Pharmacokinetics and bioequivalence of sunitinib and Sutent® in Chinese healthy subjects: an open-label, randomized, crossover study

Purpose: The purpose of this study was to examine the pharmacokinetics (PK), bioequivalence and safety of generic sunitinib and its original product Sutent® in healthy Chinese subjects through a phase-I clinical trial. Methods: The study selected two groups of 24 healthy Chinese subjects in a 1:1 ratio through random allocation. Each participant received either 12.5 mg of sunitinib or Sutent® per cycle. A total of 15 different time points were employed for blood sample collection during each cycle. Furthermore, a comprehensive assessment of the drugs' safety was consistently maintained throughout the trial. Results: The average adjusted geometric mean ratios (GMR) (90% CI) for the primary PK parameters Cmax, AUC0-t and AUC0-∞ were 97.04% (93.06%-101.19%), 98.45% (93.27%-103.91%) and 98.22% (93.15%-103.56%), respectively. The adjusted GMRs for essential pharmacokinetic (PK) parameters all met the requirements for bioequivalence, with values within the acceptable range of 80%-125%. In addition, the two drugs showed comparable results for the other PK parameters. These results indicate that the two drugs were bioequivalent. Furthermore, both drugs showed well safety. Conclusion: The research results proved that the PK and safety profiles of sunitinib in healthy Chinese subjects were comparable to those of Sutent®. These results advocate the clinical application of generic sunitinib as a potential alternative to original product Sutent® in the treatment of certain medical conditions.

Small Molecule Kinase Inhibitor Drugs (1995-2021): Medical Indication, Pharmacology, and Synthesis

The central role of dysregulated kinase activity in the etiology of progressive disorders, including cancer, has fostered incremental efforts on drug discovery programs over the past 40 years. As a result, kinase inhibitors are today one of the most important classes of drugs. The FDA approved 73 small molecule kinase inhibitor drugs until September 2021, and additional inhibitors were approved by other regulatory agencies during that time. To complement the published literature on clinical kinase inhibitors, we have prepared a review that recaps this large data set into an accessible format for the medicinal chemistry community. Along with the therapeutic and pharmacological properties of each kinase inhibitor approved across the world until 2020, we provide the synthesis routes originally used during the discovery phase, many of which were only available in patent applications. In the last section, we also provide an update on kinase inhibitor drugs approved in 2021.

Sunitinib in patients with imatinib-resistant gastrointestinal stromal tumor: A single center experience study

AIM

The outcome of patients with advanced gastrointestinal stromal tumor (GIST) has improved with the use of imatinib. Despite high response rates with this drug resistance eventually develops in nearly all patients. We present an analysis of prospectively collected data on sunitinib efficacy and safety in patients with imatinib-resistant GIST.

SUBJECTS AND METHODS

Between November 2006 and October 2007, patients with GIST were accrued in an approved sunitinib patient access protocol. Key eligibility criteria included tumor resistance to imatinib and/or patient intolerance to this drug. Patients received sunitinib at a starting dose of 50 mg once daily for 4 weeks in a 6 week cycle, with standardized dose modification titrated to toxicity. Patients were continued on sunitinib until disease progression or unacceptable toxicity. The endpoints were safety, overall survival (OS) and objective response rate (ORR).

RESULTS

Fifteen patients, all of whom had imatinib resistance and none intolerance, with median age of 48 (26-69) years, were treated on the protocol. The most common sites of primary disease were small intestine (40%), stomach (26.7%) and retroperitoneal (26.7%). A median of 10 (1-47) cycles of sunitinib were delivered, 9 (60%) patients required dose reductions due to toxicity whereas dose delay of > 2 weeks was required in only one (6.7%) patient. There were no toxicity-related drug discontinuations. Hypothyroidism (n = 4; 26.7%) and hand-foot syndrome (n = 3; 20%) were the most common toxicities. There were no complete and 4 (26.7%) partial responses while prolonged disease stability was seen in 8 (53.3%) patients. At a median follow-up of 81 months in surviving patients, the median progression-free and overall survivals were 15.5 and 18.7 months, respectively.

CONCLUSIONS

Sunitinib appears to be an effective and well-tolerated treatment for Indian patients with imatinib-resistant GIST with outcomes similar to that reported previously. Adverse effects can be reasonably well managed using a dose modification strategy.

In-silico identification of inhibitors against mutated BCR-ABL protein of chronic myeloid leukemia: a virtual screening and molecular dynamics simulation study

Aberrant and proliferative expression of the oncogene BCR-ABL in the bone marrow cells had been proven as the prime cause of chronic myeloid leukemia (CML). It has been established that tyrosine kinase domain of BCR-ABL protein is a potential therapeutic target for the treatment of CML. Imatinib is considered as a first-generation drug that can inhibit the enzymatic action by inhibiting the ATP binding with BCR-ABL protein. Later on, insensitivity of CML cells towards Imatinib has been observed may be due to mutation in tyrosine kinase domain of the ABL receptor. Subsequently, some other second-generation drugs have also been reported viz. Baustinib, Nilotinib, Dasatinib, Ponatinib, Bafetinib, etc., which can able to combat against mutated domain of ABL tyrosine kinase protein. By taking into account of bioavailability and resistance developed, there is an utmost need to find some more inhibitors for the mutated ABL tyrosine kinase protein. For virtual screening, a data-set has been generated by collecting the all available drug like natural compounds from ZINC and Drug Bank databases. Comparative docking analysis was also carried out on the active site of ABL tyrosine kinase receptor with reported reference inhibitors. Molecular dynamics simulation of the best screened interacting complex was done for 50 ns to validate the stability of the system. These selected inhibitors were further validated and analyzed through pharmacokinetics properties and series of ADMET parameters by in silico methods. Considering the above said parameters proposed molecules are concluded as potential leads for drug designing pipeline against CML.

