Incorporating VEGF-targeted therapy in advanced urothelial cancer

Abstract

Patients with relapsed or refractory urothelial carcinoma (UC) have poor prognosis coupled with few options for systemic treatment. The role of angiogenesis in the evolution of cancers has been established, and studies have shown that it plays a key role in the pathogenesis of UC. Many targeted agents have been used in phase I–II trials for the treatment of UC, with encouraging but modest results. Recently, studies combining angiogenesis inhibitors with other chemotherapeutic agents were able to achieve objective responses higher than most commonly used second-line therapies in UC. Future efforts in investigating these therapies in UC rely on identification of biomarkers and other predictors of response to anti-VEGF therapy.

Introduction

Bladder cancer is the ninth most common malignancy in the world [Torre et al. 2015], with an annual incidence of almost 75,000 new cases in the United States and an estimated 16,000 deaths each year [Siegel et al. 2015]. In Europe, an estimated 118,000 cases and 52,000 deaths from bladder cancer occurred in 2012 [Marcos-Gragera et al. 2015].

The predominant histological subtype, urothelial or transitional cell carcinoma, accounts for 90% of all bladder cancers, with other less-common histologic subtypes being squamous cell carcinoma, adenocarcinoma and small cell carcinoma. Less frequently, urothelial carcinoma can also arise from other sites in the urinary tract such as the renal pelvis, ureter and urethra and the term ‘urothelial carcinoma’ (UC) is commonly applied in clinical practice to refer to all the tumors in the urinary tract.

Approximately 70% of urothelial cancers present as ‘superficial’ or non-muscle invasive tumors, a term used to denote their invasion into the submucosal layer of the bladder wall without involvement of the muscularis propria [Kirkali et al. 2005]. Patients presenting with superficial disease have a favorable prognosis, and are treated successfully with intravesical therapy and tumor resection. However, many patients with superficial disease subsequently recur, with 10–20% ultimately progressing to muscle-invasive disease [Cookson et al. 1997]. A total of 25% of patients present with advanced muscle-invasive or metastatic disease, and carry a poor prognosis with an estimated median survival of 14 months [Von Der Maase et al. 2005]. The standard of care for the treatment of metastatic UC is cisplatin-based chemotherapy regimens that include combinations such as gemcitabine and cisplatin (GC) and methotrexate, vinblastine adriamycin, cisplatin (MVAC). While these regimens have initial high response rates ranging from 40% to 70%, with median progression-free survival (PFS) of approximately 8 months and a 5-year overall survival (OS) of 15% [Von Der Maase et al. 2000, 2005].

The survival outlook for patients with metastatic UC currently remains poor, with only modest responses to first line therapy and no standard second line therapies available. Molecular pathways underlying the evolution of UCs have recently been elucidated, and ongoing clinical trials have focused on exploring biologic and targeted agents for treatment of this disease. Of the many pathways explored for understanding the pathogenesis of bladder cancer and its therapeutic implications, there has been significant data to implicate angiogenesis as a key contributing factor in the disease biology, and as a rational target for targeted therapy. This article will focus on the role of angiogenesis in the pathogenesis of UC and review the published data from clinical trials evaluating anti-VEGF directed therapy in UC.

Angiogenesis

Angiogenesis is an essential physiological process that occurs during normal development and tissue repair. It involves the proliferation of endothelial cells for the formation of new blood vessels, which deliver oxygen and nutrients to the tissues. Under normal physiological conditions, endothelial cells are quiescent, maintaining a nonangiogenic phenotype. Stressors such as tissue growth, inflammation, immune cell activation and hypoxia transform the endothelial cells to an angiogenic phenotype resulting in new blood vessel formation.

Malignant tissues induce a similar ‘switch’ in the endothelial cells in order to maintain adequate vascular framework for the maintenance of nutrient and oxygen supply. There is extensive experimental evidence to support the claim that tumors and metastases are angiogenesis dependent [Folkman, 1985, 1992; Hanahan et al. 1996]. According to Folkman, several angiogenesis inhibitors that maintain a quiescent vasculature in normal cells are downregulated during tumorigenesis, shifting the balance in favor of the angiogenic inducers or activators, with subsequent endothelial cell proliferation and neovascularization [Hanahan et al. 1996].

