Kinase Inhibition with BAY 43–9006 in Renal Cell Carcinoma

Therapeutic considerations in patients with metastatic renal cell carcinoma previously treated with antiangiogenic therapies

The recent application of antiangiogenic therapies has opened a new corridor of treatment in metastatic renal cell carcinoma. These therapies influence intracellular pathways that are important in angiogenesis and tumor progression. Although each of these agents produces objective responses as well as progression-free survival benefits, durable complete responses have not generally been observed, and thus, resistance to these chronic therapies is almost universal. The increasing use and eventual resistance to these agents has defined an increasing population of patients with targeted therapy-refractory disease. However, there are limited clinical and preclinical data to guide treatment decisions for these patients. This review will examine the existing data in this setting, describe ongoing clinical investigations, and discuss challenges unique to this patient population.

How many drug targets are there?

For the past decade, the number of molecular targets for approved drugs has been debated. Here, we reconcile apparently contradictory previous reports into a comprehensive survey, and propose a consensus number of current drug targets for all classes of approved therapeutic drugs. One striking feature is the relatively constant historical rate of target innovation (the rate at which drugs against new targets are launched); however, the rate of developing drugs against new families is significantly lower. The recent approval of drugs that target protein kinases highlights two additional trends: an emerging realization of the importance of polypharmacology, and also the power of a gene-family-led approach in generating novel and important therapies.

Phosphate Recognition in Structural Biology

Drug-discovery research in the past decade has seen an increased selection of targets with phosphate recognition sites, such as protein kinases and phosphatases, in the past decade. This review attempts, with the help of database-mining tools, to give an overview of the most important principles in molecular recognition of phosphate groups by enzymes. A total of 3003 X-ray crystal structures from the RCSB Protein Data Bank with bound organophosphates has been analyzed individually, in particular for H-bonding interactions between proteins and ligands. The various known binding motifs for phosphate binding are reviewed, and similarities to phosphate complexation by synthetic receptors are highlighted. An analysis of the propensities of amino acids in various classes of phosphate-binding enzymes showed characteristic distributions of amino acids used for phosphate binding. This review demonstrates that structure-based lead development and optimization should carefully address the phosphate-binding-site environment and also proposes new alternatives for filling such sites.

Kidney cancer therapy: new perspectives and avenues

Immunotherapy with interleukin-2 and interferon-alpha has been the only viable option in metastatic renal cell cancer for almost two decades. In the last several years, significant advances in the understanding of the underlying biological and molecular mechanisms of renal cell carcinoma, particularly the role of tumour angiogenesis, have led to the identification of rational therapeutic targets and permitted the design of molecularly targeted therapeutics. At present, new compounds targeting specific signalling pathways are available and have successfully passed clinical testing. The use of small molecules, such as multitargeted tyrosine kinase inhibitors, the mTOR inhibitors and monoclonal antibodies, is dramatically changing the existing concepts of systemic treatment for metastatic kidney cancer.

Novel treatment strategies for malignant melanoma: a new beginning?

Malignant melanoma is one of the most common cancer types among the Caucasian population. While the prognosis is excellent for patients diagnosed at an early stage and treated by adequate surgery, unresectable or advanced metastatic diseases shrink the overall survival at 5 years dramatically to less than 10%. For disseminated malignant melanoma, the appropriate systemic medical treatment is still controversial. Fortunately, progress in the molecular biology and in the understanding of pathogenesis has been made recently and should in the near future translate into molecular-based therapeutic strategies. In this review, we briefly describe the status of current treatment strategies and existing standards for malignant melanoma. We will focus on the new and emerging compounds including recent developments of targeted therapy such as antiangiogenic and immunomodulatory drugs, Bcl-2 antisense therapy, raf kinase inhibitors, heat shock protein modulators, anti-cytotoxic T lymphocyte-associated antigen (CTLA)-4 monoclonal antibody and finally PARP and proteasome inhibitors.

Point mutations of protein kinases and individualised cancer therapy

The treatment of cancer is rapidly changing, with an increasing focus on converting our improved understanding of the molecular basis of disease into clinical benefit for patients. Protein kinases that are mutated in cancer represent attractive targets, as they may result in cellular dependency on the mutant kinase or its associated pathway for survival, a condition known as 'oncogene addiction'. Early clinical experiences have demonstrated dramatic clinical benefit of targeting oncogenic mutations in diseases that have been largely resistant to traditional cytotoxic chemotherapy. Further, mutational activation of kinases can indicate which patients are likely to respond to targeted therapeutics. However, these experiences have also illuminated a number of critical challenges that will have to be addressed in the development of effective drugs across different cancers, to fully realise the potential of individualised molecular therapy. This review utilises examples of genetic activation of kinases to illustrate many of the lessons learned, as well as those yet to be implemented.

Non-Rash Skin Toxicities Associated with Novel Targeted Therapies

Many novel targeted agents have emerged against a variety of malignancies. Although papulopustular rash is the most commonly observed side effect associated with many of these agents, several non-rash skin toxicities have been identified that frequently result in the delay or discontinuation of anticancer therapy. These toxicities include skin hyperpigmentation, xerosis, pruritus, hair growth and color abnormalities, periungual and nail alterations, and hand-foot skin reaction. It is important to recognize these toxicities, so that they can be diagnosed early and treatment or dose modification can be initiated, if necessary. This review discusses several non-rash dermatologic toxicities observed with targeted therapeutic agents and guidelines for their diagnosis and treatment.

