Synergistic interaction between 17-AAG and phosphatidylinositol 3-kinase inhibition in human malignant glioma cells

The phosphatidylinositol 3'-kinase (PI3K)/Akt pathway is often constitutively activated in malignant glioma cells, in many cases as a result of mutation of phosphatase and tensin homologue deleted on chromosome ten (PTEN), an endogenous inhibitor of Akt, which renders tumor cells resistant to cytotoxic insults, including those related to anticancer drugs. Pharmacological inhibition of this pathway may potentially restore or augment the effectiveness of conventional chemotherapy or other signaling-targeted agents. Because the heat shock protein (HSP) is involved in the conformational maturation of a number of signaling proteins critical to the proliferation of malignant glioma cells, we hypothesized that the combination of the PI3K inhibitor LY294002 and the HSP90 inhibitor 17-allyl-aminogeldanamycin (17-AAG) would promote glioma cytotoxicity by decreasing both the activation status and levels of Akt, as well as downregulating the levels of other relevant signaling effectors. We, therefore, examined the effects of LY294002 and 17-AAG, alone and in combination, on signal transduction and apoptosis in a series of malignant glioma cell lines. Simultaneous exposure to these inhibitors significantly induced cell death, and irreversibly inhibited proliferative activity and colony forming ability of the glioma cell lines. Quantitative analysis revealed that enhancement by LY294002 of 17-AAG-induced cytotoxicity was synergistic, leading to a pronounced increase in active caspase-3 and poly (adenosine diphosphate-ribose) polymerase (PARP) cleavage together with the release of cytochrome c and apoptosis inducing factor (AIF). No significant growth inhibition or caspase activation was seen in control cells. The enhanced cytotoxicity of this combination was associated with diminished Akt activation and a significant downregulation of epidermal growth factor receptor (EGFR), Raf-1, and mitogen activated protein kinase. Combination of 17-AAG and LY294002 did not modify phospho-JNK/SPK and phospho-p38. Cells exposed to 17-AAG and LY294002 displayed a significant reduction in cell-cycle regulatory proteins, such as retinoblastoma (Rb), cyclin dependent kinase (CDK)4, CDK6, cyclin D1, and cyclin D3. Taken together, these findings suggest that the PI3K/Akt pathway plays a critical role in regulating the apoptotic response to 17-AAG and that targeting this pathway could provide a potent strategy to treat patients with malignant gliomas.     

The heat shock protein antagonist 17-AAG potentiates the activity of enzastaurin against malignant human glioma cells

Recent studies have suggested that the proliferation of malignant gliomas may result from activation of protein kinase C (PKC)-mediated pathways. Enzastaurin (LY317615), an acyclic bisindolylmaleimide, is an oral inhibitor of PKCbeta as well as other isoforms. The initial objective of this study was to assess the efficacy of enzastaurin in a series of malignant human glioma cell lines with diverse genomic alterations. Although enzastaurin independently produced a dose-dependent inhibition of cellular proliferation and decreased cell viability in each of the glioma cell lines examined, and partially down-regulated Akt and GSK3beta phosphorylation, median effective concentrations were at the upper limits of, or above, the clinically achievable range in all cell lines tested. We therefore examined whether the efficacy of enzastaurin could be enhanced by combination with the HSP90 antagonist, 17-AAG, which inhibits Akt and other signaling intermediates by a distinct mechanism. In comparison to the effect of enzastaurin alone, combination of enzastaurin with 17-AAG led to marked enhancement of antiproliferative and cytotoxic effects. Simultaneous exposure to both agents significantly increased the release of cytochrome c, as well as caspase 3 activation, Bax cleavage, and inhibition of Akt phosphorylation. Cells exposed to enzastaurin and 17-AAG also displayed a significant reduction in cell cycle regulatory proteins, such as CDK4 and CDK6. Taken together, these findings suggest that the efficacy of enzastaurin can be potentiated by the addition of 17-AAG, and indicate that combining molecularly targeted therapies may provide a more effective strategy than single-agent therapy to treat patients with malignant gliomas.     

