Radiosensitization of human breast cancer cells by a novel ErbB family receptor tyrosine kinase inhibitor

Inhibition of the thioredoxin system for radiosensitization therapy of cancer

Radiotherapy (RT) stands as a cornerstone in the clinical armamentarium against various cancers due to its proven efficacy. However, the intrinsic radiation resistance exhibited by cancer cells, coupled with the adverse effects of RT on normal tissues, often compromises its therapeutic potential and leads to unwanted side effects. This comprehensive review aims to consolidate our understanding of how radiosensitizers inhibit the thioredoxin (Trx) system in cellular contexts. Notable radiosensitizers, including gold nanoparticles (GNPs), gold triethylphosphine cyanide ([Au(SCN) (PEt3)]), auranofin, ceria nanoparticles (CONPs), curcumin and its derivatives, piperlongamide, indolequinone derivatives, micheliolide, motexafin gadolinium, and ethane selenide selenidazole derivatives (SeDs), are meticulously elucidated in terms of their applications in radiotherapy. In this review, the sensitization mechanisms and the current research progress of these radiosensitizers are discussed in detail, with the overall aim of providing valuable insights for the judicious application of Trx system inhibitors in the field of cancer radiosensitization therapy.

Quantifying the Effects of Combination Trastuzumab and Radiation Therapy in Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer

Background: Trastuzumab induces cell cycle arrest in HER2-overexpressing cells and demonstrates potential in radiosensitizing cancer cells. The purpose of this study is to quantify combination trastuzumab and radiotherapy to determine their synergy. Methods: In vitro, HER2+ cancer cells were treated with trastuzumab, radiation, or their combination, and imaged to evaluate treatment kinetics. In vivo, HER2+ tumor-bearing mice were treated with trastuzumab and radiation, and assessed longitudinally. An additional cohort was treated and sacrificed to quantify CD45, CD31, α-SMA, and hypoxia. Results: The interaction index revealed the additive effects of trastuzumab and radiation in vitro in HER2+ cell lines. Furthermore, the results revealed significant differences in tumor response when treated with radiation (p < 0.001); however, no difference was seen in the combination groups when trastuzumab was added to radiotherapy (p = 0.56). Histology revealed increases in CD45 staining in tumors receiving trastuzumab (p < 0.05), indicating potential increases in immune infiltration. Conclusions: The in vitro results showed the additive effect of combination trastuzumab and radiotherapy. The in vivo results showed the potential to achieve similar efficacy of radiotherapy with a reduced dose when combined with trastuzumab. If trastuzumab and low-dose radiotherapy induce greater tumor kill than a higher dose of radiotherapy, combination therapy can achieve a similar reduction in tumor burden.

Designing Personalized Treatment Plans for Breast Cancer

Breast cancer remains the leading cause of cancer deaths among women around the world. Contemporary treatment for breast cancer is complex and involves highly specialized medical professionals collaborating in a series of information-intensive processes. This poses significant challenges to optimization of treatment plans for individual patients. We propose a novel framework that enables personalization and customization of treatment plans for early stage breast cancer patients undergoing radiotherapy. Using a series of simulation experiments benchmarked with real-world clinical data, we demonstrate that the treatment plans generated from our proposed framework consistently outperform those from the existing practices in balancing the risk of local tumor recurrence and radiation-induced adverse effects. Our research sheds new light on how to combine domain knowledge and patient data in developing effective decision-support tools for clinical use. Although our research is specifically geared toward radiotherapy planning for breast cancer, the design principles of our framework can be applied to the personalization of treatment plans for patients with other chronic diseases that typically involve complications and comorbidities.

Breast cancers utilize hypoxic glycogen stores via PYGB, the brain isoform of glycogen phosphorylase, to promote metastatic phenotypes

In breast cancer, tumor hypoxia has been linked to poor prognosis and increased metastasis. Hypoxia activates transcriptional programs in cancer cells that lead to increased motility and invasion, as well as various metabolic changes. One of these metabolic changes, an increase in glycogen metabolism, has been further associated with protection from reactive oxygen species damage that may lead to premature senescence. Here we report that breast cancer cells significantly increase glycogen stores in response to hypoxia. We found that knockdown of the brain isoform of an enzyme that catalyzes glycogen breakdown, glycogen phosphorylase B (PYGB), but not the liver isoform, PYGL, inhibited glycogen utilization in estrogen receptor negative and positive breast cancer cells; whereas both independently inhibited glycogen utilization in the normal-like breast epithelial cell line MCF-10A. Functionally, PYGB knockdown and the resulting inhibition of glycogen utilization resulted in significantly decreased wound-healing capability in MCF-7 cells and a decrease in invasive potential of MDA-MB-231 cells. Thus, we identify PYGB as a novel metabolic target with potential applications in the management and/or prevention of metastasis in breast cancer.

Assessment of Radiation Resistance and Therapeutic Targeting of Cancer Stem Cells: A Raman Spectroscopic Study of Glioblastoma

Radiation is the standard therapy used for treating Glioblastoma (GBM), a grade IV brain cancer. Glioma Stem-like Cells (GSCs), an integral part of GBM, enforces resistance to radiation therapy of GBM. Studying the differential biomolecular composition of GSCs with varying levels of radiation sensitivity can aid in identifying the molecules and their associated pathways which impose resistance to cells thereby unraveling new targets which would serve as potential adjuvant therapy. Raman spectroscopy being a noninvasive, label free technique can determine the biomolecular constituent of cells under live conditions. In this study, we have deduced Raman spectral signatures to predict the radiosensitivity of any GSC accurately using the inherent and radiation induced biomolecular composition. Our study identified the differential regulation of several biomolecules which can be potential targets for adjuvant therapy. We radiosensitized the resistant GSCs using small molecule inhibitors specific to the metabolic pathways of these biomolecules. Efficient antitumor therapy can be attained with lower dosage of radiation along with these inhibitors and thus improving the survival rate of GBM patients with reduced side-effects from radiation.

Pharmacology of Epidermal Growth Factor Inhibitors

Research into the molecular bases of malignant diseases has yielded the development of many novel agents with potential antitumor activity. Evidence for a causative role for the epidermal growth factor receptor (EGFR), which is now regarded as an excellent target for cancer chemotherapy in human cancer, leads to the development of EGFR inhibitors. Two classes of anti-EGFR agents are currently in clinical use: monoclonal antibodies directed at the extracellular domain of the receptor, and the low-molecular-weight receptor tyrosine kinase inhibitors acting intracellularly by competing with adenosine triphosphate for binding to the tyrosine kinase portion of the EGFR. The effect on the receptor interferes with key biological functions including cell cycle arrest, potentiation of apoptosis, inhibition of angiogenesis and cell invasion and metastasis. Cetuximab, a monoclonal antibody, and the receptor tyrosine kinase inhibitors gefitinib and erlotinib are currently approved for the treatment of patients with cancer. New agents with clinical activity are entering the clinic, and new combinatorial approaches are being explored with the aim of improving the potency and pharmacokinetics of EGFR inhibition, to increase the synergistic activity in combination with chemotherapy and overcome resistance to the EGFR inhibitors.

