ZD1839 ('Iressa'), a specific oral epidermal growth factor receptor-tyrosine kinase inhibitor, potentiates radiotherapy in a human colorectal cancer xenograft model

Gefitinib ('Iressa', ZD1839) and new epidermal growth factor receptor inhibitors

The epidermal growth factor receptor (EGFR) is a promising target for cancer therapy and a number of EGFR-targeted agents have been developed. Those most advanced in development are the EGFR tyrosine kinase inhibitors gefitinib (‘Iressa’, ZD1839) and erlotinib (‘Tarceva’, OSI-774), and the monoclonal antibody cetuximab (‘Erbitux’, IMC-C225). This review provides a clinical overview of these agents, highlighting their antitumour activities in different tumour types. Epidermal growth factor receptor–targeted agents are generally well tolerated and are not typically associated with the severe adverse events often seen with cytotoxic chemotherapy. Gefitinib is the agent with the most extensive clinical experience, particularly in non-small-cell lung cancer (NSCLC). Recently, gefitinib became the first-approved EGFR-targeted agent, for use in patients with previously treated advanced NSCLC in Japan, the USA and other countries. Further studies are required to explore the full potential of these novel agents either as monotherapy or combination therapy.

Epidermal growth factor receptor: a promising target in solid tumours

The epidermal growth factor receptor (EGFR) is expressed in a wide variety of solid tumours. It has been demonstrated that the EGFR-associated signaling pathway plays an important role in carcinogenesis and cancer progression. In the new therapeutic paradigm of molecular-targeted cancer therapy, interference with intracellular signaling cascades is an appealing treatment approach. Inhibitory strategies under study include monoclonal antibodies, tyrosine kinase inhibitors, EGFR-ligand conjugates, EGFR immunoconjugates, and antisense oligonucleotides. Many of these strategies have demonstrated efficacy against EGFR-expressing tumour cells in preclinical studies, prompting a large number of clinical trials. In particular, clinical studies using monoclonal antibody blockade and EGFR tyrosine kinase inhibitors have suggested that EGFR blockade is a well-tolerated and effective treatment strategy; however, more trials are needed to precisely define how these agents will fit into modern cancer care.

Rationale and clinical basis for combining gefitinib (IRESSA, ZD1839) with radiation therapy for solid tumors

PURPOSE

The role of dysregulated epidermal growth factor receptor-tyrosine kinase (EGFR-TK) activity in promoting tumor resistance to radiation therapy is discussed, and evidence supporting the rationale for the use of gefitinib (IRESSA, ZD1839) to enhance tumor radiosensitivity is reviewed.

METHODS AND MATERIALS

A review of the literature regarding the role of EGFR-TK signaling in tumor response to radiation therapy was conducted, and results were summarized from preclinical and clinical studies of gefitinib in the treatment of solid tumors alone and in combination with radiation therapy.

RESULTS

Preclinical results indicate that EGFR-TK activity in tumors can block the cytotoxic effects of radiation therapy and enhance tumor repopulation, resulting in failure of local tumor control. In xenograft tumor models, gefitinib in combination with ionizing radiation resulted in additive to synergistic growth inhibition. In randomized clinical trials, gefitinib has demonstrated efficacy with favorable tolerability as monotherapy for patients with advanced non-small-cell lung cancer or head-and-neck carcinomas who had previously received standard therapies.

CONCLUSIONS

These results indicate that there is potential for improved responses by combining gefitinib with radiation therapy in non-small-cell lung cancer, head-and-neck cancers, and other solid tumors.

