Identifying the safety profile of a novel infectivity-enhanced conditionally replicative adenovirus, Ad5-delta24-RGD, in anticipation of a phase I trial for recurrent ovarian cancer

Understanding and addressing barriers to successful adenovirus-based virotherapy for ovarian cancer

Ovarian cancer is the leading cause of death among women with gynecological cancer, with an overall 5-year survival rate below 50% due to a lack of specific symptoms, late stage at time of diagnosis and a high rate of recurrence after standard therapy. A better understanding of heterogeneity, genetic mutations, biological behavior and immunosuppression in the tumor microenvironment have allowed the development of more effective therapies based on anti-angiogenic treatments, PARP and immune checkpoint inhibitors, adoptive cell therapies and oncolytic vectors. Oncolytic adenoviruses are commonly used platforms in cancer gene therapy that selectively replicate in tumor cells and at the same time are able to stimulate the immune system. In addition, they can be genetically modified to enhance their potency and overcome physical and immunological barriers. In this review we highlight the challenges of adenovirus-based oncolytic therapies targeting ovarian cancer and outline recent advances to improve their potential in combination with immunotherapies.

Defining a murine ovarian cancer model for the evaluation of conditionally-replicative adenovirus (CRAd) virotherapy agents

BACKGROUND

Virotherapy represents a promising approach for ovarian cancer. In this regard, conditionally replicative adenovirus (CRAd) has been translated to the context of human clinical trials. Advanced design of CRAds has sought to exploit their capacity to induce anti-tumor immunization by configuring immunoregulatory molecule within the CRAd genome. Unfortunately, employed murine xenograft models do not allow full analysis of the immunologic activity linked to CRAd replication.

RESULTS

We developed CRAds based on the Ad5/3-Delta24 design encoding cytokines. Whereas the encoded cytokines did not impact adversely CRAd-induced oncolysis in vitro, no gain in anti-tumor activity was noted in immune-incompetent murine models with human ovarian cancer xenografts. On this basis, we explored the potential utility of the murine syngeneic immunocompetent ID8 ovarian cancer model. Of note, the ID8 murine ovarian cancer cell lines exhibited CRAd-mediated cytolysis. The use of this model now enables the rational design of oncolytic agents to achieve anti-tumor immunotherapy.

CONCLUSIONS

Limits of widely employed murine xenograft models of ovarian cancer limit their utility for design and study of armed CRAd virotherapy agents. The ID8 model exhibited CRAd-induced oncolysis. This feature predicate its potential utility for the study of CRAd-based virotherapy agents.

Advances in oncolytic adenovirus therapy for pancreatic cancer

Survival rates for pancreatic cancer patients have remained unchanged for the last four decades. The most aggressive, and most common, type of pancreatic cancer is pancreatic ductal adenocarcinoma (PDAC), which has the lowest 5-year survival rate of all cancers globally. The poor prognosis is typically due to late presentation of often non-specific symptoms and rapid development of resistance to all current therapeutics, including the standard-of-care cytotoxic drug gemcitabine. While early surgical intervention can significantly prolong patient survival, there are few treatment options for late-stage non-resectable metastatic disease, resulting in mostly palliative care. In addition, a defining feature of pancreatic cancer is the immunosuppressive and impenetrable desmoplastic stroma that blocks access to tumour cells by therapeutic drugs. The limited effectiveness of conventional chemotherapeutics reveals an urgent need to develop novel therapies with different mechanisms of action for this malignancy. An emerging alternative to current therapeutics is oncolytic adenoviruses; these engineered biological agents have proven efficacy and tumour-selectivity in preclinical pancreatic cancer models, including models of drug-resistant cancer. Safety of oncolytic adenoviral mutants has been extensively assessed in clinical trials with only limited toxicity to normal healthy tissue being reported. Promising efficacy in combination with gemcitabine was demonstrated in preclinical and clinical studies. A recent surge in novel adenoviral mutants entering clinical trials for pancreatic cancer indicates improved efficacy through activation of the host anti-tumour responses. The potential for adenoviruses to synergise with chemotherapeutics, activate anti-tumour immune responses, and contribute to stromal dissemination render these mutants highly attractive candidates for improved patient outcomes. Currently, momentum is gathering towards the development of systemically-deliverable mutants that are able to overcome anti-viral host immune responses, erythrocyte binding and hepatic uptake, to promote elimination of primary and metastatic lesions. This review will cover the key components of pancreatic cancer oncogenesis; novel oncolytic adenoviruses; clinical trials; and the current progress in overcoming the challenges of systemic delivery.

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.

Oncolytic viruses: From bench to bedside with a focus on safety

Oncolytic viruses are a relatively new class of anti-cancer immunotherapy agents. Several viruses have undergone evaluation in clinical trials in the last decades, and the first agent is about to be approved to be used as a novel cancer therapy modality. In the current review, an overview is presented on recent (pre)clinical developments in the field of oncolytic viruses that have previously been or currently are being evaluated in clinical trials. Special attention is given to possible safety issues like toxicity, environmental shedding, mutation and reversion to wildtype virus.