Identification of Dual Natural Inhibitors for Chronic Myeloid Leukemia by Virtual Screening, Molecular Dynamics Simulation and ADMET Analysis

Chronic myeloid leukemia (CML) is a disease of bone marrow stem cells caused by excessive growth and accumulation of granulocytes in the blood. Aberrant expression of the BCR-ABL proteins in bone marrow stem cells have found out in 95 % cases of CML. Tyrosine Kinase domains (SH2 and SH3) of BCR-ABL proteins are the potent targets to inhibit the process. Initially, imatinib is preferred as an efficient inhibitor to control functional activity of disease. Recently, it has been reported that the advanced stage of CML developed resistance against imatinib. In continuation, dasatinib is the first drug to combat against this disease by targeting multiple receptors and proven better as compared to imatinib. Here, an attempt has been made to identify similar analogs of dasatinib. Virtual screening was performed against various natural compound databases to get some potent natural compounds which are able to inhibit more than one receptor. Binding affinity of screened natural compounds was compared with some of the well-known inhibitors like imatinib, dasatinib, nilotinib etc., by analyzing their docking score and binding efficiency with the receptor. Stability of the best ligand-receptor complex was checked by performing 10 ns molecular dynamics simulation. ADMET properties of the obtained screened compounds were analyzed to check drug like property. Based on the aforementioned analysis, it has been suggested that these screened potent compounds are capable to inhibit multiple receptor proteins like ABL and SRC and consequently combat against the deadly disease CML.

YL529, a novel, orally available multikinase inhibitor, potently inhibits angiogenesis and tumour growth in preclinical models

BACKGROUND AND PURPOSE

Targeted chemotherapy using small-molecule inhibitors of angiogenesis and proliferation is a promising strategy for cancer therapy.

EXPERIMENTAL APPROACH

YL529 was developed via computer-aided drug design, de novo synthesis and high-throughput screening. The biochemical, pharmacodynamic and toxicological profiles of YL529 were investigated using kinase and cell viability assays, a mouse tumour cell-containing alginate bead model, a zebrafish angiogenesis model and several human tumour xenograft models in athymic mice.

KEY RESULTS

In vitro, YL529 selectively inhibited the activities of VEGFR2/VEGFR3 and serine/threonine kinase RAF kinase. YL529 inhibited VEGF165 -induced phosphorylation of VEGFR2, as well as the proliferation, migration, invasion and tube formation of human umbilical vascular endothelial cells. It also significantly blocked vascular formation and angiogenesis in the zebrafish model. Moreover, YL529 strongly attenuated the proliferation of A549 cells by disrupting the RAF/mitogen-activated protein (MAP) or extracellular signal-regulated kinase (Erk) kinase (MEK) kinase kinase/MAPK pathway. Oral administration of YL529 (37.5-150 mg(-1) ·kg(-1) ·day(-1) ) to nude mice bearing established tumour xenografts significantly prevented the growth (60-80%) of A549, SPC-A1, A375, OS-RC-2 and HCT116 tumours without detectable toxicity. YL529 markedly reduced microvessel density and increased tumour cell apoptosis in the tumours formed in mice inoculated with the lung cancer cells, SPC-A1 and A549, and the colon carcinoma cells, HCT116.

CONCLUSIONS AND IMPLICATIONS

YL529, an orally active multikinase inhibitor, shows therapeutic potential for solid tumours, and warrants further investigation as a possible anticancer agent.

Inhibitory effects of SU5416, a selective vascular endothelial growth factor receptor tyrosine kinase inhibitor, on experimental corneal neovascularization

PURPOSE

Treatment of neovascularization in ocular diseases with vascular endothelial growth factor (VEGF) inhibition shows promising results. SU5416 is a low-molecular-weight tyrosine kinase inhibitor. It selectively inhibits the membrane-bound tyrosine kinase activity of VEGF-2 receptor (Flk-1/KDR) and blocks the intracellular signaling process. The aim of this study was to evaluate the effect of SU5416 on corneal neovascularization.

METHODS

Corneas were cauterized with silver nitrate/potassium nitrate sticks in 20 eyes of 20 BALB/C mice. In the study group (n = 10), SU5416 (25 mg/kg) dissolved in dimethyl sulfoxide was given as an intraperitoneal injection in a single daily dose for 7 days. The other group of 10 mice given intraperitoneal dimethyl sulfoxide alone served as a control group. After 7 days, corneal neovascularization was evaluated using photographs captured by fluorescein angiography. Colored photographs were taken by a biomicroscope with a digital camera. Data were expressed as mean neovascular length and mean number of new vessels for each animal. The values were computed and compared between the groups.

RESULTS

The mean burn stimulus intensities were not different between the groups. In the study group, the mean length of the vessels and the mean number of vessels were 0.49 ± 0.05 and 11.20 ± 1.69 mm, respectively. In the control group, the mean length of the vessels and the mean number of the vessels were 0.89 ± 0.11 and 17.80 ± 1.03 mm, respectively. There is a statistically significant difference in the mean length and the mean number of new vessels between the study and control groups (p < 0.001).

CONCLUSION

Selective inhibition of VEGFR-2 (Flk-1/KDR) tyrosine kinase with SU5416 was shown to have an inhibitory effect on corneal neovascularization in this animal model. VEGFR-2 (Flk-1/KDR) tyrosine kinase inhibition may represent a different pathway for treatment of the neovascularization process in ocular pathologies. Fluorescein angiography photographs of new vessels on the cornea may provide a better evaluation of neovascularization than colored images in animal models.

Mechanisms of resistance to imatinib and sunitinib in gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST), the most common mesenchymal neoplasm of the GI tract and one of the most common sarcomas, is dependent on the expression of the mutated KIT or platelet-derived growth factor receptor in most cases. Imatinib mesylate potently abrogates the effects of KIT signaling by directly binding into the ATP-binding pocket of the kinase. It is becoming increasingly apparent that the binding affinity of imatinib for the receptor is dependent on the type and location of mutation. Within KIT, patients whose tumor has an exon 9 mutation are treated by many clinicians with higher doses of imatinib than those patients with mutations within exon 11. Additionally, there are over 400 unique mutations within exon 11 that may have distinctly different binding affinity for imatinib as well as other kinases. Secondary KIT mutations generally occur at a codon where imatinib binds resulting in KIT reactivation and resistance. Sunitinib malate, a second-generation KIT inhibitor is active in imatinib-resistant disease and is FDA-approved for use in this setting. In this review, we describe the biology of the genes and gene mutations responsible for GIST and discuss known and potential clinical implications.

Strategies for kinome profiling in cancer and potential clinical applications: chemical proteomics and array-based methods

Kinases are key enzymes involved in deregulated signal transduction associated with cancer development and progression. The advent of personalized medicine drives the development of new diagnostic tools for patient stratification and therapy selection Ginsburg and Willard (Transl Res 154:277-287, 2009). Since deregulation of kinase-mediated signal transduction is implied in tumorigenesis, the analysis of all kinases (the kinome) active in a particular tumor may yield tumor-specific information on aberrant cell signalling pathways. Tumor tissue kinase activity profiles may correlate with response to therapy and therefore may be used for future therapy selection. In this Trend paper we describe peptide array and mass spectrometry-based technologies and new developments for kinome profiling, and we present an outlook towards future implementation of therapy selection based on kinome profiling in clinical practice.

