Editorial Open Access
Copyright ©2010 Baishideng Publishing Group Co., Limited. All rights reserved.
World J Biol Chem. Jul 26, 2010; 1(7): 209-220
Published online Jul 26, 2010. doi: 10.4331/wjbc.v1.i7.209
Targeted therapies in epithelial ovarian cancer: Molecular mechanisms of action
Hiroaki Itamochi, Department of Obstetrics and Gynecology, Tottori University School of Medicine, 36-1 Nishicho, Yonago 683-8504, Japan
Author contributions: Itamochi H contributed to this paper.
Correspondence to: Hiroaki Itamochi, MD, PhD, Junior Associate Professor, Department of Obstetrics and Gynecology, Tottori University School of Medicine, 36-1 Nishicho, Yonago 683-8504, Japan. itamochi@med.tottori-u.ac.jp
Telephone: +81-859-386647 Fax: +81-859-386649
Received: June 1, 2010
Revised: July 8, 2010
Accepted: July 15, 2010
Published online: July 26, 2010

Abstract

Ovarian cancer is the leading cause of death in women with gynecological cancer. Most patients are diagnosed at an advanced stage and have a poor prognosis. Currently, surgical tumor debulking, followed by platinum- and taxane-based chemotherapy is the standard treatment for advanced ovarian cancer. However, these patients are at great risk of recurrence and emerging drug resistance. Therefore, novel treatment strategies are required to improve outcomes for women with advanced ovarian cancer. A variety of molecular targeted agents, the majority of which are monoclonal antibodies and small-molecule protein-kinase inhibitors, have been explored in the management of ovarian cancer. The targets of these agents include angiogenesis, the human epidermal growth factor receptor family, ubiquitin-proteasome pathway, epigenetic modulators, poly(ADP-ribose) polymerase (PARP), and mammalian target of rapamycin (mTOR) signaling pathway, which are aberrant in tumor tissue. The antiangiogenic agent, bevacizumab, has been reported as the most effective targeted agent and should be included in the standard chemotherapeutic regimen for advanced ovarian cancer. PARP inhibitors, which are mainly used in breast and ovarian cancer susceptibility gene-mutated patients, and mTOR inhibitors are also attractive treatment strategies, either alone or combination with chemotherapy, for ovarian cancer. Understanding the tumor molecular biology and identification of predictive biomarkers are essential steps for selection of the best treatment strategies. This article reviews the molecular mechanisms of the most promising targeted agents that are under early phase clinical evaluation for ovarian cancer.

Key Words: Targeted therapy; Epithelial ovarian cancer; Molecular target; Monoclonal antibody; Small-molecule inhibitor



INTRODUCTION

Ovarian cancer is the leading cause of death in women with gynecological cancer. The incidence of ovarian cancer was projected in 2007 to be 230 555 new cases and 141 452 deaths worldwide, which represents 4.3% of all cancer deaths in women[1]. The 5-year survival rate of ovarian cancer ranges from 19% to 90%, depending on the spread of disease at diagnosis. More than 70% of patients with ovarian cancer are diagnosed at the advanced stage, which is associated with high morbidity and mortality[2]. However, new therapeutic agents introduced recently have improved overall survival from ovarian cancer (Figure 1)[2].

Figure 1
Figure 1 Overall 5-year survival by year. Therapy by alkylating agents (e.g. melphalan) was the standard of care for epithelial ovarian cancer until the 1970s. The US Food and Drug Administration approved the therapeutic agent cisplatin in 1978 and paclitaxel at the end of 1992, as indicated in the figure. Overall 5-year survival of epithelial ovarian cancer was increased after introduction of these agents.

Until 1996, standard treatment for advanced ovarian cancer included surgical tumor debulking, followed by adjuvant chemotherapy that consisted of a platinum compound and an alkylating agent[3]. Two pivotal trials, the Gynecologic Oncology Group (GOG) 111 and a European-Canadian study, known as OV-10, have shown that incorporating paclitaxel into first-line therapy improves the survival rate of patients with International Federation of Gynecology and Obstetrics (FIGO) stage III or IV ovarian cancer[4,5]. A subsequent international study, the GOG 182 International Collaborative Ovarian Neoplasm 5 (ICON5) study, sought to improve the efficacy of standard platinum-taxane therapy by incorporating newer cytotoxic agents in sequential doublet and triplet combinations[6]. Unfortunately, no combination of several agents used in standard therapy has improved overall survival; thus, carboplatin with paclitaxel remains the standard regimen as first-line treatment for ovarian cancer and the response rate exceeds 80%. However, approximately 70% of patients with FIGO stage III or IV ovarian cancer recur within 5 years and drug resistance emerges[2,7]. These patients with platinum- and taxane-resistant disease are usually treated with other agents, such as liposomal doxorubicin, gemcitabine, topotecan, or etoposide. The overall response rates with these other drugs, however, are only 10%-25% with relatively short durations of response[8]. Therefore, novel treatment strategies are required to improve outcomes for women with advanced ovarian cancer.

Recently, various molecular targeted agents have been developed and used in the management of a variety of malignancies, including ovarian cancer[9]. Unlike most traditional cytotoxic anticancer drugs, these drugs target tumor cells, tumor stroma, tumor vasculature, and cellular signaling mechanisms that are aberrant in tumor tissue. Tumor cells are effectively selected and growth retardation and apoptosis are induced with minimizing toxicity to normal cells. Thus, targeted therapy agents, the majority of which are monoclonal antibodies and small-molecule protein-kinase inhibitors, are expected to be attractive treatment options for malignancies. This article reviews the molecular mechanisms of various targeted therapies and drugs that are under early-phase clinical evaluation in ovarian cancer.

TARGETING ANGIOGENESIS

Angiogenesis, the formation of new blood vessels (neovascularization) from existing vasculature, is one of the crucial processes for tumor growth, invasion, and metastasis[10]. This process is regulated by a number of growth factor receptor pathways[11]. One of the major pathways involved in tumor angiogenesis is the vascular endothelium growth factor (VEGF) family and its receptors (VEGFR). The mammalian VEGF family consists of seven structurally related glycoproteins including VEGF-A (usually referred to as VEGF), VEGF-B, VEGF-C, VEGF-D, VEGF-E, and placental growth factors 1 and 2[12]. The major mediator of tumor angiogenesis in the VEGF family is VEGF-A, which is expressed as various mature isoforms of 121, 145, 165, 183, 189, and 206 amino acids through alternative splicing of the VEGF-A gene. VEGF-A165 is the predominant isoform and is commonly overexpressed in a variety of human tumors. The expression of VEGF is often upregulated in tumors by numerous environmental factors, such as hypoxia-inducible transcription factors 1α and 2α, low pH, inflammatory cytokines (e.g. interleukin-6), growth factors [e.g. basic fibroblast growth factor and platelet-derived growth factors (PDGFs)], sex hormones (androgens and estrogens), and chemokines (e.g. stromal-cell-derived factor 1)[13]. Activation of oncogenes [e.g. ras, src, epidermal growth factor receptor (EGFR), and human epidermal growth factor receptor 2 (HER2)] and loss or mutational inactivation of tumor-suppressor genes (e.g. p53, VHL, and PTEN) have also been reported as genetic factors for VEGF induction (Figure 2).

Figure 2
Figure 2 Vascular endothelium growth factor family members and their specific binding ligands. The mammalian vascular endothelium growth factor (VEGF) family consists of seven structurally related glycoproteins with VEGF-A as the major mediator of tumor angiogenesis among them. The VEGF ligands bind to three structurally similar receptors, and each tyrosine kinase activates the intracellular signaling cascade, including mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3,4,5-kinase (PI3K)/Akt pathways. Subsequently, the pro-angiogenic signaling pathways are activated. PLCγ: Phospholipase C γ; NP: Neuropilin; VEGFR: VEGF receptors; FLT: Fms-related tyrosine kinase; KDR: Kinase insert domain receptor.

These VEGF ligands bind to three structurally similar receptors: VEGFR1 [also known as fms-related tyrosine kinase 1 (FLT1)]; VEGRF2 (also known as kinase insert domain receptor); and VEGFR3 (also known as FLT4). VEGF-A binds both VEGFR1 and VEGFR2, which are found mainly on vascular endothelial cells, although VEFGR2 has a predominant role[14]. VEGF3 has been reported to be important for lymphangiogenesis. Neuropilin (NP)1 and NP2 (also known as NRP1 and NRP2) act as co-receptors for the VEGFRs, increasing the binding affinity of VEGFs to their receptors. After ligand binding to VEGFRs, each tyrosine kinase activates the intracellular signaling cascade, including mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3,4,5-kinase (PI3K)/Akt pathways[13]. Subsequently, pro-angiogenic effects, such as stimulation of endothelial progenitor cell mobilization from the bone marrow, promotion of endothelial cell proliferation, migration, survival, and differentiation are activated. VEGF also increases vascular permeability and vasodilation[13].

