Anti-tumor efficacy of a transcriptional replication-competent adenovirus, Ad-OC-E1a, for osteosarcoma pulmonary metastasis

Oncolyic Virotherapy for Prostate Cancer: Lighting a Fire in Winter

As the most common cancer of the genitourinary system, prostate cancer (PCa) is a global men's health problem whose treatments are an urgent research issue. Treatment options for PCa include active surveillance (AS), surgery, endocrine therapy, chemotherapy, radiation therapy, immunotherapy, etc. However, as the cancer progresses, the effectiveness of treatment options gradually decreases, especially in metastatic castration-resistant prostate cancer (mCRPC), for which there are fewer therapeutic options and which have a shorter survival period and worse prognosis. For this reason, oncolytic viral therapy (PV), with its exceptional properties of selective tumor killing, relatively good safety in humans, and potential for transgenic delivery, has attracted increasing attention as a new form of anti-tumor strategy for PCa. There is growing evidence that OV not only kills tumor cells directly by lysis but can also activate anticancer immunity by acting on the tumor microenvironment (TME), thereby preventing tumor growth. In fact, evidence of the efficacy of this strategy has been observed since the late 19th century. However, subsequently, interest waned. The renewed interest in this therapy was due to advances in biotechnological methods and innovations at the end of the 20th century, which was also the beginning of PCa therapy with OV. Moreover, in combination with chemotherapy, radiotherapy, gene therapy or immunotherapy, OV viruses can have a wide range of applications and can provide an effective therapeutic result in the treatment of PCa.

Oncolytic Viruses and Their Potential as a Therapeutic Opportunity in Osteosarcoma

Osteosarcoma remains an unmet medical need. Oncolytic viruses are gaining traction as novel cancer therapeutics. These viruses are either naturally nonpathogenic or engineered to be safe by specific genetic deletions yet retain the ability to infect and kill human cancer cells and elicit anticancer immunity. Some versions are being specifically designed and tested in patients with osteosarcoma, though due to their generalized mechanism of action most are being tested in patients across a broad range of cancer types. The activity of these viruses is impacted not only by the susceptibility of tumor cells to infection but also by the tumor microenvironment (TME) and by tumor immunogenicity. Here we review the field of oncolytic viruses with a particular emphasis on highlighting any available data in preclinical osteosarcoma models or in patients with osteosarcoma. While in general the viruses have been shown safe to administer to patients by a variety of routes, their therapeutic efficacy to date has been limited. Given the low rate of adverse events and the likely absence of long-term side effects, the utility of oncolytic viruses will most likely be realized when used in combination with other agents.

Preclinical Testing of an Oncolytic Parvovirus: Standard Protoparvovirus H-1PV Efficiently Induces Osteosarcoma Cell Lysis In Vitro

Osteosarcoma is the most frequent malignant disease of the bone. On the basis of early clinical experience in the 1960s with H-1 protoparvovirus (H-1PV) in osteosarcoma patients, this effective oncolytic virus was selected for systematic preclinical testing on various osteosarcoma cell cultures. A panel of five human osteosarcoma cell lines (CAL 72, H-OS, MG-63, SaOS-2, U-2OS) was tested. Virus oncoselectivity was confirmed by infecting non-malignant human neonatal fibroblasts and osteoblasts used as culture models of non-transformed mesenchymal cells. H-1PV was found to enter osteosarcoma cells and to induce viral DNA replication, transcription of viral genes, and translation to viral proteins. After H-1PV infection, release of infectious viral particles from osteosarcoma cells into the supernatant indicated successful viral assembly and egress. Crystal violet staining revealed progressive cytomorphological changes in all osteosarcoma cell lines. Infection of osteosarcoma cell lines with the standard H-1PV caused an arrest of the cell cycle in the G2 phase, and these lines had a limited capacity for standard H-1PV virus replication. The cytotoxicity of wild-type H-1PV virus towards osteosarcoma cells was compared in vitro with that of two variants, Del H-1PV and DM H-1PV, previously described as fitness variants displaying higher infectivity and spreading in human transformed cell lines of different origins. Surprisingly, wild-type H-1PV displayed the strongest cytostatic and cytotoxic effects in this analysis and thus seems the most promising for the next preclinical validation steps in vivo.

