Inhibition of the epidermal growth factor receptor family of tyrosine kinases as an approach to cancer chemotherapy: progression from reversible to irreversible inhibitors

QSAR analysis of VEGFR-2 inhibitors based on machine learning, Topomer CoMFA and molecule docking

VEGFR-2 kinase inhibitors are clinically approved drugs that can effectively target cancer angiogenesis. However, such inhibitors have adverse effects such as skin toxicity, gastrointestinal reactions and hepatic impairment. In this study, machine learning and Topomer CoMFA, which is an alignment-dependent, descriptor-based method, were employed to build structural activity relationship models of potentially new VEGFR-2 inhibitors. The prediction ac-curacy of the training and test sets of the 2D-SAR model were 82.4 and 80.1%, respectively, with KNN. Topomer CoMFA approach was then used for 3D-QSAR modeling of VEGFR-2 inhibitors. The coefficient of q2 for cross-validation of the model 1 was greater than 0.5, suggesting that a stable drug activity-prediction model was obtained. Molecular docking was further performed to simulate the interactions between the five most promising compounds and VEGFR-2 target protein and the Total Scores were all greater than 6, indicating that they had a strong hydrogen bond interactions were present. This study successfully used machine learning to obtain five potentially novel VEGFR-2 inhibitors to increase our arsenal of drugs to combat cancer.

Discovery, Optimization, and Evaluation of Novel N-(Benzimidazol-5-yl)-1,3,4-thiadiazol-2-amine Analogues as Potent STAT3 Inhibitors for Cancer Treatment

Signal transducer and activator of transcription 3 (STAT3) is an attractive target for cancer therapy. However, identifying potent and selective STAT3 small-molecule inhibitors with drug-like properties remains challenging. Based on a scaffold combination strategy, compounds with a novel N-(benzimidazol-5-yl)-1,3,4-thiadiazol-2-amine scaffold were designed and their inhibition of the interleukin-6 (IL-6)/JAK/STAT3 pathway was tested in HEK-Blue IL-6 reporter cells. After optimization of lead compound 12, compound 40 was identified as a selective STAT3 inhibitor that directly binds the SH2 domain to inhibit STAT3 phosphorylation, translocation, and downstream gene transcription. Compound 40 exhibited antiproliferative activities against STAT3-overactivated DU145 (IC50 value = 2.97 μM) and MDA-MB-231 (IC50 value = 3.26 μM) cancer cells and induced cell cycle arrest and apoptosis. In the DU145 xenograft model, compound 40 showed in vivo antitumor efficacy following intraperitoneal administration, with a tumor growth inhibition rate of 65.3% at 50 mg/kg, indicating promise for further development.

To Investigate Growth Factor Receptor Targets and Generate Cancer Targeting Inhibitors

Receptor tyrosine kinase (RTK) regulates multiple pathways, including Mitogenactivated protein kinases (MAPKs), PI3/AKT, JAK/STAT pathway, etc. which has a significant role in the progression and metastasis of tumor. As RTK activation regulates numerous essential bodily processes, including cell proliferation and division, RTK dysregulation has been identified in many types of cancers. Targeting RTK is a significant challenge in cancer due to the abnormal upregulation and downregulation of RTK receptors subfamily EGFR, FGFR, PDGFR, VEGFR, and HGFR in the progression of cancer, which is governed by multiple RTK receptor signalling pathways and impacts treatment response and disease progression. In this review, an extensive focus has been carried out on the normal and abnormal signalling pathways of EGFR, FGFR, PDGFR, VEGFR, and HGFR and their association with cancer initiation and progression. These are explored as potential therapeutic cancer targets and therefore, the inhibitors were evaluated alone and merged with additional therapies in clinical trials aimed at combating global cancer.

Design, synthesis, and docking studies of afatinib analogs bearing cinnamamide moiety as potent EGFR inhibitors

Two series of afatinib derivatives bearing cinnamamide moiety (10a-n and 11a-h) were designed, synthesized and evaluated for the IC50 values against four cancer cell lines (A549, PC-3, MCF-7 and Hela). Two selected compounds (10e, 10k) were further evaluated for the inhibitory activity against EGFR and VEGFR2/KDR kinases. Seven of the compounds showed excellent cytotoxicity activity and selectivity with the IC50 values in single-digit μM to nanomole range. Three of them are equal to more active than positive control afatinib against one or more cell lines. The most promising compound 10k showed the best activity against A549, PC-3, MCF-7 and Hela cancer cell lines and EGFR kinase, with the IC50 values of 0.07 ± 0.02 μM, 7.67 ± 0.97 μM, 4.65 ± 0.90 μM and 4.83 ± 1.28 μM, which were equal to more active than afatinib (0.05 ± 0.01 μM, 4.1 ± 2.47 μM, 5.83 ± 1.89 μM and 6.81 ± 1.77 μM), respectively. Activity of compounds 10e (IC50 9.1 nM) and 10k (IC50 3.6 nM) against EGFR kinase were equal to the reference compound afatinib (IC50 1.6 nM). Structure-activity relationships (SARs) and docking studies indicated that replacement of the aqueous solubility 4-(dimethylamino)but-2-enamide group by cinnamamide moiety didn't decrease the antitumor activity. The results suggested that methoxy substitution had a significant impact on the activity and methoxy substituted on C-4 or C-2,3,4 position was benefit for the activity.

Homogeneous single-label tyrosine kinase activity assay for high throughput screening

Protein post-translational modifications (PTMs) are regulatory mechanisms carried out by different enzymes in a cell. Kinase catalyzed phosphorylation is one of the most important PTM affecting the protein activity and function. We have developed a single-label quenching resonance energy transfer (QRET) assay to monitor tyrosine phosphorylation in a homogeneous high throughput compatible format. Epidermal growth factor receptor (EGFR) induced phosphorylation was monitored using Eu(3+)-chelate labeled peptide and label-free phosphotyrosine specific antibody in presence of a soluble quencher molecule. In the QRET kinase assay, antibody binding to phosphorylated Eu(3+)-peptide protects the Eu(3+)-chelate from luminescence quenching, monitoring high time-resolved luminescence (TRL) signals. In the presence of specific kinase inhibitor, antibody recognition and Eu(3+)-chelate protection is prevented, allowing an efficient luminescence quenching. The assay functionality was demonstrated with a panel of EGFR inhibitors (AG-1478, compound 56, erlotinib, PD174265, and staurosporine). The monitored IC50 values ranged from 0.08 to 155.3 nM and were comparable to those found in the literature. EGFR activity and inhibition assays were performed using low nanomolar enzyme and antibody concentration in a 384-well plate format, demonstrating its compatibility for high throughput screening (HTS).

Antiproliferative activities of halogenated pyrrolo[3,2-d]pyrimidines

In vitro evaluation of the halogenated pyrrolo[3,2-d]pyrimidines identified antiproliferative activities in compounds 1 and 2 against four different cancer cell lines. Upon screening of a series of pyrrolo[3,2-d]pyrimidines, the 2,4-Cl compound 1 was found to exhibit antiproliferative activity at low micromolar concentrations. Introduction of iodine at C7 resulted in significant enhancement of potency by reducing the IC50 into sub-micromolar levels, thereby suggesting the importance of a halogen at C7. This finding was further supported by an increased antiproliferative effect for 4 as compared to 3. Cell-cycle and apoptosis studies conducted on the two potent compounds 1 and 2 showed differences in their cytotoxic mechanisms in triple negative breast cancer MDA-MB-231 cells, wherein compound 1 induced cells to accumulate at the G2/M stage with little evidence of apoptotic death. In contrast, compound 2 robustly induced apoptosis with concomitant G2/M cell cycle arrest in this cell model.

