Oncolytic Adenovirus ICOVIR-7 in Patients with Advanced and Refractory Solid Tumors

Present and Future of Immunotherapy for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) lacks the expression of estrogen receptors (ERs), human epidermal growth factor receptor 2 (HER2), and progesterone receptors (PRs). TNBC has the poorest prognosis among breast cancer subtypes and is more likely to respond to immunotherapy due to its higher expression of PD-L1 and a greater percentage of tumor-infiltrating lymphocytes. Immunotherapy has revolutionized TNBC treatment, especially with the FDA's approval of pembrolizumab (Keytruda) combined with chemotherapy for advanced cases, opening new avenues for treating this deadly disease. Although immunotherapy can significantly improve patient outcomes in a subset of patients, achieving the desired response rate for all remains an unmet clinical goal. Strategies that enhance responses to immune checkpoint blockade, including combining immunotherapy with chemotherapy, molecularly targeted therapy, or radiotherapy, may improve response rates and clinical outcomes. In this review, we provide a short background on TNBC and immunotherapy and explore the different types of immunotherapy strategies that are currently being evaluated in TNBC. Additionally, we review why combination strategies may be beneficial, provide an overview of the combination strategies, and discuss the novel immunotherapeutic opportunities that may be approved in the near future for TNBC.

Translation of oncolytic viruses in sarcoma

Sarcomas are a rare and highly diverse group of malignancies of mesenchymal origin. While sarcomas are generally considered resistant to immunotherapy, recent studies indicate subtype-specific differences in clinical response to checkpoint inhibitors (CPIs) that are associated with distinct immune phenotypes present in sarcoma subtypes. Oncolytic viruses (OVs) are designed to selectively infect and kill tumor cells and induce intratumoral immune infiltration, enhancing immunogenicity and thereby sensitizing tumors to immunotherapy. Herein we review the accumulated clinical data evaluating OVs in sarcoma. Small numbers of patients with sarcoma were enrolled in early-stage OV trials as part of larger solid tumor cohorts demonstrating safety but providing limited insight into the biological effects due to the low patient numbers and lack of histologic grouping. Several recent studies have investigated talimogene laherparepvec (T-VEC), an approved oncolytic herpes simplex virus (HSV-1), in combination therapy regimens in sarcoma patient cohorts. These studies have shown promising responses in heavily pre-treated and immunotherapy-resistant patients associated with increased intratumoral immune infiltration. As new and more potent OVs enter the clinical arena, prospective evaluation in subtype-specific cohorts with correlative studies to define biomarkers of response will be critical to advancing this promising approach for sarcoma therapy.

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.

Molecular insights and promise of oncolytic virus based immunotherapy

Discovering a therapeutic that can counteract the aggressiveness of this disease's mechanism is crucial for improving survival rates for cancer patients and for better understanding the most different types of cancer. In recent years, using these viruses as an anticancer therapy has been thought to be successful. They mostly work by directly destroying cancer cells, activating the immune system to fight cancer, and expressing exogenous effector genes. For the treatment of tumors, oncolytic viruses (OVs), which can be modified to reproduce only in tumor tissues and lyse them while preserving the healthy non-neoplastic host cells and reinstating antitumor immunity which present a novel immunotherapeutic strategy. OVs can exist naturally or be created in a lab by altering existing viruses. These changes heralded the beginning of a new era of less harmful virus-based cancer therapy. We discuss three different types of oncolytic viruses that have already received regulatory approval to treat cancer as well as clinical research using oncolytic adenoviruses. The primary therapeutic applications, mechanism of action of oncolytic virus updates, future views of this therapy will be covered in this chapter.

Harnessing adenovirus in cancer immunotherapy: evoking cellular immunity and targeting delivery in cell-specific manner

Recombinant adenovirus (rAd) regimens, including replication-competent oncolytic adenovirus (OAV) and replication-deficient adenovirus, have been identified as potential cancer therapeutics. OAV presents advantages such as selective replication, oncolytic efficacy, and tumor microenvironment (TME) remodeling. In this perspective, the principles and advancements in developing OAV toolkits are reviewed. The burgeoning rAd may dictate efficacy of conventional cancer therapies as well as cancer immunotherapies, including cancer vaccines, synergy with adoptive cell therapy (ACT), and TME reshaping. Concurrently, we explored the potential of rAd hitchhiking to adoptive immune cells or stem cells, highlighting how this approach facilitates synergistic interactions between rAd and cellular therapeutics at tumor sites. Results from preclinical and clinical trials in which immune and stem cells were infected with rAd have been used to address significant oncological challenges, such as postsurgical residual tumor tissue and metastatic tissue. Briefly, rAd can eradicate tumors through various mechanisms, resulting from tumor immunogenicity, reprogramming of the TME, enhancement of cellular immunity, and effective tumor targeting. In this context, we argue that rAd holds immense potential for enhancing cellular immunity and synergistically improving antitumor effects in combination with novel cancer immunotherapies.

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.

Anticancer Activity of Measles-Mumps-Rubella MMR Vaccine Viruses against Glioblastoma

BACKGROUND

Oncolytic viruses (OVs) have been utilized since 1990s for targeted cancer treatment. Our study examined the Measles-Mumps-Rubella (MMR) vaccine's cancer-killing potency against Glioblastoma (GBM), a therapy-resistant, aggressive cancer type.

METHODOLOGY

We used GBM cell lines, primary GBM cells, and normal mice microglial cells, to assess the MMR vaccine's efficacy through cell viability, cell cycle analysis, intracellular viral load via RT-PCR, and Transmission Electron Microscopy (TEM).

RESULTS

After 72 h of MMR treatment, GBM cell lines and primary GBM cells exhibited significant viability reduction compared to untreated cells. Conversely, normal microglial cells showed only minor changes in viability and morphology. Intracellular viral load tests indicated GBM cells' increased sensitivity to MMR viruses compared to normal cells. The cell cycle study also revealed measles and mumps viruses' crucial role in cytopathic effects, with the rubella virus causing cell cycle arrest.

CONCLUSION

Herein the reported results demonstrate the anti-cancer activity of the MMR vaccine against GBM cells. Accordingly, the MMR vaccine warrants further study as a potential new tool for GBM therapy and relapse prevention. Therapeutic potential of the MMR vaccine has been found to be promising in earlier studies as well.

Development and application of oncolytic viruses as the nemesis of tumor cells

Viruses and tumors are two pathologies that negatively impact human health, but what occurs when a virus encounters a tumor? A global consensus among cancer patients suggests that surgical resection, chemotherapy, radiotherapy, and other methods are the primary means to combat cancer. However, with the innovation and development of biomedical technology, tumor biotherapy (immunotherapy, molecular targeted therapy, gene therapy, oncolytic virus therapy, etc.) has emerged as an alternative treatment for malignant tumors. Oncolytic viruses possess numerous anti-tumor properties, such as directly lysing tumor cells, activating anti-tumor immune responses, and improving the tumor microenvironment. Compared to traditional immunotherapy, oncolytic virus therapy offers advantages including high killing efficiency, precise targeting, and minimal side effects. Although oncolytic virus (OV) therapy was introduced as a novel approach to tumor treatment in the 19th century, its efficacy was suboptimal, limiting its widespread application. However, since the U.S. Food and Drug Administration (FDA) approved the first OV therapy drug, T-VEC, in 2015, interest in OV has grown significantly. In recent years, oncolytic virus therapy has shown increasingly promising application prospects and has become a major research focus in the field of cancer treatment. This article reviews the development, classification, and research progress of oncolytic viruses, as well as their mechanisms of action, therapeutic methods, and routes of administration.