Additive antitumour effect of the epidermal growth factor receptor tyrosine kinase inhibitor gefitinib (Iressa, ZD1839) and the antioestrogen fulvestrant (Faslodex, ICI 182,780) in breast cancer cells

A high expression level of epidermal growth factor receptor (EGFR)/HER1 has been suggested to lead to a shorter survival time and resistance to endocrine therapy in patients with breast cancer. To test the hypothesis that inhibition of the EGFR signalling pathway affects the antitumour effect of endocrine therapy, an EGFR tyrosine kinase inhibitor (EGFR-TKI), gefitinib, and an oestrogen receptor (ER) antagonist, fulvestrant, were administered to human breast cancer cells. A total of five human breast cancer cell lines were used. The effects of single or combined treatments with gefitinib and/or fulvestrant on cell growth, cell cycle progression and apoptosis were analysed. Changes in the expression levels of cyclin-dependent kinase inhibitors, p21 and p27, an antiapoptotic factor, Bcl-2, and a proapoptotic factor, Bax, were also investigated. All cell lines tested were sensitive to gefitinib (50% growth inhibitory concentration, 10–28.5 μM). Breast cancer cell lines with a high expression level of HER1 or HER2 were more sensitive to gefitinib than the others. Gefitinib induced a significant G1–S blockade in ER-positive KPL-3C cells. Gefitinib induced significant apoptosis in HER1-overexpressing MDA-MB-231 cells. Gefitinib additively increased the antitumour effect of fulvestrant in all three ER-positive cell lines in a medium supplemented with 17β-oestradiol. The combined treatment promoted cell cycle retardation in KPL-3C cells, which is associated with an upregulation of p21 by fulvestrant and gefitinib, respectively. Apoptosis was associated with downregulation of Bcl-2 by gefitinib in MDA-MB-231 cells. These results suggest an additive interaction between the EGFR-TKI gefitinib and the antioestrogen fulvestrant in ER-positive breast cancer cells.

Adenoviral Gene Transfer of the Human Inducible Nitric Oxide Synthase Gene Enhances the Radiation Response of Human Colorectal Cancer Associated with Alterations in Tumor Vascularity

Nitric oxide is a potent radiosensitizer of tumors, but its use clinically is limited by serious side effects when administered systemically. We have demonstrated previously that gene transfer of the inducible nitric oxide synthase gene (iNOS) into colorectal cancer cells enhances radiation-induced apoptosis in vitro. The objectives of this study were to further characterize the effects of iNOS gene transfer on the radiosensitivity of human colorectal cancer cells in vitro and tumors grown in athymic nude mice. Adenoviral gene transfer of iNOS (AdiNOS) into human colorectal cancer cell lines (HCT-116 and SNU-1040 cells) significantly enhanced the effects of radiation with sensitizing enhancement ratios (0.1) of 1.65 and 1.6, respectively. The radiation enhancement induced by iNOS was associated with increased iNOS expression and nitric oxide production and prevented by L-NIO, an enzymatic inhibitor of iNOS. AdiNOS treatment of HCT-116 tumors combined with radiation (2 Gy x three fractions) led to a 3.4-fold greater (P < 0.005) tumor growth delay compared with radiation (RT) alone. AdiNOS plus RT also caused significant (P < 0.01) tumor regression with 63% of tumors regressing compared with only 6% of tumors treated with RT. AdiNOS plus RT significantly (P < or = 0.001) increased the percentage of apoptotic cells (22 +/- 4%) compared with either tumors treated with control vector plus RT (9 +/- 1%), AdiNOS alone (9 +/- 3%), or no treatment (2 +/- 1%). These radiosensitizing effects of AdiNOS occurred at low infection efficiency (4% of tumor infected), indicating a significant bystander effect.

Quality-of-life benefits and evidence of antitumour activity for patients with brain metastases treated with gefitinib

Brain metastases are a common complication of non-small-cell lung cancer (NSCLC). The role of chemotherapy in the treatment of brain metastases has not been clearly defined. Emerging case reports of patients with recurrent NSCLC treated as part of the Expanded Access Programme reveal that gefitinib (‘Iressa’, ZD1839) has clinical activity in some patients with brain metastases. Here, we describe a number of case studies documenting the response of patients with brain metastases to treatment with gefitinib. Many of these patients had quality-of-life benefits with improvement of neurological and systemic symptoms; some had a partial response of their brain metastases and even complete responses have been seen in a few patients. One case report also describes a durable long-term response with concurrent treatment with gefitinib and radiotherapy. Such results call for larger trials designed to evaluate and define the role of gefitinib in the treatment of brain metastases in NSCLC patients, either as a single agent or in combination with radiation therapy.

