Raf kinases: Oncogenesis and drug discovery

Combined targeting of BRAF and CRAF or BRAF and PI3K effector pathways is required for efficacy in NRAS mutant tumors

Background

Oncogenic RAS is a highly validated cancer target. Attempts at targeting RAS directly have so far not succeeded in the clinic. Understanding downstream RAS-effectors that mediate oncogenesis in a RAS mutant setting will help tailor treatments that use RAS-effector inhibitors either alone or in combination to target RAS-driven tumors.

Methodology/Principal Findings

In this study, we have investigated the sufficiency of targeting RAS-effectors, RAF, MEK and PI3-Kinase either alone or in combination in RAS mutant lines, using an inducible shRNA in vivo mouse model system. We find that in colon cancer cells harboring a KRAS^G13D mutant allele, knocking down KRAS alone or the RAFs in combination or the RAF effectors, MEK1 and MEK2, together is effective in delaying tumor growth in vivo. In melanoma cells harboring an NRAS^Q61L or NRAS^Q61K mutant allele, we find that targeting NRAS alone or both BRAF and CRAF in combination or both BRAF and PIK3CA together showed efficacy.

Conclusion/Significance

Our data indicates that targeting oncogenic NRAS-driven melanomas require decrease in both pERK and pAKT downstream of RAS-effectors for efficacy. This can be achieved by either targeting both BRAF and CRAF or BRAF and PIK3CA simultaneously in NRAS mutant tumor cells.

How ERK1/2 activation controls cell proliferation and cell death: Is subcellular localization the answer?

Extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) are members of the mitogen-activated protein kinase super family that can mediate cell proliferation and apoptosis. The Ras-Raf-MEK-ERK signaling cascade controlling cell proliferation has been well studied but the mechanisms involved in ERK1/2-mediated cell death are largely unknown. This review focuses on recent papers that define ERK1/2 translocation to the nucleus and the proteins involved in the cytosolic retention of activated ERK1/2. Cytosolic retention of ERK1/2 denies access to the transcription factor substrates that are responsible for the mitogenic response. In addition, cytosolic ERK1/2, besides inhibiting survival and proliferative signals in the nucleus, potentiates the catalytic activity of some proapoptotic proteins such as DAP kinase in the cytoplasm. Studies that further define the function of cytosolic ERK1/2 and its cytosolic substrates that enhance cell death will be essential to harness this pathway for developing effective treatments for cancer and chronic inflammatory diseases.

Delphinidin attenuates neoplastic transformation in JB6 Cl41 mouse epidermal cells by blocking Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase signaling

Recent studies suggest that anthocyanidins play a pivotal role in the chemopreventive effects of fruits and vegetables. However, the underlying molecular mechanisms and cellular targets remain unknown. Neoplastic transformation of cells and inflammation are considered to be major events contributing to carcinogenesis. Here, we report that delphinidin, a major dietary anthocyanidin, inhibits tumor promoter-induced transformation and cyclooxygenase-2 (COX-2) expression in JB6 promotion-sensitive mouse skin epidermal (JB6 P+) cells by directly targeting Raf and mitogen-activated protein kinase kinase (MEK). Delphinidin inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic transformation and COX-2 expression at both the protein and transcriptional levels. The activation of activator protein-1 and nuclear factor-kappaB induced by TPA was dose dependently inhibited by delphinidin treatment. Delphinidin strongly suppressed Raf1 and MEK1 kinase activities and subsequently attenuated TPA-induced phosphorylation of MEK, extracellular signal-regulated kinase (ERK), p90RSK, and MSK. Although delphinidin suppressed ERK and c-Jun NH(2)-terminal kinase activities, it was more effective at inhibiting Raf1 or MEK1 activities. Pull-down and competition assays revealed that delphinidin binds with Raf1 or MEK1 noncompetitively with ATP. Delphinidin also dose dependently suppressed JB6 P+ cell transformation induced by epidermal growth factor and H-Ras, both of which are involved in the activation of Raf/MEK/ERK signaling. Together, these findings suggested that the targeted inhibition of Raf1 and MEK activities and COX-2 expression by delphinidin contribute to the chemopreventive potential of fruits and vegetables.

