Oncolytic adenovirus encoding tumor necrosis factor-related apoptosis inducing ligand (TRAIL) inhibits the growth and metastasis of triple-negative breast cancer

Oncolytic Adenovirus for the Targeting of Paclitaxel-Resistant Breast Cancer Stem Cells

Adjuvant systemic therapies effectively reduce the risk of breast cancer recurrence and metastasis, but therapy resistance can develop in some patients due to breast cancer stem cells (BCSCs). Oncolytic adenovirus (OAd) represents a promising therapeutic approach as it can specifically target cancer cells. However, its potential to target BCSCs remains unclear. Here, we evaluated a Cox-2 promoter-controlled, Ad5/3 fiber-modified OAd designed to encode the human sodium iodide symporter (hNIS) in breast cancer models. To confirm the potential of OAds to target BCSCs, we employed BCSC-enriched estrogen receptor-positive (ER+) paclitaxel-resistant (TaxR) cells and tumorsphere assays. OAd-hNIS demonstrated significantly enhanced binding and superior oncolysis in breast cancer cells, including ER+ cells, while exhibiting no activity in normal mammary epithelial cells. We observed improved NIS expression as the result of adenovirus death protein deletion. OAd-hNIS demonstrated efficacy in targeting TaxR BCSCs, exhibiting superior killing and hNIS expression compared to the parental cells. Our vector was capable of inhibiting tumorsphere formation upon early infection and reversing paclitaxel resistance in TaxR cells. Importantly, OAd-hNIS also destroyed already formed tumorspheres seven days after their initiation. Overall, our findings highlight the promise of OAd-hNIS as a potential tool for studying and targeting ER+ breast cancer recurrence and metastasis.

Oncolytic virus-based combination therapy in breast cancer

Breast cancer continues to pose significant challenges in the field of oncology, necessitating innovative treatment approaches. Among these, oncolytic viruses have emerged as a promising frontier in the battle against various types of cancer, including breast cancer. These viruses, often genetically modified, have the unique ability to selectively infect and destroy cancer cells while leaving healthy cells unharmed. Their efficacy in tumor eradication is not only owing to direct cell lysis but also relies on their capacity to activate the immune system, thereby eliciting a potent and sustained antitumor response. While oncolytic viruses represent a significant advancement in cancer treatment, the complexity and adaptability inherent to cancer require a diverse array of therapies. The concept of combining oncolytic viruses with other treatment modalities, such as chemotherapy, immunotherapy, and targeted therapies, has received significant attention. This synergistic approach capitalizes on the strengths of each therapy, thus creating a comprehensive strategy to tackle the heterogeneous and evolving nature of breast cancer. The purpose of this review is to provide an in-depth discussion of preclinical and clinical viro-based combination therapy in the context of breast cancer.

New hopes for the breast cancer treatment: perspectives on the oncolytic virus therapy

Oncolytic virus (OV) therapy has emerged as a promising frontier in cancer treatment, especially for solid tumours. While immunotherapies like immune checkpoint inhibitors and CAR-T cells have demonstrated impressive results, their limitations in inducing complete tumour regression have spurred researchers to explore new approaches targeting tumours resistant to current immunotherapies. OVs, both natural and genetically engineered, selectively replicate within cancer cells, inducing their lysis while sparing normal tissues. Recent advancements in clinical research and genetic engineering have enabled the development of targeted viruses that modify the tumour microenvironment, triggering anti-tumour immune responses and exhibiting synergistic effects with other cancer therapies. Several OVs have been studied for breast cancer treatment, including adenovirus, protoparvovirus, vaccinia virus, reovirus, and herpes simplex virus type I (HSV-1). These viruses have been modified or engineered to enhance their tumour-selective replication, reduce toxicity, and improve oncolytic properties.Newer generations of OVs, such as Oncoviron and Delta-24-RGD adenovirus, exhibit heightened replication selectivity and enhanced anticancer effects, particularly in breast cancer models. Clinical trials have explored the efficacy and safety of various OVs in treating different cancers, including melanoma, nasopharyngeal carcinoma, head and neck cancer, and gynecologic malignancies. Notably, Talimogene laherparepvec (T-VEC) and Oncorine have. been approved for advanced melanoma and nasopharyngeal carcinoma, respectively. However, adverse effects have been reported in some cases, including flu-like symptoms and rare instances of severe complications such as fistula formation. Although no OV has been approved specifically for breast cancer treatment, ongoing preclinical clinical trials focus on four groups of viruses. While mild adverse effects like low-grade fever and nausea have been observed, the effectiveness of OV monotherapy in breast cancer remains insufficient. Combination strategies integrating OVs with chemotherapy, radiotherapy, or immunotherapy, show promise in improving therapeutic outcomes. Oncolytic virus therapy holds substantial potential in breast cancer treatment, demonstrating safety in trials. Multi-approach strategies combining OVs with conventional therapies exhibit more promising therapeutic effects than monotherapy, signalling a hopeful future for OV-based breast cancer treatments.

