Immunotherapy for Bladder Cancer: Latest Advances and Ongoing Clinical Trials

ABSTRACT

For nearly 50 years, immunotherapy has been used in patients with bladder cancer in the form of Mycobacterium bovis Bacillus Calmette-Guerin (BCG), which is still the first-line therapy for non-muscle invasive disease. However, the remarkable results obtained with checkpoint inhibitor drugs, including Pembrolizumab and Atezolizumab, have fueled the quest to optimize these and other forms of immunotherapy for both non-muscle invasive as well as advanced bladder cancer. In this review we summarize the current state of the rapidly evolving field of immunotherapy in bladder cancer highlighting novel approaches and ongoing trials in this exciting area of research.

KEYWORDS:

• BCG
• bladder cancer
• checkpoint inhibitors
• immune targeted therapy
• immunotherapy

Introduction

Bladder cancer (BC) has the highest lifetime treatment cost per patient of all cancers and has a place among the top 15 most common cancers globally. In 2020, the global incidence of BC was 573,278, of which almost 90,000 occurred in the U.S. alone. These numbers are expected to rise in the coming years, especially in developed countries in Europe and North America, as people over the age of 60 will constitute around half of the population in these countries (Richters et al. 2020; Sung et al. 2021). A crucial step to determine the appropriate course of action for each patient with BC is the initial staging and grading of their disease. This process classifies the patient’s disease into non-muscle invasive bladder cancer (NMIBC) or muscle-invasive bladder cancer (MIBC) with or without metastases, and low-grade vs. high-grade (HG). Staging is usually done by performing a conventional transurethral resection of bladder tumor (cTURBT). Adequacy of resection is defined by the presence of detrusor muscle in the obtained specimen (Babjuk et al. 2022; Chang et al. 2016). Some of the main limitations this technique poses are a rate of staging inaccuracy of up to 42% and a high percentage of pathologic specimens lacking detrusor muscle (ranging from 30% to 66%)(Caglic et al. 2020; Cornelissen et al. 2020; Maheshwari et al. 2020). Using holmium laser enucleation instead of cTURBT for select tumors has increased adequate excision rates, which range from 78% to 100%, and an improved safety profile, though the approach is not appropriate for all tumors (Maheshwari et al. 2020). Another approach to improve staging accuracy is the increased use of preoperative multiparametric MRI (mpMRI), which is used to classify the tumor in one of the five categories of the Vesical Imaging-Reporting and Data System (VI-RADS) scale(Caglic et al. 2020). This scale, much like PI-RADS in prostate cancer, is intended to predict the possibility of clinically significant cancer. Due to its high sensitivity but low specificity to assess nodal metastases, this tool must be primarily used for local staging and not as a means to dismiss nodal involvement (Ahmadi et al. 2021; Caglic et al. 2020).

BC is a disease with a unique tumor microenvironment composed of immune cells, cytokines, and enriched immune gene expression patterns, making it a great candidate for treatment with immunotherapy (Nair et al. 2020). In fact, BC was one of the first cancers treated with immunotherapy in the form of Mycobacterium bovis Bacillus Calmette-Guérin (BCG), which was introduced as a treatment for NMIBC in 1976 (Gandhi et al. 2013; Herr and Morales 2008). Despite the effectiveness of BCG, rates of progression and recurrence still range from 5% to 50%, depending on initial risk stratification, and carries risks of treatment toxicity (Babjuk et al. 2022; Balar et al. 2021a). Nonetheless, the responsiveness of BC to immunotherapy in principle, and recent advances in new immunotherapeutics, lead to continued optimism for immunotherapy approaches to improve treatment of both localized and advanced bladder cancer (See Figure 1). This article aims to provide an overview of the latest advances in immunotherapy in patients with bladder cancer by providing information on ongoing trials, the benefits and limitations of each new treatment, and future research questions that must be addressed.

Figure 1. Treatment algorithms for A) NMIBC, B) non-metastatic muscle-invasive BC and C) metastatic MIBC.

NMIBC

BCG

Despite the use of BCG in the treatment of NMIBC for nearly 50 years, its exact mechanism of action remains elusive. It is believed that BCG acts preferentially on urothelial tumor cells by binding to fibronectin through fibronectin attachment protein (FAP) expressed on the BCG cell surface (Han et al. 2020; Pettenati and Ingersoll 2018). Normal urothelium appears to be relatively protected from BCG due to the large amount of negatively charged proteins on the surface that repel the similarly charged BCG (Han et al. 2020). After binding, BCG is internalized by the malignant cells, although it is unclear if this happens in a transitory manner or at all because the amount of BCG and mycobacterial DNA disappears rapidly from the urine after instillation (Crispen and Kusmartsev 2020; Pettenati and Ingersoll 2018). Independent of this interaction with the tumor cell, BCG activates the immune system by two separate pathways. First, it acts as a pathogen-associated molecular pattern (PAMP) activating Toll-like receptors and inducing the production of inflammatory cytokines (especially IL-6, IL-8), tumor necrosis factor (TNF), and granulocyte-macrophage colony-stimulating factor (GM-CSF) that promote the recruitment and activation of neutrophils and mononuclear cells (Han et al. 2020; Pettenati and Ingersoll 2018). This fact can be demonstrated with the presence of epithelioid granulomas with giant cells in the bladder wall after BCG instillation (Pettenati and Ingersoll 2018). Second, BCG stimulates a T helper 1 (Th1) cell-biased adaptive immune response by activating CD4+ T cells, which are critical for successful BCG treatment (See Figure 2) (Crispen and Kusmartsev 2020; Han et al. 2020; Pettenati and Ingersoll 2018). Aside from these already known mechanisms, BCG also possesses a direct cytotoxic activity, causing both apoptosis and necrosis of tumor cells. Apoptosis is induced by activating caspase 8 (extrinsic apoptosis pathway) and caspase 9 (intrinsic apoptosis pathway), while necrosis results from the production of reactive oxygen species (ROS), leading to DNA and protein damage in tumoral cells (Han et al. 2020).

Figure 2. Intravesical BCG instillation mechanism of action. As per current knowledge, BCG induces an antitumor immune response via two pathways. (a) After instillation into the bladder, PAMPs on BCG are recognized by different pattern recognition receptors (e.G., Toll-like receptors (TLR)) leading to the activation of the innate immune system, which results in the production of various cytokines and recruitment of neutrophils and macrophages. (b) BCG also induces an adaptive immune response by activating Th1 CD4+ T cells. Both of these pathways culminate in increased necrosis/apoptosis of tumor cells. PAMP: Pathogen-Associated Molecular Pattern; MHC II: Major Histocompatibility Complex class II; TLR: Toll-like receptor; GM-CSF: Granulocyte-macrophage colony-stimulating factor; APC: Antigen-presenting cells.

Before BCG was approved and widely used, intravesical chemotherapy instillations were the best available therapy, consisting of a single intravesical instillation (SI) of a chemotherapeutic agent, like mitomycin C or epirubicin, during the first 24 h after cTURBT. This approach demonstrated a 14% reduction in recurrence rate and a number needed to treat of 7.2 compared to cTURBT alone (Abern et al. 2013; Babjuk et al. 2022). BCG therapy consists of six weekly instillations for the induction phase, starting a couple of weeks after cTRUBT, followed by three maintenance instillations at 3, 6, and 12 months. This regimen has demonstrated a remarkable 32% reduction in recurrence rate compared to SI and an initial complete response rate (CR) ranging from 55% to 75% for high-risk papillary tumors and CIS, respectively (Babjuk et al. 2022; Pettenati and Ingersoll 2018).