Enhancement of docetaxel-induced cytotoxicity by blocking epidermal growth factor receptor and cyclooxygenase-2 pathways in squamous cell carcinoma of the head and neck.

PURPOSE: The addition of molecular targeted agents to enhance the cytotoxicity of chemotherapeutic agents is a promising strategy in cancer treatment. The combination of cyclooxygenase-2 inhibitors and epidermal growth factor receptor tyrosine kinase inhibitors, such as celecoxib and ZD1839 (gefitinib), was reported to achieve synergistic cell growth inhibition in squamous cell carcinoma of the head and neck. Therefore, we postulated that the addition of celecoxib and ZD1839 to docetaxel, a cytotoxic agent, might further increase antitumor activity. EXPERIMENTAL DESIGN: The combination of celecoxib, ZD1839, and docetaxel was studied for its effect on cell growth and apoptosis by cell growth inhibition and Annexin V assays. The relevant molecular targets of these agents and apoptotic markers were examined by immunoblotting analyses in the presence or absence of these three drugs. Morphologic changes of the microtubule cytoskeleton, a known target of docetaxel, were also evaluated by staining for alpha-tubulin after the combination treatment. RESULTS: We showed that this triple combination significantly enhanced cell growth inhibition and docetaxel-induced apoptosis. Docetaxel mainly induced caspase-8 activation, whereas the addition of celecoxib and ZD1839 augmented the caspase-8 activation and enhanced caspase-9 activation. One of the underlying mechanisms for augmentation of docetaxel-induced apoptosis by celecoxib and ZD1839 is to further inhibit the activation of prosurvival pathway molecules, such as extracellular signal-regulated kinase and AKT, and the promotion of aberrant apoptosis. CONCLUSIONS: Our studies suggest that the combination of docetaxel with a cyclooxygenase-2 inhibitor and an epidermal growth factor receptor tyrosine kinase inhibitor may further improve efficacy of docetaxel and other taxane-based therapies in squamous cell carcinoma of the head and neck.     

The role of EGFR-directed therapy in the treatment of breast cancer

The epidermal growth factor receptor (EGFR) is a member of the tyrosine kinase group of growth factor receptors. Following the binding of ligands such as the epidermal growth factor (EGF) with EGFR, activation of signal transduction pathways can lead to changes in cellular proliferation and differentiation. EGFR is highly expressed by many tumors, and is associated with disease with poor prognostic features. EGFR and its downstream signaling pathways are, therefore, promising antitumor targets for drug development. Using ZD1839 ('Iressa') as an example of a small molecule inhibitor of EGFR, the utility of targeting EGFR in the treatment of breast cancer will be discussed. ZD1839 is an example of an orally active, selective EGFR tyrosine kinase inhibitor, which has shown extensive preclinical activity and evidence of being active combined with a favorable tolerability profile. Breast cancers have been shown to express high levels of EGFR and hormone-resistant disease is associated with an increased expression of both EGFR and EGFR ligands. ZD 1839 has shown in vitro activity as both monotherapy and in combination with other agents such as paclitaxel or doxorubicin, inhibiting the growth of breast cancer cells that are resistant to endocrine agents such as tamoxifen. Against hormone-responsive cells, the combination of ZD1839 with endocrine therapy produces synergistic activity. ZD1839 has also shown growth inhibitory activity against xenografts initiated from ductal carcinoma in situ tissues, indicating that EGFR inhibition may have a role in the treatment of early-stage breast cancer. EGFR is, therefore, a rational target for the development of novel therapies, and promising preclinical studies indicate that EGFR-targeted therapy may have a role in the treatment of breast cancer. The results of clinical trials with ZD 1839 in breast cancer patients are awaited with interest.     

The epidermal growth factor receptor tyrosine kinase inhibitor ZD1839 (Iressa) suppresses c-Src and Pak1 pathways and invasiveness of human cancer cells.