Safety and efficacy of VCN-01, an oncolytic adenovirus combining fiber HSG-binding domain replacement with RGD and hyaluronidase expression

PURPOSE

Tumor targeting upon intravenous administration and subsequent intratumoral virus dissemination are key features to improve oncolytic adenovirus therapy. VCN-01 is a novel oncolytic adenovirus that combines selective replication conditional to pRB pathway deregulation, replacement of the heparan sulfate glycosaminoglycan putative-binding site KKTK of the fiber shaft with an integrin-binding motif RGDK for tumor targeting, and expression of hyaluronidase to degrade the extracellular matrix. In this study, we evaluate the safety and efficacy profile of this novel oncolytic adenovirus.

EXPERIMENTAL DESIGN

VCN-01 replication and potency were assessed in a panel of tumor cell lines. VCN-01 tumor-selective replication was evaluated in human fibroblasts and pancreatic islets. Preclinical toxicity, biodistribution, and efficacy studies were conducted in mice and Syrian hamsters.

RESULTS

Toxicity and biodistribution preclinical studies support the selectivity and safety of VCN-01. Antitumor activity after intravenous or intratumoral administration of the virus was observed in all tumor models tested, including melanoma and pancreatic adenocarcinoma, both in immunodeficient mice and immunocompetent hamsters.

CONCLUSIONS

Oncolytic adenovirus VCN-01 characterized by the expression of hyaluronidase and the RGD shaft retargeting ligand shows an efficacy-toxicity prolife in mice and hamsters by intravenous and intratumoral administration that warrants clinical testing.

A systematic comparison of the anti-tumoural activity and toxicity of the three Adv-TKs

Adenovirus 5 vectors, known respectively as, the first generation, second generation and oncolytic adenovirus, have been studied extensively in preclinical and clinical trials. However, hitherto few systemic evaluations of the efficacy and toxicity of these adenoviral vectors that have reflected the vertical history of adenovirus based cancer gene therapy strategies have been undertaken. This study has chosen Adv-TK, the well-established adjuvant treatment in cancer, and compared its efficacy and safety with those of the two newly synthesized oncolytic adenovirus vectors encoding the HSV-TK gene, namely M7 and M8. The results obtained showed that systemic administration of 1×10⁸ pfu M7 had an anti-tumour efficacy similar to that of 3×10¹⁰ pfu Adv-TK whilst M8 performed even better. Furthermore, compared to Adv-TK, M7 and M8 reduced the incidence of metastases and substantially prolonged the survival time of the mice xenografted with human orthotopic gastric carcinomas with disseminated metastasis. Even more exciting, however, were the similar toxic and immune safety results obtained from the administration of high doses of M7 or M8 in comparison with Adv-TK in immunocompetent and permissive syrian hamster. The data here exhibit a comprehensive display of the efficacy and safety of the three mutants and provide evidence for the future preclinical use of the M7 and M8 viruses.

A phase I clinical trial of Ad5/3-Δ24, a novel serotype-chimeric, infectivity-enhanced, conditionally-replicative adenovirus (CRAd), in patients with recurrent ovarian cancer

OBJECTIVE

The conditionally replicative adenovirus Ad5/3-Δ24 has a type-3 knob incorporated into the type-5 fiber that facilitates enhanced ovarian cancer infectivity. Preclinical studies have shown that Ad5/3-Δ24 achieves significant oncolysis and anti-tumor activity in ovarian cancer models. The purpose of this study was to evaluate in a phase I trial the feasibility and safety of intraperitoneal (IP) Ad5/3-Δ24 in recurrent ovarian cancer patients.

METHODS

Eligible patients were treated with IP Ad5/3-Δ24 for 3 consecutive days in one of three dose cohorts ranging 1 × 10(10)-1 × 10(12)vp. Toxicity was assessed utilizing CTC grading and efficacy with RECIST. Ascites, serum, and other samples were obtained to evaluate gene transfer, generation of wildtype virus, viral shedding, and antibody response.

RESULTS

Nine of 10 patients completed treatment per protocol. A total of 15 vector-related adverse events were experienced in 5 patients. These events included fever or chills, nausea, fatigue, and myalgia. All were grades 1-2 in nature, transient, and medically managed. Of the 8 treated patients evaluable for response, six patients had stable disease and 2 patients had progressive disease. Three patients had decreased CA-125 from pretreatment levels one month after treatment. Ancillary biologic studies indicated Ad5/3-Δ24 replication in patients in the higher dose cohorts. All patients experienced an anti-adenoviral neutralizing antibody effect.

CONCLUSIONS

This study suggests the feasibility and safety of a serotype chimeric infectivity-enhanced CRAd, Ad5/3-Δ24, as a potential therapeutic option for recurrent ovarian cancer patients.

