Modulation of DNA Repair In vitro after Treatment with Chemotherapeutic Agents by the Epidermal Growth Factor Receptor Inhibitor Gefitinib (ZD1839)

Pharmacologic Induction of BRCAness in BRCA-Proficient Cancers: Expanding PARP Inhibitor Use

The poly(ADP-ribose) polymerase (PARP) family of proteins has been implicated in numerous cellular processes, including DNA repair, translation, transcription, telomere maintenance, and chromatin remodeling. Best characterized is PARP1, which plays a central role in the repair of single strand DNA damage, thus prompting the development of small molecule PARP inhibitors (PARPi) with the intent of potentiating the genotoxic effects of DNA damaging agents such as chemo- and radiotherapy. However, preclinical studies rapidly uncovered tumor-specific cytotoxicity of PARPi in a subset of cancers carrying mutations in the BReast CAncer 1 and 2 genes (BRCA1/2), which are defective in the homologous recombination (HR) DNA repair pathway, and several PARPi are now FDA-approved for single agent treatment in BRCA-mutated tumors. This phenomenon, termed synthetic lethality, has now been demonstrated in tumors harboring a number of repair gene mutations that produce a BRCA-like impairment of HR (also known as a 'BRCAness' phenotype). However, BRCA mutations or BRCAness is present in only a small subset of cancers, limiting PARPi therapeutic utility. Fortunately, it is now increasingly recognized that many small molecule agents, targeting a variety of molecular pathways, can induce therapeutic BRCAness as a downstream effect of activity. This review will discuss the potential for targeting a broad range of molecular pathways to therapeutically induce BRCAness and PARPi synthetic lethality.

Nobiletin as an inducer of programmed cell death in cancer: a review

Cancer resistance to therapy is a big issue in cancer therapy. Tumours may develop some mechanisms to reduce the induction of cell death, thus stimulating tumour growth. Cancer cells may show a low expression and activity of tumour suppressor genes and a low response to anti-tumour immunity. These mutations can increase the resistance of cancer cells to programmed cell death mechanisms such as apoptosis, ferroptosis, pyroptosis, autophagic cell death, and some others. The upregulation of some mediators and transcription factors such as Akt, nuclear factor of κB, signal transducer and activator of transcription 3, Bcl-2, and others can inhibit cell death in cancer cells. Using adjuvants to induce the killing of cancer cells is an interesting strategy in cancer therapy. Nobiletin (NOB) is a herbal-derived agent with fascinating anti-cancer properties. It has been shown to induce the generation of endogenous ROS by cancer cells, leading to damage to critical macromolecules and finally cell death. NOB may induce the activity of p53 and pro-apoptosis mediators, and also inhibit the expression and nuclear translocation of anti-apoptosis mediators. In addition, NOB may induce cancer cell killing by modulating other mechanisms that are involved in programmed cell death mechanisms. This review aims to discuss the cellular and molecular mechanisms of the programmed cell death in cancer by NOB via modulating different types of cell death in cancer.

Inhibition of DNA‑PK by gefitinib causes synergism between gefitinib and cisplatin in NSCLC

Lung cancer has the highest incidence and mortality rates among the malignant tumor types worldwide. Platinum‑based chemotherapy is the main treatment for advanced non‑small‑cell lung cancer (NSCLC), and epidermal growth factor receptor‑tyrosine kinase inhibitors (EGFR‑TKIs) have greatly improved the survival of patients with EGFR‑sensitive mutations. However, there is no standard therapy for treating patients who are EGFR‑TKI resistant. Combining EGFR‑TKIs and platinum‑based chemotherapy is the most popular strategy in the clinical practice. However, the synergistic mechanism between EGFR‑TKIs and platinum remains unknown. Therefore, the aim of the present study was to determine the synergistic mechanism of gefitinib (an EGFR‑TKI) and cisplatin (a main platinum‑based drug). MTT assay, apoptosis analysis, tumorsphere formation and an orthotropic xenograft mouse model were used to examine the combination effects of gefitinib and cisplatin on NSCLC. Co‑immunoprecipitation and immunofluorescence were used to identify the underlying mechanism. It was found that gefitinib could selectively inhibit EGFR from entering the nucleus, decrease DNA‑PK activity and enhance the cytotoxicity of cisplatin on NSCLC. Collectively, the results suggested that inhibition of DNA‑dependent protein kinase by gefitinib may be due to the synergistic mechanism between gefitinib and cisplatin. Thus, the present study provides a novel insight into potential biomarkers for the selection of combination therapy of gefitinib and cisplatin.

Design, synthesis, and biological evaluation of quinazoline derivatives containing piperazine moieties as antitumor agents

A series of novel quinazoline derivatives containing piperazine analogs are synthesized via substitution reactions with 6,7-disubstituted 4-chloroquinazoline and benzyl piperazine (amido piperazine). Potent antiproliferative activities are observed against A549, HepG2, K562, and PC-3 with N-(3-chlorophenyl)-2-(4-(7-methoxy-6-(3-morpholino-propoxy)quinazoline-4-yl)piperazine-1-yl)acetamidename C9 showing excellent activity. This active derivative was screened for cell migration ability, proliferation effects, and apoptosis against A549 and PC-3 cells, with the result showing biological activity almost equal to that of the control gefitinib.

The expression of copper transporters associated with the ototoxicity induced by platinum-based chemotherapeutic agents

BACKGROUND

Antitumor agents based on platinum have gained a well-established place in the treatment of several forms of cancer. Their efficiency is hampered by serious toxic effects against healthy tissues as well. Ototoxicity is a serious side effect leading to hearing impairment and represents an important issue affecting the patients' quality of life. The currently used platinum chemotherapeutics exert different toxicity towards cochlear cells. The aim of our study was to answer some questions regarding the differential uptake and cellular pharmacodynamics of Cisplatin (CDDP), Carboplatin (CBDCA) and Oxaliplatin (L-OHP) in the HEI-OC1 cochlear cell line.

METHODS

We studied the expression of copper transporters CTR1, ATP7A and ATP7B which are presumably involved in the uptake, cellular transport and efflux of platinum compounds by immunofluorescence microscopy and flow-cytometry. The cellular uptake of the compounds was evaluated through the determination of intracellular platinum concentration by atomic absorption spectroscopy. The effects of the treatment of HEI-OC1 cells with platinum compounds were also evaluated: cytotoxicity with the Cell Titer Blue viability test, formation of reactive oxygen species with 2',7' -dichlorofluorescein diacetate, genotoxicity with the comet assay and apoptosis with the cleaved PARP ELISA test.

RESULTS

CTR1, ATP7A and ATP7B were all expressed by HEI-OC1 cells. The treatment with the platinum compounds led to a modulation of their expression, manifested in a differential platinum uptake. Treatment with Cisplatin led to the highest intracellular concentration of platinum compared to Oxaliplatin and Carboplatin at the same dose. Treatment with CuSO4 reduced platinum uptake of all the compounds, significantly in the case of Cisplatin and Carboplatin. CDDP was the most cytotoxic against HEI-OC1 cells, with an IC50 = 65.79  μM, compared to 611.7 μM for L-OHP and 882.9 μM for CBDCA, at the same molar concentration. The production of ROS was the most intense after CDDP, followed by L-OHP and CBDCA. In the comet assay, at the 100 μM concentration, L-OHP and CBDCA induced DNA adducts while CDDP induced adducts as well as DNA strand breaks. CBDCA and L-OHP lead to a significant increase of cleaved PARP at 24h (p < 0.001), suggesting an important apoptotic process induced by these compounds at the used concentrations.

CONCLUSIONS

The results obtained in the current study suggest that the modulation of copper transporters locally may represent a new strategy against platinum drugs ototoxicity.

RAS/MAPK signaling functions in oxidative stress, DNA damage response and cancer progression

Mitogen-activated protein kinase (MAPK) signaling pathways organize a great constitution network that regulates several physiological processes, like cell growth, differentiation, and apoptotic cell death. Due to the crucial importance of this signaling pathway, dysregulation of the MAPK signaling cascades is involved in the pathogenesis of various human cancer types. Oxidative stress and DNA damage are two important factors which in common lead to carcinogenesis through dysregulation of this signaling pathway. Reactive oxygen species (ROS) are a common subproduct of oxidative energy metabolism and are considered to be a significant physiological modulator of several intracellular signaling pathways including the MAPK pathway. Studies demonstrated that the MAP kinases extracellular signal-regulated kinase (ERK) 1/2 and p38 were activated in response to oxidative stress. In addition, DNA damage is a partly common circumstance in cell life and may result in mutation, cancer, and even cell death. Recently, accumulating evidence illustrated that the MEK/ERK pathway is associated with the suitable performance of cellular DNA damage response (DDR), the main pathway of tumor suppression. During DDR, the MEK/ERK pathway is regularly activated, which contributes to the appropriate activation of DDR checkpoints to inhibit cell division. Therefore, the aim of this review is to comprehensively discuss the critical function of MAPK signaling in oxidative stress, DNA damage, and cancer progression.