PURPOSE: Abnormalities in the expression and signaling pathways downstream of the epidermal growth factor receptor (EGFR) contribute to the progression, invasion, and maintenance of the malignant phenotype in human cancers, including those of the head and neck and breast. Accordingly, agents such as the EGFR tyrosine kinase inhibitor (EGFR-TKI) ZD1839 (Iressa) are promising, biologically based treatments that are in various stages of preclinical and clinical development. The process of tumor progression requires, among other steps, increased transformation, directional migration, and enhanced cell survival; this study explored the effect of ZD1839 on the stimulation of c-Src and p21-activated kinase 1 (Pak1), which are vital for transformation, directional motility, and cell survival of cancer cells. EXPERIMENTAL DESIGN: We examined the effect of ZD1839 on biochemical and functional assays indicative of directional motility and cell survival, using human head and neck squamous cancer cells and breast cancer cells. RESULTS: ZD1839 effectively inhibited c-Src activation and Pak1 activity in exponentially growing cancer cells. In addition, ZD1839 suppressed EGF-induced stimulation of EGFR autophosphorylation on Y1086 and Grb2-binding Y1068 sites, c-Src phosphorylation on Y215, and Pak1 activity. ZD1839 also blocked EGF-induced cytoskeleton remodeling, redistribution of activated EGFR, and in vitro invasiveness of cancer cells. CONCLUSIONS: These studies suggest that the EGFR-TKI ZD1839 may cause potent inhibition of the Pak1 and c-Src pathways and, therefore, have potential to affect the invasiveness of human cancer cells deregulated in these growth factor receptor pathways.     

Treatment schedule is of importance when gefitinib is combined with irradiation of glioma and endothelial cells in vitro

Amplified epidermal growth factor receptor (EGFR) signaling is supposed to contribute to clinical radiation resistance of glioblastoma multiforme (GBM). Therefore, inhibition of EGFR signaling pathways by the selective EGFR tyrosine kinase inhibitor, gefitinib (ZD1839, Iressa), may increase the therapeutic effects of radiotherapy. The effects of different schedules for administration of gefitinib on sensitivity to irradiation of the human glioma cell lines (251MG and SF-767), a rat glioma cell line (BT4C), and an immortalized rat brain endothelial cell line (RBE4) is reported. Differences in effects of the combined treatment on cell toxicity were determined by a fluorometric cytotoxicity assay, and nuclear DNA fragmentation was used for quantification of apoptosis. Pre-administration with gefitinib for 30 min prior to irradiation followed by continuous incubation with gefitinib significantly increased the cytotoxicity of SF-767, BT4C, and RBE4 cells. However, the human glioma cell line 251MG was protected against radiation-induced damage by this treatment schedule, at lower concentrations of gefitinib. Pre-administration with gefitinib for 24 h prior to irradiation without following incubation with gefitinib increased the cytotoxicity of SF-767 and BT4C cells. Post-irradiation treatment with gefitinib significantly increased the cytotoxicity in all cell lines except for 251MG. We demonstrated heterogeneity in the cytotoxic effects of gefitinib between cell lines. Response to gefitinib might be due to other mechanisms than through the EGF receptor as some of the cell lines showed sensitivity to gefitinib despite no or low expression of EGFR. This study also demonstrates the importance of timing of gefitinib administration when this agent is combined with irradiation.     

Response to epidermal growth factor receptor inhibitors in non-small cell lung cancer cells: limited antiproliferative effects and absence of apoptosis associated with persistent activity of extracellular signal-regulated kinase or Akt kinase pathways.

