EGF receptor signaling enhances in vivo invasiveness of DU-145 human prostate carcinoma cells

Xenografts on nude mouse diaphragm of human DU145 prostate carcinoma cells: mesothelium removal by outgrowths and angiogenesis

Human prostate carcinoma DU145 cells, androgen-independent malignant cells, implanted in the athymic nu/nu male mouse, developed numerous tumors on peritoneal and retro-peritoneal organs whose growth aspects and vascular supply have yet to be investigated with fine structure techniques. A series of necropsies from moribund implanted mice diaphragms were examined with light, scanning, and transmission electron microscopy. DU145 xenografts installations, far away from the implanted site, were described as the smallest installation to large diaphragm outgrowths in moribund mice. Carcinomas did not show extracellular matrix and, reaching more than 0.15 mm in thickness, they revealed new structures in these outgrowths. Voids to be gland-like structures with mediocre secretion and, unexpectedly, intercellular spaces connected with fascicles of elongated DU145 cells that merged with a vascular supply originated from either the tumor cells and/or some perimysium vessels. In the largest carcinomas, most important vascular invasions coincidently accompanied the mouse lethality, similarly to human cancers. This androgen-independent model would be useful to study tumor outgrowth's changes related to testing anticancer strategy, including anti-angiogenic therapies involving toxicity, simultaneously with those of other vital organs with combined biomolecular and fine structure techniques.

Multifaceted Interplay between Hormones, Growth Factors and Hypoxia in the Tumor Microenvironment

Hormones and growth factors (GFs) are signaling molecules implicated in the regulation of a variety of cellular processes. They play important roles in both healthy and tumor cells, where they function by binding to specific receptors on target cells and activating downstream signaling cascades. The stages of tumor progression are influenced by hormones and GF signaling. Hypoxia, a hallmark of cancer progression, contributes to tumor plasticity and heterogeneity. Most solid tumors contain a hypoxic core due to rapid cellular proliferation that outgrows the blood supply. In these circumstances, hypoxia-inducible factors (HIFs) play a central role in the adaptation of tumor cells to their new environment, dramatically reshaping their transcriptional profile. HIF signaling is modulated by a variety of factors including hormones and GFs, which activate signaling pathways that enhance tumor growth and metastatic potential and impair responses to therapy. In this review, we summarize the role of hormones and GFs during cancer onset and progression with a particular focus on hypoxia and the interplay with HIF proteins. We also discuss how hypoxia influences the efficacy of cancer immunotherapy, considering that a hypoxic environment may act as a determinant of the immune-excluded phenotype and a major hindrance to the success of adoptive cell therapies.

Prostate cancer liver metastasis: Dormancy and resistance to therapy

Liver metastasis causes nearly half of death from solid tumors. Metastatic lesions, to the liver in particular, can become detectable years or decades after primary tumor removal, leaving an uncertain long-term prognosis in patients. Prostate cancer (PCa), a prominent metastatic dormant cancer, has the worst prognosis when found in the liver compared to other metastatic sites. These metastatic nodules display a therapy resistance in the liver pro-metastatic microenvironment; the resistance appears to be conferred by both dormancy and independent of dormancy when the nodules emerge. Within the review, the molecular underpinnings of how the liver aids and protects PCa cells seeding, colonization and resistance will be discussed.

The pan-therapeutic resistance of disseminated tumor cells: Role of phenotypic plasticity and the metastatic microenvironment

Cancer metastasis is the leading cause of mortality in patients with solid tumors. The majority of these deaths are associated with metastatic disease that occurs after a period of clinical remission, anywhere from months to decades following removal of the primary mass. This dormancy is prominent in cancers of the breast and prostate among others, leaving the survivors uncertain about their longer-term prognosis. The most daunting aspect of this dormancy and re-emergence is that the micrometastases in particular, and even large lethal outgrowths are often show resistance to agents to which they have not been exposed. This suggests that in addition to specific mutations that target single agents, there also exist adaptive mechanisms that provide this pan-resistance. Potential molecular underpinnings of which are the topic of this review.

HUNK phosphorylates EGFR to regulate breast cancer metastasis

Epidermal growth factor receptor (EGFR) is commonly over-expressed in metastatic breast cancer yet metastatic breast cancer is generally resistant to anti-EGFR therapies, and the mechanism for resistance to EGFR inhibitors in this setting is not fully understood. Hormonally up-regulated neu-associated kinase (HUNK) kinase is up-regulated in aggressive breast cancers and is thought to play a role in breast cancer metastasis. However, no studies have been conducted to examine a relationship between EGFR and HUNK in breast cancer metastasis. We performed a kinase substrate screen and identified that EGFR is phosphorylated by HUNK. Our studies show that HUNK phosphorylates EGFR at T654, enhancing receptor stability and downstream signaling. We found that increased phosphorylation of T654 EGFR correlates with increased epithelial to mesenchymal, migration and invasion, and metastasis. In addition, we found that HUNK expression correlates with overall survival and distant metastasis free survival. This study shows that HUNK directly phosphorylates EGFR at T654 to promote metastasis and is the first study to show that the phosphorylation of this site in EGFR regulates metastasis.

Effective treatment of cancer metastasis using a dual-ligand nanoparticle

Metastasis is responsible for the majority of deaths of breast cancer patients. While cytotoxic drugs are available with high potency to kill breast cancer cells, they are not designed to specifically seek and navigate in the dynamic and continuously changing microenvironment of metastatic disease. To effectively delivery chemotherapeutic agents to metastasis, we designed a dual-ligand nanoparticle loaded with doxorubicin by using two different types of ligands targeting EGFR and α_vβ₃ integrin. Metastatic cancer cells continuously change resulting in heterogeneity even across adjacent micrometastatic regions with variable expression of these targetable receptors. Using a mouse model of breast cancer metastasis, in vivo and ex vivo imaging showed that both EGFR and α_vβ₃ integrin-targeting were required to reliably direct the nanoparticle to metastasis and capture the spread and exact topology of the disease. Survival studies compared the anticancer efficacy of the standard drug, EGFR-targeting nanoparticle, α_vβ₃ integrin-targeting nanoparticle and the dual-ligand nanoparticle. While all the other treatments produced moderate therapeutic outcomes, treatment with the dual-ligand nanoparticle yielded significant improvement and event-free survival in a mouse model of breast cancer metastasis.

Transcriptional repressor Kaiso promotes epithelial to mesenchymal transition and metastasis in prostate cancer through direct regulation of miR-200c

The loss of miR-200 family, through DNA methylation, results in cancer cells undergoing an epithelial to mesenchymal transition (EMT), and metastasis. In this study, we established that the transcriptional repressor Kaiso directly binds methylated regions of the miR-200 family, and this is reversed with 5-aza treatment. sh-Kaiso PC-3 cells display increased miR-200-a/b/c, miR-141, and miR-429 expression, with miR-200c demonstrating the most significant increase. Interestingly, overexpression of EGFR or treatment with EGF decreases miR-200c expression and this is reversed after treatment with EGFR specific kinase inhibitor PD153035. However, EGF did not have a significant effect on miR-200c in sh-Kaiso DU-145 or PC-3 cell lines, suggesting Kaiso silences miR-200c through the activation of EGFR signaling. Overexpression of Kaiso in LNCaP cells results in decreased expression of miR-200-a/b/c, miR-141, and miR-429, along with increased expression of ZEB1, p-EGFR and total EGFR levels. Overexpression of miR200c in PC-3 cells results in decreased expression of EGFR, ZEB1, ERK1/2 and Kaiso. Additionally, sh-Kaiso PC-3 demonstrates reduced in vivo tumor formation and metastasis. Thus, our data suggests that EGFR signaling regulates the silencing of miR-200 family through Kaiso binding to methylated regions in the promoter.