Triple-Negative Breast Cancer: Basic Biology and Immuno-Oncolytic Viruses

Triple-negative breast cancer (TNBC) is the most lethal subtype of breast cancer. TNBC diagnoses account for approximately one-fifth of all breast cancer cases globally. The lack of receptors for estrogen, progesterone, and human epidermal growth factor 2 (HER-2, CD340) results in a lack of available molecular-based therapeutics. This increases the difficulty of treatment and leaves more traditional as well as toxic therapies as the only available standards of care in many cases. Recurrence is an additional serious problem, contributing substantially to its higher mortality rate as compared to other breast cancers. Tumor heterogeneity also poses a large obstacle to treatment approaches. No driver of tumor development has been identified for TNBC, and large variations in mutational burden between tumors have been described previously. Here, we describe the biology of six different subtypes of TNBC, based on differential gene expression. Subtype differences can have a large impact on metastatic potential and resistance to treatment. Emerging antibody-based therapeutics, such as immune checkpoint inhibitors, have available targets for small subsets of TNBC patients, leading to partial responses and relatively low overall efficacy. Immuno-oncolytic viruses (OVs) have recently become significant in the pursuit of effective treatments for TNBC. OVs generally share the ability to ignore the heterogeneous nature of TNBC cells and allow infection throughout a treated tumor. Recent genetic engineering has allowed for the enhancement of efficacy against certain tumor types while avoiding the most common side effects in non-cancerous tissues. In this review, TNBC is described in order to address the challenges it presents to potential treatments. The OVs currently described preclinically and in various stages of clinical trials are also summarized, as are their strategies to enhance therapeutic potential.

An enhancer variant associated with breast cancer susceptibility in Black women regulates TNFSF10 expression and antitumor immunity in triple-negative breast cancer

Women of African ancestry have the highest mortality from triple-negative breast cancer (TNBC) of all racial groups. To understand the genomic basis of breast cancer in the populations, we previously conducted genome-wide association studies and identified single nucleotide polymorphisms (SNPs) associated with breast cancer in Black women. In this study, we investigated the functional significance of the top associated SNP rs13074711. We found the SNP served as an enhancer variant and regulated TNFSF10 (TRAIL) expression in TNBC cells, with a significant association between the SNP genotype and TNFSF10 expression in breast tumors. Mechanistically, rs13074711 modulated the binding activity of c-MYB at the motif and thereby controlled TNFSF10 expression. Interestingly, TNFSF10 expression in many cancers was consistently lower in African Americans compared with European Americans. Furthermore, TNFSF10 expression in TNBC was significantly correlated with the expression of antiviral immune genes and was regulated by type I interferons (IFNs). Accordingly, loss of TNFSF10 resulted in a profound decrease in apoptosis of TNBC cells in response to type I IFNs and poly(I:C), a synthetic analogue of double stranded virus. Lastly, in a syngeneic mouse model of breast cancer, TNFSF10-deficiency in breast tumors decreased tumor-infiltrated CD4+ and CD8+ T cell quantities. Collectively, our results suggested that TNFSF10 plays an important role in the regulation of antiviral immune responses in TNBC, and the expression is in part regulated by a genetic variant associated with breast cancer in Black women. Our results underscore the important contributions of genetic variants to immune defense mechanisms.

Genetic Modifications That Expand Oncolytic Virus Potency

Oncolytic viruses (OVs) are a promising type of cancer therapy since they selectively replicate in tumor cells without damaging healthy cells. Many oncolytic viruses have progressed to human clinical trials, however, their performance as monotherapy has not been as successful as expected. Importantly, recent literature suggests that the oncolytic potential of these viruses can be further increased by genetically modifying the viruses. In this review, we describe genetic modifications to OVs that improve their ability to kill tumor cells directly, to dismantle the tumor microenvironment, or to alter tumor cell signaling and enhance anti-tumor immunity. These advances are particularly important to increase virus spread and reduce metastasis, as demonstrated in animal models. Since metastasis is the principal cause of mortality in cancer patients, having OVs designed to target metastases could transform cancer therapy. The genetic alterations reported to date are only the beginning of all possible improvements to OVs. Modifications described here could be combined together, targeting multiple processes, or with other non-viral therapies with potential to provide a strong and lasting anti-tumor response in cancer patients.