Anticancer chemosensitization and radiosensitization by the novel poly(ADP-ribose) polymerase-1 inhibitor AG14361

BACKGROUND

Poly(ADP-ribose) polymerase-1 (PARP-1) facilitates the repair of DNA strand breaks. Inhibiting PARP-1 increases the cytotoxicity of DNA-damaging chemotherapy and radiation therapy in vitro. Because classical PARP-1 inhibitors have limited clinical utility, we investigated whether AG14361, a novel potent PARP-1 inhibitor (inhibition constant <5 nM), enhances the effects of chemotherapy and radiation therapy in human cancer cell cultures and xenografts.

METHODS

The effect of AG14361 on the antitumor activity of the DNA alkylating agent temozolomide, topoisomerase I poisons topotecan or irinotecan, or x-irradiation or gamma-radiation was investigated in human cancer cell lines A549, LoVo, and SW620 by proliferation and survival assays and in xenografts in mice by tumor volume determination. The specificity of AG14361 for PARP-1 was investigated by microarray analysis and by antiproliferation and acute toxicity assays in PARP-1-/- and PARP-1+/+ cells and mice. After intraperitoneal administration, the concentration of AG14361 was determined in mouse plasma and tissues, and its effect on PARP-1 activity was determined in tumor homogenates. All statistical tests were two-sided.

RESULTS

AG14361 at 0.4 micro M did not affect cancer cell gene expression or growth, but it did increase the antiproliferative activity of temozolomide (e.g., in LoVo cells by 5.5-fold, 95% confidence interval [CI] = 4.9-fold to 5.9-fold; P =.004) and topotecan (e.g., in LoVo cells by 1.6-fold, 95% CI = 1.3-fold to 1.9-fold; P =.002) and inhibited recovery from potentially lethal gamma-radiation damage in LoVo cells by 73% (95% CI = 48% to 98%). In vivo, nontoxic doses of AG14361 increased the delay of LoVo xenograft growth induced by irinotecan, x-irradiation, or temozolomide by two- to threefold. The combination of AG14361 and temozolomide caused complete regression of SW620 xenograft tumors. AG14361 was retained in xenografts in which PARP-1 activity was inhibited by more than 75% for at least 4 hours.

CONCLUSION

AG14361 is, to our knowledge, the first high-potency PARP-1 inhibitor with the specificity and in vivo activity to enhance chemotherapy and radiation therapy of human cancer.

Synergistic interaction between the EGFR tyrosine kinase inhibitor gefitinib ("Iressa") and the DNA topoisomerase I inhibitor CPT-11 (irinotecan) in human colorectal cancer cells

Epidermal growth factor receptor [EGFR (HER1, erbB1)] is a receptor with associated tyrosine kinase activity, and is expressed in colorectal cancers and many other solid tumors. We examined the effect of the selective EGFR tyrosine kinase inhibitor (EGFR-TKI) gefitinib ("Iressa") in combination with the DNA topoisomerase I inhibitor CPT-11 (irinotecan) on human colorectal cancer cells. EGFR mRNA and protein expression were detected by RT-PCR and immunoblotting in all 7 colorectal cancer cell lines studied. Gefitinib inhibited the cell growth of the cancer cell lines in vitro with an IC(50) range of 1.2-160 microM by 3,(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Lovo cells exhibited the highest level of protein and autophosphorylation of EGFR and were the most sensitive to gefitinib. The combination of gefitinib and CPT-11 induced supra-additive inhibitory effects in COLO320DM, WiDR and Lovo cells, assessed by an in vitro MTT assay. Administration of gefitinib and CPT-11 had a supra-additive inhibitory effect on WiDR cells and tumor shrinkage was observed in Lovo cell xenografts established in nude mice, whereas no additive effect of combination therapy was observed in COLO320DM cells. To elucidate the mechanisms of synergistic effects, the effect of CPT-11-exposure on phosphorylation of EGFR was examined by immunoprecipitation. CPT-11 increased phosphorylation of EGFR in Lovo and WiDR cells in time- and dose-dependent manners. This EGFR activation was completely inhibited by 5 microM gefitinib and gefitinib-induced apoptosis was enhanced by combination with CPT-11, measured by PARP activation although no PARP activation was induced by 5 microM CPT-11 alone. These results suggested that these modification of EGFR by CPT-11, in Lovo cells, is a possible mechanism for the synergistic effect of CPT-11 and gefitinib. These findings imply that the EGFR-TKI gefitinib and CPT-11 will be effective against colorectal tumor cells that express high levels of EGFR, and support clinical evaluation of gefitinib in combination with CPT-11, in the treatment of colorectal cancers.