Oncogenic B-RAF negatively regulates the tumor suppressor LKB1 to promote melanoma cell proliferation

The LKB1-AMPK signaling pathway serves as a critical cellular sensor coupling energy homeostasis to cell growth, proliferation, and survival. However, how tumor cells suppress this signaling pathway to gain growth advantage under conditions of energy stress is largely unknown. Here, we show that AMPK activation is suppressed in melanoma cells with the B-RAF V600E mutation and that downregulation of B-RAF signaling activates AMPK. We find that in these cells LKB1 is phosphorylated by ERK and Rsk, two kinases downstream of B-RAF, and that this phosphorylation compromises the ability of LKB1 to bind and activate AMPK. Furthermore, expression of a phosphorylation-deficient mutant of LKB1 allows activation of AMPK and inhibits melanoma cell proliferation and anchorage-independent cell growth. Our findings provide a molecular linkage between the LKB1-AMPK and the RAF-MEK-ERK pathways and suggest that suppression of LKB1 function by B-RAF V600E plays an important role in B-RAF V600E-driven tumorigenesis.

Morelloflavone, a biflavonoid, inhibits tumor angiogenesis by targeting rho GTPases and extracellular signal-regulated kinase signaling pathways

Morelloflavone, a biflavonoid extracted from Garcinia dulcis, has shown antioxidative, antiviral, and anti-inflammatory properties. However, the function and the mechanism of this compound in cancer treatment and tumor angiogenesis have not been elucidated to date. In this study, we postulated that morelloflavone might have the ability to inhibit angiogenesis, the pivotal step in tumor growth, invasiveness, and metastasis. We showed that morelloflavone could inhibit vascular endothelial growth factor (VEGF)-induced cell proliferation, migration, invasion, and capillary-like tube formation of primary cultured human umbilical vascular endothelial cells in a dose-dependent manner. Morelloflavone effectively inhibited microvessel sprouting of endothelial cells in the mouse aortic ring assay and the formation of new blood microvessels induced by VEGF in the mouse Matrigel plug assay. Furthermore, morelloflavone inhibited tumor growth and tumor angiogenesis of prostate cancer cells (PC-3) in xenograft mouse tumor model in vivo, suggesting that morelloflavone inhibited tumorigenesis by targeting angiogenesis. To understand the underlying mechanism of morelloflavone on the inhibitory effect of tumor growth and angiogenesis, we showed that morelloflavone could inhibit the activation of both RhoA and Rac1 GTPases but have little effect on the activation of Cdc42 GTPase. Additionally, morelloflavone inhibited the phosphorylation and activation of Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase/ERK pathway kinases without affecting VEGF receptor 2 activity. Together, our results indicate that morelloflavone exerts antiangiogenic action by targeting the activation of Rho-GTPases and ERK signaling pathways. These findings are the first to reveal the novel functions of morelloflavone in tumor angiogenesis and its molecular basis for the anticancer action.

Biological effects of hexitol and altritol-modified siRNAs targeting B-Raf

Increasing the effectiveness of siRNAs through chemical modification is an important task. Here we describe altritol and hexitol modified oligonucleotides targeting the B-Raf oncogene that is critical for the growth and survival of melanoma cells. Using assays for apoptosis, DNA synthesis, colony formation and B-Raf protein and message levels, we demonstrate that certain hexitol modifications can improve the effectiveness of B-Raf siRNAs and also increase duration of action. Altritol modified siRNAs were similar to or slightly less effective than unmodified B-Raf siRNA. Modifications at the 3' or 5' end of the sense strand, at the 3' end of the antisense strand, or within either strand were well tolerated. The basis for the increased effectiveness of the hexitol-modified siRNAs is not fully understood but may be partly due to increased stability to nucleases.