Functional oncogene signatures guide rationally designed combination therapies to synergistically induce breast cancer cell death

A critical first step in the personalized approach to cancer treatment is the identification of activated oncogenes that drive each tumor. The Identification of driver oncogenes on a patient-by-patient basis is complicated by the complexity of the cancer genome and the fact that a particular genetic alteration may serve as a driver event only in a subset of tumors that harbor it. In this study, we set out to identify the complete set of functional oncogenes in a small panel of breast cancer cell lines. The cell lines in this panel were chosen because they each contain a known receptor tyrosine kinase (RTK) oncogene. To identify additional drivers, we integrated functional genetic screens with copy number and mutation analysis, and cancer genome knowledge databases. The resulting functional oncogene signatures were able to predict responsiveness of cell lines to targeted inhibitors. However, as single agents, these drugs had little effect on clonogenic potential. By contrast, treatment with drug combinations that targeted multiple oncogenes in the signatures, even at very low doses, resulted in the induction of apoptosis and striking synergistic effects on clonogenicity. In particular, targeting a driver oncogene that mediates AKT phosphorylation in combination with targeting the anti-apoptotic BCL2L1 protein had profound effects on cell viability. Importantly, because the synergistic induction of cell death was achieved using low levels of each individual drug, it suggests that a therapeutic strategy based on this approach could avoid the toxicities that have been associated with the combined use of multiple-targeted agents.

Trastuzumab and Hypofractionated Whole Breast Radiotherapy: A Victorious Combination?

INTRODUCTION

The purpose of this study was to examine the impact of trastuzumab on acute skin and cardiac toxicity in patients with breast cancer treated with chemotherapy with or without trastuzumab and adjuvant whole breast hypofractionated radiotherapy (hypo-RT).

MATERIALS AND METHODS

The study was conducted on 727 patients treated from April 2009 to October 2016. Patients received 42.4 Gy in 16 daily fractions (2.65 Gy per fraction). A boost was only administered in cases with grade (G) 3 primary tumor and close or positive margins. Acute and late toxicity was assessed prospectively during and after hypo-RT, based on the Radiation Therapy Oncology Group scale. Multivariable logistic regression models were used to examine the onset of acute skin toxicity (≥ G2) in the whole study population, and the impact of trastuzumab on the onset of acute skin (≥ G2) or cardiac toxicity in the subgroup of 176 patients given chemotherapy.

RESULTS

A total of 176 patients received chemotherapy with anthracycline and taxane, and 51 (29%) of them were also treated with trastuzumab. Acute G1, G2, and G3 skin toxicity occurred, respectively, in 56.8%, 27.3%, and 1.1% of the patients given chemotherapy alone, and in 64.7%, 19.6%, and 0% of those given trastuzumab as well. Among the patients given chemotherapy, left ventricular ejection fraction (LVEF) toxicity developed with a severity of G1 (LVEF < 60%-50%) in 12 (6.8%) patients, G2 (LVEF < 50%-40%) in 2 (1.1%) patients, and G3 (LVEF < 40%) in 1 (0.6%) patient. Among the patients also given trastuzumab, 7 (13.7%) patients had G1 LVEF toxicity, and 1 (2%) patient had G2 LVEF toxicity. We found that patients given trastuzumab were at higher risk of cardiac toxicity ≥ G1 (odds ratio, 4.3; P = .01), and at lower risk of acute skin toxicity ≥ G2 (odds ratio, 0.4; P = .03) than patients given chemotherapy alone.

CONCLUSIONS

This analysis showed that trastuzumab with adjuvant hypo-RT for patients with breast cancer was generally well-tolerated in routine clinical practice. A longer follow-up will be necessary to assess late cardiac toxicity.

Riluzole synergizes with paclitaxel to inhibit cell growth and induce apoptosis in triple-negative breast cancer

PURPOSE

One in eight women will develop breast cancer, 15-20% of whom will have triple-negative breast cancer (TNBC), an aggressive breast cancer with no current targeted therapy. We have demonstrated that riluzole, an FDA-approved drug for treating amyotrophic lateral sclerosis, inhibits growth of TNBC. In this study, we explore potential synergism between riluzole and paclitaxel, a chemotherapeutic agent commonly used to treat TNBC, in regulating TNBC proliferation, cell cycle arrest, and apoptosis.

METHODS

TNBC cells were treated with paclitaxel and/or riluzole and synergistic effects on cell proliferation were quantified via MTT assay and CompuSyn analysis. Apoptosis was observed morphologically and by measuring cleaved PARP/caspase three products. Microarray analysis was performed using MDA-MB-231 cells to examine cell cycle genes regulated by riluzole and any enhanced effects on paclitaxel-mediated cell cycle arrest, determined by FACS analysis. These results were confirmed in vivo using a MDA-MB-231 xenograft model.

RESULTS

Strong enhanced or synergistic effects of riluzole on paclitaxel regulation of cell cycle progression and apoptosis was demonstrated in all TNBC cells tested as well as in the xenograft model. The MDA-MB-231, SUM149, and SUM229 cells, which are resistant to paclitaxel treatment, demonstrated the strongest synergistic or enhanced effect. Key protein kinases were shown to be upregulated in this study by riluzole as well as downstream cell cycle genes regulated by these kinases.

CONCLUSIONS

All TNBC cells tested responded synergistically to riluzole and paclitaxel strongly suggesting the usefulness of this combinatorial treatment strategy in TNBC, especially for patients whose tumors are relatively resistant to paclitaxel.

Inferring Intracellular Signal Transduction Circuitry from Molecular Perturbation Experiments

The development of network inference methodologies that accurately predict connectivity in dysregulated pathways may enable the rational selection of patient therapies. Accurately inferring an intracellular network from data remains a very challenging problem in molecular systems biology. Living cells integrate extremely robust circuits that exhibit significant heterogeneity, but still respond to external stimuli in predictable ways. This phenomenon allows us to introduce a network inference methodology that integrates measurements of protein activation from perturbation experiments. The methodology relies on logic-based networks to provide a predictive approximation of the transfer of signals in a network. The approach presented was validated in silico with a set of test networks and applied to investigate the epidermal growth factor receptor signaling of a breast epithelial cell line, MFC10A. In our analysis, we predict the potential signaling circuitry most likely responsible for the experimental readouts of several proteins in the mitogen-activated protein kinase and phosphatidylinositol-3 kinase pathways. The approach can also be used to identify additional necessary perturbation experiments to distinguish between a set of possible candidate networks.

Oncogenic signaling in amphiregulin and EGFR-expressing PTEN-null human breast cancer

A subset of triple negative breast cancer (TNBC) is characterized by overexpression of the epidermal growth factor receptor (EGFR) and loss of PTEN, and patients with these determinants have a poor prognosis. We used cell line models of EGFR‐positive/PTEN null TNBC to elucidate the signaling networks that drive the malignant features of these cells and cause resistance to EGFR inhibitors. In these cells, amphiregulin (AREG)‐mediated activation of EGFR results in up‐regulation of fibronectin (FN1), which is known to be a mediator of invasive capacity via interaction with integrin β1. EGFR activity in this PTEN null background also results in Wnt/beta‐catenin signaling and activation of NF‐κB. In addition, AKT is constitutively phosphorylated in these cells and is resistant to gefitinib. Expression profiling demonstrated that AREG‐activated EGFR regulates gene expression differently than EGF‐activated EGFR, and functional analysis via genome‐scale shRNA screening identified a set of genes, including PLK1 and BIRC5, that are essential for survival of SUM‐149 cells, but are uncoupled from EGFR signaling. Thus, our results demonstrate that in cells with constitutive EGFR activation and PTEN loss, critical survival genes are uncoupled from regulation by EGFR, which likely mediates resistance to EGFR inhibitors.

Activation of EGFR by AREG alters signaling and gene expression compared to EGF.

Activation of EGFR by AREG reduces mTORC1 pathway expression and phosphorylation.

EGF‐positive, PTEN‐null TNBC cells are poised for Wnt/beta‐catenin signaling.

Wnt/beta‐catenin activity occurs in a subset of cells and is enhanced in mammospheres.

Regulation of growth/survival genes is uncoupled from EGFR in PTEN‐null TNBC cells.