Many proteins have been identified as angiogenic activators, including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), angiogenin, transforming growth factor (TGF)-α, TGF-β, tumor necrosis factor (TNF)-α, platelet-derived endothelial growth factor, granulocyte colony-stimulating factor, placental growth factor (PGF), interleukin (IL)-8, hepatocyte growth factor, and epidermal growth factor [Polverini et al. 1984; Folkman et al. 1987; Blood and Zetter 1990; Liotta et al. 1991].

VEGF is a powerful angiogenic agent in normal and malignant tissues that plays an important role in neovascularization. The VEGF family consists of five glycoproteins, namely VEGF-A, VEGF-B, VEGF-C, VEGF-D, and PGF. The best characterized in this family is VEGF-A, which is produced by a number of different cell types (e.g. epithelial cells, inflammatory and hematopoietic cells, endothelial cells), and acts selectively on vascular endothelial cells, stimulating angiogenesis in vitro and in vivo [Dvorak et al. 1995; Ferrara et al. 2003; Hicklin et al. 2005; Ellis et al. 2008].

The VEGF ligands bind to three structurally similar type III receptor tyrosine kinases, designated VEGFR1 (also known as FLT1), VEGFR2 (also known as KDR) and VEGFR3 (also known as FLT4) and activate a network of distinct downstream signaling pathways that leads to endothelial cell proliferation, migration, survival and angiogenesis [Kowanetz et al. 2006]. VEGFR1 and VEGFR2 have a role in angiogenesis while VEGFR3 mostly mediates signals related to lymphangiogenesis through activation of the PI3K/AKT/MAPK pathway [Aldebasi et al. 2013].

VEGF also induces permeability in endothelial cells, enabling extravasation of plasma proteins into the extravascular space, leading to clotting and deposition of a fibrin gel that serves as a provisional matrix for the growth of new blood vessels and mesenchymal cells [Dvorak et al. 1995]. In the VEGF family, VEGF-A has been most extensively characterized for its role in angiogenesis, and as a pharmacological targeted for anti-angiogenic therapy.

Angiogenesis in bladder cancer

Chodak and colleagues were the first to demonstrate the presence of a proangiogenic phenotype in patients with transitional cell carcinoma. They noted that that urine from patients with transitional-cell carcinoma of the bladder was able to stimulate capillary–endothelial–cell migration in vitro [Chodak et al. 1981]. A number of proangiogenic factors have been identified in bladder cancer cell lines and tissues and the levels of VEGF [Zaravinos et al. 2012], hypoxia-inducible factor (HIF-1a) [Chai et al. 2008], basic fibroblast growth factor-2 (bFGF) [Zaravinos et al. 2012], platelet-derived growth factor (PDGF) [Mizutani et al. 1997; Li et al. 2001], matrix-metalloproteinase-9 [Reis et al. 2012], thrombospondin-1 [Grossfeld et al. 1997] and IL-8 [Reis et al. 2012] have been associated with poor patient outcomes.

Campbell and colleagues have shown that VEGF and bFGF appear to be two primary inducers of angiogenesis in bladder cancer cell lines, and high levels of these have been noted in the urine collected from bladder cancer patients [Williams et al. 2000; Nguyen et al. 1993; O’brien et al. 1995, Campbell et al. 1998; Crew et al. 1999]. Serum levels of VEGF have been correlated with tumor stage and grade, vascular invasion, presence of metastases, and inversely correlated with disease-free survival [Bernardini et al. 2001].

