Introduction

Ovarian cancer is the fourth most common cause of cancer death in women, with a worldwide incidence of 200,000 cases causing 115,000 deaths per year. As described elsewhere, the current standard of care for women with stage IC (and stage IB with adverse histological features) to stage III disease is surgery followed by adjuvant chemotherapy. Further lines of treatment can be given when patients relapse but cure is not possible. Ovarian cancer is considered to be a chemosensitive disease, with nearly 75% of patients initially responding to platinum-based treatment. The choice of agent upon relapse depends on the timing of relapse; if this is over 6 months from previous platinum administration, this can be repeated either as a single agent or as part of a combination regimen, as patients are still considered to be platinum sensitive. If relapse occurs within 6 months of previous platinum administration, non-platinum drugs such as pegylated liposomal doxorubicin are used. There is an increased understanding of the complicated biological pathways involved in the development of gynaecological cancers, their subsequent metastagenesis and the mechanisms involved in chemoresistance. Many clinical studies are underway investigating the use of novel agents in patients with gynaecological malignancies, either alone, concurrently with chemotherapy or sequentially, in an attempt to improve response rates/durations and thereby survival. This chapter will outline several of the new classes of novel agents which are at various stages of development, detail their putative mechanisms of action and their potential indications, and include brief summaries of their toxicity profiles from studies to date. Many of the phase II studies of new agents include patients in the platinum-refractory group, whose tumours are intrinsically resistant to chemotherapy and radiotherapy, and who therefore have low rates of response to conventional treatment.

Vascular Endothelial Growth Factor and Angiogenesis Inhibition

Angiogenesis or neovascularization is a normal physiological process involving the remodelling of vasculature and formation of new blood vessels. Angiogenesis plays a vital role in tumour formation and metastasis because both primary lesions and metastatic tumours must develop a new vascular supply in order to survive (Folkman 1971, 1990). Early initiation of angiogenesis is essential for cancer survival, and occurs when stimulatory factors overcome inhibitory factors, promoting the formation of new blood vessels (Bergers and Benjamin 2003).

Research investigating the molecular basis of angiogenesis has identified multiple pathways that contribute to tumour angiogenesis. These include vascular endothelial growth factor (VEGF), fibroblast growth factor and platelet-derived growth factor (PDGF). Based on the central role of VEGF in tumour angiogenesis and growth, this has emerged as the most promising therapeutic target for angiogenesis inhibition. The VEGF molecule interacts with cell surface VEGF receptors (VEGFRs) that initiate signalling through downstream pathways to promote growth and differentiation of vascular endothelial cells and formation of new blood vessels.

The biological roles of VEGF predict that its expression should be related to clinical outcome in cancer patients. Indeed, VEGF expression has been correlated with both disease-free survival and overall survival (OS) in a variety of gynaecological cancers. VEGF expression has been evaluated in women with ovarian carcinoma in several studies, which collectively provide consistent evidence that higher VEGF levels are associated with aggressive clinical behaviour in ovarian carcinoma. Kassim et al (2004) found some degree of VEGF expression in all ovarian cancer specimens examined, and the level of VEGF expression was significantly higher in tumour specimens compared with benign ovarian tissue. In addition, rising titres of VEGF from tumour specimens correlated with increasing stage and decreased survival. This relationship seems to be independent of important clinical and pathological prognostic factors. Furthermore, in women with ovarian cancer, high serum levels of VEGF are an independent risk factor for ascites, advanced-stage disease, undifferentiated histology, more metastases and decreased survival (Cooper et al 2002, Li et al 2004).

There are limited data regarding VEGF expression in endometrial cancer specimens. Holland et al (2003) documented VEGF expression in 100% of the endometrial cancer specimens examined. In addition, they found no expression of VEGF in benign endometrial tissue. The functional significance of the VEGF/VEGFR axis in endometrial cancer remains to be demonstrated.

In tissue specimens from patients with cervical cancer, VEGF expression has been noted immunohistochemically in 94% of samples (Loncaster et al 2000). Intratumour levels of VEGF are increased in patients with cervical cancer compared with levels in normal cervical tissue. For these women with cervical cancer, increasing intratumoral levels of VEGF also correlated with higher stage, increased risk of lymphovascular space invasion, greater likelihood of parametrial spread, and lymph node metastasis (Cheng et al 1999).