Pharmacodynamics of 2-[4-[(1E)-1-(hydroxyimino)-2,3-dihydro-1H-inden-5-yl]-3-(pyridine-4-yl)-1H-pyrazol-1-yl]ethan-1-ol (GDC-0879), a potent and selective B-Raf kinase inhibitor: understanding relationships between systemic concentrations, phosphorylated mitogen-activated protein kinase kinase 1 inhibition, and efficacy

The Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase signaling pathway is involved in cellular responses relevant to tumorigenesis, including cell proliferation, invasion, survival, and angiogenesis. 2-[4-[(1E)-1-(Hydroxyimino)-2,3-dihydro-1H-inden-5-yl]-3-(pyridine-4-yl)-1H-pyrazol-1-yl]ethan-1-ol (GDC-0879) is a novel, potent, and selective B-Raf inhibitor. The objective of this study was to characterize the relationship between GDC-0879 plasma concentrations and tumor growth inhibition in A375 melanoma and Colo205 colon cancer xenografts and to understand the pharmacodynamic (PD) marker response requirements [phosphorylated (p)MEK1 inhibition] associated with tumor growth inhibition in A375 xenografts. Estimates of GDC-0879 plasma concentrations required for tumor stasis obtained from fitting tumor data to indirect response models were comparable, at 4.48 and 3.27 microM for A375 and Colo205 xenografts, respectively. This was consistent with comparable in vitro potency of GDC-0879 in both cell lines. The relationship between GDC-0879 plasma concentrations and pMEK1 inhibition in the tumor was characterized in A375 xenografts after oral doses of 35, 50, and 100 mg/kg. Fitting pMEK1 inhibition to an indirect response model provided an IC(50) estimate of 3.06 microM. pMEK1 inhibition was further linked to A375 tumor volume data from nine different GDC-0879 dosing regimens using an integrated pharmacokinetic-PD model. A simulated PD marker response curve plot of K (rate constant describing tumor growth inhibition) versus pMEK1 inhibition generated using pharmacodynamic parameters estimated from this model, showed a steep pMEK1 inhibition-response curve consistent with an estimated Hill coefficient of approximately equal 8. A threshold of >40% pMEK1 inhibition is required for tumor growth inhibition, and a minimum of approximately 60% pMEK1 inhibition is required for stasis in A375 xenografts treated with GDC-0879.

Deconstructing feedback-signaling networks to improve anticancer therapy with mTORC1 inhibitors

Targeting mTOR complex 1 (mTORC1), which regulates general protein translation, represents one of the most attractive approaches to treating cancer, since upregulation of this pathway is a common hallmark in many tumors. Nevertheless, the use of rapamycin and its analogs in the clinic has revealed that mTORC1 pathway is embedded in a network of signaling cross-talks and feedbacks which might reduce its effectiveness in cancer. We have recently described a novel signaling feedback stemming from mTORC1 inhibition, which leads to the activation of ERK-MAPK (MAPK) pathway. The observation that MAPK is activated by rapamycin and its analogs in vitro, in mouse models, and cancer patient biopsies sets the rationale for the combined use of MAPK and mTORC1 inhibitors in cancer therapy. In this extra-view, we integrate our findings into the mTORC1 signaling network and discuss its relevance for the design of combinatorial therapies with mTORC1 inhibitors.

Sorafenib potently inhibits papillary thyroid carcinomas harboring RET/PTC1 rearrangement

PURPOSE

Papillary thyroid carcinomas (PTC) are the most common type of thyroid malignancy with one of the two mutations, RET/PTC rearrangement or BRAF mutation. Both mutations are able to activate the MEK/ERK signaling transduction pathway and result in the activation of transcription factors that regulate cellular proliferation, differentiation, and apoptosis. Sorafenib (Nexavar, BAY 43-9006) is a multikinase inhibitor, and in this study, we tested its effects on PTC cells carrying either mutation.

EXPERIMENTAL DESIGN

The effects of sorafenib on cell proliferation and signaling were evaluated in vitro on PTC cells using growth curves, cell cycle analysis, and immunoblotting. Using an orthotopic mouse model, we determined the antitumor effects of sorafenib in vivo.