Angiogenesis has been quantified using microvessel density (MVD) in tissues, thus providing prognostic information by relaying the tumor’s ability to grow and metastasize. MVD has been demonstrated to be a useful prognostic indicator in a variety of malignancies including melanoma [Folkman, 1987], breast cancer [Weidner et al. 1992], and prostate cancer [Weidner et al. 1993]. Increased MVD has been associated with tumor progression and poor survival [Weidner et al. 1993; Barnhill et al. 1998]. In bladder cancer, MVD has been noted to be an independent prognostic indicator, correlating with grade, stage, potential for metastases and poor survival [Bochner et al. 1995; Jaeger et al. 1995; Canoglu et al. 2004].

Inhibition of VEGF pathway

Since there is considerable evidence to show that tumor growth and metastasis is angiogenesis dependent, angiogenesis is a relevant target for anticancer therapy. Recognition of the VEGF pathway as a key regulator of angiogenesis has led to the development of several VEGF-targeted agents such as anti-VEGF antibodies (bevacizumab), soluble VEGF ‘decoy’ receptors (aflibercept), anti-VEGFR antibodies (ramucirumab) and small-molecule tyrosine kinase inhibitors (TKIs) (sunitinib, pazopanib).

The antitumor effect of VEGF inhibition occurs as a result of multiple mechanisms, including inhibition of endothelial cell proliferation [Mancuso et al. 2006] and endothelial cell apoptosis [Gerber et al. 1998; Fujio et al. 1999]. It also leads to ‘normalization’ of tumor vasculature [Jain, 2001], which results in temporary improvement of blood flow and oxygen delivery to the tumor, thus potentially improving chemotherapy delivery to the tumor. Inhibition of VEGF leads to reduced blood vessel leakiness, and therefore reduced tumor interstitial pressure. The net effect of improved tumor blood flow and reduced tumor interstitial pressure leads to enhanced delivery of chemotherapeutic agents to the tumor cells, thus supporting the rationale of combining anti-VEGF therapies with cytotoxic chemotherapy.

Since VEGF signaling leads to endothelial cell proliferation and survival, it is important in physiological functions such as angiogenesis, maintenance of vascular tone, and in sustaining the integrity of vascular lining in the cardiovascular system, including the vasculature within the glomeruli. Therefore, inhibition of VEGF signaling leads to disruption of normal angiogenesis, vascular homeostasis, vascular tone and permeability. Consequently, the clinical side effects of VEGF inhibition include hypertension, arterial thromboembolic events, cardiac dysfunction, compromised wound healing and tissue repair, and proteinuria.

Here we will summarize the anti-VEGF therapies that have been investigated in UC, and their implications in the treatment of this disease (Table 1).

Table 1.

Phase I–II trials investigating anti-angiogenic agents in urothelial cancers (UC).

Drug	Regimen	Setting	N (%)	ORR	Median PFS (months)	Median OS (months)
Anti-VEGF antibodies
Bevacizumab	Gemcitabine + cisplatin + bevacizumab [Hahn et al. 2011]	First-line	43	72	8.2	19.1
	Gemcitabine + carboplatin + bevacizumab [Balar et al. 2013]	First-line	51	49	6.5	13.9
Aflibercept	Aflibercept [Twardowski et al. 2010]	Second-line	22	4.5	2.79	n/a
Small-molecule tyrosine kinase inhibitors
Sunitinib	Gemcitabine + cisplatin + sunitinib [Geldart et al. 2015]	First line	63	64	8	12
	Gemcitabine + cisplatin + sunitinib [Galsky et al. 2013]	First line	36	49	Study terminated secondary to toxicity
	Sunitinib [Bellmunt et al. 2011]	Second line	38	8	4.3	8.1
	Sunitinib [Gallagher et al. 2007]	Second line 50 mg/day (4 weeks on, 2 weeks off)	45	7	2.4	7.1
		37.5 mg daily	32	3	2.3	6
Sorafenib	Sorafenib [Sridhar et al. 2011]	First line	17	0	1.9	5.9
	Gemcitabine + cisplatin + sorafenib	First line	40	52.5	6.2	11.2
	Gemcitabine + cisplatin + placebo [Krege et al. 2014]		49	47	6	10.4
Pazopanib	Pazopanib [Necchi et al. 2012]	Second line	41	17.1	2.6	4.7
	Pazopanib [Pili et al. 2013]	Second line	18	0	1.86	Study terminated early
	Vinflunine + pazopanib [Gerullis et al. 2013]	Second line	5	0	Study terminated early
	Pazopanib + paclitaxel [Srinivas et al. 2015]	Second line	28	54	6.2	10
Antibodies targeting VEGFR
Ramucirumab	Docetaxel versus docetaxel + ramucirumab [Petrylak, 2015]	Second line	44, 46	4.5, 19.6	2.4, 5.1	Pending
VEGFR tyrosine kinase inhibitors
Vandetanib	Docetaxel + vandetanib versus docetaxel + placebo [Choueiri et al. 2012]	Second line	142	7, 11	2.56, 1.58	5.85, 7.03