Despite initial effectiveness for many patients, 30–40% of patients with intermediate and high-risk NMIBC experience BCG treatment failure for a variety of reasons (Pettenati and Ingersoll 2018). One suspected mechanism of failure is poor immune cell infiltration after the BCG instillation (Han et al. 2020; Pettenati and Ingersoll 2018). The reduced immune cell recruitment is thought to be due to tumor cell production of anti-apoptotic and anti-inflammatory cytokines like PGE2, TGF-ß, and IL-10, which produce an immunosuppressive tumor microenvironment, leading to decreased infiltration and improper functioning of CD4+ and CD8+ T cells, APCs and NK cells. Likewise, an increased presence of immunosuppressive cells like tumor-associated macrophages, myeloid-derived suppressor cells, regulatory T cells, and a high expression of PD-L1 on the tumor cells and tumor-associated myeloid cells also contribute to the failure of BCG to result in an appropriate anti-tumor response (Crispen and Kusmartsev 2020; Han et al. 2020).

The subsequent treatment of patients who fail BCG is still controversial. According to the American Urological Association (Chang et al. 2016) and the European Association of Urology (Babjuk et al. 2022), patients who qualify as having BCG failure must be offered RC since they will unlikely benefit from more intravesical BGC. The rates of 10-year disease-free survival in high-risk NMIBC patients who have BCG failure and undergo RC have been reported as high as 86% for T0 tumors and 78% for T1 tumors (Lebacle et al. 2021). While RC is considered the most effective treatment in this setting, it is a major operation and comes with potential negative impacts on quality of life resulting in some patients being ineligible and some patients refusing RC. Guidelines suggest enrolling such patients in a clinical trial ideally, or treatment with other intravesical or systemic agents (Babjuk et al. 2022; Chang et al. 2016; Lebacle et al. 2021).

Several studies have shown BCG immunization might improve BCG efficacy (Crispen and Kusmartsev 2020; Larsen et al. 2020; Pettenati and Ingersoll 2018). Mice who received a subcutaneous BCG vaccine before BCG intravesical instillation showed an increased inflammatory response and faster T cell infiltration into the bladder compared to unvaccinated mice (Biot et al. 2012). Also, a retrospective analysis of clinical data support this theory by demonstrating an 80% 5-year disease-free survival (DFS) in patients with previous positive purified protein derivative (PPD) tests compared to only 45% in patients with negative PPD tests (Biot et al. 2012; Larsen et al. 2020; Pettenati and Ingersoll 2018). This approach must be further tested for safety and efficacy in a prospective manner before it can be integrated into standard clinical practice.

Over the years, different BCG strains have been developed through serial passage (Pettenati and Ingersoll 2018). The most used and studied strains in the last decade are Tice, Connaught, and RIVM (Del Giudice et al. 2021). Studies comparing their impact on recurrence-free survival (RFS) have shown similar results, though Tice or RIVM for induction and maintenance therapy have demonstrated a better RFS than Connaught (Witjes et al. 2016). While Connaught appeared to induce a more robust immune response after induction, this response waned during maintenance (Del Giudice et al. 2021). Production of the Connaught strain was discontinued in 2018 (Pettenati and Ingersoll 2018). Aside from these findings, studies have not found a significant difference in overall survival (OS) with the different substrains(Kamat et al. 2018; Pettenati and Ingersoll 2018; Vegt et al. 1995). S1602 is a phase III clinical trial started in 2017 with 1000 BCG-naive and PPD-negative patients with HG NMIBC. The purpose of this trial is to compare intravesical instillation of Tokyo-172 BCG strain to instillation of Tice and prove non-inferiority of Tokyo-172 in terms of time to high-grade recurrence (TTHGR). It will also assess whether subcutaneous injection of Tokyo-172 BCG previous to intravesical instillations with the same strain will pose any benefit compared to patients only receiving intravesical treatment (Svatek et al. 2018). This study will be completed in 2025 and will give a better insight into how different strains and previous BCG vaccination affect patient outcomes. It is important to also mention that a wide array of recombinant/modified BCG strains are being developed in preclinical trials (Rentsch et al. 2020; Singh et al. 2022). One particular strain (VPM1002BC) has advanced to human trials and appears to have an acceptable safety profile and efficacy according to the data from a phase I study (Rentsch et al. 2020). Phase II clinical testing of this strain was designed to evaluate its efficacy, safety, and tolerability after intravesical instillation in patients previously defined as BCG unresponsive. The results showed an RFS of up to 49.3% at 60 weeks after trial registration and remained at 43.7% at 3 years (Rentsch et al. 2022). These are promising results, but further investigation is needed to identify an optimal strain.

IL-15 superagonist

As mentioned above, BCG exerts its antitumoral activity by activating both the innate and adaptive immune responses. This fact has led researchers to theorize that the use of cytokines could potentiate the antitumoral activity of BCG. IL-15 plays an important role in the activation and proliferation of NK cells and CD8+ T cells (Gomes-Giacoia et al. 2014; Huntington et al. 2009; Rosser et al. 2021). IL-15 is coupled with IL-15 receptor α (IL-15 Rα) on the surface of APCs and presented to NK cells and CD8+ T cells to bind CD122/CD132 expressed on their cell surface (Rosser et al. 2021). A modified and enhanced version of human IL-15 (known as ALT-803) was developed by coupling IL-15 with a fusion protein composed of IL-15 Rα sushi domain and the Fc portion of human IgG1 (Gomes-Giacoia et al. 2014; Rosser et al. 2021). In vivo, ALT-803 has 25 times the activity that native IL-15 has (Gomes-Giacoia et al. 2014). In 2018, Rosser et al. presented the results of phase Ib of a phase Ib/IIb clinical trial at the American Society of Clinical Oncology (ASCO) annual meeting. This trial explored the safety and maximum tolerated dose (MTD) of the combination treatment of IL-15 superagonist plus BCG therapy in BCG-naive patients with NMIBC. Results showed a CR in all patients at 24 months, with none of them demonstrating progression or disease recurrence. The majority of the AEs were grade 1 or 2, with no grade 4 or 5 AEs (NCT02138734). Based upon these outstanding results, the multi-institutional phase II/III QUILT-3.032 was launched with a recruitment goal of 200 patients. It is intended to assess the efficacy of this therapeutic combination in patients with BCG-unresponsive HG NMIBC NCT03022825. Preliminary results in 160 patients demonstrate a CR in 71% of patients with CIS, while 91% of patients avoided cystectomy, and PFS at 24 months was 96%. PD patients had DFS of 57% at 12 months and 48% at 24 months follow-up. 95% of the patients with PD avoided cystectomy. These results would place combination therapy with ALT-803 plus BCG as the most efficacious treatment available for BCG unresponsive HG NMIBC patients (Chang et al. 2022).