RESULTS

The concentration needed for 50% growth inhibition (GI(50)) by sorafenib was 0.14 mumol/L for the PTC cells with the RET/PTC1 rearrangement, and 2.5 mumol/L for PTC cells with a BRAF mutation, both readily achievable serum concentrations. After 3 weeks of oral administration of sorafenib (80 mg/kg/d) in mice, small (94% reduction compared with controls) or no tumor growth was detected in mice inoculated with PTC cells bearing the RET/PTC1 rearrangement, whereas the tumor volume of the orthotopic tumor implants of PTC cells with a BRAF mutation was reduced 53% to 54% (as compared with controls).

CONCLUSIONS

PTC cells carrying the RET/PTC1 rearrangement were more sensitive to sorafenib than PTC cells carrying a BRAF mutation. Because RET/PTC rearrangements are unique to thyroid carcinomas, our findings support the clinical evaluation of sorafenib for patients with PTC and the identification of patients most likely to respond to sorafenib treatment.

Constitutive activation of Raf-1 induces glioma formation in mice

In human glioblastoma multiforme (GBM), RAS activity is upregulated in the majority of the tumors. Furthermore, the levels of phospho-mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK), a downstream effector of RAS, are also increased. In mice, activated KRas cooperates with the loss of INK4a-ARF locus or with activated Akt to induce gliomas, confirming an important role for this pathway in glioma biology. However, to correctly target therapies against the RAS signaling pathway, it is necessary to identify the effectors that contribute to RAS-mediated gliomagenesis. In this study, we investigated the contribution of RAF signaling in glioma oncogenesis. We find that the levels of RAF-1 and BRAF proteins and RAF kinase activity are increased in human GBM samples. We confirm the importance of this finding by demonstrating a causal role for a constitutively active Raf-1 mutant in glioma formation in mice. Specifically, we find that activated Raf-1 cooperates with Arf loss or Akt activation to generate gliomas similar to activated KRas under the same conditions. Our study suggests that the oncogenic effect of KRas in glioma formation may be transduced at least in part through Raf signaling and that therapeutic targeting of this pathway may be beneficial in glioma treatment.

Inter-cellular adhesion disruption and the RAS/RAF and beta-catenin signalling in lung cancer progression

Cadherin cell adhesion molecules play an essential role in creating tight intercellular association and their loss has been correlated with poor prognosis in human cancer. Mutational activation of protein kinases and loss of cell adhesion occur together in human lung adenocarcinoma but how these two pathways interconnect is only poorly understood. Mouse models of human lung adenocarcinoma with oncogene expression targeted to subtypes of lung epithelial cells led to formation of adenomas or adenocarcinomas that lacked metastatic potential. Conditional genetic abrogation of epithelial tumour cell adhesion in mice with benign lung tumours induced by oncogenic RAF kinase has been demonstrated to induce intratumourous vascularization (angiogenic switch), progression to invasive adenocarcinoma and micrometastasis. Importantly, breaking cell adhesion in benign oncogene-driven lung tumour cells activated beta-catenin signalling and induced the expression of several genes that are normally expressed in intestine rather than the lung. I will discuss potential routes to nuclear beta-catenin signalling in cancer and how nuclear beta-catenin may epigenetically alter the plasticity of tumour cells during malignant progression.

Raf and MEK protein kinases are direct molecular targets for the chemopreventive effect of quercetin, a major flavonol in red wine