ORR, overall response rate; OS, overall survival; PFS, progression-free survival; VEGF, vascular endothelial growth factor.

Anti-VEGF monoclonal antibodies

Bevacizumab

Bevacizumab is a humanized monoclonal antibody directed against VEGF that recognizes all isoforms of VEGF-A, that is currently approved by the FDA for treatment of patients with metastatic colorectal cancer [Hurwitz et al. 2004], non-small cell lung cancer [Sandler et al. 2006] and renal cell carcinoma [Escudier et al. 2007b].

Given its therapeutic potential in combination with chemotherapy, bevacizumab was evaluated for the treatment of metastatic UC in an initial phase II trial [Hahn et al. 2011]. A total of 43 patients with metastatic UC were treated with bevacizumab in combination with GC in the first line setting, and a complete response (CR) was noted in eight patients (19%), partial response (PR) in 23 patients (53%), and an overall response rate of 72%. With a median follow-up of 27.2 months, the median PFS was 8.2 months [95% confidence interval (CI) 6.8–10.3 months] and median OS of 19.1 months (95% CI 12.4–22.7 months). This combination was able to achieve a higher PFS and OS than GC combination (PFS 7.7 months; OS 14 months) that is standard of care in this setting [Von Der Maase et al. 2005]. The combination of these agents, however, resulted in significant toxicities, which included grade 3–4 neutropenia (35%), thrombocytopenia (12%), anemia (12%), grade 3–5 deep vein thrombosis/pulmonary embolism (21%), hemorrhage (7%), cardiac (7%), hypertension (5%), and proteinuria (2%).

Similarly, the combination of bevacizumab with gemcitabine and carboplatin in a phase II trial (n = 51), and yielded a 49% response rate (3 complete; 20 partial), median PFS of 6.5 months and median OS of 13.9 months [Balar et al. 2013]. While the study did not meet its predesignated PFS, the median OS was greater than expected. Treatment-related grade 3 or 4 toxicity occurred in 39% of patients with the most common toxicity being neutropenia that occurred in 16 patients (31%). Grade 3 or 4 vascular thrombotic events (VTEs) occurred in 10 patients (20%). Results from a randomized double-blinded phase III trial comparing gemcitabine, cisplatin and bevacizumab with gemcitabine, cisplatin and placebo in patients with advanced transitional cell carcinoma are currently pending.

These trials indicate the potential of increased objective responses when bevacizumab is added to platinum-based chemotherapy for the treatment of metastatic disease. However, patients with advanced UC are elderly and have several coexisting comorbidities, end organ impairment or poor performance status, which significantly impairs the use of this combination therapy given its side effect profile.

Aflibercept

Aflibercept is a recombinant fusion protein that contains the VEGF-binding domains of VEGFR1 and VEGFR2 fused to the Fc domain of human IgG1, and functions as a soluble decoy receptor for VEGF. Aflibercept inactivates multiple members of the VEGF family including VEGF-A, VEGF-B, and PlGF by preventing binding to their receptors, with a potentially higher affinity for VEGF-A when compared with anti-VEGF monoclonal antibodies [Holash et al. 2002]. In nonclinical studies, aflibercept was demonstrated to block tumor growth in vivo with a potent antiangiogenic action [Kim et al. 2002].