Overexpression of VEGF is often observed in many solid tumors and has been associated with increased risk of metastatic disease and poor prognosis in a variety of malignancies including ovarian cancer[15-17]. Furthermore, coexpression of VEGF and VEGFR2 has recently been discovered in both ovarian cancer cells and ovarian tumor tissues, which might indicate excision of the autocrine VEGFA/VEFGR2 loop in ovarian cancer[18-20]. Therefore, the VEGF signaling pathways are thought to be promising targets to treat ovarian cancer patients.

VEGF inhibitors

Bevacizumab (Avastin): Bevacizumab is a recombinant humanized monoclonal IgG1 antibody that targets VEGF-A, and shows clinical benefit in patients with metastatic colorectal cancer, non-small cell lung cancer, and breast cancer[21]. This antibody binds and neutralizes all biologically active forms of VEGF-A (e.g. VEGF-A165) and then suppresses tumor growth and inhibits metastatic disease progression[22,23]. In addition, anti-VEGF drugs are thought to enhance the effects of chemotherapy[24]. Tumor vasculature is structurally and functionally abnormal. It has been proposed that bevacizumab improves the structure and function of tumor vessels (normalization). These morphological changes lead to functional change (e.g. decreased interstitial fluid pressure, increased tumor oxygenation, and improved penetration of drugs in these tumors), thus making tumors more sensitive to chemotherapy.

Two phase II studies of bevacizumab monotherapy (15 mg/kg intravenously every 21 d) for patients with ovarian cancer or peritoneal cancer have recently been conducted[25,26]. In the GOG 170D study, 62 patients, including 26 platinum-resistant patients, were eligible and assessable, and 13 of these (21.0%) experienced clinical response with two complete responses[25]. The major grade 3/4 adverse events were hypertension (9.7%), gastrointestinal (GI) events (6.5%) without GI perforation, venous thrombosis (1.6%), and proteinuria (1.6%). In the other phase II trial on 44 platinum-resistant patients, partial response (PR) was observed in seven patients (15.9%). Serious adverse events occurred in 18 patients (40.9%) and included GI perforation (11.4%), arterial thromboembolic events (6.8%), and death (6.8%). Grade 3/4 adverse events included hypertension (9.1%), proteinuria (15.9%), bleeding (2.3%) and wound-healing complications (2.3%).

Several phase II trials have been conducted to assess the efficacy and safety of bevacizumab in combination with other targeted therapy or chemotherapy[27-29]. In a phase II study, 13 patients with recurrent ovarian, primary peritoneal and fallopian tube cancer were given bevacizumab (15 mg/kg every 21 d), together with erlotinib (150 mg/d), an EGFR tyrosine kinase inhibitor[29]. There were two major objective responses for a response rate of 15.4%. However, this study was stopped because two patients had fatal GI perforations. Two phase II trials of bevacizumab (10 mg/kg every 2 wk) in combination with oral cyclophosphamide (50 mg/d) for patients with recurrent ovarian cancer have been reported[27,28]. These two studies demonstrated objective response rates of 24% (17 patients) and 53% (eight patients), respectively. Four episodes (5.7%) of GI perforation of fistulae and three treatment-related deaths were observed in one study[28]. Two phase III studies, GOG 218 and ICON7, to examine standard chemotherapy (paclitaxel + carboplatin) and combined effects with bevacizumab are on-going, and the results are expected soon. Another on-going phase III study, the Ovarian Cancer Education Awareness Network trial, is evaluating the efficacy of bevacizumab in combination with carboplatin and gemcitabine in patients with ovarian, primary peritoneal, or fallopian tube cancer.

Cediranib (AZD2171; Recentin): Cediranib is a highly potent, small-molecule, oral tyrosine kinase inhibitor of VEGFR1, 2 and 3, and c-Kit, which competes for the ATP-binding site within the receptor kinase domain[30,31]. Cediranib, therefore, is thought to be effective in prevention of tumor progression, not only by inhibiting VEGFR-2 activity and angiogenesis, but also by concomitantly inhibiting VEGFR-3 activity and lymphangiogenesis.

In a phase II study on patients with recurrent ovarian, fallopian tube, and peritoneal cancer, cediranib was administered orally[32]. The original dose was 45 mg/d, but the dose was lowered to 30 mg because of toxicity observed in the first 11 patients. Forty-six patients were treated and eight showed a PR, which gave an objective response rate of 17.4%. Major grade 3 toxicities included hypertension (46%), fatigue (24%), and diarrhea (13%). Grade 4 toxicities included central nervous system hemorrhage (n = 1), hypertriglyceridemia/hypercholesterolemia/elevated lipase (n = 1), and dehydration/elevated creatinine (n = 1). No GI perforations or fistulas occurred. Thus, cediranib has been shown to be an active drug in recurrent ovarian cancer, with the predictable toxicities observed with other tyrosine kinase inhibitors. A phase III randomized study (ICON6) on patients with ovarian, fallopian tube, and primary peritoneal carcinoma is comparing three treatment arms: (1) chemotherapy alone (carboplatin and paclitaxel); (2) concurrent cediranib; and (3) concurrent and maintenance cediranib.

VEGF Trap (AVE-0005; Aflibercept): VEGF Trap is a fusion protein that combined the Fc region of IgG1 with domain two of VEGFR1 and domain three of VEGFR2 (VEGFRδ1R2) that acts as a decoy receptor, binding with high affinity to the VEGF-A ligand and thus preventing VEGFR1 and VEGFR2 binding and subsequent stimulation[33]. It also has strong binding affinity for PIGF.

Preliminary results from a randomized phase II trial of VEGF Trap in patients with recurrent ovarian cancer have demonstrated a PR in 8% of patients and ascites resolution in 29%[34]. The most frequent grade 3/4 adverse events included hypertension (18%), proteinuria (7%), and headache (4%). GI perorations were observed in two patients (1%). A phase I/II trial of VEGF Trap in combination with docetaxel in patients with recurrent ovarian cancer, primary peritoneal cancer, and fallopian tube cancer is ongoing.

PDGF inhibitors

The families of PDGFs and its receptors (PDGFRs) modulate angiogenesis by regulating endothelial cell survival and pericyte/vascular smooth muscle cell recruitment[35-37]. The PDGF family includes five dimeric isoforms (PDGF-AA, -AB, -BB, -CC, and -DD) that have distinct abilities to bind to and activate the PDGFRs (PDGFRα/β heterodimers, PDGFRα and β homodimers).

Furthermore, PDGF enhances the proliferation of human ovarian surface epithelial cells and ovarian cancer cells[38,39]. Expression of PDGF and PDGFα was found in 73.3% and 35.6% of malignant ovarian tumors, respectively, but not in any benign tumors or normal ovaries[40]. In addition, the expression of PDGFRα was an independent poor prognostic factor in patients with ovarian cancer. Thus, PDGF signaling pathways could be novel targets for ovarian cancer therapy.

Imatinib mesylate (STI571; Gleevec or Glivec): Imatinib, a derivative of 2-phenylaminopyrimidine, has been created using the structure of the ATP-binding site of the Abl protein kinase[41]. Imatinib also inhibits PDGFR and the stem-cell factor receptor c-Kit (CD117) tyrosine kinases and is used to treat chronic myelogenous leukemia, Philadelphia-chromosome-positive acute lymphoid leukemia, and c-Kit-positive GI stromal tumors[42].

Two phase II studies have evaluated imatinib in patients with recurrent ovarian cancer or primary peritoneal carcinoma[43,44]. In the University of Texas M.D. Anderson Cancer Center trial, imatinib was given orally at 600 mg/d[43]. However, no complete or partial responses were documented in the 12 evaluable patients. In the GOG 170E trial, 56 patients were treated with imatinib at 400 mg twice daily, but only one patient responded. Thus, imatinib monotherapy has limited activity in patients with recurrent ovarian cancer.

The combination effect of imatinib and docetaxel was evaluated in patients with platinum-resistant ovarian cancer[45]. However, a response rate was reported in 21.7% (5/23) and there was no clear benefit of this combination over docetaxel alone.

Other antiangiogenic drugs

In a phase II trial, vandetanib (ZD6474; Zactima), a small-molecule, oral tyrosine kinase inhibitor of VEFGR and EGFR, was given as monotherapy in patients with recurrent ovarian cancer[46]. Twelve patients entered the study; however, no significant clinical benefit in this disease setting has been reported.

Other multi-targeted tyrosine kinase inhibitors, with the targets including VEGFRs, such as sunitinib (SU11248; Sutent), sorafenib (BAY43-9006; Nexavar), pazopanib (GW786034; Votrient), motesanib, and BIBF 1200, are also being evaluated in phase II or III settings.