Precise targeting of cancer metastasis using multi-ligand nanoparticles incorporating four different ligands

Metastasis displays a highly heterogeneous cellular population with cancer cells continuously evolving. As a result, a single-ligand nanoparticle cannot account for the continuously changing expression of targetable biomarkers over time and space. To effectively direct nanoparticles to metastasis, we developed a multi-ligand nanoparticle by using four different types of ligands on the same nanoparticle that target biomarkers on the endothelium associated with metastatic disease. These vascular targets included αvβ3 integrin, P-selectin, EGFR and fibronectin. Using terminal and in vivo imaging studies, the targeting performance of the multi-ligand nanoparticles was compared to the single-ligand nanoparticle variants. All four single-ligand nanoparticle variants achieved significant targeting of lung metastasis in the 4T1 mouse model of breast cancer metastasis with about 2.5% of the injected dose being deposited into metastasis. A dual-ligand nanoparticle resulted in a nearly 2-fold higher deposition into lung metastases than its single-ligand counterparts. The multi-ligand nanoparticle significantly outperformed its targeting nanoparticle counterparts achieving a deposition of ∼7% of its injected nanoparticles into lung metastases. Using the high sensitivity of radionuclide imaging, PET imaging showed that a multi-ligand nanoparticle labeled with [18F]fluoride was able to precisely target metastatic disease at its very early stage of development in three different animal models of metastatic breast cancer.

Correlations between EGFR gene polymorphisms and pleural metastasis of lung adenocarcinoma

Proliferation, growth, and differentiation of cells are strictly controlled by the signal system of epidermal growth factor receptor (EGFR). If any link of the EGFR signals system is interfered with or damaged, the proliferation, growth, and differentiation of cells would become uncontrolled. EGFR is overexpressed in a variety of malignant tumors, such as non-small-cell lung cancer, colorectal cancer and breast cancer. Results of the study have proved that EGFR overexpression is closely associated with mutations and variants of the EGFR genes, whose mutations and variants are associated with occurrence, metastasis, and prognosis of different types of tumors, including lung cancer. This study is aimed at investigating whether the polymorphisms of CA simple sequence repeat in intron 1 (CA-SSR1), -216G/T, and R497K in the EGFR are able to induce EGFR activation and whether overexpression is associated with pleural metastasis of lung adenocarcinoma. A total of 432 lung adenocarcinoma patients with pleural metastasis (metastasis group) and 424 patients with lung adenocarcinoma but without pleural metastasis (nonmetastasis group) were enrolled in this study. For all patients, the CA-SSR1 genotypes were determined by capillary electrophoresis, polymerase chain reaction amplification, and direct DNA sequencing, and the R497K and -216G/T genotypes were determined by polymerase chain reaction amplification and direct DNA sequencing. EGFR expression was evaluated by immunohistochemical staining in primary tumor tissues with different -216G/T, R497K, and CA-SSR1 genotypes. Our results showed significant differences between pleural metastasis and nonmetastasis groups in the genotype and allele distribution of -216G/T, R497K, and CA-SSR1 polymorphisms of the EGFR gene. The -216T allele, Arg allele, and shorter CA-SSR1 (<17) had significantly increased risks of pleural metastasis compared with the -216G allele, Lys allele, and longer CA-SSR1 (≥17), respectively. The expression of EGFR was higher in patients with genotypes of -216T/T or -216G/T, Arg/Arg or Arg/Lys, and shorter CA-SSR1 (<17) than that in patients with genotypes of -216G/G, Lys/Lys, and longer CA-SSR1 (≥17), respectively. These results indicate that -216G/T, R497K, and CA-SSR1 polymorphisms are associated with the risk of pleural metastasis of lung adenocarcinoma, which may be related to the overexpression of EGFR protein induced by -216G/T, R497K, and CA-SSR1 polymorphisms.

Formation of intracellular lumina in human prostate carcinoma (DU145) cells, maturation into signet cells, and the cribriform morphology of tumors

The intracellular or intracytoplasmic lumen (IL) is an enigmatic histological structure that occurs in various tumor cells. A reassessment of diverse ILs fine-structure micrographs obtained out of previous studies encompassing the human prostate carcinoma (DU145) cell line and xenotransplanted carcinomas enabled us to propose aspects of ILs development in cancer cells: a combination of altered expressions in intercellular contacts and their cytoskeletal components would favor a disarray of self-apical polarity orientation; those defects, associated with a local, entwined enriched membranous structures growing as microvilli-like formations out of a disrupted endoplasm and trans-Golgi sorting, create ILs in cells' perikarya. These misplaced intracytoplasmic domains can become enlarged through spaces made between the finger-like structures by accruing membranes of coalescent intracytoplasmic vesicles then adding microvilli and glycocalyx to constitute ILs. Cationic mucins added with or without a progressive or total loss of microvilli and content generate signet or ring cell, while ILs enlarge. Variable build-ups of these cells' populations in carcinomas result in architectural mix-up of adjacent cells around these voids, misconstrued as new lumen, and establish a "cribriform" tumor pattern that often implies a poor cancer prognosis. Alternatively, cytotoxic changes caused by anticancer pro-oxidant treatment favor membrane alterations and exaggerate the ILs in xenotransplants into intracellular crypts that accompany other tumor degenerative changes.

Epidermal growth factor promotes a mesenchymal over an amoeboid motility of MDA-MB-231 cells embedded within a 3D collagen matrix. EUROPEAN PHYSICAL JOURNAL PLUS 2016;131:8. [PMID: 31367506 PMCID: PMC6668350 DOI: 10.1140/epjp/i2016-16008-8]

The receptor of epidermal growth factor (EGFR) critically regulates tumor cell invasion and is a potent therapeutic target for treatment of many types of cancers, including carcinomas and glioblastomas. It is known that EGF regulates cell motility when tumor cells are embedded within a 3D biomatrix. However, roles of EGF in modulating tumor cell motility phenotype are largely unknown. In this article, we report that EGF promotes a mesenchymal over an amoeboid motility phenotype using a malignant breast tumor cell line, MDA-MB-231, embedded within a 3D collagen matrix. Amoeboid cells are rounded in shape, while mesenchymal cells are elongated, and their migrations are governed by a distinctly different set of biomolecules. Using single cell tracking analysis, we also show that EGF promotes cell dissemination through a significant increase in cell persistence along with a moderate increase of speed. The increase of persistence is correlated with the increase of the percentage of the mesenchymal cells within the population. Our work reveals a novel role of microenvironmental cue, EGF, in modulating heterogeneity and plasticity of tumor cell motility phenotype. In addition, it suggests a potential visual cue for diagnosing invasive states of breast cancer cells. This work can be easily extended beyond breast cancer cells.

P2Y2 Receptor and EGFR Cooperate to Promote Prostate Cancer Cell Invasion via ERK1/2 Pathway

As one member of G protein-coupled P2Y receptors, P2Y2 receptor can be equally activated by extracellular ATP and UTP. Our previous studies have proved that activation of P2Y2 receptor by extracellular ATP could promote prostate cancer cell invasion and metastasis in vitro and in vivo via regulating the expressions of some epithelial-mesenchymal transition/invasion-related genes (including IL-8, E-cadherin, Snail and Claudin-1), and the most significant change in expression of IL-8 was observed after P2Y2 receptor activation. However, the signaling pathway downstream of P2Y2 receptor and the role of IL-8 in P2Y2-mediated prostate cancer cell invasion remain unclear. Here, we found that extracellular ATP/UTP induced activation of EGFR and ERK1/2. After knockdown of P2Y2 receptor, the ATP -stimulated phosphorylation of EGFR and ERK1/2 was significantly suppressed. Further experiments showed that inactivation of EGFR and ERK1/2 attenuated ATP-induced invasion and migration, and suppressed ATP-mediated IL-8 production. In addition, knockdown of IL-8 inhibited ATP-mediated invasion and migration of prostate cancer cells. These findings suggest that P2Y2 receptor and EGFR cooperate to upregulate IL-8 production via ERK1/2 pathway, thereby promoting prostate cancer cell invasion and migration. Thus blocking of the P2Y2-EGFR-ERK1/2 pathway may provide effective therapeutic interventions for prostate cancer.

