The GPER Agonist LNS8801 Induces Mitotic Arrest and Apoptosis in Uveal Melanoma Cells.

Uveal melanoma is the most common primary intraocular malignancy in adults and has a high incidence of metastatic disease. Current treatments have shown limited clinical activity in patients with uveal melanoma with metastasis and there is an urgent need for new effective therapies. Recent findings have shown that women with uveal melanoma have better survival rates than men. The G protein-coupled estrogen receptor-1 (GPER) has distinct functions from those of the classic estrogen receptors ERα/ß and its activation by specific agonists has tumor-suppressive roles in several cancers. However, the role of GPER had not previously been investigated in uveal melanoma. We demonstrated that downregulation of GPER in uveal melanoma cells decreased expression of p53 and stimulated cell growth. In contrast, the clinical GPER agonist, LNS8801, upregulated p53 and p21, induced melanocytic differentiation markers, inhibited cell proliferation and cell migration, and induced apoptosis. Furthermore, LNS8801 treatment arrested the cells in G2-M-phase of the cell cycle with concomitant activation of mitotic markers and disruption of the mitotic spindle apparatus. LNS8801 significantly inhibited tumor growth of uveal melanoma xenografts in vivo, suggesting that GPER agonists may be a novel treatment for uveal melanoma. Significance: Current treatments against metastatic uveal melanoma have shown limited clinical activity and there is an urgent need for effective therapies. Here, we demonstrate that the GPER agonist LNS8801 induced both GPER-dependent and GPER-independent effects and elicited potent anticancer activities in vitro and in vivo. Our results complement and support the ongoing clinical trial of LNS8801 in advanced uveal melanoma.

Intermittent MEK inhibition for the treatment of metastatic uveal melanoma.

Introduction: Uveal melanoma (UM) is associated with poor outcomes in the metastatic setting and harbors activating mutations resulting in upregulation of MAPK signaling in almost all cases. The efficacy of selumetinib, an oral allosteric inhibitor of MEK1/2, was limited when administered at a continual dosing schedule of 75 mg BID. Preclinical studies demonstrate that intermittent MEK inhibition reduces compensatory pathway activation and promotes T cell activation. We hypothesized that intermittent dosing of selumetinib would reduce toxicity, allow for the administration of increased doses, and achieve more complete pathway inhibition, thus resulting in improved antitumor activity. Methods: We conducted a phase Ib trial of selumetinib using an intermittent dosing schedule in patients with metastatic UM. The primary objective was to estimate the maximum tolerated dose (MTD) and assess safety and tolerability. Secondary objectives included assessment of the overall response rate (RR), progression-free survival (PFS) and overall survival (OS). Tumor biopsies were collected at baseline, on day 3 (on treatment), and between days 11-14 (off treatment) from 9 patients for pharmacodynamic (PD) assessments. Results: 29 patients were enrolled and received at least one dose of selumetinib across 4 dose levels (DL; DL1: 100 mg BID; DL2: 125 mg BID; DL3: 150 mg BID; DL4: 175 mg BID). All patients experienced a treatment-related adverse event (TRAE), with 5/29 (17%) developing a grade 3 or higher TRAE. Five dose limiting toxicities (DLT) were observed: 2/20 in DL2, 2/5 in DL3, 1/1 in DL4. The estimated MTD was 150 mg BID (DL3), with an estimated probability of toxicity of 29% (90% probability interval 16%-44%). No responses were observed; 11/29 patients achieved a best response of stable disease (SD). The median PFS and OS were 1.8 months (95% CI 1.7, 4.5) and 7.1 months (95% CI 5.3, 11.5). PD analysis demonstrated at least partial pathway inhibition in all samples at day 3, with reactivation between days 11-14 in 7 of those cases. Conclusions: We identified 150 mg BID as the MTD of intermittent selumetinib, representing a 100% increase over the continuous dose MTD (75 mg BID). However, no significant clinical efficacy was observed using this dosing schedule.

Adjuvant crizotinib in high-risk uveal melanoma following definitive therapy.