Considerable attention has focused on the health-promoting effects of red wine and its nonflavonoid polyphenol compound resveratrol. However, the underlying molecular mechanisms and molecular target(s) of red wine or other potentially active ingredients in red wine remain unknown. Here, we report that red wine extract (RWE) or the red wine flavonoid quercetin inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced transformation of JB6 promotion-sensitive mouse skin epidermal (JB6 P+) cells. The activation of activator protein-1 and nuclear factor-kappaB induced by TPA was dose dependently inhibited by RWE or quercetin treatment. Western blot and kinase assay data revealed that RWE or quercetin inhibited mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK) 1 and Raf1 kinase activities and subsequently attenuated TPA-induced phosphorylation of ERK/p90 ribosomal S6 kinase. Although either RWE or quercetin suppressed Raf1 kinase activity, they were more effective in inhibiting MEK1 activity. Importantly, quercetin exerted stronger inhibitory effects than PD098059, a well-known pharmacologic inhibitor of MEK. Resveratrol did not affect either MEK1 or Raf1 kinase activity. Pull-down assays revealed that RWE or quercetin (but not resveratrol) bound with either MEK1 or Raf1. RWE or quercetin also dose dependently suppressed JB6 P+ cell transformation induced by epidermal growth factor or H-Ras, both of which are involved in the activation of MEK/ERK signaling. Docking data suggested that quercetin, but not resveratrol, formed a hydrogen bond with the backbone amide group of Ser(212), which is the key interaction for stabilizing the inactive conformation of the activation loop of MEK1.

Distribution of BRAF T1799A(V600E) mutations across various types of benign nevi: implications for melanocytic tumorigenesis

PURPOSE

The BRAF mutation is common in melanomas, but variation in rates across melanoma subtypes points to a complex interplay between BRAF activation and other factors (eg, sun exposure). Nevi also harbor the BRAF mutation. A description of mutation distribution in nevi could provide insight into the significance of this event in melanocytic tumorigenesis.

EXPERIMENTAL DESIGN

One hundred thirty-five nevi from 116 patients were evaluated for the T-->A mutation at nucleotide 1799. The nevi were inclusive of congenital (n = 34) and acquired (n = 101) nevi, dysplastic (n = 11) and nondysplastic (n = 124) nevi, and anogenital (n = 24) and common cutaneous (n = 111) nevi.

RESULTS

The overall mutation rate was 81%. The rate varied only slightly by anatomic site: BRAF mutations were detected in 21 of 21 (100%) nevi of the head and neck, 62 of 76 (82%) nevi of the trunk, 8 of 14 (62%) nevi of the extremities, and 18 of 24 (75%) anogenital nevi. For acquired nevi, there was no association between BRAF mutations and sun exposure as inferred from anatomic site. There were no significant differences in the mutation rates between congenital and acquired nevi (76% versus 81%; P = 0.5).

CONCLUSIONS

The BRAF mutation is uniformly distributed in various types of nevi. Its presence in congenital and anogenital nevi points to mechanisms of induction other than sun exposure. Its ubiquitous presence suggests that it poses no significant threat of malignant transformation, raising doubts about its relevance in melanoma development and its suitability as a target of directed therapy in patients with melanoma.

Selective Raf inhibition in cancer therapy

Over the past 5 years, the Raf kinase family has emerged as a promising target for protein-directed cancer therapy development. The goal of this review is to first provide a concise summary of the data validating Raf proteins as high-interest therapeutic targets. The authors then outline the mode of action of Raf kinases, emphasizing how Raf activities and protein interactions suggest specific approaches to inhibiting Raf. The authors then summarize the set of drugs, antisense reagents and antibodies available or in development for therapeutically targeting Raf or Raf-related proteins, as well as existing strategies combining these and other therapeutic agents. Finally, the authors discuss recent results from systems biology analyses that have the potential to increasingly guide the intelligent selection of combination therapies involving Raf-targeting agents and other therapeutics.

Genetics of melanoma tumorigenesis

Melanoma therapy is moving away from combinatorial approaches and towards newer targeted strategies. With the identification of mutations in various RAS pathway genes, there are now tremendous opportunities to bring inhibitors of RAS signalling to the clinical arena.