Mucosal injury from targeted anti-cancer therapy

BACKGROUND

With the increased use of so-called targeted anti-cancer therapies, there has been a change in toxicities that patients are experiencing. As most targeted therapies are given in conjunction with more traditional chemotherapeutic agents, toxicities of these combination therapies are also evolving. Whilst we increasingly understand the mechanisms underlying the toxicities of chemotherapy and radiotherapy, the addition of targeted treatments requires a new understanding of both toxicity and interacting mechanisms.

AIMS

The aims of this review (which formed the basis of an invited plenary lecture at the 2006 Annual conference of the Multinational Association of Supportive Care in Cancer) were to define targeted anti-cancer therapy, to describe its known impact on the mucosa, either alone, or in combination with chemotherapy with or without radiotherapy, and finally to provide an outline for future directions in research into mucosal injury from targeted anti-cancer therapies.

METHODOLOGY

Two separate literature reviews were conducted. The combined reviews produced 700 papers of which approximately 70 were included in the review.

RESULTS

As with mucosal injury (or mucositis) in general, the studies are hampered by a lack of mucosal injury as primary endpoint, and the variable definitions and levels of reporting. The depth to which mucosal injury was studied was also inadequate. However, it is clear that the key to understanding toxicity is to understand the mechanism of action of the drug, from which it should be possible to predict the toxicities that will occur.

CONCLUSIONS

With the increasing use of targeted anti-cancer therapies, mucosal injury, particularly in its manifestations of diarrhoea, and mouth ulcers, is becoming even more prominent. More publications of basic and clinical research in this area is required.

Targeted therapy for renal cell carcinoma: a new therapeutic paradigm

Renal cell carcinoma is the most common tumor of the kidney. It has an unpredictable behavior and poor response to systemic therapy. Developing newer therapy for this disease is a priority considering the high recurrence rate and the small subset of patients who benefit from the use of cytokines such as interferon-alpha or interleukin-2. Identifying molecular targets and targeting various biomarkers has revolutionized the therapeutic approach to advanced and metastatic renal cell carcinoma. Although some of the antiangiogenic agents and receptor tyrosine kinase inhibitors appear promising, further understanding of their mechanism of action and the patient population who would benefit most from such agents is still being explored. As numerous targeted agents are entering the clinical investigation arena in a relatively short period of time, newer challenges in renal cell carcinoma therapeutics are emerging. Some of the future challenges in using targeted antineoplastic agents in renal cell carcinoma will include evaluating their long-term safety and benefit, using the particular drug in the appropriate patient population after appropriate stratification and studying the combination of some of these drugs for synergy or additive effects.

Sorafenib

PURPOSE OF REVIEW

Sorafenib is an oral, multikinase inhibitor that was recently approved for use in metastatic renal cancer. It is currently undergoing investigation in locally advanced renal cancer and in other tumor types.

RECENT FINDINGS

Sorafenib was initially developed as an inhibitor of Raf kinase; however, it has broad spectrum activity against multiple tyrosine kinases, including angiogenic factors VEGFR and PDGFR. Common toxicities experienced with sorafenib include hypertension, hand-foot syndrome, rash, diarrhea and fatigue. Early clinical trials suggested that sorafenib acts as a cytostatic agent, as many patients experienced prolonged disease stabilization but insufficient tumor shrinkage to meet RECIST criteria for response. To assess whether sorafenib's growth inhibition translated into a clinical benefit, a phase II randomized discontinuation trial was designed. This trial demonstrated that sorafenib increased progression-free survival in patients with metastatic renal cell cancer; the phase II data were confirmed in a large international phase III trial.

SUMMARY

In this review, we will discuss the clinical development of sorafenib and its role in the treatment of renal cancer. Additionally, we will highlight critical methods of clinical trial design and biomarker development that contribute to the development of sorafenib.

Inflammation of actinic keratoses subsequent to therapy with sorafenib, a multitargeted tyrosine-kinase inhibitor

The Ras-Raf-MEK-ERK signalling pathway is frequently dysregulated in human malignancies, as is angiogenesis and the vascular endothelial growth factor receptor (VEGF/VEGFR) pathway. These kinases are therefore important anticancer targets. The novel, oral treatment sorafenib (BAY 43-9006), has been shown to be an inhibitor of VEGFR, Raf and platelet-derived growth factor in clinical trials against a variety of cancers, with the greatest activity to date observed in metastatic renal cancer. Although side-effects with this targeted therapy are usually not dose-limiting, they frequently involve the skin, and consist of a maculopapular rash, palmar-plantar dysaesthesia, alopecia and xerosis. In this report, we present two patients in whom treatment with sorafenib resulted in inflammation of actinic keratosis, which in some cases progressed to invasive squamous cell carcinoma. This side-effect is of clinical importance, as early recognition is critical for early treatment and may represent a source of additional morbidity to these patients.

Malignant melanoma: genetics and therapeutics in the genomic era

Cell for cell, probably no human cancer is as aggressive as melanoma. It is among a handful of cancers whose dimensions are reported in millimeters. Tumor thickness approaching 4 mm presents a high risk of metastasis, and a diagnosis of metastatic melanoma carries with it an abysmal median survival of 6-9 mo. What features of this malignancy account for such aggressive behavior? Is it the migratory history of its cell of origin or the programmed adaptation of its differentiated progeny to environmental stress, particularly ultraviolet radiation? While the answers to these questions are far from complete, major strides have been made in our understanding of the cellular, molecular, and genetic underpinnings of melanoma. More importantly, these discoveries carry profound implications for the development of therapies focused directly at the molecular engines driving melanoma, suggesting that we may have reached the brink of an unprecedented opportunity to translate basic science into clinical advances. In this review, we attempt to summarize our current understanding of the genetics and biology of this disease, drawing from expanding genomic information and lessons from development and genetically engineered mouse models. In addition, we look forward toward how these new insights will impact on therapeutic options for metastatic melanoma in the near future.