CD47 blockade inhibits tumor progression human osteosarcoma in xenograft models

Osteosarcoma is the most common bone tumors in children and adolescents. Despite intensive chemotherapy, patients with advanced disease still have a poor prognosis, illustrating the need for alternative therapies. In this study, we explored the use of antibodies that block CD47 with a tumor growth suppressive effect on osteosarcoma. We first found that up-regulation of CD47 mRNA levels in the tumorous tissues from eight patients with osteosarcoma when compared with that in adjacent non-tumorous tissues. Further western-blot (WB) and immunohistochemistry (IHC) demonstrated that CD47 protein level was highly expressed in osteosarcoma compared to normal osteoblastic cells and adjacent non-tumorous tissues. Osteosarcoma cancer stem cell markers staining shown that the majority of CD44⁺ cells expressed CD47 albeit with different percentages (ranging from 80% to 99%). Furthermore, high CD47 mRNA expression levels were associated with a decreased probability of progression-free and overall survival. In addition, blockade of CD47 by specific Abs suppresses the invasive ability of osteosarcoma tumor cells and further inhibits spontaneous pulmonary metastasis of KRIB osteosarcoma cells in vivo. Finally, CD47 blockade increases macrophage phagocytosis of osteosarcoma tumor cells. In conclusion, our findings demonstrate that CD47 is a critical regulator in the metastasis of osteosarcoma and suggest that targeted inhibition of this antigen by anti-CD47 may be a novel immunotherapeutic approach in the management of this tumor.

Strategies and developments of immunotherapies in osteosarcoma

Osteosarcoma (OS) is a frequently observed primary malignant tumor. Current therapy for osteosarcoma consists of comprehensive treatment. The long-term survival rate of patients exhibiting nonmetastatic OS varies between 65-70%. However, a number of OS cases have been observed to be resistant to currently used therapies, leading to disease recurrence and lung metastases, which are the primary reasons leading to patient mortality. In the present review, a number of pieces of evidence provide support for the potential uses of immunotherapy, including immunomodulation and vaccine therapy, for the eradication of tumors via upregulation of the immune response. Adoptive T-cell therapy and oncolytic virotherapy have been used to treat OS and resulted in objective responses. Immunologic checkpoint blockade and targeted therapy are also potentially promising therapeutic tools. Immunotherapy demonstrates significant promise with regard to improving the outcomes for patients exhibiting OS.

Comparison of prostate-specific promoters and the use of PSP-driven virotherapy for prostate cancer

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of cancer deaths in men today. Although virus-based gene therapy is a promising strategy to combat advanced prostate cancer, its current effectiveness is limited partially due to inefficient cellular transduction in vivo. To overcome this obstacle, conditional oncolytic viruses (such as conditional replication adenovirus (CRAD)) are developed to specifically target prostate without (or with minimal) systemic toxicity due to viral self-replication. In this study, we have analyzed and compared three prostate-specific promoters (PSA, probasin, and MMTV LTR) for their specificity and activity both in vitro and in vivo. Both mice model with xenograft prostate tumor model and canine model were used. The best PSP was selected to construct a prostate-specific oncolytic adenovirus (CRAD) by controlling the adenoviral E1 region. The efficacy and specificity of CRAD on prostate cancer cells were examined in cell culture and animal models.

Potent growth-inhibitory effect of TRAIL therapy mediated by double-regulated oncolytic adenovirus on osteosarcoma

Osteosarcoma (OS) severely threatens the health of young people and understanding on the molecular mechanisms of OS etiology enables gene therapy to become an effective therapeutic modality. However, insufficient expression level of genes using existing vectors limits the clinical application of gene therapy for OS. To solve the problem, we developed an oncolytic adenoviral vector, OAT, which can selectively and efficiently replicate in OS cells to enhance the expression of transferred genes. We demonstrated that OAT-mediated TRAIL expression is significantly elevated after infection of OS cells than replication-incompetent Ad5 vector. Increased antitumor capacity was observed in OS cells after OAT-TRAIL treatment both in vitro and in vivo. In normal cells, adenoviral replication, TRAIL expression and growth-inhibiting effect were quite limited when OAT-TRAIL was administrated, showing a high biosafety of this oncolytic adenoviral vector. Collectively, we generated an efficient and promising expression vector for OS gene therapy.

Antitumor effects of bladder cancer-specific adenovirus carrying E1A-androgen receptor in bladder cancer

The high frequency of recurrence and poor survival rate of bladder cancer demand exploration of novel strategies. Gene therapy via adenovirus has shown promising potential for the treatment of tumors. We constructed a bladder cancer-specific adenovirus carrying E1A-androgen receptor (AR) under the control of UPII promoter and prostate stem cell antigen enhancer (PSCAE), designated as Ad/PSCAE/UPII/E1A-AR, and investigated its antitumor effects in vitro and in vivo. We demonstrated that Ad/PSCAE/UPII/E1A-AR could be selectively replicated in bladder tumor cell lines (5637, BIU87, EJ and T24) when compared with control adenovirus Ad/PSCAE/UPII/Luc. However, there was no evidence of cytotoxicity for normal human bladder cell line SV-HUC-1 and hepatoma cell line SMMC7721. AR agonist R1881 could strengthen the oncolytic effect of Ad/PSCAE/UPII/E1A-AR in bladder cancer cells. In addition, we demonstrated that intratumoral injection of Ad/PSCAE/UPII/E1A-AR into established subcutaneous human EJ tumors in nude mice could significantly regress the growth of tumor and markedly prolong survival for tumor-bearing mice; on the other hand, saline-treated tumors continued to grow rapidly. Our studies indicate that Ad/PSCAE/UPII/E1A-AR could effectively treat bladder cancer in vitro and in vivo. Furthermore, our findings provide a promising therapeutic modality for the treatment of bladder cancer.

