Platinum-based chemotherapy is commonly used for the treatment of locally advanced and metastatic bladder cancer. However, there are currently no methods to predict chemotherapy response in this disease setting. A better understanding of the biology of bladder cancer has led to developments of molecular biomarkers that may help guide clinical decision making. These biomarkers, while promising, have not yet been validated in prospective trials and are not ready for clinical applications. As alkylating agents, platinum drugs kill cancer cells mainly through induction of DNA damage. A microdosing approach is currently being tested to determine if chemoresistance can be identified by measuring platinum-induced DNA damage using highly sensitive accelerator mass spectrometry technology. The hope is that these emerging strategies will help pave the road towards personalized therapy in advanced bladder cancer.
Bladder urothelial cancer is the 4th most common cancer in males and 9th in females and a major cause of morbidity and mortality worldwide. In the United States, approximately 70,530 individuals were diagnosed with bladder cancer in 2010 and 14,680 died from it [
For patients with muscle-invasive, nonmetastatic disease, radical cystectomy with bilateral pelvic lymph node dissection remains the mainstay of treatment. Recurrence can be frequent even after surgery. For example, about 50% of patients with deep, muscle-invasive disease will develop metastatic disease even after surgery [
Improving survival outcomes in advanced bladder cancer will require moving beyond conventional histopathologic evaluation such as stage and grade. Molecular biomarkers have the potential to more accurately determine prognosis and assign patients to appropriate treatments. Such biomarkers are already being used in other solid tumors such as breast, colon, and lung. For example, high expression of the ERCC1 gene is prognostic of improved survival and predictive of reduced response to platinum-based therapy in non-small cell cancer (NSCLC) [
The current standard treatment in the United States for muscle-invasive bladder cancer is radical cystectomy with bilateral pelvic lymph node dissection. These patients often develop metastatic disease despite aggressive surgical intervention. In organ-confined pT2 disease, the 5-year survival rate is approximately 68% [
The rationale for neoadjuvant chemotherapy prior to cystectomy is to treat micrometastatic disease that is present at diagnosis. It also helps downstage the tumor and increases the potential for complete resection of tumor. Furthermore, neoadjuvant chemotherapy allows delivery of systemic therapy through intact blood vessels and can be better tolerated before the patient is debilitated by surgery. There is level I evidence with two randomized trials to support the use of neoadjuvant chemotherapy [
A US Intergroup trial (INT 0080) randomized 307 patients with stage T2-4, N0, M0 bladder cancer to three cycles of neoadjuvant methotrexate, vinblastine, doxorubicin, and cisplatin (MVAC) or no chemotherapy followed by cystectomy [
The benefit of neoadjuvant chemotherapy was confirmed by a meta-analysis of 11 randomized trials with 3005 patients. It was found that those who received neoadjuvant platinum-based combination chemotherapy compared to local therapy alone had a 14% reduction in the risk of death [
Even though CMV and MVAC were used in the above-mentioned prospective trials, the gemcitabine and cisplatin (GC) combination is commonly used in the neoadjuvant setting. There is no randomized trial supporting the use of the GC regimen in this setting. Clinicians mainly extrapolated the data in the metastatic setting showing similar efficacy but better tolerability with the GC regimen compared to MVAC.
Neoadjuvant cisplatin-based chemotherapy is not widely used in practice even though there is level I evidence indicating a significant survival advantage for patients with muscle-invasive bladder cancer [
The postoperative adjuvant approach has several advantages. It allows for selection of patients at highest risk for surgical failure based on accurate pathologic staging, avoids delay in potentially curative surgery especially in nonresponders to chemotherapy, and prevents overtreating patients who may have a reasonable outcome from surgery alone. The drawbacks include difficulty in administering chemotherapy postoperatively as a result of declines in performance status or development of complications and delays in treating occult metastatic disease.
The results from the adjuvant trials have been conflicting and difficult to interpret. Two small trials have shown a significant difference in favor of adjuvant chemotherapy. One trial randomized 91 patients with pT3-T4a or node-positive bladder cancer to four cycles of adjuvant chemotherapy or to observation after radical cystectomy [
Other trials revealed no benefit with adjuvant chemotherapy. A Swiss trial randomized 77 patients with muscle-invasive (pT2), nonmetastatic bladder cancer to observation or 3 cycles of cisplatin. There was no significant difference in the overall survival at 5 years between the treatment and control group (57 versus 54%) [
The positive trials were criticized for having major deficiencies including small sample size, early stopping of patient entry, inappropriate statistical analyses, and poor reporting of results [
The standard treatment for patients with metastatic bladder cancer is systemic chemotherapy. Although bladder cancer is a chemosensitive tumor, the median survival with chemotherapy is only around 14 months. The five-year survival rate remains poor at about 15% [
In the search for a less toxic yet still effective regimen, a randomized phase III trial of 405 patients compared GC to MVAC [
Another randomized phase III trial assigned 263 patients to high-dose-intensity MVAC (2-week cycles) with granulocyte colony-stimulating factor (G-CSF) versus standard MVAC (4-week cycles) to see if overall survival can be improved [
Currently, chemotherapy for bladder cancer is taking the approach of one formula for all. Most patients presently receive a platinum-based regimen, usually GC. However, only about half of the bladder cancers will respond to chemotherapy. Extensive research is ongoing to better understand the biology of the disease process in order to improve clinical outcomes. Conventional prognostic factors such as the grade and stage of the tumor and tools like nomograms are useful in predicting the outcomes associated with surgery and the risk of recurrence but are inadequate in predicting response to chemotherapy [
Single gene markers for prognosis and prediction of response in bladder cancer.