Deregulated E2F Activity as a Cancer-Cell Specific Therapeutic Tool

The transcription factor E2F, the principal target of the tumor suppressor pRB, plays crucial roles in cell proliferation and tumor suppression. In almost all cancers, pRB function is disabled, and E2F activity is enhanced. To specifically target cancer cells, trials have been undertaken to suppress enhanced E2F activity to restrain cell proliferation or selectively kill cancer cells, utilizing enhanced E2F activity. However, these approaches may also impact normal growing cells, since growth stimulation also inactivates pRB and enhances E2F activity. E2F activated upon the loss of pRB control (deregulated E2F) activates tumor suppressor genes, which are not activated by E2F induced by growth stimulation, inducing cellular senescence or apoptosis to protect cells from tumorigenesis. Deregulated E2F activity is tolerated in cancer cells due to inactivation of the ARF-p53 pathway, thus representing a feature unique to cancer cells. Deregulated E2F activity, which activates tumor suppressor genes, is distinct from enhanced E2F activity, which activates growth-related genes, in that deregulated E2F activity does not depend on the heterodimeric partner DP. Indeed, the ARF promoter, which is specifically activated by deregulated E2F, showed higher cancer-cell specific activity, compared to the E2F1 promoter, which is also activated by E2F induced by growth stimulation. Thus, deregulated E2F activity is an attractive potential therapeutic tool to specifically target cancer cells.

Rational selection of an ideal oncolytic virus to address current limitations in clinical translation

Oncolytic virus therapy (OVT) is a promising modality that leverages the propensity of natural or engineered viruses to selectively replicate in and kill cancer cells. Over the past decade, (pre)clinical studies have focused on the development and testing of adenovirus, herpes simplex virus, and vaccinia virus-based vectors. These studies have identified barriers to success confronting the field. Here, we propose a set of selection criteria or ideal properties of a successful oncolytic virus, which include lack of pathogenicity, low seroprevalence, selectivity (infection and replication), transgene carrying capacity, and genome stability. We use these requirements to analyze the oncolytic virus landscape, and then identify a potentially optimal species for platform development - vesicular stomatitis virus.

Effects of pre-existing anti-adenovirus antibodies on transgene expression levels and therapeutic efficacies of arming oncolytic adenovirus

Oncolytic adenoviruses (OAds), most of which are based on species C human adenovirus serotype 5 (Ad5) (OAd5), have recently received much attention as potential anticancer agents. High seroprevalence of anti-Ad5 neutralizing antibodies is a major hurdle for Ad5-based gene therapy. However, the impacts of anti-Ad5 neutralizing antibodies on OAd5-mediated transgene expression in the tumor and antitumor effects remain to be fully elucidated. In this study, we examined the impact of anti-Ad5 neutralizing antibodies on the OAd5-mediated antitumor effects and OAd5-mediated transgene expression. The luciferase expression of OAd-tAIB-Luc, which contains the cytomegalovirus promoter-driven luciferase gene, was inhibited in human cultured cells in the presence of human serum. Although the inhibitory effects of human serum possessing the low anti-Ad5 neutralizing antibody titers were overcome by long-term infection, the in vitro tumor cell lysis activities of OAd-tAIB-Luc were entirely attenuated by human serum containing the high titers of anti-Ad5 neutralizing antibodies. OAd-tAIB-Luc-mediated luciferase expression in the subcutaneous tumors 3 days after administration and tumor growth suppression levels following intratumoral administration were significantly lower in mice possessing the high titers of anti-Ad5 neutralizing antibodies, compared to those in control mice. These results suggested that pre-existing anti-Ad5 antibodies attenuated both transgene expression and potential antitumor effects of OAd5 following intratumoral administration.

Immunotherapy in triple negative breast cancer: beyond checkpoint inhibitors

The development of immunotherapy agents has revolutionized the field of oncology. The only FDA-approved immunotherapeutic approach in breast cancer consists of immune checkpoint inhibitors, yet several novel immune-modulatory strategies are being actively studied and appear promising. Innovative immunotherapeutic strategies are urgently needed in triple negative breast cancer (TNBC), a subtype of breast cancer known for its poor prognosis and its resistance to conventional treatments. TNBC is more primed to respond to immunotherapy given the presence of more tumor infiltrating lymphocytes, higher PD-L1 expression, and higher tumor mutation burden relative to the other breast cancer subtypes, and therefore, immuno-oncology represents a key area of promise for TNBC research. The aim of this review is to highlight current data and ongoing efforts to establish the safety and efficacy of immunotherapeutic approaches beyond checkpoint inhibitors in TNBC.

Modern approaches to treating cancer with oncolytic viruses

According to the World Health Organization, cancer is the second leading cause of death in the world. This serves as a powerful incentive to search for new effective cancer treatments. Development of new oncolytic viruses capable of selectively destroying cancer cells is one of the modern approaches to cancer treatment. The advantage of this method – the selective lysis of tumor cells with the help of viruses – leads to an increase in the antitumor immune response of the body, that in turn promotes the destruction of the primary tumor and its metastases. Significant progress in development of this method has been achieved in the last decade. In this review we analyze the literature data on families of oncolytic viruses that have demonstrated a positive therapeutic effect against malignant neoplasms in various localizations. We discuss the main mechanisms of the oncolytic action of viruses and assess their advantages over other methods of cancer therapy as well as the prospects for their use in clinical practice.

Therapeutic Efficacy of Oncolytic Viruses in Fighting Cancer: Recent Advances and Perspective

Immunotherapy is at the cutting edge of modern cancer treatment. Innovative medicines have been developed with varying degrees of success that target all aspects of tumor biology: tumors, niches, and the immune system. Oncolytic viruses (OVs) are a novel and potentially immunotherapeutic approach for cancer treatment. OVs reproduce exclusively in cancer cells, causing the tumor mass to lyse. OVs can also activate the immune system in addition to their primary activity. Tumors create an immunosuppressive environment by suppressing the immune system’s ability to respond to tumor cells. By injecting OVs into the tumor, the immune system is stimulated, allowing it to generate a robust and long-lasting response against the tumor. The essential biological properties of oncolytic viruses, as well as the underlying mechanisms that enable their usage as prospective anticancer medicines, are outlined in this review. We also discuss the increased efficacy of virotherapy when combined with other cancer medications.