The Effect of Canertinib on Sensitivity of Cytotoxic Drugs in Tamoxifen-Resistant Breast Cancer Cells In Vitro

Aims and Objectives

To investigate and examine the reversal effects of canertinib on the activity of EGFR and tamoxifen resistance in drug-resistant human breast carcinoma cells (MCF-7/TamR).

Materials and Methods

The antiproliferative activity of canertinib alone or in combination with a conventional EGFR-targeting chemotherapies cytotoxic drugs differing in the mechanism(s) of action, such as paclitaxel, carboplatin, etoposide, vinorelbine, and daunorubicin as well as resistance mechanisms of EGFR targeting, have been investigated.

Results

With an elevated dosage of canertinib, a significant decrease in proliferation and increase in apoptosis was observed. The treatment with higher doses of canertinib resulted in a 2-3-fold increase in apoptosis. In the combined treatment, it had been noticed a significant developed apoptotic cell death rather induced by single agent treatment. A significant downregulation of the antiapoptotic protein bcl-2 was exposed by immunocytochemistry investigation. Sensitivity to paclitaxel was also measured and was found to inversely correlate to bcl-2 status.

Conclusion

Proliferation inhibition and apoptosis in MCF-7/TAM-R cells increase with increasing dosage of canertinib. This suggests that canertinib can reverse tamoxifen resistance in breast cancer cells. The antitumor effect of this EGFR-irreversible tyrosine kinase inhibitor provides a rationale for its clinical evaluation in combination with other cytotoxic drugs.

RNF144A sustains EGFR signaling to promote EGF-dependent cell proliferation

RNF144A is a single-pass transmembrane RBR E3 ligase that interacts with and degrades cytoplasmic DNA-PKcs, which is an epidermal growth factor receptor (EGFR)-interacting partner. Interestingly, RNF144A expression is positively correlated with EGFR mRNA and protein levels in several types of cancer. However, the relationship between RNF144A and EGFR is poorly understood. This study reports an unexpected role for RNF144A in the regulation of EGF/EGFR signaling and EGF-dependent cell proliferation. EGFR ligands, but not DNA-damaging agents, induce a DNA-PKcs-independent interaction between RNF144A and EGFR. RNF144A promotes EGFR ubiquitination, maintains EGFR protein, and prolongs EGF/EGFR signaling during EGF stimulation. Moreover, depletion of RNF144A by multiple independent approaches results in a decrease in EGFR expression and EGF/EGFR signaling. RNF144A knockout cells also fail to mount an immediate response to EGF for activation of G₁/S progression genes. Consequently, depletion of RNF144A reduces EGF-dependent cell proliferation. These defects may be at least in part due to a role for RNF144A in regulating EGFR transport in the intracellular vesicles during EGF treatment.

Icotinib hydrochloride enhances chemo- and radiosensitivity by inhibiting EGFR signaling and attenuating RAD51 expression and function in Hela S3 cells

Background

Radiotherapy and cisplatin-based chemotherapy are currently considered as standard treatments employed for advanced cervical cancer (CC). However, patients with local recurrence or distant metastasis continue to have poor outcomes. EGFR overexpression correlated with chemo/radioresistance, and disease failure has been well proved in the previous studies. Hence, the aim of this study was to explore the therapeutic efficacy and underlying mechanism of the sensitization to radiation or cisplatin of icotinib hydrochloride (IH), a high-selective EGFR tyrosine kinase inhibitor (TKI), in the Hela S3 human CC cell line.

Methods

Cell proliferation was measured with cell counting kit-8 (CCK-8) assay. Flow cytometry analysis was performed to examine cell cycle distribution and apoptosis. The phosphorylation of EGFR and its downstream signaling molecules were measured by Western blot analysis. γ-H2AX foci and RAD51 foci in the cellular nucleus were visualized using immunofluoresence staining. Expression levels of RAD51 in the whole cells and subceullar fractions were detected to demonstrate the impact of IH on DNA repair.

Results

IH can significantly inhibit cell proliferation, redistribute cell cycle, enhance apoptosis and impair DNA damage response of Hela S3 cells following radiation or cisplatin treatment through suppressing the activation of the EGFR signaling pathway and attenuating the expression and function of homologous recombination (HR) protein RAD51.

Conclusion

This study suggests that IH is a potential sensitizer in radiotherapy and cisplatin-based chemotherapy for CC and RAD51 may serve as a prognosis biomarker for this combination treatment.

A Potent Derivative of Indolizino[6,7-b]Indole for Treatment of Human Non-Small Cell Lung Cancer Cells

The therapeutic effect in non–small cell lung cancer (NSCLC) patients is limited because of intrinsic and acquired resistance. Thus, an unmet need exists for the development of new drugs to improve the therapeutic efficacy in NSCLC patients. In this study, the novel small molecule indolizino[6,7-b]indole derivative BO-1978 was selected to evaluate its therapeutic effects on NSCLC and its preclinical toxicity in animal models. An in vitro cytotoxicity assay revealed that BO-1978 significantly suppressed the growth of various NSCLC cell lines with or without mutations in epidermal growth factor receptor (EGFR). Mechanistically, we demonstrated that BO-1978 exhibited multiple modes of action, including inhibition of topoisomerase I/II and induction of DNA cross-linking. Treatment of NSCLC cells with BO-1978 caused DNA damage, disturbed cell cycle progression, and triggered apoptotic cell death. Furthermore, BO-1978 significantly suppressed the growth of EGFR wild-type and mutant NSCLC tumors in xenograft tumor and orthotopic lung tumor models with negligible body weight loss. The combination of BO-1978 with gefitinib further suppressed EGFR mutant NSCLC cell growth in xenograft tumor and orthotopic lung tumor models. Preclinical toxicity studies showed that BO-1978 administration did not cause apparent toxicity in mice. Based on its significant therapeutic efficacy and low drug toxicity, BO-1978 is a potential therapeutic agent for treatment of NSCLC.

Cross talk of tyrosine kinases with the DNA damage signaling pathways

Tyrosine kinases respond to extracellular and intracellular cues by activating specific cellular signaling cascades to regulate cell cycle, growth, proliferation, differentiation and survival. Likewise, DNA damage response proteins (DDR) activated by DNA lesions or chromatin alterations recruit the DNA repair and cell cycle checkpoint machinery to restore genome integrity and cellular homeostasis. Several new examples have been uncovered in recent studies which reveal novel epigenetic and non-epigenetic mechanisms by which tyrosine kinases interact with DDR proteins to dictate cell fate, i.e. survival or apoptosis, following DNA damage. These studies reveal the ability of tyrosine kinases to directly regulate the activity of DNA repair and cell cycle check point proteins by tyrosine phosphorylation. In addition, tyrosine kinases epigenetically regulate DNA damage signaling pathways by modifying the core histones as well as chromatin modifiers at critical tyrosine residues. Thus, deregulated tyrosine kinase driven epigenomic alterations have profound implications in cancer, aging and genetic disorders. Consequently, targeting oncogenic tyrosine kinase induced epigenetic alterations has gained significant traction in overcoming cancer cell resistance to various therapies. This review discusses mechanisms by which tyrosine kinases interact with DDR pathways to regulate processes critical for maintaining genome integrity as well as clinical strategies for targeted cancer therapies.