AGENTS TARGETING THE HUMAN EGFR FAMILY

The HER family consists of four distinct transmembrane tyrosine kinase receptors: HER-1 (EGFR/erbB1), HER-2/neu (erbB2), HER-3 (erbB3) and HER-4 (erbB4). These receptors are closely related structurally and share a structure that consists of a ligand-binding extracellular domain (except for HER3), a functional intracellular kinase domain, and a C-terminal signaling tail. Although HER2 has no known ligand, 10 different ligands can selectively bind to each receptor. The receptors form multiple combinations by homodimerization or heterodimerization that leads to receptor autophosphorylation on several tyrosine residues in the intracellular kinase domain through tyrosine kinase activity. Autophosphorylation leads to a series of downstream signaling pathways, such as MAPK and PI3K/Akt pathways, which are involved in cancer-cell proliferation, blocking apoptosis, activating invasion and metastasis, and stimulating tumor-induced neovascularization, thus making it an attractive target for anticancer therapies (Figure 3)[47].

Figure 3
Figure 3 Human epidermal growth factor receptor family members and their specific ligands. The human epidermal growth factor receptor (HER) family consists of four distinct transmembrane tyrosine kinase receptors, and 10 different ligands can selectively bind to each of them. The receptor undergoes homo- or hetero-dimerization that leads to receptor autophosphorylation that activates a series of downstream signaling pathways, such as mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3,4,5-kinase (PI3K)/Akt pathways that control cell growth and apoptotic signaling. AR: Amphiregulin; TGFα: Transforming growth factor α; BTC: β-cellulin; HB-EGF: Heparin-binding epidermal growth factor; EPR: Epiregulin; NRG: Neuregulins; P: Phosphate; EGFR: Epidermal growth factor receptor.

The HER family is commonly expressed in many human malignancies. In ovarian cancer, a wide variety of HER family expression has been reported [EFGR, 4%-100% (average 48%); HER-2, 0%-100% (average 40%); HER-3, 3%-90% (average 48%); and HER-4, 45%-92% (average 71%)][48]. HER overexpression, especially EGFR and HER-2, is thought to be correlated with poor prognosis and decreased therapeutic responsiveness in ovarian cancer patients, although the clinical data are contradictory. Therefore, several EGFR and HER-2 inhibitors, including tyrosine kinases inhibitors (gefitinib and erlotinib) and monoclonal antibodies (cetuximab, trastuzumab, and pertuzumab), are being tested in ovarian cancer patients.

EGFR inhibitors

Gefitinib (ZD1839; Iressa): Gefitinib is an orally active, low-molecular-weight synthetic anilinoquinazoline that selectively inhibits the activation of EGFR tyrosine kinase through competitive binding of the ATP-binding domain of the receptor[49]. Treatment of cancer cells with gefitinib increases expression of the cyclin-dependent kinase inhibitor p27KIP1, which leads to cell cycle arrest at the G0-G1 boundary in a dose- and time-dependent manner[50]. Clinical response to gefitinib is thought to correlate with activated mutations of the EGFR gene in patients with non-small cell lung cancer[51,52]. In addition, gefitinib enhances cytotoxic effects of anticancer agents (cisplatin, carboplatin, oxaliplatin, paclitaxel, docetaxel, doxorubicin, etoposide, topotecan, and raltitrexed) in various human cancer cell lines, including ovarian cancer[53].

In a phase II study (GOG170C), gefitinib was given orally at 500 mg/d to 27 patients with relapsed/persistent ovarian or primary peritoneal carcinoma[54]. PR was observed in only one patient (3.7%). The response rate, however, for patients with EGFR-positive tumors was 9% (1/11). Thus, prescreening patients for activated mutations in EGFR might improve the response rate to gefitinib. The most commonly observed grade 3 toxicities were dermatological (15%, 4/27) and diarrhea (30%, 8/27).

A phase II study on gefitinib in combination with paclitaxel and carboplatin for second-line treatment of patients with ovarian, tubal or peritoneal adenocarcinoma has been conducted[55]. This combination therapy provided a good clinical response with high overall response rates [19.2% (5/26) for resistant/refractory and 61.9% (26/42) for sensitive disease], but was associated with an increased risk of hematological disorders.

Erlotinib (OSI-774; Tarceva): Erlotinib, like gefitinib, is a potent, selective, and reversible inhibitor of EGFR tyrosine kinase and reduces EGFR autophosphorylation[56]. This inhibitor blocks cell cycle progression at the G1 phase by accumulation of retinoblastoma protein in its underphosphorylated form and accumulation of p27KIP1, and also triggers apoptosis.

Thirty-four patients with refractory, recurrent, EGFR-positive ovarian carcinoma received 150 mg of erlotinib orally once daily in a phase II study[57]. Two patients had PRs, which gave an objective response rate of 5.9%. The most frequent adverse events were rash (68%) and diarrhea (38%).

A phase Ib trial has shown the feasibility of a combination of erlotinib with docetaxel and carboplatin in patients with ovarian, fallopian tube, and primary peritoneal cancers[58]. However, further investigations are awaited.

Cetuximab (C225; Erbitux): Cetuximab is a chimeric (mouse/human) monoclonal antibody to EGFR used for treatment of advanced colorectal, head and neck cancers that binds to the extracellular domain of EGFR and blocks the binding of EGF ligand to EGFR and its subsequent activation by inhibiting ligand induced autophosphorylation of the EGFR[59]. Cetuximab downregulates the receptor from the cell surface through internalization of the EGFR and also induces antibody-dependent cellular cytotoxicity (ADCC)[60]. In addition, in vitro and in vivo studies have shown that cetuximab enhances cytotoxic effects of anticancer agents (doxorubicin, cisplatin, docetaxel, gemcitabine, and topotecan) in various human cancer cell lines[61].

In a phase II study, patients with resistant/recurrent ovarian or primary peritoneal carcinoma received cetuximab intravenously at 400 mg/m2 initially and then 250 mg/m2 weekly for two 3-wk cycles[62]. Rash (96%) was the most common drug-related adverse event. One of 25 patients achieved partial remission, with an overall response rate of 4%. Thus cetuximab monotherapy showed minimal activity in patients with recurrent ovarian cancer.

The GOG146P phase II trial assessed the activity of cetuximab in combination with carboplatin in relapsed platinum-sensitive ovarian or primary peritoneal carcinoma and reported that this combination therapy had only modest activity in patients with EGFR-positive carcinoma[62]. Similarly, a phase II study was conducted to determine the efficacy of cetuximab plus paclitaxel and carboplatin as initial treatment of stage III/IV ovarian cancer[63]. However, this combination did not demonstrate prolongation of progression-free survival when compared with historical data.

Trastuzumab (Herceptin): Trastuzumab, a recombinant humanized monoclonal antibody, binds to the juxta-membrane portion of the extracellular domain of the HER2 receptor and blocks activation of its intracellular signal-transduction pathways, such as PI3K/Akt and MAPK[64]. Other proposed mechanisms of action include inhibition of the formation of a truncated membrane-bound fragment (p95), activation of ADCC, prevention of HER2-receptor dimerization, and increased endocytotic destruction of the receptor.

Results from a phase II study (GOG160) of trastuzumab showed that 2+ or 3+ HER2 overexpression was observed in only 95 (11.4%) of 837 patients with recurrent or refractory ovarian or primary peritoneal carcinoma. Forty-one eligible patients with HER2 overexpression were given intravenous trastuzumab at 4 mg/kg initially and then at 2 mg/kg weekly. Although there was only mild toxicity (e.g. anemia, GI events, neuropathy, or fatigue), the overall response rate was low at 7.3%. The clinical value of trastuzumab monotherapy in recurrent ovarian cancer is limited by the low frequency of HER2 overexpression and low rate of objective response among patients with HER2 overexpression.

Pertuzumab (2C4; Omnitarg): Pertuzumab, a recombinant, humanized monoclonal antibody, binds to the HER2 dimerization domain (near the center of domain II), sterically blocking a binding pocket that is necessary for receptor dimerization with its partner receptors, and inhibits the signaling cascades[65]. Pertuzumab binding to HER2 induces activation of ADCC effects but does not block the truncation of HER2 in the same way as trastuzumab binding does[66].

In a phase II study of 123 recurrent ovarian cancer patients, 55 patients in cohort 1 and 62 in cohort 2 were assessable for efficacy[67]. The patients in cohort 1 received a loading dose of 840 mg of pertuzumab intravenously followed by 420 mg every 3 wk; the patients in cohort 2 received 1050 mg every 3 wk, and showed an overall response rate of 4.3%. The main adverse events observed were diarrhea (11%, grade 3) and asymptomatic left ventricular ejection fraction decreases of < 50% (one patient in cohort 1 and four patients in cohort 2).