The epidermal growth factor receptor (EGFR) is an important novel target for anticancer therapy. In this study, we examined the molecular mechanisms that underlie the antitumor effects of the anti-EGFR monoclonal antibody C225 (Cetuximab) and the selective EGFR tyrosine kinase inhibitor ZD1839 (Iressa; AstraZeneca) in non-small cell lung cancer (NSCLC) cell lines. Cell growth, assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, was inhibited at low concentrations of ZD1839 and C225 in control A431 cells, whereas the NSCLC cell lines were comparatively more resistant. In A431 cells, but not in the NSCLC cells, ZD1839 treatment resulted in a modest increase in DNA fragmentation, the externalization of phosphatidyl serine, and the activation of caspase-3, known markers of apoptotic cell death. However, poly(ADP-ribose) polymerase cleavage was not detected, and caspase inhibition by carbobenzoxy-Val-Ala-Asp-fluoromethyl ketone partially reduced ZD1839-generated DNA fragmentation. Overexpression of the antiapoptotic protein Bcl-2 in A431 cells suppressed the cytotoxicity upon anti-EGFR treatment. These results thus demonstrate that the toxic effect of ZD1839 in A431 cells is caused by a form of cell death that involves a mitochondrial step and is, at least in part, dependent on caspase activation. EGFR expression levels showed no significant correlation with sensitivity to ZD1839 and C225. Evaluation of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase and phosphatidylinositol 3'-kinase/Akt pathways showed considerable inhibition of these pathways by ZD1839 and C225 in A431 cells, whereas one or both of these pathways remained active upon anti-EGFR treatment in NSCLC cells. In addition, treatment with specific inhibitors of mitogen-activated protein kinase kinase or phosphatidylinositol 3'-kinase resulted in a smaller effect on proliferation than simultaneous treatment with both inhibitors, whereas induction of apoptosis was observed only when both pathways were blocked. Together, these data suggest that persistent activity of either of these signaling pathways is involved in the lack of sensitivity of NSCLC cell lines to EGFR inhibitors.     

Efficacy of the HSP90 inhibitor 17-AAG in human glioma cell lines and tumorigenic glioma stem cells

Glioblastoma multiforme (GBM) arises from genetic and signaling abnormalities in components of signal transduction pathways involved in proliferation, survival, and the cell cycle axis. Studies to date with single-agent targeted molecular therapy have revealed only modest effects in attenuating the growth of these tumors, suggesting that targeting multiple aberrant pathways may be more beneficial. Heat-shock protein 90 (HSP90) is a molecular chaperone that is involved in the conformational maturation of a defined group of client proteins, many of which are deregulated in GBM. 17-allylamino-17-demethoxygeldanamycin (17-AAG) is a well-characterized HSP90 inhibitor that should be able to target many of the aberrant signal transduction pathways in GBM. We assessed the ability of 17-AAG to inhibit the growth of glioma cell lines and glioma stem cells both in vitro and in vivo and assessed its ability to synergize with radiation and/or temozolomide, the standard therapies for GBM. Our results reveal that 17-AAG is able to inhibit the growth of both human glioma cell lines and glioma stem cells in vitro and is able to target the appropriate proteins within these cells. In addition, 17-AAG can inhibit the growth of intracranial tumors and can synergize with radiation both in tissue culture and in intracranial tumors. This compound was not found to synergize with temozolomide in any of our models of gliomas. Our results suggest that HSP90 inhibitors like 17-AAG may have therapeutic potential in GBM, either as a single agent or in combination with radiation.     

ZD1839, a specific epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, induces the formation of inactive EGFR/HER2 and EGFR/HER3 heterodimers and prevents heregulin signaling in HER2-overexpressing breast cancer cells.