To predict progression-free survival and overall survival in metastatic renal cancer treated with sorafenib: pilot study using dynamic contrast-enhanced Doppler ultrasound

INTRODUCTION

The objective of this study was to evaluate dynamic contrast-enhanced Doppler ultrasound (DCE-US) with perfusion software (Vascular Recognition Imaging) and contrast agent injection as a predictor of tumour response, progression-free survival (PFS) and overall survival (OS).

PATIENTS AND METHODS

Thirty patients with a metastatic renal cell carcinoma (RCC) already enrolled in a double-blind randomised study were evaluated. Examinations were performed at baseline, and after 3 and 6 weeks on sorafenib or a placebo in patients with tumour targets that were accessible to DCE-US.

RESULTS

A total of 85 examinations were performed, 30 at baseline, 28 at 3 weeks and 27 at 6 weeks. The combination of a decrease in contrast uptake exceeding 10% and stability or a decrease in tumour volume allowed us to discriminate seven good responders and 20 poor responders at 3 weeks. There was a statistically significant difference in PFS (p=10(-4)) and OS (p=10(-4)) between good and poor responders.

CONCLUSION

DCE-US is a new noninvasive imaging technique which might be an effective tool for evaluating antiangiogenic drugs in renal cancer.

Coadministration of Sorafenib with Rottlerin Potently Inhibits Cell Proliferation and Migration in Human Malignant Glioma Cells

Mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) are activated in the majority of gliomas and contribute to tumor cell growth and survival. Sorafenib (Bay43-9006; Nexavar) is a dual-action Raf and vascular endothelial growth factor receptor inhibitor that blocks receptor phosphorylation and MAPK-mediated signaling and inhibits growth in a number of tumor types. Because our initial studies of this agent in a series of glioma cell lines showed only partial growth inhibition at clinically achievable concentrations, we questioned whether inhibition of PKC signaling using the PKC-delta inhibitor rottlerin might potentiate therapeutic efficacy. Proliferation assays, apoptosis induction studies, and Western immunoblot analysis were conducted in cells treated with sorafenib and rottlerin as single agents or in combination. Sorafenib and rottlerin reduced proliferation in all cell lines when used as single agents, and the combination produced marked potentiation of growth inhibition. Flow-cytometric measurements of cells stained with Annexin V-propidium iodide and immunocytochemical assessment of cytochrome c and apoptosis-inducing factor release demonstrated that addition of rottlerin resulted in significantly higher levels of apoptosis than sorafenib alone. In addition, the combination of sorafenib and rottlerin reduced or completely inhibited the phosphorylation of extracellular signal-regulated kinase and Akt and down-regulated cell cycle regulatory proteins such as cyclin-D1, cyclin-D3, cyclin-dependent kinase (cdk)4, and cdk6 in a dose- and time-dependent manner. Our results clearly indicate that inhibition of PKC-delta signaling enhances the antiproliferative effect of sorafenib in malignant human glioma cell lines and support the examination of combinations of signaling inhibitors in these tumors.

Targeted Approaches for Treating Advanced Clear Cell Renal Carcinoma

The mainstay of any curative treatment in renal cell carcinoma (RCC) is surgery. In the case of metastatic disease at presentation, a radical nephrectomy is recommended to good performance status patients prior to the start of cytokine treatment. Interferon (IFN)-a offers in a small but significant percentage of patients advantage in overall survival. Interleukin (IL)-2-based therapy gives similar survival rates. To date, hormonal therapy and chemotherapy do not have a proven impact on survival. Recent insights demonstrate that the majority of clear cell RCC harbor abnormalities of the von Hippel-Lindau (VHL) gene. This gene plays a key role in the stimulation of angiogenesis by vascular endothelial growth factor (VEGF) in this highly vascularized tumor. This opens interesting new treatment strategies including blockade of VEGF with the monoclonal antibody bevacizumab (Avastin) and inhibition of VEGF receptor tyrosine kinases with small oral molecules such as sunitinib (SU11248, Sutent) or PTK787. Likewise, inhibition of the Raf kinase pathway with oral sorafenib (Bay 43-9006, Nexavar) or inhibition of the mTOR pathway with intravenous CCI-779 are under investigation. Preliminary clinical results with all these compounds are promising, and the results of ongoing first-line phase III studies will become available in the next years.

Sorafenib for the Treatment of Renal Cell Carcinoma

Objective:

To summarize the pharmacology, development, and clinical application of sorafenib, a specific tyrosine kinase and vascular growth factor inhibitor, for the treatment of renal cell carcinoma (RCC).

Data Sources:

Clinical literature, including both primary studies and review articles, was obtained by searching MEDLINE (1966–May 2006), using the search terms BAY 43-9006, sorafenib, renal cell carcinoma, and tyrosine kinase inhibitor. Additional information was supplied by the manufacturer, Bayer HealthCare Pharmaceuticals.

Study Selection and Data Extraction:

Review articles, abstracts, and clinical studies related to sorafenib were analyzed. An evaluation of the research exploring sorafenib as a potential therapy for RCC was conducted. Relevant information was then selected and is reviewed in this article.

Data Synthesis:

Knowledge of the cellular abnormalities that can cause solid tumors has led to the development of medications that block these pathways. Sorafenib is an oral tyrosine kinase inhibitor that both blocks the Raf kinase pathway and inhibits vascular growth factors. Phase I and II trials have demonstrated that sorafenib has activity against RCC. Dermatologic reactions (rash, desquamation), fatigue, and hypertension have been the most commonly seen treatment-related adverse events. Sorafenib received FDA approval in December 2005 for treatment of advanced RCC.