Chapter two--Adenovirus strategies for tissue-specific targeting

Cancer gene therapy approaches have benefited greatly from the utilization of molecular-based therapeutics. Of these, adenovirus-based interventions hold much promise as a platform for targeted therapeutic delivery to tumors. However, a barrier to this progression is the lack of native adenovirus receptor expression on a variety of cancer types. As such, any adenovirus-based cancer therapy must take into consideration retargeting the vector to nonnative cellular surface receptors. Predicated upon the knowledge gained in native adenovirus biology, several strategies to transductionally retarget adenovirus have emerged. Herein, we describe the biological hurdles as well as strategies utilized in adenovirus transductional targeting, covering the progress of both adapter-based and genetic manipulation-based targeting. Additionally, we discuss recent translation of these targeting strategies into a clinical setting.

Preliminary evaluation of safety of conditionally replication adenovirus M4

Conditionally replication adenovirus M4, which was constructed in our lab, was proved to have good clinical application prospect for its good anti-tumor and anti-metastasis effect. However, clinically applying M4 faces many problems. One of the most important is the safety of M4. In this study, we investigated the safety of M4 by comparing with Adv-TK, which was proved to be safe in I-III phase clinical trials. M4 and Adv-TK were injected into mice via the tail vein separately, and the mice were sacrificed at the indicated time. Blood was collected for biochemical tests, the liver was harvested for hematoxylin and eosin (H&E) staining and viral quantification, and splenic lymphocytes were separated for adenovirus specific cellular immune response. Our results showed that M4 had no obvious effect on mouse general symptoms. A transient reversible infiltration of inflammatory cells in collect abbacy was only observed in M4 group, and a transient slight increase in Cr level was detected both after M4 and Adv-TK injection. The adenovirus specific cellular immune response induced by M4 was similar to that by Adv-TK, and the distribution and metabolism of M4 in the mouse liver were also similar to those of Adv-TK. It was concluded that conditionally replication adenovirus M4 had the same safety as Adv-TK. The study provides safety basis for the coming clinical trials of M4.

A fiber chimeric CRAd vector Ad5/11-D24 double-armed with TRAIL and arresten for enhanced glioblastoma therapy

Malignant gliomas remain refractory to treatment despite advances in chemotherapy and surgical techniques. Conditionally replicating adenoviral vector (CRAd) could kill the tumor cells by selectively replicating in neoplastic cells, which represents a novel strategy for tumor therapy. Although CRAd with a 24-bp deletion in CR2 of the E1 region (CRAd5-D24) has been shown to have a better therapeutic effect over the other types of CRAd vectors, the current CRAd5-D24 still has some shortcomings for an efficient therapy of gliomas. In this study, we developed for the first time a novel vector CRAd5/11-D24.TRAIL/arresten by the following strategies: (1) modify CRAd5-D24 with Ad5/11 chimeric fiber to improve its infection efficiency for glioblastoma; and (2) insert two transgene expression cassettes into the E3 region and the region between the fiber and E4, respectively, for an enhanced therapeutic effect. The results indicated that the CRAd5/11-D24.TRAIL/arresten achieved nearly complete inhibition of glioma growth in nude mice possibly by increased antiangiogenesis and enhanced tumor apoptosis. The vector is the first reported E1A D24-deleted, Ad5/11 chimeric, and dual-armed oncolytic virus that shows markedly improved antitumor activities compared with the conventional oncolytic viruses. This novel antitumor agent should be evaluated further in future preclinical and clinical studies.

The oncolytic adenovirus AdΔΔ enhances selective cancer cell killing in combination with DNA-damaging drugs in pancreatic cancer models

Pancreatic adenocarcinomas are aggressive and frequently develop resistance to all current therapies. Replication-selective adenoviruses can overcome resistance to chemotherapeutics through their sensitizing effects on drug-induced cell killing. We previously found that adenovirus deleted in the anti-apoptotic E1B19K gene enhanced gemcitabine-induced apoptotis. Here we demonstrate that our engineered double-deleted AdΔΔ mutant (deleted in the pRb-binding E1ACR2 region and E1B19K) selectively replicates and enhances cell killing in combination with DNA-damaging cytotoxic drugs in pancreatic cancer cells. Combinations of AdΔΔ with gemcitabine, irinotecan or cisplatin resulted in two- to fourfold decreases in EC(50) (half maximal effective concentration) values and was more efficent than similar combinations with wild-type virus, the dl1520 (ONYX-015) and dl922-947 mutants. AdΔΔ replication was impaired in normal bronchial human epithelial cells and did not sensitize the cells to drugs. Gemcitabine-insensitive AsPC-1, BxPC-3 and PANC-1 cells were efficiently killed by irinotecan in combination with AdΔΔ. Suboptimal doses of AdΔΔ and gemcitabine significantly prolonged time to tumor progression in two human pancreatic tumor xenograft in vivo models, PT45 and SUIT-2. We conclude that AdΔΔ has low toxicity to normal cells while potently sensitizing pancreatic cancer cells to DNA-damaging drugs, and holds promise as an improved therapeutic strategy for pancreatic cancer.