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.

Targeted inhibition of the epidermal growth factor receptor-tyrosine kinase by ZD1839 (?Iressa?) induces cell-cycle arrest and inhibits proliferation in prostate cancer cells

The epidermal growth factor (EGF) plays a role in the development of prostate cancer, which becomes essential after androgen resistance has emerged. The EGF receptor (EGFR) is therefore a potential target for anticancer therapy. We evaluated the effects of ZD1839 ('Iressa'), an orally active EGFR-tyrosine kinase inhibitor, on prostate cancer cell lines. The effects of ZD1839 were evaluated on the anchorage dependent and independent growth of androgen-responsive (LNCaP) and androgen-independent (DU145 and PC3) cells by a cell proliferation assay, cell counting, and soft agar analysis. Flow cytometric analysis and Western blotting were used to assess the effects on the cell-cycle and on protein expression levels, respectively. ZD1839 caused a dose- and time-dependent growth inhibition in all three cell lines. A dose-dependent supra-additive increase in growth inhibition was observed when ZD1839 was combined with the antiandrogen flutamide or ionizing radiation (IR). The antiproliferative effect of ZD1839 was mainly cytostatic and associated with a block in the G(0)/G(1) phase of the cell-cycle, evident after about 12 h of treatment. In the DU145 cells this block was associated with an increase in expression of the CDK inhibitor p27(Kip1), both in the cytoplasmic and nuclear fractions. The increase in p27(Kip1) was not evident in the LNCaP and PC3 cells. No changes were observed in the expression of cyclin D1 protein. These results demonstrate the antiproliferative effects of ZD1839 on the growth of prostate cancer cells and suggest that inhibition of EGFR-associated signal transduction pathway might represent a promising novel therapeutic strategy for the treatment of prostate cancer.

Small‐Molecule Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors

The growth and proliferation of cells are usually tightly regulated processes that are activated by stimuli from their environment. Epidermal growth factor (EGF)-related peptides represent a class of molecules that can trigger cell proliferation, among several cellular processes, such as differentiation, migration, and survival. Binding of EGF-like peptides to the EGF receptor (EGFR) at the cell surface leads to a cascade of intracellular reactions that transduce signals to the nucleus, resulting in particular gene expression patterns. However, in many tumor cells, the regulation of EGFR activity is lost, due to increased or aberrant expression of the receptor or its ligands, and this contributes to many processes important for tumor growth, including cell proliferation, survival, angiogenesis, invasion, and metastasis. Many strategies have been developed that specifically target the EGFR and inhibit its activity. Of these, small-molecule tyrosine kinase inhibitors represent one of the most promising classes of anticancer agents. Here, we describe the status of small-molecule EGFR tyrosine kinase inhibitors in preclinical and clinical development.

Combined effect of gefitinib ('Iressa', ZD1839) and targeted radiotherapy with 211At-EGF

The EGFR-TKI (epidermal growth factor receptor tyrosine kinase inhibitor) gefitinib ['Iressa' (trademark of the AstraZeneca group of companies), ZD1839] increases the cellular uptake of radiolabelled epidermal growth factor (EGF). We investigated gefitinib treatment combined with astatine-211 EGF targeting in vitro using two cell lines expressing high levels of EGFR: A431 (sensitive to gefitinib) and U343MGaCl2:1 (resistant to gefitinib). In both cell lines, the uptake of 211At-EGF was markedly increased by concomitant treatment with gefitinib. Survival was investigated using both a clonogenic survival assay and a cell growth assay. Combined gefitinib and 211At-EGF treatment reduced the survival of U343 cells 3.5-fold compared with 211At-EGF alone. In A431 cells, 211At-EGF treatment resulted in very low survival, but combined treatment with gefitinib increased the survival by about 20-fold. These results indicate that combined treatment with gefitinib might increase the effect of ligand-mediated radionuclide therapy in gefitinib-resistant tumours and decrease the effect of such therapy in gefitinib-sensitive tumours.