"The Infinite Maze" of breast cancer, signaling pathways and radioresistance

The parallel growth in our understanding of tumor biology and genetics might be the key to understanding local recurrence after optimal treatment is applied. Data suggest that genetic alterations and breast cancer molecular subtypes have an effect on radiotherapy efficacy and that the HER2, EGFR/PI3K/Akt signaling pathways play a pivotal role in modulation of post-irradiation survival. These pathways have been found to be involved in radiosensitivity and/or radioresistance, tumor cell proliferation, and hypoxia. Therefore, affecting the functional activity of key players combined with radiotherapy might be the future of breast irradiation.

Pre-clinical studies of Notch signaling inhibitor RO4929097 in inflammatory breast cancer cells

Basal breast cancer, common among patients presenting with inflammatory breast cancer (IBC), has been shown to be resistant to radiation and enriched in cancer stem cells. The Notch pathway plays an important role in self-renewal of breast cancer stem cells and contributes to inflammatory signaling which promotes the breast cancer stem cell phenotype. Herein, we inhibited Notch signaling using a gamma secretase inhibitor, RO4929097, in an in vitro model that enriches for cancer initiating cells (3D clonogenic assay) and conventional 2D clonogenic assay to compare the effect on radiosensitization of the SUM149 and SUM190 IBC cell lines. RO4929097 downregulated the Notch target genes Hes1, Hey1, and HeyL, and showed a significant reduction in anchorage independent growth in SUM190 and SUM149. However, the putative self-renewal assay mammosphere formation efficiency was increased with the drug. To assess radiosensitization of putative cancer stem cells, cells were exposed to increasing doses of radiation with or without 1 μM RO4929097 in their standard (2D) and self-renewal enriching (3D) culture conditions. In the conventional 2D clonogenic assay, RO4929097 significantly sensitized SUM190 cells to ionizing radiation and has a modest radiosensitization effect in SUM149 cells. In the 3D clonogenic assays, however, a radioprotective effect was seen in both SUM149 and SUM190 cells at higher doses. Both cell lines express IL-6 and IL-8 cytokines known to mediate the efficacy of Notch inhibition and to promote self-renewal of stem cells. We further showed that RO429097 inhibits normal T-cell synthesis of some inflammatory cytokines, including TNF-α, a potential mediator of IL-6 and IL-8 production in the microenvironment. These data suggest that additional targeting agents may be required to selectively target IBC stem cells through Notch inhibition, and that evaluation of microenvironmental influences may shed further light on the potential effects of this inhibitor.

Targeting the EGFR signaling pathway in cancer therapy

INTRODUCTION

Cancer is a devastating disease; however, several therapeutic advances have recently been made, wherein EGFR and its family members have emerged as useful biomarkers and therapeutic targets. EGFR, a transmembrane glycoprotein is a member of the ERBB receptor tyrosine kinase superfamily. EGFR binds to its cognate ligand EGF, which further induces tyrosine phosphorylation and receptor dimerization with other family members leading to enhanced uncontrolled proliferation. Several anti-EGFR therapies such as monoclonal antibodies and tyrosine kinase inhibitors have been developed, which has enabled clinicians to identify and treat specific patient cohorts.

AREAS COVERED

This review covers the basic mechanism of EGFR activation and the role of EGFR signaling in cancer progression. Furthermore, current developments made toward targeting the EGFR signaling pathway for the treatment of epithelial cancers and a summary of the various anti-EGFR therapeutic agents that are currently in use are also presented in this review.

EXPERT OPINION

EGFR signaling is a part of a complex network that has been the target of effective cancer therapies. However, a further understanding of the system is required to develop an effective anticancer regimen. A combination therapy that comprises an anti-EGFR and a chemotherapeutic/chemopreventive agent will exhibit a multi-pronged approach that can be developed into a highly attractive and specific molecular oriented remedy.

Young age is associated with ipsilateral breast tumor recurrence after breast conserving surgery and radiation therapy in patients with HER2-positive/ER-negative subtype

Young breast cancer patients are more likely than old patients to experience ipsilateral breast tumor recurrence (IBTR) after breast conserving surgery (BCS). However, the pathological processes underlying this relationship have not been elucidated. We investigated the effect of young age on IBTR in a Korean cohort of women with different molecular subtypes of breast cancer. We analyzed data of 2,102 consecutive breast cancer patients who underwent BCS and post-surgical radiation therapy (RT) at two Korean institutions between 2000 and 2005. Patients were classified as young (≤ 40 years; N = 513) or old (> 40 years; N = 1,589). Breast cancer subtype was determined by estrogen receptor (ER), progesterone receptor (PR), and HER2. Median follow-up duration was 61 months. The 5-year IBTR rate was 3.4% in young patients and 1.1% in old patients (P < 0.001). Univariate analysis indicated that IBTR rate in young patients with luminal A and HER2 subtypes was significantly greater than in old patients with these subtypes (P = 0.015 and P < 0.001, respectively). Multivariate analysis, which used luminal A subtype in old patients as reference, indicated that HER2 subtype in young patients was associated with increased risk of IBTR (hazard ratio, HR = 12.24; 95% CI: 2.54-57.96). Among old patients, HER2 subtype was not associated with increased IBTR. In conclusion, young women had a higher rate of IBTR after BCS and RT than old women. This difference is mainly among women with HER2 subtype. Aggressive local control and adjuvant therapy should be considered for young women with HER2 subtype breast cancer.

Estrogen/progesterone receptor negativity and HER2 positivity predict locoregional recurrence in patients with T1a,bN0 breast cancer

PURPOSE

Data have suggested that the molecular features of breast cancer are important determinants of outcome; however, few studies have correlated these features with locoregional recurrence (LRR). In the present study, we evaluated estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) as predictors of LRR in patients with lymph node-negative disease and tumors < or = 1cm, because these patients often do not receive adjuvant chemotherapy or trastuzumab.

METHODS AND MATERIALS

The data from 911 patients with stage T1a,bN0 breast cancer who had received definitive treatment at our institution between 1997 and 2002 were retrospectively reviewed. We prospectively analyzed ER/PR/HER2 expression from the archival tissue blocks of 756 patients. These 756 patients represented the cohort for the present study.

RESULTS

With a median follow-up of 6.0 years, the 5- and 8-year Kaplan-Meier LRR rate was 1.6% and 5.9%, respectively, with no difference noted in those who underwent breast conservation therapy vs. mastectomy (p=.347). The 8-year LRR rates were greater in the patients with ER-negative (10.6% vs. 4.2%, p=.016), PR-negative (9.0% vs. 4.2%, p=.009), or HER2-positive (17.5% vs. 3.9%, p=0.009) tumors. On multivariate analysis, ER-negative and PR-negative disease (hazard ratio, 2.37; p=.046) and HER2-positive disease (hazard ratio, 3.13, p=.016) independently predicted for LRR.

CONCLUSION

Patients with ER/PR-negative or HER2-positive T1a,bN0 breast cancer had a greater risk of LRR. Therapeutic strategies, such as the use of chemotherapy and/or anti-HER2 therapies, should be considered for future clinical trials for these patients.

Lapatinib in combination with radiation diminishes tumor regrowth in HER2+ and basal-like/EGFR+ breast tumor xenografts

PURPOSE

To determine whether lapatinib, a dual epidermal growth factor receptor (EGFR)/HER2 kinase inhibitor, can radiosensitize EGFR+ or HER2+ breast cancer xenografts.

METHODS AND MATERIALS

Mice bearing xenografts of basal-like/EGFR+ SUM149 and HER2+ SUM225 breast cancer cells were treated with lapatinib and fractionated radiotherapy and tumor growth inhibition correlated with alterations in ERK1 and AKT activation by immunohistochemistry.

