Sandra Pavey

Activation of the MAPK pathway is a common event in uveal melanomas although it rarely occurs through mutation of BRAF or RAS.

In contrast to cutaneous melanoma, there is no evidence that BRAF mutations are involved in the activation of the mitogen-activated protein kinase (MAPK) pathway in uveal melanoma, although there is increasing evidence that this pathway is activated frequently in the latter tumours. In this study, we performed mutation analysis of the RAS and BRAF genes in a panel of 11 uveal melanoma cell lines and 19 primary uveal melanoma tumours. In addition, Western blot and immunohistochemical analyses were performed on downstream members of the MAPK pathway in order to assess the contribution of each of these components. No mutations were found in any of the three RAS gene family members and only one cell line carried a BRAF mutation (V599E). Despite this, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK), ERK and ELK were constitutively activated in all samples. These data suggest that activation of the MAPK pathway is commonly involved in the development of uveal melanoma, but occurs through a mechanism different to that of cutaneous melanoma.

Transcriptional Pathway Signatures Predict MEK Addiction and Response to Selumetinib (AZD6244)

Selumetinib (AZD6244, ARRY-142886) is a selective, non-ATP-competitive inhibitor of mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK)-1/2. The range of antitumor activity seen preclinically and in patients highlights the importance of identifying determinants of response to this drug. In large tumor cell panels of diverse lineage, we show that MEK inhibitor response does not have an absolute correlation with mutational or phospho-protein markers of BRAF/MEK, RAS, or phosphoinositide 3-kinase (PI3K) activity. We aimed to enhance predictivity by measuring pathway output through coregulated gene networks displaying differential mRNA expression exclusive to resistant cell subsets and correlated to mutational or dynamic pathway activity. We discovered an 18-gene signature enabling measurement of MEK functional output independent of tumor genotype. Where the MEK pathway is activated but the cells remain resistant to selumetinib, we identified a 13-gene signature that implicates the existence of compensatory signaling from RAS effectors other than PI3K. The ability of these signatures to stratify samples according to functional activation of MEK and/or selumetinib sensitivity was shown in multiple independent melanoma, colon, breast, and lung tumor cell lines and in xenograft models. Furthermore, we were able to measure these signatures in fixed archival melanoma tumor samples using a single RT-qPCR-based test and found intergene correlations and associations with genetic markers of pathway activity to be preserved. These signatures offer useful tools for the study of MEK biology and clinical application of MEK inhibitors, and the novel approaches taken may benefit other targeted therapies.

Nuclear PTEN expression and clinicopathologic features in a population-based series of primary cutaneous melanoma

Germline mutations of the PTEN tumor‐suppressor gene, on 10q23, cause Cowden syndrome, an inherited hamartoma syndrome with a high risk of breast, thyroid and endometrial carcinomas and, some suggest, melanoma. To date, most studies which strongly implicate PTEN in the etiology of sporadic melanomas have depended on cell lines, short‐term tumor cultures and noncultured metastatic melanomas. The only study which reports PTEN protein expression in melanoma focuses on cytoplasmic expression, mainly in metastatic samples. To determine how PTEN contributes to the etiology or the progression of primary cutaneous melanoma, we examined cytoplasmic and nuclear PTEN expression against clinical and pathologic features in a population‐based sample of 150 individuals with incident primary cutaneous melanoma. Among 92 evaluable samples, 30 had no or decreased cytoplasmic PTEN protein expression and the remaining 62 had normal PTEN expression. In contrast, 84 tumors had no or decreased nuclear expression and 8 had normal nuclear PTEN expression. None of the clinical features studied, such as Clarks level and Breslow thickness or sun exposure, were associated with cytoplasmic PTEN expressional levels. An association with loss of nuclear PTEN expression was indicated for anatomical site (p = 0.06) and mitotic index (p = 0.02). There was also an association for melanomas to either not express nuclear PTEN or to express p53 alone, rather than both simultaneously (p = 0.02). In contrast with metastatic melanoma, where we have shown previously that almost two‐thirds of tumors have some PTEN inactivation, only one‐third of primary melanomas had PTEN silencing. This suggests that PTEN inactivation is a late event likely related to melanoma progression rather than initiation. Taken together with our previous observations in thyroid and islet cell tumors, our data suggest that nuclear–cytoplasmic partitioning of PTEN might also play a role in melanoma progression.