Targeting Triple Negative Breast Cancer With Oncolytic Adenoviruses

Breast cancer (BC) is the most common cancer globally, accounting for 685,000 deaths in 2020. Triple-negative breast cancers (TNBC) lack oestrogen (ER) and progesterone (PR) hormone receptor expression and HER2 overexpression. TNBC represent 10–15% of all BC with high incidence in women under 50-years old that have BRCA mutations, and have a dismal prognosis. African American and Hispanic women are at higher risk partly due to the common occurrence of BRCA mutations. The standard treatment for TNBC includes surgery, radiotherapy, and chemotherapy although, resistance to all standard-of-care therapies eventually develops. It is crucial to identify and develop more efficacious therapeutics with different mechanisms of action to improve on survival in these women. Recent findings with oncolytic adenoviruses (OAds) may generate a new strategy to improve on the outcomes for women afflicted by TNBC and other types of BC. OAds are genetically engineered to selectively lyse, eliminate and recruit the host antitumour immune responses, leaving normal cells unharmed. The most common modifications are deletions in the early gene products including the E1B55 KDa protein, specific regions of the E1A protein, or insertion of tumour-specific promoters. Clinical trials using OAds for various adenocarcinomas have not yet been sufficiently evaluated in BC patients. Preclinical studies demonstrated efficacy in BC cell lines, including TNBC cells, with promising novel adenoviral mutants. Here we review the results reported for the most promising OAds in preclinical studies and clinical trials administered alone and in combination with current standard of care or with novel therapeutics. Combinations of OAds with small molecule drugs targeting the epidermal growth factor receptor (EGFR), androgen receptor (AR), and DNA damage repair by the novel PARP inhibitors are currently under investigation with reported enhanced efficacy. The combination of the PARP-inhibitor Olaparib with OAds showed an impressive anti-tumour effect. The most promising findings to date are with OAds in combination with antibodies towards the immune checkpoints or expression of cytokines from the viral backbone. Although safety and efficacy have been demonstrated in numerous clinical trials and preclinical studies with cancer-selective OAds, further developments are needed to eliminate metastatic lesions, increase immune activation and intratumoural viral spread. We discuss shortcomings of the OAds and potential solutions for improving on patient outcomes.

Progress and Prospect of Immunotherapy for Triple-Negative Breast Cancer

Breast cancer is the most commonly diagnosed cancer (estimated 2.3 million new cases in 2020) and the leading cause of cancer death (estimated 685,000 deaths in 2020) in women globally. Breast cancers have been categorized into four major molecular subtypes based on the immunohistochemistry (IHC) expression of classic hormone and growth factor receptors including the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), as well as a proliferation marker Ki-67 protein expression. Triple-negative breast cancer (TNBC), a breast cancer subtype lacking ER, PR, and HER2 expression, is associated with a high metastatic potential and poor prognosis. TNBC accounts for approximately only 15%-20% of new breast cancer diagnoses; it is responsible for most breast cancer-related deaths due to the lack of targeted treatment options for this patient population, and currently, systemic chemotherapy, radiation, and surgical excision remain the major treatment modalities for these patients with TNBC. Although breast cancer patients in general do not have a robust response to the immunotherapy, a subset of TNBC has been demonstrated to have high tumor mutation burden and high tumor-infiltrating lymphocytes, resembling the features observed on melanoma or lung cancers, which can benefit from the treatment of immune checkpoint inhibitors (ICIs). Therefore, the immunogenic nature of this aggressive disease has presented an opportunity for the development of TNBC-targeting immunotherapies. The recent US Food and Drug Administration approval of atezolizumab in combination with the chemotherapeutic agent nab-paclitaxel for the treatment of PD-L1-positive unresectable, locally advanced, or metastatic TNBC has led to a new era of immunotherapy in TNBC treatment. In addition, immunotherapy becomes an active research area, both in the cancer biology field and in the oncology field. In this review, we will extend our coverage on recent discoveries in preclinical research and early results in clinical trials from immune molecule-based therapy including cytokines, monoclonal antibodies, antibody-drug conjugates, bi-specific or tri-specific antibodies, ICIs, and neoantigen cancer vaccines; oncolytic virus-based therapies and adoptive immune cell transfer-based therapies including TIL, chimeric antigen receptor-T (CAR-T), CAR-NK, CAR-M, and T-cell receptor-T. In the end, we will list a series of the challenges and opportunities in immunotherapy prospectively and reveal novel technologies such as high-throughput single-cell sequencing and CRISPR gene editing-based screening to generate new knowledges of immunotherapy.

Clinical Trials of Oncolytic Viruses in Breast Cancer

Breast cancer is the second most common kind of cancer worldwide and oncolytic viruses may offer a new treatment approach. There are three different types of oncolytic viruses used in clinical trials; (i) oncolytic viruses with natural anti-neoplastic properties; (ii) oncolytic viruses designed for tumor-selective replication; (iii) oncolytic viruses modified to activate the immune system. Currently, fourteen different oncolytic viruses have been investigated in eighteen published clinical trials. These trials demonstrate that oncolytic viruses are well tolerated and safe for use in patients and display clinical activity. However, these trials mainly studied a small number of patients with different advanced tumors including some with breast cancer. Future trials should focus on breast cancer and investigate optimal routes of administration, occurrence of neutralizing antibodies, viral gene expression, combinations with other antineoplastic therapies, and identify subtypes that are particularly suitable for oncolytic virotherapy.

Viral vector platforms within the gene therapy landscape

Throughout its 40-year history, the field of gene therapy has been marked by many transitions. It has seen great strides in combating human disease, has given hope to patients and families with limited treatment options, but has also been subject to many setbacks. Treatment of patients with this class of investigational drugs has resulted in severe adverse effects and, even in rare cases, death. At the heart of this dichotomous field are the viral-based vectors, the delivery vehicles that have allowed researchers and clinicians to develop powerful drug platforms, and have radically changed the face of medicine. Within the past 5 years, the gene therapy field has seen a wave of drugs based on viral vectors that have gained regulatory approval that come in a variety of designs and purposes. These modalities range from vector-based cancer therapies, to treating monogenic diseases with life-altering outcomes. At present, the three key vector strategies are based on adenoviruses, adeno-associated viruses, and lentiviruses. They have led the way in preclinical and clinical successes in the past two decades. However, despite these successes, many challenges still limit these approaches from attaining their full potential. To review the viral vector-based gene therapy landscape, we focus on these three highly regarded vector platforms and describe mechanisms of action and their roles in treating human disease.

Oncolytic Virotherapy in Solid Tumors: The Challenges and Achievements

Oncolytic virotherapy (OVT) is a promising approach in cancer immunotherapy. Oncolytic viruses (OVs) could be applied in cancer immunotherapy without in-depth knowledge of tumor antigens. The capability of genetic modification makes OVs exciting therapeutic tools with a high potential for manipulation. Improving efficacy, employing immunostimulatory elements, changing the immunosuppressive tumor microenvironment (TME) to inflammatory TME, optimizing their delivery system, and increasing the safety are the main areas of OVs manipulations. Recently, the reciprocal interaction of OVs and TME has become a hot topic for investigators to enhance the efficacy of OVT with less off-target adverse events. Current investigations suggest that the main application of OVT is to provoke the antitumor immune response in the TME, which synergize the effects of other immunotherapies such as immune-checkpoint blockers and adoptive cell therapy. In this review, we focused on the effects of OVs on the TME and antitumor immune responses. Furthermore, OVT challenges, including its moderate efficiency, safety concerns, and delivery strategies, along with recent achievements to overcome challenges, are thoroughly discussed.