Markers | Function | Relation to bladder cancer |
---|---|---|
p5334 | Tumor suppressor, DNA repair, and apoptosis | p53 mutation associated with high recurrence and progression |
ERCC141-43 | DNA repair | Low expression associated with increased response to platinum-based chemotherapy |
RRM141, 49 | Synthesis of deoxyribonucleotides | High expression with improved survival and possibly resistance to gemcitabine |
hENT154-55 | Nucleoside transporter | Sensitivity to gemcitabine |
BRCA159 | DNA repair | Low expression related to increased response and prolonged survival |
MDR142, 60 | P-glycoprotein efflux pump | High expression associated with resistance to chemotherapy |
Bcl-264 | Antiapoptosis protein | Associated with more advanced stage and worse prognosis |
p53 is the most studied biomarker in bladder cancer and many other cancer types. It plays a critical role in the regulation of cell cycle and is also involved in DNA damage and repair, cell cycle arrest, and apoptosis [
In addition to having prognostic qualities, studies have suggested that p53 may be predictive of benefit to chemotherapy [
Nucleotide excision repair pathway plays a major role in DNA damage repair, and the excision repair cross-complementing group 1 (ERCC1) is key member [
Studies have also been done to evaluate ERCC1 as a biomarker in patients with advanced bladder cancer treated with cisplatin-based chemotherapy. Bellmunt et al. performed gene expression analysis by using real-time quantitative PCR in tumors of 57 patients with metastatic or locally advanced, surgically incurable patients who were treated with either GC or GC plus paclitaxel [
Ribonucleotide reductase subunit M1 (RRM1) gene encodes one of two nonidentical subunits of ribonucleotide reductase, an essential enzyme involved in the production of deoxyribonucleotides for DNA synthesis and repair [
RRM1 may have utility as a biomarker in bladder cancer as well. In the Bellmunt study where patients received GC with or without paclitaxel, there was a trend towards longer time in progression in tumors with low RRM1 expression [
Human equilibrative nucleoside transporter 1 (hENT1) is the major molecule of nucleoside transporter proteins. Gemcitabine is a pyrimidine nucleoside analogue that requires plasma membrane nucleoside transporter proteins to enter the cell and exert cytotoxicity. Studies in cultured cells showed that hENT1 deficiency is associated with gemcitabine resistance [
In a small study of 12 patients, hENT1 was detected in 3 patients and two of them presented with a complete response to gemcitabine [
The breast cancer susceptibility gene 1 (BRCA1) is a tumor suppressor gene that is central in DNA repair pathways. It encodes a nuclear protein that functions in multiple biological processes, including gene transcription, DNA damage repair, and apoptosis [
The multidrug resistance gene 1 (MDR1) encodes P-glycoprotein (Pgp), a membrane protein that acts as an energy-dependent cellular efflux pump. Pgp can reduce intracellular concentrations of chemotherapy drugs like anthracyclines and vinca alkaloids which are components of MVAC, resulting in decreased cytotoxicity. Furthermore, it appears that chemotherapy drugs induce MDR1 and lead to drug resistance [
B-cell lymphoma 2 (Bcl-2) is the representing member of the large Bcl-2 family that is important in regulating cellular apoptosis. It was originally identified in follicular lymphoma at the site of the t(14; 18) translocation [
MicroRNA (miRNA) is small noncoding regulatory RNA molecules with the stem-loop secondary structure. Its size ranges from 17 to 25 nucleotides. It was first found in worms but later was found in most eukaryotic cells [
Individual gene biomarkers may not adequately capture the complex molecular activities in tumor cells. To accurately predict chemosensitivity requires a large body of information. For example, there are over 150 genes involved in the major DNA repair pathways that are relevant to platinum-DNA adducts alone. Several studies have been conducted using a combination of genetic markers to predict response to chemotherapy. Takata et al. analyzed the gene expression profile of 27,648 genes from 27 invasive bladder cancers using a cDNA microarray [
The major limitation of studying individual genes or gene combination in cancer specimens is that
To overcome these limitations, we have taken a radically different approach to study chemoresistance to platinum therapy
Pathways leading to chemotherapy-induced cell death and resistance. The major steps are shown in the sequential order. DNA damage is the critical step in this response pathway. Cells with low chemotherapy-induced DNA damage will survive chemotherapy and are chemoresistant. We propose that chemoresistance can possibly be identified by measuring chemotherapy-induced DNA damage and that some of the underlying resistance mechanisms can potentially be elucidated by measuring the other major steps such as metabolism, cell uptake/efflux, and DNA repair. The underlined steps can be determined with AMS.
We have developed a highly sensitive technology to measure carboplatin or oxaliplatin-induced DNA damage using accelerator mass spectrometry (AMS). It is an isotope ratio mass spectrometric method that precisely determines the concentration of very rare (<1 : 109) isotope in an isolated sample [
We have performed extensive preclinical studies to show the feasibility of this microdosing approach [
Cancer therapeutics is moving towards personalized medicine to select the most effective therapy while avoiding the ineffective and/or toxic therapy based on the underlying pathophysiology of the patients and their tumors. In bladder cancer, questions remain about who will benefit most from chemotherapy as only around 50% of bladder cancer patients will have tumor response from chemotherapy. Biomarkers have shown promise in prognostication and in selecting therapy and might help answer some of these questions. For example, ERCC1 status may be important to be determined before giving platinum-based chemotherapy, or hENT1 or RRM1 before gemcitabine. Combinations of biomarkers (including microRNA) can offer more accuracy in prediction than individual ones. Our group is using a microdosing approach to identify resistance to platinum drugs [