Expression profiling reveals that methylation of TIMP3 is involved in uveal melanoma development

Uveal melanoma is associated with a high tumor‐related mortality due to the propensity to develop metastases. The mechanisms that are responsible for malignant dissemination are largely unknown and need to be explored to facilitate diagnosis and treatment of metastases. To identify molecules involved in dissemination, we used cell lines derived from a primary uveal melanoma and 2 liver metastases from the same patient as a model for tumor progression. Using a microarray representing 1,176 genes, we identified 63 differentially expressed genes. Forty genes showed a higher expression and 23 showed a lower expression in the primary cell line compared to the metastasis cell lines. These genes are involved in processes like angiogenesis, apoptosis, macrophage stimulation, and extracellular matrix regulation. In contrast, the 2 liver metastasis cell lines produced nearly identical expression profiles. Demethylation of the primary melanoma cell line by 5‐aza‐2′deoxycytidine treatment revealed that 19 genes were suppressed by hypermethylation. An important finding was the 5‐fold decreased expression of TIMP3 in the metastatic cell lines, a molecule involved in extracellular matrix degradation. We demonstrate in the cell lines that TIMP3 expression is regulated by methylation. These observations were confirmed in primary uveal melanoma and suggests a role for TIMP3 in uveal melanoma development.

Cdc25-dependent activation of cyclin A/cdk2 is blocked in G2 phase arrested cells independently of ATM/ATR.

Cyclin A/cdk2 is active during S and G2 phases of the cell cycle, but its regulation and function during G2 phase is poorly understood. In this study we have examined the regulation of cyclin A/cdk2 activity during normal G2 phase progression and in genotoxin-induced G2 arrest. We show that cyclin A/cdk2 is activated in early G2 phase by a cdc25 activity. In the G2 phase checkpoint arrest initiated in response to various forms of DNA damage, the cdc25-dependent activation of both cyclin A/cdk2 and cyclin B1/cdc2 is blocked. Ectopic expression of cdc25B, but not cdc25C, in G2 phase arrested cells efficiently activated both cyclin A/cdk2 and cyclin B1/cdc2. Finally, we demonstrate that the block in cyclin A/cdk2 activation in the G2 checkpoint arrest is independent of ATM/ATR. We speculate that the ATM/ATR-independent block in G2 phase cyclin A/cdk2 activation may act as a further layer of checkpoint control, and that blocking G2 phase cyclin A/cdk2 activation contributes to the G2 phase checkpoint arrest.

A potent Chk1 inhibitor is selectively cytotoxic in melanomas with high levels of replicative stress

There are few effective treatments for metastatic melanoma. Checkpoint kinase 1 (Chk1) inhibitors are being trialled for their efficacy in enhancing conventional chemotherapeutic agents, but their effectiveness as single agents is not known. We have examined the effectiveness of two novel Chk1 selective inhibitors, AR323 and AR678, in a panel of melanoma cell lines and normal cell types. We demonstrate that these drugs display single-agent activity, with IC50s in the low nanomolar range. The drugs produce cytotoxic effects in cell lines that are most sensitive to these drugs, whereas normal cells are only sensitive to these drugs at the higher concentrations where they have cytostatic activity. The cytotoxic effect is the consequence of inhibition of S-phase Chk1, which drives cells prematurely from late S phase into an aberrant mitosis and results in either failure of cytokinesis or cell death through an apoptotic mechanism. The sensitivity to the Chk1 inhibitors was correlated with the level of endogenous DNA damage indicating replicative stress. Chk1 inhibitors are viable single-agent therapies that target melanoma cells with high levels of endogenous DNA damage. This sensitivity suggests that Chk1 is a critical component of an adaptation to replicative stress in these cells. It also suggests that markers of DNA damage may be useful in identifying the melanomas and potentially other tumour types that are more likely to be sensitive to Chk1 inhibitors as single agents.

G2 phase cell cycle arrest in human skin following UV irradiation

The contribution of the short wavelength ultraviolet (UV) component of sunlight to the aetiology of skin cancer has been widely acknowledged, although its direct contribution to tumour initiation or progression is still poorly understood. The loss of normal cell cycle controls, particularly checkpoint controls, are a common feature of cancer. UV radiation causes both G1 and G2 phase checkpoint arrest in vitro cultured cells. In this study we have investigated the cell cycle responses to suberythemal doses of UV on skin. We have utilized short-term whole organ skin cultures, and multi parameter immunohistochemical and biochemical analysis to demonstrate that basal and suprabasal layer melanocytes and keratinocytes undergo a G2 phase cell cycle arrest for up to 48 h following irradiation. The arrest is associated with increased p16 expression but no apparent p53 involvement. This type of organ culture provides a very useful model system, combining the ease of in vitro manipulation with the ability to perform detailed molecular analysis in a normal tissue environment.