Currently, aflibercept is FDA approved for the treatment of metastatic colorectal cancer in combination with FOLFIRI, for patients who have progressed following prior oxaliplatin-based therapy [Twardowski et al. 2010; Van Cutsem et al. 2012].

A phase II trial by the California Cancer Consortium evaluated 22 patients with advanced UC who were treated with single-agent aflibercept. The results of this study failed to demonstrate any single-agent activity of aflibercept in UC, since the treatment yielded an overall response rate of 4.5% (95% CI 0.1–22.8%) and a median PFS of 2.79 months (95% CI 1.74–3.88). This study thus failed to establish a role for aflibercept in management of patients with UC.

Small-molecule TKIs

Small-molecule TKIs are orally bioavailable molecules that have demonstrated promising antitumor activity in many malignancies, such as renal cell carcinoma, thyroid carcinoma, hepatocellular carcinoma, and pancreatic neuroendocrine carcinoma. Apart from VEGFR inhibition, they also inhibit other tyrosine kinase receptors, such as platelet derived growth factor receptor (PDGFR), c-kit receptor, epidermal growth factor receptor (EGFR), fibroblast growth factor receptor (FGFR). This broader specificity of TKIs is attributable to the structural similarity of the catalytic ATP-binding site region amongst the tyrosine kinase superfamily [Mendel et al. 2003; O’Farrell et al. 2003; Sridhar et al. 2005; Wilhelm et al. 2004; Adnane et al. 2006; Kumar et al. 2005]. Given that target specificity is not limited to VEGFR tyrosine kinases, these are also referred to as multitargeted TKIs. The simultaneous inhibition of multiple signaling pathways enhances the antitumor and anti-angiogenic activity of these agents when compared to monoclonal antibodies, but also broadens its toxicity profile. The disadvantages of TKIs include short half-lives requiring frequent (daily) administration, and side effects attributable to multitarget inhibition, such as diarrhea, hand–foot syndrome and cardiovascular toxicities.

Sunitinib

Sunitinib is a multitargeted receptor TKI selective for VEGFR1, 2 and 3, PDGFR-α and -β, Flt3, RET, and Kit [Mendel et al. 2003; O’farrell et al. 2003]. Preclinical studies with sunitinib in UC cell lines and UC xenograft models have revealed its antitumor activity alone and in synergy with other antineoplastic agents. In an orthotopic mouse bladder cancer model, the use of sunitinib was associated with inhibition of bladder tumor growth and prolonged survival [Chan et al. 2012].

Sonpavde and colleagues used sunitinib and cisplatin alone and in combination against human urothelial carcinoma cell lines and noted that tumors treated with sunitinib alone or in combination with cisplatin had higher expression of cleaved caspase 3, suggesting increased apoptosis [Sonpavde et al. 2009]. These cell lines also displayed significantly reduced ki-67 and CD31 expression compared with control untreated tumors with single agent or combination therapy, suggesting reduced cellular proliferation and angiogenesis.

In another study several UC cell lines were exposed to sunitinib alone or simultaneously with cisplatin or gemcitabine. In all cell lines tested, sunitinib showed a dose- and time-dependent antitumoral effect. Poorly differentiated cell lines demonstrated resistance to sunitinib, but showed higher sensitivity to cisplatin. Sunitinib also exhibited a superior antitumor potential in combination with gemcitabine [Yoon et al. 2011]. Sunitinib as a single agent has also been shown to suppress growth in cisplatin and adriamycin resistant UC cell lines through suppression of ERK1/2 phosphorylation [Takeuchi et al. 2012].