Localization and distribution of neurons that co-express xeroderma pigmentosum-A and epidermal growth factor receptor within Rosenthal's canal

Xeroderma pigmentosum-A (XPA) is a C4-type zinc-finger scaffolding protein that regulates the removal of bulky-helix distorting DNA damage products from the genome. Phosphorylation of serine residues within the XPA protein is associated with improved protection of genomic DNA and cell death resistance. Therefore, kinase signaling is one important mechanism for regulating the protective function of XPA. Previous experiments have shown that spiral ganglion neurons (SGNs) may mobilize XPA as a general stress response to chemical and physical ototoxicants. Therapeutic optimization of XPA via kinase signaling could serve as a means to improve DNA repair capacity within neurons following injury. The kinase signaling activity of the epidermal growth factor receptor (EGFR) has been shown in tumor cell lines to increase the repair of DNA damage products that are primarily repaired by XPA. Such observations suggest that EGFR may regulate the protective function of XPA. However, it is not known whether SGNs in particular or neurons in general could co-express XPA and EGFR. In the current study gene and protein expression of XPA and EGFR were determined from cochlear homogenates. Immunofluorescence assays were then employed to localize neurons expressing both EGFR and XPA within the ganglion. This work was then confirmed with double-immunohistochemistry. Rosenthal's canal served as the reference space in these experiments and design-based stereology was employed in first-order stereology quantification of immunoreactive neurons. The results confirmed that a population of SGNs that constitutively express XPA may also express the EGFR. These results provide the basis for future experiments designed to therapeutically manipulate the EGFR in order to regulate XPA activity and restore gene function in neurons following DNA damage.

EGFR targeted therapies and radiation: Optimizing efficacy by appropriate drug scheduling and patient selection

The epidermal growth factor receptor (EGFR) plays an important role in tumor progression and treatment resistance for many types of malignancies including head and neck, colorectal, and nonsmall cell lung cancer. Several EGFR targeted therapies are efficacious as single agents or in combination with chemotherapy. Given the toxicity associated with chemoradiation and poor outcomes seen in several types of cancers, combinations of EGFR targeted agents with or without chemotherapy have been tested in patients receiving radiation. To date, the only FDA approved use of an anti-EGFR therapy in combination with radiation therapy is for locally advanced head and neck cancer. Given the important role EGFR plays in lung and colorectal cancer and the benefit of EGFR inhibition combined with chemotherapy in these disease sites, it is perplexing why EGFR targeted therapies in combination with radiation or chemoradiation have not been more successful. In this review we summarize the clinical findings of EGFR targeted therapies combined with radiation and chemoradiation regimens. We then discuss the interaction between EGFR and radiation including radiation induced EGFR signaling, the effect of EGFR on DNA damage repair, and potential mechanisms of radiosensitization. Finally, we examine the potential pitfalls with scheduling EGFR targeted therapies with chemoradiation and the use of predictive biomarkers to improve patient selection.

Combined EGFR and autophagy modulation impairs cell migration and enhances radiosensitivity in human glioblastoma cells

Glioblastoma (GBM) remains the most aggressive and lethal brain tumor due to its molecular heterogeneity and high motility and invasion capabilities of its cells, resulting in high resistance to current standard treatments (surgery, followed by ionizing radiation combined with Temozolomide chemotherapy administration). Locus amplification, gene overexpression, and genetic mutations of epidermal growth factor receptor (EGFR) are hallmarks of GBM that can ectopically activate downstream signaling oncogenic cascades such as PI3K/Akt/mTOR pathway. Importantly, alteration of this pathway, involved also in the regulation of autophagy process, can improve radioresistance in GBM cells, thus promoting the aggressive phenotype of this tumor. In this work, the endogenous EGFR expression profile and autophagy were modulated to increase radiosensitivity behavior of human T98G and U373MG GBM cells. Our results primarily indicated that EGFR interfering induced radiosensitivity according to a decrease of the clonogenic capability of the investigated cells, and an effective reduction of the in vitro migratory features. Moreover, EGFR interfering resulted in an increase of Temozolomide (TMZ) cytotoxicity in T98G TMZ-resistant cells. In order to elucidate the involvement of the autophagy process as pro-death or pro-survival role in cells subjected to EGFR interfering, the key autophagic gene ATG7 was silenced, thereby producing a transient block of the autophagy process. This autophagy inhibition rescued clonogenic capability of irradiated and EGFR-silenced T98G cells, suggesting a pro-death autophagy contribution. To further confirm the functional interplay between EGFR and autophagy pathways, Rapamycin-mediated autophagy induction during EGFR modulation promoted further impairment of irradiated cells, in terms of clonogenic and migration capabilities. Taken together, these results might suggest a novel combined EGFR-autophagy modulation strategy, to overcome intrinsic GBM radioresistance, thus improving the efficacy of standard treatments. J. Cell. Physiol. 229: 1863-1873, 2014. © 2014 Wiley Periodicals, Inc.

Topoisomerase I as a target of erlotinib and gefitinib: efficacy of combined treatments with camptothecin

Topoisomerases are essential nuclear enzymes that work to resolve topological problems that normally occur during DNA metabolism. Their involvement in crucial DNA associated-processes, such as replication, transcription and repair, mark them as a target of chemotherapeutic drugs such as camptothecins (CPTs). Therefore, finding other agents that may alter their activity is of great importance. Previous data showed that certain tyrosine kinase antagonists, tyrphostins, inhibit the catalytic activity of the cellular topoisomerase I (topo I). We examined the effect of clinically used tyrosine kinase inhibitors (TKIs), erlotinib and gefitinib, on topo I in breast and prostate cancer cells. While erlotinib and gefitinib inhibit cellular topo I in treated cells without affecting the levels of the enzyme protein, in vitro assays show that erlotinib, but not gefitinib, inhibits the DNA relaxation activity of purified topo I. Erlotinib was found to reduce the DNA-binding ability of topo I, however, the reduction in topo I activity in gefitinib-treated cells is probably due to post-translational modifications of the enzyme protein. A combined treatment of either erlotinib or gefitinib with CPT increased the effect of CPT on the activity of cellular topo I, which supports the increased anticancer effect observed in MCF7 cells. These results suggest that topo I is a novel target of erlotinib and a combination of TKIs with topo I inhibitors may be an effective treatment for breast cancer.

Treatment with gefitinib or lapatinib induces drug resistance through downregulation of topoisomerase IIα expression

The EGF receptor (EGFR) is therapeutically targeted by antibodies and small molecules in solid tumors including lung, colorectal, and breast cancer. However, chemotherapy remains important, and efforts to improve efficacy through combination with targeted agents is challenging. This study examined the effects of short and long durations of exposure to the EGFR- and HER2-targeted tyrosine kinase inhibitors (TKI) gefitinib and lapatinib, on induction of cell death and DNA damage by topoisomerase IIα (Topo IIα) poisons, in the SK-Br-3 HER2-amplified breast cancer cell line. Short exposure to either gefitinib or lapatinib for 1 hour did not affect the induction of apoptosis by the Topo IIα poisons doxorubicin, etoposide, and m-AMSA. In contrast, cells treated for 48 hours were resistant to all three drugs. Short exposure (1 hour) to TKI did not alter the number of DNA single- or double-strand breaks (DSB) induced, whereas longer exposure (48 hours) reduced the number of DNA DSBs and the formation of γ-H2AX foci. Both gefitinib and lapatinib reduced the expression and activity of Topo IIα at 48 hours. Studies using a cell line with inducible downregulation of Topo IIα showed that expression of Topo IIα, and not Topo IIβ, determined the number of DNA strand breaks induced by these chemotherapeutic agents. These results indicate that prolonged exposure to TKIs targeting EGFR and HER2 induce resistance to doxorubicin, etoposide, and m-AMSA through downregulation of Topo IIα. This may explain why their addition to chemotherapy regimens have not increased efficacy.

Thyroid cancer cell resistance to gefitinib depends on the constitutive oncogenic activation of the ERK pathway

CONTEXT

Poorly differentiated thyroid carcinomas are refractory to common anticancer therapies, and novel inhibitors are being tested in these deadly malignancies. The epidermal growth factor receptor (EGFR) tyrosine kinase represents an attractive target for treatment because it is up-regulated in thyroid cancer and plays a role in cancer progression. However, EGFR inhibitors have provided poor results in thyroid carcinomas.

OBJECTIVE

We evaluated the possible mechanism underlying the resistance of thyroid cancer cells to EGFR inhibitors.

DESIGN

We tested the effect of the EGFR tyrosine kinase inhibitor gefitinib in a panel of thyroid cancer cell lines.

RESULTS

We found that in most of the cell lines, although gefitinib inhibited EGFR phosphorylation, it was poorly effective in reducing cell viability. gefitinib, however, was able to inhibit epidermal growth factor-induced cell migration and matrix invasion. In most thyroid cancer cell lines, gefitinib significantly inhibited Akt phosphorylation by inhibiting EGFR activation, but it had limited or no effect on ERK phosphorylation. The poor cell response to gefitinib was associated with genetic alterations, leading to constitutive activation of the ERK pathway, including BRAF(V600E) and HRAS(G12A/Q61R) mutations and RET/PTC1 rearrangement. When BRAF(V600E)-positive thyroid cancer cells were incubated with the specific BRAF inhibitor PLX4032, sensitivity to gefitinib was restored. Similar results were obtained with rat sarcoma and RET/papillary thyroid cancer inhibitors.