The biological and clinical significance of the VEGF pathway in tumour angiogenesis suggests its value as a therapeutic target in gynaecological malignancies. There are three main strategies for inhibition of the VEGF pathway for therapeutic applications. The first is to target VEGF itself, the second is to target VEGFR so as to prevent binding of VEGF, and the third is to inhibit tyrosine kinase activation and downstream signalling with small molecules that work at the intracellular level.

Bevacizumab (Avastin) is the first targeted agent to show significant single-agent activity in ovarian carcinoma. It is a recombinant humanized monoclonal antibody directed against VEGF. Bevacizumab has been tested in a number of phase II trials as monotherapy in epithelial ovarian cancer (EOC). Two such trials using single-agent bevacizumab in relapsed high-grade carcinoma of the ovary were presented at the American Society of Clinical Oncology (ASCO) meetings in 2005 and 2006 (Burger et al 2007, Cannistra et al 2007). They convincingly demonstrate bevacizumab’s significant single-agent activity in patients with relapsed EOC, with objective response rates (ORR) of 21% and 16%, respectively. Additionally, 52% and 64% of cases, respectively, achieved disease stabilization with median progression-free survival (PFS) of 4.4 and 4.5 months. These results are as good or better than typical rates from traditional second-line chemotherapeutic agents in this group of patients.

Cytotoxic and antiangiogenic agents can be used in combination for enhanced activity. It has been hypothesized that combining VEGF-targeted agents with frequently administered low-dose so-called ‘metronomic chemotherapy’ may have additive or synergistic antiangiogenic or antitumour effects. In 2005, Garcia et al presented preliminary data from a phase II trial of patients with recurrent ovarian cancer who were given bevacizumab biweekly with metronomic oral cyclophosphamide. The ORR was 28% and a further substantial proportion (57%) achieved disease stabilization for at least 6 months. The median PFS was 7.5 months and OS was 13 months. This protocol is now closed and the data are undergoing final analysis, but if consistent with preliminary results, these findings would provide the rationale for a phase II randomized trial of combination versus single-agent therapy. Additional reports of outcomes for patients with EOC and primary peritoneal cancer treated with bevacizumab include three historical case series of patients treated outside clinical trials with single-agent therapy or in combination with cytotoxic drugs, suggesting activity in more heavily pretreated patients with recurrent disease, and preliminary data in 2006 demonstrating the feasibility of the combination of traditional carboplatin/paclitaxel chemotherapy combined with bevacizumab in front-line therapy (Cohn et al 2006, Monk et al 2006, Penson et al 2006, Wright et al 2006a).

Based on the encouraging phase II trial data, bevacizumab has been rapidly incorporated into phase III trials, the major focus of which is on first-line treatment. Two similar randomized trials are now underway. The Gynaecologic Oncology Group 218 trial is designed to explore the role of bevacizumab in first-line treatment and in the maintenance setting, with a three-way randomization whereby all patients receive carboplatin/paclitaxel plus bevacizumab or placebo for six cycles, with those receiving bevacizumab further randomized to drug or placebo maintenance for 15 months, with the primary endpoint being OS. It is limited to patients with stage III or IV disease. In contrast, the Gynaecological Cancer Intergroup trial (ICON 7) is a non-placebo-controlled, smaller, two-arm trial in which patients receive either carboplatin/paclitaxel for six cycles or the same treatment plus bevacizumab every 3 weeks during chemotherapy and continuing for an additional 9 months, with the primary endpoint being PFS. The patient population for this trial includes all patients with at least high-risk, early-stage disease. Bevacizumab has also been tested in the phase II setting in combination with topotecan in women with platinum-refractory ovarian cancer (McGonigle et al 2008). To date, 22 patients have been enrolled, 18 of whom were evaluable; 22.2% had a partial response (PR) and 27.8% achieved disease stabilization. Toxicity was described as being acceptable.

Bevacizumab has also been given to women with cervical carcinoma. Wright et al (2006b) gave combination bevacizumab and 5-fluorouracil or capecitabine to women with recurrent cervical cancer. In this small retrospective group of six women, one patient achieved a complete response (CR), one achieved a PR and two achieved disease stabilization. Unfortunately, all four women eventually had disease progression at a median time of 4.3 months, and none had a progression-free interval of more than 6 months.