Oncolytic Adenovirus Type 3 Coding for CD40L Facilitates Dendritic Cell Therapy of Prostate Cancer in Humanized Mice and Patient Samples

Dendritic cell (DC)-based vaccines have shown some degree of success for the treatment of prostate cancer (PC). However, the highly immunosuppressive tumor microenvironment leads to DC dysfunction, which has limited the effectiveness of these vaccines. We hypothesized that use of a fully serotype 3 oncolytic adenovirus (Ad3-hTERT-CMV-hCD40L; TILT-234) could stimulate DCs in the prostate tumor microenvironment by expressing CD40L. Activated DCs would then activate cytotoxic T cells against the tumor, resulting in therapeutic immune responses. Oncolytic cell killing due to cancer cell-specific virus replication adds to antitumor effects but also enhances the immunological effect by releasing tumor epitopes for sampling by DC, in the presence of danger signals. In this study, we evaluated the companion effect of Ad3-hTERT-CMV-hCD40L and DC-therapy in a humanized mouse model and PC histocultures. Treatment with Ad3-hTERT-CMV-hCD40L and DC resulted in enhanced antitumor responses in vivo. Treatment of established histocultures with Ad3-hTERT-CMV-hCD40L induced DC maturation and notable increase in proinflammatory cytokines. In conclusion, Ad3-hTERT-CMV-hCD40L is able to modulate an immunosuppressive prostate tumor microenvironment and improve the effectiveness of DC vaccination in PC models and patient histocultures, setting the stage for clinical translation.

Development of a New Hyaluronic Acid Based Redox-Responsive Nanohydrogel for the Encapsulation of Oncolytic Viruses for Cancer Immunotherapy

Oncolytic viruses (OVs) are emerging as promising and potential anti-cancer therapeutic agents, not only able to kill cancer cells directly by selective intracellular viral replication, but also to promote an immune response against tumor. Unfortunately, the bioavailability under systemic administration of OVs is limited because of undesired inactivation caused by host immune system and neutralizing antibodies in the bloodstream. To address this issue, a novel hyaluronic acid based redox responsive nanohydrogel was developed in this study as delivery system for OVs, with the aim to protect the OVs following systemic administration. The nanohydrogel was formulated by water in oil (W/O) nanoemulsion method and cross-linked by disulfide bonds derived from the thiol groups of synthesized thiolated hyaluronic acid. One DNA OV Ad[I/PPT-E1A] and one RNA OV Rigvir^® ECHO-7 were encapsulated into the developed nanohydrogel, respectively, in view of their potential of immunovirotherapy to treat cancers. The nanohydrogels showed particle size of approximately 300–400 nm and negative zeta potential of around −13 mV by dynamic light scattering (DLS). A uniform spherical shape of the nanohydrogel was observed under the scanning electron microscope (SEM) and transmission electron microscope (TEM), especially, the successfully loading of OV into nanohydrogel was revealed by TEM. The crosslinking between the hyaluronic acid chains was confirmed by the appearance of new peak assigned to disulfide bond in Raman spectrum. Furthermore, the redox responsive ability of the nanohydrogel was determined by incubating the nanohydrogel into phosphate buffered saline (PBS) pH 7.4 with 10 μM or 10 mM glutathione at 37 °C which stimulate the normal physiological environment (extracellular) or reductive environment (intracellular or tumoral). The relative turbidity of the sample was real time monitored by DLS which indicated that the nanohydrogel could rapidly degrade within 10 h in the reductive environment due to the cleavage of disulfide bonds, while maintaining the stability in the normal physiological environment after 5 days. Additionally, in vitro cytotoxicity assays demonstrated a good oncolytic activity of OVs-loaded nanohydrogel against the specific cancer cell lines. Overall, the results indicated that the developed nanohydrogel is a delivery system appropriate for viral drugs, due to its hydrophilic and porous nature, and also thanks to its capacity to maintain the stability and activity of encapsulated viruses. Thus, nanohydrogel can be considered as a promising candidate carrier for systemic administration of oncolytic immunovirotherapy.

Clinical Application of Oncolytic Viruses: A Systematic Review

Leveraging the immune system to thwart cancer is not a novel strategy and has been explored via cancer vaccines and use of immunomodulators like interferons. However, it was not until the introduction of immune checkpoint inhibitors that we realized the true potential of immunotherapy in combating cancer. Oncolytic viruses are one such immunotherapeutic tool that is currently being explored in cancer therapeutics. We present the most comprehensive systematic review of all oncolytic viruses in Phase 1, 2, and 3 clinical trials published to date. We performed a systematic review of all published clinical trials indexed in PubMed that utilized oncolytic viruses. Trials were reviewed for type of oncolytic virus used, method of administration, study design, disease type, primary outcome, and relevant adverse effects. A total of 120 trials were found; 86 trials were available for our review. Included were 60 phase I trials, five phase I/II combination trials, 19 phase II trials, and two phase III clinical trials. Oncolytic viruses are feverously being evaluated in oncology with over 30 different types of oncolytic viruses being explored either as a single agent or in combination with other antitumor agents. To date, only one oncolytic virus therapy has received an FDA approval but advances in bioengineering techniques and our understanding of immunomodulation to heighten oncolytic virus replication and improve tumor kill raises optimism for its future drug development.

Determinants of the efficacy of viro-immunotherapy: A review

Oncolytic virus immunotherapy is rapidly gaining interest in the field of immunotherapy against cancer. The minimal toxicity upon treatment and the dual activity of direct oncolysis and immune activation make therapy with oncolytic viruses (OVs) an interesting treatment modality. The safety and efficacy of several OVs have been assessed in clinical trials and, so far, the Food and Drug Administration (FDA) has approved one OV. Unfortunately, most treatments with OVs have shown suboptimal responses in clinical trials, while they appeared more promising in preclinical studies, with tumours reducing after immune cell influx. In several clinical trials with OVs, parameters such as virus replication, virus-specific antibodies, systemic immune responses, immune cell influx into tumours and tumour-specific antibodies have been studied as predictors or correlates of therapy efficacy. In this review, these studies are summarized to improve our understanding of the determinants of the efficacy of OV therapies in humans and to provide insights for future developments in the viro-immunotherapy treatment field.

Oncolytic viruses for cancer immunotherapy

In this review, we discuss the use of oncolytic viruses in cancer immunotherapy treatments in general, with a particular focus on adenoviruses. These serve as a model to elucidate how versatile viruses are, and how they can be used to complement other cancer therapies to gain optimal patient benefits. Historical reports from over a hundred years suggest treatment efficacy and safety with adenovirus and other oncolytic viruses. This is confirmed in more contemporary patient series and multiple clinical trials. Yet, while the first viruses have already been granted approval from several regulatory authorities, room for improvement remains.

As good safety and tolerability have been seen, the oncolytic virus field has now moved on to increase efficacy in a wide array of approaches. Adding different immunomodulatory transgenes to the viruses is one strategy gaining momentum. Immunostimulatory molecules can thus be produced at the tumor with reduced systemic side effects. On the other hand, preclinical work suggests additive or synergistic effects with conventional treatments such as radiotherapy and chemotherapy. In addition, the newly introduced checkpoint inhibitors and other immunomodulatory drugs could make perfect companions to oncolytic viruses. Especially tumors that seem not to be recognized by the immune system can be made immunogenic by oncolytic viruses. Logically, the combination with checkpoint inhibitors is being evaluated in ongoing trials. Another promising avenue is modulating the tumor microenvironment with oncolytic viruses to allow T cell therapies to work in solid tumors.