Thrombopoietin inhibits nerve growth factor-induced neuronal differentiation and ERK signalling

Thrombopoietin (TPO), a hematopoietic growth factor regulating platelet production, and its receptor (TPOR) were recently shown to be expressed in the brain where they exert proapoptotic activity. Here we used PC12 cells, an established model of neuronal differentiation, to investigate the effects of TPO on neuronal survival and differentiation. These cells expressed TPOR mRNA. TPO increased cell death in neuronally differentiated PC12 cells but had no effect in undifferentiated cells. Surprisingly, TPO inhibited nerve growth factor (NGF)-induced differentiation of PC12 cells in a dose- and time-dependent manner. This inhibition was dependent on the activity of Janus kinase-2 (JAK2). Using phospho-kinase arrays and Western blot we found downregulation of the NGF-stimulated phosphorylation of the extracellular signal-regulated kinase p42ERK by TPO with no effect on phosphorylation of Akt or stress kinases. NGF-induced phosphorylation of ERK-activating kinases, MEK1/2 and C-RAF was also reduced by TPO while NGF-induced RAS activation was not attenuated by TPO treatment. In contrast to its inhibitory effects on NGF signalling, TPO had no effect on epidermal growth factor (EGF)-stimulated ERK phosphorylation or proliferation of PC12 cells. Our data indicate that TPO via activation of its receptor-bound JAK2 delays the NGF-dependent acquisition of neuronal phenotype and decreases neuronal survival by suppressing NGF-induced ERK activity.

Flesh and blood: The story of Vav1, a gene that signals in hematopoietic cells but can be transforming in human malignancies

Cancer results from the interaction of multiple aberrations including activation of dominant oncogenes and upregulation of signal transduction pathways. Identification of the genes involved in malignant transformation is a pre-requisite for understanding cancer and improving its diagnosis and treatment. Quite a few of the genes that have been implicated in cancer are mutant or aberrantly expressed versions of genes that are important mediators of the normal growth that occurs during development. An important example of this is Vav1, a cytoplasmic signal transducer protein initially identified as an oncogene. Physiological expression of Vav1 is restricted to the hematopoietic system, where its best-known function is as a GDP/GTP nucleotide exchange factor for Rho/Rac GTPases, an activity strictly controlled by tyrosine phosphorylation. Vav1 was shown to regulate cytoskeletal rearrangement during activation of hematopoietic cells. Vav1 can also mediate other cellular functions including activation of the JNK, ERK, Ras, NF-kB, and NFAT pathways, in addition to association with numerous adapter proteins such as Shc, NCK, SLP-76, GRB2, and Crk. Although the oncogenic form of Vav1 has not been detected in clinical human tumors, its wild-type form has recently been implicated in mammalian malignancies such as neuroblastoma, melanoma, pancreatic tumors and B-cell chronic lymphocytic leukemia. This review addresses the physiological function of wild-type Vav1, its mode of activation as an oncogene, and its emerging role as a transforming protein in human cancer.

Differential selection for B-raf and Ha-ras mutated liver tumors in mice with high and low susceptibility to hepatocarcinogenesis

Activation of the Ras/Raf/MEK/ERK pathway is frequently observed in animal and human tumors. In our study, we analyzed B-raf codon 637 (formerly 624) and Ha-ras codon 61 mutations in liver tumors from C3H, B6C3F1 and C56BL mice which differ considerably with regard to their susceptibility to hepatocarcinogenesis. In total, 73% (102/140) of tumors induced by a single application of N-nitrosodiethylamine or 7,12-dimethylbenz[a]anthracene contained either B-raf or Ha-ras mutations and only <3% (4/140) were mutated in both genes. In addition, B-raf mutations were present in 76% (19/25) of early precancerous liver lesions. The prevalence of Ha-ras mutated tumors was significantly higher in the susceptible C3H and B6C3F1 mouse strains (39-50%) than in the comparatively resistant C57BL mouse (7%). B-raf mutated tumors, by contrast, were more frequent in C57BL mice (68%) than in the other two strains (17-45%). Taken together, our findings indicate that alterations affecting the Ras/Raf/MEK/ERK signalling pathway are a hallmark of carcinogen-induced liver tumors in mice. Moreover, our results show that mutational activation of B-raf in liver tumors of different mouse strains is, by contrast to Ha-ras, inversely related to their susceptibility to hepatocarcinogenesis. Although activated Ras and Raf proteins are assumed to have similar biological effects because they feed into the same signalling pathway, there seem to be subtle strain-specific differences in selection processes favouring the preferential outgrowth of either B-raf or Ha-ras mutated tumor populations in mouse liver.