Conclusions:

Sorafenib is a novel oral tyrosine kinase inhibitor effective in the treatment of RCC.

Molecular prognostic markers in ovarian cancer: toward patient-tailored therapy

In ovarian cancer the ceiling seems to be reached with chemotherapeutic drugs. Therefore a paradigm shift is needed. Instead of treating all patients according to standard guidelines, individualized molecular targeted treatment should be aimed for. This means that molecular profiles of the distinct ovarian cancer subtypes should be established. Until recently, most studies trying to identify molecular targets were single-marker studies. The prognostic role of key components of apoptotic and prosurvival pathways such as p53, EGFR, and HER2 has been extensively studied because resistance to chemotherapy is often caused by failure of tumor cells to go into apoptosis. However, it is more than likely that different ovarian cancer subtypes with extensive molecular heterogeneity exist. Therefore, exploration of the potential of specific tumor-targeted therapy, based on expression of a prognostic tumor profile, may be of interest. Recently, new profiling techniques, such as DNA and protein microarrays, have enabled high-throughput screening of tumors. In this review an overview of the current status of prognostic marker and molecular targeting research in ovarian cancer, including microarray studies, is presented.

Understanding the Importance of Smart Drugs in Renal Cell Carcinoma

OBJECTIVE

To understand the mode of action of the currently most investigated new drugs in renal cell carcinoma (RCC) and ultimately to analyze what should be the role of the urologist in this new therapeutic era.

METHODS

A comprehensive review of the peer-reviewed literature was performed on the topic of molecular pathways involved in RCC angiogenesis, vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor (VEGFR) and targeted molecular therapy for RCC.

RESULTS

Von Hippel-Lindau (VHL) disease has provided a model for understanding that the early inactivation of the VHL gene was responsible for accumulation of hypoxia-inducible factor and therefore activation of hypoxia-inducible genes such as VEGF, platelet-derived growth factor, erythropoietin, carbonic anhydrase IX and tumor growth factor alpha. The fact that such VHL inactivation also was found in up to 70% of sporadic RCC has been the rationale for developing new drugs targeting VEGF, VEGFR, platelet-derived growth factor receptor and tyrosine kinase receptors that are required for intracellular transduction.

CONCLUSION

Initial results from phase 2 trials in metastatic disease are very promising. There is a strong rationale for initiating adjuvant trials with those kind of agents in patients with high-risk localised tumors. Urologists who have a good understanding of prognostic parameters in localised RCC particularly should be involved in such new approaches.

Mechanisms of Hypertension Associated With BAY 43-9006

Purpose

BAY 43-9006 (sorafenib) is an inhibitor of Raf kinase, the vascular endothelial growth factor (VEGF) receptor-2, and angiogenesis in tumor xenografts. The current study investigated the incidence, severity, and mechanism of blood pressure (BP) elevation in patients treated with BAY 43-9006.

Patients and Methods

Twenty patients received BAY 43-9006 400 mg orally twice daily. BP and heart rate were measured at baseline and then every 3 weeks for 18 weeks. VEGF, catecholamines, endothelin I, urotensin II, renin, and aldosterone were measured at baseline and after 3 weeks of therapy. We assessed vascular stiffness at baseline, after 3 to 6 weeks of therapy, and again after 9 to 10 months of therapy.

Results

Fifteen (75%) of 20 patients experienced an increase of ≥ 10 mmHg in systolic BP (SBP), and 12 (60%) of 20 patients experienced an increase of ≥ 20 mmHg in SBP compared with their baseline value, with a mean change of 20.6 mmHg (P < .0001) after 3 weeks of therapy. There were no statistically significant changes in humoral factors, although there was a statistically significant inverse relationship between decreases in catecholamines and increases in SBP, suggesting a secondary response to BP elevation. Measures of vascular stiffness increased significantly during the period of observation.

Conclusion

Treatment with BAY 43-9006 is associated with a significant and sustained increase in BP. The lack of significant change in circulating factors suggests that these humoral factors had little role in the increase in BP.

Sorafenib: Recent Update on Activity as a Single Agent and in Combination with Interferon-α2 in Patients with Advanced-Stage Renal Cell Carcinoma

Metastatic renal cell carcinoma does not respond favorably to conventional treatment strategies and is not very responsive to cytokine therapy. Therefore, novel targeted treatment approaches have been explored for patients with renal cancer who have chemotherapy-refractory disease. Sorafenib (BAY 43-9006) is a small-molecule inhibitor that has been shown to target members of multiple classes of tyrosine kinases that are known to be involved in tumor cell proliferation and tumor angiogenesis. These kinases include vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, VEGFR-3, platelet-derived growth factor receptor, Flt-3, c-kit, and Raf kinases. Based on the significant improvement in progression-free survival, sorafenib received Food and Drug Administration approval in December 2005 for the treatment of renal cell carcinoma. In combination studies, sorafenib with other antitumor agents has demonstrated significant clinical activity in patients with renal cell carcinoma. As discussed in this mini-review, the clinical potency of sorafenib as a single agent or in combination with other antitumor agents is being evaluated in several ongoing clinical trials in patients with renal carcinoma.