CONCLUSIONS

These results indicate that thyroid cancer resistance to gefitinib is due to the constitutive activation of the mitogenic pathway by either signals downstream of EGFR or other tyrosine kinase receptors. This resistance can be overcome by the combined use of selective inhibitors.

Triptolide induced DNA damage in A375.S2 human malignant melanoma cells is mediated via reduction of DNA repair genes

Numerous studies have demonstrated that triptolide induces cell cycle arrest and apoptosis in human cancer cell lines. However, triptolide-induced DNA damage and inhibition of DNA repair gene expression in human skin cancer cells has not previously been reported. We sought the effects of triptolide on DNA damage and associated gene expression in A375.S2 human malignant melanoma cells in vitro. Comet assay, DAPI staining and DNA gel electrophoresis were used for examining DNA damage and results indicated that triptolide induced a longer DNA migration smear based on single cell electrophoresis and DNA condensation and damage occurred based on the examination of DAPI straining and DNA gel electrophoresis. The real-time PCR technique was used to examine DNA damage and repair gene expression (mRNA) and results indicated that triptolide led to a decrease in the ataxia telangiectasia mutated (ATM), ataxia-telangiectasia and Rad3-related (ATR), breast cancer 1, early onset (BRCA-1), p53, DNA-dependent serine/threonine protein kinase (DNA-PK) and O6-methylguanine-DNA methyltransferase (MGMT) mRNA expression. Thus, these observations indicated that triptolide induced DNA damage and inhibited DNA damage and repair-associated gene expression (mRNA) that may be factors for triptolide-mediated inhibition of cell growth in vitro in A375.S2 cells.

Gefitinib (ZD1839) increases the efficacy of cisplatin in ovarian cancer cells

We examined the effect of gefitinib (ZD1839), a selective epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor, on cytotoxicity to cisplatin, EGFR downstream signaling, apoptosis and the association between the inhibition of DNA repair by gefitinib and the expression of DNA-dependent protein kinase (DNA-PK) using three ovarian cancer cell lines. In the presence of gefitinib, cisplatin-induced growth inhibition and apoptosis were significantly enhanced in Caov-3 and RMG-1 cells, which express EGFR, and in A2780, which lacks EGFR but expresses HER-2. Gefitinib significantly inhibited the cisplatin-induced ERK and Akt activation in Caov-3 and RMG-1 cells but not in A2780 cells. In all three cell lines, there was delayed repair of DNA intrastrand cross-links damaged by cisplatin used in combination with gefitinib, compared with cisplatin alone. The reduction in DNA-PK levels persisted when cells were exposed to combinations of cisplatin and gefitinib in all cell lines. Moreover, the delayed repair was cancelled by anti-HER2 small-interfering RNA transfection in A2780 cells. These results suggest that combination therapy with cisplatin and gefitinib may increase the therapeutic efficacy of cisplatin by blocking EGFR downstream signaling and/or inhibiting DNA repair in ovarian cancer.

Protein-intrinsic and signaling network-based sources of resistance to EGFR- and ErbB family-targeted therapies in head and neck cancer

Agents targeting EGFR and related ErbB family proteins are valuable therapies for the treatment of many cancers. For some tumor types, including squamous cell carcinomas of the head and neck (SCCHN), antibodies targeting EGFR were the first protein-directed agents to show clinical benefit, and remain a standard component of clinical strategies for management of the disease. Nevertheless, many patients display either intrinsic or acquired resistance to these drugs; hence, major research goals are to better understand the underlying causes of resistance, and to develop new therapeutic strategies that boost the impact of EGFR/ErbB inhibitors. In this review, we first summarize current standard use of EGFR inhibitors in the context of SCCHN, and described new agents targeting EGFR currently moving through pre-clinical and clinical development. We then discuss how changes in other transmembrane receptors, including IGF1R, c-Met, and TGF-β, can confer resistance to EGFR-targeted inhibitors, and discuss new agents targeting these proteins. Moving downstream, we discuss critical EGFR-dependent effectors, including PLC-γ; PI3K and PTEN; SHC, GRB2, and RAS and the STAT proteins, as factors in resistance to EGFR-directed inhibitors and as alternative targets of therapeutic inhibition. We summarize alternative sources of resistance among cellular changes that target EGFR itself, through regulation of ligand availability, post-translational modification of EGFR, availability of EGFR partners for hetero-dimerization and control of EGFR intracellular trafficking for recycling versus degradation. Finally, we discuss new strategies to identify effective therapeutic combinations involving EGFR-targeted inhibitors, in the context of new system level data becoming available for analysis of individual tumors.

Molecular markers for cancer prognosis and treatment: have we struck gold?

The last decade has witnessed an emerging role for molecular or biochemical markers indicating a specific cellular mechanism or tissue function, often called 'biomarkers'. Biomarkers such as altered DNA, proteins and inflammatory cytokines are critical in cancer research and strategizing treatment in the clinic. In this review we look at the application of biological indicators to cancer research and highlight their roles in cancer detection and treatment. With technological advances in gene expression, genomic and proteomic analysis, biomarker discovery is expanding fast. We focus on some of the predominantly used markers in different types of malignancies, their advantages, and their limitations. Finally we conclude by looking at the future of biomarkers, their utility in the tumorigenic studies, and the progress towards personalized treatment strategies.

DNA damage response and growth factor signaling pathways in gliomagenesis and therapeutic resistance

The dismal prognosis of glioblastoma multiforme (GBM) is mainly due to the poor response of GBM patients to any therapeutic modalities, which include ionizing radiation and DNA-alkylating agents. In the last few years, the important role of the DNA damage response (DDR) pathway in tumor formation and modulation of therapeutic response has been appreciated. Interestingly, several of the genetic alterations commonly found in GBMs (such as epidermal growth factor receptor amplification and PTEN inactivation) have also recently been shown to regulate the activity of the DNA repair machinery and, consequently, the response to DNA-damaging agents used routinely in the clinic. In this review, we focus on some of these findings that suggest that at least some of the pathways driving GBM formation could be directly responsible for the therapy resistance of this tumor type. Possible therapeutic approaches exist that may either overcome or take advantage of these GBM genetic alterations to improve the response of these tumors to DNA-damaging therapy.

Mechanism of action: the unique pattern of bendamustine-induced cytotoxicity

Bendamustine has demonstrated substantial efficacy in the treatment of hematologic malignancies and continues to distinguish itself from other alkylating agents with regard to its activity in tumor cells. The mechanistic and clinical differences associated with bendamustine may be directly related to its unique structural features. Although the precise mechanisms of action are still poorly understood, bendamustine is associated with extensive and durable DNA damage. The increased potency of bendamustine may be due to secondary mechanisms such as inhibition of mitotic checkpoints, inefficient DNA repair, and initiation of p53-dependent DNA-damage stress response, all of which lead to mitotic catastrophe and apoptosis. It has also been hypothesized that the presence of a benzimidazole ring in addition to the nitrogen mustard group may influence the way bendamustine interacts with DNA and/or confer antimetabolite properties. Further elucidation of the mechanisms of action for bendamustine and the signaling pathways involved in the response to bendamustine-induced DNA damage is essential to maximize its therapeutic potential, identify biomarkers for response, and understand the potential for synergy with other agents involved in DNA damage and inhibition of DNA repair. This review will discuss the current understanding and hypotheses regarding bendamustine mechanisms of action and suggest future investigations that would shed light on the many unanswered questions.

Function of erbB receptors and DNA-PKcs on phosphorylation of cytoplasmic and nuclear Akt at S473 induced by erbB1 ligand and ionizing radiation

BACKGROUND AND PURPOSE

In the present study effect of erbB2 as well as DNA-PKcs on ionizing radiation (IR)- and erbB1 ligand-induced phosphorylation of Akt at S473 in cytoplasmic and nuclear fractions was investigated.

MATERIALS AND METHODS

DNA-PKcs proficient and deficient syngeneic colon carcinoma sublines of HCT116 and the glioblastoma cell lines MO59K and MO59J as well as the lung carcinoma cell line A549 were used. Akt-S473 phosphorylation was investigated in cells pre-treated with pharmacological inhibitors or transfected with siRNA by immunoprecipitation, Western blotting and confocal microscopy after different stimuli, i.e., ligands and IR.