Computational insights into the suicide inhibition of Plasmodium falciparum Fk506-binding protein 35

Malaria is a parasite affecting millions of people worldwide. With the risk of malarial resistance reaching catastrophic levels, novel methods into the inhibition of this disease need to be prioritized. The exploitation of active site differences between parasitic and human peptidyl-prolyl cis/trans isomerases can be used for suicide inhibition, effectively poisoning the parasite without affecting the patient. This method of inhibition was explored using Plasmodium falciparum and Homo sapiens Fk506-binding proteins as templates for quantum mechanics/molecular mechanics calculations. Modification of the natural substrate has shown suicide inhibition is a valid approach for novel anti-malarials with little risk for parasitic resistance.

Targeted therapy in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) of multi-factorial etiopathogenesis is rising worldwide. Treatment-associated toxicity problems and treatment failure in advanced disease stages with conventional therapies have necessitated a focus on alternative strategies. Molecular targeted therapy, with the potential for increased selectivity and fewer adverse effects, hold promise in the treatment of HNSCC. In an attempt to improve outcomes in HNSCC, targeted therapeutic strategies have been developed. These strategies are focusing on the molecular biology of HNSCC in an attempt to target selected pathways involved in carcinogenesis. Inhibiting tumor growth and metastasis by focusing on specific protein or signal transduction pathways or by targeting the tumor microenvironment or vasculature are some of the new approaches. Targeted agents for HNSCC expected to improve the effectiveness of current therapy include EGFR inhibitors (Cetuximab, Panitumumab, Zalutumumab), EGFR tyrosine kinase inhibitors (Gefitinib, Erloitinib), VEGFR inhibitors (Bevacizumab, Vandetanib), and various inhibitors of, e.g., Src-family kinase, PARP, proteasome, mTOR, COX, and heat shock protein. Moreover, targeted molecular therapy can also act as a complement to other existing cancer therapies. Several studies have demonstrated that the combination of targeting techniques with conventional current treatment protocols may improve the treatment outcome and disease control, without exacerbating the treatment related toxicities. Some of the targeted approaches have been proved as promising therapeutic potentials and are already in use, whereas remainder exhibits mixed result and necessitates further studies. Identification of predictive biomarkers of resistance or sensitivity to these therapies remains a fundamental challenge in the optimal selection of patients most likely to benefit from targeted treatment.

The resurgence of covalent drugs

Covalent drugs have proved to be successful therapies for various indications, but largely owing to safety concerns, they are rarely considered when initiating a target-directed drug discovery project. There is a need to reassess this important class of drugs, and to reconcile the discordance between the historic success of covalent drugs and the reluctance of most drug discovery teams to include them in their armamentarium. This review surveys the prevalence and pharmacological advantages of covalent drugs, discusses how potential risks and challenges may be addressed through innovative design, and presents the broad opportunities provided by targeted covalent inhibitors.

Quinazoline-urea, new protein kinase inhibitors in treatment of prostate cancer

Epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor-2 (VEGFR-2), two protein tyrosine kinases, are involved in pathological disorders and the progression of different types of carcinomas. Concomitant inhibition of both tyrosine kinase activities appears to be an attractive target for cancer chemotherapy. A series of new quinazoline derivatives substituted by amide, urea, or carbamic acid ester groups have been synthesized. The biological activities of these new compounds have been evaluated for their enzyme inhibition and antiproliferative activities.

A phase II study of erlotinib (OSI-774) given in combination with carboplatin in patients with recurrent epithelial ovarian cancer (NCIC CTG IND.149)

OBJECTIVES

Approximately 50% of ovarian cancers have elevated levels of epidermal growth factor receptor (EGFR) which correlates with a poor prognosis. Preclinical evidence suggests that EGFR tyrosine kinase inhibitors (TKIs), such as erlotinib (OSI-774), may potentiate the anti-tumour effects of cytotoxic agents, including carboplatin. Blocking EGFR could thus potentially reverse drug resistance. The primary objective of the study was to assess the response rate to the addition of erlotinib in patients with recurrent ovarian cancer who were receiving carboplatin.

METHODS

Patients enrolled on this study had either local or advanced recurrent ovarian cancer with measurable disease. They may have had up to 2 prior chemotherapy regimens, one of which must have contained platinum, and they must have responded to prior platinum therapy. Patients were stratified by platinum sensitivity and were treated with erlotinib 150 mg daily on a continuous dosing schedule, and carboplatin at an AUC of 5 every 21 days.

RESULTS

Fifty patients with recurrent ovarian cancer entered the study, 33 in the platinum-sensitive arm and 17 in the platinum-resistant arm. Of patients evaluable for response, there were 14 partial responses (PR) of 30 evaluable for response (57% objective response rate (ORR)) in the platinum-sensitive arm, and 1 PR of 14 evaluable for response (7% ORR) in the platinum-resistant arm.

CONCLUSIONS

The combination of erlotinib and carboplatin was active in patients with platinum-sensitive disease, but not in platinum-resistant disease. The toxicities seen were those expected with carboplatin and erlotinib.

Phase I and pharmacokinetic study of erlotinib (OSI-774) in combination with docetaxel in squamous cell carcinoma of the head and neck (SSCHN)

PURPOSE

This phase I study determined the maximal-tolerated dose, dose-limiting toxicities, pharmacokinetics, and recommended dose of erlotinib with docetaxel.

PATIENTS AND METHODS

Twenty-eight patients with head and neck cancer were enrolled. Patients were orally given erlotinib (50 mg) daily plus 35 mg/m² of docetaxel intravenously weekly × 3 every 4 weeks. Dose escalation of erlotinib was in 50-mg increments until toxicity. Pharmacokinetics were studied with LC-MS/MS, standard, and population pharmacokinetic methods.

RESULTS

Ninety-five courses were successfully given (median 3, range 1-6). The most frequent side effects were diarrhea, fatigue, skin rash, anemia, and hypoalbuminemia. Dose de-escalation for both erlotinib and docetaxel was due to skin rash, neutropenia and/or severe infection with docetaxel to 25 mg/m² and erlotinib to starting dose of 50 mg and re-escalation of docetaxel to 35 mg/m². Responses were observed in 4/26 evaluable patients (100 mg erlotinib). In 24 patients, the mean Cmax and AUC erlotinib values increased with dose and following cumulative dosing (days 7 and 8 vs. day 1, p < 0.05). The CL/F (~7 L/h), V/F (~140 L), and t1/2 (~20 h) for erlotinib were similar to the reported. The mean AUC ratio of metabolite OSI-420 to erlotinib following repetitive dosing at 100 mg (+ or - docetaxel) showed a ~50% increase (p < 0.02), possibly suggesting self-enzyme induction. Population pharmacokinetic studies showed no significant covariate affecting erlotinib pharmacokinetics.

CONCLUSIONS

The combination of erlotinib and docetaxel was associated with significant toxicity, which limited the amount of administered erlotinib. Dosing for phase II trials was docetaxel 35 mg/m² and erlotinib 50 mg. The reason for excessive toxicity is not clear, but not due to change in pharmacokinetics.

Potent cardioprotective effect of the 4-anilinoquinazoline derivative PD153035: involvement of mitochondrial K(ATP) channel activation

Background

The aim of the present study was to evaluate the protective effects of the 4-anilinoquinazoline derivative PD153035 on cardiac ischemia/reperfusion and mitochondrial function.

Methodology/Principal Findings

Perfused rat hearts and cardiac HL-1 cells were used to determine cardioprotective effects of PD153035. Isolated rat heart mitochondria were studied to uncover mechanisms of cardioprotection. Nanomolar doses of PD153035 strongly protect against heart and cardiomyocyte damage induced by ischemia/reperfusion and cyanide/aglycemia. PD153035 did not alter oxidative phosphorylation, nor directly prevent Ca²⁺ induced mitochondrial membrane permeability transition. The protective effect of PD153035 on HL-1 cells was also independent of AKT phosphorylation state. Interestingly, PD153035 activated K⁺ transport in isolated mitochondria, in a manner prevented by ATP and 5-hydroxydecanoate, inhibitors of mitochondrial ATP-sensitive K⁺ channels (mitoK_ATP). 5-Hydroxydecanoate also inhibited the cardioprotective effect of PD153035 in cardiac HL-1 cells, demonstrating that this protection is dependent on mitoK_ATP activation.