Diagnosis and multi-disciplinary management of hepatic metastases from gastrointestinal stromal tumour (GIST)

AIM

To explore the present application of diagnosis and management of hepatic metastases from GIST.

METHODS

We performed a systematic review of the literature for studies concerning hepatic metastases from GIST. A literature search was performed using the Medline/PubMed databases to identify publications relevant to the review published from January 1998 to December 2008. Totally 113 relevant articles were retrieved. Abstracts from recent ASCO symposia were hand searched for relevant articles. After the primary filtration, articles on review and with repetitive content were excluded. The articles on clinical research, which were issued in authorized journals, were selected. At last, totally 69 articles were included for review.

FINDINGS

The rate of liver metastases was reported as 15.9% in primary GISTs. The recurrence rate following surgical resection for hepatic metastases from GIST had been reported as 70-77%. For metastatic GIST patients with tyrosine kinase inhibitor (TKI) treatment, it demonstrated rates of CR, PR and SD respectively of 5.84%, 50.7%, and 32.4%. Combining repeated surgery with TKI treatment, R0/R1 resection rates range in various series between 48 and 82%. For those patients with unresectable disease confined to the liver or unable to tolerate liver resection due to co-morbidity or advanced age, RFA, HACE, TKI therapy, or even liver transplantation, can also improve survival.

CONCLUSIONS

The liver is a common metastatic site for gastrointestinal stromal tumour (GIST). Appropriate initial evaluation remains paramount for selecting the correct management strategy. Multi-disciplinary management (which includes pathology, medical oncology, surgical oncology, and imaging expertise) of this disease is important for both curative and palliative treatment in these patients. Combining repeated surgery with TKI treatment may be the most effective management for GIST patients with liver metastases.

Antiangiogenic drugs: current knowledge and new approaches to cancer therapy

Angiogenesis--process of new blood-vessel growth from existing vasculature--is an integral part of both normal developmental processes and numerous pathologies such as cancer, ischemic diseases and chronic inflammation. Angiogenesis plays a crucial role facilitating tumour growth and the metastatic process, and it is the result of a dynamic balance between proangiogenic and antiangiogenic factors. The potential to block tumour growth and metastases by angiogenesis inhibition represents an intriguing approach to the cancer treatment. Angiogenesis continues to be a topic of major scientific interest; and there are currently more antiangiogenic drugs in cancer clinical trials than those that fit into any other mechanistic category. Based on preclinical studies, researchers believe that targeting the blood vessels which support tumour growth could help treatment of a broad range of cancers. Angiogenic factors or their receptors, endothelial cell proliferation, matrix metalloproteinases or endothelial cell adhesion, are the main targets of an increasing number of clinical trials approved to test the tolerance and therapeutic efficacy of antiangiogenic agents. Unfortunately, contrary to initial expectations, it has been described that antiangiogenic treatment can cause different toxicities in cancer patients. The purpose of this article is to provide an overview of current attempts to inhibit tumour angiogenesis for cancer therapy.

Management of hypertension in angiogenesis inhibitor-treated patients

BACKGROUND

Hypertension (HTN) is one of the most frequent side-effects of systemic inhibition of vascular endothelial growth factor (VEGF) signaling. Its incidence and severity are dependent on the type of drugs, dose, and schedule used. The recognition of this side-effect is an important issue because poorly controlled HTN could lead to serious cardiovascular events. On another hand, HTN induced by anti-VEGF agents maybe a predictive factor of oncologic response. Knowledge of this clinical toxicity and/or therapeutic target or novel biomarker of drug activity can aid clinicians choosing the optimal and least toxic regimen suitable for an individual patient.

METHODS

A Medline search was carried out using the following criteria: (i) all Medline listings as of 1 January 2000 with abstracts, (ii) English language, and (iii) Humans. The following phrases were used to query the database: ('hypertension', OR 'blood pressure') AND ('anti-VEGF' OR 'VEGF inhibition' OR 'bevacizumab' OR 'sunitinib' OR 'sorafenib' OR 'VEGF Trap'). The references of each article identified were carefully reviewed for additional reference.

RESULTS

Lifestyle modification should be encouraged. However, these nonpharmacologic strategies are not always suitable to patients with altered performance status related to metastatic cancer necessitating early drug intervention. Only one randomized study showed a beneficial effect of a calcium channel blocker use to prevent or minimize HTN secondary to antiangiogenic therapy. Nitrates looks as effective in controlling such side-effect.

CONCLUSIONS

No clear recommendation for an antihypertensive agent can be made in this context because there is a lack of controlled studies addressing the subject. Blood pressure-lowering drugs should be individualized to the patient's clinical circumstances and angiogenic inhibitors should be withheld only from patients who experienced hypertensive crisis.

Uncovering Pandora's vase: the growing problem of new toxicities from novel anticancer agents. The case of sorafenib and sunitinib

As newer, molecularly targeted, anticancer drugs are entering clinical practice, a wide array of previously unrecognised and ill defined side effects of these drugs are increasingly observed. Sorafenib and sunitinib are two of these novel agents, acting on tumour angiogenesis as well as on other key proliferative pathways; recently approved for the treatment of advanced kidney cancer, they may cause peculiar cutaneous, vascular and mucosal toxicities, including hand-foot skin reaction, skin rash, hypertension and GERD-like oesophagitis/gastritis. In this review, we shall deal with these poorly recognised, but sometimes extremely distressing, toxicities; pathophysiologic mechanisms will be discussed and suggestions for treatment of each toxicity will be proposed, based on the few pieces of evidence available and, especially, on our empirical experience.

Sunitinib in the management of gastrointestinal stromal tumours (GISTs)

AIMS

Gastrointestinal stromal tumours (GISTs) are rare mesenchymal neoplasms of the gut with a 5-year survival of approximately 50%. Surgery remains the treatment of choice in resectable disease, with conventional chemotherapy largely ineffective. Over 90% of GIST possesses mutations in the c-KIT oncogene, producing an overactive tyrosine kinase, which may be driving the malignant process. Imatinib inhibits the aberrant tyrosine kinase and imatinib therapy in metastatic disease has shown significant clinical benefit. However, resistance typically develops within 2 years, with the need for further therapy. This article aims to introduce the reader to a new development in cancer therapeutics.