An oncolytic adenovirus defective in pRb-binding (dl922-947) can efficiently eliminate pancreatic cancer cells and tumors in vivo in combination with 5-FU or gemcitabine

Pancreatic adenocarcinoma has a poor prognosis and frequently develops resistance to standard chemotherapeutics. Oncolytic adenoviruses represent a promising approach to overcome treatment resistance. The replication-selective dl922-947 adenovirus, defective in pRb binding, targets cancers with deregulated cell cycle control, such as the majority of pancreatic tumors. Cell killing efficacy was higher for dl922-947 than for adenovirus type 5 (Ad5) and the clinically approved dl1520 in pancreatic cancer cells with K-ras, p16 and p53 mutations. Combinations of dl922-947 and 5-fluorouracil or gemcitabine (2'2'-difluoro-2-deoxytidine) resulted in strong synergistic cell killing in Suit-2 and the highly drug- and virus-resistant Hs766T cells. Viral uptake increased in response to drugs, but was independent of the expression levels of the viral attachment receptor coxsackie and adenovirus receptor (CAR), whereas expression levels of the internalization receptors α(v)β(3)- and α(v)β(5)-integrins were increased. Early viral E1A expression was potently induced with drugs contributing to the synergistic effects. The dl922-947 mutant was more efficacious than Ad5 in vivo in Hs766T and Suit-2 xenograft models. In combination with gemcitabine, median survival was further prolonged. We demonstrate that dl922-947 is highly efficacious in pancreatic cancers and conclude that oncolytic adenoviruses harboring the E1ACR2 deletion have great potential for development into future clinical candidates for pancreatic cancer.

Integrin targeted oncolytic adenoviruses Ad5-D24-RGD and Ad5-RGD-D24-GMCSF for treatment of patients with advanced chemotherapy refractory solid tumors

The safety of oncolytic viruses for treatment of cancer has been shown in clinical trials while antitumor efficacy has often remained modest. As expression of the coxsackie-adenovirus receptor may be variable in advanced tumors, we developed Ad5-D24-RGD, a p16/Rb pathway selective oncolytic adenovirus featuring RGD-4C modification of the fiber. This allows viral entry through alpha-v-beta integrins frequently highly expressed in advanced tumors. Advanced tumors are often immunosuppressive which results in lack of tumor eradication despite abnormal epitopes being present. Granulocyte-macrophage colony stimulating factor (GMCSF) is a potent activator of immune system with established antitumor properties. To stimulate antitumor immunity and break tumor associated immunotolerance, we constructed Ad5-RGD-D24-GMCSF, featuring GMCSF controlled by the adenoviral E3 promoter. Preliminary safety of Ad5-D24-RGD and Ad5-RGD-D24-GMCSF for treatment of human cancer was established. Treatments with Ad5-D24-RGD (N = 9) and Ad5-RGD-D24-GMCSF (N = 7) were well tolerated. Typical side effects were grade 1-2 fatigue, fever and injection site pain. 77% (10/13) of evaluable patients showed virus in circulation for at least 2 weeks. In 3 out of 6 evaluable patients, disease previously progressing stabilized after a single treatment with Ad5-RGD-D24-GMCSF. In addition, 2/3 patients had stabilization or reduction in tumor marker levels. All patients treated with Ad5-D24-RGD showed disease progression in radiological analysis, although 3/6 had temporary reduction or stabilization of marker levels. Induction of tumor and adenovirus specific immunity was demonstrated with ELISPOT in Ad5-RGD-D24-GMCSF treated patients. RGD modified oncolytic adenoviruses with or without GMCSF seem safe for further clinical development.

A new generation of serotype chimeric infectivity-enhanced conditionally replicative adenovirals: the safety profile of ad5/3-Δ24 in advance of a phase I clinical trial in ovarian cancer patients

Conditionally replicative adenoviral (CRAd) virotherapy represents a promising therapeutic approach for cancer. We have demonstrated that a serotype chimeric adenoviral 5/3 fiber-knob modification achieves enhanced ovarian cancer infectivity, conditional replication, and oncolytic activity. This study evaluated the safety of intraperitoneal (IP) Ad5/3-Δ24 in advance of a phase I clinical trial in gynecologic cancers. Syrian hamster cohorts were treated with IP Ad5/3-Δ24 or control buffer for 3 consecutive days and euthanized on study days 8, 17, 57, and 89. Blood and tissue samples were harvested from each animal. For biodistribution studies, presence and quantitation of viral levels within samples were determined via quantitative polymerase chain reaction. For safety studies, animals were assessed for adverse vector-related tissue or laboratory effects. In the biodistribution study, low levels of Ad5/3-Δ24 DNA were noted outside of the abdominal cavity. Viral DNA levels in tissues obtained from the peritoneal cavity peaked at day 8 and declined thereafter. In the safety study, no specific histopathologic changes were attributable to virus administration. Hematologic findings noted in the 1 × 10(11) viral particles (vp)/dose group on Days 4 and/or 8 were indicative of an Ad5/3-Δ24-specific generalized inflammatory response; these findings resolved by day 56. The no observable adverse effect level was determined to be 1 × 10(10) vp/dose. This study elucidates the safety profile of IP administration of the serotype chimeric infectivity-enhanced CRAd, Ad5/3-Δ24, and provides guidance for a planned phase I trial for patients with recurrent gynecologic cancers.