RESULTS

IR-induced phosphorylation of Akt in both MO59K and MO59J cell lines but not in HCT116 cells was DNA-PKcs dependent. In A549 cells, IR-induced phosphorylation of nuclear Akt-S473 was dependent on erbB1, erbB2, and DNA-PKcs. EGF induced phosphorylation of nuclear Akt-S473 in a DNA-PKcs and erbB2 independent manner.

CONCLUSION

Data indicate that the function of DNA-PKcs on IR-induced Akt-S473 phosphorylation is cell line specific. IR-induced, but not EGF-induced phosphorylation of cytoplasmic and/or nuclear Akt-S473 is erbB2 dependent.

EGFR nuclear translocation modulates DNA repair following cisplatin and ionizing radiation treatment

Epidermal growth factor receptor (EGFR) overexpression is associated with resistance to chemotherapy and radiotherapy. It modulates DNA repair after radiation-induced damage through association with the catalytic subunit of DNA protein kinase (DNA-PKcs). We investigated the role of EGFR nuclear import and its association with DNA-PKcs on DNA repair after exposure to cisplatin or ionizing radiation (IR). The model system was based on EGFR-null murine NIH3T3 fibroblasts in which EGFR expression was restored with isoforms that were wild-type (wt), derived from human cancers (L858R, EGFRvIII), or mutated in the nuclear localization signal (NLS) sequence. In cells expressing wtEGFR or EGFRvIII, there was complete unhooking of cisplatin-induced interstrand cross-links and repair of IR-induced strand breaks. In contrast, cells expressing L858R or NLS mutations showed reduced unhooking of interstrand cross-links and repair of strand breaks. Immunoprecipitation showed wtEGFR and EGFRvIII binding to DNA-PKcs, increasing 2-fold 18 hours after cisplatin therapy. Confocal microscopy and proximity ligation assay showed that this interaction in the cytoplasm and nucleus was associated with increased DNA protein kinase complex (DNA-PK) activity. Cells expressing the EGFR L858R mutation, which has constitutive kinase activity, exhibited reduced DNA repair without nuclear localization. EGFR-NLS mutants showed impaired nuclear localization and DNA-PKcs association with reduced DNA repair and DNA-PK kinase activity. In summary, EGFR nuclear localization was required for modulation of cisplatin and IR-induced repair of DNA damage. EGFR-DNA-PKcs binding was induced by cisplatin or IR but not by EGFR nuclear translocation per se. Our findings show that EGFR subcellular distribution can modulate DNA repair kinetics, with implications for design of EGFR-targeted combinational therapies.

Epidermal growth factor receptor in glioma: signal transduction, neuropathology, imaging, and radioresistance

Aberrant epidermal growth factor receptor (EGFR) signaling is common in cancer. Increased expression of wild type and mutant EGFR is a widespread feature of diverse types of cancer. EGFR signaling in cancer has been the focus of intense investigation for decades primarily for two reasons. First, aberrant EGFR signaling is likely to play an important role in the pathogenesis of cancer, and therefore, the mechanisms of EGFR-mediated oncogenic signaling are of interest. Second, the EGFR signaling system is an attractive target for therapeutic intervention. EGFR gene amplification and overexpression are a particularly striking feature of glioblastoma (GBM), observed in approximately 40% of tumors. GBM is the most common primary malignant tumor of the central nervous system in adults. In approximately 50% of tumors with EGFR amplification, a specific EGFR mutant (EGFRvIII, also known as EGFR type III, de2-7, Delta EGFR) can be detected. This mutant is highly oncogenic and is generated from a deletion of exons 2 to 7 of the EGFR gene, which results in an in-frame deletion of 267 amino acids from the extracellular domain of the receptor. EGFRvIII is unable to bind ligand, and it signals constitutively. Although EGFRvIII has the same signaling domain as the wild type receptor, it seems to generate a distinct set of downstream signals that may contribute to an increased tumorigenicity. In this review, we discuss recent progress in key aspects of EGFR signaling in GBM, focusing on neuropathology, signal transduction, imaging of the EGFR, and the role of the EGFR in mediating resistance to radiation therapy in GBM.

Targeting nonhomologous end-joining through epidermal growth factor receptor inhibition: rationale and strategies for radiosensitization

DNA double-strand breaks (DSBs) are the most lethal type of DNA damage induced by ionizing radiation or chemotherapeutic drugs used to eradicate cancer cells. The ability of cancer cells to effectively repair DSBs significantly influences the outcome of therapeutic regimens. Therefore, a new and important area of clinical cancer research is the development of DNA repair inhibitors that can be used as radio- or chemosensitizers. Nonhomologous end joining (NHEJ) is the predominant pathway for the repair of radiation-induced DSBs. A series of recent reports indicates that the epidermal growth factor receptor (EGFR) or its downstream components may modulate NHEJ through direct interaction with the DNA repair enzyme, DNA-dependent protein kinase. Because EGFR is overexpressed or activated in many cancers, these findings provide a compelling rationale for combining radiotherapy with therapies that block EGFR or its downstream signaling components. In this review, we delineate how these novel connections between a cell-surface receptor (EGFR) and a predominantly nuclear event (NHEJ) provide vulnerable nodes that can be selectively targeted to improve cancer therapy.

The contribution of cetuximab in the treatment of recurrent and/or metastatic head and neck cancer

Recurrent and/or metastatic squamous cell carcinoma of the head and neck (HNSCC) continues to be a source of significant morbidity and mortality worldwide. Agents that target the epidermal growth factor receptor (EGFR) have demonstrated beneficial effects in this setting. Cetuximab, a monoclonal antibody against the EGFR, improves locoregional control and overall survival when used as a radiation sensitizer in patients with locoregionally advanced HNSCC undergoing definitive radiation therapy with curative intent. Cetuximab is also active as monotherapy in patients whose cancer has progressed on platinum-containing therapy. In the first-line setting for incurable HNSCC, cetuximab added to platinum-based chemotherapy significantly improves overall survival compared with standard chemotherapy alone. These positive results have had a significant impact on the standard of care for advanced HNSCC. In this review, we will discuss the mechanism of action, clinical data and common toxicities that pertain to the use of cetuximab in the treatment of advanced incurable HNSCC.

Downregulation of XPF-ERCC1 enhances cisplatin efficacy in cancer cells

Bulky cisplatin lesions are repaired primarily by nucleotide excision repair (NER), in which the structure specific endonuclease XPF-ERCC1 is a critical component. It is now known that the XPF-ERCC1 complex has repair functions beyond NER and plays a role in homologous recombination (HR). It has been suggested that expression of ERCC1 correlates with cisplatin drug resistance in non-small cell lung cancer (NSCLC). In our study, using NSCLC, ovarian, and breast cancer cells, we show that the XPF-ERCC1 complex is a valid target to increase cisplatin cytotoxicity and efficacy. We targeted XPF-ERCC1 complex by RNA interference and assessed the repair capacity of cisplatin intrastrand and interstrand crosslinks by ELISA and alkaline comet assay, respectively. We also assessed the repair of cisplatin-ICL-induced double-strand breaks (DSBs) by monitoring gamma-H2AX focus formation. Interestingly, XPF protein levels were significantly reduced following ERCC1 downregulation, but the converse was not observed. The transcript levels were unaffected suggesting that XPF protein stability is likely affected. The repair of both types of cisplatin-DNA lesions was decreased with downregulation of XPF, ERCC1 or both XPF-ERCC1. The ICL-induced DSBs persist in the absence of XPF-ERCC1. The suppression of the XPF-ERCC1 complex significantly decreases the cellular viability which correlates well with the decrease in DNA repair capacity. A double knockdown of XPF-ERCC1 displays the greatest level of cellular cytotoxicity when compared with XPF or ERCC1 alone. The difference in cytotoxicity observed is likely due to the level of total protein complex remaining. These data demonstrate that XPF-ERCC1 is a valid target to enhance cisplatin efficacy in cancer cells by affecting cisplatin-DNA repair pathways.