Checkpoint inhibitors (CPI)

The immune system has certain checkpoints in place to minimize overreaction to threats like infectious organisms and abnormal/malignant cells that could result in damage to normal tissues. When T cells are activated, they increase the expression of co-inhibitory molecules, like CTLA-4 and PD-1, on their surface. The ligands for these co-inhibitory molecules are expressed both on normal cells/tissues and regulatory T cells to limit the extent of the inflammation and avoid damage to healthy tissues (Jacob et al. 2021). Many malignant cells can also express ligands to activate co-inhibitory molecules on T cells resulting in a downregulation of the immune response resulting in tumoral escape from the immune system. Monoclonal antibodies (mAb) against CTLA-4, PD-1, and PD-L1, known as checkpoint inhibitors, can prevent ligand/receptor interaction and block this downregulation and thus restore the tumor’s susceptibility to the immune system (See Figure 3). Checkpoint inhibitors have demonstrated benefit in treating several cancers in advanced states, including bladder cancer(Lebacle et al. 2021). However, the utility of CPI in patients with high-grade NMIBC who have failed BCG is less clear. Patterns of expression of PD-L1 in NMIBC are lower than in patients with MIBC (Copland et al. 2019; Lebacle et al. 2021). Treatment with BCG has proved to raise PD-L1 expression, suggesting CPI could be useful as a combination treatment or secondary treatment of recurrent tumors after BCG treatment (Hashizume et al. 2018). Several CPI is currently being studied for use in bladder cancer and are described below.

Figure 3. Mechanism of action of different Checkpoint inhibitors. (a) CTLA4 inhibitors further T cell activation by disrupting the CTLA4/CD80/86 interaction between APCs and T cells. (b) PD1 and PDL1 inhibitors also promote an active T cell population by disrupting the PD-1/PDL1 interaction between T cells and tumor cells. APC: Antigen-presenting cells; MHCI/II: Major Histocompatibility Complex; TCR: T cell Receptor.

To date, only pembrolizumab has been approved by the FDA to treat patients with NMIBC. Its use is only recommended in patients with NMIBC and BCG failure who are unwilling or unable to undergo RC(Babjuk et al. 2022; Chang et al. 2016; Jacob et al. 2021). Other CPIs under evaluation include Atezolizumab, Nivolumab, Avelumab, Durvalumab (Álvarez-Maestro et al. 2021).

Pembrolizumab

Pembrolizumab specifically binds to PD-1, is FDA-approved, and is included in the EAU guidelines for treatment of metastatic BC in platinum-ineligible patients (Babjuk et al. 2022). Currently, there are several ongoing studies to determine the safety and efficacy of pembrolizumab in patients with NMIBC. Encouraging results from a phase I study demonstrated the combination treatment of pembrolizumab plus BCG was safe and tolerated (Alanee et al. 2021). In a phase II study (KEYNOTE-057), BGC unresponsive patients with HG NMIBC received 200 mg of pembrolizumab every 3 weeks for 24 months. 40.6% of these patients showed CR, which persisted for a median of 16.2 months(Balar et al. 2021a; Pfail et al. 2021). This study led to the 2020 FDA approval of pembrolizumab to treat NMIBC patients with BCG failure and unwilling/unfit for surgery (Alanee et al. 2021; Jacob et al. 2021; Pfail et al. 2021). KEYNOTE-676 is an ongoing phase III study designed to compare treatment efficacy of pembrolizumab combined with BCG versus BCG monotherapy in patients with persistent or recurrent high-risk NMIBC after BCG induction therapy (Trial registration number: NCT03711032). The primary endpoint of KEYNOTE-676 is CR, and secondary endpoints are event-free survival (Naik, et al.), RFS, OS, and health-related quality of life (QoL) (Kamat et al. 2020). The results of this study are anticipated by 2024. NCT04164082 is an ongoing phase II trial studying the effects of intravesical combination treatment with pembrolizumab plus gemcitabine in patients with NMIBC and BCG failure to assess EFS, CR, RFS, PFS, and OS. Results are expected by March 2023.

Nivolumab

Nivolumab is another anti-PD-1 CPI mAb approved by the FDA as a second-line treatment in patients with metastatic BC (Babjuk et al. 2022). Following its promising results for patients with metastatic BC, it is also being investigated for use in NMIBC. CheckMate 9UT is a phase II randomized, open-label study comparing the efficacy and safety of Nivolumab monotherapy or Nivolumab plus experimental medication BMS -986,205 with or without BCG in BCG unresponsive patients with NMIBC. BMS -986,205 belongs to the group of indoleamine 2, 3-dioxygenase 1 inhibitors (IDO1i). CheckMate 9UT will evaluate and compare the CR, duration of CR, PFR, and adverse events (AE) between the different arms of the study. Results are expected by the end of 2024 (NCT03519256). CheckMate 7G8 is a phase III randomized, double-blind clinical trial comparing combination treatment with Nivolumab and intravesical BCG versus standard of care (SoC) BCG alone in patients with high-risk NMIBC that is persistent or recurrent after treatment with BCG. It will assess EFS, CRR, worsening-free survival, and OS. This study started in 2020, and the results are expected by the end of 2024 (NCT04149574).

Atezolizumab

Atezolizumab is a CPI that targets PD-L1 and prevents binding to both PD-1 and CD80, potentiating T cell activation(Inman et al. 2017). This drug is being tested in both intravesical and intravenous delivery. BladderGATE is a phase 1 clinical trial currently underway in Spain to assess the safety and tolerability of combination treatment with atezolizumab and BCG intravesical instillations. Results of this study can be expected by the beginning of 2024 (NCT04134000). NCT02844816 is a phase II study evaluating the efficacy of IV atezolizumab given every 21 days in patients with BCG-unresponsive recurrent NMIBC. Primary outcome measures are CRR and EFS. This study was started in 2017, and results should be available by the end of 2022. The ALBAN study is a phase III open-label, randomized clinical trial currently being conducted in France with an estimated enrollment of 516 patients. This study is designed to assess the efficacy (defined as RFS and PFS) of atezolizumab plus one year of BCG intravesical instillations in BCG-naive high-risk NMIBC patients. Results of this study will not be available until 2028 (NCT03799835). While atezolizumab remains promising based on the data obtained so far, it will be several more years before it is available for routine clinical use pending results of ongoing and future clinical trials.

Durvalumab

Durvalumab is a PD-L1 selective human immunoglobulin mAb being extensively studied as a potential treatment for both MIBC and NMIBC (Massard et al. 2016). This drug is under evaluation in a diverse repertoire of ongoing clinical trials, ranging from use as monotherapy for BCG unresponsive patients to combination treatment regimens with other experimental drugs. In a phase II, single-group study, the efficacy of IV durvalumab monotherapy in patients with BCG refractory urothelial CIS was assessed. Seventeen patients were enrolled, four patients demonstrated persistent HG NMIBC at the 3-month follow-up and abandoned the study. Of the remaining patients, 3 had CR at the 6-month follow-up, 3 progressed to MIBC, and 9 had RC. In terms of toxicity, 11 patients reported grade 1 or 2 treatment-related AE, the most common of which was diarrhea. While durvalumab had an adequate safety profile in this study, efficacy was somewhat limited. This study, however, consisted of a small cohort of patients, so further research is required to more completely evaluate efficacy (Li et al. 2022).