Efficacy of oncolytic mutants targeting pRb and p53 pathways is synergistically enhanced when combined with cytotoxic drugs in prostate cancer cells and tumor xenografts

Replication-selective oncolytic adenoviruses have proven safety records with promising clinical outcomes. However, strategies to improve efficacy are still required. Here we report greatly improved antitumor efficacy for both attenuated (dl1520) and highly potent (dl922–947) oncolytic mutants in combination with the current standard of care for late-stage hormone-independent prostate cancers, mitoxantrone or docetaxel. In agreement with previous reports, dl922–947 had superior potency compared with dl1520 both as a single agent and in combination with cytotoxic drugs. The dl922–947 mutant caused significant synergistic cell killing in both drug-insensitive and -sensitive prostate cancer cell lines, PC3 and DU145, respectively, when combined with docetaxel or mitoxantrone. The magnitude of the synergistic response was greatest for dl1520 whereas overall efficacy was greatest for dl922–947, and the latter was also more efficacious in vivo in prostate cancer models. In DU145 and PC3 cells increased viral uptake (up to 9- and 8-fold, respectively), E1A expression, and altered cell cycle progression contributed to the synergistic cell killing. A similar trend was also detected in LNCaP cells. Potent E1A expression was essential for the response. In murine xenograft models (DU145 and PC3) tumor growth inhibition was improved when suboptimal doses of docetaxel and viral mutants were combined. These findings demonstrate that the efficacy of highly potent oncolytic mutants such as dl922–947 that target the retinoblastoma protein (pRb) pathway could be further enhanced even with low drug doses, and support the deletion of the E1ACR2 region in future candidate adenoviruses for treatment of hormone-independent prostate cancers.

A phase I study of a tropism-modified conditionally replicative adenovirus for recurrent malignant gynecologic diseases

PURPOSE

To determine the maximum tolerated dose (MTD), toxicity spectrum, clinical activity, and biological effects of the tropism-modified, infectivity-enhanced conditionally replicative adenovirus (CRAd), Ad5-Δ24-Arg-Gly-Asp (RGD), in patients with malignant gynecologic diseases.

EXPERIMENTAL DESIGN

Cohorts of eligible patients were treated daily for 3 days through an i.p. catheter. Vector doses ranged from 1 × 10(9) to 1 × 10(12) viral particles per day. Toxicity was evaluated using CTCv3.0. CA-125 and Response Evaluation Criteria in Solid Tumors (RECIST) criteria were used to determine clinical efficacy. Corollary biological studies included assessment of CRAd replication, wild-type virus generation, viral shedding, and neutralizing antibody response.

RESULTS

Twenty-one patients were treated. Adverse clinical effects were limited to grade 1/2 fever, fatigue, or abdominal pain. No vector-related grade 3/4 toxicities were noted. No clinically significant laboratory abnormalities were noted. The maximum tolerated dose was not reached. Over a 1 month follow-up, 15 (71%) patients had stable disease and six (29%) had progressive disease. No partial or complete responses were noted. Seven patients had a decrease in CA-125; four had a >20% drop. RGD-specific PCR showed the presence of study vector in ascites of 16 patients. Seven revealed an increase in virus after day 3, suggesting replication of Ad5-Δ24-RGD. Minimal wild-type virus generation was detected. Viral shedding studies showed insignificant shedding in the serum, saliva, and urine. Anti-adenoviral neutralizing antibody effects were prevalent.

CONCLUSIONS

This study, the first to evaluate an infectivity-enhanced CRAd in human cancer, shows the feasibility, safety, potential antitumor response, and biological activity of this approach in ovarian cancer. Further evaluation of infectivity enhanced virotherapy approaches for malignant gynecologic diseases is warranted.

Role of RGD-containing ligands in targeting cellular integrins: Applications for ovarian cancer virotherapy (Review)

The purpose of this article was to review the current strategies of targeted therapy to integrins and define the best course of future research in ovarian cancer targeting. Cell surface integrin targeting has been used as a strategy for targeted therapy of several diseases with some success. The combination of virotherapy and integrin-targeting shows promise as a method for targeting ovarian cancer. More specifically, targeting of ovarian cancer with integrin-directed adenoviruses may lead to therapy with fewer toxicities and side effects. This article offers a review of the benefits of integrin-specific targeted therapy for several diseases and proposes a unique anti-ovarian cancer strategy involving the combination of the above with virotherapy as a potential anti-ovarian cancer treatment.