Synergistic effects of combined platelet-activating factor receptor and epidermal growth factor receptor targeting in ovarian cancer cells

Background

Genetic alterations, including the overexpression of epidermal growth factor receptor (EGFR), play a crucial role in ovarian carcinogenesis. To date, EGFR targeting has shown limited antitumor effects in ovarian cancer when administered as monotherapy. We previously identified platelet-activating factor receptor (PAFR) as being overexpressed in ovarian cancer and found that its ligand PAF evoked EGFR phosphorylation. To determine whether PAFR targeting can enhance the antitumor efficacy of EGFR inhibition, we investigated the effects of a PAFR antagonist (WEB2086) in conjunction with an EGFR inhibitor (AG1478).

Methods

The expression of EGFR and PAFR in CAOV-3 and SKOV-3 ovarian cancer cell lines was measured by Western blot and immunocytochemistry. Synergy was determined using isobologram analysis. The effects of combined PAFR and EGFR targeting on both cells were assessed by using CCK-8, transwell, flow cytometry, western blot analysis. In vivo studies were conducted using CAOV-3 cells xenografted in nu/nu mice.

Results

Treatment with combination WEB2086 and AG1478 resulted in significantly greater inhibition of proliferation and invasion compared to either drug alone. When examining equipotent combinations of WEB2086 and AG1478 to determine potential synergy, a combination index (CI) of 0.49 was identified for CAOV-3 cells and a CI of 0.58 for SKOV-3 cells indicating synergy. This co-inhibition induced significantly more apoptosis and arrested the cells at G0/G1 phase in both cell lines. The activation of PAFR and/or EGFR induced phosphorylation of the mTOR, AKT, and MAPK pathways. Combined PAFR and EGFR targeting synergistically diminished the expression of PAFR and EGFR phosphorylation and downstream signaling. In vivo studies further verified the antitumor effects of combined PAFR and EGFR targeting in a CAOV-3 xenograft model.

Conclusions

These results suggest that WEB2086 and AG1478 are synergistic in ovarian cancer cells with high expression of both PAFR and EGFR. The presented approach may have important therapeutic implications in the treatment of ovarian cancer patients.

MicroRNAs that affect prostate cancer: emphasis on prostate cancer in African Americans

Although concerted efforts have been directed toward eradicating health disparities in the United States, the disease and mortality rates for African American men still are among the highest in the world. We focus here on the role of microRNAs (miRNAs) in the signaling pathways of androgen receptors and growth factors that promote the progression of prostate cancer to more aggressive disease. We explore also how differential expression of miRNAs contributes to aggressive prostate cancer including that of African Americans.

-216G/T (rs712829), a functional variant of the EGFR promoter, is associated with the pleural metastasis of lung adenocarcinoma

Numerous mutations and variants in the epidermal growth factor receptor (EGFR) gene have been demonstrated to be associated with the occurrence, metastasis and prognosis of various types of tumors, including lung cancer. Thus, the present study aimed to investigate whether -216G/T (rs712829), a functional polymorphism of the EGFR promoter that is able to induce EGFR activation and overexpression, is associated with the pleural metastasis of lung adenocarcinoma. The study subjects were comprised of 326 patients with primary lung adenocarcinoma and 312 matched cases with pleural metastasis. The -216G/T genotypes were determined in all subjects by PCR amplification and direct DNA sequencing, and EGFR expression was also evaluated by immunohistochemical staining in the primary tumor tissues with various -216G/T genotype backgrounds. The results showed that the frequencies of allele T and genotypes G/T and T/T in the pleural metastasis group were significantly higher compared with those in the non-metastasis group, with adjusted ORs of 1.46 (95% CI, 1.015–1.963) for G/T and 1.97 (95% CI, 1.051–3.152) for T/T. Furthermore, the expression of the EGFR protein was higher in the primary lung adenocarcinoma tissues with -216T/T and -216G/T compared with those with -216G/G (P<0.05). These results collectively indicate that the -216G/T polymorphism in the EGFR promoter is associated with the risk of the pleural metastasis of lung adenocarcinoma and that this effect may be associated with -216G/T-induced overexpression of the EGFR protein.

Role of proprotein convertases in prostate cancer progression

Better understanding of the distinct and redundant functions of the proprotein convertase (PC) enzyme family within pathophysiological states has a great importance for potential therapeutic strategies. In this study, we investigated the functional redundancy of PCs in prostate cancer in the commonly used androgen-sensitive LNCaP and the androgen-independent DU145 human cell lines. Using a lentiviral-based shRNA delivery system, we examined in vitro and in vivo cell proliferation characteristics of knockdown cell lines for the endogenous PCs furin, PACE4, and PC7 in both cell lines. Of the three PCs, only PACE4 was essential to maintain a high-proliferative status, as determined in vitro using XTT proliferation assays and in vivo using tumor xenografts in nude mice. Furin knockdowns in both cell lines had no effects on cell proliferation or tumor xenograft growth. Paradoxically, PC7 knockdowns reduced in vitro cellular proliferation but had no effect in vivo. Because PCs act within secretion pathways, we showed that conditioned media derived from PACE4 knockdown cells had very poor cell growth-stimulating effects in vitro. Immunohistochemistry of PACE4 knockdown tumors revealed reduced Ki67 and higher p27(KIP) levels (proliferation and cell cycle arrest markers, respectively). Interestingly, we determined that the epidermal growth factor receptor signaling pathway was activated in PC7 knockdown tumors only, providing some explanations of the paradoxical effects of PC7 silencing in prostate cancer cell lines. We conclude that PACE4 has a distinct role in maintaining proliferation and tumor progression in prostate cancer and this positions PACE4 as a relevant therapeutic target for this disease.

Targeting signaling pathways in epithelial ovarian cancer

Ovarian carcinoma (OC) is the most lethal gynecological malignancy. Response to platinum-based chemotherapy is poor in some patients and, thus, current research is focusing on new therapy options. The various histological types of OC are characterized by distinctive molecular genetic alterations that are relevant for ovarian tumorigenesis. The understanding of these molecular pathways is essential for the development of novel therapeutic strategies.

Differential signaling of the GnRH receptor in pituitary gonadotrope cell lines and prostate cancer cell lines

The GnRH receptor (GnRHR) mediates the pituitary functions of GnRH, as well as its anti-proliferative effects in sex hormone-dependent cancer cells. Here we compare the signaling of GnRHR in pituitary gonadotrope cell lines vs. prostate cancer cell lines. We first noticed that the expression level of PKCα, PKCβII and PKCε is much higher in αT3-1 and LβT2 gonadotrope cell lines vs. LNCaP and DU-145 cell lines, while the opposite is seen for PKCδ. Activation of PKCα, PKCβII and PKCε by GnRH is relatively transient in αT3-1 and LβT2 gonadotrope cell lines and more prolonged in LNCaP and DU-145 cell lines. On the otherhand, the activation and re-distribution of the above PKCs by PMA was similar for both gonadotrope cell lines and prostate cancer cell lines. Activation of ERK1/2 by GnRH and PMA was robust in the gonadotrope cell lines, with a smaller effect observed in the prostate cancer cell lines. The Ca(2+) ionophore A23187 stimulated ERK1/2 in gonadotrope cell lines but not in prostate cancer cell lines. GnRH, PMA and A23187 stimulated JNK activity in gonadotrope cell lines, with a more sustained effect in prostate cancer cell lines. Sustained activation of p38 was observed for PMA and A23187 in Du-145 cells, while p38 activation by GnRH, PMA and A23187 in LβT2 cells was transient. Thus, differential expression and re-distribution of PKCs by GnRH and the transient vs. the more sustained nature of the activation of the PKC-MAPK cascade by GnRH in gonadotrope cell lines vs. prostate cancer cell lines respectively, may provide the mechanistic basis for the cell context-dependent differential biological responses observed in GnRH interaction with pituitary gonadotropes vs. prostate cancer cells.