Introduction: Approximately 40% of patients with uveal melanoma (UM) will develop metastatic disease. Tumors measuring at least 12mm in basal diameter with a class 2 signature, as defined by a widely used gene expression-profiling test, are associated with significantly higher risk of metastasis, with a median time to recurrence of 32 months. No therapy has been shown to reduce this risk. Materials and Methods: This was a single-arm, multicenter study in patients with high-risk UM who received definitive treatment of primary disease and had no evidence of metastasis. Patients were consecutively enrolled to receive 12 four-week cycles of adjuvant crizotinib at a starting dose of 250mg twice daily and were subsequently monitored for 36 months. The primary outcome of this study was to assess recurrence-free survival (RFS) of patients with high-risk UM who received adjuvant crizotinib. Results: 34 patients enrolled and received at least one dose of crizotinib. Two patients were unevaluable due to early withdrawal and loss to follow-up, leaving 32 patients evaluable for efficacy. Eight patients (25%) did not complete the planned 48-week course of treatment due to disease recurrence (n=5) or toxicity (n=3). All patients experienced at least one adverse event (AE), with 11/34 (32%) experiencing a Common Terminology Criteria for Adverse Events (CTCAE) grade 3 or 4 AE. After a median duration of follow up of 47.1 months, 21 patients developed distant recurrent disease. The median RFS was 34.9 months (95% CI (Confidence Interval), 23-55 months), with a 32-month recurrence rate of 50% (95% CI, 33-67%). Analysis of protein contents from peripheral blood extracellular vesicles in a subset of patient samples from baseline, on-treatment, and off-treatment, revealed a change in protein content associated with crizotinib exposure, however without a clear association with disease outcome. Conclusions: The use of adjuvant crizotinib in patients with high-risk UM did not result in improved RFS when compared to historical controls. Analysis of blood extracellular vesicles revealed changes in protein content associated with treatment, raising the possibility of future use as a biomarker. Further investigation of adjuvant treatment options are necessary for this challenging disease.

Uveal Melanoma Exosomes Induce a Prometastatic Microenvironment through Macrophage Migration Inhibitory Factor.

Uveal melanoma is a rare melanoma subtype different from cutaneous melanoma, with high incidence of liver metastasis and poor prognosis. Cancer cell-derived extracellular vesicles have been shown to induce proinflammatory and prometastatic signaling in the tumor microenvironment and at distant sites. The characterization of uveal melanoma exosome cargo and its role in metastatic spread is essential to identify targets and intervene in the early stages of metastatic development. Our study characterizes the proteomic content of uveal melanoma exosomes and identified the presence of markers with metastatic properties. We demonstrated that uveal melanoma exosomes induce activation of cell signaling pathways and the release of cytokines and growth factors from hepatocytes. These exosome-stimulated liver cells could in turn induce migration of uveal melanoma cells, confirming that the exosomes have a functional role in the cross-talk between these two cell types. We found that the proinflammatory cytokine macrophage migration inhibitory factor (MIF) was a major player in these mechanisms and its blockade inhibited cell migration in coculture with exosome-stimulated hepatocytes and prevented the development of metastases in vivo. Targeting MIF in the early stages of metastasis may represent a novel adjuvant drug therapy to prevent metastatic spread in uveal melanoma. IMPLICATIONS: This study provides the first in vivo evidence that MIF inhibition may serve as a novel adjuvant drug therapy to prevent metastasis in uveal melanoma.

A Phase Ib Study of Sotrastaurin, a PKC Inhibitor, and Alpelisib, a PI3Kα Inhibitor, in Patients with Metastatic Uveal Melanoma.

Uveal melanoma (UM) is a rare subset of melanoma characterized by the presence of early initiating GNAQ/11 mutations, with downstream activation of the PKC, MAPK, and PI3Kα pathways. Activity has been observed with the PKC inhibitors sotrastaurin (AEB071) and darovasertib (IDE196) in patients with UM. Inhibition of the PI3K pathway enhances PKC inhibition in in vivo models. We therefore conducted a phase Ib study of sotrastaurin in combination with the PI3Kα inhibitor alpelisib to identify a tolerable regimen that may enhance the activity of PKC inhibition alone. Patients with metastatic uveal melanoma (n = 24) or GNAQ/11 mutant cutaneous melanoma (n = 1) were enrolled on escalating dose levels of sotrastaurin (100-400 mg BID) and alpelisib (200-350 mg QD). The primary objective was to identify the maximum tolerated dose (MTD) of these agents when administered in combination. Treatment-related adverse events (AE) occurred in 86% (any grade) and 29% (Grade 3). No Grade 4-5-related AEs occurred. Dose Level 4 (sotrastaurin 200 mg BID and alpelisib 350 mg QD) was identified as the maximum tolerated dose. Pharmacokinetic analysis demonstrated increasing concentration levels with increasing doses of sotrastaurin and alpelisib, without evidence of interaction between agents. Pharmacodynamic assessment of pMARCKS and pAKT protein expression with drug exposure suggested modest target inhibition that did not correlate with clinical response. No objective responses were observed, and median progression-free survival was 8 weeks (range, 3-51 weeks). Although a tolerable dose of sotrastaurin and alpelisib was identified with pharmacodynamic evidence of target inhibition and without evidence of a corresponding immunosuppressive effect, limited clinical activity was observed.