RESULTS

Basal-like/EGFR+ SUM149 breast cancer tumors were completely resistant to treatment with lapatinib alone but highly growth impaired with lapatinib plus radiotherapy, exhibiting an enhancement ratio average of 2.75 and a fractional tumor product ratio average of 2.20 during the study period. In contrast, HER2+ SUM225 breast cancer tumors were highly responsive to treatment with lapatinib alone and yielded a relatively lower enhancement ratio average of 1.25 during the study period with lapatinib plus radiotherapy. Durable tumor control in the HER2+ SUM225 model was more effective with the combination treatment than either lapatinib or radiotherapy alone. Immunohistochemical analyses demonstrated that radiosensitization by lapatinib correlated with ERK1/2 inhibition in the EGFR+ SUM149 model and with AKT inhibition in the HER2+ SUM225 model.

CONCLUSION

Our data suggest that lapatinib combined with fractionated radiotherapy may be useful against EGFR+ and HER2+ breast cancers and that inhibition of downstream signaling to ERK1/2 and AKT correlates with sensitization in EGFR+ and HER2+ cells, respectively.

Altered EGFR localization and degradation in human breast cancer cells with an amphiregulin/EGFR autocrine loop

The epidermal growth factor receptor (EGFR) and its ligand amphiregulin (AR) have been shown to be co-over expressed in breast cancer. We have previously shown that an AR/EGFR autocrine loop is required for SUM149 human breast cancer cell proliferation, motility and invasion. We also demonstrated that AR can induce these altered phenotypes when expressed in the normal mammary epithelial cell line MCF10A, or by exposure of these cells to AR in the medium. In the present studies, we demonstrate that SUM149 cells and immortalized human mammary epithelial MCF10A cells that over express AR (MCF10A AR) or are cultured in the presence of exogenous AR, express higher levels of EGFR protein than MCF10A cells cultured in EGF. Pulse-chase analysis showed that EGFR protein remained stable in the presence of AR, yet was degraded in the presence of EGF. Consistent with this observation, tyrosine 1045 on the EGFR, the c-cbl binding site, exhibited less phosphorylation following stimulation with AR than following stimulation with EGF. Ubiquitination of the receptor was also dramatically less following stimulation with AR than following stimulation with EGF. Flow cytometry analysis showed that EGFR remained on the cell surface following stimulation with AR but was rapidly internalized following stimulation with EGF. Immunofluorescence and confocal microscopy confirmed the flow cytometry results. EGFR in MCF10A cells cultured in the presence of EGF exhibited a predominantly intracellular, punctate localization. In stark contrast, SUM149 cells and MCF10A cells growing in the presence of AR expressed EGFR predominantly on the membrane and at cell-cell junctions. We propose that AR alters EGFR internalization and degradation in a way that favors accumulation of EGFR at the cell surface and ultimately leads to changes in EGFR signaling.

Loss of Raf kinase inhibitory protein induces radioresistance in prostate cancer

PURPOSE

External beam radiotherapy (RT) is often used in an attempt to cure localized prostate cancer (PCa), but it is only palliative against disseminated disease. Raf kinase inhibitory protein (RKIP) is a metastasis suppressor whose expression is reduced in approximately 50% of localized PCa tissues and is absent in metastases. Chemotherapeutic agents have been shown to induce tumor apoptosis through induction of RKIP expression. Our goal was to test whether RT similarly induces apoptosis through induction of RKIP expression.

METHODS AND MATERIALS

The C4-2B PCa cell line was engineered to overexpress or underexpress RKIP. The engineered cells were tested for apoptosis in cell culture and tumor regression in mice after RT.

RESULTS

RT induced both RKIP expression and apoptosis of PCa cells. Overexpression of RKIP sensitized PCa cells to radiation-induced apoptosis. In contrast, short-hairpin targeting of RKIP, so that RT could not induce RKIP expression, protected cells from radiation-induced apoptosis. In a murine model, knockdown of RKIP in PCa cells diminished radiation-induced apoptosis. Molecular concept mapping of genes altered on manipulation of RKIP expression revealed an inverse correlation with the concept of genes altered by RT.

CONCLUSION

The data presented in this report indicate that the loss of RKIP, as seen in primary PCa tumors and metastases, confers protection against radiation-induced apoptosis. Therefore, it is conceivable that the loss of RKIP confers a growth advantage on PCa cells at distant sites, because the loss of RKIP would decrease apoptosis, favoring proliferation.

The combination of epidermal growth factor receptor inhibitors with gemcitabine and radiation in pancreatic cancer

PURPOSE

Gemcitabine-radiotherapy is a standard treatment for locally advanced pancreatic cancer. Clinical data have shown that gemcitabine plus erlotinib is superior to gemcitabine alone for advanced pancreatic cancer. Therefore, we investigated the effects of the combination of epidermal growth factor receptor inhibitors with gemcitabine and radiation on a pancreatic cancer model.

EXPERIMENTAL DESIGN

EGFR signaling was analyzed by measuring phosphorylated EGFR (pEGFR(Y845, (Y1173)) and AKT (pAKT(S473)) protein levels in pancreatic cancer cell lines and tumors. The effects of scheduling on gemcitabine-mediated cytotoxicity and radiosensitization combined with erlotinib were determined by clonogenic survival. In vivo, the effects of cetuximab or erlotinib in combination with gemcitabine-radiation on the growth of BxPC-3 tumor xenografts were measured.

RESULTS

We found in vitro that gemcitabine induced phosphorylation of EGFR at Y845 and Y1173 that was blocked by erlotinib. Treatment of BxPC-3 cells with gemcitabine before erlotinib enhanced gemcitabine-mediated cytotoxicity without abrogating radiosensitization. In vivo, cetuximab or erlotinib in combination with gemcitabine-radiation inhibited growth compared with gemcitabine-radiation (time to tumor doubling: gemcitabine + radiation, 19 +/- 3 days; cetuximab + gemcitabine + radiation, 30 +/- 3 days; P < 0.05, erlotinib + gemcitabine + radiation 28 +/- 3 days; P < 0.1). Cetuximab or erlotinib in combination with gemcitabine-radiation resulted in significant inhibition of pEGFR(Y1173) and pAKT(S473) early in treatment, and pEGFR(Y845), pEGFR(Y1173), and pAKT(S473) by the end of treatment. This study shows a novel difference pEGFR(Y845) and pEGFR(Y1173) in response to EGFR inhibition.

CONCLUSIONS

These results show that the EGFR inhibitors cetuximab and erlotinib increase the efficacy of gemcitabine-radiation. This work supports the integration of EGFR inhibitors with gemcitabine-radiation in clinical trials for pancreatic cancer.

The emerging role of cetuximab in head and neck cancer: a 2007 perspective

The integration of targeted therapies into clinical practice constitutes the paradigm of oncology treatment in the current era. Cetuximab, a recombinant human/mouse chimeric epidermal growth factor (EGFR) monoclonal antibody is a targeted agent that has seen expanding indication in recent years. Originally approved for colorectal cancer, its role in the treatment of squamous cell carcinoma of the head and neck has augmented treatment options for patients who are refractory to or cannot tolerate platinum. This article will review the science underlying cetuximab, data supporting its use in patients with locally advanced and recurrent/metastatic disease, common toxicities of therapy, and the integration of this treatment with radiation therapy.