In addition to IV administration of durvalumab, intravesical administration is also being explored as a way to limit systemic toxicity. NCT03759496 is a phase II trial conducted in Greece that intends to evaluate the safety, tolerability, and efficacy of intravesical durvalumab in patients with BGC failure and high-risk NMIBC. Results can be expected by the beginning of 2023. SUBDUE-1 is a phase I study evaluating the safety and immunological efficacy of sub-urothelial durvalumab injection in patients with MIBC or high-risk NMIBC. The researchers believe sub-urothelial injection will allow durvalumab to avoid systemic toxicity without the urothelial penetrance limitations that the intravesical instillation route poses. The primary objective of this study is to evaluate safety by using patient-reported outcome measures (PROMS) and frequency of AE (Moe et al. 2021). Combination therapy with durvalumab and BCG is being evaluated in POTOMAC, a phase III study assessing the efficacy and safety of this combination compared to standard of care therapy in patients with BGC-naive NMIBC. This study deserves special mention because of the large number of patients participating. It has thus far recruited 1018 patients, and it is divided into 3 arms: durvalumab plus BCG induction and maintenance therapy, durvalumab with BCG induction therapy only, and standard of care treatment with BCG. The estimated completion date for the POTOMAC study is September 2025 (NCT03528694). Rideau is a phase I/II study that intends to evaluate the extent to which combination therapy with local cystoscopic injection of tremelimumab (and anti-CTLA-4 mAb) plus systemic durvalumab is capable of inducing an appropriate antitumor immune response in HR NMIBC with minimal toxicity (NCT05120622). Lastly, ADAPT-BLADDER is a phase I/II study with an estimated enrollment of 186 patients. Patients will be divided into three distinct arms to assess the safety of durvalumab monotherapy, combination therapy with durvalumab plus BCG, and combination therapy with durvalumab and external beam radiation therapy (EBRT) (NCT03317158). If safety is demonstrated, phase II will be conducted with the patients who have BCG-persistent or recurrent NMIBC to evaluate the efficacy of each combination therapy in this population (NCT03317158). The versatility of this drug in different routes of administration and its potential for several different combination therapies make it an exciting agent likely to find a growing role in the future.

Avelumab

Avelumab is an anti-PD-L1 mAb approved in 2020 by the FDA as maintenance treatment for patients with MIBC with and without metastasis(Powles et al. 2020). Its use in patients with NMIBC is currently being studied by the PREVERT study, a phase II open-label clinical trial with a 67 patient cohort. The primary aim of this study is to evaluate the efficacy of combining EBRT with concomitant administration of IV avelumab in patients with BCG-unresponsive NMIBC (NCT03950362). The ABC trial is a phase 1b study assessing the safety and tolerability of combination treatment with avelumab and BCG in patients with BCG-unresponsive NMIBC. Its primary endpoint is the completion of a full BCG induction course with concomitant weekly IV avelumab, and the secondary endpoint is the completion of 6 months of BCG maintenance treatment with concomitant weekly avelumab. Preliminary results show a total of 18 patients were enrolled, 15 (83%) of them managed to complete the induction course. Thirteen (87%) of the patients who completed induction remained on treatment at the 3-month cystoscopy, and 10 of them were without evidence of recurrence and 3 had persistent disease. Importantly, no drug-related grade 4 or 5 AEs were reported. These encouraging results suggest the combination of BCG and avelumab for induction in this population is safe and tolerable. However, follow-up is still ongoing, and results for the maintenance period are still pending (NCT03892642).

Immune targeted gene therapy

Vicinium

Vicinium is an Epithelial cell adhesion molecule (EpCAM)-specific antibody fused to a fragment of pseudomonas exotoxin A (Bree et al. 2021). Vicinium is able to enter tumoral cells by binding to EpCAM. Once inside, it releases the fragment of Pseudomonas exotoxin A, which interferes with cellular protein synthesis, causing apoptosis(Bree et al. 2021; Shore et al. 2019). A phase I trial conducted in 2007 by Jones et al. demonstrated intravesical administration of vicinium is safe, tolerated, and has minimal systemic absorption (Jones et al. 2007). Shore et al. conducted a phase III trial (NCT02449239) evaluating efficacy of vicinium in patients with BCG-unresponsive NMIBC. Induction was composed of biweekly vicinium instillations for 6 weeks, followed by weekly instillations for six more weeks. After that, maintenance therapy was given every 2 weeks for up to 2 years. Preliminary results as of May 2019 were presented at the 2020 Annual AUA meeting. The investigators reported a 40% CRR of the CIS patients at 3 months follow-up. Of those patients, 52% remained disease-free at 12 months after the start of the treatment. Responders at 3 months managed to avoid RC for 34 months, compared to nonresponders who only remained RC-free for 20 months (Shore et al. 2020). This study shows promising results and points to the possibility that vicinium could delay the need for RC (Shore et al. 2020). NCT03258593 is a phase I single-arm study of the combination therapy with durvalumab and vicinium in patients with BCG-unresponsive NMIBC. Preliminary results were presented at the 2021 Annual AUA meeting. Of the 12 patients enrolled, 5 (41%) were disease-free at the 12-week follow-up and 4 (31%) at the 6-month follow-up, with 2 of those patients remaining disease-free for >12 months. In terms of safety, all 12 patients reported AEs, but only 8% presented an AE grade 3 or higher. These data suggest combination treatment of durvalumab plus vicinium is safe, well tolerated, and with promising early efficacy results (Gurram et al. 2021). Further research with larger cohorts is needed to better assess whether vicinium conveys a significant improvement in the treatment of this subset of patients.

Oncolytic viruses

The use of viral gene therapy for bladder cancer is currently under varying stages of investigation. These therapies use a tumor-specific virus as a vector to deliver a gene encoding a specific cytotoxic substance (like cytokines) to malignant cells.

Nadofaragene firadenovec

Nadofaragene firadenovec is a recombinant, replication-defective adenovirus that acts as a vector to deliver cDNA encoding interferon (IFN) alfa-2b to urothelial cells (Beinfeld 2021; Meng et al. 2019; Pfail et al. 2021). IFN has several anticarcinogenic properties due to the fact that it modulates gene expression, including genes encoding growth factors and growth factor receptors (Zou et al. 2005). The use of nadofaragene firadenovec in patients with NMIBC and BCG failure has shown remarkable results so far. NCT02773849 is a phase III ongoing clinical trial that included 157 patients with NMIBC and BCG failure. At the time of enrollment, 50 of these patients had papillary disease (PD), and 107 had CIS. Nadofaragene was administered every 3 months until up to 4 doses were completed. In the PD cohort, efficacy was determined by high-grade recurrence-free survival (HGRFS). Preliminary results showed 72.9% HGRFS at 3 months and 43.8% at 12 months. Patients who remained disease-free at 12 months were offered continued treatment. At 24 months of follow-up, 33.3% of the total enrolled patients with PD remained HGRF. In the CIS cohort, 53. 4% of patients attained CR by 3 months follow-up. 36.4% of those patients remained free of HR recurrence at 24 months of follow-up. In terms of safety, instillation site discharge was the most commonly reported AE. Most AE were grade 1 or 2 and no AE led to patient death (Boorjian et al. 2020; Lotan et al. 2021; Schuckman et al. 2021).

CG0070

CG0070 is a tumor-specific oncolytic adenovirus that carries a gene-encoding granulocyte-macrophage colony-stimulating factor (GM-CSF). It targets urothelial tumoral cells by preferentially replicating in cells with a defective retinoblastoma tumor suppressor protein (Rb) – which is disrupted in 80% of all cancers (Deininger et al. 2022). Increased viral replication and production of GM-CSF are what produce CG0070‘s oncolytic activity. BOND2 (NCT02365818) is a phase II trial that investigated the safety and efficacy of intravesical CG0070 in patients with BCG-unresponsive NMIBC. CG0070 was instilled weekly for 6 weeks for induction treatment and again for maintenance. The intended follow-up time was 18 months, however, interim results of the 6-month follow-up response were published by the investigators. Of the 45 patients evaluated at 6 months, 47% achieved CR. When divided by pathologic subset, patients with pure CIS had a remarkable 58% CRR, while patients with PD Ta or T1 achieved 33% CRR (Packiam et al. 2018). Phase III is already underway (BOND3), and the investigators intend to enroll 110 participants. These patients will be followed for 24 months with the intention to measure CRR, the median duration of response, PFS, and time to tumor progression. This larger cohort will hopefully shed more light on the efficacy of this treatment (NCT04452591). Combination treatment with CG0070 and CPIs is also being investigated; CORE1 (NCT04387461) is a phase II clinical trial exploring the safety and efficacy of combination treatment with intravesical CG0070 and IV pembrolizumab. The primary endpoint is CR at 12 months, secondary endpoints are PFS, duration of response, cystectomy-free survival, and safety. Other interesting aspects that this study will evaluate are the changes in tumor microenvironment (e.g., PD-L1 expression) after treatment, and the measurement of adenovirus serotype 5 antibody titers to explore their relationship with tumor progression (NCT04387461).