Kidney cancer: identification of novel targets for therapy

Kidney cancer, although relatively rare when compared to other malignancies, occurs not uncommonly in patients with renal disease and is often discovered incidentally during the initial nephrologic work-up, or by the savvy clinician who is familiar with the paraneoplastic signs. While surgical approaches are generally curative when the disease is confined to the kidney, one-third of the cases that present in the metastatic form and require conventional medical therapy are associated with a truly dismal patient survival rate. In light of the emerging knowledge of the molecular mechanisms of kidney cancer oncogenesis, several novel and promising therapeutic approaches are emerging. In this review, we summarize the current state of kidney cancer diagnosis and therapy, as well as some of the novel treatments that capitalize on those newly elucidated molecular pathways that are deranged in this disease.

Novel inhibitors of B-RAF based on a disubstituted pyrazine scaffold. Generation of a nanomolar lead

B-RAF, a serine/threonine kinase, plays an important role in the development of certain classes of cancer, especially melanoma. As a result of high-throughput screening of a 23,000 compound library, 2-(3,4,5-trimethoxyphenylamino)-6-(3-acetamidophenyl)pyrazine, 1, was identified as a low micromolar (IC(50) = 3.5 microM) B-RAF inhibitor. This compound was chosen as the starting point of a program aimed at producing potent inhibitors of B-RAF. We have synthesized a series of 40 novel compounds, which involved extensive modifications to the 2-(3,4,5-trimethoxyphenylamino) moiety (ring A) of 1. Their biological profiles against isolated B-RAF and mutated B-RAF in a cellular assay have been determined. These efforts led to the identification of two compounds exhibiting activities lower than 800 nM against B-RAF.

Lymphocyte therapy of renal cell carcinoma

During the past 20 years, there has been considerable interest in lymphocyte therapy as a treatment for renal cell carcinoma. There is no therapeutic role for B-lymphocyte therapy, but their products, monoclonal antibodies, now have widespread clinical applications. The major types of autologous lymphocyte therapy that have been explored in clinical trials are cytotoxic lymphokine-activated killer cells, which are natural killer cells and T-cells that have been stimulated in vitro by interleukin-2 or other similar cytokines; cytotoxic and noncytotoxic tumor infiltrating lymphocytes, which are T-cells derived from tumor tissue; other tumor antigen-stimulated T-lymphocytes derived from regional lymph nodes or peripheral blood; and noncytotoxic lymphocytes of the memory/helper phenotype. More recently, allogeneic immune therapy using nonmyeloablative hematopoietic stem cell transplant and/or donor lymphocyte therapy has also shown promise.

The role of Mcl-1 downregulation in the proapoptotic activity of the multikinase inhibitor BAY 43-9006

BAY 43-9006, a multikinase inhibitor that targets Raf, prevents tumor cell proliferation in vitro and inhibits diverse human tumor xenografts in vivo. The mechanism of action of BAY 43-9006 remains incompletely defined. In the present study, the effects of BAY 43-9006 on the antiapoptotic Bcl-2 family member Mcl-1 were examined. Treatment of A549 lung cancer cells with BAY 43-9006 diminished Mcl-1 levels in a time- and dose-dependent manner without affecting other Bcl-2 family members. Similar BAY 43-9006-induced Mcl-1 downregulation was observed in ACHN (renal cell), HT-29 (colon), MDA-MB-231 (breast), KMCH (cholangiocarcinoma), Jurkat (acute T-cell leukemia), K562 (chronic myelogenous leukemia) and MEC-2 (chronic lymphocytic leukemia) cells. Mcl-1 mRNA levels did not change in BAY 43-9006-treated cells. Instead, BAY 43-9006 enhanced proteasome-mediated Mcl-1 degradation. This Mcl-1 downregulation was followed by mitochondrial cytochrome c release and caspase activation as well as enhanced sensitivity to other proapoptotic agents. The caspase inhibitor Boc-D-fmk inhibited BAY 43-9006-induced caspase activation but not cytochrome c release. In contrast, Mcl-1 overexpression inhibited cytochrome c release and other features of BAY 43-9006-induced apoptosis. Conversely, Mcl-1 downregulation by short hairpin RNA enhanced BAY 43-9006-induced apoptosis. Collectively, these findings demonstrate that drug-induced Mcl-1 downregulation contributes to the proapoptotic effects of BAY 43-9006.

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.

Safety, pharmacokinetic, and antitumor activity of SU11248, a novel oral multitarget tyrosine kinase inhibitor, in patients with cancer

PURPOSE

To establish the safety, pharmacokinetics, and recommended dose of sunitinib, a novel oral multitargeting tyrosine kinase inhibitor with antiangiogenic and antitumor properties, in patients with advanced malignancies.

PATIENTS AND METHODS

Sunitinib was given orally for 4 weeks every 6 weeks.

RESULTS

Twenty-eight patients received doses ranging from 15 to 59 mg/m2 (ranging from 50 mg every other day to 150 mg/d). Dose-limiting toxicities reported at the maximum-tolerated doses > or = 75 mg/d were reversible grade 3 fatigue, grade 3 hypertension, and grade 2 bullous skin toxicity. Therefore, the recommended dose was 50 mg/d. At this dose, the main adverse effects were sore mouth, edema, and thrombocytopenia. Hair discoloration and yellow coloration of the skin were observed at doses > or = 50 mg/d. Pharmacokinetic data indicate that potentially active target plasma concentrations > or = 50 ng/mL can be achieved with moderate interpatient variability and a long half-life compatible with a single daily dosing. Six objective responses were observed in three renal cell carcinomas, one neuroendocrine tumor, one stromal tumor, and one unknown primary adenocarcinoma patient. At higher doses (> or = 75 mg/d), tumor responses were often associated with reduced intratumoral vascularization and central tumor necrosis, eventually resulting in organ perforation or fistula.

