Multicenter phase II study of the oral MEK inhibitor, CI-1040, in patients with advanced non-small-cell lung, breast, colon, and pancreatic cancer

Proteomic Analysis of Neuroblastoma Subtypes in Response to Mitogen-Activated Protein Kinase Inhibition: Profiling Multiple Targets of Cancer Kinase Signaling

INTRODUCTION

Survival for high-risk neuroblastoma (NB) remains poor despite aggressive therapy. Novel therapies are vital for improving prognosis. We previously showed differential NB subtype sensitivity to p42/44 mitogen-activated protein kinase (ERK/MAPK) pathway inhibition. In this study, we investigated proteomic changes associated with resistance or sensitivity to MAPK kinase (MEK) inhibition in NB subtypes.

MATERIALS AND METHODS

SH-SY5Y (N-type), BE(2)-C (I-type), and SK-N-AS (S-type) were treated with MEK inhibitor U0126 (10 microM) for 1 and 24 h. Proteins were extracted from untreated and treated cells and analyzed for differential expression by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Selected polypeptides were extracted from the gel and identified by liquid chromatography-linked tandem mass spectrometry (LC-MS/MS).

RESULTS

We identified 15 proteins that were decreased by 2.5-fold between untreated and 1 h treated cells and subsequently up-regulated 5-fold after 24 h drug treatment. N-type NB (MEK-resistant) showed the least altered proteomic profile whereas the I-type (MEK-sensitive) and S-type NB (MEK-intermediate) generated significant protein changes. The majority of proteins identified were induced by stress.

CONCLUSIONS

Protein differences exist between MEK inhibitor-treated NB subtypes. Identified polypeptides all have roles in mediating cellular stress. These data suggest that inhibition of the ERK/MAPK in NB subtypes leads to an intracellular stress response. The most resistant NB cell line to MEK inhibitor treatment generated the least protective protein profile, whereas the intermediate and most sensitive NB cells produced the most stress response. These findings suggest stress related protein expression may be targeted in assessing a response to ERK/MAPK therapeutics.

p38 MAPK turns hepatocyte growth factor to a death signal that commits ovarian cancer cells to chemotherapy-induced apoptosis

We recently showed that Hepatocyte Growth Factor (HGF), known as a survival factor, unexpectedly enhances apoptosis in human ovarian cancer cells treated with the front-line chemotherapeutics cisplatin (CDDP) and paclitaxel (PTX). Here we demonstrate that this effect depends on the p38 mitogen-activated kinase (MAPK). In fact, p38 MAPK activity is stimulated by HGF and further increased by the combined treatment with HGF and either CDDP or PTX. The expression of a dominant negative form of p38 MAPK abrogates apoptosis elicited by drugs, alone or in combination with HGF. HGF and drugs also activate the ERK1/2 MAPKs, the PI3K/AKT and the AKT substrate mTOR. However, activation of these survival pathways does not hinder the ability of HGF to enhance drug-dependent apoptosis. Altogether data show that p38 MAPK is necessary for HGF sensitization of ovarian cancer cells to low-doses of CDDP and PTX and might be sufficient to overcome activation of survival pathways. Therefore, the p38 MAPK pathway might be a suitable target to improve response to conventional chemotherapy in human ovarian cancer.

Microtubule stabilizing agents: Their molecular signaling consequences and the potential for enhancement by drug combination

Microtubule stabilization by chemotherapy is a powerful weapon in the war against cancer. Disruption of the mitotic spindle activates a number of signaling pathways, with consequences that may protect the cell or lead to its death via apoptosis. Taxol, the first microtubule stabilizing drug to be identified, has been utilized successfully in the treatment of solid tumors for two decades. Several features, however, make this drug less than ideal, and the search for next generation stabilizing drugs with increased efficacy has been intense and fruitful. Microtubule stabilizing agents (MSAs), including the taxanes, the epothilones, discodermolide, laulimalide, and eleutherobin, form an important and expanding family of chemotherapeutic agents. A strong understanding of their molecular signaling consequences is essential to their value, particularly in regard to their potential for combinatorial chemotherapy - the use of multiple agents to enhance the efficacy of cancer treatment. Here we present a critical review of research on the signaling mechanisms induced by MSAs, their relevance to apoptosis, and their potential for exploitation by combinatorial therapy.