Inhibiting PI3K/Akt pathway increases DNA damage of cervical carcinoma HeLa cells by drug radiosensitization

This study examined the role of PI3K/Akt pathway in radiosensitization of DNA damage of cervical carcinoma cells. The 50% inhibition concentration (IC50) of cisplatin and docetaxel in HeLa cells was detected by Mono-nuclear cell direct cytotoxicity assay (MTT) in vitro. HeLa cells were treated by cisplatin/docetaxel of 10 percent of IC20 alone or combined with LY294002 for 24 h, and then radiated by different doses of X-ray. The cell survival ratio was obtained by means of clone formation. One-hit multi-target model was fitted to the cell survival curve to calculate dose quasithreshold (Dq), mean lethal dose (D0), 2Gy survival fraction (SF2) and sensitization enhancement ratio (SER). The pAkt and total Akt expression was detected by Western blotting and DNA damage by neutro-comet electrophoresis. The HeLa cells were randomly divided into 7 groups in terms of different treatments: Control; radiation treatment (RT) group; LY294002+RT group; cisplatin+RT group; docetaxel+RT group; LY294002+cisplatin+RT group; LY294002+docetaxel+RT group. The apoptosis ratio of each group was measured by flow cytometry. The results showed that docetaxel and cisplatin significantly enhanced the phosphorylation of Akt in radiation-treated HeLa cells. The Dq, D0 and SF2 in LY294002-contained groups were lower than those in docetaxel or cisplatin+RT group. The SER in the LY294002+docetaxel+RT group was 1.35 times that of the docetaxel+RT group, and that in the LY294002+cisplatin+RT group 1.26 times that of the cisplatin+RT group. The Comet electrophoresis showed that tail distance in the LY294002+cisplatin+RT group or LY294002+docetaxel+ RT group was longer than in the cisplatin+RT group or docetaxel+RT group. The apoptosis ratio in the LY294002+cisplatin+RT group or LY294002+docetaxel +RT group was higher than in the cisplatin+RT group or docetaxel+RT group. It was concluded that inhibiting PI3K/Akt pathway can increase the effect of docetaxel and cisplatin on the radiosensitivity of HeLa cells and DNA damage resulted from radiation.

The dual EGFR/HER-2 tyrosine kinase inhibitor lapatinib sensitizes colon and gastric cancer cells to the irinotecan active metabolite SN-38

Members of the human epidermal receptor (HER) family are frequently associated with aggressive disease and poor prognosis in multiple malignancies. Lapatinib is a dual tyrosine kinase inhibitor targeting the epidermal growth factor receptor (EGFR) and HER-2. This study evaluated the therapeutic potential of lapatinib, alone and in combination with SN-38, the active metabolite of irinotecan (CPT-11), in colon and gastric cancer cell lines. Concentration-dependent antiproliferative effects of both lapatinib and SN-38 were observed in all colon and gastric cancer cell lines tested but varied significantly between individual cell lines (lapatinib range 0.08-11.7 muM; SN-38 range 3.6-256 nM). Lapatinib potently inhibited the growth of a HER-2 overexpressing gastric cancer cell line and demonstrated moderate activity in gastric and colon cancer cells with detectable HER-2 expression. The combination of lapatinib and SN-38 interacted synergistically to inhibit cell proliferation in all colon and gastric cancer cell lines tested. Cotreatment with lapatinib and SN-38 also resulted in enhanced cell cycle arrest and the induction of apoptosis with subsequent cellular pharmacokinetic analysis demonstrating that lapatinib promoted the increased intracellular accumulation and retention of SN-38 when compared to SN-38 treatment alone. Finally, the combination of lapatinib and CPT-11 demonstrated synergistic antitumor efficacy in the LoVo colon cancer mouse xenograft model with no apparent increase in toxicity compared to CPT-11 monotherapy. These results provide compelling preclinical rationale indicating lapatinib to be a potentially efficacious chemotherapeutic combination partner for irinotecan in the treatment of gastrointestinal carcinomas.

Involvement of the HER2 pathway in repair of DNA damage produced by chemotherapeutic agents

HER2 (ErbB2) is overexpressed in up to 30% of human breast cancers. Preclinical and clinical studies suggest synergy between some chemotherapeutic agents and the humanized anti-HER2 antibody trastuzumab (Herceptin). This study investigated the effects of etoposide and cisplatin on the repair of DNA damage in breast cancer cell lines. We examined the potential significance of HER2 nuclear expression in DNA repair. MCF-7, SK-BR-3, and MDA-MB-453 cells were treated with cisplatin and etoposide. Repair of DNA interstrand crosslinks (ICL) and strand breaks, following incubation with cisplatin and etoposide, respectively, were quantitated by the single-cell gel electrophoresis (comet) assay. Intrastrand crosslinks produced by cisplatin were assessed by ELISA. The effects of trastuzumab were measured in combination with these drugs. Similar experiments were done using HER2-negative MDA-MB-468 cells transfected with HER2 and a construct lacking the nuclear localization sequence. Incubation of breast cancer cell lines with trastuzumab delayed the repair of ICL produced by cisplatin. There were no effects on the repair of intrastrand crosslinks produced by cisplatin, or repair of DNA strand breaks following etoposide treatment. Transfection of HER2 into MDA-MB-468 cells inhibited the repair of cisplatin-induced ICL, whereas transfection of a HER2 construct lacking the nuclear localization sequence did not affect DNA repair. These results indicate that HER2 expression modulates the repair of specific DNA lesions produced by chemotherapy. The effect on ICL repair requires nuclear expression of HER2. Understanding the mechanisms of interaction between DNA-interacting agents and HER2 inhibitors will inform the design of clinical trials and optimize the therapeutic effects of these combinations.

EGFRvIII and DNA double-strand break repair: a molecular mechanism for radioresistance in glioblastoma

Glioblastoma multiforme (GBM) is the most lethal of brain tumors and is highly resistant to ionizing radiation (IR) and chemotherapy. Here, we report on a molecular mechanism by which a key glioma-specific mutation, epidermal growth factor receptor variant III (EGFRvIII), confers radiation resistance. Using Ink4a/Arf-deficient primary mouse astrocytes, primary astrocytes immortalized by p53/Rb suppression, as well as human U87 glioma cells, we show that EGFRvIII expression enhances clonogenic survival following IR. This enhanced radioresistance is due to accelerated repair of DNA double-strand breaks (DSB), the most lethal lesion inflicted by IR. The EGFR inhibitor gefitinib (Iressa) and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 attenuate the rate of DSB repair. Importantly, expression of constitutively active, myristylated Akt-1 accelerates repair, implicating the PI3K/Akt-1 pathway in radioresistance. Most notably, EGFRvIII-expressing U87 glioma cells show elevated activation of a key DSB repair enzyme, DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Enhanced radioresistance is abrogated by the DNA-PKcs-specific inhibitor NU7026, and EGFRvIII fails to confer radioresistance in DNA-PKcs-deficient cells. In vivo, orthotopic U87-EGFRvIII-derived tumors display faster rates of DSB repair following whole-brain radiotherapy compared with U87-derived tumors. Consequently, EGFRvIII-expressing tumors are radioresistant and continue to grow following whole-brain radiotherapy with little effect on overall survival. These in vitro and in vivo data support our hypothesis that EGFRvIII expression promotes DNA-PKcs activation and DSB repair, perhaps as a consequence of hyperactivated PI3K/Akt-1 signaling. Taken together, our results raise the possibility that EGFR and/or DNA-PKcs inhibition concurrent with radiation may be an effective therapeutic strategy for radiosensitizing high-grade gliomas.

Pro-survival AKT and ERK signaling from EGFR and mutant EGFRvIII enhances DNA double-strand break repair in human glioma cells

The epidermal growth factor receptor (EGFR) is frequently dysregulated in malignant glioma that leads to increased resistance to cancer therapy. Upregulation of wild type or expression of mutant EGFR is associated with tumor radioresistance and poor clinical outcome. EGFR variant III (EGFRvIII) is the most common EGFR mutation in malignant glioma. Radioresistance is thought to be, at least in part, the result of a strong cytoprotective response fueled by signaling via AKT and ERK that is heightened by radiation in the clinical dose range. Several groups including ours have shown that this response may modulate DNA repair. Herein, we show that expression of EGFRvIII promoted gamma-H2AX foci resolution, a surrogate for double-strand break (DSB) repair, and thus enhanced DNA repair. Conversely, small molecule inhibitors targeting EGFR, MEK, and the expression of dominant-negative EGFR (EGFR-CD533) significantly reduced the resolution of gamma-H2AX foci. When homologous recombination repair (HRR) and non-homologous end joining (NHEJ) were specifically examined, we found that EGFRvIII stimulated and CD533 compromised HRR and NHEJ, respectively. Furthermore, NHEJ was blocked by inhibitors of AKT and ERK signaling pathways. Moreover, expression of EGFRvIII and CD533 increased and reduced, respectively, the formation of phospho-DNA-PKcs and -ATM repair foci, and RAD51 foci and expression levels, indicating that DSB repair is regulated at multiple levels. Altogether, signaling from EGFR and EGFRvIII promotes both HRR and NHEJ that is likely a contributing factor towards the radioresistance of malignant gliomas.