Viral-based gene delivery and regulated gene expression for targeted cancer therapy

IMPORTANCE OF THE FIELD

Cancer is both a major health concern and a care-cost issue in the US and the rest of the world. It is estimated that there will be a total of 1,479,350 new cancer cases and 562,340 cancer deaths in 2009 within the US alone. One of the major obstacles in cancer therapy is the ability to target specifically cancer cells. Most existing chemotherapies and other routine therapies (such as radiation therapy and hormonal manipulation) use indiscriminate approaches in which both cancer cells and non-cancerous surrounding cells are treated equally by the toxic treatment. As a result, either the cancer cell escapes the toxic dosage necessary for cell death and consequently resumes replication, or an adequate lethal dose that kills the cancer cell also causes the cancer patient to perish. Owing to this dilemma, cancer- or organ/tissue-specific targeting is greatly desired for effective cancer treatment and the reduction of side effect cytotoxicity within the patient.

AREAS COVERED IN THIS REVIEW

In this review, the strategies of targeted cancer therapy are discussed, with an emphasis on viral-based gene delivery and regulated gene expression.

WHAT THE READER WILL GAIN

Numerous approaches and updates in this field are presented for several common cancer types.

TAKE HOME MESSAGE

A summary of existing challenges and future directions is also included.

Gene therapy for osteosarcoma: steps towards clinical studies

Gene therapy, an applied form of biotechnology, relies on the delivery of foreign DNA into cells. More than 50% of all reported clinical trials for gene therapy are for cancer, though only a scant number for osteosarcoma. Osteosarcoma is a neoplasm afflicting young adults, who in their prime years of life suffer debilitation if not death. The disease is not entirely curable, even with surgery combined with aggressive chemotherapy. Thus, other forms of therapies are being evaluated, including gene therapy. There exist two major forms of gene transfer: viral and non-viral. This review only covers proof-of-principle work carried out in cancer beyond the cell culture stage, in animals. Drawing from the experiences of gene therapy against other cancers, studies for which have already reached the clinical phase, the review discusses potential pitfalls and solutions to enhance gene therapy for osteosarcoma.

Prostate-restricted replicative adenovirus expressing human endostatin-angiostatin fusion gene exhibiting dramatic antitumor efficacy

PURPOSE

Our previous studies coadministering a replication-deficient adenovirus expressing endostatin and angiostatin fusion gene (EndoAngio) and a prostate-restricted, replication-competent adenovirus (PRRA) showed dramatic antitumor efficacy. This study integrated EndoAngio with an improved PRRA vector to make a single antiangiogenic PRRA, thereby exerting a similarly dramatic antitumor effect with feasibility for future clinical trials.

EXPERIMENTAL DESIGN

We developed an antiangiogenic PRRA with structural improvements. The antitumor efficacy of EndoAngio-PRRA was evaluated in prostate-specific antigen/prostate-specific membrane antigen (PSA/PSMA)-positive, androgen-independent CWR22rv tumor models. The tumor vasculature and cell morphology were observed by dual-photon microscopy. The antiangiogenic effect of EndoAngio delivered by PRRA and the killing activity of EndoAngio-PRRA were evaluated in vitro. Virus-inactivated conditioned media from virus-infected PSA/PSMA-positive cells were tested for apoptosis induction in prostate cancer cells.

RESULTS

Our novel EndoAngio-PRRA is a strong antiangiogenic and antitumor agent. Nine of 10 CWR22rv tumors treated by EndoAngio-PRRA completely regressed, with 1 tumor remaining in a dormant status for 26 weeks after treatment. Dual-photon microscopy revealed that EndoAngio-PRRA not only inhibited the development of tumor vasculature but also induced apoptosis in tumor cells. Subsequent in vitro study indicated that EndoAngio-PRRA exhibited stronger tumor-specific killing activity than enhanced green fluorescent protein-PRRA, which expresses enhanced green fluorescent protein instead of EndoAngio. Virus-inactivated conditioned medium from EndoAngio-PRRA-infected PSA/PSMA-positive cells induced apoptosis in C4-2 and CWR22rv cells.

CONCLUSIONS

EndoAngio-PRRA uniquely combines three distinct antitumor effects to eliminate androgen-independent prostate cancer: antiangiogenesis, viral oncolysis, and apoptosis. This novel antiangiogenic PRRA represents a powerful agent feasible for future clinical trials for prostate cancer therapy.