PURPOSE: ZD1839 is a tyrosine kinase inhibitor of the epidermal growth factor receptor (EGFR) that has shown clinical activity against EGFR-expressing tumors. Our aim was to explore the effects of ZD1839 in breast cancer cell lines expressing different levels of EGFR and the closely related HER2 receptor. EXPERIMENTAL DESIGN: We studied the growth-inhibitory effects of ZD1839 in a series of breast carcinoma cell lines. In HER2-overexpressing BT-474 breast cancer cells, we studied the effects of ZD1839 on cell growth and heterodimerization of receptors under basal and ligand-stimulated conditions. RESULTS: ZD1839 was an equally potent inhibitor of growth in breast cancer cells expressing high levels of EGFR and HER2. In BT-474 breast cancer cells, ZD1839 abolished EGF- and heregulin-induced activation of ErbB receptors and downstream signaling molecules. Because ZD1839 does not inhibit the HER2 tyrosine kinase in vitro, and because heregulin is a ligand that activates HER2 by binding to HER3 and HER4 but does not bind to the EGFR, our findings suggested that ZD1839 interfered with HER2 function in intact cells. Searching for mechanisms, we report that ZD1839 induces the formation of inactive unphosphorylated EGFR/HER2 and EGFR/HER3 heterodimers. Furthermore, ZD1839 completely abolishes basal and heregulin-induced formation of active phosphorylated HER2/HER3 heterodimers. CONCLUSIONS: ZD1839 inhibits the growth of HER2-overexpressing breast cancer cells, possibly by sequestration of HER2 and HER3 receptors in an inactive heterodimer configuration with the EGFR. Our findings suggest that there is a strong rationale to conduct clinical trials of ZD1839 in patients with HER2-overexpressing breast tumors.     

Zd 1839 "Iressa"

ZD 1839 is a highly specific EGF receptor tyrosine kinase inhibitor. Inhibition of EGF receptor transphosphorylation by ZD 1839 blocks the signal transduction at the first step, thus providing antiproliferative effects. Preclinical studies demonstrated efficacy and good bioavailability. The terminal half-life of the compound in patients is ranging from 27 to 41 hours, allowing single oral dosing. Tolerance in healthy volunteers was excellent. In phase I studies, toxicity was manageable. Most common side effects were skin rash, nausea, vomiting, and diarrhea. During those studies, clinical responses were observed in patients with various malignant tumors, in particular non small cell lung cancer. Phase II and III studies are ongoing.     

Proliferation of human neuroblastomas mediated by the epidermal growth factor receptor

Neuroblastoma is a common solid tumor of childhood that is derived from the neural crest. Expression of epidermal growth factor (EGF) receptors (EGFRs) has been associated with enhanced cell growth and aggressive behavior in other tumors. Here, we examined the expression profile of EGFRs in neuroblastoma cell lines and primary tumors. We found that all 13 neuroblastoma cell lines examined expressed EGFR1 (HER1), most at readily detectable levels. Low levels of other human EGFR family receptors were also detected in almost all cell lines. All primary tumors examined expressed readily detectable levels of HER1 and HER3 and lower levels of HER2 and HER4. EGF had a significant effect on the proliferation of neuroblastoma cell lines in vitro. EGF treatment (100 ng/mL) of the cell lines SY5Y and NLF significantly increased cell number (P < 0.01). EGF stimulated more cells to enter S and G2-M phase, as suggested by flow cytometry, indicating that EGF increases cell number by increasing proliferation, with no appreciable change in apoptosis. EGF exposure resulted in receptor autophosphorylation and activation of both the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT pathways. Exposure to 0.5 micromol/L ZD1839, a HER1-specific inhibitor, caused a 40% to 50% reduction in the number of SY5Y and NLF cells grown in medium containing 10% fetal bovine serum (P < 0.01). Even at 0.01 micromol/L, ZD1839 inhibited autophosphorylation of HER1 by EGF. At 0.1 micromol/L, it also blocked phosphorylation of AKT, but not MAPK, in NLF cells. Additional studies showed that the PI3K/AKT-specific inhibitor LY294002 had a more profound effect than the MAPK-specific inhibitor U0126 in blocking EGF-induced cell proliferation. This suggests that the PI3K/AKT pathway is the main signaling pathway responsible for the proliferation effects of EGF in neuroblastomas. Our results also indicate that ZD1839 is a potent inhibitor of neuroblastoma cell proliferation; therefore, it may be a useful, biologically based therapeutic agent for these tumors.     

Antitumor activity of ZD6474, a vascular endothelial growth factor receptor tyrosine kinase inhibitor, in human cancer cells with acquired resistance to antiepidermal growth factor receptor therapy.