Oncolytic viruses could be the next remarkable wave in cancer immunotherapy.

Recent advances of oncolytic virus in cancer therapy

Oncolytic viruses have been taking the front stage in biological therapy for cancer recently. The first and most potent virus to be used in oncolytic virotherapy is human adenovirus. Recently, ongoing extensive research has suggested that other viruses like herpes simplex virus (HSV) and measles virus can also be considered as potential candidates in cancer therapy. An HSV-based oncolytic virus, T-VEC, has completed phase Ш clinical trial and has been approved by the U.S. Food and Drug Administration (FDA) for use in biological cancer therapy. Moreover, the vaccine strain of the measles virus has shown impressive results in pre-clinical and clinical trials. Considering their therapeutic efficacy, safety, and reduced side effects, the use of such engineered viruses in biological cancer therapy has the potential to establish a milestone in cancer research. In this review, we summarize the recent clinical advances in the use of oncolytic viruses in biological therapy for cancer. Additionally, this review evaluates the potential viral candidates for their benefits and shortcomings and sheds light on the future prospects.

Role of E2Fs and mitotic regulators controlled by E2Fs in the epithelial to mesenchymal transition

The epithelial-to-mesenchymal transition (EMT) is a complex cellular process in which epithelial cells acquire mesenchymal properties. EMT occurs in three biological settings: development, wound healing and fibrosis, and tumor progression. Despite occurring in three independent biological settings, EMT signaling shares some molecular mechanisms that allow epithelial cells to de-differentiate and acquire mesenchymal characteristics that confer cells invasive and migratory capacity to distant sites. Here we summarize the molecular mechanism that delineates EMT and we will focus on the role of E2 promoter binding factors (E2Fs) in EMT during tumor progression. Since the E2Fs are presently undruggable due to their control in numerous pivotal cellular functions and due to the lack of selectivity against individual E2Fs, we will also discuss the role of three mitotic regulators and/or mitotic kinases controlled by the E2Fs (NEK2, Mps1/TTK, and SGO1) in EMT that can be useful as drug targets.

Impact statement

The study of the epithelial to mesenchymal transition (EMT) is an active area of research since it is one of the early intermediates to invasion and metastasis—a state of the cancer cells that ultimately kills many cancer patients. We will present in this review that besides their canonical roles as regulators of proliferation, unregulated expression of the E2F transcription factors may contribute to cancer initiation and progression to metastasis by signaling centrosome amplification, chromosome instability, and EMT. Since our discovery that the E2F activators control centrosome amplification and mitosis in cancer cells, we have identified centrosome and mitotic regulators that may represent actionable targets against EMT and metastasis in cancer cells. This is impactful to all of the cancer patients in which the Cdk/Rb/E2F pathway is deregulated, which has been estimated to be most cancer patients with solid tumors.

The broken cycle: E2F dysfunction in cancer

The cyclin-dependent kinase (CDK)-RB-E2F axis forms the core transcriptional machinery driving cell cycle progression, dictating the timing and fidelity of genome replication and ensuring genetic material is accurately passed through each cell division cycle. The ultimate effectors of this axis are members of a family of eight distinct E2F genes encoding transcriptional activators and repressors. E2F transcriptional activity is tightly regulated throughout the cell cycle via transcriptional and translational regulation, post-translational modifications, protein degradation, binding to cofactors and subcellular localization. Alterations in one or more key components of this axis (CDKs, cyclins, CDK inhibitors and the RB family of proteins) occur in virtually all cancers and result in heightened oncogenic E2F activity, leading to uncontrolled proliferation. In this Review, we discuss the activities of E2F proteins with an emphasis on the newest atypical E2F family members, the specific and redundant functions of E2F proteins, how misexpression of E2F transcriptional targets promotes cancer and both current and developing therapeutic strategies being used to target this oncogenic pathway.

A Phase 1 Trial of Oncolytic Adenovirus ICOVIR-5 Administered Intravenously to Cutaneous and Uveal Melanoma Patients

Oncolytic viruses represent a unique type of agents that combine self-amplification, lytic, and immunostimulatory properties against tumors. A local and locoregional clinical benefit has been demonstrated upon intratumoral injections of an oncolytic herpes virus in melanoma patients, leading to its approval in the United States and Europe for patients without visceral disease (up to stage IVM1a). However, in order to debulk and change the local immunosuppressive environment of tumors that cannot be injected directly, oncolyitc viruses need to be administered systemically. Among different viruses, adenovirus has been extensively used in clinical trials but with few evidences of activity upon systemic administration. Preclinical efficacy of a single intravenous administration of our oncolytic adenovirus ICOVIR5, an adenovirus type 5 responsive to the retinoblastoma pathway commonly deregulated in tumors, led us to use this virus in a dose-escalation phase 1 trial in metastatic melanoma patients. The results in 12 patients treated with a single infusion of a dose up to 1 × 10¹³ viral particles show that ICOVIR5 can reach melanoma metastases upon a single intravenous administration but fails to induce tumor regressions. These results support the systemic administration of armed oncolytic viruses to treat disseminated cancer.

The Current Status and Future Prospects of Oncolytic Viruses in Clinical Trials against Melanoma, Glioma, Pancreatic, and Breast Cancers

Oncolytic viral therapy has been accepted as a standard immunotherapy since talimogene laherparepvec (T-VEC, Imlygic^®) was approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA) for melanoma treatment in 2015. Various oncolytic viruses (OVs), such as HF10 (Canerpaturev—C-REV) and CVA21 (CAVATAK), are now actively being developed in phase II as monotherapies, or in combination with immune checkpoint inhibitors against melanoma. Moreover, in glioma, several OVs have clearly demonstrated both safety and a promising efficacy in the phase I clinical trials. Additionally, the safety of several OVs, such as pelareorep (Reolysin^®), proved their safety and efficacy in combination with paclitaxel in breast cancer patients, but the outcomes of OVs as monotherapy against breast cancer have not provided a clear therapeutic strategy for OVs. The clinical trials of OVs against pancreatic cancer have not yet demonstrated efficacy as either monotherapy or as part of combination therapy. However, there are several oncolytic viruses that have successfully proved their efficacy in different preclinical models. In this review, we mainly focused on the oncolytic viruses that transitioned into clinical trials against melanoma, glioma, pancreatic, and breast cancers. Hence, we described the current status and future prospects of OVs clinical trials against melanoma, glioma, pancreatic, and breast cancers.