METHODS

A literature search was performed using the MEDLINE database to identify publications relevant to the review. References within these articles were used to expand the search. Abstracts from recent ASCO symposia were hand searched for relevant articles.

FINDINGS

Sunitinib (SU11248) is a novel multi-targeted tyrosine kinase inhibitor with activity not only against the receptor tyrosine kinase product of c-KIT but also other cell-signalling pathways that may be relevant in GIST; FLT3, platelet-derived growth receptor (PDGFR) and vascular endothelial growth factor receptor (VEGFR). Two Phase II trials and one Phase III trial have investigated the activity of sunitinib against imatinib-resistant GIST. Early results showed significant benefits in time to disease progression that led to licensing of the drug in America and more recently in Europe. A Phase III trial comparing dose-increased imatinib and sunitinib in progressed GIST is currently planned.

CONCLUSIONS

Initial clinical results with sunitinib are promising and suggest a future role. Further studies are needed before sunitinib can be recommended for the routine treatment of imatinib-refractory GIST.

Molecular approaches to resolve diagnostic dilemmas: the case of gastrointestinal stromal tumor and leiomyosarcoma

Gastrointestinal stromal tumors (GISTs) and leiomyosarcomas (LMSs) are common types of mesenchymal tumors that may present a diagnostic challenge. GISTs have frequent overexpression of Kit and often encode for mutation of the KIT oncogene. In addition, patients usually experience a favorable response to targeted therapy with imatinib mesylate (Gleevec®, STI-571), but not cytotoxic chemotherapy. Up to 5% of GISTs can be completely negative for Kit on immunohistochemistry. Conversely, LMSs may rarely express Kit, but are virtually never associated with an activating KIT mutation, and are often effectively treated with cytotoxic chemotherapy but are resistant to imatinib. To aid in resolution of this clincal challenge, we performed a whole-genome gene expression study on 71 well-defined GIST and LMS samples with development of a robust, novel approach to molecular classification discussed herein.

AMG 706, an oral, multikinase inhibitor that selectively targets vascular endothelial growth factor, platelet-derived growth factor, and kit receptors, potently inhibits angiogenesis and induces regression in tumor xenografts

The growth of solid tumors is dependent on the continued stimulation of endothelial cell proliferation and migration resulting in angiogenesis. The angiogenic process is controlled by a variety of factors of which the vascular endothelial growth factor (VEGF) pathway and its receptors play a pivotal role. Small-molecule inhibitors of VEGF receptors (VEGFR) have been shown to inhibit angiogenesis and tumor growth in preclinical models and in clinical trials. A novel nicotinamide, AMG 706, was identified as a potent, orally bioavailable inhibitor of the VEGFR1/Flt1, VEGFR2/kinase domain receptor/Flk-1, VEGFR3/Flt4, platelet-derived growth factor receptor, and Kit receptors in preclinical models. AMG 706 inhibited human endothelial cell proliferation induced by VEGF, but not by basic fibroblast growth factor in vitro, as well as vascular permeability induced by VEGF in mice. Oral administration of AMG 706 potently inhibited VEGF-induced angiogenesis in the rat corneal model and induced regression of established A431 xenografts. AMG 706 was well tolerated and had no significant effects on body weight or on the general health of the animals. Histologic analysis of tumor xenografts from AMG 706-treated animals revealed an increase in endothelial apoptosis and a reduction in blood vessel area that preceded an increase in tumor cell apoptosis. In summary, AMG 706 is an orally bioavailable, well-tolerated multikinase inhibitor that is presently under clinical investigation for the treatment of human malignancies.

Pediatric KIT wild-type and platelet-derived growth factor receptor alpha-wild-type gastrointestinal stromal tumors share KIT activation but not mechanisms of genetic progression with adult gastrointestinal stromal tumors

Fewer than 15% of gastrointestinal stromal tumors (GIST) in pediatric patients harbor KIT or platelet-derived growth factor receptor alpha (PDGFRA) mutations in contrast to a mutation rate of 80% in adult GISTs. However, some therapeutic inhibitors of KIT have efficacy in pediatric GIST, suggesting that KIT may, nevertheless, play an important role in oncogenesis. In adult GIST, characteristic cytogenetic changes occur during progression to malignancy. A better understanding of mechanisms of genetic progression and KIT and PDGFRA transforming roles in pediatric GIST might facilitate treatment advances. KIT and PDGFRA mutation analysis was done in 27 pediatric GISTs. The activation status of KIT, PDGFRA, and downstream signaling intermediates was defined, and chromosomal aberrations were determined by single nucleotide polymorphism assays. Mutations in KIT or PDGFRA were identified in 11% of pediatric GISTs. KIT and the signaling intermediates AKT and mitogen-activated protein kinase were activated in pediatric GISTs. In particular, most pediatric KIT-wild-type GISTs displayed levels of KIT activation similar to levels in adult KIT-mutant GISTs. Pediatric KIT-wild-type GISTs lacked the typical cytogenetic deletions seen in adult KIT-mutant GISTs. Notably, most pediatric KIT-wild-type GISTs progress to malignancy without acquiring large-scale chromosomal aberrations, which is a phenomenon not reported previously in malignant solid tumors. KIT activation levels in pediatric KIT-wild-type GISTs are comparable with those in KIT-mutant GISTs. Therapies that inhibit KIT activation, or crucial KIT signaling intermediates, should be explored in pediatric KIT-wild-type GIST.

Imatinib-refractory gastrointestinal stromal tumors: the clinical problem and therapeutic strategies

Treatment of gastrointestinal stromal tumor (GIST) is a paradigm for targeted therapy. These mesenchymal tumors are refractory to standard chemotherapy and radiation therapy. Targeted therapy has successfully exploited the oncologic drivers of GIST--the tyrosine kinases, KIT, and the platelet-derived growth factor receptor. Therapy with imatinib has dramatically altered the natural history of patients with advanced GIST. However, patients are developing resistance to imatinib and thus presenting with a major clinical challenge. Alternative approaches to imatinib-refractory disease are needed. Newer approaches using biologic data regarding the mechanisms of resistance are being tested alone or in combination with imatinib and are the focus of this review. Effective novel agents for imatinib-refractory GIST used as single agents or in combination with imatinib will likely become future regimens to be tested in first-line metastatic disease and in the adjuvant setting.