The Impact of Gefitinib on Epidermal Growth Factor Receptor Signaling Pathways in Cancer

The ErbB family of receptor tyrosine kinases, of which the epidermal growth factor receptor (EGFR) is the prototype, is associated with the formation and malignant progression of most of the common solid tumors. These molecules play a key role in a complex network of signal transduction pathways that function in normal development as well as in neoplastic transformation. The EGFR and other family members are therefore promising targets for new anticancer therapies. In normal tissues, EGFR-tyrosine kinase (TK) activity is strictly controlled. However, in tumor cells, there are multiple mechanisms that can lead to increased or inappropriate EGFR-TK activity, including altered expression of EGFR, its ligand, or interacting molecules; decreased deactivation through phosphatases or downregulation; or mutation of the EGFR protein. Novel therapeutic approaches aimed at inhibiting increased EGFR-TK activity include antibodies that block the extracellular ligand-binding site, antibody or ligand fusion proteins that specifically target toxins to the tumor cells, or small-molecule TK inhibitors (TKIs) that act intracellularly to block downstream signal transduction from EGFR. Studies have shown that such blockade can lead to reduced cellular proliferation, inhibition of survival signals, and inhibition of tumor metastasis and angiogenesis. Additionally, some agents, including EGFR antibodies and TKIs such as gefitinib have been demonstrated to be effective against various human solid tumors in preclinical models and have shown activity in advanced non-small-cell lung cancer and other solid tumors.

Molecular mechanisms underlying the interaction between ZD1839 ('Iressa') and cisplatin/5-fluorouracil

ZD1839 ('Iressa'), an orally active, selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, is currently being investigated in clinical trials as a treatment for cancer. 'Iressa' is a trademark of the AstraZeneca group of companies. We have previously demonstrated a synergistic interaction between ZD1839 and cisplatin/5-fluorouracil (5FU) in CAL33, a human head and neck cancer cell line that markedly expresses EGFR. This study examined the effects of this drug combination on the cell cycle, cell cycle regulators, apoptosis-related factors, EGFR-related signalling and DNA repair in CAL33 cells. The cells were incubated with ZD1839 alone for 48 h, then cisplatin and 5FU were added. Exposure to the drug combination continued for a further 48 h. ZD1839 alone induced accumulation of cells in the G0/G1 phase of the cell cycle at 24 h accompanied by a concomitant increase in p21, p27 and Bax, a significant decrease in Bcl2 and a decrease in Akt phosphorylation. A decrease in DNA-PK was observed at 48 h. ZD1839 alone had no effect on caspase-3 activity, but addition of ZD1839 to cisplatin-5FU led to a significant increase in caspase-3 activity at 96 h. Thus, ZD1839 affects key cellular pathways controlling cell proliferation, apoptosis and DNA repair. These data provide a rationale to support clinical trials combining ZD1839 and cisplatin-5FU and other protocols that combine EGFR-targeting agents with chemotherapy or radiotherapy.

Long-term follow-up of patients with unresectable locally advanced non-small cell lung cancer treated with chemoradiotherapy: a retrospective analysis of the data from the Japan Clinical Oncology Group trials (JCOG0003A)