Trastuzumab signaling in ErbB2-overexpressing inflammatory breast cancer correlates with X-linked inhibitor of apoptosis protein expression

Inflammatory breast cancer (IBC) patients show poor survival and a significant incidence of epidermal growth factor receptor-2 (ErbB2) overexpression. A distinct mechanism involving increased expression of X-linked inhibitor of apoptosis protein (XIAP) and survivin, key members of the inhibitor of apoptosis protein (IAP) family, was observed post-trastuzumab (an ErbB2 monoclonal antibody) treatment in an ErbB2-overexpressing, estrogen receptor negative, IBC cellular model, SUM190PT, isolated from a primary IBC tumor. In contrast, a decrease in the IAP expression was observed in the non-IBC, ErbB2-overexpressing SKBR3 cells in which trastuzumab treatment also decreased p-AKT and cell viability. Further, in SUM190PT cells, therapeutic sensitivity to GW583340 (a dual epidermal growth factor receptor/ErbB2 kinase inhibitor) corresponded with XIAP down-regulation and abrogation of XIAP inhibition on active caspase-9 release. Specific small interfering RNA-mediated XIAP inhibition in combination with trastuzumab caused decrease in inactive procaspase-9 and inhibition of p-AKT corresponding with 45% to 50% decrease in cell viability in the SUM190PT cells, which have high steady-state p-AKT levels. Further, embelin, a small-molecule inhibitor that abrogates binding of XIAP to procaspase-9, caused significant decrease in SUM190PT viability. However, embelin in combination with trastuzumab failed to affect SUM190PT viability because it has no direct effect on XIAP, which is induced by trastuzumab treatment. These data have identified a novel functional link between ErbB2 signaling and antiapoptotic pathway mediated by XIAP. Blockade of the IAP antiapoptotic pathway alone or in combination would be an attractive strategy in IBC therapy.

Epidermal growth factor receptor-targeted therapy for pancreatic cancer

Clinical and experimental work supports the view that the epidermal growth factor receptor (EGFR) is a relevant target for cancer therapy. Expression of EGFR is exaggerated in pancreatic adenocarcinoma and activation of EGFR appears to have an important role in the growth and differentiation of this and other types of cancers. EGFR-targeted therapeutic approaches have shown clinical activity in advanced human cancers for which chemotherapy over the last 30 years has sustained a mere palliative role at best. Therefore, the need remains for novel anti-cancer therapies that effectively and specifically target epithelial tumor cells while minimizing the toxic side-effects commonly associated with cytotoxic conventional therapies. Agents capable of inhibiting EGFR activity with resultant inhibition of cell proliferation and angiogenesis have significant potential as chemotherapeutic agents for the treatment of pancreatic adenocarcinomas as well as multiple other malignancies.

Translational approaches for the prevention of estrogen receptor-negative breast cancer

Breast cancer prevention has focused heavily on endocrine interventions using selective estrogen receptor modulators and aromatase inhibitors. Tamoxifen, the stereotypical selective estrogen receptor modulator, significantly reduces the breast cancer incidence in high-risk women. Selective estrogen receptor modulators and aromatase inhibitors, however, only prevent the development of estrogen receptor-positive breast cancer and have no effect in reducing the risk of estrogen receptor-negative breast cancer, which has poor prognosis. Thus, preventive therapies for estrogen receptor-negative breast cancer are clearly needed. Recently, a number of novel chemopreventive agents targeting nonendocrine pathways have been developed and shown to prevent estrogen receptor-negative mammary tumorigenesis in animal models. These agents include rexinoids, selective cyclooxygenase-2 inhibitors, tyrosine kinase inhibitors, and others. In this review, we discuss the effects of selective estrogen receptor modulators and aromatase inhibitors, as well as novel agents targeting nonendocrine pathways. We also discuss the promise of combining these agents for the effective prevention of all forms of breast cancer.

p38MAPK-activated AKT in HER-2 overexpressing human breast cancer cells acts as an EGF-independent survival signal

BACKGROUND

HER-2 is an epidermal growth factor receptor (EGFR) family receptor tyrosine kinase that is overexpressed in about 30% of human breast cancers correlating with a poor prognosis. Previous work in our laboratory has found that HER-2 overexpression plays a role in growth factor independence, anchorage independence, motility, and invasion of naturally occurring basement membranes. We also found that AKT was activated by p38MAPK in these cells, but this activation did not play a role in invasion. Since AKT has been shown in other systems to be a survival factor, we hypothesized that HER-2 mediated activation of AKT is necessary for growth factor independence.

METHODS

Human mammary epithelial cells transduced to overexpress HER-2, HER-2, PTEN, and Myr-AKT and the primary breast cancer cell lines SUM-149 and SUM-225 were used to dissect the signaling pathways leading to growth factor independence and anchorage-independent growth in HER-2 overexpressing cells.

RESULTS

We found that, in the absence of EGF, p38MAPK-activated AKT is necessary for HER-2 overexpressing cells to survive and to form colonies in soft agar. We show that EGF works as a survival signal in the absence of p38MAPK-mediated activation of AKT. We also show that human mammary epithelial cells expressing a constitutively active AKT do not require EGF for growth or colony formation in soft agar.

CONCLUSIONS

The data presented here indicate that AKT activation can compensate for EGF-mediated cell survival signals leading to growth factor independence and anchorage-independent growth.

Integration of EGFR inhibitors with radiochemotherapy

Laboratory studies that led to the development of epidermal growth factor receptor (EGFR) inhibitors indicated that such inhibitors would be effective when given to patients with tumours that are driven by activated EGFR. However, initial clinical studies have shown modest responses to EGFR inhibitors when used alone, and it has not yet been possible to clearly identify which tumours will respond to this therapy. As a result, EGFR inhibitors are now used in combination with radiation therapy, chemotherapy and, more recently, with concurrent radiochemotherapy. In general, these clinical trials have been designed without much preclinical data. What do we need to know to make these combinations successful in the clinic?

Autocrine and juxtacrine effects of amphiregulin on the proliferative, invasive, and migratory properties of normal and neoplastic human mammary epithelial cells

Amphiregulin (AR) autocrine loops have been associated with several types of cancer. We demonstrate that SUM149 breast cancer cells have a self-sustaining AR autocrine loop. SUM149 cells are epidermal growth factor (EGF)-independent for growth, and they overexpress AR mRNA, AR membrane precursor protein, and secreted AR relative to the EGF-dependent human mammary epithelial cell line MCF10A. MCF10A cells made to overexpress AR (MCF10A AR) are also EGF-independent for growth. Treatment with the pan-ErbB inhibitor CI1033 and the anti-EGF receptor (EGFR) antibody C225 demonstrated that ligand-mediated activation of EGFR is required for SUM149 cell proliferation. AR-neutralizing antibody significantly reduced both SUM149 EGFR activity and cell proliferation, confirming that an AR autocrine loop is required for mitogenesis in SUM149 cells. EGFR tyrosine phosphorylation was dramatically decreased in both SUM149 and MCF10A AR cells after inhibition of AR cleavage with the broad spectrum metalloprotease inhibitor GM6001, indicating that an AR autocrine loop is strictly dependent on AR cleavage in culture. However, a juxtacrine assay where fixed SUM149 cells and MCF10A AR cells were overlaid on top of EGF-deprived MCF10A cells showed that the AR membrane precursor can activate EGFR. SUM149 cells, MCF10A AR cells, and MCF10A cells growing in exogenous AR were all considerably more invasive and motile than MCF10A cells grown in EGF. Moreover, AR up-regulates a number of genes involved in cell motility and invasion in MCF10A cells, suggesting that an AR autocrine loop contributes to the aggressive breast cancer phenotype.

The Impact of HER-2 Status on Local Recurrence in Women with Stage I?II Breast Cancer Treated with Breast-Conserving Therapy

This study was undertaken to determine whether overexpression of the oncogene HER-2 is associated with an increase in local recurrence in women with early stage breast cancer treated with breast-conserving therapy (BCT). A retrospective review of the medical records of all women treated with stage I-II invasive breast cancer from 1991 through 2001 was performed. Of 596 eligible patients treated in that time period, immunohistochemical testing for HER-2 expression was performed in 352 patients (59%): 266 patients (76%) were HER-2 negative and 86 patients (24%) were HER-2 positive. Median follow-up was 5.4 years. The patient characteristics for the two groups were compared for age, pathologic T and N stage, number of positive nodes, estrogen receptor (ER) and progesterone receptor (PR) status, radiation treatment, and use of hormonal therapy or chemotherapy. There were no significant differences in any of these parameters between the two groups (all p > or = 0.10). Local recurrence at 5 years was 2% in the HER-2-negative group and 0% in the HER-2-positive group (p = 0.15). There was no difference in local recurrence after BCT between HER-2-positive and negative breast cancers at 5 years. Therefore HER-2 overexpression does not appear to be a contraindication to BCT.