Similarity of aberrant DNA methylation in Barrett's esophagus and esophageal adenocarcinoma

BackgroundBarretts esophagus (BE) is the metaplastic replacement of squamous with columnar epithelium in the esophagus, as a result of reflux. It is the major risk factor for the development of esophageal adenocarcinoma (EAC). Methylation of CpG dinucleotides of normally unmethylated genes is associated with silencing of their expression, and is common in EAC. This study was designed to determine at what stage, in the progression from BE to EAC, methylation of key genes occurs.ResultsWe examined nine genes (APC, CDKN2A, ID4, MGMT, RBP1, RUNX3, SFRP1, TIMP3, and TMEFF2), frequently methylated in multiple cancer types, in a panel of squamous (19 biopsies from patients without BE or EAC, 16 from patients with BE, 21 from patients with EAC), BE (40 metaplastic, seven high grade dysplastic) and 37 EAC tissues. The methylation frequency, the percentage of samples that had any extent of methylation, for each of the nine genes in the EAC (95%, 59%, 76%, 57%, 70%, 73%, 95%, 74% and 83% respectively) was significantly higher than in any of the squamous groups. The methylation frequency for each of the nine genes in the metaplastic BE (95%, 28%, 78%, 48%, 58%, 48%, 93%, 88% and 75% respectively) was significantly higher than in the squamous samples except for CDKN2A and RBP1. The methylation frequency did not differ between BE and EAC samples, except for CDKN2A and RUNX3 which were significantly higher in EAC. The methylation extent was an estimate of both the number of methylated alleles and the density of methylation on these alleles. This was significantly greater in EAC than in metaplastic BE for all genes except APC, MGMT and TIMP3. There was no significant difference in methylation extent for any gene between high grade dysplastic BE and EAC.ConclusionWe found significant methylation in metaplastic BE, which for seven of the nine genes studied did not differ in frequency from that found in EAC. This is also the first report of gene silencing by methylation of ID4 in BE or EAC. This study suggests that metaplastic BE is a highly abnormal tissue, more similar to cancer tissue than to normal epithelium.

Spontaneous and UV radiation-induced multiple metastatic melanomas in Cdk4R24C/R24C/TPras mice.

Human melanoma susceptibility is often characterized by germ-line inactivating CDKN2A (INK4A/ARF) mutations, or mutations that activate CDK4 by preventing its binding to and inhibition by INK4A. We have previously shown that a single neonatal UV radiation (UVR) dose delivered to mice that carry melanocyte-specific activation of Hras (TPras) increases melanoma penetrance from 0% to 57%. Here, we report that activated Cdk4 cooperates with activated Hras to enhance susceptibility to melanoma in mice. Whereas UVR treatment failed to induce melanomas in Cdk4(R24C/R24C) mice, it greatly increased the penetrance and decreased the age of onset of melanoma development in Cdk4(R24C/R24C)/TPras animals compared with TPras alone. This increased penetrance was dependent on the threshold of Cdk4 activation as Cdk4(R24C/+)/TPras animals did not show an increase in UVR-induced melanoma penetrance compared with TPras alone. In addition, Cdk4(R24C/R24C)/TPras mice invariably developed multiple lesions, which occurred rarely in TPras mice. These results indicate that germ-line defects abrogating the pRb pathway may enhance UVR-induced melanoma. TPras and Cdk4(R24C/R24C)/TPras tumors were comparable histopathologically but the latter were larger and more aggressive and cultured cells derived from such melanomas were also larger and had higher levels of nuclear atypia. Moreover, the melanomas in Cdk4(R24C/R24C)/TPras mice, but not in TPras mice, readily metastasized to regional lymph nodes. Thus, it seems that in the mouse, Hras activation initiates UVR-induced melanoma development whereas the cell cycle defect introduced by mutant Cdk4 contributes to tumor progression, producing more aggressive, metastatic tumors.

Impact of the fibrinolytic enzyme system on prognosis and survival associated with non-small cell lung carcinoma.

Comprehensive studies of fibrinolysis in non-small cell lung carcinoma have been limited, and assignment of patients to high/low prognosis groups based on arbitrary cut-offs utilizing fibrinolytic measurements is unstandardized. This study was performed in 166 patients to examine the effects of cut-off values determined in three ways. Model 1 assigned patients to one of three equal groups (low, medium, high) based on fibrinolytic measurements made at diagnosis, Model 2 divided patients into low/high groups using median values, and Model 3 grouped according to the parameter being above/below normal range. In model 1, raised plasma fibrinogen, D-dimer and soluble fibrin were positively associated with poorer survival. In model 2, tissue plasminogen activator antigen was additionally related to poorer prognosis. Model 3 identified seven parameters as significantly related to survival, two not identified by the other models becoming significant [plasmin–antiplasmin, tissue plasminogen activator inhibitor-1 (PAI-1) antigen]. Using multivariate analysis, plasma fibrinogen level was the most uniformly significant parameter. Relative risk estimates indicated that raised plasma fibrinogen, soluble fibrin and D-dimer were associated with increased risk of death. Use of the normal/above normal cut-off is recommended to provide the maximum number of significant parameters relating to prognosis, and increased plasma D-dimer, PAI-1 antigen and fibrinogen were most closely related to survival/prognosis.