Urinary Bladder Cancer Overview - Signaling Pathway. Diagnostics Marker. Targeted Therapy and Clinical Trials.

Fig.1 Urinary bladder cancer signaling pathway. Targeted agents (listed in orange boxes) include those in clinical use (colored in green) and those in preclinical or early phase development (colored in red) for the treatment of urinary bladder cancer.

An Introduction to Urinary Bladder Cancer

Urinary bladder cancer (BC) is one of the most common cancers and mainly occurs in men, which usually affects older adults though it can happen at any age. Bladder cancer most often begins in the urothelial cells that line the inside of bladder. Although this cancer commonly appears in the bladder, it also can occur in other parts of the urinary tract drainage system. The symptoms of bladder cancer often include blood in urine (hematuria), painful urination, pelvic pain, back pain and frequent urination. Main causes of the cancer include smoking and other tobacco use, exposure to chemicals, past radiation exposure, chronic irritation of the lining of the bladder, and parasitic infections. The type of bladder cell where cancer begins determines the type of bladder cancer, and types of bladder cancer include urothelial carcinoma, squamous cell carcinoma and adenocarcinoma. Most of bladder cancer cases can be diagnosed at an early stage and is highly treatable. However, even early-stage bladder cancer may recur in the bladder. Thus, people with bladder cancer needs more effective approaches such as targeted therapy.

1 Main Signaling Pathways in Urinary Bladder Cancer Therapy

1.1 Receptor tyrosine kinase signaling cascade

MDA-9/synthein expression has been found to regulate EGFR signaling in bladder cancer associated with stage, grade, and invasion. Bladder cancer progress often accompanies the alterations of β-catenin, E-cadherin, vimentin, claudin-1, ZO-1, and T-cell factor-4 (TCF4) levels. The loss of Sh3gl2 (endophilin A1), a regulator of EGFR endocytosis, is associated with in muscle-invasive bladder cancer (MIBC). Silencing of Sh3gl2 can promote the proliferation and colony formation, and inhibit EGF-induced EGFR internalization, and increases EGFR activation. ERBB2 acts as an independent predictor for shorter cancer-specific survival (CSS). Overexpression of FGFR3 protein has been found in post-RC MIBC patients and correlates with shorter disease-free survival (DFS) and OS. Decreased membranous Met level is associated with unfavorable tumor phenotype.

1.2 PI3K/AKT/mTOR signaling cascade

PTEN, phosphorylated p-Akt, p-mTOR, p-p70 ribosomal S6 kinase, and p-4E-binding protein 1 (4EBP1) have been assessed to reveal that p-4E-BP1 and the tumor stage are independently related to recurrence-free survival (RFS). The activity of mammalian target of rapamycin complex 2 (mTORC2) is significantly overexpressed in MIBC. The loss of tuberous sclerosis complex 1 (TSC1) function correlates with MIBC response to everolimus. Two activating mTOR mutations E2014K and E2419K within the same MIBC can specifically cause particular mTOR signaling dependency of MIBC and consequently a specific sensitivity to pathway inhibition with everolimus. GSK-3b nuclear is highly associated with high-grade tumors, advanced stage of BC, metastasis, and worse cancer-specific survival (CSS), and aberrant nuclear accumulation of GSK-3b has been found in 91% of MIBC.

1.3 VEGF/VEGFR signaling cascade

Patients with MIBC T2 stage show lower expression levels of VEGF-C. The expression of VEGFR2 is significantly higher in MIBC. Patients with higher levels of VEGF, VEGFR1, and VEGFR2 tend to have poorer RFS in BC. Accordingly, some agents that block the molecular machinery of VEGF-VEGFR signaling cascade show considerable promise in MIBC clinical trials.