CONCLUSION

At the dose of 50 mg/d (4 weeks on, 2 weeks off), sunitinib displays manageable toxicity. Antitumor activity supports further studies in patients with renal cell carcinoma, gastrointestinal, neuroendocrine, and stromal tumors. Future studies may consider including prospective imaging techniques such as high frequency ultrasound to monitor tumor density.

Second-line strategies for metastatic renal cell carcinoma: classics and novel approaches

OBJECTIVES

Renal cell carcinoma is an aggressive malignancy with a high propensity for both early and metachronous regional and distant metastasis. While surgical resection is the mainstay of therapy for patients with localized disease, the prognosis for patients with distant metastasis is poor with a 5-year survival rate of less than 10%. Response rates to first-line immunotherapy or immunochemotherapy range from 10-35%; responses achieved are predominantly partial remissions of short duration. Until today, there is no standard therapeutic procedure for the growing number of patients who relapse following first-line therapy and desire further active treatment.

MATERIALS AND METHODS

This article reviews classic and recent publications about second- and third-line approaches, their potential efficacy and toxicity.

RESULTS

Several novel approaches have raised well-founded hope. Especially the application of monoclonal antibodies targeting VEGF signalling as well as different receptor tyrosine kinase inhibitors have the potential to change the face of second-line treatment of patients with metastatic RCC. Both groups of agents are focused in current phase III trials, either as mono- and/or combination therapy.

CONCLUSIONS

Until today, second-line treatment of patients with metastatic RCC progressing under therapy with biological response modifiers remains an unresolved issue. The results of ongoing clinical trials evaluating novel targeted approaches can be expected with suspense.

Synergistic inhibition of human melanoma proliferation by combination treatment with B-Raf inhibitor BAY43-9006 and mTOR inhibitor Rapamycin

BACKGROUND

Targeted inhibition of protein kinases is now acknowledged as an effective approach for cancer therapy. However, targeted therapies probably have limited success because cancer cells have alternate pathways for survival and proliferation thereby avoiding inhibition. We tested the hypothesis that combination of targeted agents would be more effective than single agents in arresting melanoma cell proliferation.

METHODS

We evaluated whether BAY43-9006, an inhibitor of the B-Raf kinase, and rapamycin, an inhibitor of the mTOR kinase, would inhibit serum-stimulated proliferation of human melanoma cell lines, either alone or in combination. Proliferation was measured by quantitating melanoma cell numbers with a luciferase for ATP. Phosphorylation of proteins downstream of targeted kinase(s) was assayed by immunoblots. Statistical significance was determined with the Student-T test. Isobologram analysis was performed to distinguish additive versus synergistic effects of combinations of drugs.

RESULTS

Serum-stimulated proliferation of multiple human melanoma cell lines was inhibited by BAY43-9006 and by rapamycin. Melanoma cells containing the B-Raf mutation V599E were more sensitive than cells with wild-type B-raf to 10 nM doses of both BAY43-9006 and rapamycin. Regardless of B-Raf mutational status, the combination of low dose rapamycin and BAY43-9006 synergistically inhibited melanoma cell proliferation. As expected, rapamycin inhibited the phosphorylation of mTOR substrates, p70S6K and 4EBP1, and BAY43-9006 inhibited phosphorylation of ERK, which is dependent on B-Raf activity. We also observed unexpected rapamycin inhibition of the phosphorylation of ERK, as well as BAY43-9006 inhibition of the phosphorylation of mTOR substrates, p70S6K and 4EBP1.

CONCLUSION

There was synergistic inhibition of melanoma cell proliferation by the combination of rapamycin and BAY 43-9006, and unexpected inhibition of two signaling pathways by agents thought to target only one of those pathways. These results indicate that combinations of inhibitors of mTOR and of the B-raf signaling pathways may be more effective as a treatment for melanoma than use of either agent alone.

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.

Novel treatments for metastatic renal cell carcinoma

The mainstay of any curative treatment in renal cell carcinoma (RCC) is surgery. In case of metastatic disease at presentation a radical nephrectomy is recommended to good performance status patients prior to start of interferon-alfa treatment. Interferon-alpha (IFN-alpha) offers in a small but significant percentage of patients advantage in overall survival; interleukin-2 (IL-2) based therapy gives similar survival rates. To date hormonal and chemotherapy do not have a proven impact on survival. The recent new insights in the molecular biology of clear RCC has revealed a key-role for vascular endothelial growth factor (VEGF) in the stimulation of angiogenesis in this highly vascularized tumour. This opens interesting new treatment strategies including: blockage of VEGF with the monoclonal antibody bevacizumab and inhibition of VEGF receptor tyrosine kinases (with small oral molecules such as SU11248 or PTK787). Likewise, inhibition of the Raf kinase pathway (with oral Bay 43-9006) or inhibition of the mTOR pathway (with i.v. CCI-779) are under investigation. Preliminary clinical results with all these compounds are interesting and the results of ongoing phase III studies will become available in the next years.

Cutaneous side-effects of kinase inhibitors and blocking antibodies

Although kinase inhibitors raise hope for people with cancer, patients and their clinicians are commonly confronted with the cutaneous side-effects that are associated with the use of these drugs. This review is the result of collaborations between dermatologists, medical oncologists, and pathologists, and discusses the cutaneous side-effects seen after treatment with the inhibitors of epidermal-growth-factor receptor (EGFR), imatinib, sorafenib, and sunitinib. Some of the side-effects caused by these agents are very distressing, partly because they are chronic owing to the long duration of treatment. Therefore, patients need early and appropriate dermatological management. Moreover, several studies have reported a link between the antitumour efficacy of EGFR inhibitors and cutaneous side-effects. Elucidation of this connection could lead to the identification of crucial predictive factors for tumour response.