Unique toxicities have been ascribed to the administration of bevacizumab and other anti-VEGF molecules. Most of these toxicities (such as proteinurea, hypertension and bleeding) are generally mild and are either self-limiting or easily manageable. Other adverse effects, although uncommon, may be serious; these include arterial thromboembolism, wound-healing complications, and gastrointestinal perforation or fistulae.

Targeting the VEGF/VEGFR axis may affect the survival of both proliferating and quiescent endothelial cells, leading to the disruption of normal vasculature. The increase in arterial thromboembolic events, including cerebral infarction, transient ischaemic attacks, myocardial infarction and angina, may be related to this phenomenon. Hypertension is one of the most common side-effects of bevacizumab therapy, with an overall incidence of 22–32% (Gordon and Cunningham 2005). The mechanism responsible for bevacizumab-related hypertension is not fully understood, but it is thought to be related to decreased production of nitric oxide as a result of VEGF inhibition. Most patients with hypertension can be managed with oral antihypertensive agents.

VEGF is known to play a critical role in the physiological angiogenesis required for wound healing. This could be of particular importance when considering antiangiogenic therapy as front-line adjuvant treatment of ovarian cancer after cytoreductive surgery. Concerns about wound healing in postoperative patients have resulted in the decision to start bevacizumab/placebo therapy at cycle 2 within the Gynaecologic Oncology Group 218 trial. This would be more than 28 days after surgery.

The complication of bowel perforation is now well documented with bevacizumab and, although uncommon, is of concern. It has been suggested that the number of prior cytotoxic regimens and the presence of bowel obstruction might predispose to this complication, although our ability to identify high-risk patients requires further investigation.

Other agents targeting the VEGF pathway are also being developed rapidly. VEGF-Trap inactivates VEGF by acting as a decoy receptor for VEGF, preventing binding of the ligand to its natural receptors. Promising data have been reported regarding VEGF-Trap in preclinical and phase I studies in patients with advanced solid malignancies (Dupont et al 2004, Hu et al 2005). One patient in the phase I study had carboplatin-, taxane- and gemcitabine-resistant advanced ovarian cancer and achieved a response evaluation criteria in solid tumours (RECIST)-defined PR, a 67% reduction in CA125 levels, radiographic resolution of abdominal ascites and subjective improvement of performance status after four cycles of VEGF-Trap. It is currently being evaluated in the phase II setting in patients with recurrent ovarian carcinoma.

Cediranib (AZD2171) is a potent oral tyrosine kinase inhibitor (TKI) of VEGF1, 2, 3 and c-Kit. It has been tested in a phase II study reported at the ASCO meeting in 2008 as a single agent in recurrent ovarian, peritoneal or tubal cancer (Matulonis et al 2008). Preliminary results from 28 patients, 16 of whom had platinum-resistant disease, revealed an ORR of 18.5%. Common toxicities included hypertension (n = 13), fatigue (n = 5) and diarrhoea (n = 3). A further phase II study of this agent, reported in 2008, has shown similar promising efficacy data and toxicity profiles (Hirte et al 2008).

Sunitinib, an oral multitargeted TKI known to be effective against, amongst others, VEGFR and PDGF receptors, has recently been tested in the phase II setting as a single agent in patients with EOC, primary peritoneal and fallopian tube cancers (Biagi et al 2008). Preliminary results reported at the ASCO meeting in 2008 revealed that 12 out of 17 patients had a PR or disease stabilization. The tolerability profile of this drug is well known from its extensive use in other tumour types, and includes fatigue, mucositis, dysgeusia, hypertension, nausea and hand–foot reaction. Further studies involving larger patient groups are warranted in order to further assess the efficacy of sunitinib in gynaecological cancers.