Transcriptional analysis of metastatic uveal melanoma survival nominates NRP1 as a therapeutic target.

Uveal melanoma is a rare form of melanoma with particularly poor outcomes in the metastatic setting. In contrast with cutaneous melanoma, uveal melanoma lacks BRAF mutations and demonstrates very low response rates to immune-checkpoint blockade. Our objectives were to study the transcriptomics of metastatic uveal melanoma with the intent of assessing gene pathways and potential molecular characteristics that might be nominated for further exploration as therapeutic targets. We initially analyzed transcriptional data from The Cancer Genome Atlas suggesting PI3K/mTOR and glycolysis as well as IL6 associating with poor survival. From tumor samples collected in a prospective phase II trial (A091201), we performed a transcriptional analysis of human metastatic uveal melanoma observing a novel role for epithelial-mesenchymal transition associating with survival. Specifically, we nominate and describe initial functional validation of neuropillin-1 from uveal melanoma cells as associated with poor survival and as a mediator of proliferation and migration for uveal melanoma in vitro. These results immediately nominate potential next steps in clinical research for patients with metastatic uveal melanoma.

Use of antibody arrays to probe exosome and extracellular vesicle mediated functional changes in cells.

Exosomes are small (30-200nm) membrane-bound vesicles released by all cells. They have been found in many clinical sample types, particularly those that are obtained in minimally-invasive fashion, including serum/plasma, urine, cerebrospinal and other fluids. They serve as an ideal source of biomarkers as their contents reflect the cell of origin and disease status of patients. Exosomes can serve as a "liquid biopsy," a non-invasive means to assess disease/health status in real-time. They can provide insights into disease mechanisms as they carry and transfer important signaling molecules, which may induce changes in the recipient cells. This is particularly relevant for metastatic cancers, as exosomes can prime the pre-metastatic niche. Many different approaches can be used to characterize the effects of the transfer of exosome content into the recipient cells, including global, untargeted approaches and protein-specific, targeted approaches. We describe herein our studies on the use of antibody arrays to probe for protein expression changes in hepatocytes that result from treating these cells with exosomes derived from uveal melanoma cells.

Inhibition of NF-κB-Dependent Signaling Enhances Sensitivity and Overcomes Resistance to BET Inhibition in Uveal Melanoma.

Bromodomain and extraterminal protein inhibitors (BETi) are epigenetic therapies aimed to target dysregulated gene expression in cancer cells. Despite early successes of BETi in a range of malignancies, the development of drug resistance may limit their clinical application. Here, we evaluated the mechanisms of BETi resistance in uveal melanoma, a disease with little treatment options, using two approaches: a high-throughput combinatorial drug screen with the clinical BET inhibitor PLX51107 and RNA sequencing of BETi-resistant cells. NF-κB inhibitors synergistically sensitized uveal melanoma cells to PLX51107 treatment. Furthermore, genes involved in NF-κB signaling were upregulated in BETi-resistant cells, and the transcription factor CEBPD contributed to the mechanism of resistance. These findings suggest that inhibitors of NF-κB signaling may improve the efficacy of BET inhibition in patients with advanced uveal melanoma. SIGNIFICANCE: These findings provide evidence that inhibitors of NF-κB signaling synergize with BET inhibition in in vitro and in vivo models, suggesting a clinical utility of these targeted therapies in patients with uveal melanoma.

Stromal fibroblast growth factor 2 reduces the efficacy of bromodomain inhibitors in uveal melanoma.