Disruption of the Y-Box Binding Protein-1 Results in Suppression of the Epidermal Growth Factor Receptor and HER-2

The overexpression of the epidermal growth factor receptor (EGFR) and HER-2 underpin the growth of aggressive breast cancer; still, it is unclear what governs the regulation of these receptors. Our laboratories recently determined that the Y-box binding protein-1 (YB-1), an oncogenic transcription/translation factor, induced breast tumor cell growth in monolayer and in soft agar. Importantly, mutating YB-1 at Ser(102), which resides in the DNA-binding domain, prevented growth induction. We reasoned that the underlying cause for growth attenuation by YB-1(Ser(102)) is through the regulation of EGFR and/or HER-2. The initial link between YB-1 and these receptors was sought by screening primary tumor tissue microarrays. We determined that YB-1 (n = 389 cases) was positively associated with EGFR (P < 0.001, r = 0.213), HER-2 (P = 0.008, r = 0.157), and Ki67 (P < 0.0002, r = 0.219). It was inversely linked to the estrogen receptor (P < 0.001, r = -0.291). Overexpression of YB-1 in a breast cancer cell line increased HER-2 and EGFR. Alternatively, mutation of YB-1 at Ser(102) > Ala(102) prevented the induction of these receptors and rendered the cells less responsive to EGF. The mutant YB-1 protein was also unable to optimally bind to the EGFR and HER-2 promoters based on chromatin immunoprecipitation. Furthermore, knocking down YB-1 with small interfering RNA suppressed the expression of EGFR and HER-2. This was coupled with a decrease in tumor cell growth. In conclusion, YB-1(Ser(102)) is a point of molecular vulnerability for maintaining the expression of EGFR and HER-2. Targeting YB-1 or more specifically YB-1(Ser(102)) are novel approaches to inhibiting the expression of these receptors to ultimately suppress tumor cell growth.

Irreversible pan-ErbB tyrosine kinase inhibitor CI-1033 induces caspase-independent apoptosis in colorectal cancer DiFi cell line

The epidermal growth factor receptor (EGFR) is overexpressed in the majority of colorectal carcinomas and represents a target for therapeutic interventions with signal transduction inhibitors. We investigated the ability of CI-1033 to induce apoptosis and inhibition of proliferation in the colorectal cancer cell lines DiFi and Caco-2, which both express high levels of EGFR. While in Caco-2 cells CI-1033 treatment at a concentration 0.1 microM for 72 hours demonstrated only antiproliferative (53.7 +/- 4.3%) but no pro-apoptotic effects, treatment of DiFi cells resulted in a reduced proliferation rate (31.4 +/- 3.1%) and in apoptosis (44.2 +/- 8.9%). In order to define proteins involved in the regulation of apoptosis, we aimed to determine differences in the proteome profile of both cell lines before and after treatment with CI-1033. Cellular proteins were analyzed by 2-D gel electrophoresis followed by computational image analysis and mass spectrometry. Our data show that DiFi cells differ from Caco-2 cells in nine significantly upregulated proteins, and their potential role in apoptosis is described. We demonstrate that induction of apoptosis was triggered via caspase-independent pathways. Overexpression of leukocyte elastase inhibitor (LEI) and translocation of cathepsin D to the cytosol accompanied by upregulation of other defined proteins resulted in Bax-independent AIF translocation from mitochondria into the nucleus and apoptosis. Definition of these proteins can pave the way for functional studies and contribute to a better understanding of the effects of CI-1033 and the pathways of caspase-independent cell death.

Heat shock protein 90 inhibitor 17-allylamino-17-demethoxygeldanamycin potentiates the radiation response of tumor cells grown as monolayer cultures and spheroids by inducing apoptosis

Activation of the PI3K-Akt pathway is known to induce tumor radioresistance. In the current study, we examined the ability of 17AAG, which decreases the levels of Hsp90 client proteins including components of the PI3K-Akt pathway, to sensitize radioresistant human squamous cell carcinoma cells to X-irradiation. Human squamous cell carcinoma cell lines (SQ20B, SCC61 and SCC13) were incubated for 16 h at 37 degrees C in medium containing 17AAG. Radiation sensitivity was determined by clonogenic assays, and protein levels were examined by western blotting. Apoptosis was determined in monolayer cells by AO/EB double staining and in spheroids using the TdT-mediated dUTP nick end labeling assay. 17AAG (0.2 microM) enhanced the radiosensitivity more effectively in radioresistant SQ20B and SCC13 cells than in radiosensitive SCC61 cells. However, in all three cell lines, 17AAG increased radiation-induced apoptosis by reducing the expression of EGFR and ErbB-2 and inhibiting the phosphorylation of Akt. Furthermore, 17AAG (1 microM) sensitized SQ20B spheroids to radiation, and inhibition of Akt activation by 17AAG increased radiation-induced apoptosis in spheroids. The findings suggest that 17AAG effectively sensitizes radioresistant cells to radiation by inhibiting the PI3K-Akt pathway. Targeting the PI3K-Akt pathway with 17AAG could be a useful strategy for radiosensitization of carcinomas.

Epidermal growth factor inhibition in solid tumours

The epidermal growth factor receptor (EGFR) plays an important role in the carcinogenesis of many human malignancies and is therefore an attractive target against which anticancer therapy may be effective. At present, there are two ways in which this may be achieved clinically: antibodies against EGFR and inhibitors of the EGFR tyrosine kinase. This review describes presently approved agents cetuximab (monoclonal EGFR antibody), gefitinib and erlotinib (EGFR tyrosine kinase inhibitors) in detail. Efficacy data for these agents in various human malignancies is presented. Various other agents that are in the early stages of development at present have also been mentioned.

Hypofractionated Accelerated Radiotherapy With Cytoprotection Combined With Trastuzumab, Liposomal Doxorubicine, and Docetaxel in c-erbB-2???Positive Breast Cancer

OBJECTIVES

Trastuzumab, an antic-erbB-2 monoclonal antibody, has become a standard component of chemotherapy for c-erbB-2-positive advanced breast carcinoma. Despite the experimental evidence of its radiosensitizing properties, trastuzumab has never been used in combination with radiotherapy for the treatment of patients with locally advanced disease.

PATIENTS AND METHODS

Twenty-two patients with c-erbB-2-positive locally advanced chemoresistant (7 patients) or with high-risk breast cancer (15 patients) were recruited in a treatment protocol combining hypofractionated/accelerated radiotherapy (hypoARC) supported with high-dose amifostine (1000 mg subcutaneous), concurrently with trastuzumab (4 mg/kg every 2 weeks). Thirteen of these patients (including all 7 inoperable cases) received concurrently chemotherapy with liposomal doxorubicin and docetaxel (25 mg/m2 and 40 mg/m2 every 2 weeks, respectively).

RESULTS

Administration of trastuzumab together with highly accelerated amifostine-supported radiotherapy was feasible without an increase in early and late radiation toxicity. This was obtained despite the concurrent administration of aggressive chemotherapy. Complete responses were noted in 5 of 7 patients with locally, often far advanced, chemoresistant disease. None of the complete responders or the 15 high-risk breast cancer patients relapsed within the 3- to 26-month follow-up period.

CONCLUSION

Inclusion of trastuzumab in the radiochemotherapy protocols for breast cancer does not increase radiation or systemic toxicity. The concurrent administration of aggressive radiotherapy with docetaxel and liposomal doxorubicin is feasible when supported with amifostine. The value of such regimens in the treatment of locally advanced or high risk c-erbB-2 positive breast cancer patients deserves further evaluation.

