In this manuscript, we performed a forward genetic screen using a whole genome shRNA library to identify negative regulators of vemurafenib resistance. We identified loss of NF1 and CUL3 as drivers of vemurafenib resistance. NF1 is a known driver of vemurafenib resistance in melanoma through its action as a negative regulator of RAS. However, the mechanism by which CUL3, a key protein in E3 ubiquitin ligase complexes, is involved in vemurafenib resistance was unknown. We found that loss of CUL3 was associated with an increase in RAC1 activity and MEKS298 phosphorylation. However, the addition of the Src family inhibitor saracatinib prevented resistance to vemurafenib in CUL3KD cells and reversed RAC1 activation. This finding suggests that inhibition of the Src family suppresses MAPKi resistance in CUL3KD cells by inactivation of RAC1. Our results also indicated that the loss of CUL3 does not promote the activation of RAC1 through stabilization, suggesting that CUL3 is involved in the stability of upstream regulators of RAC1. Collectively, our study identifies the loss of CUL3 as a driver of MAPKi resistance through activation of RAC1 and demonstrates that inhibition of the Src family can suppress the MAPKi resistance phenotype in CUL3KD cells by inactivating RAC1 protein.

Cancer Cells Resist Mechanical Destruction in Circulation via RhoA/Actomyosin-Dependent Mechano-Adaptation.

During metastasis, cancer cells are exposed to potentially destructive hemodynamic forces including fluid shear stress (FSS) while en route to distant sites. However, prior work indicates that cancer cells are more resistant to brief pulses of high-level FSS in vitro relative to non-transformed epithelial cells. Herein, we identify a mechano-adaptive mechanism of FSS resistance in cancer cells. Our findings demonstrate that cancer cells activate RhoA in response to FSS, which protects them from FSS-induced plasma membrane damage. We show that cancer cells freshly isolated from mouse and human tumors are resistant to FSS, that formin and myosin II activity protects circulating tumor cells (CTCs) from destruction, and that short-term inhibition of myosin II delays metastasis in mouse models. Collectively, our data indicate that viable CTCs actively resist destruction by hemodynamic forces and are likely to be more mechanically robust than is commonly thought.

Anatomical and behavioral impact of a lentiviral tool tapping onto hippocampal serotonin reuptake in rats.

We aimed at the further characterization of rats in which SERT gene silencing was achieved by hippocampal injection of a lentiviral vector, carrying three si-RNA to block SERT mRNA at 66% of normal levels. Improved self-control and reduced restlessness were already demonstrated in these rats. Present further studies consisted of male adult rats, bilaterally inoculated within the hippocampus; control rats received lentivirus particles inactivated with heat. Both groups were maintained in isolation for 5 months, starting from inoculation. Neurochemical changes were studied by proton magnetic resonance spectroscopy (1H-MRS): we found increased hippocampal viability and bioenergetic potential; however, rats showed a behaviorally depressive pattern, also characterized by enhanced affiliation. Based on the extent of such effects, the whole lenti-SERT group was divided into two subgroups, termed intermediate- and extreme- phenotype profiles. While all rats had a widespread modification within dorsal/ventral striatum, amygdala, and hypothalamus, only the former subgroup showed an involvement of Raphé medialis, while, for the latter subgroup, an increase of SERT within hippocampus was unexpectedly caused. Within the less-affected "intermediate" rats, hippocampal 5-HT7 receptors were down-modulated, and also similarly within substantia nigra, septum, and neocortex. This picture demonstrates that additional rather than fewer neurobiological changes accompany a lower phenotypic expression. Overall, tapping hippocampal SERT affected the balance between habits versus strategies of coping by promoting morphogenetic processes indicative of a serotonergic fiber plasticity. Supplementary studies about serotonergic dynamics and neurogenesis within fronto-striatal circuits are needed.

High content screening identifies monensin as an EMT-selective cytotoxic compound.