Identification of a novel antagonist of the ErbB1 receptor capable of inhibiting migration of human glioblastoma cells

BACKGROUND

Receptors of the ErbB family are involved in the development of various cancers, and the inhibition of these receptors represents an attractive therapeutic concept. Upon ligand binding, ErbB receptors become activated as homo- or heterodimers, leading to the activation of downstream signaling cascades that result in the facilitation of cell proliferation and migration. A region of the extracellular part of the receptor, termed the 'dimerization arm', is important for the formation of receptor dimers and represents an attractive target for the design of ErbB inhibitors.

METHODS

An ErbB1 targeting peptide, termed Herfin-1, was designed based on a model of the tertiary structure of the EGF-EGFR ternary complex. The binding kinetics of this peptide were determined employing surface plasmon resonance analyses. ErbB1-4 expression and phosphorylation in human glioblastoma cell lines U87 and U118 were determined by Western blotting using specific antibodies. Cell proliferation was determined by MTS staining. Cell migration was examined using a Chemotaxis Migration Kit. Neurite outgrowth from primary cerebellar granule neurons was evaluated by fluorescence microscopy and image processing.

RESULTS

The present study shows that Herfin-1 functions as an ErbB1 antagonist. It binds to the extracellular domain of ErbB1 with a KD value of 361 nM. In U87 and U118 cells, both expressing high levels of ErbB1, Herfin-1 inhibits EGF-induced ErbB1 phosphorylation and cell migration. Additionally, Herfin-1 was found to increase neurite outgrowth in cerebellar granule neurons, likely through the inhibition of a sustained weak ErbB1 activation.

CONCLUSIONS

Targeting the ErbB1 receptor dimerization interface is a promising strategy to inhibit receptor activation in ErbB1-expressing glioma cells.

Nuclear Kaiso indicates aggressive prostate cancers and promotes migration and invasiveness of prostate cancer cells

Kaiso, a p120 catenin-binding protein, is expressed in the cytoplasmic and nuclear compartments of cells; however, the biological consequences and clinical implications of a shift between these compartments have yet to be established. Herein, we report an enrichment of nuclear Kaiso expression in cells of primary and metastatic prostate tumors relative to the normal prostate epithelium. Nuclear expression of Kaiso correlates with Gleason score (P < 0.001) and tumor grade (P < 0.001). There is higher nuclear expression of Kaiso in primary tumor/normal matched samples and in primary tumors from African American men (P < 0.0001). We further found that epidermal growth factor (EGF) receptor up-regulates Kaiso at the RNA and protein levels in prostate cancer cell lines, but more interestingly causes a shift of cytoplasmic Kaiso to the nucleus that is reversed by the EGF receptor-specific kinase inhibitor, PD153035. In both DU-145 and PC-3 prostate cancer cell lines, Kaiso inhibition (short hairpin RNA-Kaiso) decreased cell migration and invasion even in the presence of EGF. Further, Kaiso directly binds to the E-cadherin promoter, and inhibition of Kaiso in PC-3 cells results in increased E-cadherin expression, as well as re-establishment of cell-cell contacts. In addition, Kaiso-depleted cells show more epithelial morphology and a reversal of the mesenchymal markers N-cadherin and fibronectin. Our findings establish a defined oncogenic role of Kaiso in promoting the progression of prostate cancer.

Inhibition of EGFR-AKT axis results in the suppression of ovarian tumors in vitro and in preclinical mouse model

Ovarian cancer is the leading cause of cancer related deaths in women. Genetic alterations including overexpression of EGFR play a crucial role in ovarian carcinogenesis. Here we evaluated the effect of phenethyl isothiocyanate (PEITC) in ovarian tumor cells in vitro and in vivo. Oral administration of 12 µmol PEITC resulted in drastically suppressing ovarian tumor growth in a preclinical mouse model. Our in vitro studies demonstrated that PEITC suppress the growth of SKOV-3, OVCAR-3 and TOV-21G human ovarian cancer cells by inducing apoptosis in a concentration-dependent manner. Growth inhibitory effects of PEITC were mediated by inhibition of EGFR and AKT, which are known to be overexpressed in ovarian tumors. PEITC treatment caused significant down regulation of constitutive protein levels as well as phosphorylation of EGFR at Tyr1068 in various ovarian cancer cells. In addition, PEITC treatment drastically reduced the phosphorylation of AKT which is downstream to EGFR and disrupted mTOR signaling. PEITC treatment also inhibited the kinase activity of AKT as observed by the down regulation of p-GSK in OVCAR-3 and TOV-21G cells. AKT overexpression or TGF treatment blocked PEITC induced apoptosis in ovarian cancer cells. These results suggest that PEITC targets EGFR/AKT pathway in our model. In conclusion, our study suggests that PEITC could be used alone or in combination with other therapeutic agents to treat ovarian cancer.

FGFR1-induced epithelial to mesenchymal transition through MAPK/PLCγ/COX-2-mediated mechanisms

Tumour invasion and metastasis is the most common cause of death from cancer. For epithelial cells to invade surrounding tissues and metastasise, an epithelial-mesenchymal transition (EMT) is required. We have demonstrated that FGFR1 expression is increased in bladder cancer and that activation of FGFR1 induces an EMT in urothelial carcinoma (UC) cell lines. Here, we created an in vitro FGFR1-inducible model of EMT, and used this model to identify regulators of urothelial EMT. FGFR1 activation promoted EMT over a period of 72 hours. Initially a rapid increase in actin stress fibres occurred, followed by an increase in cell size, altered morphology and increased migration and invasion. By using site-directed mutagenesis and small molecule inhibitors we demonstrated that combined activation of the mitogen activated protein kinase (MAPK) and phospholipase C gamma (PLCγ) pathways regulated this EMT. Actin stress fibre formation was regulated by PLCγ activation, and was also important for the increase in cell size, migration and altered morphology. MAPK activation regulated migration and E-cadherin expression, indicating that combined activation of PLCγ and MAPK is required for a full EMT. We used expression microarrays to assess changes in gene expression downstream of these signalling cascades. COX-2 was transcriptionally upregulated by FGFR1 and caused increased intracellular prostaglandin E(2) levels, which promoted migration. In conclusion, we have demonstrated that FGFR1 activation in UC cells lines promotes EMT via coordinated activation of multiple signalling pathways and by promoting activation of prostaglandin synthesis.

Altered CXCR3 isoform expression regulates prostate cancer cell migration and invasion

BACKGROUND

Carcinoma cells must circumvent the normally suppressive signals to disseminate. While often considered 'stop' signals for adherent cells, CXCR3-binding chemokines have recently been correlated positively with cancer progression though the molecular basis remains unclear.

RESULTS

Here, we examined the expression and function of two CXCR3 variants in human prostate cancer biopsies and cell lines. Globally, both CXCR3 mRNA and protein were elevated in localized and metastatic human cancer biopsies compared to normal. Additionally, CXCR3A mRNA level was upregulated while CXCR3B mRNA was downregulated in these prostate cancer specimens. In contrast to normal prostate epithelial cells (RWPE-1), CXCR3A was up to half the receptor in the invasive and metastatic DU-145 and PC-3 prostate cancer cells, but not in the localized LNCaP cells. Instead of inhibiting cell migration as in RWPE-1 cells, the CXCR3 ligands CXCL4/PF4 and CXCL10/IP10 promoted cell motility and invasiveness in both DU-145 and PC-3 cells via PLCβ3 and μ-calpain activation. CXCR3-mediated diminution of cell motility in RWPE-1 cells is likely a result of cAMP upregulation and m-calpain inhibition via CXCR3B signal transduction. Interestingly, overexpression of CXCR3B in DU-145 cells decreased cell movement and invasion.

CONCLUSION

These data suggest that the aberrant expression of CXCR3A and down-regulation of CXCR3B may switch a progression "stop" to a "go" signal to promote prostate tumor metastasis via stimulating cell migration and invasion.