Combination therapy of pertuzumab with gemcitabine was tested in a randomized phase II trial in 130 patients with platinum-resistant ovarian, fallopian tube, or primary peritoneal cancer[68]. The patients were randomly assigned to gemcitabine (800 mg/m2 on days 1 and 8 of a 21-d cycle) plus either placebo or pertuzumab (840 mg loading dose followed by 420 mg every 3 wk), and showed objective response rates of 13.8% and 4.6%, respectively. In patients whose tumors had low HER3 mRNA expression, an increased treatment benefit was observed in the gemcitabine + pertuzumab arm. Therefore, pertuzumab may be effective in platinum-resistant ovarian cancer and low HER3 mRNA expression may predict pertuzumab clinical benefit.

AGENTS TARGETING THE UBIQUITIN PROTEASOME PATHWAY

The highly conserved ubiquitin-proteasome pathway is involved in lysosome-independent intracellular protein degradation in eukaryotes[69]. Target substrate proteins are tagged for destruction in this pathway by the covalent attachment of a polyubiquitin chain (polyubiquitination). This polyubiquitination is generated by activation of the ubiquitin-conjugating system, which is composed of three classes of enzymes: ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), and ubiquitin ligases (E3s). Polyubiquitinated proteins are then subjected to proteolysis through the proteasome in the cytoplasm and nucleus.

This proteolysis system is an essential regulator of cellular functions, such as signal transduction, transcription, cell cycle, and antigen processing[70,71]. Cancer-associated proteins are also regulated by the ubiquitin-proteasome system including tumor suppressors (e.g. p53 and p27), cell-surface receptors (e.g. EGFR and HER2), and cell cycle and oncogenic transcription regulators (e.g. cyclins and nuclear factor-κB). Therefore, inhibition of this pathway could regulate cancer growth and metastasis.

Proteasome inhibitors

Bortezomib (PS-341; Velcade): Bortezomib, a boronic acid derivative, inhibits very selectively the proteasome activity to bind with the chymotryptic and caspase sites with lower affinity within the 20S proteasome[71]. It is currently used for treating multiple myeloma and mantle cell lymphoma.

In a phase II study, patients with recurrent platinum-sensitive epithelial ovarian cancer (EOC) or primary peritoneal cancer were treated with bortezomib intravenously on days 1, 4, 8 and 11 and every 21 d thereafter, at a dose of 1.5 mg/m2 (cohort 1) and 1.3 mg/m2 (cohort 2)[72]. Objective response rates were 3.8% (1/26) and 6.9% (2/29) in cohort 1 and cohort 2, respectively. Thus, bortezomib monotherapy has minimal activity in the treatment of ovarian cancer.

AGENTS TARGETING EPIGENETIC MODULATORS

Epigenetic modulation of gene expression is important in orchestrating key biological processes that include DNA methylation, histone covalent modifications, and nucleosomal remodeling[73]. Several enzymes, such as DNA methyltransferases (DNMTs), histone deacetylases (HDACs), histone methyltransferases, and complex nucleosomal remodeling factors contribute to these gene regulations. Aberrant epigenetic regulation of gene expression has been reported to contribute to carcinogenesis through silencing of tumor suppressor genes, activation of oncogenes, loss of imprinting, genomic instability, X-chromosome inactivation, and harmful expression of inserted viral sequences. In addition, the degree of epigenetic abnormalities increases during malignant transformation[74]. DNMT and HDAC inhibitors are two of the most studied enzymes in the anticancer therapy.

DNMTs catalyze the transfer of a methyl group derived from S-adenosyl-methionine to the carbon-5 position of the cytosine ring within the structure of cytosine-guanine (CpG) dinucleotides[75]. Methylation of the CpG islands associated with gene promoter regions leads to transcriptional silencing. Hypermethylation of CpG islands is observed commonly in a variety of cancers, including ovarian cancer, and is associated with tumor initiation, progression, and drug resistance[73,76,77]. Several hypermethylated genes have been reported in ovarian cancers, including classical tumor suppressors [breast and ovarian cancer susceptibility gene (BRCA)1, p16, and MLH1], putative tumor suppressors (OPCML, SPARC, ANGPTL2, CTGF, and RASSF1A, imprinted genes (ARH1, PEG3, DLEC1, ARL11, and TCEAL7), proapoptotic genes (LOT1, DAPK, TMS1/ASC, and PAR-4), cell adhesion (ICAM-1, CDH1), cell signaling (HSulf-1), genome stability (PALB2), taxane resistance (TUBB3), and embryonic development (HOXA10 and HOXA11)[78,79].

Histone acetyltransferases (HATs) and HDACs also regulate transcription of DNA[9]. Histone acetylation by HATs loosen DNA binding around histones and enable transcription factors and RNA polymerases to access the DNA. In contrast, HDACs remove acetyl groups from an ε-N-acetyl lysine amino acid on a histone associated with transcriptional gene silencing through direct interaction with DNMTs[73]. Interestingly, HDAC inhibitors have been shown to induce arrest of cellular growth and apoptosis in cancer cells, including ovarian cancer, by restoring gene expression (e.g. tumor suppressor genes)[80-82].

DNMT inhibitors

Cytosine nucleoside (cytidine) analogs of azacytdine (5-azacitidine; Vidaza) and decitabine (5-aza-2’-deoxycytidine; Dacogen) given at much higher doses were developed initially as chemotherapeutic agents. At lower doses, however, these agents replace cytosine during DNA replication. Subsequent incorporation of these agents into DNA binds to and inhibits DNMTs. Azacytidine is also incorporated into RNA during transcription and inhibits translation of proteins[9].

Azacytdine and decitabine are approved to treat myelodysplastic syndrome. Phase I and II clinical trials are ongoing to examine treatment of ovarian cancer[79]. A phase I study has been completed recently of decitabine combined with carboplatin in patients with recurrent platinum-resistant EOC[83].

HDAC inhibitors

Vorinostat [suberoylanilide hydroxamic acid; Zolinza]: Vorinostat is an oral small-molecule HDAC inhibitor approved for treatment of cutaneous T-cell lymphoma. It binds to the catalytic zinc-pocket on class I, II, and IV HDAC and inhibits these activities[84].

Thirty-seven patients with recurrent or persistent ovarian or primary peritoneal carcinoma received a 400 mg daily oral dose of vorinostat in a phase II trial (GOG170H)[85]. One patient showed response PR with an objective response rate of 3.7%. Two grade 4 toxicities (one leukopenia and one neutropenia) were reported, and the most common grade 3 toxicities were constitutional (11%) and GI (11%) symptoms. The most frequent adverse events were rash (68%) and diarrhea (38%). Therefore, vorinostat has minimal activity as a single-agent in unscreened patients with ovarian cancer.

Belinostat (PXD101): Belinostat is a low-molecular-weight, hydroxamic acid inhibitor of class I and II HDAC. It has been investigated for relapsed or refractory peripheral T-cell lymphoma and for cancer of unknown primary.

In a phase II trial, 18 patients with metastatic or recurrent platinum-resistant EOC and 14 patients with micropapillary/borderline (LMP) ovarian tumors were treated intravenously with 1000 mg/m2 of belinostat on days 1-5 and every 21 d thereafter[86]. One patient with an LMP tumor had a PR. The most frequent adverse events were grade 3 thrombosis (9%), hypersensitivity (3%), and elevated alkaline phosphatase (3%). Thus, belinostat is tolerated well and shows some activity in patients with LMP disease.

OTHER PROMISING MOLECULAR TARGETs
Poly(ADP-ribose) polymerase inhibitors

The poly(ADP-ribose) polymerases (PARPs) are a large family of multifunctional enzymes[87]. PARP-1, the most abundant isoform, plays a key role in the repair of DNA single-strand breaks (SSBs) through the base excision repair pathway. The residual PARP activity (approximately 10%) is due to PARP-2. The inhibition of PARP leads to the accumulation of DNA SSBs, which causes DNA double-strand breaks (DSBs) at replication forks. These DSBs are effectively repaired in normal cells mainly by the BRCA1- and BRCA2-dependent homologous recombination (HR) DNA repair pathway. In the absence of either BRCA1 or BRCA2, these lesions are not repaired, which results in cell cycle arrest and cell death, although there is an alternate pathway to non-homologous end-joining for DSB repair (Figure 4).

Figure 4
Figure 4 Effect of DNA repair systems on poly(ADP-ribose) polymerase activity. Double-strand breaks (DSBs) lead to the activation of poly(ADP-ribose) polymerases (PARPs). PARP plays a key role in the repair of SSBs. Treatment with a PARP inhibitor induces DSBs and selectively kills homologous recombination (HR)/breast and ovarian cancer susceptibility gene (BRCA)-deficient cells.

Women with inherited mutations in BRCA1 on chromosome 17q21 or BRCA2 on chromosome 13q31 are at significantly higher risk of developing breast and ovarian cancer than are women in the general population. The lifetime risks of ovarian cancer are 54% for BRCA1 and 23% for BRCA2 mutation carriers[88]. Inherited mutations in those genes are found in 5%-10% of all ovarian cancer patients. However, > 50% of high-grade serous or undifferentiated carcinomas showed loss of BRCA function, either by genetic or epigenetic events, which resulted in HR DNA repair defects[89].