Apoptosis induced by the kinase inhibitor BAY 43-9006 in human leukemia cells involves down-regulation of Mcl-1 through inhibition of translation

BAY 43-9006 is a kinase inhibitor that induces apoptosis in a variety of tumor cells. Here we report that treatment with BAY 43-9006 results in marked cytochrome c and AIF release into the cytosol, caspase-9, -8, -7, and -3 activation, and apoptosis in human leukemia cells (U937, Jurkat, and K562). Pronounced apoptosis was also observed in blasts from patients with acute myeloid leukemia. These events were accompanied by ERK1/2 inactivation and caspase-independent down-regulation of Mcl-1. Inducible expression of a constitutively active MEK1 construct did not prevent Mcl-1 down-regulation, suggesting that this event is not related to MEK/ERK pathway inactivation. Furthermore, BAY 43-9006 did not induce major changes in Mcl-1 mRNA levels monitored by real-time PCR or Mcl-1 promoter activity demonstrated by luciferase reporter assays, but it did enhance Mcl-1 down-regulation in actinomycin D-treated cells. Inhibition of protein synthesis by cycloheximide or proteasome function with MG132 and pulse-chase studies with [35S]methionine demonstrated that BAY 43-9006 did not diminish Mcl-1 protein stability, nor did it enhance Mcl-1 ubiquitination, but instead markedly attenuated Mcl-1 translation in association with the rapid and potent dephosphorylation of the eIF4E translation initiation factor. Finally, ectopic expression of Mcl-1 in leukemic cells markedly inhibited BAY 43-9006-mediated cytochrome c cytosolic release, caspase-9, -7, and -3 activation, as well as cell death, indicating that Mcl-1 operates upstream of cytochrome c release and caspase activation. Together, these findings demonstrate that BAY 43-9006 mediates cell death in human leukemia cells, at least in part, through down-regulation of Mcl-1 via inhibition of translation.

Novel treatment strategies in clear-cell metastatic renal cell carcinoma

Metastatic renal-cell carcinoma (mRCC) is highly resistant to cytotoxic agents or hormones and is currently mainly treated with cytokine-based therapy. Transient responses and moderate survival advantages have been achieved in a subset of patients with these aspecific biological response modifiers. Side-effects are considerable, especially with high-dose interleukin (IL)-2. Efforts made in the field of specific immunotherapy have focused on optimization of dendritic cell vaccination and on administration of monoclonal antibodies, either cold (unconjugated) or hot (radioactively labeled). Furthermore, allogeneic bone marrow transplantation is able to induce remissions but, regrettably, is related to substantial morbidity and mortality. Neutralization of the biological activity of some immunosuppressive cytokines produced by RCC (IL-6 and tumor necrosis factor-alpha) with monoclonal antibodies is currently under investigation. Insights gained into the processes and pathways underlying carcinogenesis have led to the development of new treatment strategies. These treatments can be used for clear cell RCC, since they focus on blocking gene products that are upregulated by mutations in the von Hippel-Lindau gene. Specific strategies include anti-vascular endothelial growth factor monoclonal antibody (bevacizumab) or inhibition of its receptor kinases (oral SU11248 or PTK787), or targeting the Raf kinase pathway (by BAY 43-9006) or the mammalian target of rapamycin (mTOR) pathway (by CCI-779). Early clinical results are promising, but their place in the treatment of RCC has to be determined.

Role of novel targeted therapies in the clinic

The number and variety of novel, molecular-targeted agents offers realistic hope for significant advances in cancer treatment. The potential of these new treatment approaches is unquestionable, but the reality is something that only thorough clinical evaluation and experience can reveal. Clinical experience of targeted therapies is at an early stage but it is likely that we will have an increasing number of treatment options available to us in the near future. This manuscript explores our current understanding of molecular-targeted therapies and considers: What approach should be used? (single vs multitarget agents); When should they be administered? (identifying the optimal point for intervention); How should they be used? (monotherapy or combination therapy regimens); and Who should we be giving them to? (acknowledging the need for patient selection).

Melanoma genetics and the development of rational therapeutics

Melanoma is a cancer of the neural crest-derived cells that provide pigmentation to skin and other tissues. Over the past 4 decades, the incidence of melanoma has increased more rapidly than that of any other malignancy in the United States. No current treatments substantially enhance patient survival once metastasis has occurred. This review focuses on recent insights into melanoma genetics and new therapeutic approaches being developed based on these advances.

Angiogenesis and lung cancer: prognostic and therapeutic implications

Lung cancer is the most common cause of cancer death worldwide, with most patients dying with metastatic disease. The prognosis for the majority of patients remains poor. It is evident that advances in the treatment of this and other tumor types will require new approaches, and recent research has focused on molecular-targeted therapies. A key therapeutic strategy is inhibition of specific processes essential for tumor vascular development (a concept known to be beneficial in colorectal cancer) and a range of such antiangiogenic agents are currently in development. The most promising of these target the proangiogenic vascular endothelial growth factor (VEGF), either by preventing VEGF-receptor binding or inhibiting downstream receptor signaling. However, other more direct approaches against tumor vasculature are also in development. Since antiangiogenic agents often exert an indirect, cytostatic effect, many are being evaluated in combination with conventional chemotherapies in order to optimize the anticancer effects of both strategies. Additionally, the combination of several antiangiogenic agents is also being explored. This has become possible given the large number of agents currently available. As part of this evaluation process, the assessment of surrogate markers of target inhibition and treatment effect is ongoing in the hope of identifying reliable surrogate markers to aid the development of this new generation of anticancer agents.