Blocking epidermal growth factor receptor activation by 3,3'-diindolylmethane suppresses ovarian tumor growth in vitro and in vivo

Genetic alterations, including the overexpression of epidermal growth factor receptor (EGFR) (in approximately 70% of ovarian tumors), play a crucial role in the signal transduction pathways that regulate key cellular functions, such as cell survival and proliferation, and are responsible for compromising traditional chemotherapy. 3,3'-Diindolylmethane (DIM) is an indole compound present in Brassica vegetables. In our previous studies, we demonstrated that BR-DIM, a formulated version of DIM, suppressed the growth of ovarian cancer cells by causing cell cycle arrest and apoptosis. In the present study, we delineated the mechanism by which DIM suppressed the growth of SKOV-3, OVCAR-3, and TOV-21G human ovarian cancer cells. DIM treatment caused significant down-regulation of the constitutive EGFR protein level as well as phosphorylation of EGFR at Tyr1068, Tyr992, Tyr845, and Tyr1173 in various ovarian cancer cells. To determine whether DIM suppressed the activation of EGFR by activating phosphorylation, cells were treated with epidermal growth factor. Epidermal growth factor treatment significantly blocked the DIM-mediated inhibition of EGFR activation and apoptosis in both SKOV-3 and OVCAR-3 cells. In addition, DIM treatment drastically reduced the phosphorylation of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK), which are downstream to EGFR, without affecting their protein levels. DIM treatment also inhibited the kinase activity of ERK, as observed by the down-regulation of phospho-E twenty-six like transcription factor 1 (p-ELK1) in all three ovarian cancer cell lines. DIM significantly suppressed the growth of ovarian tumors in vivo. Tumor growth suppressive effects of DIM in SKOV-3 tumor xenografts were associated with reduced phosphorylation of EGFR, MEK, and ERK. These results indicate that DIM induces apoptosis in ovarian cancer cells by inhibiting the EGFR-ERK pathway in vitro and in vivo.

Knock-down of amphiregulin inhibits cellular invasion in inflammatory breast cancer

We have previously shown that SUM-149 human breast cancer cells require an amphiregulin (AREG) autocrine loop for cell proliferation. We also demonstrated that AREG can increase epidermal growth factor receptor (EGFR) stability and promote EGFR localization to the plasma membrane. In the present studies we successfully knocked-down AREG expression in SUM-149 cells by lentiviral infection of AREG shRNA. In the absence of AREG expression, SUM-149 cell growth was slowed, but not completely inhibited. Furthermore, cells infected with AREG shRNA constructs showed an increase in EGFR protein expression by Western blot. Immunofluorescence and confocal microscopy showed that following AREG knock-down, EGFR continued to localize to the cell surface. Soft agar assays demonstrated that AREG knock-down cells retain anchorage-independent growth capacity. Additionally mammosphere forming assays and Adefluor staining analysis showed that knock-down of AREG expression did not affect the expression of stem cell phenotypes. However, following AREG knock-down, SUM-149 cells demonstrated a dramatic decrease in their ability to invade a Matrigel matrix. Consistent with this observation, microarray analysis comparing cells infected with a non-silencing vector to the AREG knock-down cells, identified genes associated with the invasive phenotype such as RHOB and DKK1, and networks associated with cell motility such as integrin-linked kinase signaling, and focal adhesion kinase signaling. AREG was also found to modulate WNT and Notch signaling in these cells. Thus, AREG functions in regulating the invasive phenotype, and we propose that this regulation may be through altered signaling that occurs when AREG activates plasma membrane localized EGFR.

Detecting gene-gene interactions in prostate disease in African American men

BACKGROUND

The most common male malignancy in the United States is prostate cancer; however its rate of occurrence varies significantly among ethnic groups. In a previous cDNA microarray study on CaP tumors from African American (AA) and Caucasian (CA) patients, we identified 97 candidate genes that exhibited opposite gene expression polarity with respect to race groups; genes up-regulated in AA were simultaneously down-regulated in CA.

PURPOSE

The purpose of this study was to narrow the 97 member gene list, to a smaller number of genes in order to focus studies on a limited number of genes/SNPs that might explain prostate cancer disparity in African Americans.

METHODS

We performed genotype-phenotype, SNP and expression transcript levels correlations using HapMap Yoruba population with 85 of our 97 prostate candidate genes using SCAN database.

RESULTS

Findings revealed an association of SNPs surrounding ABCD3 gene with basal gene expression of RanGAP1 is important in prostate tumors in AA. Hence, to confirm our results in clinical biospecimen, we monitored expression of ABCD3 in a novel panel of African American and Caucasian prostate cancer paired cell lines. The LNCaP, C4-2B showed 2-fold increase; MDA-2PC-2B cell line, derived from AA, showed highest fold-change, 10-fold. The EGFR over expressing DU-145 WT cell line exhibited a 4-fold increase in expression relative to non transfected DU-145 prostate cell lines. Furthermore, Ingenuity Network analysis implicated our AA prostate candidate genes are involved in three network hubs, ERK, MapK and NFkB pathways.

CONCLUSIONS

Taken together, these findings are intriguing because other members of the ABC gene family, namely, ABCC3, ABCD1, and ABCD2 have been shown to confer chemoresistance in certain cancer types. Equally important, is the fact that activation of the MapK/ERK pathway via EGFR stimulation is vital for increased transcription of numerous cancer related genes. It is especially noteworthy that overexpression of EGFR has been widely observed in AA prostate tumors. Collectively our findings lead us to think that a novel signaling cascade, through which increased aggressiveness and chemoresistance is achieved, may explain prostate cancer health disparity in AA males and the nature of aggressive CaP tumors in general.

Differential impact of EGFR-targeted therapies on hypoxia responses: implications for treatment sensitivity in triple-negative metastatic breast cancer

Background

In solid tumors, such as breast cancer, cells are exposed to hypoxia. Cancer cells adapt their metabolism by activating hypoxia-inducible factors (HIFs) that promote the transcription of genes involved in processes such as cell survival, drug resistance and metastasis. HIF-1 is also induced in an oxygen-independent manner through the activation of epidermal growth factor receptor tyrosine kinase (EGFR-TK). Triple-negative breast cancer (TNBC) is a subtype of invasive breast cancer characterized by negative expression of hormonal and HER2 receptors, and this subtype generally overexpresses EGFR. Sensitivity to three EGFR inhibitors (cetuximab, gefitinib and lapatinib, an HER2/EGFR-TK inhibitor) was evaluated in a metastatic TNBC cell model (MDA-MB-231), and the impact of these drugs on the activity and stability of HIF was assessed.

Methodology/Principal Findings

MDA-MB-231 cells were genetically modified to stably express an enhanced green fluorescent protein (EGFP) induced by hypoxia; the Ca9-GFP cell model reports HIF activity, whereas GFP-P564 reports HIF stability. The reporter signal was monitored by flow cytometry. HIF-1 DNA-binding activity, cell migration and viability were also evaluated in response to EGFR inhibitors. Cell fluorescence signals strongly increased under hypoxic conditions (> 30-fold). Cetuximab and lapatinib did not affect the signal induced by hypoxia, whereas gefitinib sharply reduced its intensity in both cell models and also diminished HIF-1 alpha levels and HIF-1 DNA-binding activity in MDA-MB-231 cells. This gefitinib feature was associated with its ability to inhibit MDA-MB-231 cell migration and to induce cell mortality in a dose-dependent manner. Cetuximab and lapatinib had no effect on cell migration or cell viability.

Conclusion

Resistance to cetuximab and lapatinib and sensitivity to gefitinib were associated with their ability to modulate HIF activity and stability. In conclusion, downregulation of HIF-1 through EGFR signaling seems to be required for the induction of a positive response to EGFR-targeted therapies in TNBC.

Hormone refractory carcinoma prostate with peritoneal metastases and malignant ascites without skeletal involvement: A case report and review of literature

Peritoneal carcinomatosis is rare in prostate cancer especially in the absence of skeletal or other visceral metastases. We report a case of hormone refractory adenocarcinoma prostate presenting with only peritoneal metastases and massive malignant ascites. Palliation with docetaxel based cytotoxic chemotherapy resulted in clinical improvement of refractory ascites decreasing respiratory embarrassment and thereby improving the quality of life.