Assessment of the Na/I symporter as a reporter gene to visualize oncolytic adenovirus propagation in peritoneal tumours

PURPOSE

In vivo imaging of the spread of oncolytic viruses using the Na/I symporter (NIS) has been proposed. Here, we assessed whether the presence of NIS in the viral genome affects the therapeutic efficacy of the oncolytic adenovirus dl922-947 following intraperitoneal administration, in a mouse model of peritoneal ovarian carcinoma.

METHODS

We generated AdAM7, a dl922-947 oncolytic adenovirus encoding the NIS coding sequence. Iodide uptake, NIS expression, infectivity and cell-killing activity of AdAM7, as well as that of relevant controls, were determined in vitro. In vivo, the propagation of this virus in the peritoneal cavity of tumour-bearing mice was determined using SPECT/CT imaging and its therapeutic efficacy was evaluated.

RESULTS

In vitro infection of ovarian carcinoma IGROV-1 cells with ADAM7 led to functional expression of NIS. However, the insertion of NIS into the viral genome resulted in a loss of efficacy of the virus in terms of replication and cytotoxicity. In vivo, on SPECT/CT imaging AdAM7 was only detectable in the peritoneal cavity of animals bearing peritoneal ovarian tumours for up to 5 days after intraperitoneal administration. Therapeutic experiments in vivo demonstrated that AdAM7 is as potent as its NIS-negative counterpart.

CONCLUSION

This study demonstrated that despite the detrimental effect observed in vitro, insertion of the reporter gene NIS in an oncolytic adenovirus did not affect its therapeutic efficacy in vivo. We conclude that NIS is a highly relevant reporter gene to monitor the fate of oncolytic adenovectors in live subjects.

Improved potency and selectivity of an oncolytic E1ACR2 and E1B19K deleted adenoviral mutant in prostate and pancreatic cancers

PURPOSE

Replication-selective oncolytic adenoviruses are a promising class of tumor-targeting agents with proven safety in hundreds of patients. However, clinical responses have been limited and viral mutants with higher potency are needed. Here, we report on the generation of a novel set of mutants with improved efficacy in prostate and pancreatic carcinoma models. Currently, no curative treatments are available for late-stage metastatic prostate or rapidly progressing pancreatic cancers.

EXPERIMENTAL DESIGN

Adenovirus type 5 mutants were created with deletions in the E1ACR2 region for tumor selectivity and/or the E1B19K gene for attenuated replication in vivo; all constructs retain the E3 genes intact. Cell-killing efficacy, replication, and cytotoxicity in combination with chemotherapeutics were investigated in normal cells (PrEC and NHBE), seven carcinoma cell lines, and human (PC3 and DU145) and murine (TRAMPC, CMT-64, and CMT-93) tumor models in vivo.

RESULTS

The double-deleted AdDeltaDelta (DeltaE1ACR2 and DeltaE1B19K) mutant had high cell-killing activity in prostate, pancreatic, and lung carcinomas. Replication was similar to wild-type in all tumor cells and was attenuated in normal cells to levels less than the single-deleted AdDeltaCR2 mutant. AdDeltaDelta combined with the chemotherapeutics docetaxel and mitoxantrone resulted in synergistically enhanced cell killing and greatly improved antitumor efficacy in prostate xenografts in vivo. In murine immunocompetent in vivo models efficacy was greater for mutants with the E3B genes intact even in the absence of viral replication, indicating attenuated macrophage-dependent clearance.

CONCLUSIONS

These data suggest that the novel oncolytic mutant AdDeltaDelta is a promising candidate for targeting of solid tumors specifically in combination with chemotherapeutics.

Identifying the safety profile of Ad5.SSTR/TK.RGD, a novel infectivity-enhanced bicistronic adenovirus, in anticipation of a phase I clinical trial in patients with recurrent ovarian cancer

PURPOSE

The purpose of this study was to evaluate the biodistribution and toxicity of Ad5.SSTR/TK.RGD, an infectivity-enhanced adenovirus expressing a therapeutic suicide gene and somatostatin receptor type 2 (for noninvasive assessment of gene transfer with nuclear imaging) in advance of a planned phase I clinical trial for recurrent ovarian carcinoma.

EXPERIMENTAL DESIGN

Cohorts of Syrian hamsters were treated i.p. for 3 consecutive days with Ad5.SSTR/TK.RGD or control buffer with or without the prodrug ganciclovir (GCV) and euthanized on day 4, 19, or 56. Tissue and serum samples were evaluated for the presence of virus using qPCR analysis and were assessed for vector-related tissue or laboratory effects.

RESULTS

Levels of Ad5.SSTR/TK.RGD in blood and tissues outside of the abdominal cavity were low, indicating minimal systemic absorption. GCV did not affect Ad5.SSTR/TK.RGD biodistribution. The mean Ad5.SSTR/TK.RGD viral level was 100-fold lower on day 19 than day 4, suggesting vector elimination over time. Animals in the Ad5.SSTR/TK.RGD +/- GCV cohort had clinical laboratory parameters and microscopic lesions in the abdominal organs indicative of an inflammatory response. Toxicity in this dose cohort seemed to be reversible over time.