Oncolytic viruses for triple negative breast cancer and beyond

Biological therapy is considered an alternative treatment capable of eliciting the same effects on tumors as surgery, radiotherapy, and chemotherapy. As a major player in biological therapy, oncolytic viruses (OVs) have attracted great attention and achieved good results. Specifically, the successful application of OVs in head and neck cancer, as well as melanoma, promoted its research in triple negative breast cancer (TNBC). TNBC is a high-risk molecular type of breast cancer, characterized by strong invasion, easy recurrence, and metastasis. Due to the absence of estrogen and progesterone receptors, as well as the absence of overexpression or gene amplification of human epidermal growth factor receptor 2 (HER2), endocrine therapy and anti HER-2 targeted therapy have proven ineffective. Although chemotherapy has shown substantial efficacy in some TNBC patients, the occurrence of drug resistance and poor prognosis have prompted the exploration of new and effective treatment methods. The emerging concept of OVs provides a new platform to treat TNBC. Indeed, several studies have confirmed the therapeutic effects of OVs in TNBC. Numerous studies have also investigated the efficacy of OVs in other malignances, including solid tumor clinical trials, thus further demonstrating the promising application of oncolytic virotherapy for TNBC. The primary focus of the current review is the examination of OV mechanisms underlying their antitumor properties, while also summarizing the ongoing progress in OV research regarding TNBC treatment, as well as the various combinatorial strategies comprising OVs and other therapies. We also briefly introduce specific relevant clinical trials and discuss some of the progress in the research of novel OVs for the treatment of other malignancies, thereby affirming the significant therapeutic potential of OVs for the treatment of TNBC, as well as other cancers.

Regulation of Cancer Metastasis by TRAIL/Death Receptor Signaling

Death ligands such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL; TNFSF10) and their corresponding death receptors (e.g., DR5) not only initiate apoptosis through activation of the extrinsic apoptotic pathway but also exert non-apoptotic biological functions such as regulation of inflammation and cancer metastasis. The involvement of the TRAIL/death receptor signaling pathway in the regulation of cancer invasion and metastasis is complex as both positive and negative roles have been reported. The underlying molecular mechanisms are even more complicated. This review will focus on discussing current knowledge in our understanding of the involvement of TRAIL/death receptor-mediated signaling in the regulation of cancer cell invasion and metastasis.

CXCL12 Retargeting of an Oncolytic Adenovirus Vector to the Chemokine CXCR4 and CXCR7 Receptors in Breast Cancer

Breast cancer is the most frequently diagnosed cancer in women under 60, and the second most diagnosed cancer in women over 60. While significant progress has been made in developing targeted therapies for breast cancer, advanced breast cancer continues to have high mortality, with poor 5-year survival rates. Thus, current therapies are insufficient in treating advanced stages of breast cancer; new treatments are sorely needed to address the complexity of advanced-stage breast cancer. Oncolytic virotherapy has been explored as a therapeutic approach capable of systemic administration, targeting cancer cells, and sparing normal tissue. In particular, oncolytic adenoviruses have been exploited as viral vectors due to their ease of manipulation, production, and demonstrated clinical safety profile. In this study, we engineered an oncolytic adenovirus to target the chemokine receptors CXCR4 and CXCR7. The overexpression of CXCR4 and CXCR7 is implicated in the initiation, survival, progress, and metastasis of breast cancer. Both receptors bind to the ligand, CXCL12 (SDF-1), which has been identified to play a crucial role in the metastasis of breast cancer cells. This study incorporated a T4 fibritin protein fused to CXCL12 into the tail domain of an adenovirus fiber to retarget the vector to the CXCR4 and CXCR7 chemokine receptors. We showed that the modified virus targets and infects CXCR4- and CXCR7-overexpressing breast cancer cells more efficiently than a wild-type control vector. In addition, the substitution of the wild-type fiber and knob with the modified chimeric fiber did not interfere with oncolytic capability. Overall, the results of this study demonstrate the feasibility of retargeting adenovirus vectors to chemokine receptor-positive tumors.