Multifunctional roles of gelsolin in health and diseases

Gelsolin, a Ca(2+) -regulated actin filament severing, capping, and nucleating protein, is an ubiquitous, multifunctional regulator of cell structure and metabolism. More recent data show that gelsolin can act as a transcriptional cofactor in signal transduction and its own expression and function can be influenced by epigenetic changes. Here, we review the functions of the plasma and cytoplasmic forms of gelsolin, and their manifold impacts on cancer, apoptosis, infection and inflammation, cardiac injury, pulmonary diseases, and aging. An improved understanding of the functions and regulatory mechanisms of gelsolin may lead to new considerations of this protein as a potential biomarker and/or therapeutic target.

LHRH-conjugated lytic peptides directly target prostate cancer cells

Prostate cancer is the second leading cause of cancer deaths among men. For patients with hormone-refractory disease, few treatments are available once the tumor has metastasized beyond the prostate. In the present study, two conjugated lytic peptide sequences (named JCHLHRH and JC21LHRH) were designed to target luteinizing hormone-releasing hormone receptors (LHRH-R). Our results indicate that human prostate cancer cell lines were sensitive to both LHRH-conjugated and non-conjugated lytic peptides, with IC(50) concentrations for LNCaP cells, 4.4 and 9.1μM; for DU-145 cells, 4.8 and 5.7μM; and for PC-3 cells, 4.4 and 8.2μM, respectively. JCHLHRH and JC21LHRH were nontoxic to normal primary human prostate epithelial cells or to bone marrow stromal cells in co-culture. There were morphological changes in PC-3 cells after 3h of exposure to either peptide; after 6h, there were significant reductions in cell numbers. Exposure of PC-3 cells for 24h to either JCHLHRH or JC21LHRH blocked their growth over 3 days. Since JCHLHRH and JC21LHRH have specificity for and anti-proliferative activity against tumor cells, and low toxicity for normal prostate cells, these peptides could serve as a new type of therapy for prostate cancer.

Epidermal growth factor receptor signaling in nonsmall cell lung cancer

Epidermal growth factor is a 170-kd protein that binds to a specific tyrosine kinase receptor, epidermal growth factor receptor (EGFR), on the cell surface. EGFR function is dysregulated in various malignancies including nonsmall cell lung cancer (NSCLC) leading to activation of several signal transduction pathways including K-RAS, PIK3, and STAT3 and STAT5, that promote cell cycle progression, proliferation, invasion, angiogenesis, and inhibit apoptosis. EGFR overexpression is seen in a majority of cases of NSCLC, but its prognostic role is controversial. EGFR inhibitors currently undergoing clinical trials in NSCLC include monoclonal antibodies or small molecule tyrosine kinase inhibitors. The only EGFR inhibitor currently approved for the treatment of NSCLC is erlotinib, a small molecule tyrosine kinase inhibitor. Although women, nonsmokers, patients with adenocarcinoma and patients with Asian ethnicity seem to have better outcomes with erlotinib, the factors predictive for response to these agents are currently the focus of investigation.

Novel three-dimensional organotypic liver bioreactor to directly visualize early events in metastatic progression

Metastatic seeding leads to most of the morbidity from carcinomas. However, little is known of this key event as current methods to study the cellular behaviors utilize nonrepresentative in vitro models or follow indirect subsequent developments in vivo. Therefore, we developed a system to visualize over a multiday to multiweek period the interactions between tumor cells and target organ parenchyma. We employ an ex vivo microscale perfusion culture system that provides a tissue-relevant environment to assess metastatic seeding behavior. The bioreactor recreates many features of the fluid flow, scale, and biological functionality of a hepatic parenchyma, a common site of metastatic spread for a wide range of carcinomas. As a test of this model, prostate and breast carcinoma cells were introduced. Tumor cell invasion and expansion could be observed by two-photon microscopy of red fluorescent protein (RFP)- and CellTracker-labeled carcinoma cells against a green fluorescent protein (GFP)-labeled hepatic tissue bed over a 14-day period. Tumors visible to the naked eye could be formed by day 25, without evident necrosis in the >0.3-mm tumor mass. These tumor cells failed to grow in the absence of the supporting three-dimensional (3D) hepatic microtissue, suggesting paracrine or stromal support function for the liver structure in tumor progression. Initial ultrastructural studies suggest that early during the tumor-parenchyma interactions, there are extensive interactions between and accommodations of the cancer and host cells, suggesting that the tumor-related epithelial-mesenchymal transition (EMT) reverts, at least transiently, to promote metastatic seeding. In sum, our 3D ex vivo organotypic liver tissue system presents a critical vehicle to examine tumor-host interactions during cancer metastasis and/or invasion. It also circumvents current limitations in assays to assess early events in metastasis, and provides new approaches to study molecular events during tumor progression.

Oncogenic EGFR signaling networks in glioma

The epidermal growth factor receptor (EGFR) is a primary contributor to glioblastoma (GBM) initiation and progression. Here, we examine how EGFR and key downstream signaling networks contribute to the hallmark characteristics of GBM such as rapid cancer cell proliferation and diffused invasion. Additionally, we discuss current therapeutic options for GBM patients and elaborate on the mechanisms through which EGFR promotes chemoresistance. We conclude by offering a perspective on how the potential of integrative systems biology may be harnessed to develop safe and effective treatment strategies for this disease.

Combining chemical genomics screens in yeast to reveal spectrum of effects of chemical inhibition of sphingolipid biosynthesis

BACKGROUND

Single genome-wide screens for the effect of altered gene dosage on drug sensitivity in the model organism Saccharomyces cerevisiae provide only a partial picture of the mechanism of action of a drug.

RESULTS

Using the example of the tumor cell invasion inhibitor dihydromotuporamine C, we show that a more complete picture of drug action can be obtained by combining different chemical genomics approaches--analysis of the sensitivity of rho0 cells lacking mitochondrial DNA, drug-induced haploinsufficiency, suppression of drug sensitivity by gene overexpression and chemical-genetic synthetic lethality screening using strains deleted of nonessential genes. Killing of yeast by this chemical requires a functional mitochondrial electron-transport chain and cytochrome c heme lyase function. However, we find that it does not require genes associated with programmed cell death in yeast. The chemical also inhibits endocytosis and intracellular vesicle trafficking and interferes with vacuolar acidification in yeast and in human cancer cells. These effects can all be ascribed to inhibition of sphingolipid biosynthesis by dihydromotuporamine C.

CONCLUSION

Despite their similar conceptual basis, namely altering drug sensitivity by modifying gene dosage, each of the screening approaches provided a distinct set of information that, when integrated, revealed a more complete picture of the mechanism of action of a drug on cells.

Gene silencing for epidermal growth factor receptor variant III induces cell-specific cytotoxicity

Epidermal growth factor receptor variant III (EGFRvIII) is a constitutively active mutant form of EGFR that is expressed in 40% to 50% of gliomas and several other malignancies. Here, we describe the therapeutic effects of silencing EGFRvIII on glioma cell lines in vitro and in vivo. A small interfering RNA molecule against EGFRvIII was introduced into EGFRvIII-expressing glioma cells (U87Delta) by electroporation resulting in complete inhibition of expression of EGFRvIII as early as 48 h post-treatment. During EGFRvIII silencing, a decrease in the proliferation and invasiveness of U87Delta cells was accompanied by an increase in apoptosis (P < 0.05). Notably, EGFRvIII silencing inhibited the signal transduction machinery downstream of EGFRvIII as evidenced by decreases in the activated levels of Ras and extracellular signal-regulated kinase. A lentivirus capable of expressing anti-EGFRvIII short hairpin RNA was also able to achieve progressive silencing of EGFRvIII in U87Delta cells in addition to inhibiting cell proliferation, invasiveness, and colony formation in a significant manner (P < 0.05). Silencing EGFRvIII in U87Delta cultures with this virus reduced the expression of factors involved in epithelial-mesenchymal transition including N-cadherin, beta-catenin, Snail, Slug, and paxillin but not E-cadherin. The anti-EGFRvIII lentivirus also affected the cell cycle progression of U87Delta cells with a decrease in G(1) and increase in S and G(2) fractions. In an in vivo model, tumor growth was completely inhibited in severe combined immunodeficient mice (n = 10) injected s.c. with U87Delta cells treated with the anti-EGFRvIII lentivirus (P = 0.005). We conclude that gene specific silencing of EGFRvIII is a promising strategy for treating cancers that contain this mutated receptor.