The role of celecoxib in Rad51 expression and cell survival affected by gefitinib in human non-small cell lung cancer cells

Celecoxib (Celebrex) is a cyclooxygenase-2 (COX-2) selective inhibitor and gefitinib (Iressa(R), ZD1839) is a selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor for human non-small cell lung cancer (NSCLC). The addition of celecoxib to gefitinib to prolong the survival of patients with NSCLC still remains controversial and needs to be investigated. The Rad51 protein is essential for homologous recombination repair, and is overexpressed in chemo- or radioresistant carcinomas. In this study, we characterize the role of celecoxib in the cytotoxicity, ERK1/2 activation and Rad51 expression affected by gefitinib in NSCLC cells. We show that celecoxib can enhance the cytotoxicity induced by gefitinib in NSCLC cells. Treatment with celecoxib alone has no effect on the ERK1/2 activation, Rad51 mRNA and protein levels, however, combined treatment with gefitinib results in a significant reduction of phospho-ERK1/2 and Rad51 protein levels, and triggers the degradation of Rad51 via a 26S proteasome-dependent pathway. Expression of constitutively active MKK1/2 vectors (MKK1/2-CA) significantly rescues the decreased ERK1/2 activity, and restores Rad51 protein levels and cell survival under co-treatment with gefitinib and celecoxib. Furthermore, blocking ERK1/2 activation by U0126 (MKK1/2 inhibitor) and knocking down Rad51 expression by transfection with small interfering RNA of Rad51 can enhance the cytotoxicity of celecoxib.

EGFR Inhibition in the Treatment of Non-Small Cell Lung Cancer

Epidermal growth factor receptor (EGFR) inhibitors have introduced the concept of targeted therapy to the treatment of non-small cell lung cancer (NSCLC). These agents appear most effective in patients with tumors that are highly dependent on EGFR signaling pathways, a population that disproportionately includes females, nonsmokers, individuals of East Asian origin, and patients with adenocarcinoma histology. Currently available EGFR-inhibiting drugs include the tyrosine kinase inhibitors (TKIs) erlotinib, gefitinib, and lapatinib, which are administered orally and interfere with the intracellular tyrosine kinase domain, and the monoclonal antibodies (mAbs) cetuximab and panitumumab, which are administered intravenously and interfere with extracellular ligand binding. While the use of EGFR TKIs as monotherapy prolongs survival in metastatic NSCLC, they have demonstrated no benefit when added to conventional, cytotoxic chemotherapy. In contrast, the anti-EGFR mAb cetuximab appears most effective when combined with chemotherapy or radiation. Despite dramatic initial responses to treatment in some cases, NSCLC eventually becomes resistant to EGFR inhibition. Possible mechanisms include secondary mutations that interfere with drug binding, oncogenic pathways driven by other receptor tyrosine kinases, and independent activity of downstream signaling molecules. Efforts to overcome such resistance include irreversibly binding EGFR TKIs, multi-targeted TKIs, and combinations with chemotherapy, radiation, and other targeted therapies.

Clinical target promiscuity: lessons from ras molecular trials

Mutated ras has been identified in approximately 30% of human tumors, and dysregulation of ras function and signal transduction pathways is a critical step in tumorigenesis. Herein, we review the early data that supports the concept that the intrinsic radiosensitivity of tumor cells can be altered by oncogenic ras expression and that this impacts the PI3K-dependent signaling cascade. This ras-induced radioresistance can be reversed using prenyl transferase inhibitors (PTIs.). We discuss the effects of PTIs as a radiosensitizer in both in vivo and in vitro studies and show that PTIs can lead to increased radiosensitization in vivo through a variety of potential mechanisms that enhance radiation-induced cell kill. We critically evaluate the use of ras biomarkers in predicting the clinical response to PTIs that may explain the mixed results seen thus far in clinical trials using PTIs as a clinical radiosensitizer. We conclude that Ras-mediated radioresistance is the result of multiple intercommunicating pathways functioning against a complex genetic background and a solitary biomarker may not be adequate to predict for PTI-mediated radiosensitization. Nonetheless, our knowledge of the ras-signaling pathway has led to development and testing of specific therapies directed against PI3K-AKT signaling pathways as a future approach towards clinical radiosensitization.

The role of repair protein Rad51 in synergistic cytotoxicity and mutagenicity induced by epidermal growth factor receptor inhibitor (Gefitinib, IressaR) and benzo[a]pyrene in human lung cancer

Rad51 protein is essential for homologous recombination repair of DNA damage, and is over-expressed in chemo- or radioresistant carcinomas. The polycyclic hydrocarbon carcinogen benzo[a]pyrene (B[a]P) affects MAPKs transduction pathways. Gefitinib (IressaR, ZD1839) is a selective epidermal growth factor receptor tyrosine kinase inhibitor that blocks growth factor-mediated cell proliferation and ERK1/2 activation. We hypothesized that gefitinib enhances B[a]P-mediated cytotoxicity by decreasing ERK1/2 activation. Exposure of human lung cancer cells to gefitinib decreased B[a]P-elicited ERK1/2 activation and induced Rad51 protein expression. Gefitinib and B[a]P co-treatment decreased Rad51 protein stability by triggering degradation via a 26S proteasome-dependent pathway. Expression of constitutive active MKK1/2 vectors (MKK1/2-CA) rescues the decreased ERK1/2 activity, and restores Rad51 protein level and stability under gefitinib and B[a]P co-treatment. Gefitinib enhances B[a]P-induced growth inhibition, cytotoxicity and mutagenicity. Co-treatment with gefitinib and B[a]P can further inhibit cell growth significantly after depletion of endogenous Rad51 by siRad51 RNA transfection. Enhancement of ERK1/2 activation by MKK1-CA expression decrease B[a]P- and gefitinib-induced cytotoxicity, and B[a]P-induced mutagenicity. Rad51 protein protects lung cancer cells from synergistic cytotoxic and mutagenic effects induced by gefitinib and B[a]P. Suppression of Rad51 protein expression may be a novel lung cancer therapeutic modality to overcome drug resistance to gefitinib.

Synergism between etoposide and 17-AAG in leukemia cells: critical roles for Hsp90, FLT3, topoisomerase II, Chk1, and Rad51

PURPOSE

DNA-damaging agents, such as etoposide, while clinically useful in leukemia therapy, are limited by DNA repair pathways that are not well understood. 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG), an inhibitor of the molecular chaperone heat shock protein 90 (Hsp90), inhibits growth and induces apoptosis in FLT3(+) leukemia cells. In this study, we evaluated the effects of etoposide and 17-AAG in leukemia cells and the roles of Hsp90, FMS-like tyrosine kinase 3 (FLT3), checkpoint kinase 1 (Chk1), Rad51, and topoisomerase II in this inhibition.

EXPERIMENTAL DESIGN

The single and combined effects of 17-AAG and etoposide and the mechanism of these effects were evaluated. FLT3 and the DNA repair-related proteins, Chk1 and Rad51, were studied in small interfering RNA (siRNA)-induced cell growth inhibition experiments in human leukemia cells with wild-type or mutated FLT3.

RESULTS

We found that etoposide and the Hsp90/FLT3 inhibitor 17-AAG, had synergistic inhibitory effects on FLT3(+) MLL-fusion gene leukemia cells. Cells with an internal tandem duplication (ITD) FLT3 (Molm13 and MV4;11) were more sensitive to etoposide/17-AAG than leukemias with wild-type FLT3 (HPB-Null and RS4;11). A critical role for FLT3 was shown in experiments with FLT3 ligand and siRNA targeted to FLT3. An important role for topoisomerase II and the DNA repair-related proteins, Chk1 and Rad51, in the synergistic effects was suggested from the results.

CONCLUSIONS

The repair of potentially lethal DNA damage by etoposide in leukemia cells is dependent on intact and functioning FLT3 especially leukemias with ITD-FLT3. These data suggest a rational therapeutic strategy for FLT3(+) leukemias that combines etoposide or other DNA-damaging agents with Hsp90/FLT3 inhibitors such as 17-AAG.