A bird's eye view of the advanced approaches and strategies for overshadowing triple negative breast cancer

Triple negative breast cancer (TNBC) is one of the most aggressive form of breast cancer. It is characterized by the absence of estrogen, progesterone and human epidermal growth factor receptors. The main issue with TNBC is that it exhibits poor prognosis, high risk of relapse, short progression-free survival and low overall survival in patients. This is because the conventional therapy used for managing TNBC has issues pertaining to poor bioavailability, lower cellular uptake, increased off-target effects and development of resistance. To overcome such pitfalls, several other approaches are explored. In this context, the present manuscript showcases three of the most widely used approaches which are (i) nanotechnology-based approach; (ii) gene therapy approach and (iii) Phytochemical-based approach. The ultimate focus is to present and explain the insightful reports based on these approaches. Further, the review also expounds on the identified molecular targets and novel targeting ligands which are explored for managing TNBC effectively. Thus, in a nutshell, the review tries to highlight these existing treatment approaches which might inspire for future development of novel therapies with a potential of overshadowing TNBC.

Development of oncolytic virotherapy: from genetic modification to combination therapy

Oncolytic virotherapy (OVT) is a novel form of immunotherapy using natural or genetically modified viruses to selectively replicate in and kill malignant cells. Many genetically modified oncolytic viruses (OVs) with enhanced tumor targeting, antitumor efficacy, and safety have been generated, and some of which have been assessed in clinical trials. Combining OVT with other immunotherapies can remarkably enhance the antitumor efficacy. In this work, we review the use of wild-type viruses in OVT and the strategies for OV genetic modification. We also review and discuss the combinations of OVT with other immunotherapies.

Therapeutic potency of oncolytic virotherapy in breast cancer targeting, current status and perspective

Breast cancer is the most common cause of cancer death in women and presents a serious therapeutic challenge worldwide. Traditional treatments are less successful at targeting cancer tumors, leading to recurrent treatment-resistant secondary malignancies. Oncolytic virotherapy (OV) is a novel anticancer strategy with therapeutic implications at targeting cancer cells by using mechanisms that differ from conventional therapies. Administration of OVs either alone or in combination with standard therapies provide new insights regarding the effectiveness and improvement of treatment responses for breast cancer patients. This review summarizes cellular, animal and clinical studies investigating therapeutic potency of oncolytic virotherapy in breast cancer treatment for a better understanding and hence a better management of this disease.

Oncolytic Virotherapy for Breast Cancer Treatment

Breast cancer continues to be a leading cause of mortality among women. While at an early stage, localized breast cancer is easily treated; however, advanced stages of disease continue to carry a high mortality rate. The discrepancy in treatment success highlights that current treatments are insufficient to treat advanced-stage breast cancer. As new and improved treatments have been sought, one therapeutic approach has gained considerable attention. Oncolytic viruses are uniquely capable of targeting cancer cells through intrinsic or engineered means. They come in many forms, mainly from four major virus groups as defined by the Baltimore classification system. These vectors can target and kill cancer cells, and even stimulate immunotherapeutic effects in patients. This review discusses not only individual oncolytic viruses pursued in the context of breast cancer treatment but also the emergence of combination therapies with current or new therapies, which has become a particularly promising strategy for treatment of breast cancer. Overall, oncolytic virotherapy is a promising strategy for increased treatment efficacy for advanced breast cancer and consequently provides a unique platform for personalized treatments in patients.

Oncolytic viruses: emerging options for the treatment of breast cancer

Breast cancer (BC) is the most common type of cancer among women and is the second most common cause of cancer-related deaths, following lung cancer. Severe toxicity associated with a long-term use of BC chemo- and radiotherapy makes it essential to look for newer therapeutics. Additionally, molecular heterogeneity at both intratumoral and intertumoral levels among BC subtypes is known to result in a differential response to standard therapeutics. Oncolytic viruses (OVs) have emerged as one of the most promising treatment options for BC. Many preclinical and clinical studies have shown that OVs are effective in treating BC, both as a single therapeutic agent and as a part of combination therapies. Combination therapies involving multimodal therapeutics including OVs are becoming popular as they allow to achieve the synergistic therapeutic effects, while minimizing the associated toxicities. Here, we review the OVs for BC therapy in preclinical studies and in clinical trials, both as a monotherapy and as part of a combination therapy. We also briefly discuss the potential therapeutic targets for BC, as these are likely to be critical for the development of new OVs.