Conclusions/Significance

We conclude that PD153035 is a potent cardioprotective compound and acts in a mechanism involving mitoK_ATP activation.

Ultraviolet irradiation-induces epidermal growth factor receptor (EGFR) nuclear translocation in human keratinocytes

Epidermal growth factor receptor (EGFR) plays a critical role in mediating ultraviolet (UV) irradiation-induced signal transduction and gene expression in human keratinocytes. EGFR activation results from increased phosphorylation on specific tyrosine residues in the C-terminal intracellular domain. It has recently been reported that following growth factor stimulation EGFR translocates from the surface membrane to the nucleus, where it may directly regulate gene transcription. We have investigated the ability of UV irradiation to induce EGFR nuclear translocation in human primary and HaCaT keratinocytes. UV irradiation caused rapid nuclear translocation of EGFR. Significant accumulation of EGFR in the nucleus was observed within 15 min after UV irradiation exposure. Maximal translocation occurred at 30 min post-UV irradiation, and resulted in a 10-fold increase in EGFR in the nucleus, as determined by Western blot analysis of nuclear extracts and confirmed by immunofluorescence. Inhibition of nuclear export by Leptomycin B did not alter UV irradiation-induced nuclear accumulation. EGFR tyrosine kinase inhibitor (PD169540) reduced UV irradiation-induced EGFR nuclear translocation 50%. Mutation of either tyrosine 1148 or tyrosine 1173 reduced nuclear translocation 70%, while mutation of tyrosine 1068 was without effect. In addition, over-expression of receptor type protein tyrosine phosphatase-kappa (RPTP-kappa), which specifically dephosphorylates EGFR tyrosines, decreased UV irradiation-induced EGFR nuclear translocation in human keratinocytes. These data demonstrate that UV irradiation stimulates rapid EGFR nuclear translocation, which is dependent on phosphorylation of specific EGFR tyrosine residues. EGFR nuclear translocation may act in concert with conventional signaling pathways to mediate UV irradiation-induced responses in human keratinocytes.

The EGFRvIII variant in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common brain tumour and has the worst prognosis. Epidermal growth factor receptor (EGFR) gene amplification, mutation and re-arrangement (all of which enhance tumour growth, survival, progression and resistance to therapy) are frequently observed in primary GBM. The most common EGFR variant in GBM, the EGFRvIII, is characterised by a deletion of 267 amino acids in the extracellular domain, leading to a receptor which is unable to bind ligand yet is constitutively active. Together with its impaired internalisation and degradation, the EGFRvIII enhances the tumourigenic potential of GBM by activating and sustaining mitogenic, anti-apoptotic and pro-invasive signalling pathways. This EGFRvIII-mediated enhanced tumourigenicity combined with the lack of EGFRvIII expression in normal tissue makes it an ideal candidate for targeted therapy. This review summarizes the current knowledge about the role of EGFRvIII in GBM and discusses therapeutic agents targeting EGFRvIII that are being evaluated as treatments for GBM.

Phase II study of erlotinib plus temozolomide during and after radiation therapy in patients with newly diagnosed glioblastoma multiforme or gliosarcoma

PURPOSE

This open-label, prospective, single-arm, phase II study combined erlotinib with radiation therapy (XRT) and temozolomide to treat glioblastoma multiforme (GBM) and gliosarcoma. The objectives were to determine efficacy of this treatment as measured by survival and to explore the relationship between molecular markers and treatment response.

PATIENTS AND METHODS

Sixty-five eligible adults with newly diagnosed GBM or gliosarcoma were enrolled. We intended to treat patients not currently treated with enzyme-inducing antiepileptic drugs (EIAEDs) with 100 mg/d of erlotinib during XRT and 150 mg/d after XRT. Patients receiving EIAEDs were to receive 200 mg/d of erlotinib during XRT and 300 mg/d after XRT. After XRT, the erlotinib dose was escalated until patients developed tolerable grade 2 rash or until the maximum allowed dose was reached. All patients received temozolomide during and after XRT. Molecular markers of epidermal growth factor receptor (EGFR), EGFRvIII, phosphatase and tensin homolog (PTEN), and methylation status of the promotor region of the MGMT gene were analyzed from tumor tissue. Survival was compared with outcomes from two historical phase II trials.

RESULTS

Median survival was 19.3 months in the current study and 14.1 months in the combined historical control studies, with a hazard ratio for survival (treated/control) of 0.64 (95% CI, 0.45 to 0.91). Treatment was well tolerated. There was a strong positive correlation between MGMT promotor methylation and survival, as well as an association between MGMT promotor-methylated tumors and PTEN positivity shown by immunohistochemistry with improved survival.

CONCLUSION

Patients treated with the combination of erlotinib and temozolomide during and following radiotherapy had better survival than historical controls. Additional studies are warranted.

Discovering novel 3-nitroquinolines as a new class of anticancer agents

AIM

To design and synthesize a novel class of antitumor agents, featuring the 3-nitroquinoline framework.

METHODS

Based on the enzyme-binding features of Ekb1, introducing a nitro group at the 3-position of the quinoline core, a series of novel 3-nitroquinolines was designed and synthesized. The inhibition of epidermal growth factor receptor (EGFR) activity by these compounds was evaluated and analyzed by the sulforhodamine B assay for their inhibitory activities toward human epidermoid carcinoma (A431) cells and breast cancer (MDA-MB-468) cells, which are known to overexpress the EGFR kinase.

RESULTS

A series of novel 3-nitroquinoline derivatives were synthesized and evaluated for their antiproliferative effect against the EGFR-overexpressing tumor cell lines. Several compounds for concentration-response studies showed prominent inhibitory activities with IC50 values in the micromolar or nanomolar range. The structure-activity relationship was discussed in terms of the inhibitory activity against the proliferation of 2 human carcinoma cell lines.

CONCLUSION

This study was the first to identify new structural types of antiproliferative agents against the EGFR-overexpressing tumor cell lines by the incorporation of the nitro group at the 3-position of the quinoline core structure, providing promising new templates for the further development of anticancer agents.

A liquid chromatography mass spectrometry assay for determination of PD168393, a specific and irreversible inhibitor of erbB membrane tyrosine kinases, in rat serum

For the first time, a rapid, sensitive and simple liquid chromatography/tandem mass spectrometry (LC-MS/MS) method using an atmospheric pressure chemical ionization (APCI) source for the quantification of PD168393 in rat serum was developed and validated. Serum samples were pretreated with methanol for protein precipitation. The chromatographic separation was performed on a Jupiter-C5 column (250 mm x 2.0 mm i.d.) pre-equilibrated with 0.1% formic acid. The tandem mass spectrometer was tuned in the multiple reaction monitoring mode to monitor the m/z transitions 369/313 for PD168393 and m/z 343/308 for the internal standard triazolam, using positive ion mode. The MS/MS response was linear over the concentration range from 2 ng/mL to 5000 ng/mL, with a lower limit of quantification (LLQ) of 2 ng/mL. At the lowest quality control (4 ng/mL), the intra- and inter-day precisions (CV%) for PD168393 were less than 10% and the accuracies were between 92% and 111%. The validated method can be used in most or all stages of the screening and optimizing process for future method validation of pharmacokinetic studies.

