**3. Antiangiogenic strategies in ovarian cancer**

Key mediators of physiological angiogenesis include products of the vascular endothelial growth factor (VEGF) gene family including VEGF-A (often abbreviated to VEGF), VEGF-B, C and D and placental growth factor. The receptor family includes VEGFR-1, 2 and 3. Different combinations of ligand-receptor interaction result in diverse outcomes such as promotion of survival, proliferation of endothelium, increased permeability and lymphangiogenesis. The binding of VEGF-A to VEGFR-2 is most important in endothelial proliferation and the regulation of permeability [15].

In physiology VEGF is important for the cyclical angiogenesis that takes place in the female reproductive tract [16]. Many tumour cell lines overexpress VEGF and in one series over 97% of human ovarian lines had overexpression [17]. Clinically, expression levels have been found to be an independent prognostic factor in several studies [18] and have also been found to correlate with peritoneal dissemination and ascites formation [19].

Given the role of VEGF in physiology as well as pre-clinical and observational data supporting a role for VEGF in cancer, several VEGF-directed therapies exist.

#### **3.1. Bevacizumab**

Bevacizumab (BEV) is a humanized monoclonal antibody able to bind all VEGF-A isoforms [20]. It is the most extensively studied of the antiangiogenic agents in EOC. Two phase III studies (GOG-218 and ICON7) tested adjuvant BEV. In GOG-218 [21] patients received 6 cycles of carboplatin/paclitaxel q3w and either 1) placebo (cycles 2–22), 2) BEV induction (cycles 2–6) then placebo maintenance (7–22) or 3) BEV induction (cycles 2–6) then maintenance (7–22). BEV was given at 15 mg/kg. The median PFS was 14.1 months in the BEV throughout arm compared to 11.2 months in the induction-only arm and 10.3 months for the control. Overall survival was not significantly different. 22.9% developed grade ≥ 2 hypertension in the BEV throughout arm vs. 7.2% in the control arm. In ICON7 [22], high-risk patients were given carboplatin/paclitaxel q3w with either placebo or bevacizumab (7.5 mg/kg) for cycles 2–18. Median PFS was 19.0 months in the BEV arm vs. 17.3 months (HR 0.81, p < 0.01). Among patients with incompletely resected IIIC or IV disease the median PFS was 15.9 vs. 10.5 months in the control arm. Bleeding (39 vs. 11%), hypertension (18 vs. 2%), thromboembolism (7 vs. 3%) and GI perforations (10 vs. 3 patients) were higher with BEV. Mean global QoL score was higher, at 54 weeks, in the control arm (76.1 vs. 69.7 points - EORTC questionnaire) [23]. Recent exploratory analysis of a 'high-risk' subgroup revealed significantly increased OS (restricted means) in the BEV group of 39.3 vs. 34.5 months [24].

There were similarities and differences between these trials. Both suggested greater benefit in a subpopulation with higher stage and suboptimal debulking. They also agreed that QoL was not improved with BEV. Conversely, different doses and durations of treatment were used and overall survival data also differed, perhaps confounded by the 40% crossover in GOG 218. BEV received regulatory approval from the EMA using 15 mg/kg [25] although ESMO guidelines supported the 7.5 mg/kg dose used in ICON7, which is also prescribed in the UK currently [26]. Analysis of both trials showed greatest separation of the PFS curves at the end of BEV treatment (12 or 15 months), raising questions about extending maintenance duration. This is being investigated in the phase III BOOST study (NCT01462890).

Bev has also been studied for recurrence. In AURELIA [27], patients with platinum-resistant disease and ≤2 prior lines of chemotherapy were given single agent investigator-choice chemotherapy either alone or with BEV continued until progression/toxicity. Median PFS was higher in the BEV arm, 6.7 vs. 3.4 months with an ORR of 27.3 vs. 11.1%. Of the 113 patients with baseline ascites 17% required paracentesis in the control arm vs. 2% in the BEV arm and PROMs for GI symptoms were better with BEV [28]. OS was not significantly different in the context of 40% crossover but a recent exploratory analysis suggestive a survival advantage in those who received BEV during or after the study [29]. Adverse events were consistent with previous studies. BEV has been granted FDA and EMA approval for this indication.