ErbB receptors and cell polarity: new pathways and paradigms for understanding cell migration and invasion

The ErbB family of receptor tyrosine kinases is involved in initiation and progression of a number of human cancers, and receptor activation or overexpression correlates with poor patient survival. Research over the past two decades has elucidated the molecular mechanisms underlying ErbB-induced tumorigenesis, which has resulted in the development of effective targeted therapies. ErbB-induced signal transduction cascades regulate a wide variety of cell processes, including cell proliferation, apoptosis, cell polarity, migration and invasion. Within tumors, disruption of these core processes, through cooperative oncogenic lesions, results in aggressive, metastatic disease. This review will focus on the ErbB signaling networks that regulate migration and invasion and identify a potential role for cell polarity pathways during cancer progression.

Epidermal growth factor upregulates motility of Mat-LyLu rat prostate cancer cells partially via voltage-gated Na+ channel activity

The main aim of this investigation was to determine whether a functional relationship existed between epidermal growth factor (EGF) and voltage-gated sodium channel (VGSC) upregulation, both associated with strongly metastatic prostate cancer cells. Incubation with EGF for 24 h more than doubled VGSC current density. Similar treatment with EGF significantly and dose-dependently enhanced the cells' migration through Transwell filters. Both the patch clamp recordings and the migration assay suggested that endogenous EGF played a similar role. Importantly, co-application of EGF and tetrodotoxin, a highly selective VGSC blocker, abolished 65% of the potentiating effect of EGF. It is suggested that a significant portion of the EGF-induced enhancement of migration occurred via VGSC activity.

T cells are crucial for the anti-metastatic effect of anti-epidermal growth factor receptor antibodies

Experimental evidences supporting the epidermal growth factor receptor (EGFR) as an important molecule for tumor metastasis had been accumulated. Currently, anti-EGFR monoclonal antibodies (mAbs) constitute a promising approach for the treatment of patients with metastatic tumors. However, the mechanisms associated with the potent anti-metastatic effect of these mAbs have not been completely elucidated due to the lack of appropriate syngeneic preclinical models. In this paper, we have investigated the effects of 7A7, an antibody specific to murine EGFR, on the metastatic properties of D122 murine lung carcinoma. 7A7 mAb significantly impaired metastatic spread of D122 cells in C57BL/6 mice by direct anti-proliferative and pro-apoptotic effects on tumor metastasis. 7A7 mAb capacity to inhibit EGFR activation on D122 cells could contribute to its anti-metastatic effect. In addition, 7A7 mAb was able to induce in vitro antibody-dependent cell-mediated cytotoxicity on D122 cells. Interestingly, 7A7 mAb treatment increased the number of natural killer cells, T lymphocytes and dendritic cells infiltrating the metastatic sites. More strikingly, depletion of CD8(+) and CD4(+) T cells in vivo completely abrogated the 7A7 mAb anti-metastatic activity whereas function of natural killer cells was irrelevant. This study supports an in vivo role for T cell response in the mechanism of action of anti-EGFR mAbs, suggesting the induction of an adjuvant effect.

A novel mechanism of resistance to epidermal growth factor receptor antagonism in vivo

Epidermal growth factor receptor (EGFR) is widely expressed in a number of solid tumors including colorectal cancers. Overexpression of this receptor is one means by which a cell can achieve positive signals for survival and proliferation; another effective means is by constitutive activation of EGFR. We have elucidated the role of constitutive EGFR signaling in malignant progression by stably transfecting colon cancer cells with a human transforming growth factor-alpha cDNA (a ligand for EGFR) under repressible control by tetracycline. We show that constitutive expression of transforming growth factor-alpha and its subsequent constitutive activation of EGFR allows for cancer cell survival in response to environmental stress in vitro and in vivo as well. The reversal of constitutive EGFR activation results in the loss of downstream mitogen-activated protein kinase and Akt activation, and a reduction in xenograft size that is associated with decreased proliferation and increased apoptosis. We used CI-1033, a small molecule antagonist of EGFR, to dissect an activation pathway that shows the ability of ERBb2 to activate Akt, but not Erk in the face of EGFR antagonism. This novel escape mechanism is a possible explanation of why anti-EGFR therapies have shown disappointing results in clinical trials.

Phospholipase Cgamma1 stimulates transcriptional activation of the matrix metalloproteinase-3 gene via the protein kinase C/Raf/ERK cascade

The phospholipid hydrolase phospholipase Cgamma1 (PLCgamma1) plays a major role in regulation of cell proliferation, development, and cell motility. Overexpression of PLCgamma1 is associated with tumor development, and it is overexpressed in some tumors. Matrix metalloproteinase-3 (MMP-3) is a protein involved in tumor invasion and metastasis. Here, we demonstrate that overexpression of PLCgamma1 stimulates MMP-3 expression at the transcriptional level via the PKC-mediated Raf/MEK1/ERK signaling cascade. We propose that modulation of PLCgamma1 activity might be of value in controlling the activity of MMPs, which are important regulators of invasion and metastasis in malignant tumors.

Migration of tumor cells in 3D matrices is governed by matrix stiffness along with cell-matrix adhesion and proteolysis

Cell migration on 2D surfaces is governed by a balance between counteracting tractile and adhesion forces. Although biochemical factors such as adhesion receptor and ligand concentration and binding, signaling through cell adhesion complexes, and cytoskeletal structure assembly/disassembly have been studied in detail in a 2D context, the critical biochemical and biophysical parameters that affect cell migration in 3D matrices have not been quantitatively investigated. We demonstrate that, in addition to adhesion and tractile forces, matrix stiffness is a key factor that influences cell movement in 3D. Cell migration assays in which Matrigel density, fibronectin concentration, and beta1 integrin binding are systematically varied show that at a specific Matrigel density the migration speed of DU-145 human prostate carcinoma cells is a balance between tractile and adhesion forces. However, when biochemical parameters such as matrix ligand and cell integrin receptor levels are held constant, maximal cell movement shifts to matrices exhibiting lesser stiffness. This behavior contradicts current 2D models but is predicted by a recent force-based computational model of cell movement in a 3D matrix. As expected, this 3D motility through an extracellular environment of pore size much smaller than cellular dimensions does depend on proteolytic activity as broad-spectrum matrix metalloproteinase (MMP) inhibitors limit the migration of DU-145 cells and also HT-1080 fibrosarcoma cells. Our experimental findings here represent, to our knowledge, discovery of a previously undescribed set of balances of cell and matrix properties that govern the ability of tumor cells to migration in 3D environments.

Protein kinase Cdelta signaling downstream of the EGF receptor mediates migration and invasiveness of prostate cancer cells

Tumor progression to the invasive phenotype occurs secondary to upregulated signaling from growth factor receptors that drive key cellular responses like proliferation, migration, and invasion. We hypothesized that Protein kinase Cdelta (PKCdelta)-mediated transcellular contractility is required for migration and invasion of prostate tumor cells. Two invasive human prostate cancer cell lines, DU145 cells overexpressing wildtype human EGFR (DU145WT) and PC3 cells, were studied. PKCdelta is overexpressed in these cells relative to normal prostate epithelial cells, and is activated downstream of EGFR leading to cell motility via modulation of myosin light chain activity. Abrogation of PKCdelta using Rottlerin and specific siRNA significantly decreased migration and invasion of both cell lines in vitro. Both PKCdelta and phosphorylated PKCdelta protein levels were higher in human prostate cancer tissue relative to normal donor prostate as assessed by Western blotting and immunohistochemistry. Thus, we conclude that PKCdelta inhibition can limit migration and invasion of prostate cancer cells.