Other non-immunological treatments

Fibroblast growth factor receptor (FGFR) inhibitors

FGFRs are a family of transmembrane tyrosine kinases that regulate biological processes like cellular proliferation, differentiation, and death (Al-Obaidy and Cheng 2021; Hu et al. 2022). Mutated FGFR is more commonly found in low-stage urothelial tumors than in advanced-stage BC (Kardoust Parizi et al. 2021). Currently, erdafitinib (a pan-FGFR inhibitor) is the only FGFR inhibitor approved by the FDA for the treatment of MIBC with or without metastases, which have progressed on platinum chemotherapy(Al-Obaidy and Cheng 2021; Hu et al. 2022).

NCT04172675 is a study that will compare the efficacy of erdafitinib versus the investigator’s choice of intravesical chemotherapy with Gemcitabine or Mitomycin C in patients with BCG-unresponsive NMIBC. This study deserves special mention due to its high estimated enrollment (280 patients), and its long follow-up time frame (up to 4 years). Dovitinib is a multi-tyrosine kinase inhibitor that targets vascular endothelial growth factor receptor (VEGFR) 1–3, platelet-derived growth factor receptor (PDGFR)-β, and FGFR 1–3 (Pili et al. 2014). This drug is currently being studied in phase II clinical trial (NCT01732107) to assess its effectiveness and safety profile in patients with BCG-unresponsive NMIBC who are unfit or unwilling to undergo RC.

A summary of the clinical trials exploring the safety and efficacy of the various agents highlighted above, as well as information on the target NMIBC patient population and study status, is provided in Table 1.

Table 1. Summary of the mentioned clinical trials on NMIBC.

Trial Registration Number	Protocol Name	Target Population	Status
NCT03091660	S1602, A Phase III Randomized Trial to Evaluate the Influence of BCG Strain Differences and T Cell Priming With Intradermal BCG Befor Intravesical Therapy for BCG-Naive High-Grade Non-Muscle Invasive Bladder Cancer	BCG-naive patients with high-grade NMIBC	Active, Not recruiting
NCT03022825	QUILT-3.032: A Multicenter Clinical Trial of Intravesical Bacillus Calmette-Guerin (BCG) in Combination With ALT-803 (N-803) in Patients With BCG Unresponsive High-Grade Non-Muscle Invasive Bladder Cancer	Patients with BCG unresponsive HG-NMIBC	Recruiting
NCT03711032	A Phase III, Randomized, Comparator-controlled Clinical Trial to Study the Efficacy and Safety of Pembrolizumab (MK-3475) in Combination With Bacillus Calmette-Guerin (BCG) in Participants With High-risk Non-muscle Invasive Bladder Cancer (HR NMIBC) That is Either Persistent or Recurrent Following BCG Induction or That is Naïve to BCG Treatment (KEYNOTE-676)	Patients with persistent or recurrent HR-NMIBC following BCG Induction or HR-NMIBC that is naïve to BCG treatment	Recruiting
NCT04164082	Phase II Trial of Intravesical Gemcitabine and MK-3475 (Pembrolizumab) in the Treatment of Patients With BCG-Unresponsive Non-Muscle Invasive Bladder Cancer	Patients with BCG-unresponsive NMIBC	Recruiting
NCT03519256	A Phase II, Randomized, Open-label Study of Nivolumab or Nivolumab/BMS -986,205 Alone or Combined With Intravesical BCG in Participants With BCG-Unresponsive, High-Risk, Non-Muscle Invasive Bladder Cancer	Patients with BCG-unresponsive, HR-NMIBC	Active, not recruiting
NCT04149574	A Phase III, Randomized, Double-blind Trial of Nivolumab in Combination With Intravesical BCG Versus Standard of Care BCG Alone in Participants With High-risk Non-muscle Invasive Bladder Cancer That Is Persistent or Recurrent After Treatment With BCG	Participants with HR NMIBC that Is persistent or recurrent after treatment with BCG	Active, not recruiting
NCT04134000	Phase Ib Trial of Atezolizumab and BCG in High Risk BCG naïve Non-muscle Invasive Bladder Cancer (NMIBC) Patients: BladderGATE Study	Patients with BCG naïve HR-NMIBC	Recruiting
NCT02844816	Phase II Trial of Atezolizumab in BCG-Unresponsive Non-Muscle Invasive Bladder Cancer	Patients with BCG-unresponsive NMIBC	Active, not recruiting
NCT03799835	An Open Label, Randomized, Phase III Trial, Evaluating Efficacy of Atezolizumab in Addition to One Year BCG (Bacillus CaLmette-Guerin) Bladder Instillation in BCG-naive Patients With High-risk Non-muscle Invasive Bladder cANcer	BCG-naive patients with HR-NMIBC	Recruiting
NCT03759496	Intravesical Administration of Durvalumab (MEDI4736) to Patients With High-risk, Non-muscle-invasive Bladder Cancer (NMIBC). A Phase II Study With Correlative	Patients with BCG- unresponsive HR-NMIBC	Active, not recruiting
ACTRN12620000063910	Sub-urothelial durvalumab injection-1 (SUBDUE-1): A novel approach to immunotherapy for bladder cancer	Adult patients with either HR NMIBC or MIBC, who are scheduled to undergo RC or who are unfit or unwilling to receive systemic neoadjuvant chemotherapy for MIBC	—————
NCT05120622	Phase I/II Trial of Local Cystoscopic Injection of Tremelimumab Plus Systemic Durvalumab (MEDI4736) for High Risk Non-Muscle Invasive Bladder Cancer	Patients with HR NMIBC that are scheduled to undergo RC or patients with recurrent CIS after BCG treatment	Recruiting
NCT03317158	Phase I/II StuDy of Modern ImmunotherApy in BCG-RelaPsing UroThelial Carcinoma of the BLADDER - (ADAPT-BLADDER) HCRN GU16-243	Patients with BCG-unresponsive NMIBC	Recruiting
NCT03950362	Bladder PREserVation by RadioTherapy and Immunotherapy in BCG Unresponsive Non-muscle Invasive Bladder Cancer	Patients with BCG unresponsive HR-NMIBC, unfit or unwilling to undergo RC	Not yet recruiting
NCT03892642	Phase Ib Study of Avelumab Plus Bacille Calmette-Guerin (BCG) in Patients With Non-muscle Invasive Bladder Cancer (ABC Trial)	Patients with BCG-unresponsive NMIBC	Active, not recruiting
NCT02449239	Open-Label, Multicenter, Ph 3 Study to Evaluate the Efficacy and Tolerability of Intravesical Vicinium™ in Subjects With Non Muscle-Invasive Carcinoma in Situ and/or High-Grade Papillary Disease of the Bladder Treated With BCG	Patients with BCG unresponsive Non Muscle-Invasive Carcinoma in Situ and/or High-Grade Papillary Disease of the Bladder	Active, not recruiting
NCT03258593	A Phase I Single-Arm Study of the Combination of Durvalumab (MEDI4736) and Vicineum (Oportuzumab Monatox, VB4–845) in Subjects With High-Grade Non-Muscle-Invasive Bladder Cancer Previously Treated With Bacillus Calmette-Gu(SqrRoot)(Copyright)Rin (BCG)	Patients with BCG unresponsive HG-NMIBC	Recruiting
NCT02773849	A Phase III, Open Label Study to Evaluate the Safety and Efficacy of INSTILADRIN® (rAd-IFN)/Syn3) Administered Intravesically to Patients With High Grade, BCG Unresponsive Non-Muscle Invasive Bladder Cancer (NMIBC)	Patients with BCG unresponsive HG-NMIBC	Active, not recruiting
NCT02365818	An Open Label, Single Arm, Phase II, Multicenter Study of the Safety and Efficacy of CG0070 Oncolytic Vector Regimen in Patients With Non-Muscle Invasive Bladder Carcinoma Who Have Failed BCG (Bacillus Calmette-Guerin) Therapy and Refused Cystectomy	Patients with BCG unresponsive HR-NMIBC, unfit or unwilling to undergo RC	Completed
NCT04452591	A Phase III Study of CG0070 in Patients With Non-Muscle Invasive Bladder Cancer (NMIBC) Unresponsive to Bacillus-Calmette-Guerin (BCG)	Patients with BCG unresponsive HR-NMIBC, unfit or unwilling to undergo RC	Recruiting
NCT04387461	A Phase II, Single Arm Study of CG0070 Combined With Pembrolizumab in Patients With Non Muscle Invasive Bladder Cancer (NMIBC) Unresponsive to Bacillus Calmette-Guerin (BCG)	Patients with BCG unresponsive NMIBC, unfit or unwilling to undergo RC	Recruiting