Effect of photodynamic therapy on the extracellular matrix and associated components

In many countries, photodynamic therapy (PDT) has been recognized as a standard treatment for malignant conditions (for example, esophageal and lung cancers) and non-malignant ones such as age-related macular degeneration and actinic keratoses. The administration of a non-toxic photosensitizer, its selective retention in highly proliferating cells and the later activation of this molecule by light to form reactive oxygen species that cause cell death is the principle of PDT. Three important mechanisms are responsible for the PDT effectiveness: a) direct tumor cell kill; b) damage of the tumor vasculature; c) post-treatment immunological response associated with the leukocyte stimulation and release of many inflammatory mediators like cytokines, growth factors, components of the complement system, acute phase proteins, and other immunoregulators. Due to the potential applications of this therapy, many studies have been reported regarding the effect of the treatment on cell survival/death, cell proliferation, matrix assembly, proteases and inhibitors, among others. Studies have demonstrated that PDT alters the extracellular matrix profoundly. For example, PDT induces collagen matrix changes, including cross-linking. The extracellular matrix is vital for tissue organization in multicellular organisms. In cooperation with growth factors and cytokines, it provides cells with key signals in a variety of physiological and pathological processes, for example, adhesion/migration and cell proliferation/differentiation/death. Thus, the focus of the present paper is related to the effects of PDT observed on the extracellular matrix and on the molecules associated with it, such as, adhesion molecules, matrix metalloproteinases, growth factors, and immunological mediators.

Phase I Clinical and Pharmacodynamic Evaluation of Oral CI-1033 in Patients with Refractory Cancer

PURPOSE

To determine the tolerability and pharmacokinetics of CI-1033 given daily for 7 days of a 21-day cycle. Tumor response and changes in erbB receptor tyrosine kinase activity in tumor and skin tissue were examined, and modulation of potential biomarkers in plasma was explored.

DESIGN

This was a dose-finding phase I study in patients with advanced solid malignancies. Patients were evaluated for safety, pharmacokinetics, and tumor response. Pharmacodynamic markers, such as Ki67, p27, and erbB receptor status, were assessed in tumor and skin tissue using immunohistochemical and immunoprecipitation methodologies. Plasma biomarkers HER2, vascular endothelial growth factor, interleukin-8, and matrix metalloproteinase-9 were evaluated using immunologic techniques.

RESULTS

Fifty-three patients were enrolled in the study. Dose-limiting toxicity (emesis, persistent rash, and mouth ulcer) was observed at 750 mg. The maximum tolerated dose was 650 mg. There were no confirmed objective responses. CI-1033 treatment showed down-regulation of epidermal growth factor receptor, HER2, and Ki67 in a variety of tumor tissues and up regulation of p27 in skin tissue. Plasma HER2 was reduced following CI-1033 administration, but no consistent change in vascular endothelial growth factor, interleukin-8, or matrix metalloproteinase-9 was noted. CI-1033 plasma concentrations were proportional to dose.

CONCLUSION

The safety and pharmacokinetic profile of CI-1033 was favorable for multidose oral administration. Evidence of modulation of erbB receptor activity in tumor and skin tissue was accompanied by changes in markers of proliferation and cell cycle inhibition. Additional clinical trials are warranted in defining the role of CI-1033 in the treatment of cancer and further assessing the utility of antitumor markers.

Panitumumab the first fully human monoclonal antibody: from the bench to the clinic

Panitumumab (formerly known as ABX-EGF) is the first fully human monoclonal antibody to epidermal growth factor receptor to enter clinical trials for the treatment of solid tumors. Like cetuximab (Erbitux; BMS), it is directed against the extracellular ligand-binding domain of the receptor and results in blockade of the essential downstream signaling pathways that are known to govern apoptosis, proliferation and differentiation of both normal and neoplastic cell types in a wide array of tissues. It has a very high affinity for epidermal growth factor receptor and has been generally well tolerated and associated with very few infusion reactions. As a fully human agent, panitumumab has not been associated with the formation of any antibodies directed against it that has been evidenced by a very reliable pharmacokinetic profile with possible dosing schedules ranging from 1 to 3 weeks. Similar to other agents targeting the epidermal growth factor receptor pathway, a rash has been the primary toxicity and is dose dependent up to 2.5 mg/kg at which dose 100% of all patients have been affected. The anti-tumor activity of panitumumab has been tested in vitro and in vivo, and inhibition of tumor growth has been observed in numerous cancer models, particularly lung, kidney and colorectal. It has been efficacious and well tolerated both as monotherapy and in combination with other chemotherapeutic agents. Several phase I trials, two phase II trials and most recently a phase III trial in pretreated colorectal cancer have been carried out to date. Currently, there is also a randomized phase III trial (Panitumumab Advanced Colorectal Cancer Evaluation Study) investigating the role of panitumumab in the first-line treatment of colorectal cancer. No unfavorable drug-drug interactions have been observed nor has there been any effect on the pharmacokinetics of drugs with which it is being used. Recent progress in preclinical and clinical studies of panitumumab is reviewed.

The Combi-Targeting Concept: In vitro and In vivo Fragmentation of a Stable Combi-Nitrosourea Engineered to Interact with the Epidermal Growth Factor Receptor while Remaining DNA Reactive

PURPOSE

JDA58 (NSC 741282), a "combi-molecule" optimized in the context of the "combi-targeting concept," is a nitrosourea moiety tethered to an anilinoquinazoline. Here, we sought to show its binary epidermal growth factor receptor (EGFR)/DNA targeting property and to study its fragmentation in vitro and in vivo.

EXPERIMENTAL DESIGN

The fragmentation of JDA58 was detected in cells in vitro and in vivo by fluorescence microscopy and tandem mass spectrometry. EGFR phosphorylation and DNA damage were determined by Western blotting and comet assay, respectively. Tumor data were examined for statistical significance using the Student's t test.

RESULTS

JDA58 inhibited EGFR tyrosine kinase (IC(50), 0.2 micromol/L) and blocked EGFR phosphorylation in human DU145 prostate cancer cells. It induced significant levels of DNA damage in DU145 cells in vitro or in vivo and showed potent antiproliferative activity both in vitro and in a DU145 xenograft model. In cell-free medium, JDA58 was hydrolyzed to JDA35, a fluorescent amine that could be observed in tumor cells both in vitro and in vivo. In tumor cells in vitro or in vivo, or in plasma collected from mice, the denitrosated species JDA41 was the predominant metabolite. However, mass spectrometric analysis revealed detectable levels of the hydrolytic product JDA35 in tumor cells both in vitro and in vivo.

CONCLUSIONS

The results in toto suggest that growth inhibition in vitro and in vivo may be sustained by the intact combi-molecule plus JDA35 plus JDA41, three inhibitors of EGFR, and the concomitantly released DNA-damaging species. This leads to a model wherein a single molecule carries a complex multitargeted-multidrug combination.

Drugs targeted against protein kinases

Current treatments for cancer (surgery, radiation and chemotherapy) are successful for early stage localised disease but have severe side effects. New treatments are needed to increase the cure rate and life expectancy of patients. With the discovery of oncogenes, tumour suppressor genes and an understanding of their role in the development of the malignant disease, a new era of therapy has begun. Cancer is a manifestation of deregulated signalling pathways that mediate cell growth and programmed cell death. Protein kinases are essential elements in these signalling pathways. In the US, Novartis launched Gleevec (imantinib, STI-571) in May 2001 as the first anticancer drug whose mechanism of action is kinase inhibition. In Phase I trials, 23/24 patients with chronic myelogenous leukaemia (CML) had complete remissions and the drug is relatively non-toxic. Herceptin (trastuzumab) is a monoclonal antibody (mAb) against a member of the growth factor receptor family (HER-2/neu) that was launched in 1998 by Genentech for the treatment of breast cancer. Trastuzumab has an excellent antitumour profile, particularly when used in combination with doxorubicin and paclitaxol. These drugs are pioneering the treatment of cancer based on the molecular understanding of the disease. Numerous drugs that target growth factor receptors and their signalling pathways are in advanced clinical trials. Herein, antibodies against receptors and small molecule inhibitors of kinases in signalling pathways will be summarised. Inter-disciplinary preclinical studies have identified chemicals that target specific kinases. We believe that clinical studies of these agents will yield new anticancer agents that target specific diseases and that are less toxic than current agents.