Intravenous administration of the conditionally replicative adenovirus Ad5-Delta24RGD induces regression of osteosarcoma lung metastases

Metastatic osteosarcoma (OS) has a very poor prognosis. New treatments are therefore wanted. The conditionally replicative adenovirus Ad5-Δ24RGD has shown promising anti-tumor effects on local cancers, including OS. The purpose of this study was to determine whether intravenous administration of Ad5-Δ24RGD could suppress growth of human OS lung metastases. Mice bearing SaOs-lm7 OS lung metastases were treated with Ad5-Δ24RGD at weeks 1, 2 and 3 or weeks 5, 6 and 7 after tumor cell injection. Virus treatment at weeks 1–3 did not cause a statistically significant effect on lung weight and total body weight. However, the number of macroscopic lung tumor nodules was reduced from a median of >158 in PBS-treated control mice to 58 in Ad5-Δ24RGD-treated mice (p = 0.15). Moreover, mice treated at weeks 5–7 showed a significantly reduced lung weight (decrease of tumor mass, p < 0.05), a significantly increased body weight gain (decrease of disease symptoms, p < 0.005) and a reduced number of macroscopic lung tumor nodules (median 60 versus > 149, p = 0.12) compared to PBS treated control animals. Adenovirus hexon expression was detected in lung tumor nodules at sacrifice three weeks after the last intravenous adenovirus administration, suggesting ongoing viral infection. These findings suggest that systemic administration of Ad5-Δ24RGD might be a promising new treatment strategy for metastatic osteosarcoma.

Evolving gene therapy approaches for osteosarcoma using viral vectors: review

This review begins with an introduction to the malignant bone tumor, osteosarcoma [OS] and then moves to a discussion of the commonly used vectors for gene transfer. We first briefly highlight non-viral vectors including polymeric and liposomal delivery systems but concentrate predominantly on the 5 leading viral vectors used in cancer gene therapy, specifically retroviruses, adeno-associated viruses, herpes viruses and lentiviruses with the most detailed analysis reserved for adenoviruses. The 3 main strategies for gene therapy in osteosarcoma are next summarized. As part of this review, the several prodrug-converting enzymes utilized in OS suicide gene therapy are examined. The text then turns to a discussion of adenovirus-mediated gene transfer and the need for tumor targeting via transductional or transcriptional approaches. Because of practical problems with use of replication-incompetent viruses in achieving complete tumor kill in vivo, virotherapy utilizing replication competent viruses has come to the fore. This topic is, thus, next reviewed which allows for a natural transition to a discussion of armed therapeutic viruses many of which are conditionally replicating adenoviruses carrying transgenes with established anti-tumor efficacy. We recognize that several other issues have arisen which hamper progress in the field of cancer gene therapy. We, therefore, review viral-induced toxicity in the host and vector delivery issues which have been found to potentially influence safety. We end with a brief perspective including commenting on animal models used in examining delivery strategies for osteosarcoma gene therapy. The challenges remaining are touched upon most especially the need to deal with pulmonary metastatic disease from OS.

Adult human sarcomas. II. Medical oncology

Human sarcoma cells can be killed by radio- and chemotherapy, but tumor cells acquiring resistance frequently kill the patient. A keen understanding of the intracellular course of oncogenic cascades leads to the discovery of small molecular inhibitors of the involved phosphorylated kinases. Targeted therapy complements chemotherapy. Oncogene silencing is feasible by small interfering RNA. The restoration of some of the mutated or deleted tumor-suppressor genes (p53, Rb, PTEN, hSNF, INK/ARF and WT) by demethylation or reacetylation of their histones has been accomplished. Genetically engineered or naturally oncolytic viruses selectively lyse tumors and leave healthy tissues intact. Adeno- or retroviral vectors deliver genes of immunological costimulators, tumor antigens, chemo- or cytokines and/or tumor-suppressor proteins into tumor (sarcoma) cells. Suicide gene delivery results in apoptosis induction. Genes of enzymes that target prodrugs as their substrates render tumor cells highly susceptible to chemotherapy, with the prodrug to be targeted intracellularly. It will be combinations of sophisticated surgical removal of the nonencapsulated and locally invasive primary sarcomas, advanced forms of radiotherapy to the involved sites and immunotherapy with sarcoma vaccines that will cure primary sarcomas. Adoptive immunotherapy with immune lymphocytes will be operational in metastatic disease only when populations of regulatory T cells are controlled. Targeted therapy with small molecular inhibitors of oncogene cascades, the driving forces of sarcoma cells, alteration of the tumor stroma from a supportive to a tumor-hostile environment, reactivation or replacement of wild-type tumor-suppressor genes, and radio-chemotherapy (with much reduced toxicity) will eventually accomplish the cure of metastatic sarcomas.