In the OCEANS study [30], the addition of BEV to carboplatin/gemcitabine in patients with platinum-sensitive disease resulted in a median PFS of 12.4 months vs. 8.4 months. OS was not significantly (38% crossover). Hypertension, proteinuria and non-CNS bleeding were significantly more common in the BEV arm. BEV was also tested in the platinum-sensitive setting with carboplatin/paclitaxel, in the factorial GOG-213 trial [31]. Median OS with BEV was 42.2 months compared to 37.3 months without (p = 0.056). BEV has EMA regulatory approval in this setting.

#### **3.2. VEGFR tyrosine kinase inhibitor (TKI) therapy**

trial in platinum-resistant EOC and is being investigated in a phase III trial against either PLD or topotecan [13]. It has also shown *in vitro* synergy with cisplatin raising hopes of clinical application to reverse platinum resistance [14]. Trabectedin itself is undergoing phase III test-

Key mediators of physiological angiogenesis include products of the vascular endothelial growth factor (VEGF) gene family including VEGF-A (often abbreviated to VEGF), VEGF-B, C and D and placental growth factor. The receptor family includes VEGFR-1, 2 and 3. Different combinations of ligand-receptor interaction result in diverse outcomes such as promotion of survival, proliferation of endothelium, increased permeability and lymphangiogenesis. The binding of VEGF-A to VEGFR-2 is most important in endothelial proliferation and the regula-

In physiology VEGF is important for the cyclical angiogenesis that takes place in the female reproductive tract [16]. Many tumour cell lines overexpress VEGF and in one series over 97% of human ovarian lines had overexpression [17]. Clinically, expression levels have been found to be an independent prognostic factor in several studies [18] and have also been found to

Given the role of VEGF in physiology as well as pre-clinical and observational data support-

Bevacizumab (BEV) is a humanized monoclonal antibody able to bind all VEGF-A isoforms [20]. It is the most extensively studied of the antiangiogenic agents in EOC. Two phase III studies (GOG-218 and ICON7) tested adjuvant BEV. In GOG-218 [21] patients received 6 cycles of carboplatin/paclitaxel q3w and either 1) placebo (cycles 2–22), 2) BEV induction (cycles 2–6) then placebo maintenance (7–22) or 3) BEV induction (cycles 2–6) then maintenance (7–22). BEV was given at 15 mg/kg. The median PFS was 14.1 months in the BEV throughout arm compared to 11.2 months in the induction-only arm and 10.3 months for the control. Overall survival was not significantly different. 22.9% developed grade ≥ 2 hypertension in the BEV throughout arm vs. 7.2% in the control arm. In ICON7 [22], high-risk patients were given carboplatin/paclitaxel q3w with either placebo or bevacizumab (7.5 mg/kg) for cycles 2–18. Median PFS was 19.0 months in the BEV arm vs. 17.3 months (HR 0.81, p < 0.01). Among patients with incompletely resected IIIC or IV disease the median PFS was 15.9 vs. 10.5 months in the control arm. Bleeding (39 vs. 11%), hypertension (18 vs. 2%), thromboembolism (7 vs. 3%) and GI perforations (10 vs. 3 patients) were higher with BEV. Mean global QoL score was higher, at 54 weeks, in the control arm (76.1 vs. 69.7 points - EORTC questionnaire) [23]. Recent exploratory analysis of a 'high-risk' subgroup revealed significantly

ing in patients with platinum partially-sensitive disease (NCT01379989).

**3. Antiangiogenic strategies in ovarian cancer**

correlate with peritoneal dissemination and ascites formation [19].

ing a role for VEGF in cancer, several VEGF-directed therapies exist.

increased OS (restricted means) in the BEV group of 39.3 vs. 34.5 months [24].

tion of permeability [15].