Olaparib (AZD2281), an oral small-molecule PARP inhibitor, was tested in BRCA-mutated patients with ovarian, primary peritoneal, and fallopian tube cancer[90]. In the study, 20 patients (40%) responded to the therapy. Currently, randomized trials of olaparib and other PARP inhibitors in patients with ovarian cancer are underway.

Mammalian target of rapamycin inhibitors

Activation of the PI3K/Akt pathway and its downstream mammalian target of rapamycin (mTOR) signaling appear to represent drug resistance and poor prognosis in many cancers[91,92]. In ovarian cancer, amplified PI3K and activated Akt have been found in 12%-68% of tumors and are closely associated with upregulation of mTOR signaling[92]. mTOR, a cytosolic serine/threonine kinase, consists of two functionally different complexes, mTOR complex 1 (mTORC1) and mTORC2 (Figure 5). mTORC1 regulates protein synthesis by directly phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) and also affects the activity of p70 S6 kinase 1 (S6K1), which leads to cell growth and G1 cell cycle progression[93]. mTORC2 has been shown to be an upstream regulator of Akt, whereas mTORC1 is downstream of Akt, and the activity is upregulated by a compensatory response to mTORC1 downregulation in certain circumstances.

Figure 5
Figure 5 Key regulators of the mammalian target of rapamycin signaling pathway. Mammalian target of rapamycin (mTOR) forms the catalytic core of two functionally distinct complexes, mTOR complex 1 (mTORC1) and mTORC2. Diverse environmental factors, including growth factors (e.g. insulin, insulin-like growth factor 1 and epidermal growth factor) and stresses (e.g. hypoxia or energy) promote mTORC1-dependent cell growth and down-regulate autophagy. The negative feedback loop signals of mTORC1/p70-S6 kinase 1 (S6K1) suppress the mTORC2/Akt signaling pathway. PTEN: Phosphatase and tensin homolog deleted from chromosome 10; TSC: Tuberous sclerosis complex; Raptor: Regulatory-associated protein of mTOR; Rictor: Rapamycin-insensitive companion of mTOR; MEK: Mitogen-activated protein kinase kinase; RSK: Ribosomal s6 kinase; PRAS40: Proline-rich PKB/Akt substrate of 40 kDa; ATG1: Autophagy-related gene 1; PKCα: Protein kinase C α; SGK1: Serine/threonine-protein kinase 1; GSK-3: Glycogen synthase kinase 3; REDD1: Regulated in development and DNA damage responses 1; AMPK: AMP-activated protein kinase; LKB1: Liver kinase B1; MAPK: Mitogen-activated protein kinase; PI3K: Phosphatidylinositol 3,4,5-kinase; P: Phosphate.

Temsirolimus (CCI779; Torisel), a synthetic, ester analog of rapamycin, is indicated for the treatment of advanced renal cell carcinoma. It inhibits downstream signaling of mTOR, such as 4E-BP and S6K1, which leads to G1 phase cell cycle arrest and apoptosis[92]. A phase II clinical trial (GOG170I) of temsirolimus monotherapy in patients with EOC has recently been completed, and a phase I study of temsirolimus in combination with topotecan is underway in patients with gynecological cancers.

CONCLUSION

A wide range of novel targeted agents has been developed based on molecular biology. Among these agents, angiogenesis inhibitors are the most promising therapy for patients with ovarian cancer. Antiangiogenic drugs can be included as maintenance therapy in the standard chemotherapeutic regimens for advanced ovarian cancer. However, the combination effects of antiangiogenic and cytotoxic agents, currently used as first- or second-line regimens, need to be elucidated. PARP inhibitors and mTOR inhibitors are also attractive targeted agents for ovarian cancer therapy.

Ovarian cancer has a heterogeneous biology, in the same way as most other malignant tumors, and there is no predominant aberrant pathway in most cases. Therefore, understanding of the tumor molecular biology and identification of predictive biomarkers are essential steps for selection of the best treatment strategies to improve survival in patients with ovarian cancer. Further investigation into the molecular biology and genetics of ovarian cancer is warranted.

Footnotes

Peer reviewers: Johan Lennartsson, PhD, Ludwig Institute for Cancer Research, Uppsala University, Box 595, SE-751 24 Uppsala, Sweden; Wen-Chun Hung, PhD, Professor, Chair, Institute of Biomedical Sciences, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaohsiung 804, Taiwan, China