Phase 1 clinical and pharmacokinetics evaluation of oral CI-1033 in patients with refractory cancer

PURPOSE

To determine the tolerability and pharmacokinetics of oral CI-1033, a pan-erbB tyrosine kinase inhibitor, administered over 14 consecutive days of a 21-day cycle.

DESIGN

Phase 1, multicenter trial involving patients with solid tumors that are refractory to standard therapy. CI-1033 was administered initially at 300 mg/day to a minimum cohort of three patients. Dose escalation proceeded at </=40% increments. Patients were evaluated for toxicity, pharmacokinetic profile, and evidence of response.

RESULTS

Thirty-two patients entered the trial and were evaluable for safety assessment. Dose-limiting toxicity (diarrhea, rash, and/or anorexia) occurred at the 560 mg dose level; the maximum tolerated dose was 450 mg. No patients achieved objective responses and six patients achieved stable disease. Plasma CI-1033 concentrations increased with increasing dose. CI-1033 was not eliminated in urine to any appreciable extent.

CONCLUSIONS

CI-1033 is suitable for phase 2 testing at the 450 mg/day dose level when administered for 14 days in a 21-day cycle. The pharmacokinetic profile is consistent with biologically relevant plasma concentrations over the dosing interval.

Basic characterization of 64Cu-ATSM as a radiotherapy agent

64Cu-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM) is a promising radiotherapy agent for the treatment of hypoxic tumors. In an attempt to elucidate the radiobiological basis of 64Cu-ATSM radiotherapy, we have investigated the cellular response patterns in vitro cell line models. Cells were incubated with 64Cu-ATSM, and the dose-response curves were obtained by performing a clonogenic survival assay. Radiation-induced damage in DNA was evaluated using the alkali comet assay and apoptotic cells were detected using Annexin V-FITC and propidium iodide staining methods. Washout rate and subcellular distribution of 64Cu in cells were investigated to further assess the effectiveness of 64Cu-ATSM therapy on a molecular basis. A direct comparison of subcellular localization of Cu-ATSM was made with the flow tracer analog Cu-pyruvladehyde-bis(N4-methylthiosemicarbazone). In this study, 64Cu-ATSM was shown to reduce the clonogenic survival rate of tumor cells in a dose-dependent manner. Under hypoxic conditions, cells took up 64Cu-ATSM and radioactive 64Cu was highly accumulated in the cells. In the 64Cu-ATSM-treated cells, DNA damage by the radiation emitted from 64Cu was detected, and inhibition of cell proliferation and induction of apoptosis was observed at 24 and 36 h after the treatment. The typical features of postmitotic apoptosis induced by radiation were observed following 64Cu-ATSM treatment. The majority of the 64Cu taken up into the cells remained in the postmitochondrial supernatant (the cellular residue after removal of the nuclei and mitochondria), which indicates that the beta- particle emitted from 64Cu may be as effective as the Auger electrons in 64Cu-ATSM therapy. These data allow us to postulate that 64Cu-ATSM will be able to attack the hypoxic tumor cells directly, as well as potentially affecting the peripheral nonhypoxic regions indirectly by the beta- particle decay of 64Cu.

Y-box-binding protein 1 confers EGF independence to human mammary epithelial cells

The epidermal growth factor receptor (EGFR) is linked to poor outcome in breast cancer, and resistance to hormonal therapy is often accompanied by activation of growth factor receptors. To investigate the mechanism(s) by which EGFR becomes activated in breast cancer, we screened a cDNA expression library for genes that mediate EGF-independent proliferation of human mammary epithelial cells (HMECs). We isolated the NSEP1 cDNA encoding Y-box-binding protein 1 (YB-1), a multifunctional transcriptional and translational regulator. This cDNA conferred growth factor independence to HMECs. YB-1-transduced cells overexpressed EGFR, but ErbB-2 (Her-2/neu) levels were unchanged. Moreover, EGFR was constitutively phosphorylated in the absence of exogenous ligand. In these cells, an EGFR-blocking antibody failed to inhibit proliferation, conditioned medium activity could not be detected, and the synthesis of EGFR ligands was reduced compared to parental cells. This suggests that EGFR is activated in a ligand-independent fashion. However, cell growth could be blocked with an ErbB kinase inhibitor, indicating that EGFR signaling plays a major role in YB-1-induced growth factor independence. Taken together, our results demonstrate that YB-1 overexpression can induce EGF independence in HMECs via activation of the EGFR pathway. This could represent one of the mechanisms by which YB-1 contributes to breast tumor aggressiveness.

Antiapoptotic signaling pathways in non-small-cell lung cancer: biology and therapeutic strategies

One of the hallmarks of lung cancer is the deregulation of apoptotic or programmed cell death mechanisms usually found in normal cells that allow for corrupted cells to undergo cellular suicide. This includes mechanisms that attenuate proapoptotic pathways and/or amplify antiapoptotic pathways. Increasing evidence suggests that lung cancer cells use multiple and perhaps redundant pathways to maintain survival. Increasing knowledge of these pathways offers a better understanding of the biology of lung cancer as well as novel therapeutic strategies that can enhance lung cancer cell death. This review discusses the apoptotic machinery and signal transduction pathways that regulate apoptosis, methods of identifying the presence of activated survival signaling pathways in human lung cancers, and the clinical significance and relevance for therapy for patients with lung cancer.

Overview of the Current Status of Human Epidermal Growth Factor Receptor Inhibitors in Lung Cancer

Although chemotherapy remains the standard of care for lung cancer, new less toxic drugs are urgently needed. Targeted agents represent a new era in cancer therapy, and non-small-cell lung cancer (NSCLC) is at the forefront of many development programs. An exciting target is the human epidermal growth factor receptor (EGFR, ie, HER1), and agents targeting this receptor, including gefitinib, cetuximab, and erlotinib (OSI-774; Tarceva), are being investigated. These agents have antitumor activity and are less toxic than most therapies. Based on phase II data, gefitinib received US approval for third-line treatment of patients with locally advanced or metastatic NSCLC. Cetuximab is licensed in the United States for patients with metastatic colorectal carcinoma. However, erlotinib, recently approved in the United States for second- and third-line treatment of patients with locally advanced or metastatic NSCLC, is the only agent of this class to improve survival as monotherapy in patients with advanced, refractory NSCLC, as shown in a phase III placebo-controlled trial. Phase III trials of erlotinib and gefitinib combined with chemotherapy were disappointing, which could be the result of drug scheduling, chemotherapy combinations, or other factors. Patient characteristics may also affect outcome, and research is ongoing to identify predictive markers of response to enable patient selection and improve outcome. Recently identified mutations within the HER1/EGFR tyrosine kinase (TK) domain may provide insight into why some patients respond rapidly to HER1/EGFR tyrosine kinase inhibitors. Surrogate markers of efficacy are also being investigated, including rash, which could be used to monitor and optimize antitumor activity. Therefore, although more work is required, data indicate that HER1/EGFR inhibitors will play an important role in treating patients with NSCLC.

Molecular targets for potentiation of radiation-induced cell killing

Molecular target-based drugs have been emerging as a cancer treatment. Clinical trials using the combined approach of radiation therapy and molecular target-based drugs have been performed to evaluate the feasibility of this approach, and improve the response of tumors to radiation. To achieve maximum radiotherapeutic gain, understanding of the interaction of radiation and drugs are indispensable. Preclinical data have already demonstrated synergistic enhancement of radiation-induced cell killing by several molecular target-based drugs. Among these, the effect of drugs that target receptor tyrosine kinase and its signal transduction pathways on radiosensitivity has been intensively investigated. In this review, established and potential molecular targets for potentiation of radiation-induced cell killing are summarized, and preclinical data regarding investigations of new molecular targets for radiosensitization will be introduced. In addition, the results and toxicities of clinical trials using combined radiation therapy and molecular target-based drugs are summarized.