MIBC

The treatment for MIBC differs substantially from NMIBC in that it is based primarily on radical cystectomy (RC) with the addition of neoadjuvant chemotherapy (NAC) for cisplatin-eligible patients. Compared with RC alone, cisplatin-combination chemotherapy has demonstrated an 8% absolute improvement in survival at 5 years (Babjuk et al. 2022). The only approved uses of immunotherapy in MIBC are as adjuvant therapy in cisplatin-ineligible patients without metastasis or as first-line therapy in cisplatin and carboplatin-ineligible patients with metastasis(Babjuk et al. 2022). This panorama might change in the near future with the advent of molecular staging, which The Cancer Genome Atlas has classified as five molecular subtypes of MIBC: Luminal (subdivided into luminal-papillary, luminal-infiltrated, and luminal), basal-squamous, and neuronal. The most common of these subtypes are the luminal-papillary and the basal-squamous (Ahmadi et al. 2021; Warrick et al. 2020). Each molecular subtype demonstrates a specific pattern of expression of mRNA that can potentially be used for targeted therapies to disrupt the altered pathways.

Checkpoint inhibitors (CPI)

The FDA has already approved several CPIs to treat patients with advanced BC. The use of CPI has been an excellent option for patients with advanced BC, especially those who are not eligible to receive platinum-based chemotherapy. Both luminal-infiltrated and basal-squamous molecular subtypes have an increased expression of PD-L1 and CTLA-4 (Ahmadi et al. 2021; Iacovino et al. 2022). CPIs as targeted therapy for these subtypes could show an increased response. However, molecular staging and its use in guiding targeted therapies are still being investigated and are not yet part of regular clinical practice(Ahmadi et al. 2021; Iacovino et al. 2022). The FDA has approved 5 CPI (atezolizumab, pembrolizumab, nivolumab, durvalumab, and avelumab) for the treatment of patients with MIBC who have disease progression during or following platinum-based chemotherapy. Aside from this, atezolizumab and pembrolizumab were also approved as a first-line treatment in cisplatin-ineligible patients with MIBC, and high expression of PD-L1 (Babjuk et al. 2022; FDA 2020b; Patel et al. 2020). Pembrolizumab can also be used as first-line treatment in patients ineligible for any platinum-based chemotherapy, without regard to their PD-L1 status. This is the only approved indication for PD-L1 testing in patients with BC (Babjuk et al. 2022). KEYNOTE-045 was a study conducted in 2014 comparing the efficacy of pembrolizumab versus either paclitaxel, docetaxel, or vinflunine in patients with MIBC with or without metastases. This trial demonstrated an increased ORR in patients who received pembrolizumab (21.1%) compared to those on the chemotherapy arm (11.4%). OS rates at 4 years were 16.7% for pembrolizumab and 10.1% for patients on chemotherapy. Follow-up at 5 years yielded similar results, with higher OS in the pembrolizumab group (14.9% versus 8.7%) (NCT02256436). Pembrolizumab has also been studied as neoadjuvant therapy. Current clinical practice relies on NAC to increase the proportion of disease-free patients (pT0) at the time of RC (38% with NAC versus 15% without NAC). PURE-01 is a phase II, single-arm clinical trial that evaluated the potential use of pembrolizumab as neoadjuvant therapy instead of chemotherapy. Their results showed 42% of the patients were disease-free before RC (Necchi et al. 2018). In addition, several studies are evaluating the effectiveness of adding CPIs to NAC or chemoradiotherapy (NCT04241185, NCT03924856), which could potentially reveal a new approach to neoadjuvant therapy in MIBC (Galsky et al. 2021). Other combinations like pembrolizumab plus Tazemetostat (an EZH2 gene inhibitor) and pembrolizumab plus acalabrutinib (selective irreversible inhibitor of Bruton’s tyrosine kinase) are also being investigated (NCT03854474, NCT02351739) (Byrd et al. 2016; Julia and Salles 2021). Atezolizumab was studied as a first-line treatment for cisplatin-ineligible patients in the IMvigor-210 clinical trial in 2017, with encouraging results that led to its approval for this indication (Balar et al. 2017). Atezolizumab as adjuvant therapy was studied in NCT03620435, a phase I clinical trial exploring the safety and efficacy of combination chemoradiotherapy plus atezolizumab after RC in patients with MIBC. The study was stopped early because even with a reduced dose of atezolizumab, patients were still presenting grade 3 AEs, which indicated that toxicity with this combination was unacceptable and not recommended. However, the main limitation of this study is a very small sample of 8 participants (Marcq et al. 2020). NCT03775265 is a randomized phase 3 trial with an expected enrollment of 475 patients. This trial will help to evaluate and compare the safety and efficacy of chemoradiotherapy with and without atezolizumab (NCT03775265). Other potential combination therapies with atezolizumab, are being evaluated on the MORPHEUS-UC clinical trial (NCT03869190) (Advani et al. 2018).

An exciting development in CPI use is the one brought forward by the JAVELIN bladder 100 study. In this clinical trial, OS and PFS were compared in patients with unresectable MIBC given maintenance treatment with best supportive care (BSC) versus avelumab plus BSC. The results of this trial were outstanding, demonstrating significantly increased OS and PFS in patients with avleumab and BSC than in patients only receiving BSC (OS 23.8 vs. 15% respectively; PFS 19.3 vs. 6.3% respectively) (Grivas et al. 2022). Avelumab is now approved and recommended as maintenance therapy for patients with MIBC who have not progressed with platinum-based chemotherapy (Babjuk et al. 2022; FDA 2020a). Follow-up of these patients continues and the improvement in OS has also been maintained. New trials looking for combination therapies with avelumab to increase its observed efficacy as maintenance treatment are already underway (NCT05327530).