CONCLUSIONS

These studies provide justification for planned dosing of Ad5.SSTR/TK.RGD for a planned phase I clinical trial and insights regarding anticipated toxicity.

Adenoviral vector-based strategies for cancer therapy

Definitive treatment of cancer has eluded scientists for decades. Current therapeutic modalities like surgery, chemotherapy, radiotherapy and receptor-targeted antibodies have varied degree of success and generally have moderate to severe side effects. Gene therapy is one of the novel and promising approaches for therapeutic intervention of cancer. Viral vectors in general and adenoviral (Ad) vectors in particular are efficient natural gene delivery systems and are one of the obvious choices for cancer gene therapy. Clinical and preclinical findings with a wide variety of approaches like tumor suppressor and suicide gene therapy, oncolysis, immunotherapy, anti-angiogenesis and RNA interference using Ad vectors have been quite promising, but there are still many hurdles to overcome. Shortcomings like increased immunogenicity, prevalence of preexisting anti-Ad immunity in human population and lack of specific targeting limit the clinical usefulness of Ad vectors. In recent years, extensive research efforts have been made to overcome these limitations through a variety of approaches including the use of conditionally-replicating Ad and specific targeting of tumor cells. In this review, we discuss the potential strengths and limitations of Ad vectors for cancer therapy.

INGN 007, an oncolytic adenovirus vector, replicates in Syrian hamsters but not mice: comparison of biodistribution studies

Preclinical biodistribution studies with INGN 007, an oncolytic adenovirus (Ad) vector, supporting an early stage clinical trial were conducted in Syrian hamsters, which are permissive for Ad replication, and mice, which are a standard model for assessing toxicity and biodistribution of replication-defective (RD) Ad vectors. Vector dissemination and pharmacokinetics following intravenous administration were examined by real-time PCR in nine tissues and blood at five time points spanning 1 year. Select organs were also examined for the presence of infectious vector/virus. INGN 007 (VRX-007), wild-type Ad5 and AdCMVpA (an RD vector) were compared in the hamster model, whereas only INGN 007 was examined in mice. DNA of all vectors was widely disseminated early after injection, but decayed rapidly in most organs. In the hamster model, DNA of INGN 007 and Ad5 was more abundant than that of the RD vector AdCMVpA at early times after injection, but similar levels were seen later. An increased level of INGN 007 and Ad5 DNA but not AdCMVpA DNA in certain organs early after injection, and the presence of infectious INGN 007 and Ad5 in lung and liver samples at early times after injection, strongly suggests that replication of INGN 007 and Ad5 occurred in several Syrian hamster organs. There was no evidence of INGN 007 replication in mice. In addition to providing important information about INGN 007, the results underscore the utility of the Syrian hamster as a permissive immunocompetent model for Ad5 pathogenesis and oncolytic Ad vectors.

Molecular engineering of viral gene delivery vehicles

Viruses can be engineered to efficiently deliver exogenous genes, but their natural gene delivery properties often fail to meet human therapeutic needs. Therefore, engineering viral vectors with new properties, including enhanced targeting abilities and resistance to immune responses, is a growing area of research. This review discusses protein engineering approaches to generate viral vectors with novel gene delivery capabilities. Rational design of viral vectors has yielded successful advances in vitro, and to an extent in vivo. However, there is often insufficient knowledge of viral structure-function relationships to reengineer existing functions or create new capabilities, such as virus-cell interactions, whose molecular basis is distributed throughout the primary sequence of the viral proteins. Therefore, high-throughput library and directed evolution methods offer alternative approaches to engineer viral vectors with desired properties. Parallel and integrated efforts in rational and library-based design promise to aid the translation of engineered viral vectors toward the clinic.

Toxicology profiles of a novel p53-armed replication-competent oncolytic adenovirus in rodents, felids, and nonhuman primates

Conditionally replicating adenovirus (CRAd) has demonstrated to be safe in clinical studies. We generated a triple-regulated p53-armed CRAd, SG600-p53, in which the partially deleted E1a and E1b genes are regulated under the human telomerase reverse transcriptase promoter and the hypoxia response element. SG600-p53 was proven to be effective both in vitro and in vivo. In this study, the preclinical safety profiles of SG600-p53 in animal models were investigated. SG600-p53 had no adverse effects on mouse behavioral and nervous systems at 1.0 x 10(11) viral particles (VP)/kg, 2.0 x 10(11) VP/kg and 4.0 x 10(11) VP/kg doses, and on cat cardiovascular and respiratory systems at 2.0 x 10(10) VP/kg, 4.0 x 10(10) VP/kg, and 8.0 x 10(10) VP/kg doses. In acute toxicity test in mice, the maximum tolerated dose (2.5 x 10(13) VP/kg) induced cachexia, decreased activity, and eye closure in 9/20 mice which could be self-resolved within 30 min. Sensitized by five repeated ip injections at 1.0 x 10(10) VP/kg each ip and excitated by one iv injection at 1.0 x 10(11) VP/kg, guinea pigs did not show any sign of systemic anaphylaxis. In repeat-dose toxicological studies, the no-observable-adverse-effect levels of SG600-p53 in rats (1.0 x 10(11) VP/kg) and cynomolgus monkeys (5.0 x 10(11) VP/kg) were 12-fold and 60-fold of the proposed clinical dose, respectively. Intramuscular injections of SG600-p53 in cynomolgus monkeys caused inflammation at injection sites, which was alleviative at the end of observation period. The anti-virus antibody was produced in animal sera and decreased gradually 4 weeks later. No histopathological changes were found by bone marrow examination. Our data in different animal models suggest that SG600-p53 is a safe antitumor therapeutic agent.