To clarify the long-term survival data and factors that are correlated with survival outcome of unresectable locally advanced non-small cell lung cancer (NSCLC) following chemoradiotherapy, we analyzed patients who entered the Japan Clinical Oncology Group (JCOG) clinical trials for unresectable locally advanced NSCLC. Between October 1989 and August 1997, 240 patients (male 207, female 33; PS (performance status) 0 58, PS 1 172, PS 2 9, unknown 1; stage IIB 2, IIIA 62, IIIB 175, unknown 1) entered the 6 trials. All patients received chemotherapy and radiotherapy. The associations between survival outcome and treatment-related factors were analyzed using Cox regression analysis. Median survival times and 5-year survival rates in the trials were 11.9-19.7 months and 0-17.6%, respectively. Median survival time was 16.1 months and the 5- and 7-year survival rates of all 240 patients were 14.4% and 12.0%, respectively. No deaths were observed 7 years after initiation of the treatment or later. For stage IIIA and IIIB patients, the 5-year survival rates were 16.3% and 13.4%, respectively. Node status and age were significantly associated with survival, but no factors of the treatment were associated with survival of patients with unresectable locally advanced NSCLC. The present retrospective analysis showed that approximately 12% of patients with unresectable locally advanced NSCLC could be cured by various chemoradiotherapy regimens.

Combined-modality treatment of solid tumors using radiotherapy and molecular targeted agents

PURPOSE

Molecular targeted agents have been combined with radiotherapy (RT) in recent clinical trials in an effort to optimize the therapeutic index of RT. The appeal of this strategy lies in their potential target specificity and clinically acceptable toxicity.

DESIGN

This article integrates the salient, published research findings into the underlying molecular mechanisms, preclinical efficacy, and clinical applicability of combining RT with molecular targeted agents. These agents include inhibitors of intracellular signal transduction molecules, modulators of apoptosis, inhibitors of cell cycle checkpoints control, antiangiogenic agents, and cyclo-oxygenase-2 inhibitors.

RESULTS

Molecular targeted agents can have direct effects on the cytoprotective and cytotoxic pathways implicated in the cellular response to ionizing radiation (IR). These pathways involve cellular proliferation, DNA repair, cell cycle progression, nuclear transcription, tumor angiogenesis, and prostanoid-associated inflammation. These pathways can also converge to alter RT-induced apoptosis, terminal growth arrest, and reproductive cell death. Pharmacologic modulation of these pathways may potentially enhance tumor response to RT though inhibition of tumor repopulation, improvement of tumor oxygenation, redistribution during the cell cycle, and alteration of intrinsic tumor radiosensitivity.

CONCLUSION

Combining RT and molecular targeted agents is a rational approach in the treatment of solid tumors. Translation of this approach from promising preclinical data to clinical trials is actively underway.

Critical role of both p27KIP1 and p21CIP1/WAF1 in the antiproliferative effect of ZD1839 ('Iressa'), an epidermal growth factor receptor tyrosine kinase inhibitor, in head and neck squamous carcinoma cells

High expression of the epidermal growth factor receptor (EGFR) has been implicated in the development of squamous-cell carcinomas of head and neck (SCCHN). ZD1839 ('Iressa') is an orally active, selective EGFR-TKI (EGFR-tyrosine kinase inhibitor) that blocks signal transduction pathways implicated in proliferation and survival of cancer cells, and other host-dependent processes promoting cancer growth. We have demonstrated that ZD1839 induces growth arrest in SCCHN cell lines by inhibiting EGFR-mediated signaling. Cell cycle kinetic analysis demonstrated that ZD1839 induces a delay in cell cycle progression and a G1 arrest together with a partial G2/M block; this was associated with increased expression of both p27(KIP1) and p21(CIP1/WAF1) cyclin-dependent kinase (CDK) inhibitors. The activity of CDK2, the main target of CIP/KIP CDK inhibitors, was reduced in a dose-dependent fashion after 24 h of ZD1839 treatment and this effect correlated to the increased amount of p27(KIP1) and p21(CIP1/WAF1) proteins associated with CDK2-cyclin-E and CDK2-cyclin-A complexes. In addition, ZD1839-induced growth inhibition was significantly reduced in cell transfectants expressing p27(KIP1) or p21(CIP1/WAF1) antisense constructs. Overall, these results as well as the timing of the effect of ZD1839 on G1 arrest and p27(KIP1) and p21(CIP1/WAF1) upregulation, suggest a mechanistic connection between these events.

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.