Antibody-Drug complexes (ADC)

Antibody-drug complexes (ADC) are, as the name implies, mAb directed against a specific tumoral antigen that carries a cytotoxic drug that is released inside of cells following internalization. The cytotoxic drug accumulates in the tumoral tissue through this specific delivery mechanism and causes cell death. A linker molecule is needed to bind the mAb and cytotoxic components of the complex. The linker has significant impact on the safety and efficacy of this therapy because if the linker is cleaved easily, efficacy will be higher due to improved ease in dissolving the complex and releasing the drug inside of the malignant cells. However, safety may be negatively impacted because a higher amount of cytotoxic drug will be released from the mAb before reaching its target (Pj et al. 2018). Other ways by which these medications produce their antitumor response are by facilitating phagocytosis, blocking signal transmission by direct binding, and direct antibody-dependent cytotoxicity (Abel et al. 2021; Pj et al. 2018). As of 2022, the only FDA-approved ADC are enfortumab vedotin (EV) and sacituzumab govitecan (SG). EV is approved for patients with MIBC with and without metastases who have received previous treatment with CPIs and platinum-based chemotherapy. SG is only approved for patients with metastatic disease and previous therapy with CPIs, and platinum-based chemotherapy (Babjuk et al. 2022).

Enfortumab vedotin

Enfortumab is a mAb specific for nectin-4, a transmembrane protein that plays an integral part in cell–cell adhesion (Challita-Eid et al. 2016). This protein is found with increased frequency in breast and bladder cancer tumors (Pj et al. 2018). Vedotin causes microtubule disruption (Challita-Eid et al. 2016). EV demonstrated promising activity during EV-201 (NCT03219333), a phase II clinical trial which showed 44% ORR in patients with MIBC previously treated with CPI and platinum-based chemotherapy (Cohort 1) (Babjuk et al. 2022). Cohort 2 was composed of cisplatin-ineligible patients with MIBC and previous CPI therapy. Results for Cohort 2 were also encouraging, with an ORR of 52% and 20% corresponding to CR (Balar et al. 2021b). Ongoing trials continue to evaluate the efficacy of EV, trying to find an appropriate regimen or combination that yields even better outcomes. In 2019, EV-103 (NCT03288545) studied the combination of EV plus pembrolizumab in cisplatin-ineligible patients with MIBC, with the primary intent of evaluating the safety of the combination. The resulting data for the secondary endpoints (efficacy) showed an impressive ORR of 73.3% with 15.6% having a CR (Rosenberg et al. 2020). These outstanding results led to the activation of EV-302 (NCT04223856), a phase III ongoing clinical trial that intends to compare combination treatments with EV plus pembrolizumab, EV plus pembrolizumab plus platinum-based chemotherapy, and platinum-based chemotherapy plus gemcitabine in a large group of treatment-naive patients with MIBC. It is important to mention that EV has shown a manageable safety profile, but apparent treatment-related deaths were reported in both EV-103 and EV-201 (Balar et al. 2021b). The latter study specified the four patients who died during the study were over 75 years old and had multiple comorbidities (Rosenberg et al. 2020).

Sacituzumab govitecan (SG)

SG is composed of a mAb specific for human trophoblast cell-surface antigen (TROP2) linked to the topoisomerase inhibitor SN-38. In 2021, TROPHY-U-01, a phase II study demonstrated a 27% ORR in patients with metastatic BC that had progressed with previous chemotherapy and CPIs. Due to this finding, and the few therapeutic options available for this subset of patients, the FDA granted accelerated approval of the drug (Tagawa et al. 2021). TROPiCS-04 (NCT04527991) is an ongoing phase III multicenter trial designed to corroborate the findings of TROPHY-U-01 (Vulsteke et al. 2022). Chou et al. studied the expression patterns of TROP2 and NECTIN4 in 1483 MIBC tumor samples from patients in 4 different cohorts to evaluate to what extent tumor cell sensitivity to SG and EV was impacted by a change in TROP2 and NECTIN4 expression patterns. They found a similar frequency of expression of NECTIN4 and TROP2 through all molecular subtypes (as defined by the CTGA), except in the neuronal subtype. They also observed that cells with a similar expression of both proteins adaptatively lowered their NECTIN4 expression when chronically exposed to EV, but TROP2 levels remained stable. SV maintained the same potency in vitro in EV-resistant cells. This data suggests that patients who develop EV resistance could still be able to receive treatment with SG if this same pattern is maintained in vivo (Chou et al. 2022). Combination treatment with SG and EV is being evaluated to determine its safety and feasibility (NCT04724018). Since both medications have different targets with an equal frequency of expression, concurrent treatment could yield better outcomes and less resistance. Other combinations currently being tested are SG with several CPIs. JAVELIN Bladder Medley is evaluating whether the addition of SG to avelumab as maintenance treatment could increase the efficacy previously observed with avelumab monotherapy (NCT05327530).

Trastuzumab emtansine

Several targets are being explored for the development or repurpose of ADCs for the treatment of BC. Human epidermal growth factor 2 (HER2) is a commonly expressed antigen throughout several solid malignancies. Trastuzumab, a mAb specific for HER2, is widely used to treat HER2+ breast cancer. A recently published metanalysis by Gan et al. stated a significant correlation between HER2 expression and different stages of BC (from CIS to metastatic BC), suggesting HER2 could be an ideal target for BC treatment (Gan et al. 2021). Trastuzumab-emtansine is an ADC already approved as a treatment for patients with HER2+ breast cancer who have failed therapy with trastuzumab and taxanes (Gan et al. 2021). NCT02675829 is an ongoing trial evaluating the use of trastuzumab-emtansine in several different HER2+ solid tumors, including bladder cancer.

Oncolytic viruses

There are presently no approved uses of viral gene therapy in patients with MIBC. Nevertheless, several ongoing clinical trials are trying to change this. NCT04610671 is a phase I trial evaluating the previously mentioned CG0070 in combination with nivolumab in cisplatin-ineligible patients with MIBC. This study aims to estimate the safety profile of the combination and analyze the changes it produces in the tumor microenvironment. MV-NIS is an oncolytic, attenuated measles virus currently being investigated as neoadjuvant therapy in patients who are ineligible to receive NAC (NCT03171493). This trial reported an excellent safety profile for MV-NIS, with only one treatment-related AE (hematuria). Four out of 8 patients had tumor downstaging, and T0 was evidenced in 2 out of 4 patients in the expansion cohort (Naik et al. 2022). A phase II trial will further explore its efficacy and safety. OH2, a genetically modified herpes simplex 2 virus that delivers GM-CSF to tumoral cells, is currently being studied in a phase II clinical trial (NCT05248789) to evaluate its efficacy in patients with MIBC with or without metastases that have progressed despite immunotherapy or radiotherapy.