334 Ovarian Cancer - From Pathogenesis to Treatment

**3.1. Bevacizumab**

Whereas BEV binds directly to VEGF, VEGFR TKIs affect signalling via competitive inhibition of the intracellular kinase domain. They have the advantage of being orally bioavailable and multitargeted. Conversely, plasma concentration is unpredictable and off-target effects narrow the therapeutic window.

Cediranib inhibits VEGR-1,2 and 3 and c-Kit. ICON 6 [32] randomised patients with recurrent platinum-sensitive disease to chemotherapy plus: placebo concurrently + maintenance (Arm A), cediranib concurrently + placebo maintenance (Arm B) or cediranib concurrently + maintenance (Arm C). Median PFS was 11 months in Arm C vs. 8.7 months in Arm A (p < 0.0001). Recent OS data [33] by restricted means showed 34.2 months vs. 29.4 months in Arms C and A respectively (95% CI for the difference: −0.1-9.8). During chemotherapy grade ≥ 3 fatigue (16 vs. 8%), diarrhoea (10 vs. 2%), hypertension (12 vs. 3%), febrile neutropenia (7 vs. 3%) and thrombosis (3 vs. 1%) were higher with cediranib. 48% discontinued treatment due to toxic effects in Arm C compared to 17% in Arm A and 37% in B. Although recent analysis showed no detriment in QOL at 1 year [34], filing for regulatory approval for cediranib had been previously withdrawn. Nonetheless cediranib maintenance is undergoing investigation in ICON9 (see below).

**3.5. Predictive biomarkers in anti-angiogenic therapy**

**4. PARP inhibitor therapy**

region of 5–30% of ovarian cancers.

**4.2. PARP inhibitors in ovarian cancer**

Given the relatively modest median PFS benefits and lack of OS benefit in some trials combined with toxicity and economic considerations, biomarkers for patient selection are needed. None have yet been validated for routine use although many have been suggested. Studies have been retrospective and focussed on different markers including gene-expression signatures, serum and tissue proteomic biomarkers. There have been some intriguing results including a 63-gene signature that identifies an immune subgroup that may be harmed by bevacizumab

Novel Systemic Treatments in High Grade Ovarian Cancer

http://dx.doi.org/10.5772/intechopen.71583

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DNA constantly undergoes single and double-strand breaks (SSBs/DSBs). SSBs are repaired predominantly by base excision repair (BER). PARPs are nuclear proteins with diverse functions including in BER and chromatin remodelling. PARP-1 is the most abundant member which upon binding to SSBs activates its ADP-ribosyltransferase catalytic domain allowing PARylation and recruitment of DNA repair effectors [41]. DSBs are mostly repaired by homologous recombination (HR) or non-homologous end joining (NHEJ), the latter being error-prone [42]. HR involves a number of key proteins including BRCA1, BRCA2, RAD51 and PALB2. A detailed discussion

The Australian Ovarian Cancer Study Group screened 1001 patients with stage I-IV ovarian cancer for point mutations or large deletions in BRCA genes. 14.4% of patients overall had a germline mutation (including 17.1% with serous histology) [44]. A similar frequency was found in The Cancer Genome Atlas (TCGA) [45] although globally the prevalence varies between ethnic groups. In addition to germline mutations, BRCA genes can be somatically mutated, epigenetically silenced or the protein inactivated through post-translational mechanisms, e.g. EMSY amplification [46]. Various series have found somatic mutations of BRCA in 3–6% of EOC [47]. In contrast to somatic mutations, epigenetic silencing by promoter methylation is a dynamic process and may be harder to quantify. Studies report prevalence in the

However, BRCA1 and 2 are just two of many proteins involved in HR. TCGA undertook exomic analysis of 316 ovarian cancers as well as studies of promoter methylation, RNA expression and copy number changes [45]. Pathway analysis demonstrated that 51% of tumours had either mutations or silencing of components in the HR pathways. (**Figure 2**).