The role of epidermal growth factor receptor in head and neck squamous cell carcinoma

Growth factor receptors play a crucial role in the cell proliferation pathways involved in the development of cancer. One such receptor, the epidermal growth factor receptor (EGFR), is upregulated in many types of human tumors, particularly head and neck squamous cell carcinoma (HNSCC). EGFR overexpression in HNSCC has been the basis for investigation of therapeutic strategies that target EGFR. EGFR-blocking methods under evaluation involve immunotoxins, monoclonal antibodies, EGFR-specific tyrosine kinase inhibitors, and antisense approaches. These molecular targeting tactics have produced a number of agents that are currently in various stages of preclinical investigation, along with clinical trials to assess their potential as anticancer treatments.

EGFR blockade with ZD1839 ("Iressa") potentiates the antitumor effects of single and multiple fractions of ionizing radiation in human A431 squamous cell carcinoma. Epidermal growth factor receptor

PURPOSE

Signaling pathways initiated by the epidermal growth factor receptor (EGFR) play important roles in the response to ionizing radiation. In this study the consequences of inhibiting the EGFR on the response of A431 cells (human vulvar squamous cell carcinoma cells that overexpress EGFR) to radiation, were investigated in vitro and in vivo, using the selective EGFR-tyrosine kinase inhibitor, ZD1839 ("Iressa").

METHODS AND MATERIALS

The effect of ZD1839 on proliferation, apoptosis, and clonogenic survival after radiation was determined in vitro. For in vivo studies, athymic nude mice with established subcutaneous A431 xenografts (approximately 100 mm(3)) were treated with either a single 10 Gy fraction or 4 daily 2.5 Gy fractions of radiation with or without ZD1839 (75 mg/kg/day intraperitoneally for 10 days) to determine effects on tumor growth delay.

RESULTS

Treatment of A431 cells with ZD1839 in vitro reduced proliferation, increased apoptosis, and reduced clonogenic survival after radiation. Strikingly greater than additive effects of ZD1839 in combination with radiation on tumor growth delay were observed in vivo after either a single 10 Gy fraction (enhancement ratio: 1.5) or multiple 4 x 2.5 Gy fractions (enhancement ratio: 4). ZD1839 reduced tumor vascularity, as well as levels of vascular endothelial growth factor (VEGF) protein and mRNA induced by stimulation with epidermal growth factor (EGF), suggesting a possible role of inhibition of angiogenesis in the effect.

CONCLUSIONS

Inhibiting EGFR-mediated signal transduction cascades with ZD1839 potentiates the antitumor effect of single and multiple fractions of radiation. These data provide preclinical rationale for clinical trials of EGFR inhibitors including ZD1839 in combination with radiation.

Recent advances in the pharmacological treatment of colorectal cancer

Recent advances in the treatment of colorectal cancer have lead to significant gains in response rates and survival. The combination of newer agents such as irinotecan and oxaliplatin with 5-fluorouracil/leucovorin using various dosing schedules in the metastatic setting has resulted in a steady improvement in the outcome of patients with colorectal cancer. Experimental therapies such as epidermal growth factor receptor inhibitors, vascular endothelial growth factor inhibitors and cyclooxygenase-2 inhibitors, have shown promise in early clinical trials and have acceptable toxicity profiles. Efforts towards improving risk-stratification of stage II colorectal cancer patients and optimising therapy in patients with advanced disease, have focused on molecular and genetic markers. It is hoped that the addition of new therapies to existing drug combinations, as well as further advances in the understanding of colorectal cancer biology, will lead to further improvement in survival and quality of life for patients.

Advances in molecular therapies in patients with brain tumors

BACKGROUND

We are witnessing the development of new treatment modalities for primary brain tumors. An area under intense investigation is the use of small molecules targeting intracellular signaling pathways that interfere with growth, invasion, and metastasis of high-grade gliomas.

METHODS

We review clinical trials of small molecules in adults with brain tumors. This search included electronic databases, specialty journals, textbooks, proceedings, and Web sites of the National Cancer Institute and other cooperative brain tumor groups in Europe and the United States.