Alterations in transcriptional programs promote tumor development and progression and are targetable by bromodomain and extraterminal (BET) protein inhibitors. However, in a multi-site clinical trial testing the novel BET inhibitor, PLX51107, in solid cancer patients, liver metastases of uveal melanoma (UM) patients progressed rapidly following treatment. Mechanisms of resistance to BET inhibitors in UM are unknown. We show that fibroblast growth factor 2 (FGF2) rescued UM cells from growth inhibition by BET inhibitors, and FGF2 effects were reversible by FGF receptor (FGFR) inhibitors. BET inhibitors also increased FGFR protein expression in UM cell lines and in patient tumor samples. Hepatic stellate cells (HSCs) secrete FGF2, and HSC-conditioned medium provided resistance of UM cells to BET inhibitors. PLX51107 was ineffective in vivo, but the combination of a FGFR inhibitor, AZD4547, and PLX51107 significantly suppressed the growth of xenograft UM tumors formed from subcutaneous inoculation of UM cells with HSCs and orthotopically in the liver. These results suggest that co-targeting of FGFR signaling is required to increase the responses of metastatic UM to BET inhibitors.

BRD4-targeted therapy induces Myc-independent cytotoxicity in Gnaq/11-mutatant uveal melanoma cells.

Uveal melanoma (UM) is an aggressive intraocular malignancy with limited therapeutic options. Both primary and metastatic UM are characterized by oncogenic mutations in the G-protein alpha subunit q and 11. Furthermore, nearly 40% of UM has amplification of the chromosomal arm 8q and monosomy of chromosome 3, with consequent anomalies of MYC copy number. Chromatin regulators have become attractive targets for cancer therapy. In particular, the bromodomain and extra-terminal (BET) inhibitor JQ1 has shown selective inhibition of c-Myc expression with antiproliferative activity in hematopoietic and solid tumors. Here we provide evidence that JQ1 had cytotoxic activity in UM cell lines carrying Gnaq/11 mutations, while in cells without the mutations had little effects. Using microarray analysis, we identified a large subset of genes modulated by JQ1 involved in the regulation of cell cycle, apoptosis and DNA repair. Further analysis of selected genes determined that the concomitant silencing of Bcl-xL and Rad51 represented the minimal requirement to mimic the apoptotic effects of JQ1 in the mutant cells, independently of c-Myc. In addition, administration of JQ1 to mouse xenograft models of Gnaq-mutant UM resulted in significant inhibition of tumor growth.Collectively, our results define BRD4 targeting as a novel therapeutic intervention against UM with Gnaq/Gna11 mutations.

Overexpression of DDX43 mediates MEK inhibitor resistance through RAS Upregulation in uveal melanoma cells.

The majority of uveal melanomas carry oncogenic mutations in the G proteins GNAQ and GNA11, with consequent activation of the MAPK pathway. Selective MEK inhibitors, such as selumetinib, have shown clinical benefit in uveal melanoma. However, mechanisms of drug resistance limit their efficacy in some patients. Analysis of MEK inhibitor-resistant uveal melanoma cell lines revealed the induction of RAS protein expression and activity. This effect was mediated by the RNA helicase DDX43, which was remarkably overexpressed in these cells. Depletion of DDX43 in MEK inhibitor-resistant cells decreased RAS proteins and inhibited ERK and AKT pathways. On the contrary, ectopic expression of DDX43 in parental uveal melanoma cells induced RAS protein levels and rendered cells resistant to MEK inhibition. Similar to DDX43 depletion, downregulation of KRAS, HRAS, and NRAS inhibited downstream pathways in the resistant cells, overcoming mutant GNAQ signaling. We also analyzed the expression of DDX43 in liver metastases of patients with uveal melanoma by RT-PCR, and found a significant overexpression of DDX43 in patients who did not benefit from selumetinib therapy. In conclusion, DDX43 induces RAS protein expression and signaling, mediating a novel mechanism of MEK inhibitor resistance. The detection of DDX43 in patients with uveal melanoma could lead to more targeted therapies for this disease.

Effect of selumetinib vs chemotherapy on progression-free survival in uveal melanoma: a randomized clinical trial.