The potential of antiangiogenic therapy in non-small cell lung cancer

The long-term prognosis for patients with advanced non-small cell lung cancer (NSCLC) remains poor despite the availability of several cytotoxic chemotherapy regimens. The use of targeted therapies, particularly those against the key mediator of angiogenesis vascular endothelial growth factor (VEGF), has the potential to improve outcomes for NSCLC patients. Bevacizumab, a recombinant humanized monoclonal anti-VEGF antibody, is the most clinically advanced antiangiogenic agent in NSCLC. In a phase III study, bevacizumab showed significantly improved overall and progression-free survival when used in combination with standard first-line chemotherapy in patients with advanced NSCLC. Bevacizumab was generally well tolerated in patients with NSCLC; however, tumor-related bleeding adverse events have been noted in some patients, predominantly those with squamous cell histology or centrally located tumors. Several small-molecule VEGF receptor tyrosine kinase inhibitors have also shown promise in phase I and II trials in NSCLC. This review summarizes the most important findings of angiogenesis inhibitors in NSCLC and discusses the potential for the use of these novel agents in different settings of NSCLC.

Mechanisms of adverse effects of anti-VEGF therapy for cancer

Advances in understanding the role of vascular endothelial growth factor (VEGF) in normal physiology are giving insight into the basis of adverse effects attributed to the use of VEGF inhibitors in clinical oncology. These effects are typically downstream consequences of suppression of cellular signalling pathways important in the regulation and maintenance of the microvasculature. Downregulation of these pathways in normal organs can lead to vascular disturbances and even regression of blood vessels, which could be intensified by concurrent pathological conditions. These changes are generally manageable and pose less risk than the tumours being treated, but they highlight the properties shared by tumour vessels and the vasculature of normal organs.

Sunitinib: a novel tyrosine kinase inhibitor. A brief review of its therapeutic potential in the treatment of renal carcinoma and gastrointestinal stromal tumors (GIST)

Sunitinib malate is a novel oral multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activities. Sunitinib was recently approved in first-line treatment for patients with advanced renal cell carcinoma (RCC) and for the treatment of patients with gastrointestinal stromal tumors (GIST) after disease progression or intolerance to imatinib mesylate therapy. We report the very interesting results of the phase II trials after cytokin failure and of the randomized recent trial of sunitinib versus cytokin-based therapy in first-line treatment for patients with metastatic RCC, as well as the promising results of the recent trials on patients with GIST after disease progression or intolerance to imatinib mesylate therapy. Oral sunitinib demonstrates a high level of efficacy with acceptable tolerability with the 50 mg daily for 4 weeks followed by 2 weeks off schedule; a continuous schedule could be of interest. Hypertension and asthenia are the most common side effects with sunitinib. Regardless of these encouraging results, studies investigating sunitinib in first-line treatment (for patients with GIST), adjuvant and neoadjuvant settings are awaited, as well as trials using sunitinb in combination with chemotherapy or other targeted therapies. Clinical trials investigating sunitinib in other tumor types are ongoing.

New molecular targets and novel agents in the treatment of advanced urothelial cancer

Standard cytotoxic regimens for metastatic bladder cancer, such as gemcitabine/cisplatin or methotrexate, vinblastine, doxorubicin, and cipslatin (M-VAC), yield impressive overall response rates of 45% to 70%. Despite this, long-term, disease-free, overall survival is rare, and most patients eventually succumb to the disease. Much work has been undertaken evaluating the clinical and molecular factors associated with progressive bladder cancer, and this has, in turn, led to the development of both novel targets and agents. These include standard cytotoxics such as pemetrexed, an antifolate and antimetabolite agent that has demonstrated an overall response rate of 30% in early studies, and small-molecule tyrosine kinase inhibitors such as sunitinib, which will be studied as maintenance therapy for patients who respond to first-line chemotherapy. The evaluation of new targets and new agents in the midst of limited patient, logistical, and financial resources will be one of the more difficult challenges for investigators over the next several years.

The role of VEGF and EGFR inhibition: implications for combining anti-VEGF and anti-EGFR agents

Multiple cellular pathways influence the growth and metastatic potential of tumors. This creates heterogeneity, redundancy, and the potential for tumors to bypass signaling pathway blockade, resulting in primary or acquired resistance. Combining therapies that inhibit different signaling pathways has the potential to be more effective than inhibition of a single pathway and to overcome tumor resistance. Vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) inhibitors have become key therapies in several tumor types. Close relationships between these factors exist: VEGF signaling is up-regulated by EGFR expression and, conversely, VEGF up-regulation independent of EGFR signaling seems to contribute to resistance to EGFR inhibition. Therefore, inhibition of both pathways could improve antitumor efficacy and overcome resistance to EGFR inhibition. Preclinical studies have shown that VEGF and EGFR inhibitors can have additive effects and that combined inhibition is effective in EGFR inhibitor-resistant cell lines. Clinical trials have also produced promising data: combining the anti-VEGF monoclonal antibody bevacizumab with the anti-EGFR antibody cetuximab or the EGFR tyrosine kinase inhibitor erlotinib increases benefit compared with either of these anti-EGFR agents alone or combined with chemotherapy. The potential of this novel approach to anticancer therapy will be elucidated by large, ongoing clinical trials.

Sorafenib and sunitinib in the treatment of advanced non-small cell lung cancer

Despite the optimization of chemotherapy regimens, treatment outcomes for advanced non-small cell lung cancer (NSCLC) are still considered to be disappointing. Thus, clinical research of new treatment strategies is warranted. Several targeted agents have been introduced into clinical trials in NSCLC, but to date, only a few of these new agents can offer hope of a substantial impact on the natural history of the disease. One of the main reasons for the failure of several clinical trials of targeted therapy in lung cancer is that there is multilevel cross-stimulation among the targets of the new biological agents along several pathways of signal transduction that lead to neoplastic events; blocking only one of these pathways, as most first-generation targeted agents do, allows others to act as salvage or escape mechanisms for cancer cells. Sorafenib and sunitinib are two oral multitargeted receptor tyrosine kinase inhibitors. Sorafenib is a multikinase inhibitor that inhibits the kinase activity of both C-RAF and B-RAF and targets the vascular endothelial growth factor receptor family (VEGFR-2 and VEGFR-3) and platelet-derived growth factor receptor family (PDGFR-beta and stem cell factor receptor [KIT]). Sunitinib is a multitargeted inhibitor of PDGFR, KIT, fms-like tyrosine kinase 3, and VEGFR. The kinases targeted and inhibited by sorafenib and sunitinib directly and indirectly regulate tumor growth, survival, and angiogenesis, and this might be expected to result in broad antitumor efficacy. Sorafenib and sunitinib have been approved by the U.S. Food and Drug Administration for the treatment of metastatic renal cell carcinoma; sunitinib has also been approved for the treatment of gastrointestinal stromal tumors. Their mechanism of action, preclinical data, and phase II studies suggest efficacy in the treatment of advanced NSCLC.