S- Editor Cheng JX L- Editor Kerr C E- Editor Zheng XM

References
1.  American Cancer Society. Global Cancer Facts & Figures 2007.  Available from: http://www.cancer.org.  [PubMed]  [DOI]  [Cited in This Article: ]
2.  Heintz AP, Odicino F, Maisonneuve P, Quinn MA, Benedet JL, Creasman WT, Ngan HY, Pecorelli S, Beller U. Carcinoma of the ovary. FIGO 6th Annual Report on the Results of Treatment in Gynecological Cancer. Int J Gynaecol Obstet. 2006;95 Suppl 1:S161-S192.  [PubMed]  [DOI]  [Cited in This Article: ]
3.  Bristow RE, Tomacruz RS, Armstrong DK, Trimble EL, Montz FJ. Survival effect of maximal cytoreductive surgery for advanced ovarian carcinoma during the platinum era: a meta-analysis. J Clin Oncol. 2002;20:1248-1259.  [PubMed]  [DOI]  [Cited in This Article: ]
4.  McGuire WP, Hoskins WJ, Brady MF, Kucera PR, Partridge EE, Look KY, Clarke-Pearson DL, Davidson M. Cyclophosphamide and cisplatin compared with paclitaxel and cisplatin in patients with stage III and stage IV ovarian cancer. N Engl J Med. 1996;334:1-6.  [PubMed]  [DOI]  [Cited in This Article: ]
5.  Piccart MJ, Bertelsen K, James K, Cassidy J, Mangioni C, Simonsen E, Stuart G, Kaye S, Vergote I, Blom R. Randomized intergroup trial of cisplatin-paclitaxel versus cisplatin-cyclophosphamide in women with advanced epithelial ovarian cancer: three-year results. J Natl Cancer Inst. 2000;92:699-708.  [PubMed]  [DOI]  [Cited in This Article: ]
6.  Bookman MA, Brady MF, McGuire WP, Harper PG, Alberts DS, Friedlander M, Colombo N, Fowler JM, Argenta PA, De Geest K. Evaluation of new platinum-based treatment regimens in advanced-stage ovarian cancer: a Phase III Trial of the Gynecologic Cancer Intergroup. J Clin Oncol. 2009;27:1419-1425.  [PubMed]  [DOI]  [Cited in This Article: ]
7.  Markman M, Markman J, Webster K, Zanotti K, Kulp B, Peterson G, Belinson J. Duration of response to second-line, platinum-based chemotherapy for ovarian cancer: implications for patient management and clinical trial design. J Clin Oncol. 2004;22:3120-3125.  [PubMed]  [DOI]  [Cited in This Article: ]
8.  Agarwal R, Kaye SB. Ovarian cancer: strategies for overcoming resistance to chemotherapy. Nat Rev Cancer. 2003;3:502-516.  [PubMed]  [DOI]  [Cited in This Article: ]
9.  Ma WW, Adjei AA. Novel agents on the horizon for cancer therapy. CA Cancer J Clin. 2009;59:111-137.  [PubMed]  [DOI]  [Cited in This Article: ]
10.  Folkman J. Tumor angiogenesis: therapeutic implications. N Engl J Med. 1971;285:1182-1186.  [PubMed]  [DOI]  [Cited in This Article: ]
11.  Hanahan D, Folkman J. Patterns and emerging mechanisms of the angiogenic switch during tumorigenesis. Cell. 1996;86:353-364.  [PubMed]  [DOI]  [Cited in This Article: ]
12.  Hicklin DJ, Ellis LM. Role of the vascular endothelial growth factor pathway in tumor growth and angiogenesis. J Clin Oncol. 2005;23:1011-1027.  [PubMed]  [DOI]  [Cited in This Article: ]
13.  Kerbel RS. Tumor angiogenesis. N Engl J Med. 2008;358:2039-2049.  [PubMed]  [DOI]  [Cited in This Article: ]
14.  Ferrara N, Davis-Smyth T. The biology of vascular endothelial growth factor. Endocr Rev. 1997;18:4-25.  [PubMed]  [DOI]  [Cited in This Article: ]
15.  Ishigami SI, Arii S, Furutani M, Niwano M, Harada T, Mizumoto M, Mori A, Onodera H, Imamura M. Predictive value of vascular endothelial growth factor (VEGF) in metastasis and prognosis of human colorectal cancer. Br J Cancer. 1998;78:1379-1384.  [PubMed]  [DOI]  [Cited in This Article: ]
16.  Ohta Y, Tomita Y, Oda M, Watanabe S, Murakami S, Watanabe Y. Tumor angiogenesis and recurrence in stage I non-small cell lung cancer. Ann Thorac Surg. 1999;68:1034-1038.  [PubMed]  [DOI]  [Cited in This Article: ]
17.  Shimogai R, Kigawa J, Itamochi H, Iba T, Kanamori Y, Oishi T, Shimada M, Sato S, Kawaguchi W, Sato S. Expression of hypoxia-inducible factor 1alpha gene affects the outcome in patients with ovarian cancer. Int J Gynecol Cancer. 2008;18:499-505.  [PubMed]  [DOI]  [Cited in This Article: ]
18.  Boocock CA, Charnock-Jones DS, Sharkey AM, McLaren J, Barker PJ, Wright KA, Twentyman PR, Smith SK. Expression of vascular endothelial growth factor and its receptors flt and KDR in ovarian carcinoma. J Natl Cancer Inst. 1995;87:506-516.  [PubMed]  [DOI]  [Cited in This Article: ]
19.  Sher I, Adham SA, Petrik J, Coomber BL. Autocrine VEGF-A/KDR loop protects epithelial ovarian carcinoma cells from anoikis. Int J Cancer. 2009;124:553-561.  [PubMed]  [DOI]  [Cited in This Article: ]
20.  Spannuth WA, Nick AM, Jennings NB, Armaiz-Pena GN, Mangala LS, Danes CG, Lin YG, Merritt WM, Thaker PH, Kamat AA. Functional significance of VEGFR-2 on ovarian cancer cells. Int J Cancer. 2009;124:1045-1053.  [PubMed]  [DOI]  [Cited in This Article: ]
21.  Ellis LM, Hicklin DJ. VEGF-targeted therapy: mechanisms of anti-tumour activity. Nat Rev Cancer. 2008;8:579-591.  [PubMed]  [DOI]  [Cited in This Article: ]
22.  Kim KJ, Li B, Houck K, Winer J, Ferrara N. The vascular endothelial growth factor proteins: identification of biologically relevant regions by neutralizing monoclonal antibodies. Growth Factors. 1992;7:53-64.  [PubMed]  [DOI]  [Cited in This Article: ]
23.  Kim KJ, Li B, Winer J, Armanini M, Gillett N, Phillips HS, Ferrara N. Inhibition of vascular endothelial growth factor-induced angiogenesis suppresses tumour growth in vivo. Nature. 1993;362:841-844.  [PubMed]  [DOI]  [Cited in This Article: ]
24.  Jain RK. Normalization of tumor vasculature: an emerging concept in antiangiogenic therapy. Science. 2005;307:58-62.  [PubMed]  [DOI]  [Cited in This Article: ]
25.  Burger RA, Sill MW, Monk BJ, Greer BE, Sorosky JI. Phase II trial of bevacizumab in persistent or recurrent epithelial ovarian cancer or primary peritoneal cancer: a Gynecologic Oncology Group Study. J Clin Oncol. 2007;25:5165-5171.  [PubMed]  [DOI]  [Cited in This Article: ]
26.  Cannistra SA, Matulonis UA, Penson RT, Hambleton J, Dupont J, Mackey H, Douglas J, Burger RA, Armstrong D, Wenham R. Phase II study of bevacizumab in patients with platinum-resistant ovarian cancer or peritoneal serous cancer. J Clin Oncol. 2007;25:5180-5186.  [PubMed]  [DOI]  [Cited in This Article: ]
27.  Chura JC, Van Iseghem K, Downs LS Jr, Carson LF, Judson PL. Bevacizumab plus cyclophosphamide in heavily pretreated patients with recurrent ovarian cancer. Gynecol Oncol. 2007;107:326-330.  [PubMed]  [DOI]  [Cited in This Article: ]
28.  Garcia AA, Hirte H, Fleming G, Yang D, Tsao-Wei DD, Roman L, Groshen S, Swenson S, Markland F, Gandara D. Phase II clinical trial of bevacizumab and low-dose metronomic oral cyclophosphamide in recurrent ovarian cancer: a trial of the California, Chicago, and Princess Margaret Hospital phase II consortia. J Clin Oncol. 2008;26:76-82.  [PubMed]  [DOI]  [Cited in This Article: ]
29.  Nimeiri HS, Oza AM, Morgan RJ, Friberg G, Kasza K, Faoro L, Salgia R, Stadler WM, Vokes EE, Fleming GF. Efficacy and safety of bevacizumab plus erlotinib for patients with recurrent ovarian, primary peritoneal, and fallopian tube cancer: a trial of the Chicago, PMH, and California Phase II Consortia. Gynecol Oncol. 2008;110:49-55.  [PubMed]  [DOI]  [Cited in This Article: ]
30.  Heckman CA, Holopainen T, Wirzenius M, Keskitalo S, Jeltsch M, Ylä-Herttuala S, Wedge SR, Jürgensmeier JM, Alitalo K. The tyrosine kinase inhibitor cediranib blocks ligand-induced vascular endothelial growth factor receptor-3 activity and lymphangiogenesis. Cancer Res. 2008;68:4754-4762.  [PubMed]  [DOI]  [Cited in This Article: ]
31.  Wedge SR, Kendrew J, Hennequin LF, Valentine PJ, Barry ST, Brave SR, Smith NR, James NH, Dukes M, Curwen JO. AZD2171: a highly potent, orally bioavailable, vascular endothelial growth factor receptor-2 tyrosine kinase inhibitor for the treatment of cancer. Cancer Res. 2005;65:4389-4400.  [PubMed]  [DOI]  [Cited in This Article: ]
32.  Matulonis UA, Berlin S, Ivy P, Tyburski K, Krasner C, Zarwan C, Berkenblit A, Campos S, Horowitz N, Cannistra SA. Cediranib, an oral inhibitor of vascular endothelial growth factor receptor kinases, is an active drug in recurrent epithelial ovarian, fallopian tube, and peritoneal cancer. J Clin Oncol. 2009;27:5601-5606.  [PubMed]  [DOI]  [Cited in This Article: ]