PURPOSE: The epidermal growth factor receptor (EGFR) autocrine signaling pathway is involved in cancer development and progression. EGFR inhibitors such as C225 (cetuximab), a chimeric human-mouse anti-EGFR monoclonal antibody, and ZD1839 (gefitinib), a small molecule EGFR-selective tyrosine kinase inhibitor, are in advanced clinical development. The potential emergence of cancer cell resistance in EGFR-expressing cancers treated with EGFR inhibitors could determine lack of activity of these drugs in some cancer patients. Vascular endothelial growth factor (VEGF) is secreted by cancer cells and plays a key role in the regulation of tumor-induced endothelial cell proliferation and permeability. ZD6474 is a small molecule VEGF flk-1/KDR (VEGFR-2) tyrosine kinase inhibitor that also demonstrates inhibitory activity against EGFR tyrosine kinase. EXPERIMENTAL DESIGN: The antitumor activity of ZD1839, C225, and ZD6474 was tested in athymic mice bearing human GEO colon cancer xenografts. GEO cell lines resistant to EGFR inhibitors were established from GEO xenografts growing in mice treated chronically with ZD1839 or C225. Expression of EGFR was evaluated by flow cytometry. Expression of various proteins involved in intracellular cell signaling was assessed by Western blotting. Tumor growth data were evaluated for statistical significance using the Student's t test. All Ps were two-sided. RESULTS: Although chronic administration of optimal doses of C225 or ZD1839 efficiently blocked GEO tumor growth in the majority of mice, tumors slowly started to grow within 80-90 days, despite continuous treatment. In contrast, continuous treatment of mice bearing established GEO xenografts with ZD6474 resulted in efficient tumor growth inhibition for the entire duration of dosing (up to 150 days). ZD6474 activity was also determined in mice pretreated with ZD1839 or C225. When GEO growth was apparent after 4 weeks of treatment with EGFR inhibitors, mice were either re-treated with EGFR inhibitors or treated with ZD6474. GEO tumor growth was blocked only in mice treated with ZD6474, whereas tumor progression was observed in mice re-treated with C225 or ZD1839. GEO tumors growing during treatment with C225 or with ZD1839 were established as cell lines (GEO-C225-RES and GEO-ZD1839-RES, respectively). Cell membrane-associated EGFR expression was only slightly reduced in these cell lines compared with parental GEO cells. Western blotting revealed no major change in the expression of the EGFR ligand transforming growth factor alpha of bcl-2, bcl-xL, p53, p27, MDM-2, akt, activated phospho-akt, or mitogen-activated protein kinase. However, both GEO-C225-RES and GEO-ZD1839-RES cells exhibited a 5-10-fold increase in activated phospho-mitogen-activated protein kinase and in the expression of cyclooxygenase-2 and of VEGF compared with GEO cells. GEO-C225-RES and GEO-ZD1839-RES growth as xenografts in nude mice was not significantly affected by treatment with either C225 or ZD1839 but was efficiently inhibited by ZD6474. CONCLUSIONS: Long-term treatment of GEO xenografts with selective EGFR inhibitors results in the development of EGFR inhibitor-resistant cancer cells. Growth of EGFR inhibitor-resistant tumors can be inhibited by ZD6474. These data indicate that inhibition of VEGF signaling has potential as an anticancer strategy, even in tumors that are resistant to EGF inhibitors.     

Geldanamycin and 17-allylamino-17-demethoxygeldanamycin potentiate the in vitro and in vivo radiation response of cervical tumor cells via the heat shock protein 90-mediated intracellular signaling and cytotoxicity