From Benchtop to Bedside: A Review of Oncolytic Virotherapy

Oncolytic viruses (OVs) demonstrate the ability to replicate selectively in cancer cells, resulting in antitumor effects by a variety of mechanisms, including direct cell lysis and indirect cell death through immune-mediate host responses. Although the mechanisms of action of OVs are still not fully understood, major advances have been made in our understanding of how OVs function and interact with the host immune system, resulting in the recent FDA approval of the first OV for cancer therapy in the USA. This review provides an overview of the history of OVs, their selectivity for cancer cells, and their multifaceted mechanism of antitumor action, as well as strategies employed to augment selectivity and efficacy of OVs. OVs in combination with standard cancer therapies are also discussed, as well as a review of ongoing human clinical trials.

Trial Watch-Oncolytic viruses and cancer therapy

Oncolytic virotherapy relies on the administration of non-pathogenic viral strains that selectively infect and kill malignant cells while favoring the elicitation of a therapeutically relevant tumor-targeting immune response. During the past few years, great efforts have been dedicated to the development of oncolytic viruses with improved specificity and potency. Such an intense wave of investigation has culminated this year in the regulatory approval by the US Food and Drug Administration (FDA) of a genetically engineered oncolytic viral strain for use in melanoma patients. Here, we summarize recent preclinical and clinical advances in oncolytic virotherapy.

Oncolytic Immunotherapy for Treatment of Cancer

Immunotherapy entails the treatment of disease by modulation of the immune system. As detailed in the previous chapters, the different modes of achieving immune modulation are many, including the use of small/large molecules, cellular therapy, and radiation. Oncolytic viruses that can specifically attack, replicate within, and destroy tumors represent one of the most promising classes of agents for cancer immunotherapy (recently termed as oncolytic immunotherapy). The notion of oncolytic immunotherapy is considered as the way in which virus-induced tumor cell death (known as immunogenic cancer cell death (ICD)) allows the immune system to recognize tumor cells and provide long-lasting antitumor immunity. Both immune responses toward the virus and ICD together contribute toward successful antitumor efficacy. What is now becoming increasingly clear is that monotherapies, through any of the modalities detailed in this book, are neither sufficient in eradicating tumors nor in providing long-lasting antitumor immune responses and that combination therapies may deliver enhanced efficacy. After the rise of the genetic engineering era, it has been possible to engineer viruses to harbor combination-like characteristics to enhance their potency in cancer immunotherapy. This chapter provides a historical background on oncolytic virotherapy and its future application in cancer immunotherapy, especially as a combination therapy with other treatment modalities.

Promising oncolytic agents for metastatic breast cancer treatment

New therapies for metastatic breast cancer patients are urgently needed. The long-term survival rates remain unacceptably low for patients with recurrent disease or disseminated metastases. In addition, existing therapies often cause a variety of debilitating side effects that severely impact quality of life. Oncolytic viruses constitute a developing therapeutic modality in which interest continues to build due to their ability to spare normal tissue while selectively destroying tumor cells. A number of different viruses have been used to develop oncolytic agents for breast cancer, including herpes simplex virus, adenovirus, vaccinia virus, measles virus, reovirus, and others. In general, clinical trials for several cancers have demonstrated excellent safety records and evidence of efficacy. However, the impressive tumor responses often observed in preclinical studies have yet to be realized in the clinic. In order for the promise of oncolytic virotherapy to be fully realized for breast cancer patients, effectiveness must be demonstrated in metastatic disease. This review provides a summary of oncolytic virotherapy strategies being developed to target metastatic breast cancer.

Classification of current anticancer immunotherapies

During the past decades, anticancer immunotherapy has evolved from a promising therapeutic option to a robust clinical reality. Many immunotherapeutic regimens are now approved by the US Food and Drug Administration and the European Medicines Agency for use in cancer patients, and many others are being investigated as standalone therapeutic interventions or combined with conventional treatments in clinical studies. Immunotherapies may be subdivided into "passive" and "active" based on their ability to engage the host immune system against cancer. Since the anticancer activity of most passive immunotherapeutics (including tumor-targeting monoclonal antibodies) also relies on the host immune system, this classification does not properly reflect the complexity of the drug-host-tumor interaction. Alternatively, anticancer immunotherapeutics can be classified according to their antigen specificity. While some immunotherapies specifically target one (or a few) defined tumor-associated antigen(s), others operate in a relatively non-specific manner and boost natural or therapy-elicited anticancer immune responses of unknown and often broad specificity. Here, we propose a critical, integrated classification of anticancer immunotherapies and discuss the clinical relevance of these approaches.