The use of sunitinib for the treatment of UC has been studied in multiple phase II trials in the first- and second-line settings. In the SUCCINT study, sunitinib was added to the standard of care GC for the treatment of 63 patients with advanced/metastatic UC [Geldart et al. 2015]. A total of 63 patients were enrolled and treated with up to six cycles of cisplatin 70 mg/m² (day 1), and gemcitabine 1000 mg/m² (days 1 and 8) in a 21-day cycle. Sunitinib was administered orally at 37.5 mg daily from days 2 through 15 of the chemotherapy cycle. However, due to high rates of grade 3–4 hematologic toxicities, the dose was reduced to 25 mg later in the study. The study had an overall response rate of 64%, but the increased incidence of Grade 3–4 toxicities (predominantly hematologic) impeded the safe administration of this combination. The study did not meet its prespecified endpoint of PFS at 6 months, and further study of the combination in a phase III trial was not recommended.

In another phase II study, Galsky and colleagues studied the combination gemcitabine (800 mg/m² on days 1 and 8 of a 21-day cycle) and cisplatin (60 mg/m² on day 1 of a 21-day cycle) with sunitinib (37.5 mg daily on days 1–14) as first-line treatment for metastatic disease (trial 1) and in the neoadjuvant setting for muscle invasive disease (trial 2) [Galsky et al. 2013]. In the trial evaluating the combination as first line treatment for metastatic disease, the response rate was 49% (95% CI 31–67%); and the pathologic CR obtained in the neoadjuvant setting was 22% (2/9). Grade 3–4 hematologic toxicities occurred in 70% (23/33) of patients in trial 1 and 22% (2/9) of patients in trial 2. Because of excessive toxicities, the combination was not well tolerated and the study was closed early.

As a single agent, sunitinib was studied in a multicenter phase II trial as first-line treatment in patients with metastatic urothelial cancer ineligible for cisplatin based chemotherapy. Sunitinib was administered daily at 50 mg for 4 weeks with a 2-week break prior to the next cycle. Of the 38 patients in the study, 3 showed (8%) PRs and 19 (50%) patients showed stable disease (SD), with 17 (45%) of them maintaining a response for ⩾3 months. The clinical benefit obtained from this treatment (PR + SD) was 58%. Median time to progression (TTP) was 4.8 months and median OS 8.1 months. Treatment with single-agent sunitinib was well tolerated, with toxicities consistent with its profile [Bellmunt et al. 2011].

Different dosing regimens of sunitinib have been studied in clinical trials, in order to determine the efficacy of its antitumor activity and tolerability. In UC, a phase II trial was conducted to evaluate sunitinib 50 mg/day given 4 weeks on and 2 weeks off (cohort A) versus 37.5 mg daily (cohort B) in patients with advanced disease. In both the cohorts, sunitinib did not achieve the predetermined threshold of ⩾20% response rate, however, 29% had a clinical benefit (defined as PR or SD lasting >3 months) from treatment indicating antitumor activity of sunitinib.

Thus, while sunitinib has demonstrated promising preclinical and clinical activity against UC, its clinical application has been limited secondary to lack of efficacy small clinical trials, and its toxicity profile, which has limited its tolerability, especially when used in combination with other antitumor agents.

Sorafenib

Sorafenib is an oral multikinase inhibitor that targets the Ras/Raf/extracellular signal regulated kinase (ERK) signaling pathway at the level of Raf kinase, and vascular endothelial growth factor receptors (VEGFR-1, 2, and 3) and PDGFR thus inhibiting cellular proliferation and angiogenesis. Sorafenib also has activity against c-KIT and FLT3 kinases [Wilhelm et al. 2004; Sridhar et al. 2005; Adnane et al. 2006]. It has demonstrated safety and efficacy in clinical trials, it is currently approved for the treatment of renal cell carcinoma and hepatocellular carcinoma [Abou-Alfa et al. 2006; Escudier et al. 2007a; Llovet et al. 2008].