IMPORTANCE: Uveal melanoma is characterized by mutations in GNAQ and GNA11, resulting in mitogen-activated protein kinase pathway activation. OBJECTIVE: To assess the efficacy of selumetinib, a selective, non-adenosine triphosphate competitive inhibitor of MEK1 and MEK2, in uveal melanoma. DESIGN, SETTING, AND PARTICIPANTS: Randomized, open-label, phase 2 clinical trial comparing selumetinib vs chemotherapy conducted from August 2010 through December 2013 among 120 patients with metastatic uveal melanoma at 15 academic oncology centers in the United States and Canada. INTERVENTIONS: One hundred one patients were randomized in a 1:1 ratio to receive selumetinib, 75 mg orally twice daily on a continual basis (n = 50), or chemotherapy (temozolomide, 150 mg/m2 orally daily for 5 of every 28 days, or dacarbazine, 1000 mg/m2 intravenously every 21 days [investigator choice]; n = 51) until disease progression, death, intolerable adverse effects, or withdrawal of consent. After primary outcome analysis, 19 patients were registered and 18 treated with selumetinib without randomization to complete the planned 120-patient enrollment. Patients in the chemotherapy group could receive selumetinib at the time of radiographic progression. MAIN OUTCOMES AND MEASURES: Progression-free survival, the primary end point, was assessed as of April 22, 2013. Additional end points, including overall survival, response rate, and safety/toxicity, were assessed as of December 31, 2013. RESULTS: Median progression-free survival among patients randomized to chemotherapy was 7 weeks (95% CI, 4.3-8.4 weeks; median treatment duration, 8 weeks; interquartile range [IQR], 4.3-16 weeks) and among those randomized to selumetinib was 15.9 weeks (95% CI, 8.4-21.1 weeks; median treatment duration, 16.1 weeks; IQR, 8.1-25.3 weeks) (hazard ratio, 0.46; 95% CI, 0.30-0.71; P < .001). Median overall survival time was 9.1 months (95% CI, 6.1-11.1 months) with chemotherapy and 11.8 months (95% CI, 9.8-15.7 months) with selumetinib (hazard ratio, 0.66; 95% CI, 0.41-1.06; P = .09). No objective responses were observed with chemotherapy. Forty-nine percent of patients treated with selumetinib achieved tumor regression, with 14% achieving an objective radiographic response to therapy. Treatment-related adverse events were observed in 97% of patients treated with selumetinib, with 37% requiring at least 1 dose reduction. CONCLUSIONS AND RELEVANCE: In this hypothesis-generating study of patients with advanced uveal melanoma, selumetinib compared with chemotherapy resulted in a modestly improved progression-free survival and response rate; however, no improvement in overall survival was observed. Improvement in clinical outcomes was accompanied by a high rate of adverse events. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01143402.

The phosphoinositide 3-kinase α selective inhibitor BYL719 enhances the effect of the protein kinase C inhibitor AEB071 in GNAQ/GNA11-mutant uveal melanoma cells.

G-protein mutations are one of the most common mutations occurring in uveal melanoma activating the protein kinase C (PKC)/mitogen-activated protein kinase and phosphoinositide 3-kinase (PI3K)/AKT pathways. In this study, we described the effect of dual pathway inhibition in uveal melanoma harboring GNAQ and GNA11 mutations via PKC inhibition with AEB071 (sotrastaurin) and PI3K/AKT inhibition with BYL719, a selective PI3Kα inhibitor. Growth inhibition was observed in GNAQ/GNA11-mutant cells with AEB071 versus no activity in wild-type cells. In the GNAQ-mutant cells, AEB071 decreased phosphorylation of myristoylated alanine-rich C-kinase substrate, a substrate of PKC, along with ERK1/2 and ribosomal S6, but persistent AKT activation was present. BYL719 had minimal antiproliferative activity in all uveal melanoma cell lines, and inhibited phosphorylation of AKT in most cell lines. In the GNA11-mutant cell line, similar effects were observed with ERK1/2 inhibition, mostly inhibited by BYL719. With the combination treatment, both GNAQ- and GNA11-mutant cell lines showed synergistic inhibition of cell proliferation and apoptotic cell death. In vivo studies correlated with in vitro findings showing reduced xenograft tumor growth with the combination therapy in a GNAQ-mutant model. These findings suggest a new therapy treatment option for G-protein-mutant uveal melanoma with a focus on specific targeting of multiple downstream pathways as part of combination therapy.