33.  Moroney JW, Sood AK, Coleman RL. Aflibercept in epithelial ovarian carcinoma. Future Oncol. 2009;5:591-600.  [PubMed]  [DOI]  [Cited in This Article: ]
34.  Tew WP, Colombo N, Ray-Coquard I, del Campo J, Scambia G, Spriggs D. VEGF-Trap for patients (pts) with recurrent platinum-resistant epithelial ovarian cancer (EOC) : preliminary results of a randomized, multicenter phase II study. J Clin Oncol. 2007;25:A5508.  [PubMed]  [DOI]  [Cited in This Article: ]
35.  Hellström M, Kalén M, Lindahl P, Abramsson A, Betsholtz C. Role of PDGF-B and PDGFR-beta in recruitment of vascular smooth muscle cells and pericytes during embryonic blood vessel formation in the mouse. Development. 1999;126:3047-3055.  [PubMed]  [DOI]  [Cited in This Article: ]
36.  Cao R, Bråkenhielm E, Li X, Pietras K, Widenfalk J, Ostman A, Eriksson U, Cao Y. Angiogenesis stimulated by PDGF-CC, a novel member in the PDGF family, involves activation of PDGFR-alphaalpha and -alphabeta receptors. FASEB J. 2002;16:1575-1583.  [PubMed]  [DOI]  [Cited in This Article: ]
37.  Reinmuth N, Liu W, Jung YD, Ahmad SA, Shaheen RM, Fan F, Bucana CD, McMahon G, Gallick GE, Ellis LM. Induction of VEGF in perivascular cells defines a potential paracrine mechanism for endothelial cell survival. FASEB J. 2001;15:1239-1241.  [PubMed]  [DOI]  [Cited in This Article: ]
38.  Dabrow MB, Francesco MR, McBrearty FX, Caradonna S. The effects of platelet-derived growth factor and receptor on normal and neoplastic human ovarian surface epithelium. Gynecol Oncol. 1998;71:29-37.  [PubMed]  [DOI]  [Cited in This Article: ]
39.  Apte SM, Bucana CD, Killion JJ, Gershenson DM, Fidler IJ. Expression of platelet-derived growth factor and activated receptor in clinical specimens of epithelial ovarian cancer and ovarian carcinoma cell lines. Gynecol Oncol. 2004;93:78-86.  [PubMed]  [DOI]  [Cited in This Article: ]
40.  Henriksen R, Funa K, Wilander E, Bäckström T, Ridderheim M, Oberg K. Expression and prognostic significance of platelet-derived growth factor and its receptors in epithelial ovarian neoplasms. Cancer Res. 1993;53:4550-4554.  [PubMed]  [DOI]  [Cited in This Article: ]
41.  Druker BJ, Tamura S, Buchdunger E, Ohno S, Segal GM, Fanning S, Zimmermann J, Lydon NB. Effects of a selective inhibitor of the Abl tyrosine kinase on the growth of Bcr-Abl positive cells. Nat Med. 1996;2:561-566.  [PubMed]  [DOI]  [Cited in This Article: ]
42.  Buchdunger E, Cioffi CL, Law N, Stover D, Ohno-Jones S, Druker BJ, Lydon NB. Abl protein-tyrosine kinase inhibitor STI571 inhibits in vitro signal transduction mediated by c-kit and platelet-derived growth factor receptors. J Pharmacol Exp Ther. 2000;295:139-145.  [PubMed]  [DOI]  [Cited in This Article: ]
43.  Coleman RL, Broaddus RR, Bodurka DC, Wolf JK, Burke TW, Kavanagh JJ, Levenback CF, Gershenson DM. Phase II trial of imatinib mesylate in patients with recurrent platinum- and taxane-resistant epithelial ovarian and primary peritoneal cancers. Gynecol Oncol. 2006;101:126-131.  [PubMed]  [DOI]  [Cited in This Article: ]
44.  Schilder RJ, Sill MW, Lee RB, Shaw TJ, Senterman MK, Klein-Szanto AJ, Miner Z, Vanderhyden BC. Phase II evaluation of imatinib mesylate in the treatment of recurrent or persistent epithelial ovarian or primary peritoneal carcinoma: a Gynecologic Oncology Group Study. J Clin Oncol. 2008;26:3418-3425.  [PubMed]  [DOI]  [Cited in This Article: ]
45.  Matei D, Emerson RE, Schilder J, Menning N, Baldridge LA, Johnson CS, Breen T, McClean J, Stephens D, Whalen C. Imatinib mesylate in combination with docetaxel for the treatment of patients with advanced, platinum-resistant ovarian cancer and primary peritoneal carcinomatosis : a Hoosier Oncology Group trial. Cancer. 2008;113:723-732.  [PubMed]  [DOI]  [Cited in This Article: ]
46.  Annunziata CM, Walker AJ, Minasian L, Yu M, Kotz H, Wood BJ, Calvo K, Choyke P, Kimm D, Steinberg SM. Vandetanib, designed to inhibit VEGFR2 and EGFR signaling, had no clinical activity as monotherapy for recurrent ovarian cancer and no detectable modulation of VEGFR2. Clin Cancer Res. 2010;16:664-672.  [PubMed]  [DOI]  [Cited in This Article: ]
47.  Ciardiello F, Tortora G. EGFR antagonists in cancer treatment. N Engl J Med. 2008;358:1160-1174.  [PubMed]  [DOI]  [Cited in This Article: ]
48.  Lafky JM, Wilken JA, Baron AT, Maihle NJ. Clinical implications of the ErbB/epidermal growth factor (EGF) receptor family and its ligands in ovarian cancer. Biochim Biophys Acta. 2008;1785:232-265.  [PubMed]  [DOI]  [Cited in This Article: ]
49.  Cohen MH, Williams GA, Sridhara R, Chen G, McGuinn WD Jr, Morse D, Abraham S, Rahman A, Liang C, Lostritto R. United States Food and Drug Administration Drug Approval summary: Gefitinib (ZD1839; Iressa) tablets. Clin Cancer Res. 2004;10:1212-1218.  [PubMed]  [DOI]  [Cited in This Article: ]
50.  Baselga J, Averbuch SD. ZD1839 ('Iressa') as an anticancer agent. Drugs. 2000;60 Suppl 1:33-40; discussion 41-42.  [PubMed]  [DOI]  [Cited in This Article: ]
51.  Lynch TJ, Bell DW, Sordella R, Gurubhagavatula S, Okimoto RA, Brannigan BW, Harris PL, Haserlat SM, Supko JG, Haluska FG. Activating mutations in the epidermal growth factor receptor underlying responsiveness of non-small-cell lung cancer to gefitinib. N Engl J Med. 2004;350:2129-2139.  [PubMed]  [DOI]  [Cited in This Article: ]
52.  Paez JG, Jänne PA, Lee JC, Tracy S, Greulich H, Gabriel S, Herman P, Kaye FJ, Lindeman N, Boggon TJ. EGFR mutations in lung cancer: correlation with clinical response to gefitinib therapy. Science. 2004;304:1497-1500.  [PubMed]  [DOI]  [Cited in This Article: ]
53.  Ciardiello F, Caputo R, Bianco R, Damiano V, Pomatico G, De Placido S, Bianco AR, Tortora G. Antitumor effect and potentiation of cytotoxic drugs activity in human cancer cells by ZD-1839 (Iressa), an epidermal growth factor receptor-selective tyrosine kinase inhibitor. Clin Cancer Res. 2000;6:2053-2063.  [PubMed]  [DOI]  [Cited in This Article: ]
54.  Schilder RJ, Sill MW, Chen X, Darcy KM, Decesare SL, Lewandowski G, Lee RB, Arciero CA, Wu H, Godwin AK. Phase II study of gefitinib in patients with relapsed or persistent ovarian or primary peritoneal carcinoma and evaluation of epidermal growth factor receptor mutations and immunohistochemical expression: a Gynecologic Oncology Group Study. Clin Cancer Res. 2005;11:5539-5548.  [PubMed]  [DOI]  [Cited in This Article: ]
55.  Pautier P, Joly F, Kerbrat P, Bougnoux P, Fumoleau P, Petit T, Rixe O, Ringeisen F, Carrasco AT, Lhommé C. Phase II study of gefitinib in combination with paclitaxel (P) and carboplatin (C) as second-line therapy for ovarian, tubal or peritoneal adenocarcinoma (1839IL/0074). Gynecol Oncol. 2010;116:157-162.  [PubMed]  [DOI]  [Cited in This Article: ]
56.  Moyer JD, Barbacci EG, Iwata KK, Arnold L, Boman B, Cunningham A, DiOrio C, Doty J, Morin MJ, Moyer MP. Induction of apoptosis and cell cycle arrest by CP-358,774, an inhibitor of epidermal growth factor receptor tyrosine kinase. Cancer Res. 1997;57:4838-4848.  [PubMed]  [DOI]  [Cited in This Article: ]
57.  Gordon AN, Finkler N, Edwards RP, Garcia AA, Crozier M, Irwin DH, Barrett E. Efficacy and safety of erlotinib HCl, an epidermal growth factor receptor (HER1/EGFR) tyrosine kinase inhibitor, in patients with advanced ovarian carcinoma: results from a phase II multicenter study. Int J Gynecol Cancer. 2005;15:785-792.  [PubMed]  [DOI]  [Cited in This Article: ]
58.  Vasey PA, Gore M, Wilson R, Rustin G, Gabra H, Guastalla JP, Lauraine EP, Paul J, Carty K, Kaye S. A phase Ib trial of docetaxel, carboplatin and erlotinib in ovarian, fallopian tube and primary peritoneal cancers. Br J Cancer. 2008;98:1774-1780.  [PubMed]  [DOI]  [Cited in This Article: ]
59.  Kawamoto T, Sato JD, Le A, Polikoff J, Sato GH, Mendelsohn J. Growth stimulation of A431 cells by epidermal growth factor: identification of high-affinity receptors for epidermal growth factor by an anti-receptor monoclonal antibody. Proc Natl Acad Sci USA. 1983;80:1337-1341.  [PubMed]  [DOI]  [Cited in This Article: ]