Differentiation of pheochromocytoma PC12 cells induced by human urine extract and the involvement of the extracellular signal-regulated kinase signaling pathway

OBJECTIVE

The aim of this study was to investigate the effects of a human urine preparation on the differentiation of tumor cells.

DESIGN

The pheochromocytoma PC12 cells were used to examine the effects of a human urine preparation, CDA-2 on the induction of differentiation markers, neurofilaments, and compared with that induced by nerve growth factor (NGF). The MAPK/ERK kinase (MEK) inhibitor U0126 was used to examine the involvement of mitogen-activated protein kinase (MAPK) signaling pathway in this differentiation inducing effect.

RESULTS

We find that CDA-2 could induce differentiation of pheochromocytoma PC12 cells, as evidenced by the markedly increased expression of neurofilaments to a level comparable to those induced by NGF. This phenomenon was accompanied by the phosphorylation of extracellular-signal-regulated kinase (ERK) and could be inhibited by the MEK inhibitor, U0126.

CONCLUSIONS

Our results demonstrate the presence of active components in the human urine extract that can induce differentiation of PC12 cells and may involve the ERK signaling pathway. This may provide new insights for seeking novel differentiation agents and offer hope for cancer patients.

Multiple signaling pathways must be targeted to overcome drug resistance in cell lines derived from melanoma metastases

Although >66% of melanomas harbor activating mutations in BRAF and exhibit constitutive activity in the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase signaling pathway, it is unclear how effective MEK inhibition will be as a sole therapeutic strategy for melanoma. We investigated the anticancer activity of MEK inhibition in a panel of cell lines derived from radial growth phase (WM35) and vertical growth phase (WM793) of primary melanomas and metastatic melanomas (1205Lu, 451Lu, WM164, and C8161) in a three-dimensional spheroid model and found that the metastatic lines were completely resistant to MEK inhibition (U0126 and PD98059) but the earlier stage cell lines were not. Similarly, these same metastatic melanoma lines were also resistant to inhibitors of the phosphatidylinositol 3-kinase/Akt pathway (LY294002 and wortmannin). Under adherent culture conditions, the MEK inhibitors blocked growth through the induction of cell cycle arrest and up-regulation of p27, but this was readily reversible following inhibitor washout. However, when the phosphatidylinositol 3-kinase and MEK inhibitors were combined, the growth and invasion of the metastatic melanoma three-dimensional spheroids were blocked. Taken together, these results suggest that the most aggressive melanomas are resistant to strategies targeting one signaling pathway and that multiple signaling pathways may need to be targeted for maximal therapeutic efficacy. It is further suggested that BRAF mutational status is not predictive of response to MEK inhibition under three-dimensional culture conditions.

Beyond 5-fluorouracil: new horizons in systemic therapy for advanced colorectal cancer

Worldwide, colorectal cancer is a common cancer and a major cause of morbidity and mortality. Patients frequently present with, or later develop, metastatic disease. Median survival with supportive care alone is approximately 6 - 8 months. However, a number of recent developments have greatly increased the range of therapeutic options, improving median survival to > 20 months. Cytotoxic agents such as capecitabine, irinotecan and oxaliplatin are now established treatment strategies. In parallel, an improved understanding of tumour biology has led to the development of non-cytotoxic targeted therapies. Examples include bevacizumab (targeting tumour angiogenesis) and cetuximab (targeting the epidermal growth factor receptor). These agents have recently been incorporated into standard management. This paper reviews these and other advances in the care of patients with advanced colorectal cancer and discusses a number of agents that are currently under development.

Second-line treatment of postmenopausal women with advanced breast carcinoma

Breast cancer is the most prevalent cancer in women and, currently, there is no standard of care for the treatment of metastatic disease. Treatment options are based on a number of tumor- and patient-related factors. This review explores some of these options, including the use of hormonal manipulation in the treatment of hormone-positive disease, current chemotherapy options and the use of targeted therapies, such as trastuzumab.