Hepatic artery chemoembolization for 110 gastrointestinal stromal tumors: response, survival, and prognostic factors

BACKGROUND

The efficacy of hepatic artery chemoembolization (HACE) was evaluated for gastrointestinal stromal tumors (GISTs) metastatic to the liver.

METHODS

Records for patients with metastatic GIST who underwent HACE between January 1993 and March 2005 were reviewed and cross-sectional images were used to determine objective tumor response. Progression-free survival in the liver (PFS-liver) and overall survival (OS) were calculated with the Kaplan-Meier method. Patient, tumor, and treatment variables were analyzed to identify factors influencing survival.

RESULTS

Of the 110 patients identified, the radiologic response to HACE could be evaluated in 85 patients, 12 of whom (14%) demonstrated partial responses, 63 of whom (74%) demonstrated stable disease, and 10 of whom (12%) demonstrated progressive disease. PFS-liver rates were 31.2%, 8.2%, and 5.4% at 1, 2, and 3 years, respectively; the median PFS time was 8.2 months. OS rates were 62% at 1 year, 32% at 2 years, and 20% at 3 years; the median OS time was 17.2 months. Patients who had >5 liver metastases and received only 1 HACE treatment were found to have a shorter PFS compared with patients with fewer metastases or those who received > or =2 HACE sessions. Extensive liver involvement, the presence of extrahepatic metastases, and progression of liver disease after HACE were associated with poor OS. Use of imatinib prolonged OS time.

CONCLUSIONS

HACE produced a durable tumor response or disease stabilization in the majority of patients with GISTs metastatic to liver. Extent of liver disease, presence of extrahepatic disease, number of embolization treatments, and use of imatinib were found to have prognostic influence on PFS, OS, or both.

Hypothyroidism in patients with metastatic renal cell carcinoma treated with sunitinib

Sunitinib is an inhibitor of the vascular endothelial growth factor and platelet-derived growth factor receptors, and it has antitumor activity in metastatic renal cell carcinoma and gastrointestinal stromal tumors. To further investigate the fatigue associated with sunitinib therapy, thyroid function tests were performed on patients with metastatic renal cell carcinoma who were receiving sunitinib. Seventy-three patients with metastatic renal cell carcinoma were treated with sunitinib at the Cleveland Clinic Taussig Cancer Center, and 66 of them had thyroid function test results available. Fifty-six (85%) of the 66 patients had one or more abnormality in their thyroid function test results, consistent with hypothyroidism, and 47 (84%) of the 56 patients with abnormal thyroid function tests had signs and/or symptoms possibly related to hypothyroidism. Thyroid hormone replacement was undertaken in 17 patients, and symptoms improved in nine of them. Thyroid function test abnormalities appear to be common in patients with metastatic renal cell carcinoma treated with sunitinib, and routine monitoring is warranted.

Targeting angiogenesis for the treatment of sarcoma

PURPOSE OF REVIEW

More therapeutic options are needed for bone and soft tissue sarcomas, especially for patients with metastatic disease. Recent randomized clinical trials conducted in colon, breast and lung cancer have shown the anti-vascular endothelial growth factor agent, bevacizumab, alone or in combination with chemotherapy, improves response and survival. Preclinical studies have demonstrated the anti-tumor effects of varied anti-angiogenic agents in sarcoma cell lines and tumor models.

RECENT FINDINGS

Preclinical studies in sarcomas have evaluated the role of targeted agents including platelet-derived growth factor, matrix metalloproteinases, urokinase receptor and varied small-molecule tyrosine kinase inhibitors. Novel angiogenesis inhibitors are being studied in the treatment of sarcoma, including monoclonal antibodies against vascular endothelial growth factor, cis- and trans-retinoic acids, thalidomide, and tyrosine kinase inhibitors. Phase I, II and III clinical trials continue to evaluate these agents alone, in combinations together and combined with standard chemotherapy. We review herein the preclinical rationale and clinical trial results of anti-angiogenesis therapy in the treatment of soft tissue and bone sarcoma.

SUMMARY

Preclinical mechanistic study and clinical trials are continuing in order to evaluate the therapeutic role and ultimately validate the efficacy of the varied anti-angiogenesis agents in soft tissue and bone sarcoma.

Sunitinib malate

Recently, there has been a growing interest in understanding the role of receptor tyrosine kinases (RTK), such as vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), stem cell factor receptor (KIT), and fms-like tyrosine kinase 3 (FLT3), in promoting tumor angiogenesis, tumor growth and metastasis. Sunitinib (sunitinib malate; SU11248; SUTENT; Pfizer Inc, New York, NY, USA) is a novel, orally bio-available, oxindole, multi-targeted tyrosine kinase inhibitor with high binding affinity for VEGFR and PDGFR which has shown anti-tumor and anti-angiogenic activities. This drug recently received approval from the US Food and Administration (FDA) in two indications simultaneously: advanced renal cell carcinoma (adRCC) and gastrointestinal stromal tumors (GIST), in patients who are resistant or intolerant to the treatment with imatinib. The present article reviews the recent pharmacologic and clinical data related to the use of this new promising drug in the field of oncology.

Tyrosine kinase inhibitors of vascular endothelial growth factor receptors in clinical trials: current status and future directions

Angiogenesis plays a central role in the process of tumor growth and metastatic dissemination. The vascular endothelial growth factor (VEGF) family of peptide growth factors and receptors are key regulators of this process. Agents directed either against VEGF or VEGF receptors (VEGFRs) have been developed. The tyrosine kinase inhibitors of VEGFRs are low-molecular-weight, ATP-mimetic proteins that bind to the ATP-binding catalytic site of the tyrosine kinase domain of VEG-FRs, resulting in blockade of intracellular signaling. Several of these agents are currently in different phases of clinical development. Large randomized phase III trials have demonstrated the efficacy of sunitinib and sorafenib in the treatment of patients affected by gastrointestinal stromal tumors and renal cancer refractory to standard therapies, respectively. Positive results also have been reported with the combination of ZD6474 and chemotherapy in previously treated non-small cell lung cancer patients. For other agents, such as vatalanib, contrasting outcomes in metastatic colorectal cancer patients have been reported: the final results of these trials are expected in 2006. However, several key questions remain to be addressed, regarding the choice of an adequate dose or schedule, the presence of "off-target" effects, the safety of long-term administration, and the research of new clinical end points or methodological approaches for the optimal clinical development of these agents.