Epidermal growth factor receptor overexpression results in increased tumor cell motility in vivo coordinately with enhanced intravasation and metastasis

Although overexpression of the epidermal growth factor receptor (EGFR; ErbB1) has been correlated with poor prognosis in breast and other cancers, clinical trials of ErbB1 inhibitors have shown limited efficacy in inhibiting tumor proliferation. To evaluate other possible roles of ErbB1 in tumor malignancy besides proliferation, we have developed a series of tools for analysis of intravasation. Overexpression of ErbB1 in MTLn3 mammary adenocarcinoma cells results in increased intravasation and lung metastasis from tumors formed by injection of cells in the mammary fat pad. However, increased ErbB1 expression has no effect on primary tumor growth and lung seeding efficiency of cells injected i.v. Chemotactic responses to low concentrations of EGF in vitro and cell motility in vivo in the primary tumor measured using intravital imaging are significantly increased by ErbB1 overexpression. The increased cell motility is restricted to ErbB1-overexpressing cells in tumors containing mixtures of cells expressing different ErbB1 levels, arguing for a cell-autonomous effect of increased ErbB1 expression rather than alteration of the tumor microenvironment. In summary, we propose that ErbB1 overexpression makes more significant contributions to intravasation than growth in some tumors and present a novel model for studying ErbB1 contributions to tumor metastasis via chemotaxis and intravasation.

Directional persistence of EGF-induced cell migration is associated with stabilization of lamellipodial protrusions

Migrating cells can sustain a relatively constant direction of lamellipodial protrusion and locomotion over timescales ranging from minutes to hours. However, individual waves of lamellipodial extension occur over much shorter characteristic times. Little understanding exists regarding how cells might integrate biophysical processes across these disparate timescales to control the directional persistence of locomotion. We address this issue by examining the effects of epidermal growth factor (EGF) stimulation on long-timescale directional persistence and short-timescale lamellipodial dynamics of EGF receptor-transfected Chinese hamster ovary cells migrating on fibronectin-coated substrata. Addition of EGF increased persistence, with the magnitude of increase correlating with fibronectin coating concentration. Kymographic analysis of EGF-stimulated lamellipodial dynamics revealed that the temporal stability of lamellipodial protrusions similarly increased with fibronectin concentration. A soluble RGD peptide competitor reduced both the persistence of long-timescale cell paths and the stability of short-timescale membrane protrusions, indicating that cell-substratum adhesion concomitantly influences lamellipodial dynamics and directional persistence. These results reveal the importance of adhesion strength in regulating the directional motility of cells and suggest that the short-timescale kinetics of adhesion complex formation may play a key role in modulating directional persistence over much longer timescales.

Luteinising hormone-releasing hormone analogue reverses the cell adhesion profile of EGFR overexpressing DU-145 human prostate carcinoma subline

Cetrorelix, a luteinising hormone-releasing hormone (LHRH) analogue, has been shown to limit growth of the human androgen-independent prostate cell line DU-145, although other inhibitory actions may also be affected. Both growth and invasion of DU-145 cells are linked to autocrine epidermal growth factor receptor (EGFR) signalling. Invasiveness requires not only cells to migrate to conduits, but also reduced adhesiveness between tumour cells to enable separation from the tumour mass. Thus, we investigated whether Cetrorelix alters the DU-145 cell-cell adhesion and if this occurs via altered EGFR signalling. Pharmacologic levels of Cetrorelix limited the invasiveness of a highly invasive DU-145 subline overexpressing full-length EGFR (DU-145 WT). Extended exposure of the cells to Cetrorelix resulted in increased levels of the cell-cell adhesion complex molecules E-cadherin, alpha- and beta-catenin, and p120. Puromycin blocked the increases in E-cadherin and beta-catenin levels, suggesting that de novo protein synthesis is required. The Cetrorelix effect appears to occur via transmodulation of EGFR by a protein kinase C (PKC)-dependent mechanism, as there were no changes in DU-145 cells expressing EGFR engineered to negate the PKC transattenuation site (DU-145 A654); downregulation of EGFR signalling produced a similar upregulation in adhesion complex proteins, further suggesting a role for autocrine signalling. Cetrorelix increased the cell-cell adhesiveness of DU-145 WT cells to an extent similar to that seen when autocrine EGFR signalling is blocked; as expected, DU-145 A654 cell-cell adhesion also was unaffected by Cetrorelix. The increased adhesiveness is expected as the adhesion complex molecules moved to the cells' periphery. These data offer direct insight into the possible crosstalk pathways between the LHRH and EGFR receptor signalling. The ability of Cetrorelix to downregulate EGFR signalling and subsequently reverse the antiadhesiveness found in metastatic prostate cancer highlights a novel potential target for therapeutic strategies.

Sustained antiproliferative mechanisms by RB24, a targeted precursor of multiple inhibitors of epidermal growth factor receptor and a DNA alkylating agent in the A431 epidermal carcinoma of the vulva cell line

Recently, with the purpose of enhancing the potency of epidermal growth factor receptor (EGFR)-based therapies, we designed a novel strategy termed ‘Cascade-release targeting’ that seeks to develop molecules capable of degrading to multiple tyrosine kinase (TK) inhibitors and highly reactive electrophiles, in a stepwise fashion. Here we report on the first prototype of this model, RB24, a masked methyltriazene, that in addition to being an inhibitor on its own was designed to degrade to RB14, ZR08, RB10+a DNA alkylating methyldiazonium species. The cascade degradation of RB24 requires the generation of two reactive electrophiles: (a) an iminium ion and (b) a methyldiazonium ion. Thus, we surmise that these species could alkylate the active site of EGFR, thereby irreversibly blocking its action and that DNA damage could be induced by the methyldiazonium. Using the EGFR-overexpressing human epidermoid carcinoma of the vulva cell line, A431, we demonstrate herein that (a) RB24 and its derived species (e.g. RB14, ZR08) irreversibly inhibit EGFR autophosphorylation, (b) RB24 induced significant levels of DNA strand breaks, (c) sustained inhibition of EGFR by RB24 was associated with blockade of MAPK activation and c-fos gene expression, (d) RB24 induced irreversible cell growth inhibition with a 100-fold greater potency than Temodal™, a clinical methyltriazene. The pronounced growth inhibitory potency of RB24 was attributed to its ability to simultaneously damage DNA and irreversibly block EGFR TK activity.

DU145 human prostate carcinoma invasiveness is modulated by urokinase receptor (uPAR) downstream of epidermal growth factor receptor (EGFR) signaling

Tumor cell motility and invasion have been linked to upregulated signaling from both the epidermal growth factor receptor (EGFR) and that for urokinase-type plasminogen activator (uPAR). However, we do not know whether these events are interdependent or unrelated, despite the obvious diagnostic and therapeutic implications. Gene microarray analyses have suggested that EGFR signaling via phospholipase C-gamma (PLCgamma) induces uPAR transcription. We utilized two sublines of the DU145 human prostate carcinoma cell line that are genetically engineered to differentially activate the EGFR/PLCgamma cascade and are variously invasive in vitro and in vivo. uPAR protein levels in these cells were found to be dependent on PLC signaling, pharmacologic inhibition of PLC signaling reduced uPAR expression. To determine whether uPAR was a required element in EGFR-mediated invasion, we stably expressed uPAR cDNA in either sense or antisense orientation in the two DU145 sublines. Interestingly, uPA production was modulated in parallel, although to a lesser degree, with uPAR in these sublines. Antisense to uPAR significantly restricted invasion of the highly invasive DU145 WT cells through Matrigel and reduced aggressiveness of tumors in nude mice. Up-regulation of uPAR significantly increased the invasiveness of the moderately invasive DU145 parental (DU145 P) cells through Matrigel, but this increased invasiveness was not seen in mice. uPA activity appears to contribute to invasiveness at least through Matrigel, as antibody to uPA or amiloride limited the transmigration. These results support a model of tumor invasion promoted by autocrine EGFR signaling involving reinforcing altered gene expression, of uPAR at least, that further induces cell motility. Herein, a number of key molecules whose expression levels are interrelated, including both EGFR and uPAR, are required but none are sufficient in the absence of other keys molecules in promoting tumor progression.