Potent and selective mitogen-activated protein kinase kinase (MEK) 1,2 inhibitors. 1. 4-(4-bromo-2-fluorophenylamino)-1- methylpyridin-2(1H)-ones

The role of MEK 1,2 in cancer tumorgenesis has been clearly demonstrated preclinically, and two selective inhibitors are currently undergoing clinical evaluation to determine their role in the human disease. We have discovered 4-(4-bromo-2-fluorophenylamino)-1-methylpyridin-2(1H)-ones as a new class of ATP noncompetitive MEK inhibitors. These inhibitors exhibit excellent cellular potency and good pharmacokinetic properties and have demonstrated the ability to inhibit ERK phosphorylation in HT-29 tumors from mouse xenograft studies.

Is the small heat shock protein alphaB-crystallin an oncogene?

In the last 5 years, global gene expression profiling has allowed for the subclassification of the heterogeneous disease of breast cancer into new subgroups with prognostic significance. However, for most subgroups, the nature of the contributions of individual genes to the clinical phenotypes remains largely unknown. In this issue of the JCI, Moyano and colleagues further examine the oncogenic potential of the small heat shock protein alpha-basic-crystallin, commonly expressed in tumors of the basal-like breast cancer subtype associated with poor prognosis, and show that it is an oncogenic protein in the breast.

Inhibitors of signal transduction protein kinases as targets for cancer therapy

Cancer development requires that tumour cells attain several capabilities, including increased replicative potentials, anchorage and growth-factor independency, evasion of apoptosis, angiogenesis and metastasis. Many of these processes involve the actions of protein kinases, which have emerged as key regulators of all aspects of neoplasia. Perturbed protein kinase activity is repeatedly found to be associated with human malignancies, making these proteins attractive targets for anti-cancer therapy. The last decade has witnessed an exponential increase in the development of specific small protein kinase inhibitors. Many of them are in clinical trials in patients with different types of cancer and some are successfully used in clinic. This review describes different approaches that are currently applied to develop such specific protein kinase inhibitors and provides an overview of protein kinase inhibitors that are currently in clinical trials or are administered in the clinic. Focus is directed on inhibitors against receptor tyrosine kinases and protein kinases participating in the signalling cascades.

The effects of a novel MEK inhibitor PD184161 on MEK-ERK signaling and growth in human liver cancer

The MEK-ERK growth signaling pathway is important in human hepatocellular carcinoma (HCC). To evaluate the targeting of this pathway in HCC, we characterized a novel, orally-active MEK inhibitor, PD184161, using human HCC cells (HepG2, Hep3B, PLC, and SKHep) and in vivo human tumor xenografts. PD184161 inhibited MEK activity (IC50 = 10-100 nM) in a time- and concentration-dependent manner more effectively than PD098059 or U0126. PD184161 inhibited cell proliferation and induced apoptosis at concentrations of > or = 1.0 microM in a time- and concentration-dependent manner. In vivo, tumor xenograft P-ERK levels were significantly reduced 3 to 12 hours after an oral dose of PD184161 (P < .05). Contrarily, tumor xenograft P-ERK levels following long-term (24 days) daily dosing of PD184161 were refractory to this signaling effect. PD184161 significantly suppressed tumor engraftment and initial growth (P < .0001); however, established tumors were not significantly affected. In conclusion, PD184161 has antitumor effects in HCC in vitro and in vivo that appear to correlate with suppression of MEK activity. These studies demonstrate that PD184161 is unable to suppress MEK activity in HCC xenografts in the long term. Thus, we speculate that the degree of success of MEK targeted treatment in HCC and other cancers may, in part, depend on the discovery of mechanisms governing MEK inhibitor signaling resistance.

Targeting the ERK signaling pathway in cancer therapy

The extracellular signal-regulated kinase (ERK) signaling pathway is a major determinant in the control of diverse cellular processes such as proliferation, survival, differentiation and motility. This pathway is often up-regulated in human tumors and as such represents an attractive target for the development of anticancer drugs. Because of its multiple roles in the acquisition of a complex malignant phenotype, specific blockade of the ERK pathway is expected to result in not only an anti-proliferative effect but also in anti-metastatic and anti-angiogenic effects in tumor cells. Recently potent small-molecule inhibitors targeting the components of the ERK pathway have been developed. Among them, BAY 43-9006 (Raf inhibitor), and PD184352, PD0325901 and ARRY-142886 (MEK1/2 inhibitors) have reached the clinical trial stage. We briefly discuss the possibility that combination of ERK pathway inhibitors (cytostatic agents) and conventional anticancer drugs (cytotoxic agents) provides an excellent basis for the development of new chemotherapeutic strategies against cancer.