Differential radiosensitisation by ZD1839 (Iressa), a highly selective epidermal growth factor receptor tyrosine kinase inhibitor in two related bladder cancer cell lines

The epidermal growth factor receptor (EGFR) is expressed in a wide variety of epithelial tumours including carcinoma of the bladder. Stimulation of the EGFR pathway is blocked by ZD1839 (Iressa), a highly selective EGFR tyrosine kinase inhibitor. Radical radiotherapy is an established organ sparing treatment option for muscle invasive bladder cancer and this study has explored the possibility for the use of ZD1839 as a radiosensitiser in this scenario. The effect of combination treatment with ZD1839 (0.01 μM) and ionising radiation in the established bladder cancer cell lines MGH-U1 and its radiosensitive mutant clone S40b was measured by clonogenic assays. A highly significant radiosensitising effect was seen in both cell lines (P<0.001 for MGH-U1 and S40b cell lines). This effect was independent of the concentration of the drug and the duration of exposure prior to treatment with ionising radiation. Cell cycle kinetics of both cell lines was not significantly altered with ZD1839 (0.01 μM) as a single agent. A modest induction of apoptosis was observed with ZD1839 (0.01 μM) as a single agent, but a marked induction was observed with the combination treatment of ZD1839 and ionising radiation. These results suggest a potentially important role for ZD1839 in combination with radiotherapy in the treatment of muscle invasive bladder cancer.

Epidermal growth factor receptor-targeted treatment for advanced colorectal carcinoma

Substantial effort has focused on the development of novel targeted agents for treating patients with late-stage colorectal carcinoma. These agents are designed specifically to inhibit biochemical processes associated with pathogenesis. Numerous molecules targeting the epidermal growth factor receptor have been investigated as therapeutic agents and appear to herald a shift in the treatment paradigm for colorectal carcinoma.

Antitumor activity of HER-2 inhibitors

Activation of intracellular mitogenic signal transduction pathways driven by the ErbB family of receptor tyrosine kinases has been implicated in a variety of cancers. Amongst these, the tumorigenic roles of the Epidermal Growth Factor receptor (EGFR) and HER-2 have been most extensively studied. Therapeutic antibodies and small molecule kinase inhibitors targeting EGFR have recently received regulatory agency approval for the treatment of colon and lung cancer, respectively. In this review, I briefly describe these agents and their potential use in inhibiting the growth of tumors that overexpress HER-2. I also discuss other therapeutics currently available or being developed specifically to target HER-2 dependent tumors.

Multiple mechanisms of action of ZR2002 in human breast cancer cells: a novel combi-molecule designed to block signaling mediated by the ERB family of oncogenes and to damage genomic DNA

The mechanism of action of ZR2002, a chimeric amino quinazoline designed to possess mixed EGFR tyrosine kinase (TK) inhibitory and DNA targeting properties, was compared to those of ZR01, a reversible inhibitor of the same class and PD168393, a known irreversible inhibitor of EGFR. ZR2002 exhibited 4-fold stronger EGFR TK inhibitory activity than its structural homologue ZR01 but was approximately 3-fold less active than the 6-acrylamidoquinazoline PD168393. It preferentially blocked EGF and TGFalpha-induced cell growth over PDGF and serum. It also inhibited signal transduction in heregulin-stimulated breast tumour cells, indicating that it does not only block EGFR but also its closely related erbB2 gene product. In contrast to its structural homologues, ZR2002 was capable of inducing significant levels of DNA strand breaks in MDA-MB-468 cells after a short 2 hr drug exposure at a concentration as low as 10 microM. Reversibility studies using whole cell autophosphorylation and growth assays in human breast cell lines showed that in contrast to its reversible inhibitor counterpart ZR01, ZR2002 induced irreversible inhibition of EGF-stimulated autophosphorylation in MDA-MB-468 cells and irreversible inhibition of cell growth. Moreover despite possessing a weaker binding affinity than PD168393, it induced a significantly more sustained antiproliferative effect than the latter after a pulse 2 hr exposure. More importantly, in contrast to ZR01 and PD168393, ZR2002 was capable of inducing significant levels of cell death by apoptosis in MDA-MB-468 cells. The results in toto suggest that the superior antiproliferative potency of ZR2002 may be due to its ability to induce a protracted blockade of receptor tyrosine kinase-mediated signaling while damaging cellular DNA, a combination of events that may trigger cell-killing by apoptosis.

Radiosensitization by pan ErbB inhibitor CI-1033 in vitro and in vivo

PURPOSE

Overexpression of the ErbB family of receptor tyrosine kinases has been associated with uncontrolled growth of many tumor types and, therefore, presents a promising molecular target for cancer therapy. CI-1033 is a small molecule tyrosine kinase inhibitor that differs from other 4-anilinoquinazolines by being a pan ErbB (instead of epidermal growth factor receptor-specific) irreversible (instead of reversible) inhibitor. Therefore, we investigated the antitumor effect of CI-1033 alone and in combination with ionizing radiation in vitro and in vivo.

EXPERIMENTAL DESIGN

We selected three human colon carcinoma cell-lines (LoVo, Caco-2, which express activated epidermal growth factor receptor and ErbB-2 family members, and SW620, which does not), and analyzed the effects of CI-1033 both in vitro and in vivo. For in vivo studies LoVo and Caco-2 cells were implanted s.c. in the flank of nude mice. After the tumor reached approximately 100 mm(3), treatment was initiated with 20 mg/kg of CI-1033 (orally once daily x 5 for 3 successive weeks), radiation treatment (a total of 30 Gy given in 2 Gy once daily x 5 for 3 successive weeks), or a combination of both CI-1033 and radiation treatment.

RESULTS

We found that exposure of LoVo and Caco-2, but not SW620 cells, to CI-1033 in the range of 1-3 micro M could inhibit constitutive signaling by tyrosine kinases, arrest cell growth, inhibit cells in G(1), stimulate expression of p53, and induce apoptosis. The inhibition of cell growth by CI-1033 seemed to produce only minimal radiosensitization in LoVo and Caco-2 cells. In contrast, the combination of CI-1033 and radiation produced significant (P < 0.0005 and P = 0.0002, respectively) and prolonged suppression of tumor growth in both the tumor types when compared with either treatment alone.

CONCLUSIONS

These findings suggest that CI-1033 can increase the effectiveness of radiation therapy. The extent of suppression of tyrosine kinase activity by CI-1033, rather than the amount of activity in untreated cells, seemed to be more closely associated with the efficacy of combination treatment.

Safety, Pharmacokinetics, and Activity of ABX-EGF, a Fully Human Anti–Epidermal Growth Factor Receptor Monoclonal Antibody in Patients With Metastatic Renal Cell Cancer

Purpose

To determine the antitumor activity of ABX-EGF, a fully human monoclonal antibody to the epidermal growth factor receptor (EGFr), in previously treated patients with metastatic renal cell carcinoma, and to characterize its toxicity, immunogenicity, pharmacokinetics, and pharmacodynamics.

Patients and Methods

The antitumor activity, as well as the toxicity, pharmacokinetics, pharmacodynamics, and immunogenicity of ABX-EGF, were assessed.

Results

Eighty-eight patients were treated with ABX-EGF doses of 1.0, 1.5, 2.0, or 2.5 mg/kg weekly with no loading dose. EGFr immunostaining was performed on 76 tumor biopsy specimens (86%), and 69 (91%) scored positive. Major responses occurred in three patients, and two patients had minor responses. Forty-four patients (50%) also had stable disease at their first 8-week assessment, and the median progression-free survival (PFS) was 100 days (95% CI, 58 to 140 days). Low hemoglobin and high alkaline phosphatase predicted for short PFS. The principal toxicity, an acneiform rash, occurred in 68%, 95%, 87%, and 100% of patients who received at least three doses of ABX-EGF at 1.0, 1.5, 2.0, and 2.5 mg/kg/wk, respectively. A trend indicated that the severity of the rash may relate to PFS. No human antihuman antibodies were detected. ABX-EGF pharmacokinetics fit a model that incorporated both linear and saturable EGFr-mediated clearance mechanisms, and interindividual variability was low. At 2.5 mg/kg/wk, ABX-EGF concentrations throughout treatment exceeded those estimated to saturate nonlinear clearance and inhibit xenograft growth by 90%.