Recombinant Viruses for Cancer Therapy

Recombinant viruses are novel therapeutic agents that can be utilized for treatment of various diseases, including cancers. Recombinant viruses can be engineered to express foreign transgenes and have a broad tropism allowing gene expression in a wide range of host cells. They can be selected or designed for specific therapeutic goals; for example, recombinant viruses could be used to stimulate host immune response against tumor-specific antigens and therefore overcome the ability of the tumor to evade the host's immune surveillance. Alternatively, recombinant viruses could express immunomodulatory genes which stimulate an anti-cancer immune response. Oncolytic viruses can replicate specifically in tumor cells and induce toxic effects leading to cell lysis and apoptosis. However, each of these approaches face certain difficulties that must be resolved to achieve maximum therapeutic efficacy. In this review we discuss actively developing approaches for cancer therapy based on recombinant viruses, problems that need to be overcome, and possible prospects for further development of recombinant virus based therapy.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

Interleukin 8 activity influences the efficacy of adenoviral oncolytic immunotherapy in cancer patients

After the landmark approval of T-VEC, oncolytic viruses are finding their way to the clinics. However, response rates have still room for improvement, and unfortunately there are currently no available markers to predict responses for oncolytic immunotherapy. Interleukin 8 (IL-8) production is upregulated in many cancers and it also connects to several pathways that have been shown to impair the efficacy of adenoviral immunotherapy. We studied the role of IL-8 in 103 cancer patients treated with oncolytic adenoviruses. We found high baseline serum IL-8 concentration to be independently associated with poor prognosis (p<0.001). Further, normal baseline IL-8 was associated with improved prognostic potential of calculation of the neutrophil-to-lymphocyte ratio (p<0.001). Interestingly, a decrease in IL-8 concentration after treatment with oncolytic adenovirus predicted better overall survival (p<0.001) and higher response rate, although this difference was not significant (p=0.066). We studied the combination of adenovirus and IL-8 neutralizing antibody ex vivo in single cell suspensions and in co-cultures of tumor-associated CD15+ neutrophils and CD3+ tumor-infiltrating lymphocytes derived from fresh patient tumor samples. These results indicate a role for IL-8 as a biomarker in oncolytic virotherapy, but additionally provide a rationale for targeting IL-8 to improve treatment efficacy. In conclusion, curtailing the activity of IL-8 systemically or locally in the tumor microenvironment could improve anti-tumor immune responses resulting in enhanced efficacy of adenoviral immunotherapy of cancer.

Hitting the nail on the head: combining oncolytic adenovirus-mediated virotherapy and immunomodulation for the treatment of glioma

Glioblastoma is a highly aggressive malignant brain tumor with a poor prognosis and the median survival 14.6 months. Immunomodulatory proteins and oncolytic viruses represent two treatment approaches that have recently been developed for patients with glioblastoma that could extend patient survival and result in better treatment outcomes for patients with this disease. Together, these approaches could potentially augment the treatment efficacy and strength of these anti-tumor therapies. In addition to oncolytic activities, this combinatory approach introduces immunomodulation locally only where cancerous cells are present. This thereby results in the change of the tumor microenvironment from immune-suppressive to immune-vulnerable via activation of cytotoxic T cells or through the removal of glioma cells immune-suppressive capability. This review discusses the strengths and weaknesses of adenoviral oncolytic therapy, and highlights the genetic modifications that result in more effective and targeted viral agents. Additionally, the mechanism of action of immune-activating agents is described and the results of previous clinical trials utilizing these treatments in other solid tumors are reviewed. The feasibility, synergy, and limitations for treatments that combine these two approaches are outlined and areas for which more work is needed are considered.

A Comparative Study of Replication-Incompetent and -Competent Adenoviral Therapy-Mediated Immune Response in a Murine Glioma Model

Oncolytic virotherapy is a treatment approach with increasing clinical relevance, as indicated by the marked survival benefit seen in animal models and its current exploration in human patients with cancer. The use of an adenovirus vector for this therapeutic modality is common, has significant clinical benefit in animals, and its efficacy has recently been linked to an anti-tumor immune response that occurs following tumor antigen presentation. Here, we analyzed the adaptive immune system's response following viral infection by comparing replication-incompetent and replication-competent adenoviral vectors. Our findings suggest that cell death caused by replication-competent adenoviral vectors is required to induce a significant anti-tumor immune response and survival benefits in immunocompetent mice bearing intracranial glioma. We observed significant changes in the repertoire of immune cells in the brain and draining lymph nodes and significant recruitment of CD103+ dendritic cells (DCs) in response to oncolytic adenoviral therapy, suggesting the active role of the immune system in anti-tumor response. Our data suggest that the response to oncolytic virotherapy is accompanied by local and systemic immune responses and should be taken in consideration in the future design of the clinical studies evaluating oncolytic virotherapy in patients with glioblastoma multiforme (GBM).

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.

Epithelial Junction Opener Improves Oncolytic Adenovirus Therapy in Mouse Tumor Models

A central resistance mechanism in solid tumors is the maintenance of epithelial junctions between malignant cells that prevent drug penetration into the tumor. Human adenoviruses (Ads) have evolved mechanisms to breach epithelial barriers. For example, during Ad serotype 3 (Ad3) infection of epithelial tumor cells, massive amounts of subviral penton-dodecahedral particles (PtDd) are produced and released from infected cells to trigger the transient opening of epithelial junctions, thus facilitating lateral virus spread. We show here that an Ad3 mutant that is disabled for PtDd production is significantly less effective in killing of epithelial human xenograft tumors than the wild-type Ad3 virus. Intratumoral spread and therapeutic effect of the Ad3 mutant was enhanced by co-administration of a small recombinant protein (JO; produced in Escherichia coli) that incorporated the minimal junction opening domains of PtDd. We then demonstrated that co-administration of JO with replication-competent Ads that do not produce PtDd (Ad5, Ad35) resulted in greater attenuation of tumor growth than virus injection alone. Furthermore, we genetically modified a conditionally replicating Ad5-based oncolytic Ad (Ad5Δ24) to express a secreted form of JO upon replication in tumor cells. The JO-expressing virus had a significantly greater antitumor effect than the unmodified AdΔ24 version. Our findings indicate that epithelial junctions limit the efficacy of oncolytic Ads and that this problem can be address by co-injection or expression of JO. JO has also the potential for improving cancer therapy with other types of oncolytic viruses.

Oncolytic adenovirus-mediated therapy for prostate cancer

Prostate cancer is a leading cause of cancer-related death and morbidity in men in the Western world. Tumor progression is dependent on functioning androgen receptor signaling, and initial administration of antiandrogens and hormone therapy (androgen-deprivation therapy) prevent growth and spread. Tumors frequently develop escape mechanisms to androgen-deprivation therapy and progress to castration-resistant late-stage metastatic disease that, in turn, inevitably leads to resistance to all current therapeutics, including chemotherapy. In spite of the recent development of more effective inhibitors of androgen–androgen receptor signaling such as enzalutamide and abiraterone, patient survival benefits are still limited. Oncolytic adenoviruses have proven efficacy in prostate cancer cells and cause regression of tumors in preclinical models of numerous drug-resistant cancers. Data from clinical trials demonstrate that adenoviral mutants have limited toxicity to normal tissues and are safe when administered to patients with various solid cancers, including prostate cancer. While efficacy in response to adenovirus administration alone is marginal, findings from early-phase trials targeting local-ized and metastatic prostate cancer suggest improved efficacy in combination with cytotoxic drugs and radiation therapy. Here, we review recent progress in the development of multimodal oncolytic adenoviruses as biological therapeutics to improve on tumor elimination in prostate cancer patients. These optimized mutants target cancer cells by several mechanisms including viral lysis and by expression of cytotoxic transgenes and immune-stimulatory factors that activate the host immune system to destroy both infected and noninfected prostate cancer cells. Additional modifications of the viral capsid proteins may support future systemic delivery of oncolytic adenoviruses.