RESULTS

Several drugs with the ability to down-regulate the growth and invasion of malignant gliomas are at various stages of testing. Most of these focus on interfering with oncogenic and tumor survival pathways. Examples include inhibitors of tyrosine kinases, farnesyltransferases, and matrix metalloproteinases. These molecules are at different stages of testing, and a conclusive picture of which drug is most effective, either alone or in combination, needs better definition. The metalloproteinase inhibitor marimastat with temozolomide has given the best results to date in phase II trials, increasing the rate of 6-month progression-free survival for recurrent glioblastoma multiforme and anaplastic gliomas.

CONCLUSIONS

As our understanding of the biology of gliomas increases and new drugs targeting specific molecular pathways enter well-designed cooperative trials, the control and prognosis of these tumors should improve.

Nuclear medicine imaging to predict response to radiotherapy: a review

PURPOSE

To review available literature on positron emission tomography (PET) and single photon emission computerized tomography (SPECT) for the measurement of tumor metabolism, hypoxia, growth factor receptor expression, and apoptosis as predictors of response to radiotherapy.

METHODS AND MATERIALS

Medical literature databases (Pubmed, Medline) were screened for available literature and critically analyzed as to their scientific relevance.

RESULTS

Studies on 18F-fluorodeoxyglucose PET as a predictor of response to radiotherapy in head-and-neck carcinoma are promising but need confirmation in larger series. 18F-fluorothymine is stable in human plasma, and preliminary clinical data obtained with this marker of tumor cell proliferation are promising. For imaging tumor hypoxia, novel, more widely available radiopharmaceuticals with faster pharmacokinetics are mandatory. Imaging of ongoing apoptosis and growth factor expression is at a very early stage, but results obtained in other domains with radiolabeled peptides appear promising. Finally, for most of the tracers discussed, validation against a gold standard is needed.

CONCLUSION

Optimization of the pharmacokinetics of relevant radiopharmaceuticals as well as validation against gold-standard tests in large patient series are mandatory if PET and SPECT are to be implemented in routine clinical practice for the purpose of predicting response to radiotherapy.

Expanding the therapeutic repertoire of epidermal growth factor receptor blockade: radiosensitization

Expression of epidermal growth factor receptor (EGFR) has been associated with radioresistance in cancer. Moreover, tumour cell recovery after irradiation paradoxically occurs, in part, as a result of activation of EGFR signalling by such treatment. A recent article by Huang, Li, Armstrong and Harari provides strong rationale for considering the anti-EGFR agent ZD1839 ('Iressa') as a radiosensitizing strategy. With the use of several in vitro and xenograft models of human squamous cell head and neck carcinoma, ZD1939 was shown to markedly improve radiotherapeutic response, with superior tumour inhibition and delayed tumour regrowth. Mechanisms underlying this effect included anti-proliferative and pro-apoptotic activity, with significant perturbation of tumour angiogenesis.

ZD1839 (Iressa): for more than just non-small cell lung cancer

ZD1839 (Iressa) is an orally active, selective epidermal growth factor receptor tyrosine kinase inhibitor that blocks signal transduction pathways involved in cell proliferation. Preclinical studies demonstrated that ZD1839 is a promising agent for the treatment of a wide range of tumors and has additive-to-synergistic effects when combined with radiation or chemotherapy in various cell lines and xenografts. Phase I clinical trials have reported that ZD1839 has acceptable tolerability and antitumor activity. In addition to non-small cell lung cancer, phase II/III studies are currently investigating ZD1839 as monotherapy or in combination therapy against prostate, breast, head and neck, gastric, and colorectal tumors.

Epidermal growth factor receptor and bladder cancer

Muscle-invasive bladder cancer is a disease which causes significant morbidity and mortality. The two main forms of treatment for this disease include radical cystectomy and radical radiotherapy, but five year survival after treatment remains low at 40%. Many clinical and molecular risk factors have been shown to be associated with poor prognosis. One such factor is the expression of epidermal growth factor receptor (EGFR), which is overexpressed by many epithelial tumours, including bladder cancers. There are several methods of inhibiting the activity of EGFR and it may be that use of an anti-EGFR therapy, in combination with more conventional treatment, provides a method of improving the prognosis for muscle-invasive bladder cancer.