Conclusion

ABX-EGF was generally well tolerated. The objective response rate was low in previously treated patients with metastatic renal cell carcinoma. Although skin rash may be a pharmacodynamic marker of drug action, its potential as a surrogate marker of clinical benefit requires further evaluation.

Antiangiogenic and antitumor agents. Design, synthesis, and evaluation of novel 2-amino-4-(3-bromoanilino)-6-benzylsubstituted pyrrolo[2,3-d]pyrimidines as inhibitors of receptor tyrosine kinases

Several different classes of growth factor receptors containing tyrosine kinases (RTK) are directly or indirectly involved in angiogenesis. Inhibition of these RTKs has provided a new paradigm in the treatment of tumors by restricting their growth and metastasis. We have designed, synthesized and evaluated eleven novel 2-amino-4-(3-bromoanilino)-6-substituted benzyl pyrrolo[2,3-d]pyrimidines as the first in a series of RTK inhibitors. These analogues were synthesized from appropriate alpha-bromomethylbenzyl ketones by cyclocondensation with 2,6-diamino-4-pyrimidone to afford the 2-amino-4-oxo-6-substituted benzyl pyrrolo[2,3-d]pyrimidines. Chlorination of the 4-position followed by displacement with 3-bromoaniline afforded the target compounds. In some instances, the 2-amino moiety of the pyrrolo[2,3-d]pyrimidines was protected prior to the chlorination and displacement followed by deprotection. The compounds were evaluated as inhibitors of vascular endothelial growth factor receptors VEGFR-2 (Flk-1, KDR) and VEGFR-1 (Flt-1); epidermal growth factor receptor (EGFR); and platelet-derived growth factor receptor-beta (PDGFR-beta). Selected compounds were also evaluated against the growth of A431 cells (which overexpress EGFR) in culture and as inhibitors of angiogenesis in the chicken embryo chorioallantonic membrane (CAM) assay. In each evaluation, a known standard compound was used as a comparison. Of the 11 analogues, five were more potent or equipotent as compared to standard compounds against the growth factor receptors. Two analogues showed superior inhibition of A431 cells in culture compared to the standard compounds. Three analogues were equipotent with the standard compound in the CAM assay and four of the analogues were dual inhibitors of RTKs. The structure-activity relationship for inhibition of different RTKs was quite distinct and different, and for VEGFR-2 and EGFR diametrically opposite. The inhibitory data against the RTKs in this study demonstrates that variation of the substituent(s) in the benzyl ring of these 2-amino-4-anilino 6-benzyl pyrrolo[2,3-d]pyrimidines does indeed control both the potency and specificity of inhibitory activity against RTKs.

Induction of apoptosis by ionizing radiation and CI-1033 in HuCCT-1 cells

CI-1033 is a quinazoline-based HER family tyrosine kinase inhibitor that is currently being evaluated as a potential anticancer agent. The present study examines the molecular mechanism by which CI-1033 induces apoptosis either as a single agent or in combination with radiation. Although CI-1033 alone did not induce apoptosis, the simultaneous exposure of cells to CI-1033 and radiation induced significant levels of apoptosis. The sequential treatment of cells with CI-1033 followed by radiation induced an even greater effect with 62.6% of cells undergoing apoptosis but this enhanced effect was not seen if cells were treated first with radiation and then CI-1033. The combination treatment induces apoptosis of HuCCT-1 via upregulation of FasL and Bid cleavage. These data suggest that modulation of the Fas-FasL pathway and activation of Bid could be useful for increasing the anti-tumor effect of CI-1033 in this type of cancer.

Experimental therapy of malignant mesothelioma: new perspectives from anti-angiogenic treatments

We reviewed the published literature of clinical studies in malignant mesothelioma (MM), including phase II as well as older single-agent and combination chemotherapy trials with more than 15 patients. While response rates exceeding 30% have been achieved with established cytotoxic drugs in MM therapy, novel chemotherapeutic agents and their combinations appear more promising. This applies especially to the anti-metabolites (i.e. pemetrexed) that produced response rates of up to 45% in combination with platinum compounds. Moreover, agents targeting novel proliferative and survival pathways in MM are developed to improve treatment outcomes. Here, we focused on the role of several angiogenic growth factors in MM biology and the data of MM-oriented studies on angiostatic agents tested in a phase I-II trial. It seems likely that no single treatment modality will be effective by itself. Studies that use combinations of the newer agents, including angiostatic drugs, with chemotherapy, should be conducted.

Epidermal growth factor receptor and response of head-and-neck carcinoma to therapy

PURPOSE

To present an overview of the significance of erbB tyrosine kinase family members as prognostic-predictive factors and as targets of therapeutic intervention in patients with head-and-neck carcinomas (HNCs).

METHODS AND MATERIALS

The data of clinical studies addressing the correlation between the expression of erbB family tyrosine kinases, particularly epidermal growth factor receptor (EGFR), and the prognosis and pattern of failure were reviewed, along with the response of HNCs to EGFR antagonists such as a chimeric monoclonal antibody and a couple of small molecule tyrosine kinase inhibitors.

RESULTS

Correlative biomarker studies showed that most HNCs express high levels of EGFR and/or other members of the erbB family. Several studies have demonstrated that patients with EGFR-overexpressing tumors had significantly worse overall survival. Compelling evidence has emerged showing that EGFR-overexpressing HNCs respond more poorly to radiotherapy (RT), although data of its impact on the response to chemotherapy are scarce. Clinical studies have so far showed that tyrosine kinase inhibitors have rather limited antitumor activities when given alone. Stimulated by promising preclinical data, the value of EGFR antagonists in the combined modality setting, particularly with RT, is being addressed in clinical trials.

CONCLUSION

Members of the erbB receptor tyrosine kinase family, particularly EGFR, were found to be a strong biomarker for poor prognosis and HNC resistance to RT. The available data showed that EGFR antagonists given as single modality therapies yield rather limited antitumor activity. The results of trials testing the efficacy of combining EGFR antagonist with RT or chemotherapy will emerge within the next few years.

Emerging treatments in oncology: focus on tyrosine kinase (erbB) receptor inhibitors

OBJECTIVE

To describe the role of tyrosine kinase (TK) and its subreceptors in the development of cancer and the role of TK inhibitors in cancer treatment.

DATA SOURCES

Published articles identified through MEDLINE using search terms such as tyrosine kinase, erbB1, erbB2, erbB3, erbB4, epidermal growth factor receptors (EGFR), and EGFR inhibitors. Additional sources were identified from bibliographies in the articles and from Web sites and reports from the National Cancer Institute, American Society of Clinical Oncology, and European Organization for Research and Treatment of Cancer.

DATA SYNTHESIS

Progress in identifying the biochemical and molecular causes of cancer has led to discovery of abnormalities that characterize cancer cells and represent targets for development of drug therapies. TK receptors represent one such target when these are present in elevated quantities and/or aberrant forms. Abnormalities in these cell surface receptors have been correlated with development and progression of cancer, poor response to chemotherapeutic agents, and low survival rates. Several subtypes of TK receptors have been identified, and mutations in these have been associated with neoplasms of the breast, lung, colon, ovaries, and other organs. Approved agents, such as trastuzumab (Herceptin-Genentech) work by blocking a subtype of TK receptors that has been associated with breast cancer growth. Gefitinib (Iressa-AstraZeneca) was recently approved for treatment of non-small-cell lung cancer in patients who have failed treatment with traditional chemotherapeutic agents. Other agents such as cetuximab, erlotinib, and canertinib are in advanced stages of clinical trials and may be available for general clinical use in the next few years.