Differential sensitivity of chemoresistant neuroblastoma subtypes to MAPK-targeted treatment correlates with ERK, p53 expression, and signaling response to U0126

PURPOSE

Neuroblastoma tumors are comprised of neuroblastic (N), substrate-adherent (S), and intermediate (I) cells. Because cell growth and differentiation often involve p44/p42 mitogen-activated protein kinase (MAPK) pathway signaling, we explored MAPK signaling and growth response in three NB cell types after MAPK kinase (MEK) inhibition to evaluate the feasibility of MAPK-targeted treatment strategies.

METHODS

Three human NB cell cultures, SH-SY5Y (N-type), BE(2)-C (I-type), and SK-N-AS (S-type), were treated in monolayer cultures with increasing concentrations of the MEK inhibitor U0126. MAPK pathway intermediates MEK and ERK, their activated (phosphorylated) forms p-MEK and p-ERK, and p53 expression were assessed by Western blot at 1 and 24 hours. At 72 hours, cell counts determined growth inhibition and DNA fragmentation ELISA assessed apoptosis.

RESULTS

Among all three lines, total ERK and MEK expression were unaffected by U0126. However, constitutive total ERK and p53 expression were significantly greater in BE(2)-C (I-type) cells than in SH-SY5Y (N-type) and SK-N-AS (S-type). Active ERK (p-ERK) levels decreased in dose response to U0126 at 1 and 24 hours in all lines. Conversely, p-MEK levels increased with increasing U0126 concentrations at 1 hour in SH-SY5Y (N-type) and at 24 hours in all lines. BE(2)-C (I-type) cell counts decreased in concentration-dependent fashion with U0126, whereas SH-SY5Y (N-type) and SK-N-AS (S-type) showed a biphasic response with increased cell counts at 1 micromol/L U0126 and slightly decreased cell counts at 10 mumol/L U0126.

CONCLUSION

This study demonstrates that BE(2)-C (I-type) cells exhibit greater constitutive total ERK and p53 expression than SH-SY5Y (N-type) and SK-N-AS (S-type). Although all three lines exhibit p-ERK decreases with MEK inhibition, only BE(2)-C (I-type) cells significantly decrease their proliferation with U0126 treatment. Although MEK inhibition holds promise in targeting I-type NB cells, successfully treating this heterogeneous tumor may require combining agents against N- and S-type cells.

Identification of Inhibitors of the Kinase Activity of Oncogenic V600EBRAF in an Enzyme Cascade High-Throughput Screen

The Cancer Genome Project has identified several oncogenic mutations in BRAF that represent important opportunities for cancer drug discovery. The V600EBRAF mutation accounts for approximately 90% of the mutations identified. A strong case has emerged from molecular, cellular, and structural studies for the identification and development of inhibitors of this mutated BRAF protein. The authors have developed and run a high-throughput screen to find inhibitors of V600EBRAF using an enzyme cascade assay in which oncogenic BRAF activates MEK1, which in turn activates ERK2, which then phosphorylates the transcription factor ELK1. A phosphospecific antibody, Europium-labeled secondary antibody, and a time-resolved fluorescent readout were used to measure phosphorylation of ELK1. Overall assay variation was 12.4%. The assay was used to screen 64,000 compounds with an overall Z′ factor of 0.58 ± 0.12. A series of 3,5, di-substituted pyridines were identified as inhibitors of the cascade assay. These compounds did not inhibit a shortened activated MEK1 to ELK1 cascade but were active (0.5-27.9 μM) in a V600EBRAF assay and represent a potential starting point for future drug discovery and development.

Identification of coumarin derivatives as a novel class of allosteric MEK1 inhibitors

A homogenous TR-FRET-based in vitro coupling assay for the MAP3Ks-MEK1-ERK2 kinase cascade was established and was used to screen for inhibitors of the ERK/MAPK pathway. A series of coumarin derivatives were identified from the screen. These compounds potently inhibit the activation of the unactivated human MEK1 by upstream MAP3Ks (including BRAF and COT), but do not inhibit the activity of the activated MEK1. In addition, the potency of these compounds in inhibiting MEK1 activation is not affected by varying the ATP concentration, suggesting that these inhibitors are not competitive with ATP. As expected, the coumarin compounds potently inhibit LPS-induced TNFalpha production and ERK phosphorylation in THP-1 cells, with the most potent compound having an IC(50) of 90nM. Molecular modeling studies suggest that these coumarins bind to an allosteric site in the inactive conformation of MEK1. This site has been shown to be utilized by the biarylamine series of MEK inhibitors such as PD318088. Very interestingly, the identified coumarin derivatives are almost identical to a series of inhibitors recently reported that block LPS-induced TNFalpha production. Our findings have therefore raised the possibility that other naturally occurring or synthetic coumarins with anti-cancer and anti-inflammatory activities might exert their biological function through the inhibition of MEK1.