Urinary Bladder Cancer Diagnosis

2.1 Molecular markers for urinary bladder cancer

Non-muscle-invasive and muscle-invasive bladder cancers possess distinct pathways in carcinogenesis. One pathway involves mutation of FGF receptor 3, which leads to low-grade non muscle invasive papillary tumors that often recur but rarely invade. By contrast, muscle-invasive bladder cancer and carcinoma display deletions or mutations of the TP53, RB1, ERBB2, or PTEN. HRAS gene is the first human oncogene identified from a human bladder cancer cell line, which is frequently overexpressed in non-muscle-invasive cancer. FGFR3 (fibroblast growth factor receptor 3) is a receptor tyrosine kinase that is one of the most frequently mutated genes in bladder cancer. FGFR3 involves in bladder cancer from low-grade stage. TP53 is a transcription factor with many functions, such as induction of apoptosis, inhibition of cell proliferation, and arrest of the cell cycle. Nuclear accumulation of TP53 can be used as a predicting factor of poor prognosis in advanced bladder cancer. As a tumor suppressor gene, RB1 is a negative regulator of the cell cycle, and its alterations are related to carcinogenesis in several cancers. Loss of RB1 expression in muscle-invasive bladder cancer has been an adverse prognostic biomarker. TSC1 is a tumor suppressor gene of mTOR signaling in complex with TSC2 in BC. Other genes, such as the ERBB2/HER2 and PTEN, have been identified to be involved in the progression of advanced bladder cancer. miR-145 and miR-29c as tumor suppressors, miR-183 and miR-17-5p as oncogenic miRNAs, and several cell-free RNAs, such as miR-497 or miR-214 could be promising novel circulating biomarkers used for BC diagnosis.

2.2 Protein markers for urinary bladder cancer

BLCA-1 and BLCA-4 are members of six bladder-specific nuclear matrix proteins (NMPs) and are considered specific urinary markers of bladder cancer. Fibronectin as a maker is a multifunctional, extracellular matrix glycoprotein, which is increased in the urine content in case of the bladder cancer. Clusterin is a heterodimeric disulfide-linked glycoprotein, which is overexpressed in bladder cancer particularly in invasive disease and is associated with poor prognosis. CEACAM1 (Carcinoembryonic antigen-related cell adhesion molecule 1, also known as CD66a) is a novel urinary marker for bladder cancer. Calprotectin is a protein with antimicrobial properties as a prognostic indicator resulting in upregulation in bladder cancer. Stathmin-1 and CD147 are two urinary proteins studied for their correlation with bladder cancer. The overexpression of stathmin-1 and CD147 are associated with aggressive bladder cancer and a poor prognosis. γ-synuclein involves in the pathogenesis of neurodegenerative diseases and is also used as a marker in bladder tumors. DJ-1 as marker is overexpressed in aggressive high-grade bladder cancer. Reg-1 (lithostathine-1-alpha) is highly expressed in bladder tumors. Urinary levels of matrix metallopeptidase 9 (MMP9) are increased in most invasive bladder cancer.

3 Targeted Therapy for Urinary Bladder Cancer

Numerous molecular mechanisms involved in the pathogenesis of urinary bladder cancer render promising approaches for targeted therapy. Major molecules of cell signaling pathways, such as the receptor tyrosine kinase, PI3K/AKT/mTOR and VEGF/VEGFR pathways, are altered in bladder cancer cells by oncogenes through overexpression or mutation, leading to dysregulated cell signaling and cell proliferation. Here, we summarize the potential targets and new drugs developed that have been used in recent, ongoing and future clinical trials to try to improve the clinical outcomes of this disease (Table1-11).

3.1 Urinary bladder cancer therapy for receptor tyrosine kinase pathway

EGFR is a receptor overexpressed in many bladder tumours and correlates with a poor prognosis. The effect of inhibiting EGFR in bladder cancer was investigated in several studies. Cetuximab is an antibody and evaluated in the treatment of BC. Cetuximab combined with afatinib (an inhibitor of EGFR and erbB-2) was more effective than cetuximab alone. Addition of bevacizumab (an antibody against VEGF-A) to cetuximab and photodynamic therapy resulted in significant inhibition of tumor vessels. Several other EGFR-targeted therapies have been evaluated in clinical trials and a number of clinical trials are ongoing. For instance, erlotinib monotherapy was studied in the neoadjuvant setting in patients with MIBC. Besides, agents targeting erbB-2 are being investigated in phase II trials in patients with bladder cancer. Examples include a variety of trials in which trastuzumab or lapatinib are being combined with chemotherapy or given as single agents. Some inhibitors targeting the FGFR-3 have been assessed for BC treatment including PD173074, R3Mab, BGJ-398, dovitinib and gemcitabine.