Ansamycin antibiotics inhibit function of the heat shock protein (HSP) 90, causing selective degradation of several intracellular proteins regulating such processes as proliferation, cell cycle regulation, and prosurvival signaling cascades. HSP90 has been identified previously as a molecular target for anticancer agents, including ionizing radiation (IR). Therefore, we hypothesized that the ansamycin geldanamycin and its 17-allylamino-17-demethoxy analog (17-AAG), which inhibit HSP90, would enhance tumor cell susceptibility to the cytotoxicity of IR. Treatment of two human cervical carcinoma cell lines (HeLa and SiHa) with geldanamycin and 17-AAG resulted in cytotoxicity and, when combined with IR, enhanced the radiation response, each effect with a temporal range from 6 to 48 h after drug exposure. In addition, mouse in vivo models using 17-AAG at clinically achievable concentrations yielded results that paralleled the in vitro radiosensitization studies of both single and fractioned courses of irradiation. The increase in IR-induced cell death appears to be attributable to a combination of both programmed and nonprogrammed cell death. We also measured total levels of several prosurvival and apoptotic signaling proteins. Akt1, extracellular signal-regulated kinase-1, Glut-1, HER-2/neu, Lyn, cAMP-dependent protein kinase, Raf-1, and vascular endothelial growth factor expression were down-regulated in 17-AAG-treated cells, identifying these factors as molecular markers and potential therapeutic targets. Finally, a series of immortalized and human papillomavirus-transformed cell lines were used to demonstrate that the radiosensitizing effects of 17-AAG were limited to transformed cells, suggesting a possible differential cytotoxic effect. This work shows that altered HSP90 function induces significant tumor cytotoxicity and radiosensitization, suggesting a potential therapeutic utility.     

Combinatorial efficacy achieved through two-point blockade within a signaling pathway-a chemical genetic approach

Whether the apparent efficacy of a specific kinase inhibitor is attributable solely to inhibition of its primary target, or to combined inhibition of additional unidentified kinases, is a critical issue in cancer therapy. We used a chemical genetic approach to generate a selective inhibitor of v-erbB [a transforming allele of epidermal growth factor receptor (EGFR)] and interrogated inhibition in known downstream signaling pathways. On the basis of this analysis, we hypothesized that dual inhibition of v-erbB and phosphatidylinositol 3' (PI3) kinases could show improved potency. We, therefore, used two different cell lines to examine the effects of v-erbB or EGFR inhibitors, in combination with PI3 kinase inhibitors, in mouse models for EGFR-driven cancers. When treated with NaPP1, v-erbB-as1-transformed fibroblasts showed cell-cycle arrest and decreased activity of Akt kinase. Inhibitors of v-erbB-as1 and of PI3 kinase showed enhanced efficacy in treating established 3T3:v-erbB-as1 tumor allografts. We extended these results to the human glioma cell line U87:MG transduced with DeltaEGFR, a tumor-derived activated allele, treating tumor-bearing mice with vehicle, the EGFR inhibitor ZD1839, LY294002, or ZD1839 plus LY294002. In human glioma xenografts, inhibition of EGFR cooperated similarly with inhibition of PI3 kinase. Our experiments provide a preclinical mechanistic basis for combining biologically based therapies directed against two targets within a complex signaling cascade.     

The sensitivity of lung cancer cell lines to the EGFR-selective tyrosine kinase inhibitor ZD1839 ('Iressa') is not related to the expression of EGFR or HER-2 or to K-ras gene status

ZD1839 ('Iressa') is an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) that inhibits EGFR signaling. Emerging evidence indicates that ZD1839 has clinical potential in lung cancer, but very little is known about the molecular characteristics of lung cancers that may determine sensitivity to ZD1839. We examined a panel of 19 lung cancer cell lines to investigate possible association between ZD1839 sensitivity and histological type, expression level and constitutive phosphorylation of EGFR and K-ras gene status. Our results indicate that neither expression level nor constitutive activation status of EGFR seems to predict sensitivity to ZD1839. In addition, ZD1839 sensitivity was not associated with expression of human epidermal growth factor receptor-2 (HER-2), another member of this tyrosine kinase receptor family nor with co-expression of EGFR and HER-2. Finally, no correlation was found between the presence of activating mutations of the K-ras gene, an important downstream mediator of the EGFR-transduced signals and the relative resistance to ZD1839. These findings warrant future study to clarify how ZD1839 inhibits lung cancer cell growth and to find a useful marker for prediction of sensitivity to this novel and promising agent for the treatment of lung cancers.     