Identification of a selective ERK inhibitor and structural determination of the inhibitor-ERK2 complex

Selective inhibition of extracellular signal-regulated kinase (ERK) represents a potential approach for the treatment of cancer and other diseases; however, no selective inhibitors are currently available. Here, we describe an ERK-selective inhibitor, FR180204, and determine the structural basis of its selectivity. FR180204 inhibited the kinase activity of ERK1 and ERK2, with K(i) values 0.31 and 0.14microM, respectively. Lineweaver-Burk analysis of the binding interaction revealed that FR180204 acted as competitive inhibitor of ATP. In mink lung epithelial Mv1Lu cells, FR180204 inhibited TGFbeta-induced luciferase-expression. X-ray crystal structure analysis of the human ERK2/FR180204 complex revealed that Q105, D106, L156, and C166, which form the ATP-binding pocket on ERK, play important roles in the drug/protein interaction. These results suggest that FR180204 is an ERK-selective and cell-permeable inhibitor, and could be useful for elucidating the roles of ERK as well as for drug development.

The Role of Mitogen-Activated ERK-Kinase Inhibitors in Lung Cancer Therapy

The Ras-Raf-MAPK pathway has been implicated in lung carcinogenesis and, potentially, the maintenance of the malignant phenotype in these tumors. Mutations in ras and B-raf genes have been described in lung cancer, representing one of the few examples of tandem mutations in a signaling cascade. As a result, numerous approaches to inhibiting this pathway in lung cancer have been explored in the past decade. The most promising approach to date appears to be the inhibition of mitogen-activated ERK kinase or MEK. In this review, the potential utility of MEK inhibitors in the therapy of lung cancer is discussed.

Raf kinase as a target for anticancer therapeutics

The Ras-Raf-MEK-ERK (ERK) pathway is a logical therapeutic target because it represents a common downstream pathway for several key growth factor tyrosine kinase receptors which are often mutated or overexpressed in human cancers. Although considered mainly growth-promoting, in certain contexts, this pathway also seems to be apoptosis-suppressing. Several novel agents targeting this pathway have now been developed and are in clinical trials. One of the most interesting new agents is BAY 43-9006. Although initially developed as a Raf kinase inhibitor, it can also target several other important tyrosine kinases including VEGFR-2, Flt-3, and c-Kit, which contributes to its antiproliferative and antiangiogenic properties. To date, encouraging results have been seen with BAY 43-9006, particularly in renal cell cancers which are highly vascular tumors. This review will provide an overview of the ERK signaling pathway in normal and neoplastic tissue, with a specific focus on novel therapies targeting the ERK pathway at the level of Raf kinase.

K-ras as a target for cancer therapy

The central role K-, H- and N-Ras play in regulating diverse cellular pathways important for cell growth, differentiation and survival is well established. Dysregulation of Ras proteins by activating mutations, overexpression or upstream activation is common in human tumors. Of the Ras proteins, K-ras is the most frequently mutated and is therefore an attractive target for cancer therapy. The complexity of K-ras signaling presents many opportunities for therapeutic targeting. A number of different approaches aimed at abrogating K-ras activity have been explored in clinical trials. Several of the therapeutic agents tested have demonstrated clinical activity, supporting ongoing development of K-ras targeted therapies. However, many of the agents currently being evaluated have multiple targets and their antitumor effects may not be due to K-Ras inhibition. To date, no selective, specific inhibitor of K-ras is available for routine clinical use. In this review, we will summarize the structure and function of K-ras with attention to its role in tumorigenesis and discuss the successes and failures of the various strategies designed to therapeutically target this important oncogene.