60.  Kawaguchi Y, Kono K, Mimura K, Sugai H, Akaike H, Fujii H. Cetuximab induce antibody-dependent cellular cytotoxicity against EGFR-expressing esophageal squamous cell carcinoma. Int J Cancer. 2007;120:781-787.  [PubMed]  [DOI]  [Cited in This Article: ]
61.  Ciardiello F, Tortora G. A novel approach in the treatment of cancer: targeting the epidermal growth factor receptor. Clin Cancer Res. 2001;7:2958-2970.  [PubMed]  [DOI]  [Cited in This Article: ]
62.  Schilder RJ, Pathak HB, Lokshin AE, Holloway RW, Alvarez RD, Aghajanian C, Min H, Devarajan K, Ross E, Drescher CW. Phase II trial of single agent cetuximab in patients with persistent or recurrent epithelial ovarian or primary peritoneal carcinoma with the potential for dose escalation to rash. Gynecol Oncol. 2009;113:21-27.  [PubMed]  [DOI]  [Cited in This Article: ]
63.  Konner J, Schilder RJ, DeRosa FA, Gerst SR, Tew WP, Sabbatini PJ, Hensley ML, Spriggs DR, Aghajanian CA. A phase II study of cetuximab/paclitaxel/carboplatin for the initial treatment of advanced-stage ovarian, primary peritoneal, or fallopian tube cancer. Gynecol Oncol. 2008;110:140-145.  [PubMed]  [DOI]  [Cited in This Article: ]
64.  Hudis CA. Trastuzumab--mechanism of action and use in clinical practice. N Engl J Med. 2007;357:39-51.  [PubMed]  [DOI]  [Cited in This Article: ]
65.  Franklin MC, Carey KD, Vajdos FF, Leahy DJ, de Vos AM, Sliwkowski MX. Insights into ErbB signaling from the structure of the ErbB2-pertuzumab complex. Cancer Cell. 2004;5:317-328.  [PubMed]  [DOI]  [Cited in This Article: ]
66.  Molina MA, Codony-Servat J, Albanell J, Rojo F, Arribas J, Baselga J. Trastuzumab (herceptin), a humanized anti-Her2 receptor monoclonal antibody, inhibits basal and activated Her2 ectodomain cleavage in breast cancer cells. Cancer Res. 2001;61:4744-4749.  [PubMed]  [DOI]  [Cited in This Article: ]
67.  Gordon MS, Matei D, Aghajanian C, Matulonis UA, Brewer M, Fleming GF, Hainsworth JD, Garcia AA, Pegram MD, Schilder RJ. Clinical activity of pertuzumab (rhuMAb 2C4), a HER dimerization inhibitor, in advanced ovarian cancer: potential predictive relationship with tumor HER2 activation status. J Clin Oncol. 2006;24:4324-4332.  [PubMed]  [DOI]  [Cited in This Article: ]
68.  Makhija S, Amler LC, Glenn D, Ueland FR, Gold MA, Dizon DS, Paton V, Lin CY, Januario T, Ng K. Clinical activity of gemcitabine plus pertuzumab in platinum-resistant ovarian cancer, fallopian tube cancer, or primary peritoneal cancer. J Clin Oncol. 2010;28:1215-1223.  [PubMed]  [DOI]  [Cited in This Article: ]
69.  Hanna J, Finley D. A proteasome for all occasions. FEBS Lett. 2007;581:2854-2861.  [PubMed]  [DOI]  [Cited in This Article: ]
70.  Burger AM, Seth AK. The ubiquitin-mediated protein degradation pathway in cancer: therapeutic implications. Eur J Cancer. 2004;40:2217-2229.  [PubMed]  [DOI]  [Cited in This Article: ]
71.  Orlowski RZ, Kuhn DJ. Proteasome inhibitors in cancer therapy: lessons from the first decade. Clin Cancer Res. 2008;14:1649-1657.  [PubMed]  [DOI]  [Cited in This Article: ]
72.  Aghajanian C, Blessing JA, Darcy KM, Reid G, DeGeest K, Rubin SC, Mannel RS, Rotmensch J, Schilder RJ, Riordan W. A phase II evaluation of bortezomib in the treatment of recurrent platinum-sensitive ovarian or primary peritoneal cancer: a Gynecologic Oncology Group study. Gynecol Oncol. 2009;115:215-220.  [PubMed]  [DOI]  [Cited in This Article: ]
73.  Jones PA, Baylin SB. The epigenomics of cancer. Cell. 2007;128:683-692.  [PubMed]  [DOI]  [Cited in This Article: ]
74.  Esteller M. Epigenetics in cancer. N Engl J Med. 2008;358:1148-1159.  [PubMed]  [DOI]  [Cited in This Article: ]
75.  Herman JG, Baylin SB. Gene silencing in cancer in association with promoter hypermethylation. N Engl J Med. 2003;349:2042-2054.  [PubMed]  [DOI]  [Cited in This Article: ]
76.  Toyota M, Issa JP. Epigenetic changes in solid and hematopoietic tumors. Semin Oncol. 2005;32:521-530.  [PubMed]  [DOI]  [Cited in This Article: ]
77.  Barton CA, Hacker NF, Clark SJ, O'Brien PM. DNA methylation changes in ovarian cancer: implications for early diagnosis, prognosis and treatment. Gynecol Oncol. 2008;109:129-139.  [PubMed]  [DOI]  [Cited in This Article: ]
78.  Matei DE, Nephew KP. Epigenetic therapies for chemoresensitization of epithelial ovarian cancer. Gynecol Oncol. 2010;116:195-201.  [PubMed]  [DOI]  [Cited in This Article: ]
79.  Asadollahi R, Hyde CA, Zhong XY. Epigenetics of ovarian cancer: from the lab to the clinic. Gynecol Oncol. 2010;118:81-87.  [PubMed]  [DOI]  [Cited in This Article: ]
80.  Butler LM, Agus DB, Scher HI, Higgins B, Rose A, Cordon-Cardo C, Thaler HT, Rifkind RA, Marks PA, Richon VM. Suberoylanilide hydroxamic acid, an inhibitor of histone deacetylase, suppresses the growth of prostate cancer cells in vitro and in vivo. Cancer Res. 2000;60:5165-5170.  [PubMed]  [DOI]  [Cited in This Article: ]
81.  Sonnemann J, Hartwig M, Plath A, Saravana Kumar K, Müller C, Beck JF. Histone deacetylase inhibitors require caspase activity to induce apoptosis in lung and prostate carcinoma cells. Cancer Lett. 2006;232:148-160.  [PubMed]  [DOI]  [Cited in This Article: ]
82.  Takai N, Kawamata N, Gui D, Said JW, Miyakawa I, Koeffler HP. Human ovarian carcinoma cells: histone deacetylase inhibitors exhibit antiproliferative activity and potently induce apoptosis. Cancer. 2004;101:2760-2770.  [PubMed]  [DOI]  [Cited in This Article: ]
83.  Fang F, Balch C, Schilder J, Breen T, Zhang S, Shen C, Li L, Kulesavage C, Snyder AJ, Nephew KP. A phase 1 and pharmacodynamic study of decitabine in combination with carboplatin in patients with recurrent, platinum-resistant, epithelial ovarian cancer. Cancer. 2010;Epub ahead of print.  [PubMed]  [DOI]  [Cited in This Article: ]
84.  Lane AA, Chabner BA. Histone deacetylase inhibitors in cancer therapy. J Clin Oncol. 2009;27:5459-5468.  [PubMed]  [DOI]  [Cited in This Article: ]
85.  Modesitt SC, Sill M, Hoffman JS, Bender DP. A phase II study of vorinostat in the treatment of persistent or recurrent epithelial ovarian or primary peritoneal carcinoma: a Gynecologic Oncology Group study. Gynecol Oncol. 2008;109:182-186.  [PubMed]  [DOI]  [Cited in This Article: ]
86.  Mackay HJ, Hirte H, Colgan T, Covens A, MacAlpine K, Grenci P, Wang L, Mason J, Pham PA, Tsao MS. Phase II trial of the histone deacetylase inhibitor belinostat in women with platinum resistant epithelial ovarian cancer and micropapillary (LMP) ovarian tumours. Eur J Cancer. 2010;46:1573-1579.  [PubMed]  [DOI]  [Cited in This Article: ]
87.  Rouleau M, Patel A, Hendzel MJ, Kaufmann SH, Poirier GG. PARP inhibition: PARP1 and beyond. Nat Rev Cancer. 2010;10:293-301.  [PubMed]  [DOI]  [Cited in This Article: ]
88.  King MC, Marks JH, Mandell JB. Breast and ovarian cancer risks due to inherited mutations in BRCA1 and BRCA2. Science. 2003;302:643-646.  [PubMed]  [DOI]  [Cited in This Article: ]
89.  Press JZ, De Luca A, Boyd N, Young S, Troussard A, Ridge Y, Kaurah P, Kalloger SE, Blood KA, Smith M. Ovarian carcinomas with genetic and epigenetic BRCA1 loss have distinct molecular abnormalities. BMC Cancer. 2008;8:17.  [PubMed]  [DOI]  [Cited in This Article: ]
90.  Fong PC, Yap TA, Boss DS, Carden CP, Mergui-Roelvink M, Gourley C, De Greve J, Lubinski J, Shanley S, Messiou C. Poly(ADP)-ribose polymerase inhibition: frequent durable responses in BRCA carrier ovarian cancer correlating with platinum-free interval. J Clin Oncol. 2010;28:2512-2519.  [PubMed]  [DOI]  [Cited in This Article: ]
91.  Vivanco I, Sawyers CL. The phosphatidylinositol 3-Kinase AKT pathway in human cancer. Nat Rev Cancer. 2002;2:489-501.  [PubMed]  [DOI]  [Cited in This Article: ]
92.  Trinh XB, van Dam PA, Dirix LY, Vermeulen PB, Tjalma WA. The rationale for mTOR inhibition in epithelial ovarian cancer. Expert Opin Investig Drugs. 2009;18:1885-1891.  [PubMed]  [DOI]  [Cited in This Article: ]
93.  Guertin DA, Sabatini DM. Defining the role of mTOR in cancer. Cancer Cell. 2007;12:9-22.  [PubMed]  [DOI]  [Cited in This Article: ]