The effects of ZD1839 (Iressa), a highly selective EGFR tyrosine kinase inhibitor, as a radiosensitiser in bile duct carcinoma cell lines

The signaling pathway that is initiated by binding of epidermal growth factor receptor (EGFR) and results in sustained signaling through PI3K plays an important role in a tumor's response to ionizing radiation. The current in vitro study explored both the effects of ZD1839 (Iressa), a highly selective EGFR tyrosine kinase inhibitor, as a radiosensitiser for bile duct carcinoma cell lines and ZD1839's general effects on cell growth in the same two lines. Secondly, we ensured suppression of radiation-induced phosphorylation of EGFR by ZD1839 using an immunoprecipitation technique. Furthermore, we examined radiation-induced phosphorylation of ERK, p38, JNK, and AKT with or without inhibitor with use of Western blot techniques and performed clonogenic assays to confirm radiosensitivity in the presence of a drug. ZD1839 inhibited cell growth of both cell lines and suppressed radiation-induced phosphorylation of EGFR. After exposure to radiation, there was an increase in phosphorylation of AKT as shown by Western blot. Treatment with either ZD1839 or LY294002 (the latter, a PI3K inhibitor) suppressed phosphorylation of AKT by Western blot. Both ZD1839 and LY294002 significantly suppressed colony formation by clonogenic assay; however, U0126 (a MEK1/2 inhibitor), SB203580 (a p38 inhibitor), and SP600125 (a JNK inhibitor) had no effect on colony formation. These results suggest that AKT may be a useful target molecule for enhancement of radiotherapy effect and that ZD1839 may have an important role in combination with radiotherapy for patients with bile duct carcinoma.     

Influence of epidermal growth factor receptor (EGFR), p53 and intrinsic MAP kinase pathway status of tumour cells on the antiproliferative effect of ZD1839 ("Iressa")

of ZD1839 ("Iressa") is an orally active, selective epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI), which blocks signal transduction pathways implicated in proliferation and survival of cancer cells, and other host-dependent processes promoting cancer growth. Permanent downstream activation of the mitogen-activated protein kinase pathway can theoretically bypass the upstream block of epidermal growth factor receptor-dependent mitogen-activated protein kinase activation at the epidermal growth factor receptor level. We investigated the impact of epidermal growth factor receptor content, p53 status and mitogen-activated protein kinase signalling status on ZD1839 sensitivity in a panel of human tumour cell lines: seven head and neck cancer cell lines and two colon cancer cell lines (LoVo, HT29) with derivatives differing only by a specific modification in p53 status (LoVo p53 wt + p53 mut cells, HT29 p53 mut + p53 wt rescued cells). The antiproliferative activity of ZD1839 was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test. ZD1839 concentrations ranged from 0.2-200 microM (48 h exposure). Epidermal growth factor receptor expression, p53 status and p42/p44 (for testing a constitutively active mitogen-activated protein kinase pathway status) were determined by competition analysis (Scatchard plots), denaturing gradient cell electrophoresis and Western blot, respectively. Epidermal growth factor receptor levels ranged from 388 to 33794 fmol mg(-1) protein, a range that is similar to that found in head and neck tumours. The IC(50) values for cell sensitivity to ZD1839 ranged from 6 to 31 microM and a significant inverse correlation (P=0.022, r=0.82) between IC(50) values and epidermal growth factor receptor levels was observed. There was no influence of p53 status on the sensitivity to ZD1839. In two head and neck cancer cell lines with comparably elevated epidermal growth factor receptor expression, a two-fold higher ZD1839 IC(50) value was found for the one with a constitutively active mitogen-activated protein kinase. In conclusion, ZD1839 was active against cells with a range of epidermal growth factor receptor levels, although more so in cells with higher epidermal growth factor receptor expression. Activity was unaffected by p53 status, but was reduced in cells strongly dependent on epidermal growth factor receptor signalling in the presence of an intrinsically activated mitogen-activated protein kinase pathway.