Predictive and Prognostic Clinical Variables in Cancer Patients Treated With Adenoviral Oncolytic Immunotherapy

The development of oncolytic viruses has recently made great progress towards being available to cancer patients. With the breakthrough into clinics, it is crucial to analyze the existing clinical experience and use it as a basis for treatment improvements. Here, we report clinical data from 290 patients treated with oncolytic adenovirus. Using clinical variables and treatment characteristics, we constructed statistical models with regard to treatment response and overall survival (OS). Additionally, we investigated effects of neutralizing antibodies, tumor burden, and peripheral blood leucocyte counts on these outcomes. We found the absence of liver metastases to correlate with an improved rate of disease control (P = 0.021). In multivariate evaluation, patients treated with viruses coding for immunostimulatory granulocyte macrophage colony-stimulating factor were linked to better prognosis (hazard ratio (HR) 0.378, P < 0.001), as well as women with any cancer type (HR 0.694, P = 0.017). In multivariate analysis for imaging response, patients treated via intraperitoneal injection were more likely to achieve disease control (odds ratio (OR) 3.246, P = 0.027). Patients with low neutrophil-to-lymphocyte ratio before treatment had significantly longer OS (P < 0.001). These findings could explain some of the variation seen in treatment outcomes after virotherapy. Furthermore, the results offer hypotheses for treatment optimization and patient selection in oncolytic adenovirus immunotherapy.

Redirecting adenovirus tropism by genetic, chemical, and mechanical modification of the adenovirus surface for cancer gene therapy

INTRODUCTION

Despite remarkable advancements, clinical evaluations of adenovirus (Ad)-mediated cancer gene therapies have highlighted the need for improved delivery and targeting.

AREA COVERED

Genetic modification of Ad capsid proteins has been extensively attempted. Although genetic modification enhances the therapeutic potential of Ad, it is difficult to successfully incorporate extraneous moieties into the capsid and the engineering process is laborious. Recently, chemical modification of the Ad surface with nanomaterials and targeting moieties has been found to enhance Ad internalization into the target by both passive and active mechanisms. Alternatively, external stimulus-mediated targeting can result in selective accumulation of Ad in the tumor and prevent dissemination of Ad into surrounding nontarget tissues. In the present review, we discuss various genetic, chemical, and mechanical engineering strategies for overcoming the challenges that hinder the therapeutic efficacy of Ad-based approaches.

EXPERT OPINION

Surface modification of Ad by genetic, chemical, or mechanical engineering strategies enables Ad to overcome the shortcomings of conventional Ad and enhances delivery efficiency through distinct and unique mechanisms that unmodified Ad cannot mimic. However, although the therapeutic potential of Ad-mediated gene therapy has been enhanced by various surface modification strategies, each strategy still possesses innate limitations that must be addressed, requiring innovative ideas and designs.

Oncolytic Adenovirus: Strategies and Insights for Vector Design and Immuno-Oncolytic Applications

Adenoviruses (Ad) are commonly used both experimentally and clinically, including oncolytic virotherapy applications. In the clinical area, efficacy is frequently hampered by the high rates of neutralizing immunity, estimated as high as 90% in some populations that promote vector clearance and limit bioavailability for tumor targeting following systemic delivery. Active tumor targeting is also hampered by the ubiquitous nature of the Ad5 receptor, hCAR, as well as the lack of highly tumor-selective targeting ligands and suitable targeting strategies. Furthermore, significant off-target interactions between the viral vector and cellular and proteinaceous components of the bloodstream have been documented that promote uptake into non-target cells and determine dose-limiting toxicities. Novel strategies are therefore needed to overcome the obstacles that prevent efficacious Ad deployment for wider clinical applications. The use of less seroprevalent Ad serotypes, non-human serotypes, capsid pseudotyping, chemical shielding and genetic masking by heterologous peptide incorporation are all potential strategies to achieve efficient vector escape from humoral immune recognition. Conversely, selective vector arming with immunostimulatory agents can be utilized to enhance their oncolytic potential by activation of cancer-specific immune responses against the malignant tissues. This review presents recent advantages and pitfalls occurring in the field of adenoviral oncolytic therapies.

Oncolytic virotherapy for treatment of breast cancer, including triple-negative breast cancer

Breast cancer is a heterogeneous disease, characterized by several distinct biological subtypes, among which triple-negative breast cancer (TNBC) is one associated with a poor prognosis. Oncolytic virus replication is an immunogenic phenomenon, and viruses can be armed with immunostimulatory molecules to boost virus triggered antitumoral immune responses. Cyclophosphamide (CP) is a chemotherapy drug that is associated with cytotoxicity and immunosuppression at higher doses, whereas immunostimulatory and anti-angiogenic properties are observed at low continuous dosage. Therefore, the combination of oncolytic immuno-virotherapy with low-dose CP is an appealing approach. We investigated the potency of oncolytic adenovirus Ad5/3-D24-GMCSF on a TNBC cell line and in vivo in an orthotopic xenograft mouse model, in combination with low-dose CP or its main active metabolite 4-hydroperoxycyclophosphamide (4-HP-CP). Furthermore, we summarized the breast cancer-specific human data on this virus from the Advanced Therapy Access Program (ATAP). Low-dose CP increased the efficacy of Ad5/3-D24-GMCSF in vitro and in a TNBC mouse model. In ATAP, treatments appeared safe and well-tolerated. Thirteen out of 16 breast cancer patients treated were evaluable for possible benefits with modified RECIST 1.1 criteria: 1 patient had a minor response, 2 had stable disease (SD), and 10 had progressive disease (PD). One patient is alive at 1,771 d after treatment. Ad5/3-D24-GMCSF in combination with low-dose CP showed promising efficacy in preclinical studies and possible antitumor activity in breast cancer patients refractory to other forms of therapy. This preliminary data supports continuing the clinical development of oncolytic adenoviruses for treatment of breast cancer, including TNBC.

A century of oncolysis evolves into oncolytic immunotherapy

Treating cancer patients with oncolytic viruses that activate the immune system to fight cancer is an increasingly appealing option. Potency of the approach seems promising while safety has been consistent. Biological correlative data indicates that combining oncolytic immunostimulatory viruses with other existing treatments is tempting and many trials are ongoing.

Biodistribution Analysis of Oncolytic Adenoviruses in Patient Autopsy Samples Reveals Vascular Transduction of Noninjected Tumors and Tissues

In clinical trials with oncolytic adenoviruses, there has been no mortality associated with treatment vectors. Likewise, in the Advanced Therapy Access Program (ATAP), where 290 patients were treated with 10 different viruses, no vector-related mortality was observed. However, as the patient population who received adenovirus treatments in ATAP represented heavily pretreated patients, often with very advanced disease, some patients died relatively soon after receiving their virus treatment mandating autopsy to investigate cause of death. Eleven such autopsies were performed and confirmed disease progression as the cause of death in each case. The regulatory requirement for investigating the safety of advanced therapy medical products presented a unique opportunity to study tissue samples collected as a routine part of the autopsies. Oncolytic adenoviral DNA was recovered in a wide range of tissues, including injected and noninjected tumors and various normal tissues, demonstrating the ability of the vector to disseminate through the vascular route. Furthermore, we recovered and cultured viable virus from samples of noninjected brain metastases of an intravenously treated patient, confirming that oncolytic adenovirus can reach tumors through the intravascular route. Data presented here give mechanistic insight into mode of action and biodistribution of oncolytic adenoviruses in cancer patients.