Anti-angiogenic drugs: from bench to clinical trials

Angiogenesis, the generation of new capillaries through a process of pre-existing microvessel sprouting, is under stringent control and normally occurs only during embryonic and post-embryonic development, reproductive cycle, and wound repair. However, in many pathological conditions (solid tumor progression, metastasis, diabetic retinopathy, hemangioma, arthritis, psoriasis and atherosclerosis among others), the disease appears to be associated with persistent upregulated angiogenesis. The development of specific anti-angiogenic agents arises as an attractive therapeutic approach for the treatment of cancer and other angiogenesis-dependent diseases. The formation of new blood vessels is a complex multi-step process. Endothelial cells resting in the parent vessels are activated by an angiogenic signal and stimulated to synthesize and release degradative enzymes allowing endothelial cells to migrate, proliferate and finally differentiate to give rise to capillary tubules. Any of these steps may be a potential target for pharmacological intervention. In spite of the disappointing results obtained initially in clinical trials with anti-angiogenic drugs, recent reports with positive results in phases II and III trials encourage expectations in their therapeutic potential. This review discusses the current approaches for the discovery of new compounds that inhibit angiogenesis, with emphasis on the clinical developmental status of anti-angiogenic drugs.

Gastrointestinal stromal tumors: Imatinib and beyond

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. Clinicians previously classified GISTs as "benign" or "malignant," but now place resected tumors in risk categories that are based on size and mitotic rate. Historically, GIST patients were managed with surgery alone, as chemotherapy and radiotherapy have minimal activity in this disease. In the pre-imatinib era, patients with recurrent or metastatic disease generally did very poorly. GIST therapy was revolutionized following the discovery of oncogenic mutations in the c-kit gene, as well as in the platelet-derived growth factor receptor. Subsequently, it has been confirmed that the KIT receptor tyrosine kinase is both a diagnostic marker and a useful therapeutic target in GIST. Imatinib, a potent inhibitor of KIT activity, is now standard front-line therapy for advanced GIST. With the introduction of imatinib, there have been dramatic improvements in response rates, time to progression, and survival. Imatinib is now being investigated and shows promise in the neoadjuvant and adjuvant settings. Unfortunately, many patients eventually recur or progress during imatinib therapy. For these patients, imatinib dose escalation and/or surgical evaluation are appropriate. Additionally, a novel tyrosine kinase inhibitor such as SU11248 (sunitinib) is a reasonable option for progressive, imatinib-resistant disease. With the identification of other downstream pathways, several other promising therapies are under current investigation either alone or in combination with imatinib and surgery.

Efficacy of the kinase inhibitor SU11248 against gastrointestinal stromal tumor mutants refractory to imatinib mesylate

PURPOSE

The majority of gastrointestinal stromal tumors harbor mutations in the receptor tyrosine kinases KIT or platelet-derived growth factor receptor A (PDGFRA), and respond to treatment with the tyrosine kinase inhibitor imatinib. Some tumors, however, show primary resistance to imatinib treatment, and most others become resistant during treatment. The most common mechanism of imatinib resistance involves specific mutations in the kinase domains of KIT or PDGFRA. We tested the activity of SU11248, an orally active small-molecule tyrosine kinase inhibitor, to inhibit important imatinib-resistant KIT and PDGFRA mutants.

EXPERIMENTAL DESIGN

Primary imatinib-resistant tumor cells and cell lines expressing clinically identified imatinib-resistant KIT-V654A, KIT-T670I, or PDGFRA-D842V mutant isoforms were evaluated for sensitivity to SU11248 by Western immunoblotting and proliferation assays. Three patients with the KIT-V654A mutation were treated with SU11248.

RESULTS

Based on ex vivo assays, SU11248 potently inhibits KIT kinase activity of V654A and T670I mutants and suppresses proliferation of the cells expressing these mutations. Sensitivity of KIT-V654A and KIT-T670I mutants to SU11248 was confirmed using cell lines expressing these mutants. In contrast, SU11248 did not potently inhibit the PDGFRA-D842V mutant. In agreement with these results, two of the three imatinib-resistant patients with the KIT-V654A mutation responded to SU11248 treatment.

CONCLUSIONS

These studies suggest that SU11248 may be a useful therapeutic agent to treat gastrointestinal stromal tumors harboring the imatinib-resistant KIT-V654A or KIT-T670I mutations, but it has no effect on the activity of the PDGFRA-D842V mutant. Specific kinase inhibitors should be designed to inhibit the constitutive activating PDGFRA mutation at codon 842.

Inhibition of endothelial cell proliferation and angiogenesis by orlistat, a fatty acid synthase inhibitor

Orlistat, an antiobesity drug, is cytostatic and cytotoxic to tumor cells. The antitumor activity of orlistat can be attributed to its ability to inhibit the thioesterase domain of fatty acid synthase (FAS). The objective of the present study was to test the effect of orlistat on endothelial cell proliferation and angiogenesis. Orlistat inhibits endothelial cell FAS, blocks the synthesis of fatty acids, and prevents endothelial cell proliferation. More significantly, orlistat inhibits human neovascularization in an ex vivo assay, which suggests that it may be useful as an antiangiogenic drug. The mechanism of these effects can be traced to the fact that orlistat prevents the display of the vascular endothelial growth factor (VEGF) receptor (VEGFR2/KDR/Flk1) on the endothelial cell surface. Thus, orlistat is an antiangiogenic agent with a novel mechanism of action.

Combined surgical and molecular therapy: the gastrointestinal stromal tumor model

OBJECTIVE

This review describes the pathologic and epidemiologic features of gastrointestinal stromal tumor (GIST) as well as the contemporary management of this tumor. The integration of surgery and treatment with targeted molecular agents in the treatment of GIST is highlighted.

SUMMARY BACKGROUND DATA

GIST is the most common mesenchymal tumor of the gastrointestinal tract. Its cellular origin from the interstitial cell of Cajal and distinctness from smooth muscles tumors were only recently appreciated. The discovery of the centrality of KIT proto-oncogene mutations in the pathogenesis of this tumor, and the development of imatinib mesylate, a specific inhibitor of KIT tyrosine kinase function have revolutionized the treatment of GIST.