Crizotinib, a c-Met inhibitor, prevents metastasis in a metastatic uveal melanoma model.

Uveal melanoma is the most common primary intraocular malignant tumor in adults and half of the primary tumors will develop fatal metastatic disease to the liver and the lung. Crizotinib, an inhibitor of c-Met, anaplastic lymphoma kinase (ALK), and ROS1, inhibited the phosphorylation of the c-Met receptor but not of ALK or ROS1 in uveal melanoma cells and tumor tissue. Consequently, migration of uveal melanoma cells was suppressed in vitro at a concentration associated with the specific inhibition of c-Met phosphorylation. This effect on cell migration could be recapitulated with siRNA specific to c-Met but not to ALK or ROS1. Therefore, we developed a uveal melanoma metastatic mouse model with EGFP-luciferase-labeled uveal melanoma cells transplanted by retro-orbital injections to test the effect of crizotinib on metastasis. In this model, there was development of melanoma within the eye and also metastases to the liver and lung at 7 weeks after the initial transplantation. When mice were treated with crizotinib starting 1 week after the transplantation, we observed a significant reduction in the development of metastases as compared with untreated control sets. These results indicate that the inhibition of c-Met activity alone may be sufficient to strongly inhibit metastasis of uveal melanoma from forming, suggesting crizotinib as a potential adjuvant therapy for patients with primary uveal melanoma who are at high risk for the development of metastatic disease.

Inhibition of mutant GNAQ signaling in uveal melanoma induces AMPK-dependent autophagic cell death.

Oncogenic mutations in GNAQ and GNA11 genes are found in 80% of uveal melanoma. These mutations result in the activation of the RAF/MEK signaling pathway culminating in the stimulation of ERK1/2 mitogen-activated protein kinases. In this study, using a siRNA strategy, we show that mutant GNAQ signals to both MEK and AKT, and that combined inhibition of these pathways with the MEK inhibitor selumetinib (AZD6244) and the AKT inhibitor MK2206 induced a synergistic decrease in cell viability. This effect was genotype dependent as autophagic markers like beclin1 and LC3 were induced in GNAQ-mutant cells, whereas apoptosis was the mechanism of cell death of BRAF-mutant cells, and cells without either mutation underwent cell-cycle arrest. The inhibition of MEK/ATK pathways induced activation of AMP-activated protein kinase (AMPK) in the GNAQ-mutant cells. The downregulation of AMPK by siRNA or its inhibition with compound C did not rescue the cells from autophagy, rather they died by apoptosis, defining AMPK as a key regulator of mutant GNAQ signaling and a switch between autophagy and apoptosis. Furthermore, this combination treatment was effective in inhibiting tumor growth in xenograft mouse models. These findings suggest that inhibition of MEK and AKT may represent a promising approach for targeted therapy of patients with uveal melanoma.

Impact of combined mTOR and MEK inhibition in uveal melanoma is driven by tumor genotype.

Uveal melanomas possess activation of the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT/mammalian Target of Rapamycin (mTOR) pathways. MAPK activation occurs via somatic mutations in the heterotrimeric G protein subunits GNAQ and GNA11 for over 70% of tumors and less frequently via V600E BRAF mutations. In this report, we describe the impact of dual pathway inhibition upon uveal melanoma cell lines with the MEK inhibitor selumetinib (AZD6244/ARRY-142886) and the ATP-competitive mTOR kinase inhibitor AZD8055. While synergistic reductions in cell viability were observed with AZD8055/selumetinib in both BRAF and GNAQ mutant cell lines, apoptosis was preferentially induced in BRAF mutant cells only. In vitro apoptosis assay results were predictive of in vivo drug efficacy as tumor regressions were observed only in a BRAF mutant xenograft model, but not GNAQ mutant model. We went on to discover that GNAQ promotes relative resistance to AZD8055/selumetinib-induced apoptosis in GNAQ mutant cells. For BRAF mutant cells, both AKT and 4E-BP1 phosphorylation were modulated by the combination; however, decreasing AKT phosphorylation alone was not sufficient and decreasing 4E-BP1 phosphorylation was not required for apoptosis. Instead, cooperative mTOR complex 2 (mTORC2) and MEK inhibition resulting in downregulation of the pro-survival protein MCL-1 was found to be critical for combination-induced apoptosis. These results suggest that the clinical efficacy of combined MEK and mTOR kinase inhibition will be determined by tumor genotype, and that BRAF mutant malignancies will be particularly susceptible to this strategy.