Cellular responses to EGFR inhibitors and their relevance to cancer therapy

EGFR is a trans-membrane receptor tyrosine kinase that belongs to the HER family of receptors. The EGFR family plays an essential role in normal organ development by mediating morphogenesis and differentiation. Unlike normal cells that have tight regulatory mechanisms controlling EGFR pathways, tumor cells often have dysregulated EGFR signaling through receptor overexpression and/or mutation. This leads to proliferation under adverse conditions, invasion of surrounding tissues, and increased angiogenesis as well as resistance to radiation and chemotherapy. Therefore, EGFR is a legitimate therapeutic target. Numerous EGFR inhibitors are under development, but to date only four of them are FDA-approved, including two that inhibit the receptor's intracellular tyrosine kinase activity (gefitinib and erlotinib) and two that block extracellular ligand binding (cetuximab, and most recently panitumumab). In this review, we focus on how these different inhibitors affect EGFR signaling and the mechanisms by which they potentiate the effects of chemotherapy and radiation therapy. Numerous clinical trials have been conducted with these agents either as monotherapy, in combination with chemotherapy, or concurrently with radiation. Unfortunately, many of the clinical trials reported so far have shown at best limited gains; therefore, understanding the actions of these agents is essential to improving their efficacy in the treatment of cancers.

Validation of the comet-X assay as a pharmacodynamic assay for measuring DNA cross-linking produced by the novel anticancer agent RH1 during a phase I clinical trial

PURPOSE

RH1 is a novel anticancer agent with potent DNA-cross linking activity. RH1 has the potential to be activated within tumors over expressing NQO1, giving maximal antitumour activity with reduced toxicity in normal tissues. RH1 has recently completed a Cancer Research UK sponsored phase I clinical trial at two different centers in the United Kingdom. The comet-X assay was a secondary endpoint in this trial and assay validation was necessary. We describe here this validation process. Whilst it is impossible to cover all variations/conditions of a pharmacodynamic assay, we have strived to evaluate and demonstrate that this assay conforms to the three R's of validation, that is robustness, reliability and reproducibility.

METHODS

K562 and peripheral blood mononuclear cells were treated with either radiation alone, or with a combination of radiation and drug. These samples were then embedded in low melting point agarose and subjected to a modified version of the alkaline single cell gel electrophoresis (Comet) assay, described here as the comet-X assay. Variations in the preparation, electrophoresis, storage and scoring of these samples was investigated. In addition radiation and drug dose response curves were constructed. Finally stability of QC standards was investigated over a 30-month period.

RESULTS

We have demonstrated a linear radiation-dose response in cells up to 20 Gy and drug induced DNA cross-linking up to 50 nM. From the radiation dose response curves we were able to show that the relative inaccuracy measured against a global mean value was less than 25% and the relative (within day) imprecision was less than 30% over all doses. Between day runs produced an intra assay imprecision of 21.2%. Variables involved in the electrophoresis process showed the voltage across all slides in the tank ranged from 3.1 to -2.0 (mV) whilst the current ranged from 0.8-5.5 mA. QC standards were prepared from PBMCs of healthy donors and frozen at -80 degrees C. The stability of these frozen QC standards was measured over a 30-month period. No significant deterioration in any of the control, irradiated or drug treated samples was observed.

CONCLUSIONS

The comet-X assay has been shown to be a robust, reliable and reproducible assay. It is ideally suited for the evaluation of the pharmacodynamic effects of DNA cross-linking agents undergoing early clinical trials. Furthermore, this assay may provide valuable data, in conjunction with pharmacokinetics, when measuring toxicity and efficacy as part of the RH1 phase I clinical trial.

Amrubicin, a novel 9-aminoanthracycline, enhances the antitumor activity of chemotherapeutic agents against human cancer cells in vitro and in vivo

Amrubicin, a completely synthetic 9-aminoanthracycline derivative, is an active agent in the treatment of untreated extensive disease-small-cell lung cancer and advanced non-small-cell lung cancer. Amrubicin administered intravenously at 25 mg/kg substantially prevented the growth of five of six human lung cancer xenografts established in athymic nude mice, confirming that amrubicin as a single agent was active in human lung tumors. To survey which antitumor agent available for clinical use produces a synergistic interaction with amrubicin, we examined the effects in combinations with amrubicinol, an active metabolite of amrubicin, of several chemotherapeutic agents in vitro using five human cancer cell lines using the combination index (CI) method of Chou and Talalay. Synergistic effects were obtained on the simultaneous use of amrubicinol with cisplatin, irinotecan, gefitinib and trastuzumab, with CI values after 3 days of exposure being <1. Additive effect was observed with the combination containing vinorelbine with CI values indistinguishable from 1, while the combination of amrubicinol with gemcitabine was antagonistic. All combinations tested in vivo were well tolerated. The combinations of cisplatin, irinotecan, vinorelbine, trastuzumab, tegafur/uracil, and to a lesser extent, gemcitabine with amrubicin caused significant growth inhibition of human tumor xenografts without pronouncedly enhancing body weight loss, compared with treatment using amrubicin alone at the maximum tolerated dose. Growth inhibition of tumors by gefitinib was not antagonized by amrubicin. These results suggest that amrubicin appears to be a possible candidate for combined use with cisplatin, irinotecan, vinorelbine, gemcitabine, tegafur/uracil or trastuzumab.

Inhibition of the epidermal growth factor receptor in bladder cancer cells treated with the DNA-damaging drug etoposide markedly increases apoptosis

OBJECTIVE

To investigate the effect of the epidermal growth factor receptor (EGFR) on the induction of apoptosis by the chemotherapeutic agent etoposide (VP16), and to examine the effect of combining VP16 with gefitinib to see if the cell-survival mechanism can be prevented.

MATERIALS AND METHODS

The bladder cancer cell lines RT4 and T24, representing low- and high-malignancy grades respectively, were treated with VP16 (10 or 50 microM) and the level of apoptosis determined using a commercial kit. EGFR receptor activity was determined by western blotting using antibodies against phosphorylated EGFR. The EGFR was either activated by heparin-binding (HB)-EGF (1 nM) or inhibited with the specific EGFR inhibitor gefitinib (1 or 5 microM). The pan-caspase inhibitor Z-VAD (30 microM) was used to test the involvement of caspase activity.

RESULTS

Treatment of T24 bladder cancer cells with VP16 (50 microM) for 48 h induced phosphorylation of the EGFR and activation of the EGFR prevented the apoptosis induced by VP16. Thus, treatment of T24 cells with 50 microM VP16 for 48 h resulted in 19% apoptosis. However, activation of the EGFR with HB-EGF (1 nM) with VP16 (50 microM) significantly reduced the level of apoptosis by 25% (P < 0.05) showing that activating the EGFR has a cell-survival function. Inhibiting the EGFR with gefitinib (5 microM) blocked the VP16-induced activation of the EGFR. Combined treatment with gefitinib and VP16 resulted in 45% apoptotic cells, i.e. more than double the percentage of apoptotic cells with VP16 alone. This was found in both T24 and RT4 cells. Gefitinib used alone (1 and 5 microM) generated no apoptosis in the cells. Treatment of T24 cells with Z-VAD showed that apoptosis induced by both VP16 alone and VP16 with gefitinib was caspase-mediated.

CONCLUSION

These results suggest that activation of the EGFR induced a cell-survival function when bladder cancer cells were treated with the DNA-damaging drug VP16, and that combined treatment with VP16 and the EGFR inhibitor gefitinib might improve the efficacy of treatment.

PBK/TOPK promotes tumour cell proliferation through p38 MAPK activity and regulation of the DNA damage response

The contribution of the insulin-like growth-factor-I receptor (IGF-IR) to tumour progression is well documented. To identify new mediators of IGF-IR function in cancer, we recently isolated genes differentially expressed in cells overexpressing the IGF-IR. Among these was the serine/threonine kinase PBK/TOPK (PDZ-binding kinase/T-LAK cell-originated protein kinase), previously associated with highly proliferative cells and tissues. Here, we show that PBK is expressed at high levels in tumour cell lines compared with non-transformed cells. IGF-I could induce PBK expression only in transformed cells, whereas epidermal growth factor could induce PBK in non-transformed MCF-10A breast epithelial cells. Suppression of PBK expression using small interfering RNA did not prevent progression through the cell cycle, but caused decreased proliferation over time in culture, and reduced clonogenic growth in soft agarose. PBK knockdown impaired p38 activation after long-term stimulation with different growth factors and reduced DU145 cells motility. Suppressed PBK expression also resulted in an impaired response to DNA damage that was evident by the decreased generation of gamma-H2AX, increased DNA damage and decreased cell survival. Taken together, the data indicate that PBK is necessary for appropriate activation and function of the p38 pathway by growth factors. Thus, enhanced expression of PBK may facilitate tumour growth by mediating p38 activation and by helping cells to overcome DNA damage.