Molekulare Therapie in der Gastroenterologie und Hepatologie

During recent years, molecular techniques have significantly impacted our understanding and therapeutic concepts in gastrointestinal and liver disease. In a number of diseases, diagnostic work-up includes molecular data that supplements the phenotypical evaluation. This includes monogenic diseases as well as the identification of genetic risk factors (e. g. NOD2/CARD15 mutation in Crohn's disease) and viral disease. Attempts to replace liver transplantation in hereditary liver disease by targeted molecular interventions (e. g. via viral vectors) are still experimental, but the associated techniques have improved considerably. The molecular identification of therapeutic targets was followed by the development of specifically tailored therapeutics. These agents are mainly used in the treatment of chronic inflammatory bowel disease and gastrointestinal tumors.

Phase I and pharmacodynamic study of the oral MEK inhibitor CI-1040 in patients with advanced malignancies

PURPOSE

This phase I study was undertaken to define the toxicity, pharmacokinetics, pharmacodynamics, maximum tolerated dose (MTD), and clinical activity of CI-1040, a small-molecule inhibitor of the dual-specificity kinases MEK(mitogen-activated protein kinase kinase) -1 and MEK2 , in patients with advanced malignancy.

PATIENTS AND METHODS

CI-1040 was tested in multiple daily dosing frequencies administered for 21 days repeated every 28 days leading ultimately to continuous administration, and effect of food on absorption was tested. Single dose and steady-state pharmacokinetics were assessed during cycle 1 and phosphorylated extracellular receptor kinase (pERK) levels were assessed in WBCs and also in tumor tissue from selected patients.

RESULTS

Seventy-seven patients received CI-1040 at dose levels ranging from 100 mg QD to 800 mg tid. Grade 3 asthenia was dose limiting at the highest dose level tested, 800 mg tid administered with food. Ninety-eight percent of all drug-related adverse events were grade 1 or 2 in severity; most common toxicities included diarrhea, asthenia, rash, nausea, and vomiting. Plasma concentrations of CI-1040 and its active metabolite, PD 0184264, increased in a less than dose proportional manner from 100 to 800 mg QD. Administration with a high-fat meal resulted in an increase in drug exposure. The MTD and recommended phase II dose was 800 mg BID administered with food. Sixty-six patients were assessable for response. One partial response was achieved in a patient with pancreatic cancer and 19 patients (28%) achieved stable disease lasting a median of 5.5 months (range, 4 to 17 months). Inhibition of tumor pERK (median, 73%; range, 46% to 100%) was demonstrated in 10 patients.

CONCLUSION

CI-1040 was well tolerated at 800 mg BID administered with food. Both target suppression and antitumor activity were demonstrated in this phase I study.

Targeting signal transduction pathways in colorectal cancer--more than skin deep

Colorectal cancer is the second leading cause of cancer death in the United States. The nihilism that previously often characterized the treatment of patients with this disease has been replaced by a measure of excitement, given recent therapeutic advances. These advances have been stimulated in part through identification of cellular processes characteristic of colorectal cancers that permit therapeutic targeting with favorable therapeutic index. Inhibition of the epidermal growth factor receptor in the clinic has provided proof of principle that interruption of signal transduction cascades in patients with colorectal cancer has therapeutic potential. This experience has also taught us that resistance to such rationally developed targeted therapeutic strategies is common. In this article, we review the role of signal transduction in colorectal cancer, introduce promising molecular targets, and outline therapeutic approaches under development. We will describe the barriers to success, and highlight paradigms to facilitate rapid and successful evaluation of new agents, in a clinical context that has (by virtue of recent clinical successes) become a somewhat crowded playing field.