Table 1 Clinical trials of EGFR inhibitor Cetuximab

According to statistics, a total of 1 Cetuximab projects targeting urinary bladder cancer EGFR is currently in clinical stage and is not recruiting.

Table 2 Clinical trials of EGFR inhibitor afatinib

According to statistics, a total of 2 afatinib projects targeting urinary bladder cancer EGFR are currently in clinical stage and are recruiting.

Table 3 Clinical trials of EGFR inhibitor erlotinib

According to statistics, a total of 1 erlotinib project targeting urinary bladder cancer EGFR is currently in clinical stage and is not recruiting.

Table 4 Clinical trials of erbB-2 inhibitor trastuzumab

According to statistics, a total of 6 trastuzumab projects targeting urinary bladder cancer erbB-2 are currently in clinical stage, of which 1 are recruiting and 5 are not recruiting.

Table 5 Clinical trials of FGFR-3 inhibitor BGJ-398

According to statistics, a total of 2 BGJ-398 projects targeting urinary bladder cancer FGFR-3 are currently in clinical stage, of which 1 is recruiting and 1 is not recruiting.

Table 6 Clinical trials of FGFR-3 inhibitor gemcitabine

According to statistics, a total of 58 gemcitabine projects targeting urinary bladder cancer FGFR-3 are currently in clinical stage, of which 39 are recruiting and 19 are not recruiting.

3.2 Urinary bladder cancer therapy for PI3K/AKT/mTOR pathway

Preclinical results showed that combining rapamycin (mTOR inhibitor) with inhibitors of MAPK and signal transducer and activator of transcription 3 (STAT3) can significantly prolong survival in a bladder cancer model compared with rapamycin alone. Besides, combining rapamycin with a PI3K inhibitor can obviously inhibit UMUC3 cell tumour growth. All studies suggested that rapamycin treatment is promising for bladder cancer. Some phase II clinical trials combined temsirolimus or everolimus with chemotherapy are evaluated currently targeting mTOR and the PI3K-Akt pathway in patients with bladder cancer. Other trials have evaluated a single-agent approach of temsirolimus or everolimus. BKM120 (buparlisib) is a PI3K inhibitor that is investigated in an ongoing trial.

Table 7 Clinical trials of mTOR inhibitor rapamycin

According to statistics, a total of 4 rapamycin projects targeting urinary bladder cancer mTOR are currently in clinical stage, of which 2 are recruiting and 2 are not recruiting.

Table 8 Clinical trials of mTOR inhibitor temsirolimus

According to statistics, a total of 4 temsirolimus projects targeting urinary bladder cancer mTOR are currently in clinical stage, of which 2 are recruiting and 2 are not recruiting.

Table 9 Clinical trials of mTOR inhibitor everolimus

According to statistics, a total of 1 everolimus project targeting urinary bladder cancer mTOR is currently in clinical stage and is not recruiting.

3.3 Urinary bladder cancer therapy for VEGF/VEGFR pathway

Many agents targeting VEGFs and VEGFRs in patients with bladder cancer have already been reported in clinical trials. Four studies assessed the use of bevacizumab (targeting VEGF-A) or sunitinib (targeting VEGFRs) combined with chemotherapy in the neoadjuvant setting. One study of sunitinib has been terminated since substantial toxic effects. Some studies have analysed monotherapy of sunitinib, aflibercept (a fusion protein targets VEGFs) or pazopanib (targets VEGFRs) as second-line treatment strategies in phase II trials in patients with advanced urothelial cancer. All VEGF-targeted therapies show promise for clinical application.

Table 10 Clinical trials of VEGF-A inhibitor bevacizumab

According to statistics, a total of 2 bevacizumab projects targeting urinary bladder cancer VEGF-A are currently in clinical stage and recruiting.

Table 11 Clinical trials of VEGFRs inhibitor sunitinib

According to statistics, a total of 1 sunitinib project targeting urinary bladder cancer VEGFRs is currently in clinical stage, and is not recruiting.