CONCLUSION

Cancer continues to be a difficult disease to treat, but newly identified cellular targets have resulted in new medications, and these promising agents are giving hope for additional options for patients with various solid tumors.

Enhancement of tumor radioresponse by combined treatment with gefitinib (Iressa, ZD1839), an epidermal growth factor receptor tyrosine kinase inhibitor, is accompanied by inhibition of DNA damage repair and cell growth in oral cancer

Molecular blockade of EGFR with either an EGFR MAb or an EGFR TKI enhances the radiosensitivity of human SCCs. In the present study, we investigated whether treatment with the EGFR TKI gefitinib (Iressa, ZD1839) improves the response to radiotherapy in the OSCC cell lines HSC2 and HSC3. We examined potential mechanisms that may contribute to the enhanced radiation response induced by gefitinib. Growth inhibition was observed in vitro with radiation or gefitinib. A cooperative antiproliferative effect was obtained when cancer cells were treated with radiation followed by gefitinib. Cells treated with a combination of radiation and gefitinib arrested in G(1) and G(2)-M phases, with a decrease in the S-phase population. While radiation alone did not significantly affect MEK1/2 and p38 MAPK autophosphorylation, the combination of gefitinib and radiation completely inhibited the downstream signaling of EGFR. Results from DNA damage repair analysis in cultured OSCC cells demonstrated that gefitinib had a strong inhibitory effect on DNA-PKc pathways after radiation. Tumor xenograft studies demonstrated that the combination of gefitinib and radiation caused growth inhibition and tumor regression of well-established OSCC tumors in athymic mice; tumor volume was reduced from 1,008.2 to 231.4 mm(3) in HSC2 cells (p < 0.01) and from 284.2 to 12.4 mm(3) in HSC3 cells (p < 0.01). Immunohistochemical analysis of OSCC xenografts revealed that gefitinib caused a striking decrease in tumor cell proliferation when combined with radiotherapy. Overall, we conclude that gefitinib enhances tumor radioresponse by multiple mechanisms that may involve antiproliferative growth inhibition and effects on DNA repair after exposure to radiation.

Pharmacogenomics: road to anticancer therapeutics nirvana?

Interindividual differences in the toxicity and response to anticancer therapies are currently observed for essentially all available treatment regimens. Such 'unpredictable' drug responses are particularly dangerous in the context of anticancer agents that have narrow therapeutic indices. Pharmacogenomics attempts to elucidate the inherited basis of interindividual differences in drug response, with the eventual goal of minimizing such variability through the use of 'individualized' treatments. There are several emerging examples of genetic polymorphisms of drug-metabolizing enzymes, DNA repair genes and drug targets that have been shown to influence the toxicity and efficacy of anticancer treatment. This review discusses the role of genetic variants of UGT1A1, TS and EGFR to exemplify the potential impact of phramacogenomics on the field of anticancer therapeutics.

Enhancement of Radiosensitivity in Head and Neck Cancer Cells by ZD1839 (‘IRESSA’), A Selective Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor

Overexpression of epidermal growth factor receptor (EGFR) is frequently observed in many solid tumor types, including head and neck squamous cell carcinomas (HNSCC). Recent laboratory experiments have demonstrated that high EGFR levels correlate with increased tumor resistance to radiation. This study investigated the relationship between EGFR expression levels and radiosensitivity in 5 HNSCC cell lines (HSC2, HSC3, HSC4, SCC25, and Ca9-22) and whether treatment with ZD1839 ('Iressa'), a selective EGFR-tyrosine kinase inhibitor (TKI), would improve tumor cell response to radiotherapy. ZD1839 suppressed the growth of HNSCC cell lines in a dose- and time-dependent manner. Radiosensitivity of these HNSCC cell lines, assessed by a clonogenic survival assay, differed greatly and the expression of EGFR varied. EGFR expression levels (EGFR numbers/cell) correlated with increased tumor resistance to radiation (f[x]= 4.54 X, R2 = 0.715; f[x]: EGFR numbers/cell, X: radiosensitivity; D10). Following exposure of the HNSCC cells to 1.0 microM ZD1839 and radiation (0-10 Gy), greater than additive growth inhibitory effects were observed. These results suggest that ZD1839 could enhance tumor radiosensitivity and inhibit tumor growth after radiation, indicating that this combination could have clinical potential in the treatment of patients with head and neck cancer.

Activation of Stat3 by receptor tyrosine kinases and cytokines regulates survival in human non-small cell carcinoma cells

Overexpression of receptor tyrosine kinases including the epidermal growth factor receptor (EGF-R) as well as nonreceptor tyrosine kinases, such as Src, have been implicated in the formation of human lung cancers. In addition, cytokines like interleukin-6 (IL-6) have been demonstrated to modulate lung cancer cell growth and elevated levels of IL-6 have been shown to be an adverse prognostic factor for patients with lung cancer. Despite a large body of evidence pointing to their potential importance, few direct studies into the role of signal transducers and activators of transcription (STAT) pathways in human lung cancer have been undertaken. Here we demonstrate that multiple nonsmall cell lung cancer cell lines demonstrate constitutive Stat3 DNA-binding activity. Stat3 DNA-binding activity is specifically upregulated by the addition of epidermal growth factor (EGF), IL-6, and hepatocyte-derived growth factor (HGF). Furthermore, the stimulation of Stat3 DNA-binding activity by EGF requires the activity of EGF-R tyrosine kinase as well as Src-kinase, while the upregulation of Stat3 activity by IL-6 or HGF requires only Src-kinase activity. Treatment of A549 lung cancer cells with PD180970 or SU6656, both pharmacological inhibitors of Src-kinase, resulted in reduced Src and Stat3 activity, cell cycle arrest in G2, and reduced viability of cells accompanied by induction of apoptosis. Treatment of Stat3-positive A549 and H358 cells with antisense Stat3 oligonucleotides results in complete loss of Stat3 DNA-binding activity and apoptosis, while Stat3-positive H1299 cells remained healthy. Finally, an adenoviral vector expressing a dominant-negative Stat3 isoform results in loss of Stat3 DNA-binding activity, apoptosis, and reduced cellular viability. These results demonstrate a role of Stat3 in transducing survival signals downstream of tyrosine kinases such as Src, EGF-R, and c-Met, as well as cytokines such as IL-6, in human nonsmall cell lung cancers.

Erlotinib (Tarceva): a promising drug targeting epidermal growth factor receptor tyrosine kinase

Overexpression of the epidermal growth factor receptor (EGFR) is correlated with a poor prognosis in several human malignancies. In addition, cancers overexpressing EGFR respond poorly to both chemotherapy and radiation therapy. Therefore, EGFR is a viable target for cancer therapy. This review will address how EGFR blockade modulates signal transduction, leading to alterations in the cell cycle progression with secondary inhibition of proliferation and differentiation of cancer cells. As a prototypical example, erlotinib (Tarceva), a reversible EGFR tyrosine kinase inhibitor will be discussed. This drug has demonstrated promising antitumor activity in Phase II trials in several solid tumors and definitive Phase III studies to demonstrate clinical benefit have completed accrual.