The TRAIL system is over-expressed in breast cancer and FLIP a marker of good prognosis

BACKGROUND

Breast cancer is the most common cancer in women. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway transmits apoptotic signals. Novel anticancer agents that activate this system are in clinical development, including anti-breast cancer.

METHODS

The tissue microarray technique was applied. We used an array of breast cancer tissues from a large group of patients (>800) to assess the protein expression of TRAIL-R1, TRAIL-R2, the long isoform of FLICE-inhibitory protein and total FLICE-inhibitory protein (FLIP(L) and FLIP(T)). Disease-free survival was examined by Kaplan-Meier estimates and the log-rank test. The independence of prognostic factors was determined by Cox multivariate analysis.

RESULTS

High intra-tumoral expression of all these proteins of the TRAIL pathway was found. The TRAIL receptors and FLIP(L) were not associated with survival. On univariate analysis, strong FLIP(T) expression was associated with a significantly better survival (p = 0.001). On multivariate analysis using the Cox proportional hazards model, FLIP(T) phenotype was significantly associated with a good prognosis in this series (HR 0.52, 95 % CI 0.35-0.78, p = 0.039). Results indicate that this association is valid for all the biological subtypes of breast cancer. The expression of FLIP(T) was especially high in the luminal subtype, known for its good prognosis.

CONCLUSIONS

These findings support the use of agonistic TRAIL antibodies and drugs targeting FLIP in breast cancer patients. Over-expression of FLIP(T) but not TRAIL-R1, TRAIL-R2 or FLIP(L) provides stage-independent prognostic information in breast cancer patients. This indicates a clinically less aggressive phenotype.

Trial Watch:: Oncolytic viruses for cancer therapy

Oncolytic viruses are natural or genetically modified viral species that selectively infect and kill neoplastic cells. Such an innate or exogenously conferred specificity has generated considerable interest around the possibility to employ oncolytic viruses as highly targeted agents that would mediate cancer cell-autonomous anticancer effects. Accumulating evidence, however, suggests that the therapeutic potential of oncolytic virotherapy is not a simple consequence of the cytopathic effect, but strongly relies on the induction of an endogenous immune response against transformed cells. In line with this notion, superior anticancer effects are being observed when oncolytic viruses are engineered to express (or co-administered with) immunostimulatory molecules. Although multiple studies have shown that oncolytic viruses are well tolerated by cancer patients, the full-blown therapeutic potential of oncolytic virotherapy, especially when implemented in the absence of immunostimulatory interventions, remains unclear. Here, we cover the latest advances in this active area of translational investigation, summarizing high-impact studies that have been published during the last 12 months and discussing clinical trials that have been initiated in the same period to assess the therapeutic potential of oncolytic virotherapy in oncological indications.

Replication-competent adenovirus expressing TRAIL synergistically potentiates the antitumor effect of gemcitabine in bladder cancer cells

Replication-competent adenovirus armed with therapeutic tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene has been shown to sensitize cancer cells to chemotherapy and radiotherapy. However, the synergistic antitumor effect of replication-competent adenovirus expressing TRAIL and the cytotoxic chemotherapy in bladder cancer remains to be determined. Bladder cancer T24 cells or mouse tumor xenografts were infected with replication-competent adenovirus armed with human TRAIL (ZD55-TRAIL) alone or in combination with gemcitabine. The mRNA and protein levels of TRAIL were determined by "Reverse transcription polymerase chain reaction" and Western blotting, respectively. Cell viability was tested by CCK8 assay. Tumor growth in the mice was monitored every week by measuring tumor size. Cell apoptosis was detected by Annexin V-FITC staining and TUNEL assay. We found that adenovirus ZD55-TRAIL efficiently replicated both in cultured bladder cancer T24 cells and T24 mouse tumor xenograft as demonstrated by the overexpression of TRAIL and E1A. Gemcitabine did not affect the expression of TRAIL. In cultured T24 cells, ZD55-TRAIL enhanced the growth inhibitory effects of gemcitabine, accompanied by increased apoptosis. Similarly, ZD55-TRAIL synergistically enhanced the antitumor effect and induction of apoptosis following gemcitabine treatment in mouse T24 xenografts. In conclusion, replicative adenovirus armed with TRAIL synergistically potentiates the antitumor effect of gemcitabine in human bladder cancer. Our study provides the basis for the development of ZD55-TRAIL in combination with conventional chemotherapy for the treatment of bladder cancer.