In UC, the aberrant activation of the ERK pathway has been documented secondary to mutations or overexpression of Ras, mutations of Raf kinase, or upstream overexpression of the EGFR or HER2 cell surface receptors [Viola et al. 1985; Vageli et al. 1996; Bue et al. 1998; Simon et al. 2001; Oxford et al. 2003]. Thus, sorafenib is a rational therapeutic choice for the treatment of UC given its targeting of the VEGF and ERK pathways. However, as a single agent, sorafenib has failed to demonstrate any objective responses in patients with advanced UC [Dreicer et al. 2009; Sridhar et al. 2011].

In a randomized double-blind multicenter phase II study comparing the combination of GC with sorafenib or placebo, in patients with locally advanced and/or metastasized urothelial cancer, 40 patients were recruited in the sorafenib arm, and 49 patients in the placebo arm. The trial found no significant differences between the two arms, with overall response rate in the sorafenib arm being 52.5% (CR 12.5%; PR 40%) and 47% in the placebo arm (CR 12%; PR 35%). The median PFS with sorafenib was 6.3, and 6.1 months with placebo. The OS with sorafenib was 11.3 months, and with placebo it was 10.6 months. Toxicity was reported to be moderately higher in the sorafenib arm, with predominant symptoms being diarrhea and hand foot syndrome. Overall, the study failed to meet its primary endpoint of improvement in PFS [Krege et al. 2014].

Pazopanib

Pazopanib is an orally bioavailable inhibitor of VEGFRs-1, 2 and 3, PDGFR-α and -β and c-Kit tyrosine kinases, that has demonstrated antitumor and anti-angiogenic activity in multiple human tumor xenografts in vivo [Kumar et al. 2005]. In a phase I study with advanced solid tumors, pazopanib was well tolerated with antitumor activity demonstrated in multiple tumor types. Currently, pazopanib is approved for the treatment of metastatic renal cell carcinoma and soft tissue sarcomas [Sternberg et al. 2010; Van Der Graaf et al. 2012].

In vitro studies with bladder tumor cell lines have shown cathepsin B activation and autophagic cell death when treated with pazopanib [Santoni et al. 2013]. Another study has also demonstrated the synergistic efficacy of pazopanib with docetaxel in docetaxel-resistant bladder cancer cells.

Several clinical trials have evaluated pazopanib as a single agent and in combination for the treatment of UC. In a phase II study conducted by Necchi and colleagues, 41 patients with relapsed/refractory UC were administered pazopanib 800 mg daily. Seven (17.1%) of the patients had a PR to treatment, and the most frequent grade 3 adverse events were hypertension, fatigue and fistulization [Necchi et al. 2012]. In another phase II study with 19 patients, pazopanib did not show any significant antitumor activity [Pili et al. 2013].

A phase I trial was conducted to study the safety and efficacy of combining pazopanib with vinflunine in patients with relapsed UC in the second-line setting. The study was designed with a 3 + 3 dose escalation plan, with four dose levels of pazopanib, starting at 200 mg. Vinflunine was dosed at 280 mg/m² for the first dose and 320 mg/m² every 3 weeks thereafter. Unfortunately, at the starting dose level of 200 mg of pazopanib, dose limiting toxicities were observed in two of five patients, and the study was interrupted at dose level 1 for safety reasons [Gerullis et al. 2013].

The most encouraging results with the application of pazopanib in the treatment of UC come from a recently conducted phase II trial, which combined pazopanib with paclitaxel for patients with advanced disease [Srinivas et al. 2015]. In the 28 evaluable patients in the study, a CR was observed in 3 patients and PR in 12 patients, resulting in an overall response rate of 54% (95% CI 33.9–72.5). SD was observed in 11 patients and two patients had progressive disease. The median PFS was 6.2 months and median OS was 10 months. The combination was also well tolerated, with hematological toxicity being the most common adverse event. The results from this study are worthy of further investigation for the treatment of UC in a phase III randomized trial.