Serum HMGB1 is a predictive and prognostic biomarker for oncolytic immunotherapy

With the emergence of effective immunotherapeutics, which nevertheless harbor the potential for toxicity and are expensive to use, biomarkers are urgently needed for identification of cancer patients who respond to treatment. In this clinical-epidemiological study of 202 cancer patients treated with oncolytic adenoviruses, we address the biomarker value of serum high-mobility group box 1 (HMGB1) protein. Overall survival and imaging responses were studied as primary endpoints and adjusted for confounding factors in two multivariate analyses (Cox and logistic regression). Mechanistic studies included assessment of circulating tumor-specific T-cells by ELISPOT, virus replication by quantitative PCR, and inflammatory cytokines by cytometric bead array. Patients with low HMGB1 baseline levels (below median concentration) showed significantly improved survival (p = 0.008, Log-Rank test) and radiological disease control rate (49.2% vs. 30.0%, p = 0.038, χ² test) as compared to high-baseline patients. In multivariate analyses, the low HMGB1 baseline status was a strong prognostic (HR 0.638, 95% CI 0.462–0.881) and the best predictive factor for disease control (OR 2.618, 95% CI 1.004–6.827). Indicative of an immune-mediated mechanism, antitumor T-cell activity in blood and response to immunogenic-transgene coding viruses associated with improved outcome only in HMGB1-low patients. Our results suggest that serum HMGB1 baseline is a useful prognostic and predictive biomarker for oncolytic immunotherapy with adenoviruses, setting the stage for prospective clinical studies.

Advanced targeted therapies in cancer: Drug nanocarriers, the future of chemotherapy

Cancer is the second worldwide cause of death, exceeded only by cardiovascular diseases. It is characterized by uncontrolled cell proliferation and an absence of cell death that, except for hematological cancers, generates an abnormal cell mass or tumor. This primary tumor grows thanks to new vascularization and, in time, acquires metastatic potential and spreads to other body sites, which causes metastasis and finally death. Cancer is caused by damage or mutations in the genetic material of the cells due to environmental or inherited factors. While surgery and radiotherapy are the primary treatment used for local and non-metastatic cancers, anti-cancer drugs (chemotherapy, hormone and biological therapies) are the choice currently used in metastatic cancers. Chemotherapy is based on the inhibition of the division of rapidly growing cells, which is a characteristic of the cancerous cells, but unfortunately, it also affects normal cells with fast proliferation rates, such as the hair follicles, bone marrow and gastrointestinal tract cells, generating the characteristic side effects of chemotherapy. The indiscriminate destruction of normal cells, the toxicity of conventional chemotherapeutic drugs, as well as the development of multidrug resistance, support the need to find new effective targeted treatments based on the changes in the molecular biology of the tumor cells. These novel targeted therapies, of increasing interest as evidenced by FDA-approved targeted cancer drugs in recent years, block biologic transduction pathways and/or specific cancer proteins to induce the death of cancer cells by means of apoptosis and stimulation of the immune system, or specifically deliver chemotherapeutic agents to cancer cells, minimizing the undesirable side effects. Although targeted therapies can be achieved directly by altering specific cell signaling by means of monoclonal antibodies or small molecules inhibitors, this review focuses on indirect targeted approaches that mainly deliver chemotherapeutic agents to molecular targets overexpressed on the surface of tumor cells. In particular, we offer a detailed description of different cytotoxic drug carriers, such as liposomes, carbon nanotubes, dendrimers, polymeric micelles, polymeric conjugates and polymeric nanoparticles, in passive and active targeted cancer therapy, by enhancing the permeability and retention or by the functionalization of the surface of the carriers, respectively, emphasizing those that have received FDA approval or are part of the most important clinical studies up to date. These drug carriers not only transport the chemotherapeutic agents to tumors, avoiding normal tissues and reducing toxicity in the rest of the body, but also protect cytotoxic drugs from degradation, increase the half-life, payload and solubility of cytotoxic agents and reduce renal clearance. Despite the many advantages of all the anticancer drug carriers analyzed, only a few of them have reached the FDA approval, in particular, two polymer-protein conjugates, five liposomal formulations and one polymeric nanoparticle are available in the market, in contrast to the sixteen FDA approval of monoclonal antibodies. However, there are numerous clinical trials in progress of polymer-protein and polymer-drug conjugates, liposomal formulations, including immunoliposomes, polymeric micelles and polymeric nanoparticles. Regarding carbon nanotubes or dendrimers, there are no FDA approvals or clinical trials in process up to date due to their unresolved toxicity. Moreover, we analyze in detail the more promising and advanced preclinical studies of the particular case of polymeric nanoparticles as carriers of different cytotoxic agents to active and passive tumor targeting published in the last 5 years, since they have a huge potential in cancer therapy, being one of the most widely studied nano-platforms in this field in the last years. The interest that these formulations have recently achieved is stressed by the fact that 90% of the papers based on cancer therapeutics with polymeric nanoparticles have been published in the last 6 years (PubMed search).

Engineered adenoviruses combine enhanced oncolysis with improved virus production by mesenchymal stromal carrier cells

Oncolytic viruses have demonstrated in pre-clinical and clinical studies safety and a unique pleiotropic activity profile of tumor destruction. Yet, their delivery suffers from virus inactivation by blood components and sequestration to healthy tissues. Therefore, mesenchymal stromal cells (MSCs) have been applied as carrier cells for shielded virus delivery to tumors after ex vivo infection with oncolytic viruses. However, infection and particle production by MSCs have remained unsatisfying. Here, we report engineered oncolytic adenoviruses (OAds) for improved virus production and delivery by MSCs. OAds are uniquely amenable to molecular engineering, which has facilitated improved tumor cell destruction. But for MSC-mediated regimens, OAd engineering needs to achieve efficient infection and replication in both MSCs and tumor cells. We show that an Ad5/3 chimeric OAd capsid, containing the adenovirus serotype 3 cell-binding domain, strongly increases the entry into human bone marrow-derived MSCs and into established and primary pancreatic cancer cells. Further, we reveal that OAd with engineered post-entry functions-by deletion of the anti-apoptotic viral gene E1B19K or expression of the death ligand TRAIL--markedly increased virus titers released from MSCs, while MSC migration was not hampered. Finally, these virus modifications, or viral expression of FCU1 for local 5-FC prodrug activation, improved tumor cell killing implementing complementary cytotoxicity profiles in a panel of pancreatic cancer cell cultures. Together, our study establishes post-entry modification of OAd replication for improving virus delivery by carrier cells and suggests a panel of optimized OAds for future clinical development in personalized treatment of pancreatic cancer.