Novel strategies in tailoring human adenoviruses into therapeutic cancer gene therapy vectors

Gene therapy is a novel approach for the treatment of cancer that has so far not been realized. The scope of this review is to try to define the remaining barriers to the successful use of adenovirus vectors for gene and viral therapy of human tumors and to suggest solutions whereby these barriers can be bypassed. It is the conviction of the authors that too many studies have been performed in animal models that are not sufficiently comprehensive to allow conclusions to be drawn for application in humans. For example, in the case of the murine experimental model, in which most studies have been performed, mice are devoid of circulating antibodies to adenovirus type 5 and adenovirus cannot replicate in mouse cells. While the problems are real enough, as witnessed by the quite limited success in human trials, some of the solutions that will be suggested here are hypothetical and have not as yet been tried, even in animals. The review has no ambition to be exhaustive but is intended as a contribution in order to forward the field of gene therapy vectors for systemic clinical application.

Gene therapy of gynaecological diseases

Gene therapy represents a potentially useful approach for the treatment of diseases refractory to conventional therapies. Various preclinical and clinical strategies have been explored for treatment of gynaecological diseases. Given the most severe unmet clinical need, much of the work has been performed with gynaecological cancers and ovarian cancer in particular. Although the safety of many treatment strategies has been demonstrated in early phase clinical trials, efficacy has been mostly limited heretofore. Major challenges include improving the vectors used with the aim of more effective and selective delivery. In addition, effective penetration into and spreading within advanced and complex tumour masses and metastases remains challenging. This review focuses on existing and developmental gene transfer applications for gynaecological diseases.

Engineering targeted viral vectors for gene therapy

Translating knowledge of genetic disease mechanisms into gene therapies has been slow with limited clinical success. One major reason is that the transfer vectors, which are most often of viral origin, are not targeted sufficiently towards the cells of interest.

To achieve successful delivery of genetic material, transductional targeting is often essential to enter the target cell and to avoid side effects from the transduction of non-target cells.

Many techniques to target viral vectors to specific cells have been developed. They can be divided into three types: systems that use adaptor proteins from other viruses (pseudotyping); systems that use adaptors to couple the targeting ligand to the vector; and systems that genetically incorporate the targeting moiety into the viral genome.

Whereas systems involving adaptor proteins are highly useful in preclinical evaluations, systems that make use of genetically incorporated targeting ligands are advantageous for clinical applications.

Combinations of several targeting principles (including ablation of natural tropism, pseudotyping and adaptors) and novel combinations (such as the adeno-associated virus (AAV) genome in a phage vector) allow systemic vector application.

An initial clinical study with a targeted retrovirus showed feasibility to transfer laboratory success to patient application, underlining that there are no principal regulatory barriers for targeted vectors.

Systemic vector applications will be facilitated by enabling the vector to move beyond the vascular endothelium at specific sites, using transcytosis or cellular vehicles. The application of existing targeting techniques to new viral vector serotypes and new vector classes is extending the therapeutic capabilities further.

Obstacles to systemic application of vectors are found in the blood as immune reactions against the vector and as binding of blood proteins to the vector. Some targeting approaches might have the potential to circumvent these obstacles.

To preclinically evaluate new targeting strategies, several models that reflect the human situation to varying degrees are available. The use of primary cells, tissue-slice systems and transgenic animals seems to be especially promising.

Imaging technologies provide the ability to monitor the vector in vivo in real time without sacrificing the animal model. These techniques facilitate vector targeting and biodistribution studies.

A key challenge in gene therapy is vector targeting to specific cells, while avoiding effects on other tissues. Several strategies have been developed recently to enable targeting of the main viral vectors, moving them a step closer to clinical use.

To achieve therapeutic success, transfer vehicles for gene therapy must be capable of transducing target cells while avoiding impact on non-target cells. Despite the high transduction efficiency of viral vectors, their tropism frequently does not match the therapeutic need. In the past, this lack of appropriate targeting allowed only partial exploitation of the great potential of gene therapy. Substantial progress in modifying viral vectors using diverse techniques now allows targeting to many cell types in vitro. Although important challenges remain for in vivo applications, the first clinical trials with targeted vectors have already begun to take place.