Sorafenib, another multitargeted TKI (predominantly affecting VEGFR, PDGF receptors, Flt3 and c-Kit) has also been tested in the phase II setting in patients with recurrent EOC and primary peritoneal cancer, the results of which were presented at the recent ASCO meeting (Matel et al 2008). Seventy-three patients who had persistent or recurrent EOC who had been treated previously with one or two cytotoxic regimens, and who had progressed within 12 months of platinum-based therapy, were treated until disease progression or toxicity requiring cessation. The primary endpoint was PFS at 6 months. Response, OS and toxicity were also documented. Toxicities (grade three to four) included rash (n = 12), metabolic (n = 10), gastrointestinal (n = 3), cardiovascular (n = 2) and pulmonary (n = 2). Twelve out of 59 evaluable patients were progression free for at least 6 months. Two PRs were reported and 20 patients achieved disease stabilization. Mature data are awaited to further define the utility of this agent.

Sorafenib has also been studied in patients with uterine cancer in the phase II settting, and preliminary results have been reported (Nimeiri et al 2008). Patients with advanced or recurrent disease who had experienced one or fewer prior regimens were treated with sorafenib 400 mg bd. Fifty-five patients were enrolled. Grade three to four toxicities included hypertension (13%), hand–foot syndrome (13%) and anaemia (6%). The response rate in patients with advanced/recurrent disease was 5% (PR), and 50% of patients achieved disease stabilization. The median OS was 10.1 months. In patients with carcinosarcoma, 27% achieved disease stabilization. The completion of the trial is awaited.

The Epidermal Growth Factor Receptor Family

The human epidermal growth factor receptor (EGFR) family of transmembrane receptor tyrosine kinases has four identified members: EGFR or HER1, HER2, HER3 and HER4. This subgroup of receptors mediate cell growth, differentiation and survival, and are dysregulated in many types of cancer. Ligand binding to the extracellular domain of the receptors enables receptor homo- or heterodimerization, which initiates phosphorylation of the intracellular tyrosine kinase domain and activation of cell signalling to reduce apoptosis and increase tumour cell proliferation.

The HER pathway is involved in ovarian cancer pathogenesis (Berchuck et al 1990, Bartlett et al 1996, Campiglio et al 1999). The majority of ovarian cancer cell lines and tumours express high levels of a number of HER receptor ligands, as well as exhibiting amplification of EGFR and HER2, and expressing all HER receptors (Campiglio et al 1999). In EOC, attention has focused on EGFR (HER1) which is expressed in 19–92% of tumours, and expression of which is associated with a poor prognosis (Ford et al 1994, Lin et al 1994, Goff et al 1996, Ilekis et al 1997, Fischer-Colbrie et al 1997).

The goal of EGFR-targeted therapies is to disrupt phosphorylation, thereby increasing apoptosis and reducing cell proliferation signals. This disruption can be achieved in several ways: inhibition of dimerization, blocking of EGFR receptor ligand binding with humanized monoclonal antibodies, and inhibition of tyrosine kinase activity with small-molecule TKIs. In the majority of trials of anti-EGFR agents in patients with EOC, the agents are investigated as monotherapy in heavily pretreated women. Objective responses are relatively low but prolonged disease stabilization has been seen in a subset of women.

The small-molecule TKIs erlotinib (Tarceva) and gefitinib (Iressa) have been tested in phase II trials of patients with relapsed and pretreated EOC. A trial of erlotinib as monotherapy in women with advanced EGFR-positive cancers treated with a mean of three prior regimens was presented at the ASCO meeting in 2001 (Finkler et al 2001). The ORR was 8.8%, with a further 7% of patients achieving disease stabilization for more than 6 months. A similar trial of gefitinib in patients with recurrent or persistent ovarian carcinoma or primary peritoneal cancer, but in which EGFR expression was not required for inclusion, led to a response rate of only 3.7% and long-term disease stabilization for more than 6 months in a further 14.8% of patients (Schilder et al 2003). The median time to progression was approximately 2 months, but 10% of patients remained progression free at 8–12 months. Interestingly, all of these patients had EGFR-positive tumours. Unlike in lung cancer, where EGFR expression and the presence of a mutation in the tyrosine kinase domain of EGFR confer sensitivity to EGFR TKIs, the relationship between EGFR positivity, EGFR mutation and response to EGFR TKIs is not clearly defined in EOC. Better definition of this relationship may help to identify the subset of women with EOC that are likely to achieve clinically meaningful responses to TKIs, and therefore define the appropriate treatment population.

