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

4-Week repeated dose rat GLP toxicity study of oncolytic ECHO-7 virus Rigvir administered intramuscularly with a 4-week recovery period

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4-week repeated dose rat GLP toxicology study with the oncolytic ECHO-7 virus Rigvir.

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No unscheduled deaths, adverse clinical signs, changes in body weight or food intake.

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Rigvir was biodistributed to the spleen.

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Rigvir was well tolerated in the rats.

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The no-observed-adverse-effect level (NOAEL) was the highest dose tested 2×10⁷ TCID₅₀.

The oncolytic ECHO-7 virus Rigvir was registered in Latvia in 2004 and later in Georgia, Armenia and Uzbekistan. No severe adverse events have been observed. During drug development good laboratory practice (GLP) pre-clinical toxicology studies are generally required by regulatory agencies. Since such studies had previously not been performed, the aim of this 4-week repeated dose GLP toxicity study was to determine the potential toxicity, and reversibility of any findings after a 4-week treatment-free period. Han-Wistar rats were randomly assigned to control, Rigvir (2×10⁶, 1×10⁷ and 2×10⁷ TCID₅₀) groups. Intramuscular administration was on days 1-3, 8-10, 15-17, and 22-24. Clinical signs, average food-intake, body weights, ophthalmology, clinical pathology parameters, bioanalysis, gross necropsy, organ weights, biodistribution and histopathology were evaluated. There were no unscheduled deaths, adverse clinical signs, no changes in body weight, body weight gain, food intake, ophthalmoscopy, clinical pathology, urine volume or composition, or organ weights. Slightly higher numbers of eosinophils in Rigvir treated animals returned to normal after recovery. Rigvir biodistributed to the spleen. Low incidence of inflammatory cell infiltration at administration sites and increased lymphoid cellularity at the regional (inguinal and popliteal) lymph nodes were observed; after recovery, only those in popliteal lymph nodes remained. Therefore, 4-week Rigvir at 2×10⁷ TCID₅₀ administration was well tolerated in rats. The no-observed-adverse-effect level (NOAEL) was the highest dose tested, 2×10⁷ TCID₅₀.

Objectives

The objectives of this study were to determine the potential toxicity of Rigvir, an ECHO-7 oncolytic virus, when administered intramuscularly for 4 weeks to rats, with a 4-week recovery period, and to evaluate the reversibility of any potential findings. In addition, the biodistribution of Rigvir in selected tissues was determined.

Simultaneous overexpression of miR-126 and miR-34a induces a superior antitumor efficacy in pancreatic adenocarcinoma

Background

Pancreatic adenocarcinoma (PAC) is one of the most fatal cancers due to its high degree of malignancy, increasing incidence, high mortality, and unsatisfactory treatment efficacy. Evidence has suggested that numerous microRNAs (miRNAs), including miR-126 and miR-34a, have potent tumor-suppressing effects on PAC, implicating a possible application of miRNA in tumor therapy. However, the therapeutic effect of a single miRNA on pancreatic cancer is limited.

Methods

We simultaneously delivered miR-126 and miR-34a into PAC cells by a carcinoembryonic antigen promoter-driven oncolytic adenovirus (AdCEAp-miR126/34a), and examined the antitumor efficacy of the therapeutic system in in vitro and in vivo experiments.

Results

In vitro cytological experiments found that the expression levels of miR-126 and miR-34a were specifically increased in the AdCEAp-miR126/34a-infected PAC cells, and the antitumor efficacy was enhanced in aspects of cancer cell viability, migration, invasion, and apoptosis, by synergistically combining the antitumor effects of overexpressed miR-126 and miR-34a and the oncolytic effect of viral replication specifically in PAC cells. The expression levels of miR-126 target genes (vascular endothelial growth factor-A and SOX2) and miR-34a target genes (cyclin D1, E2F1, and Bcl-2) were markedly decreased in the PAC cells after being infected with AdCEAp-miR126/34a. Notable suppression of the therapeutic system on tumor growth was also proven in established PAC xenograft tumor models in nude mice, which demonstrated that the combination of miR-126 and miR-34a exerts more effective antitumor outcomes than a single miRNA.