HR deficiency (HRD) in EOC provides a target that can be exploited therapeutically. It was noted that cells with non-functioning PARP develop increased nuclear foci of Rad51 implying an increased burden of lesions being repaired by HR in these cells [48]. Farmer et al. [49] tested

treatment [40]. Prospective validation is needed for this and other candidate markers.

is beyond the scope of this chapter but the process of HR is reviewed here [43]

**4.1. Homologous recombination repair in ovarian cancer**

Pazopanib inhibits VEGR1,2 and 3, c-Kit and PDGFR. The AGO-OVAR 16 study [35] evaluated first-line maintenance pazopanib. PFS was 17.9 months for pazopanib compared to 12.3 months for control. Grade 3/4 adverse events were significantly higher for pazopanib including hypertension (30.8%), neutropenia (9.9%) and diarrhoea (8.2%). Discontinuation due to AEs occurred in 33% in the pazopanib arm compared to 5.6% in the placebo arm. Regulatory approval filing was withdrawn due to perceived imbalance in benefit–risk ratio.

Other VEGFR TKIs have been studied in ovarian cancer [35]. Nintedanib was given in the first-line setting with chemotherapy and then maintenance. Again, a PFS benefit was seen but no significant OS advantage [36]. Other multitargeted VEGFR TKIs such as sunitinib and sorafenib have also been studied with similar outcomes. As a class the TKIs appear to have some effect however their multi-targeted nature and unpredictable bioavailability means that their perceived risk:benefit ratio has not led to any regulatory approvals as yet.

#### **3.3. Other antiangiogenic strategies**

The Ang-Tie pathway is distinct from the VEGF axis, involved in vascular remodelling. Trebananib is peptide-Fc fusion protein that binds Angiopoietin 1 and 2 and prevents interaction with Tie on endothelium. Although promising results were seen in phase II [37], a phase III trial (TRINOVA-2) [38] failed to meet its PFS endpoint and a third terminated early for futility (NCT01493505).

#### **3.4. Combination therapy**

Vascular disrupting agents (VDAs), in contrast to inhibiting formation of new vessels, target existing tumour vasculature. The VDA's combretastatin and fosbretabulin disrupt the endothelial cytoskeleton (by binding tubulin) aiming to cause endothelial detachment and eventual vessel obstruction. Tumour vasculature lacks pericytes and smooth muscle making them selectively susceptible. Fosbretabulin is being examined for synergy with bevacizumab and chemotherapy in platinum-resistant disease in a phase II/III trial (NCT02641639).

There is pre-clinical rationale for the combination of VEGF-targeted therapy with poly (ADPribose) polymerase inhibitors (PARPi); anti-VEGF induced hypoxia can impair DNA repair and sensitize otherwise insensitive cells to PARPi. In a phase II trial of olaparib and cediranib [39] PFS with the combination was prolonged (17.7 vs. 9.0 months) and, consistent with preclinical rationale, the difference was most marked in BRCA wild-type patients. Grade 3/4 toxicity however was 70% with the combination vs. 7% for olaparib monotherapy. The combination is currently undergoing phase III testing (ICON 9). The combination of bevacizumab and olaparib in first-line maintenance is also being studied (NCT02477644).

Combining VEGF blockade and immunotherapy also has pre-clinical rationale (see below). Combinations of anti-angiogenesis and chemotherapy have been discussed in the paragraphs above. Of note, an early phase trial of pazopanib with carboplatin/paclitaxel was terminated early because of toxicity (GI perforations and myelotoxicity).

#### **3.5. Predictive biomarkers in anti-angiogenic therapy**

Given the relatively modest median PFS benefits and lack of OS benefit in some trials combined with toxicity and economic considerations, biomarkers for patient selection are needed. None have yet been validated for routine use although many have been suggested. Studies have been retrospective and focussed on different markers including gene-expression signatures, serum and tissue proteomic biomarkers. There have been some intriguing results including a 63-gene signature that identifies an immune subgroup that may be harmed by bevacizumab treatment [40]. Prospective validation is needed for this and other candidate markers.