Other non-immunological therapies

FGFR inhibitors

Even if altered FGFR is more common in non-invasive bladder cancer, evidence suggests 20–42% of MIBCs overexpress FGFR, especially FGFR3 (Kardoust Parizi et al. 2021; Patel et al. 2020). Molecular staging of MIBC has opened a new way to approach BC treatment, and TCGA has proposed the following five different subtypes based on RNA-sequencing: luminal-papillary, luminal-infiltrated, luminal, basal-squamous, and neuronal. Luminal papillary BC is found in 35% of advanced cases and is characterized by a low risk of progression, less likelihood to respond to NAC, and an elevated frequency of FGFR gene mutations. These features make it a possible target for FGFR inhibitor therapy (Iacovino et al. 2022). PROOF-302 (NCT04197986) is an ongoing trial evaluating infigratinib as adjuvant therapy in patients with MIBC. It is a multicenter, randomized, double-blind, and placebo-controlled phase III clinical trial, and its primary endpoint is to assess the DFS in a 5-year follow-up period. Genetic mutations leading to FGFR inhibitor resistance are present in about half of patients with FGFR gene mutations (Du et al. 2020). Other resistance mechanisms, like by-pass pathway activation and mutation of other genes (other tyrosine kinases, FGFR downstream signals, alteration of mTOR pathway) also contribute to overall FGFR inhibitor resistance (Du et al. 2020). Due to this, combination therapy with CPIs and FGFR inhibitors is also being explored (NCT04045613, NCT03473756). Lastly, the National Cancer Institute is testing the combination treatment with erdafitinib and enfortumab vedotin, an antibody-drug complex, in a phase 1 trial to assess the appropriate dosing and safety of the regimen (NCT04963153).

A summary of the clinical trials exploring the safety and efficacy of the various agents highlighted above, as well as information on the target MIBC patient population and study status, is provided in Table 2.

Table 2. Summary of the mentioned clinical trials on MIBC.

Trial Registration Number/Study Name	Protocol Name	Target population	Status
NCT02256436	A Phase III Randomized Clinical Trial of Pembrolizumab (MK-3475) Versus Paclitaxel, Docetaxel or Vinflunine in Subjects With Recurrent or Progressive Metastatic Urothelial Cancer	Patients with recurrent or progressive MIBC after treatment with a first line platinum containing regimen	Completed
NCT02736266	An Open Label, Single-arm, Phase 2 Study of Neoadjuvant Pembrolizumab (MK-3475) Before Cystectomy for Patients With Muscle-invasive Urothelial Bladder Cancer.	Patients with MIBC and stage T2-T4a N0M0	Recruiting
NCT03924856	A Phase 3, Randomized, Double-blind Study to Evaluate Perioperative Pembrolizumab (MK-3475) + Neoadjuvant Chemotherapy Versus Perioperative Placebo + Neoadjuvant Chemotherapy in Cisplatin-eligible Participants With Muscle-invasive Bladder Cancer (KEYNOTE-866)	Cisplatin eligible patients with non-metastatic MIBC	Recruiting
NCT04241185	A Phase 3, Randomized, Double-blind, Placebo-controlled Clinical Trial to Study the Efficacy and Safety of Pembrolizumab (MK-3475) in Combination With Chemoradiotherapy (CRT) Versus CRT Alone in Participants With Muscle-invasive Bladder Cancer (MIBC) (KEYNOTE-992)	Chemoradiotherapy eligible patients with non-metastatic MIBC	Recruiting
NCT03854474	A Pilot Study of Tazemetostat and Pembrolizumab (MK-3475) in Advanced Urothelial Carcinoma	Patients with locally advanced or metastatic MIBC with either disease progression in spite of platinum-based chemotherapy or platinum ineligible status	Recruiting
NCT02351739	Randomized Phase 2 Trial of ACP-196 and Pembrolizumab Immunotherapy Dual CHECKpoint Inhibition In Platinum-Resistant Metastatic Urothelial Carcinoma (RAPID CHECK Study)	Patients with platinum-resistant Metastatic IBC	Completed
NCT03775265	Phase III Randomized Trial of Concurrent Chemoradiotherapy With or Without Atezolizumab in Localized Muscle Invasive Bladder Cancer	Treatment-naive patients with localized, MIBC	Recruiting
NCT03869190	A Phase Ib/II, Open-Label, Multicenter, Randomized Umbrella Study Evaluating the Efficacy and Safety of Multiple Immunotherapy-Based Treatments and Combinations in Patients With Urothelial Carcinoma (MORPHEUS-UC)	Patients with locally advanced or metastatic MIBC that have progressed during or following platinum-based chemotherapy	Recruiting
NCT03219333	A Single-arm, Open-label, Multicenter Study of Enfortumab Vedotin (ASG-22CE) for Treatment of Patients With Locally Advanced or Metastatic Urothelial Cancer Who Previously Received Immune Checkpoint Inhibitor (CPI) Therapy	Patients with locally advanced or metastatic BC that received prior treatment with CPIs	Active, not recruiting
NCT04223856	An Open-label, Randomized, Controlled Phase 3 Study of Enfortumab Vedotin in Combination With Pembrolizumab Versus Chemotherapy Alone in Previously Untreated Locally Advanced or Metastatic Urothelial Cancer	Treatment-naive patients with Locally advanced or metastatic BC	Recruiting
NCT03547973	Phase II Open Label, Study of IMMU-132 in Metastatic Urothelial Cancer After Failure of Platinum-Based Regimen or Anti-PD-1/PD-L1 Based Immunotherapy	Patients with metastatic Urothelial cancer that have progressed after treatment with platinum chemotherapy and CPIs	Recruiting
NCT04527991	A Randomized Open-Label Phase III Study of Sacituzumab Govitecan Versus Treatment of Physician’s Choice in Subjects With Metastatic or Locally Advanced Unresectable Urothelial Cancer	Patients with locally advanced or metastatic bladder cancer that has recurred or progressed following platinum-based chemotherapy and CPI.	Recruiting
NCT05327530	A Phase II, Multicenter, Randomized, Open-Label, Parallel-Arm, Umbrella Study of Avelumab (MSB0010718C) in Combination With Other AntiTumor Agents as a Maintenance Treatment in Participants With Locally Advanced or Metastatic Urothelial Carcinoma Whose Disease Did Not Progress With First-Line Platinum-Containing Chemotherapy (JAVELIN Bladder Medley)	Patients with locally advanced or metastatic urothelial carcinoma that has not progressed after receiving treatment with platinum-based chemotherapy.	Not yet recruiting
NCT02675829	A Phase 2 Trial of Ado-Trastuzumab Emtansine for Patients With HER2 Amplified or Mutant Cancers	Patients with bladder cancer and documented HER2 amplification	Recruiting
NCT04610671	A Phase 1 Study of CG0070 Combined With Nivolumab in Cisplatin Ineligible Patients With Muscle Invasive Bladder Cancer (MIBC)	Cisplatin-ineligible patients with MIBC	Recruiting
NCT03171493	Neoadjuvant Intravesical NIS Measles Virus (MV-NIS) in Patients Undergoing Cystectomy for Urothelial Carcinoma But Ineligible for Neoadjuvant Cisplatin-based Chemotherapy	Patients with MIBC who are ineligible or unwilling to undergo neoadjuvant chemotherapy.	Recruiting
NCT05248789	Efficacy and Safety Study of Oncolytic Virus (OH2) Intratumoral Injection in Locally Advanced or Metastatic Bladder Cancer a Phase II Clinical Trial	Patients with locally advanced or metastatic bladder cancer that has progressed or relapsed after radiotherapy or immunotherapy	Not yet recruiting

Conclusion

The management of BC has been changing in an accelerated pace in recent years, and we can only expect this trend to continue with the amount of investigation being put towards the discovery and assessment of novel drugs and new combination treatments. Despite immunotherapy in the management of bladder cancer being used for nearly 50 years, current novel agents appear to be playing an increasingly important role. Identification of optimal combinations and sequences of agents based upon molecular subtypes is an exciting frontier that promises to improve outcomes for patients with bladder cancer.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.