Epithelial-to-mesenchymal transition (EMT) is implicated in cancer metastasis and drug resistance. Specifically targeting cancer cells in an EMT-like state may have therapeutic value. In this study, we developed a cell imaging-based high-content screening protocol to identify EMT-selective cytotoxic compounds. Among the 2,640 compounds tested, salinomycin and monensin, both monovalent cation ionophores, displayed a potent and selective cytotoxic effect against EMT-like cells. The mechanism of action of monensin was further evaluated. Monensin (10 nM) induced apoptosis, cell cycle arrest, and an increase in reactive oxygen species (ROS) production in TEM 4-18 cells. In addition, monensin rapidly induced swelling of Golgi apparatus and perturbed mitochondrial function. These are previously known effects of monensin, albeit occurring at much higher concentrations in the micromolar range. The cytotoxic effect of monensin was not blocked by inhibitors of ferroptosis. To explore the generality of our findings, we evaluated the toxicity of monensin in 24 human cancer cell lines and classified them as resistant or sensitive based on IC50 cutoff of 100 nM. Gene Set Enrichment Analysis identified EMT as the top enriched gene set in the sensitive group. Importantly, increased monensin sensitivity in EMT-like cells is associated with elevated uptake of 3H-monensin compared to resistant cells.

Targeting epigenetics for treatment of BRAF mutated metastatic melanoma with decitabine in combination with vemurafenib: A phase lb study.

INTRODUCTION: Epigenetic modifications play an important role in progression and development of resistance in V600EBRAF positive metastatic melanoma. Therefore, we hypothesized that the action of vemurafenib (BRAF inhibitor) can be made more effective by combining with low dose decitabine (a DNA methyltransferase inhibitor). The primary objective of this phase lb study was to determine the dose limiting toxicity and maximum tolerated dose of combination of subcutaneous decitabine with oral vemurafenib in patients with V600EBRAF positive metastatic melanoma with or without any prior treatment. EXPERIMENTAL DESIGN: The study employed 3+3 dose escalation combining subcutaneous decitabine at different doses and schedules (4 cohorts) with the standard oral dose of vemurafenib 960 mg twice daily. Preclinical assessment and further analysis were also performed in A375 melanoma cell line. RESULTS: Fourteen patients received study treatment. No dose limiting toxicity was encountered and maximum tolerated dose was not reached. Important toxicities included fatigue, increased creatinine, neutropenia, leucopenia, hypophosphatemia, rash and hyperuricemia. Three patients achieved complete response, three had partial response and five had stable disease. Preclinical assessment demonstrated action of the combination which delayed the development of acquired resistance and improved duration of treatment sensitivity. CONCLUSIONS: The combination of oral vemurafenib with subcutaneous decitabine is safe and showed activity in V600EBRAF positive metastatic melanoma. Since most responses were seen in cohort 1, which utilized low-dose, long-term decitabine, future studies of this combination treatment should utilize longer duration of decitabine, at the lowest dose of 0.1 mg/kg.

Hyaluronate synthase-2 overexpression alters estrogen dependence and induces histone deacetylase inhibitor-like effects on ER-driven genes in MCF7 breast tumor cells.

In breast carcinoma cells, high levels of hyaluronan (HA) and its CD44 receptor are frequently associated with alteration in estrogen signaling. We demonstrate that stable hyaluronate synthase 2 (HAS2) overexpression in estrogen receptor α (ERα) -positive MCF7 cells oppositely altered estrogen dependence of cell growth and its sensitivity towards antiestrogens. Albeit without effect on ERα expression and estradiol binding properties, HAS2 overexpression increased ERα Ser118 phosphorylation as well as transcriptional activity of estrogen in an ERE-luciferase reporter gene assay. However, HAS2 overexpression induced partial silencing of E2 driven-genes without affecting the magnitude of regulation by estradiol. This effect was associated with half-reduction in the activity of nuclear histone deacetylases (HDACs) through a post-translational mechanism likely consecutive to the enhanced expression of the histone acetyl-transferase EP300. In conclusion, increase in HA/CD44 interactions may contribute, through an HDAC inhibitor-like and ER-independent mechanism, to the silencing of estrogen-driven genes in breast carcinoma.

Prolactin-Induced Protein regulates cell adhesion in breast cancer.