Intracellular signal transduction pathway proteins as targets for cancer therapy

Circulating cytokines, hormones, and growth factors control all aspects of cell proliferation, differentiation, angiogenesis, apoptosis, and senescence. These chemical signals are propagated from the cell surface to intracellular processes via sequential kinase signaling, arranged in modules that exhibit redundancy and cross talk. This signal transduction system comprising growth factors, transmembrane receptor proteins, and cytoplasmic secondary messengers is often exploited to optimize tumor growth and metastasis in malignancies. Thus, it represents an attractive target for cancer therapy. This review will summarize current knowledge of selected intracellular signaling networks and their role in cancer therapy. The focus will be on pathways for which inhibitory agents are currently undergoing clinical testing. Original data for inclusion in this review were identified through a MEDLINE search of the literature. All papers from 1966 through March 2005 were identified by the following search terms: "signal transduction," "intracellular signaling," "kinases," "proliferation," "growth factors," and "cancer therapy." All original research and review papers related to the role of intracellular signaling in oncogenesis and therapeutic interventions relating to abnormal cell signaling were identified. This search was supplemented by a manual search of the Proceedings of the Annual Meetings of the American Association for Cancer Research, American Society of Clinical Oncology, and the American Association for Cancer Research (AARC)--European Organisation for Research and Treatment of Cancer (EORTC)--National Cancer Institute (NCI) Symposium on New Anticancer Drugs.

Meeting Report: The International Conference on Tumor Progression and Therapeutic Resistance

A multidisciplinary conference was held November 7 to 9, 2004 in Philadelphia, PA to focus on the problem of drug resistance in cancer. A great deal of knowledge is beginning to unravel the complex molecular and cellular changes associated with malignant tumor progression. With this comes many opportunities for therapeutic development. Featuring the latest tools, models, and research findings, this conference which included over 250 members of both academia and industry was a great opportunity to learn and develop new approaches and collaborations. The Keynote speaker was Dr. Robert Horvitz (Massachusetts Institute of Technology), who won the 2002 Nobel Prize in Medicine for his pioneering work on the cell death pathway in Caenorhabditis elegans. Speakers covered various aspects of tumor progression and therapy from simple models to clinical trials.

The MAPK signalling pathways and colorectal cancer

There are three major subfamilies of mitogen-activated protein kinases (MAPK): the extracellular-signal-regulated kinases (ERK MAPK); the c-jun N-terminal kinase or stress-activated protein kinases (JNK or SAPK); and MAPK14. The ERK MAPK pathway is one of the most important for cell proliferation. The MAPK pathways are located downstream of many growth-factor receptors, including that for epidermal growth factor. Overexpression and activation of this receptor are commonly detected in colorectal cancer, and several lines of evidence indicate that overexpression and activation of ERK MAPK play an important part in progression of this cancer. ERK MAPK could be a molecular target for treatment of the disorder. This review focuses on the ERK MAPK signal-transduction pathway, the consequences of its dysregulation in colorectal cancer, and its potential as an approach to cancer treatment. Future challenges for the assessment of these targeted agents in the clinic are also presented.

Enhancement of the therapeutic efficacy of taxol by the mitogen-activated protein kinase kinase inhibitor CI-1040 in nude mice bearing human heterotransplants

Taxol may contribute to intrinsic chemoresistance by activating the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) cytoprotective pathway in human cancer cell lines and tumors. We have previously shown additivity between Taxol and the MEK inhibitor, U0126 in human cancer cell lines. Here, the combination of Taxol with an orally bioavailable MEK inhibitor, CI-1040, was evaluated in human lung tumors heterotransplanted into nude mice. Unlike xenograft models that are derived from cells with multiple genetic alterations due to prolonged passage, heterotransplanted tumor models are more clinically relevant. Combined treatment with both drugs resulted in inhibition of tumor growth in all models and tumor regressions in three of four models tested, supporting our previous observation that Taxol's efficacy is potentiated by MEK inhibition. Concurrent administration was superior to intermittent dosing. Pharmacodynamic assessments of tumors indicated that suppression of MEK was associated with induction of S473 phosphorylated Akt and reduced proliferation in the combination groups relative to single agents, in addition to suppression of fibroblast growth factor-mediated angiogenesis and reduced expression of vascular endothelial growth factor. These findings are significant and indicate that this combination may have broad therapeutic applications in a diverse range of lung tumors with different intrinsic chemosensitivities.

When kinases meet mathematics: the systems biology of MAPK signalling

The mitogen activated protein kinase/extracellular signal regulated kinase pathway regulates fundamental cellular function such as cell proliferation, survival, differentiation and motility, raising the question how these diverse functions are specified and coordinated. They are encoded through the activation kinetics of the pathway, a multitude of feedback loops, scaffold proteins, subcellular compartmentalisation, and crosstalk with other pathways. These regulatory motifs alone or in combination can generate a multitude of complex behaviour. Systems biology tries to decode this complexity through mathematical modelling and prediction in order to gain a deeper insight into the inner works of signalling networks.