Conclusion

The therapeutic system co-expressing miR-126 and miR-34a mediated by oncolytic adenovirus is a promising system for PAC target therapy.

Combining Oncolytic Virotherapy with p53 Tumor Suppressor Gene Therapy

Oncolytic virus (OV) therapy utilizes replication-competent viruses to kill cancer cells, leaving non-malignant cells unharmed. With the first U.S. Food and Drug Administration-approved OV, dozens of clinical trials ongoing, and an abundance of translational research in the field, OV therapy is poised to be one of the leading treatments for cancer. A number of recombinant OVs expressing a transgene for p53 (TP53) or another p53 family member (TP63 or TP73) were engineered with the goal of generating more potent OVs that function synergistically with host immunity and/or other therapies to reduce or eliminate tumor burden. Such transgenes have proven effective at improving OV therapies, and basic research has shown mechanisms of p53-mediated enhancement of OV therapy, provided optimized p53 transgenes, explored drug-OV combinational treatments, and challenged canonical roles for p53 in virus-host interactions and tumor suppression. This review summarizes studies combining p53 gene therapy with replication-competent OV therapy, reviews preclinical and clinical studies with replication-deficient gene therapy vectors expressing p53 transgene, examines how wild-type p53 and p53 modifications affect OV replication and anti-tumor effects of OV therapy, and explores future directions for rational design of OV therapy combined with p53 gene therapy.

Naturally Existing Oncolytic Virus M1 Is Nonpathogenic for the Nonhuman Primates After Multiple Rounds of Repeated Intravenous Injections

Cancers figure among the leading causes of morbidity and mortality worldwide. The number of new cases is expected to rise by about 70% over the next 2 decades. Development of novel therapeutic agents is urgently needed for clinical cancer therapy. Alphavirus M1 is a Getah-like virus isolated from China with a genome of positive single-strand RNA. We have previously identified that alphavirus M1 is a naturally existing oncolytic virus with significant anticancer activity against different kinds of cancer (e.g., liver cancer, bladder cancer, and colon cancer). To support the incoming clinical trial of intravenous administration of alphavirus M1 to cancer patients, we assessed the safety of M1 in adult nonhuman primates. We previously presented the genome sequencing data of the cynomolgus macaques (Macaca fascicularis), which was demonstrated as an ideal animal species for virus infection study. Therefore, we chose cynomolgus macaques of either sex for the present safety study of oncolytic virus M1. In the first round of administration, five experimental macaques were intravenously injected with six times of oncolytic virus M1 (1 × 10(9) pfu/dose) in 1 week, compared with five vehicle-injected control animals. The last two rounds of injections were further completed in the following months in the same way as the first round. Body weight, temperature, complete blood count, clinical biochemistries, cytokine profiles, lymphocytes subsets, neutralizing antibody, and clinical symptoms were closely monitored at different time points. Magnetic resonance imaging was also performed to assess the possibility of encephalitis or arthritis. As a result, no clinical, biochemical, immunological, or medical imaging or other pathological evidence of toxicity was found during the whole process of the study. Our results in cynomolgus macaques suggested the safety of intravenous administration of oncolytic virus M1 in cancer patients in the future.

Oncolytic virotherapy of canine and feline cancer

Cancer is the leading cause of disease-related death in companion animals such as dogs and cats. Despite recent progress in the diagnosis and treatment of advanced canine and feline cancer, overall patient treatment outcome has not been substantially improved. Virotherapy using oncolytic viruses is one promising new strategy for cancer therapy. Oncolytic viruses (OVs) preferentially infect and lyse cancer cells, without causing excessive damage to surrounding healthy tissue, and initiate tumor-specific immunity. The current review describes the use of different oncolytic viruses for cancer therapy and their application to canine and feline cancer.