Prolactin-Induced Prolactin (PIP) is widely expressed in breast cancer and has key cellular functions in this disease that include promoting invasion and cell cycle progression. Notably, we have recently identified a strong association between PIP-binding partners and a number of cell functions that are involved in cell adhesion. Therefore in this study, we investigated the effect of PIP on the regulation of cell adhesion using PIP-silencing in breast cancer cell lines T-47D, BT-474, and MFM-223. Our findings suggest that PIP expression is necessary for cell adhesion in a process that shows variation in the pattern of PIP regulation of cell-matrix and cell-cell adhesions based on the types of adhesion surface and breast cancer cell line. In this respect, we observed that PIP-silencing markedly reduced cell adhesion to uncoated plates in all three cell lines. In addition, in T-47D and MFM-223 cells fibronectin matrix induced baseline adhesion and reversed the PIP-silencing mediated reduction of cell adhesion. However, in BT-474 cells we did not observe an induction of baseline adhesion by fibronectin and PIP-silencing led to a marked reduction in cell adhesion to both uncoated and fibronectin-coated plates. Furthermore, we observed a significant reduction in cell-cell adhesion of BT-474 cell line following PIP-silencing. To explain an underlying mechanism for PIP regulation of cell adhesion, we found that PIP expression is necessary for the formation of α-actinin/actin-rich podosomes at the adhesion-sites of breast cancer cells. In summary, this study suggests that PIP expression regulates the process of cell adhesion in breast cancer.

Prolactin-induced protein is required for cell cycle progression in breast cancer.

Prolactin-induced protein (PIP) is expressed in the majority of breast cancers and is used for the diagnostic evaluation of this disease as a characteristic biomarker; however, the molecular mechanisms of PIP function in breast cancer have remained largely unknown. In this study, we carried out a comprehensive investigation of PIP function using PIP silencing in a broad group of breast cancer cell lines, analysis of expression microarray data, proteomic analysis using mass spectrometry, and biomarker studies on breast tumors. We demonstrated that PIP is required for the progression through G1 phase, mitosis, and cytokinesis in luminal A, luminal B, and molecular apocrine breast cancer cells. In addition, PIP expression is associated with a transcriptional signature enriched with cell cycle genes and regulates key genes in this process including cyclin D1, cyclin B1, BUB1, and forkhead box M1 (FOXM1). It is notable that defects in mitotic transition and cytokinesis following PIP silencing are accompanied by an increase in aneuploidy of breast cancer cells. Importantly, we have identified novel PIP-binding partners in breast cancer and shown that PIP binds to ß-tubulin and is necessary for microtubule polymerization. Furthermore, PIP interacts with actin-binding proteins including Arp2/3 and is needed for inside-out activation of integrin-ß1 mediated through talin. This study suggests that PIP is required for cell cycle progression in breast cancer and provides a rationale for exploring PIP inhibition as a therapeutic approach in breast cancer that can potentially target microtubule polymerization.

Aromatase gene expression in immature rat Sertoli cells: age-related changes in the FSH signalling pathway.

Aromatase, the enzyme responsible for the transformation of androgens into oestrogens, is encoded by the cyp19 gene expressed in the testis. The aim of the present study was to analyse the evolution of aromatase gene expression under FSH control in rat Sertoli cells between 10 and 30 days post partum, corresponding to the end of the proliferative period of Sertoli cells, establishment of the blood-testis barrier and acquisition of the mature phenotype. The maximum stimulatory effect of FSH on aromatase gene expression was obtained in 20-day-old rat Sertoli cells, compared with cells from 10- and 30-day-old rats, in parallel with the differentiation of Sertoli cells. Using two effectors of the protein kinase A pathway (i.e. forskolin and dibutyryl-cAMP) revealed differential effects between cells from rats aged 20 and 30 days, implying the involvement of another signalling pathway. Experiments using the specific phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002 revealed that PI3-K is strongly involved in FSH-induced aromatase expression in Sertoli cells from both 20- and 30-day-old rats. In vivo, this decrease could be explained by a negative effect exerted by germ cells because, in coculture, aromatase gene expression in 20-day-old Sertoli cells is greatly diminished.