BRAF(E600) in benign and malignant human tumours

Of the RAF family of protein kinases, BRAF is the only member to be frequently activated by mutation in cancer. A single amino acid substitution (V600E) accounts for the vast majority and results in constitutive activation of BRAF kinase function. Its expression is required to maintain the proliferative and oncogenic characteristics of BRAF(E600)-expressing human tumour cells. Although BRAF(E600) acts as an oncogene in the context of additional genetic lesions, in primary cells it appears to be associated rather with transient stimulation of proliferation. Eventually, BRAF(E600) signalling triggers cell cycle arrest with the hallmarks of cellular senescence, as is illustrated by several recent studies in cultured cells, animal models and benign human lesions. In this review, we will discuss recent advances in our understanding of the role of BRAF(E600) in benign and malignant human tumours and the implications for therapeutic intervention.

Application of a BRAF pyrosequencing assay for mutation detection and copy number analysis in malignant melanoma

Mutations in the BRAF gene are found in the majority of cutaneous malignant melanomas and subsets of other tumors. These mutations lead to constitutive activation of BRAF with increased downstream ERK (extracellular signal-regulated kinase) signaling; therefore, the development of RAF kinase inhibitors for targeted therapy is being actively pursued. A methodology that allows sensitive, cost-effective, high-throughput analysis of BRAF mutations will be needed to triage patients for specific molecular-based therapies. Pyrosequencing is a high-throughput, sequencing-by-synthesis method that is particularly useful for analysis of single nucleotide polymorphisms or hotspot mutations. Mutational analysis of BRAF is highly amenable to pyrosequencing because the majority of mutations in this gene localize to codons 600 and 601 and consist of single or dinucleotide substitutions. In this study, DNAs from a panel of melanocyte cell lines, melanoma cell lines, and melanoma tumors were used to validate a pyrosequencing assay to detect BRAF mutations. The assay demonstrates high accuracy and precision for detecting common and variant exon 15 BRAF mutations. Further, comparison of pyrosequencing data with 100K single nucleotide polymorphism microarray data allows characterization of BRAF amplification events that may accompany BRAF mutation. Pyro-sequencing serves as an excellent platform for BRAF genotyping of tumors from patients entering clinical trial.

Small-molecule therapies for cardiac hypertrophy: moving beneath the cell surface

Pathological stress from cardiovascular disease stimulates hypertrophy of heart cells, which increases the risk of cardiac morbidity and mortality. Recent evidence has indicated that inhibiting such hypertrophy could be beneficial, encouraging drug discovery and development efforts for agents that could achieve this goal. Most existing therapies that have antihypertrophic effects target outside-in signalling in cardiac cells, but their effectiveness seems limited, and so attention has recently turned to the potential of targeting intracellular signalling pathways. Here, we focus on new developments with small-molecule inhibitors of cardiac hypertrophy, summarizing both agents that have been in or are poised for clinical testing, and pathways that offer further promising potential therapeutic targets.

Targeting the Raf-MEK-ERK mitogen-activated protein kinase cascade for the treatment of cancer

Mitogen-activated protein kinase (MAPK) cascades are key signaling pathways involved in the regulation of normal cell proliferation, survival and differentiation. Aberrant regulation of MAPK cascades contribute to cancer and other human diseases. In particular, the extracellular signal-regulated kinase (ERK) MAPK pathway has been the subject of intense research scrutiny leading to the development of pharmacologic inhibitors for the treatment of cancer. ERK is a downstream component of an evolutionarily conserved signaling module that is activated by the Raf serine/threonine kinases. Raf activates the MAPK/ERK kinase (MEK)1/2 dual-specificity protein kinases, which then activate ERK1/2. The mutational activation of Raf in human cancers supports the important role of this pathway in human oncogenesis. Additionally, the Raf-MEK-ERK pathway is a key downstream effector of the Ras small GTPase, the most frequently mutated oncogene in human cancers. Finally, Ras is a key downstream effector of the epidermal growth factor receptor (EGFR), which is mutationally activated and/or overexpressed in a wide variety of human cancers. ERK activation also promotes upregulated expression of EGFR ligands, promoting an autocrine growth loop critical for tumor growth. Thus, the EGFR-Ras-Raf-MEK-ERK signaling network has been the subject of intense research and pharmaceutical scrutiny to identify novel target-based approaches for cancer treatment. In this review, we summarize the current status of the different approaches and targets that are under evaluation and development for the therapeutic intervention of this key signaling pathway in human disease.