Monoclonal antibodies against EGFR have also been investigated. The most established anti-EGFR antibody is cetuximab (Erbitux). This has been evaluated in previously untreated women with EOC in combination with standard first-line carboplatin/paclitaxel chemotherapy and as maintenance therapy. An ORR of 87% was seen and toxicity was acceptable (Aghajanian et al 2005). Its use as monotherapy is currently under investigation. Another anti-EGFR monoclonal antibody, matuzumab, has been investigated in women with recurrent EGFR-positive EOC (Seiden et al 2005); although no objective responses were seen, 21% of women achieved disease stabilization for more than 6 months.

Monoclonal antibodies directed against HER2 have also been investigated in advanced EOC. Laboratory studies have suggested that 10–15% of women have tumours that overexpress HER2 graded as 2+ or 3+ positivity by immunohistochemistry (IHC). It is unclear whether this is predictive of clinical outcome in EOC. In breast cancer, where the role of HER2 receptor overexpression is well defined, it is only a predictive factor in those with IHC 3+ positivity and it is only this subset who derive clinical benefit from anti-HER2 therapies (Slamon et al 2001). In a phase II study of the anti-HER2 monoclonal antibody trastuzumab (Herceptin) in EOC, of the 837 patients who were registered and screened, only 95 (11%) had tumours with grade 2+ or 3+ positivity. Of these patients, only 41 were treated, with an ORR of only 7.3% (Bookman et al 2003). The study concluded that the clinical value of single-agent trastuzumab in recurrent ovarian cancer is limited by the low frequency of HER2 overexpression and low rate of objective response among patients with HER2 overexpression.

The monoclonal antibody pertuzumab was the first in a new class of targeted anticancer agents termed ‘HER dimerization inhibitors’. It binds to the dimerization site of HER2, inhibiting its interaction with other HER family members. Unlike HER1, -3 and -4, HER2 has no known ligand and assumes an open conformation, with its dimerization domain permanently exposed for interaction with other ligand-activated HER receptors. HER2 is the preferred partner for dimer formation, and subsequent pathway activation via receptor phosphorylation has been shown to drive ovarian tumour cell proliferation, even in the absence of HER2 overexpression. Pertuzumab was investigated as monotherapy in a phase II trial in patients with advanced, refractory or recurrent ovarian cancer (Gordon et al 2006). A PR was achieved in 4.3% of subjects, with 41% achieving disease stabilization. However, median PFS was 20.9 weeks for HER2-positive patients compared with 5.8 weeks for HER2-negative patients and 9.1 weeks for those of unknown HER2 status. It should be noted that these patients were heavily pretreated and the median number of prior therapies was five. The study concluded that given that pertuzumab blocks all HER2-mediated signalling, in contrast to targeted blockade of EGFR or HER2 overexpression, pertuzumab may result in higher rates of clinical activity in an appropriately selected population. A randomized phase II study evaluating the combination of carboplatin-based chemotherapy with pertuzumab in comparison with carboplatin-based therapy alone in patients with relapsed, platinum-sensitive ovarian cancer is currently underway. Preliminary data presented at the ASCO meeting in 2008 reveal that the addition of pertuzumab to carboplatin-based chemotherapy is well tolerated, but efficacy data are awaited.

The small-molecule TKI lapatinib is similar to gefitinib and erlotinib, except that it has similar specificity for EGFR and HER2. Data from initial clinical experience with lapatinib have only shown mild adverse events (rash, diarrhoea, nausea, vomiting) and no grade four events. In the original phase I trial, three subjects showed a PR and 12 patients achieved disease stabilization, including two with ovarian cancer (Spector et al 2005).

Poly(ADP-Ribose) Polymerase Inhibitors

BRCA1 and BRCA2 belong to a class of genes known as tumour suppressor genes. Their protein products are important for DNA double-strand break repair (Tutt and Ashworth 2002). Mutations in BRCA1 and BRCA2 predispose to a number of hereditary cancers, including breast and ovarian. Poly(ADP-ribose) polymerase (PARP) is a DNA-binding enzyme involved in base excision repair, a key pathway in the repair of DNA single-strand breaks. Tumours in carriers of BRCA1 or BRCA2 mutations lack wild-type BRCA1 or BRCA2