METHODS

We conducted a review of the English literature on GIST. The pathology, epidemiology, diagnosis, and treatment of this tumor are summarized with particular emphasis on recent developments in the field.

RESULTS

GIST is a rare tumor that usually arises from the stomach or small intestine. It is characterized by immunohistochemical staining for KIT. Treatment of primary localized tumors is surgical. The benefit of adjuvant treatment with the KIT tyrosine kinase inhibitor imatinib is the subject of investigation. The treatment of unresectable, recurrent, or metastatic GIST is primarily imatinib treatment. The integration of surgery or ablative modalities is often employed, particularly when all disease is amenable to gross resection or destruction, or when GIST becomes resistant to imatinib. Newer tyrosine kinase inhibitors, such as sunitinib are the subject of ongoing investigation.

CONCLUSIONS

The treatment paradigm for GIST has required the integration of surgery and molecular therapy and this will likely serve as a paradigm for the treatment of other solid tumors as targeted agents are developed.

Management of metastatic gastrointestinal stromal tumour in the Glivec era: a practical case-based approach

Gastrointestinal stromal tumour is now recognized as a distinct pathological malignancy and has received much attention over the last few years. Despite almost universal resistance to chemotherapy, a novel therapy, Imatinib, which targets the KIT receptor, has changed the natural history of this disease. We have audited the first 26 consecutive patients with gastrointestinal stromal tumour treated over 4 years at a single institution. A practical guide to the management of common toxicities and drug resistance is reported with a review of the published reports. Many of the strategies used are likely to be widely applicable to the use of targeted therapies in other malignancies.

Antiangiogenic cancer therapies get their act together: current developments and future prospects of growth factor- and growth factor receptor-targeted approaches

Targeting the vascular endothelial growth factor (VEGF) in combination with standard chemotherapy has recently proved successful in the treatment of different types of advanced cancer. The achievements of combinatorial anti-VEGF monoclonal antibody bevacizumab (BEV) renewed the confidence in targeted antiangiogenic approaches to constitute a complementary therapeutic modality in addition to surgery, radiotherapy and chemotherapy. While several second-generation multitargeted tyrosine kinase inhibitors show promise in defined tumor entities, these novel antiangiogenic compounds have yet to meet or exceed the efficacy of combinatorial BEV therapy in ongoing clinical trials. Current developments of targeted antiangiogenic agents include their use in the adjuvant setting and the combination of different antiangiogenesis inhibitors to take a more comprehensive approach in blocking tumor angiogenesis. The identification of surrogate markers that can monitor the activity and efficacy of antiangiogenic drugs in patients belongs to the most critical challenges to exploit the full potential of antiangiogenic therapies. The opportunities and obstacles in further development of growth factor- and growth factor receptor-targeted antiangiogenic approaches for advanced cancer, including malignant melanoma, will be discussed herein with particular reference to selected ongoing clinical trials.

Clinical Cancer Advances 2005: major research advances in cancer treatment, prevention, and screening--a report from the American Society of Clinical Oncology

This year, for the first time, the American Society of Clinical Oncology (ASCO) is publishing Clinical Cancer Advances 2005: Major Research Advances in Cancer Treatment, Prevention, and Screening, an annual review of the most significant clinical research presented or published over the past year across all cancer types. ASCO embarked on this project to provide the public, patients, policymakers, and physicians with an accessible summary of the year's most important research advances. While not intended to serve as a comprehensive review, this report provides a year-end snapshot of research that will have the greatest impact on patient care. As you will read, there is much good news from the front lines of cancer research. These pages report on new chemotherapy regimens that sharply reduce the risk of recurrence for very common cancers; the "coming of age" of targeted cancer therapies; promising studies of drugs to prevent cancer; and improvements in quality of life for people living with the disease, among many other advances. Survival rates for cancer are on the rise, increasing from 50% to 64% over the last 30 years. Cancer still exacts an enormous toll, however. Nearly 1.4 million Americans will be diagnosed this year, and some 570,000 will die of the disease. Clearly, more research is needed to find effective therapies for the most stubborn cancer types and stages. We need to know more about the long-term effects of newer, more targeted cancer therapies, some of which need to be taken over long periods of time. And we need to devote far greater attention to tracking and improving the care of the nearly 10 million cancer survivors in the United States today. Despite these and other challenges, the message of this report is one of hope. Through the dedicated, persistent pursuit of clinical research and participation in clinical trials by people with cancer, we steadily uncover new and better ways of treating, diagnosing, and preventing a disease that touches the lives of so many. I want to thank the Editorial Board members, the Specialty Editors, and the ASCO Cancer Communications Committee for their dedicated work to develop this report, and I hope you find it useful.

Role of tyrosine kinase inhibitors in cancer therapy

Cancer chemotherapy has been one of the major medical advances in the last few decades. However, the drugs used for this therapy have a narrow therapeutic index, and often the responses produced are only just palliative as well as unpredictable. In contrast, targeted therapy that has been introduced in recent years is directed against cancer-specific molecules and signaling pathways and thus has more limited nonspecific toxicities. Tyrosine kinases are an especially important target because they play an important role in the modulation of growth factor signaling. This review focuses on small molecule inhibitors of tyrosine kinase. They compete with the ATP binding site of the catalytic domain of several oncogenic tyrosine kinases. They are orally active, small molecules that have a favorable safety profile and can be easily combined with other forms of chemotherapy or radiation therapy. Several tyrosine kinase inhibitors (TKIs) have been found to have effective antitumor activity and have been approved or are in clinical trials. The inhibitors discussed in this manuscript are imatinib mesylate (STI571; Gleevec), gefitinib (Iressa), erlotinib (OSI-1774; Tarceva), lapatinib (GW-572016), canertinib (CI-1033), semaxinib (SU5416), vatalanib (PTK787/ZK222584), sorafenib (BAY 43-9006), sutent (SU11248), and leflunomide (SU101). TKIs are thus an important new class of targeted therapy that interfere with specific cell signaling pathways and thus allow target-specific therapy for selected malignancies. The pharmacological properties and anticancer activities of these inhibitors are discussed in this review. Use of these targeted therapies is not without limitations such as the development of resistance and the lack of tumor response in the general population. The availability of newer inhibitors and improved patient selection will help overcome these problems in the future.