Identification of unique MEK-dependent genes in GNAQ mutant uveal melanoma involved in cell growth, tumor cell invasion, and MEK resistance.

PURPOSE: Metastatic uveal melanoma represents the most common intraocular malignancy with very poor prognosis and no effective treatments. Oncogenic mutations in the G-protein α-subunit q and 11 have been described in about 85% of uveal melanomas and confer constitutive activation. Multiple signaling pathways are induced as a consequence of GNAQ/11 activation, which include the MEK/ERK kinase cascade. We analyzed the transcriptional profile of cell lines treated with a mitogen-activated protein (MAP)/extracellular signal-regulated (ERK) kinase (MEK) inhibitor to identify gene targets of activated GNAQ and to evaluate the biologic importance of these genes in uveal melanoma. EXPERIMENTAL DESIGN: We conducted microarray analysis of uveal melanoma cell lines with GNAQ mutations treated with the MEK inhibitor selumetinib. For comparison, we used cells carrying BRAF(V600E) and cells without either mutation. Changes in the expression of selected genes were then confirmed by quantitative real-time PCR and immunoblotting. RESULTS: We found that GNAQ mutant cells have a MEK-dependent transcriptional output and identified a unique set of genes that are downregulated by MEK inhibition, including the RNA helicase DDX21 and the cyclin-dependent kinase regulator CDK5R1 whereas Jun was induced. We provide evidence that these genes are involved in cell proliferation, tumor cell invasion, and drug resistance, respectively. Furthermore, we show that selumetinib treatment regulates the expression of these genes in tumor tissues of patients with metastatic GNAQ/11 mutant uveal melanoma. CONCLUSIONS: Our findings define a subset of transcriptionally regulated genes by selumetinib in GNAQ mutant cells and provide new insights into understanding the biologic effect of MEK inhibition in this disease.

Differentiation-related gene-1 decreases Bim stability by proteasome-mediated degradation.

Drg1 was identified as a differentiation-related, putative metastatic suppressor gene in human colon and prostate cancer. Its expression is associated with resistance to irinotecan (CPT-11) therapy in preclinical colorectal cancer models both in vitro and in vivo. However, the functional significance of Drg1 in these processes is unknown. We have shown for the first time that Drg1 directly binds to the BH3-only proapoptotic protein Bim. Depletion of Drg1 by small interfering RNA induced up-regulation of Bim and its accumulation in the mitochondria, which correlated with loss of mitochondrial membrane potential and induction of apoptosis in cells exposed to SN-38. Further analyses revealed that Drg1 promotes degradation of Bim through the Cullin2/ElonginB-CIS ubiquitin-protein ligase complex. Conversely, in the absence of Drg1, Bim was stabilized and bound more abundantly to Hsp70. These results show that Drg1 renders cancer cells more resistant to chemotherapy through enhanced proteasome-mediated Bim degradation.

Aurora B kinase regulates the postmitotic endoreduplication checkpoint via phosphorylation of the retinoblastoma protein at serine 780.

The phenotypic change characteristic of Aurora B inhibition is the induction of polyploidy. Utilizing specific siRNA duplexes and a selective small molecule inhibitor (AZD1152) to inhibit Aurora B activity in tumor cells, we sought to elucidate the mechanism by which Aurora B inhibition results in polyploidy. Cells treated with AZD1152 progressed through mitosis with misaligned chromosomes and exited without cytokinesis and subsequently underwent endoreduplication of DNA despite activation of a p53-dependent pseudo G1 checkpoint. Concomitant with polyploid cell formation, we observed the appearance of Rb hypophosphorylation, an event that occurred independently of cyclin-dependent kinase inhibition. We went on to discover that Aurora B directly phosphorylates Rb at serine 780 both in vitro and in vivo. This novel interaction plays a critical role in regulating the postmitotic checkpoint to prevent endoreduplication after an aberrant mitosis. Thus, we propose for the first time that Aurora B determines cellular fate after an aberrant mitosis by directly regulating the Rb tumor suppressor protein.