Epidermal growth factor receptor as a target to improve treatment of lung cancer

Despite considerable efforts to reduce tobacco use, lung cancer remains the most common cancer in both men and women. Recent advances in radiation therapy and chemotherapy for lung cancer have yielded encouraging results, but survival in patients with locally advanced non-small-cell lung cancer (NSCLC) remains poor. As more and more molecular changes and their importance in malignant tissues continue to be characterized, approaches to target those aberrant pathways are being actively explored. The epidermal growth factor receptor (EGFR) is commonly overexpressed in NSCLC, particularly squamous cell carcinoma, and has been implicated in the development and progression of this disease, although a clear correlation with prognosis has not been established. Several different strategies have been developed to target and block the EGFR and its downstream effects, and some of them have been intensively studied in preclinical and clinical studies as a single-agent approach or in combination with radiation therapy or chemotherapy. In this article, we review the role of EGFR in lung cancer, as well as preclinical and clinical data on strategies to interfere with EGFR signaling alone or in combination with chemotherapy, radiation, or both.

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.

Altered molecular pathways in gliomas: An overview of clinically relevant issues

Primary central nervous system (CNS) tumors constitute a small fraction of the overall incidence of human cancer, but they represent a major source of cancer-related morbidity and mortality. The most common CNS tumor subtype in adults, high-grade astrocytoma, confers a dismal prognosis with a median survival of only 1 to 2 years. Other common adult CNS tumors, ie, low-grade astrocytomas and oligodendrogliomas, carry a less ominous, yet still poor prognosis. Unfortunately, there has been little progress in extending the survival or quality of life for glioma patients, despite nearly four decades of extensive research. This research has, however, greatly increased our understanding of the underlying molecular biology of these tumors, examples of which include the determination of elevated epidermal growth factor receptor (EGFR) as well as platelet-derived growth factor receptor (PDGF) signaling, and the inactivation of p53 , p16 , and PTEN tumor-suppressor genes (TSGs) that negatively regulate specific enzymatic activities in normal glial cells. Such observations have greatly improved our understanding of the pathogenesis of these tumors and have potential diagnostic as well as therapeutic relevance. With respect to the latter of these two issues, the identification of aberrant enzymatic activities in gliomas has promoted the development of novel therapeutic agents that target specific signaling effectors, and whose inhibition should, in theory, prove to be cytostatic, if not cytotoxic, to tumor cells. Several clinical trials are currently underway for testing these therapeutic agents in patients with primary brain tumors, and it is hoped that the targeting of pro-tumorigenic enzymatic activities will lead to better patient outcomes. In this review, we will describe the most pertinent genetic and signaling pathway alterations that are clinically relevant to the management of glial tumors.

Her2/neu-positive disease does not increase risk of locoregional recurrence for patients treated with neoadjuvant doxorubicin-based chemotherapy, mastectomy, and radiotherapy

PURPOSE

Preclinical data suggest that overexpression of Her2/neu confers cellular radioresistance. We retrospectively studied whether Her2/neu-positive disease was associated with locoregional recurrence (LRR) after postmastectomy radiotherapy (RT) for breast cancer.

METHODS AND MATERIALS

Data from 337 patients treated in four institutional prospective clinical trials neoadjuvant doxorubicin-based chemotherapy, mastectomy, and RT were reviewed. The trials were conducted between 1989 and 2000. Of the 337 patients, 108 (32%) had tumors that were tested for Her2/neu, with positivity defined by 3+ immunohistochemistry staining or gene amplification detected by fluorescence in situ hybridization. RT was delivered to the chest wall and draining lymphatics (median dose, 50 Gy) followed by a chest wall boost (median dose, 10 Gy).

RESULTS

Thirty-two patients had Her2/neu-positive disease and 76 patients had Her2/neu-negative disease. The Her2/neu-positive tumors were associated with a greater rate of estrogen receptor-negative disease (p = 0.03), the presence of supraclavicular disease at diagnosis (p = 0.027), and a greater number of positive lymph nodes after chemotherapy (p = 0.026). Despite these adverse features, the actuarial overall LRR rate was roughly equivalent for the patients with Her2/neu-positive tumors vs. those with Her2/neu-negative tumors (5-year rate 17.5% vs. 13.9%, respectively; 10-year rate 17.5% vs. 18.9%, respectively; p = 0.757). On Cox regression analysis of LRR adjusted for N stage and estrogen receptor status, the hazard ratio for Her2/neu positivity was 0.89 (95% confidence interval, 0.31-2.59; p = 0.83).

CONCLUSION

Her2/neu overexpression does not appear to predispose to LRR after neoadjuvant doxorubicin-based chemotherapy, mastectomy, and RT.

Targeted therapies for non–small-cell lung cancer: biology, rationale, and preclinical results from a radiation oncology perspective

The epidermal growth factor receptor (EGFR) is overexpressed in the majority of non-small-cell lung cancers (NSCLCs). This presents an opportune target for new treatment strategies designed to selectively interfere with the cancer cell growth cycle. Recent investigations into the biology of the EGFR and its downstream signaling pathways have reminded us of the complexity of cancer cell communications from the cytoplasm to the nucleus. Multiple pathways are activated with stimulation of the autocrine and paracrine EGFR loop, from the ras-raf-MEK activation of ERK 1/2 to the P13K-Akt pathway, each playing an important role in cancer cell survival, invasion, and angiogenesis. Preclinical studies have demonstrated that molecules targeting the EGFR, either through extracellular blockade or intracellular interference with the EGFR-associated tyrosine kinase, reversibly or irreversibly, inhibit cancer cell growth. Potent antitumor effects have been observed in human tumor xenograft models. Preclinical studies have also demonstrated cooperative effects when anti-EGFR agents are combined with radiation or chemotherapy. Many of these agents have now entered into advanced human clinical trials with modest dose-related toxicity despite chronic administration. Encouraging response rates with single-agent targeted therapy have been reported in heavily pretreated patients with advanced NSCLC. In addition, agents targeting the angiogenic pathway, which plays a key role in the regulation of angiogenesis, may play an important role in enhancing the efficacy of anti-EGFR agents. This article will focus on the biology, rationale, and preclinical studies with targeted anti-EGFR and antiangiogenic therapies for the management of NSCLC.

Combining EGFR inhibitors with radiation or chemotherapy: will preclinical studies predict clinical results?

PURPOSE

To highlight some of the preclinical data that examine the interaction of epidermal growth factor receptor (EGFR) inhibitors with radiotherapy and chemotherapy.

METHODS AND MATERIALS

Recognition of the EGFR as an important regulator of tumor cell growth in the early 1980s stimulated the development of a series of molecules specifically designed to inhibit EGFR signaling as anticancer agents. Many of these agents have now matured and are in advanced clinical trial investigations, with tumor response rates on the order of 10-20% identified across a variety of human malignancies. Initially designed primarily as "cytostatic" agents, as opposed to "cytotoxic" agents, it is possible that the EGFR inhibitors will realize their optimal clinical impact when delivered in concert with conventional cytotoxic modalities such as radiotherapy and/or chemotherapy.

RESULTS

Despite very strong in vitro and in vivo preclinical results, several major gaps remain in our knowledge regarding the EGFR inhibitor mechanisms of interaction with radiotherapy and chemotherapy, with considerable selection bias in the publication of preclinical data available to date.

CONCLUSION

By acknowledging the limitations of the available preclinical data and by expanding our mechanistic understanding of EGFR inhibitor function in representative tumor model systems, we should enhance our capacity to predict the most rational and successful methods to combine EGFR inhibitors with cytotoxic modalities in future clinical trials.