Raf kinases: function, regulation and role in human cancer

The Ras-Raf-MAPK pathway regulates diverse physiological processes by transmitting signals from membrane based receptors to various nuclear, cytoplasmic and membrane-bound targets, coordinating a large variety of cellular responses. Function of Raf family kinases has been shown to play a role during organism development, cell cycle regulation, cell proliferation and differentiation, cell survival and apoptosis and many other cellular and physiological processes. Aberrations along the Ras-Raf-MAPK pathway play an integral role in various biological processes concerning human health and disease. Overexpression or activation of the pathway components is a common indicator in proliferative diseases such as cancer and contributes to tumor initiation, progression and metastasis. In this review, we focus on the physiological roles of Raf kinases in normal and disease conditions, specifically cancer, and the current thoughts on Raf regulation.

Malignant melanoma in the 21st century, part 2: staging, prognosis, and treatment

Critical to the clinical management of a patient with malignant melanoma is an understanding of its natural history. As with most malignant disorders, prognosis is highly dependent on the clinical stage (extent of tumor burden) at the time of diagnosis. The patient's clinical stage at diagnosis dictates selection of therapy. We review the state of the art in melanoma staging, prognosis, and therapy. Substantial progress has been made in this regard during the past 2 decades. This progress is primarily reflected in the development of sentinel lymph node biopsies as a means of reducing the morbidity associated with regional lymph node dissection, increased understanding of the role of neoangiogenesis in the natural history of melanoma and its potential as a treatment target, and emergence of innovative multimodal therapeutic strategies, resulting in significant objective response rates in a disease commonly believed to be drug resistant. Although much work remains to be done to improve the survival of patients with melanoma, clinically meaningful results seem within reach.

Ras oncogenes and their downstream targets

RAS proteins are small GTPases, which serve as master regulators of a myriad of signaling cascades involved in highly diverse cellular processes. RAS oncogenes have been originally discovered as retroviral oncogenes, and ever since constitutively activating RAS mutations have been identified in human tumors, they are in the focus of intense research. In this review, we summarize the biochemical properties of RAS proteins, trace down the evolution of RAS signaling and present an overview of the spatio-temporal activation of major RAS isoforms. We further discuss RAS effector pathways, their role in normal and transformed cell physiology and summarize ongoing attempts to interfere with aberrant RAS signaling. Finally, we comment on the role of micro RNAs in modulating RAS expression, contribution of RAS to stem cell function and on high-throughput analyses of RAS signaling networks.

Kinase MEKK1 is required for CD40-dependent activation of the kinases Jnk and p38, germinal center formation, B cell proliferation and antibody production

Mice lacking activity of the kinase MEKK1 ('Map3k1(deltaKD)' mice) have defective activation of the kinase Jnk and increased production of T helper type 2 cytokines after T cell receptor ligation. Here we show that Map3k1(deltaKD) mice had defective germinal center formation and diminished production of antibodies recognizing thymus-dependent antigens. Those defects were B cell intrinsic, as MEKK1 was necessary for CD40-mediated activation of the kinases Jnk and p38 and transcription factor c-Jun, as well as for expression of cyclin D2 and activation-induced deaminase. MEKK1 was recruited to CD40 and adaptor molecule TRAF2 after CD40 ligation, and Map3k1(deltaKD) B cells were hypoproliferative after CD40 stimulation. Our data emphasize that MEKK1 is an essential component of signaling cascades needed for thymus-dependent antigen-induced B cell proliferation and antibody production.