Targeting epidermal growth factor receptor: novel therapeutics in the management of cancer

Overexpression of epidermal growth factor receptor (EGFR) in epithelial tumors, including head and neck, lung, breast, colon and other solid tumors, has frequently been correlated with poor prognosis, thus stimulating efforts to develop new cancer therapies that target EGFR. Monoclonal antibodies and tyrosine kinase inhibitors specifically targeting EGFR are the most well-studied and hold substantial promise of success. Several compounds of monoclonal antibodies and tyrosine kinase inhibitors targeting EGFR have been studied and clinical trials are now underway to test the safety and efficacy of these targeting strategies in several human tumors. This review will address each of these agents alone or in combination with radiation or chemotherapy and highlight some of these promising developments. Cetuximab (Erbitux) is being evaluated in combination with radiation or chemotherapy in Phase III trials. Other compounds such as h-R3, ABX-EGF, EMD-55900 and ICR-62 have proved to be effective in targeting malignant cells alone or in combination with traditional therapies. Tyrosine kinase inhibitors targeting the intracellular domain of EGFR, including ZD-1839 (gefitinib, Iressa), OSI-774 (Erlotinib/Tarceva), PD-153053, PD-168393 and CI-1033, have been studied in clinical setting alone or in combination with radiation or chemotherapy. ZD-1839 is being studied in a Phase III trial in patients with advanced non-small cell lung cancer. EGFR targeted treatment by monoclonal antibodies and tyrosine kinase inhibitors have been proven to sensitize tumor cells to the effects of chemotherapy and radiation therapy. The synergistic activities and nonoverlapping toxicities of these compounds allow concomitant administration with cytotoxic therapy. Challenges of evaluating EGFR targeted agents exist in selecting the optimal dosages and determining long-term toxicity.

[Epidermal growth factor inhibitors]

PURPOSE

Tyrosine kinases are implicated in the normal cellular proliferation and in malignant transformation. Among the tyrosine kinase receptors, one of best described is the Epidermal Growth Factor Receptor (EGFR), which is widely expressed in particular in epithelial cells and in many human carcinomas.

CURRENT KNOWLEDGE AND KEY POINTS

Compounds have been developed that target either the extracellular ligand-binding region of EGFR (Cetuximab) or the intracellular tyrosine kinase ATP-binding (Iressa), Tarceva. Phase I studies showed that these molecules have a favorable pharmacokinetic and pharmacodynamic profile, with excellent tolerance and easy administration. Phase II and III studies are currently testing their efficacy.

FUTURE PROSPECTS AND PROJECTS

Preliminary results show interesting activity in different tumors, alone or in combination with either chemotherapy or radiotherapy. If these results are confirmed in larger trials including a high number of patients, these agents might be very useful in combination with chemotherapy, radiotherapy or other biological targeting agents such as cellular cycle inhibitors or antiangiogenics.

Tyrosine kinases as targets in cancer therapy - successes and failures

Protein kinases play a crucial role in signal transduction and also in cellular proliferation, differentiation and various regulatory mechanisms. The inhibition of growth-related kinases, especially tyrosine kinases, might therefore provide new therapies for diseases such as cancer. Due to the enormous progress that has been made in the past few years in the identification of the human genome, in molecular and cell biology technologies, in structural biology and in bioinformatics, the number of receptor and non-receptor tyrosine kinases that have been identified as valuable molecular targets has greatly increased. Currently, more than 20 different tyrosine kinase targets are under evaluation in drug discovery projects in oncology. The progress made in the crystallisation of protein kinases, in most cases complexed with ATP-site-directed inhibitors, has confirmed that the ATPbinding domain of tyrosine kinases is an attractive target for rational drug design; more than 20 ATP-competitive, low molecular weight inhibitors are in various phases of clinical evaluation. Meanwhile, clinical proof-of-concept (POC) has been achieved with several antibodies and small molecules targeted against tyrosine kinases. With Herceptin, Glivec and Iressa (registered in Japan), the first kinase drugs have entered the market. This review describes the preclinical and clinical status of low molecular weight drugs targeted against different tyrosine kinases (e.g., epidermal growth factor receptor [EGFR], vascular endothelial growth factor receptor [VEGFR], platelet-derived growth factor receptor [PDGFR], Kit, Fms-like tyrosine kinase [Flt]-3), briefly describes new targets, and provides a critical analysis of the current situation in the area of tyrosine kinase inhibitors.

Epidermal growth factor receptor as a therapeutic target in colorectal cancer

The epidermal growth factor receptor (EGFR) is widely expressed in advanced colorectal cancers (CRCs), and higher levels of EGFR are inversely related to survival in these patients. Two general strategies have been used to block EGFR signaling: preventing ligand binding with anti-EGFR monoclonal antibodies (eg, cetuximab and ABX-EGF) and inhibiting its intrinsic tyrosine kinase with small molecules (eg, gefitinib [Iressa] and erlotinib [OSI-774,Tarceva]). Phase II trials of cetuximab suggest that it might be an effective treatment option alone or in combination with standard therapies as first- or second-line therapy. Phase I studies evaluating other EGFR inhibitors in patients with CRC have been reported. The inclusion of anti-EGFR therapies into standard treatment is the subject of current clinical trials.

HER-targeted tyrosine-kinase inhibitors

Improved understanding of tumor biology has led to the identification of numerous growth factors that are involved in malignant transformation and tumor progression. Many of these factors induce cellular responses through receptors with intrinsic tyrosine kinase (TK) activity. Therefore, inhibiting receptor TK activity is a way to effectively block the tumorigenic effects that arise from these pathways. The HER family of TK receptors is overexpressed or dysregulated in many types of human cancer. As a result these receptors were identified as targets for cancer therapy. Several agents have been developed that reversibly, or irreversibly, inhibit one, two or all of the HER receptors. Tarceva and Iressa are HER1-TK inhibitors that are advanced in development. Clinical data show that these agents as monotherapy have antitumor activity in patients with various types of solid tumor and are well tolerated; encouraging data are also produced when Tarceva or Iressa are combined with chemotherapeutic agents. Other dual or pan-HER, reversible or irreversible, TK inhibitors are being investigated in phase I trials. Early data show that they are generally well tolerated and have provided evidence of antitumor activity. HER-TK inhibitors are exciting agents that are likely to have a substantial impact on the way we treat patients with cancer.

The epidermal growth factor receptor as a novel target for cancer therapy: case studies and clinical implications

OBJECTIVES

To update the success and obstacles using therapies targeted to the epidermal growth factor receptor including IMC-C225, ZD1839, and OSI-774.

DATA SOURCES

Research articles, textbooks, clinical protocols, case studies.

CONCLUSIONS

Ongoing studies show promise using monoclonal antibodies and small-molecule tyrosine kinase inhibitors in the treatment of non-small cell lung cancer and other malignancies. Such therapies can be delivered with limited toxicity to the host, and initial studies have shown single-agent efficacy and efficacy in combination with chemotherapy and/or radiation therapy.

IMPLICATIONS FOR NURSING PRACTICE

Nurses are directly involved in the delivery of these novel therapies and the management of associated toxicities. They serve to coordinate treatment protocols and help to ensure patient understanding and compliance.

Roles of activated Src and Stat3 signaling in melanoma tumor cell growth

Activation of protein tyrosine kinases is prevalent in human cancers and previous studies have demonstrated that Stat3 signaling is a point of convergence for many of these tyrosine kinases. Moreover, a critical role for constitutive activation of Stat3 in tumor cell proliferation and survival has been established in diverse cancers. However, the oncogenic signaling pathways in melanoma cells remain to be fully defined. In this study, we demonstrate that Stat3 is constitutively activated in a majority of human melanoma cell lines and tumor specimens examined. Blocking Src tyrosine kinase activity, but not EGF receptor or JAK family kinases, leads to inhibition of Stat3 signaling in melanoma cell lines. Consistent with a role of Src in the pathogenesis of melanoma, we show that c-Src tyrosine kinase is activated in melanoma cell lines. Significantly, melanoma cells undergo apoptosis when either Src kinase activity or Stat3 signaling is inhibited. Blockade of Src or Stat3 is also accompanied by down-regulation of expression of the anti-apoptotic genes, Bcl-x(L) and Mcl-1. These findings demonstrate that Src-activated Stat3 signaling is important for the growth and survival of melanoma tumor cells.