Antibodies targeting VEGFR

Ramucirumab

Ramucirumab is an entirely humanized high-affinity monoclonal antibody directed against the extracellular domain of VEGFR2 that has been recently approved for the treatment of patients with advanced gastric or gastroesophageal junction adenocarcinoma progressing after first-line chemotherapy [Fuchs et al. 2014]. In a recent phase II study, patients with advanced UC were treated with docetaxel (n = 44) versus docetaxel with ramucirumab (n = 46). In the interim results presented in 2015, docetaxel and ramucirumab reduced the risk of disease progression, and demonstrated an improving median PFS (5.1 versus 2.4 months). The overall response rate for the combination arm was 19.6%, versus 4.5% for the docetaxel arm (p = 0.0502), and the OS data is still pending [Petrylak, 2015].

VEGFR TKIs

Vandetanib

Vandetanib is a TKI of VEGFR2, of the EGFR, and of the RET tyrosine kinase. Early clinical trials with vandetanib alone or in combination with docetaxel have demonstrated an acceptable adverse effect profile and antitumor activity [Morabito et al. 2009]. Randomized studies in non-small cell lung cancer with vandetanib and docetaxel resulted in a significant prolongation of PFS compared with docetaxel alone [Heymach et al. 2007]. Vandetanib is currently approved by the US Food and Drug Administration (FDA) for the treatment of advanced medullary thyroid cancer [Herbst et al. 2010].

Vandetanib was evaluated in advanced urothelial cancer in a phase II study whose primary objective was to determine whether vandetanib 100 mg plus docetaxel 75 mg/m² intravenously every 21 days prolonged PFS versus placebo plus docetaxel. In this study, the median PFS was 2.56 months for the docetaxel plus vandetanib arm versus 1.58 months for the docetaxel plus placebo arm, and the hazard ratio for PFS was 1.02 (95% CI 0.69–1.49; p = 0.9). Overall response rate and OS were not different between both arms. Grade 3 or higher toxicities were more commonly seen in the docetaxel plus vandetanib arm. Thus, the combination failed to establish any significant activity in UC [Choueiri et al. 2012].

Cabozantinib

Cabozantinib (XL184) is a multitargeted tyrosine kinase directed against VEGFR2, c-MET and RET that has preclinical activity against urothelial carcinoma, and is currently in clinical trials [ClinicalTrials.gov identifier: NCT02496208].

Conclusion

Till date, patients with urothelial carcinoma have few treatment options, with cisplatin-based chemotherapy regimens being the primary treatment option for these patients with modest responses [Von Der Maase et al. 2000, 2005]. Not all patients with muscle invasive or metastatic disease are eligible for cisplatin-based therapies, since poor performance status and impaired renal function are common in this patient population. Exploration of the disease biology in UC has led to investigation of many molecular pathways as potential therapeutic interventions for treatment of this disease.

Angiogenesis has a central role in the growth and progression of malignancies, including UC. Many studies have established the importance of the VEGF pathway in the evolution of bladder tumors from early to advanced stages, and have also associated angiogenesis with adverse prognosis in this disease. With therapeutic advances, targeting the VEGF pathway with monoclonal antibodies and TKIs provided a novel treatment approach for the treatment of UC.

However, despite the strong clinical rationale and availability of agents, trials in UC with antiangiogenic agents have been met with disappointing results. These trials have not shown significant improvement in treatment outcomes, and/or have been met with poor tolerability due to their toxicity, especially when administered with other chemotherapeutic agents. Since patients with metastatic UC usually present with poor performance status and multiple comorbidities, this disease population represents a challenge for engagement in clinical trials given the toxicity noted with this class of medications.

Despite these limitations, two recent studies have shown encouraging results in advanced UC [Petrylak, 2015; Srinivas et al. 2015]. These studies were able to achieve objective responses higher than most commonly used second-line therapies in UC, indicating that the antitumor activity with anti-VEGF agents can be achieved in combination with other chemotherapeutic agents.

Therefore, with our current understanding of anti-VEGF therapies in bladder cancer, future efforts in investigating these therapies in UC should focus on identifying biomarkers and other predictors of response to anti-VEGF therapy, and select the patient population entering the clinical trials.