A critical function for B-Raf at multiple stages of myelopoiesis

Raf kinases play an integral role in the classic mitogen-activated protein (MAP) kinase (Raf/MEK/extracellular signal-related kinase [ERK]) intracellular signaling cascade, but their role in specific developmental processes is largely unknown. Using a genetic approach, we have identified a role for B-Raf during hematopoietic progenitor cell development and during megakaryocytopoiesis. Fetal liver and in vitro embryonic stem (ES) cell-derived myeloid progenitor development is quantitatively impaired in the absence of B-Raf. Biochemical data suggest that this phenotype is due to the loss of a normally occurring rise in B-Raf expression and associated ERK1/2 activation during hematopoietic progenitor cell formation. However, the presence of B-raf-/- ES cell-derived myeloid progenitors in the bone marrow of adult chimeric mice indicates the lack of an obligate cell-autonomous requirement for B-Raf in myeloid progenitor development. The lack of B-Raf also impairs megakaryocytopoiesis. Thrombopoietin (Tpo)-induced in vitro expansion of ES cell-derived megakaryocyte-lineage cells fails to occur in the absence of B-Raf. Moreover, this quantitative in vitro defect in megakaryocyte-lineage expansion is mirrored by chimeric mice data that show reduced B-raf-/- genotype contribution in megakaryocytes relative to its contribution in myeloid progenitors. Together, these data suggest that B-Raf plays a cell-autonomous role in megakaryocytopoiesis and a permissive role in myeloid progenitor development.

Small-Molecule Kinase-Inhibitor Target Assessment

The identification of the cellular targets of small-molecule protein kinase inhibitors is a significant hurdle to assessing their therapeutic potential for many diseases. Here we review several biochemical and genetics-based approaches to identifying inhibitor targets. We also describe a chemical-genomics approach to kinase-inhibitor target identification and validation that matches transcriptional signatures elicited by a drug of unknown specificity and those elicited by highly specific pharmacological inhibition of engineered candidate kinase targets.

Raf Kinase Inhibitors in Oncology

The importance of the MAP kinase pathway, which includes the kinases Raf, MEK1/2, and ERK1/2, for the proliferation and survival of tumor cells recently increased with the discovery of activating BRAF mutations in human tumors. Therefore, in addition to a role in controlling tumors with Ras mutations and activated growth factor receptors, inhibitors of Raf kinase may harbor therapeutic potential in tumors carrying a BRAF oncogene. A variety of agents have been discovered to interfere with Raf kinase, including antisense oligonucleotides and small molecules. These inhibitors prevent the expression of Raf protein, block Ras/Raf interaction, or obstruct its kinase activity. Raf inhibitors that are currently undergoing clinical evaluation show promising signs of anti-cancer efficacy with a very tolerable safety profile. Clinically most advanced is the Raf inhibitor BAY 43-9006, which recently entered phase III clinical testing. This review addresses the rationale for targeting Raf kinase and the current status of various pharmacological approaches.

The role of B-RAF in melanoma

Melanoma is a form of skin cancer that has a poor prognosis and which is on the rise in Western populations. If detected early, it is easily treated by surgical excision. However, once melanoma metastasises it is notoriously resistant to existing therapies and for many patients the outlook is dismal. Thus a full description of melanoma etiology and a full understanding of the genetic lesions that underlie this disease is required to allow us to develop new and effective therapeutic strategies for its treatment. RAF proteins are a family of serine/threonine-specific protein kinases that form part of a signalling module that regulates cell proliferation, differentiation and survival. In mammals there are three isoforms, A-RAF, B-RAF and C-RAF, and recently it was shown that the B-RAF isoform is mutated in a high proportion of melanomas. In light of these exciting findings, we review what we have learned about B-RAF and its role in cutaneous melanoma.

Genetic basis of cancer of the kidney: disease-specific approaches to therapy

Studies during the past two decades have shown that kidney cancer is not a single disease; it is made up of a number of different types of cancer that occur in this organ. Clear cell renal carcinoma is characterized by mutation of the VHL gene. The VHL gene product forms a heterotrimeric complex with elongin C, elongin B, and Cul-2 to target hypoxia-inducible factors 1 and 2alpha for ubiquitin-mediated degradation. VHL-/- clear cell renal carcinoma overexpresses epidermal growth factor receptor and transforming growth factor alpha. Both hypoxia-inducible factor 1alpha and the epidermal growth factor receptor are potential therapeutic targets in clear cell renal carcinoma. Studies of the hereditary form of renal cell carcinoma (RCC) associated with hereditary papillary renal carcinoma (HPRC) determined that the c-Met proto-oncogene on chromosome 7 is the gene for HPRC and for a number of sporadic papillary RCCs. The HPRC c-Met mutations are activating mutations in the tyrosine kinase domain of the gene. The gene for a new form of hereditary RCC (Birt Hogg Dubé syndrome) associated with cutaneous tumors, lung cysts, and colon polyps or cancer has recently been identified. Studies are currently under way to determine what type of gene BHD is and how damage to this gene leads to kidney cancer. Individuals affected with hereditary leiomyomatosis renal cell carcinoma are at risk for the development of cutaneous leiomyomas, uterine leiomyomas (fibroids), and type 2 papillary RCC. The HLRC gene has been found to be the Krebs cycle enzyme, fumarate hydratase. Studies are under way to understand the downstream pathway of this cancer gene.