Advances in adenovirus-mediated p53 cancer gene therapy

INTRODUCTION

The tumor suppressor p53 gene regulates diverse cellular processes, such as cell-cycle arrest, senescence, apoptosis and autophagy, and it is frequently inactivated by genetic alterations in ∼ 50% of all types of human cancers. To restore wild-type p53 function in p53-inactivated tumors, adenovirus-mediated p53 gene therapy has been developed as a promising antitumor strategy in preclinical experiments and clinical studies.

AREAS COVERED

This review focuses on the clinical relevance of replication-deficient adenovirus vectors that carry the wild-type p53 gene (Ad-p53; Advexin, Gendicine and SCH-58500) in clinical studies of patients with various cancers and the future perspectives regarding conditionally replicating adenovirus vectors expressing the wild-type p53 gene (CRAd-p53; AdDelta24-p53, SG600-p53, OBP-702) in preclinical experiments. Moreover, the recent advances in our understanding of the molecular basis for the p53-mediated tumor suppression network induced by Ad-p53 and CRAd-p53 vectors and the combination therapies for promoting the therapeutic potential of adenovirus-mediated p53 gene therapy are discussed.

EXPERT OPINION

Exploration of the molecular mechanism underlying the p53-mediated tumor suppression network and the effective strategy for enhancing the p53-mediated cell death signaling pathway would provide novel insights into the improvement of clinical outcome in p53-based cancer gene therapy.

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.

Biosafety studies of carrier cells infected with a replication-competent adenovirus introduced by IAI.3B promoter

The use of carrier cells infected with oncolytic viruses in cancer gene therapy is an attractive method because it can overcome viral immunogenicity and induce tumor immunity and significant antitumor activity. To enable human clinical trials of this treatment, acute and chronic toxicity tests must first be performed to ensure safety. IAI.3B promoter, oncolytic adenovirus AdE3-IAI.3B introduced by IAI.3B promoter, and A549 carrier cells infected with AdE3-IAI.3B were highly active in cancer cells but not in normal cells. Freeze-thawing increased the antitumor effect of A549 carrier cells by promoting the translocation of oncolytic adenovirus particles from the nucleus to the cytoplasm following the rupture of the nuclear membranes. No deaths or abnormal blood test data resulted from acute toxicity tests conducted in nude mice after a single dose. In chronic toxicity tests in rabbits, there were no serious side effects after eight doses of 1.25 × 10⁷ cells/kg or less for 4 weeks; a significant immune response is known to elicit increased numbers of antiadenovirus antibodies and enlarge the spleen. From these results, it could be concluded that cancer gene therapy of recurrent solid tumors using carrier cells can be safely trialed in humans.

Preclinical safety evaluation of rAd5-hTERTC27 by intravenous injection

The safety of rAd5-hTERTC27, a replication defective adenovirus vector carrying hTERTC27 for possible use against hepatocellular carcinoma (HCC) was assessed. In single-dose evaluations, intravenous dose levels of up to 2×10(11)VP/kg in rats and 9×10(10)VP/kg in monkeys were well tolerated with no abnormal changes in general signs, body weight and food consumption, and no significant differences in biochemical parameters, urinalysis, ECG, and systemic necropsy observations between the rAd5 groups and solvent control group except that slight hematological change was observed. No hemolytic effect using rabbit blood, local perivasculitis following intravenous injection in rabbits or systemic anaphylaxis in guinea pigs following intravenous dosing was seen. No effects on the central nervous system of mice occurred following intravenous dosing with the exception of an increase in sleep duration at the dose of 1.2×10(11)VP/kg (p<0.05) but not at lower doses of 2×10(10) and 6×10(10)VP/kg in the hypnotic synergism test. These results demonstrate that administration of rAd5-hTERTC27 was well tolerated in an initial set of safety studies as part of an evaluation to allow human trials for the treatment of HCC.

Dual programmed cell death pathways induced by p53 transactivation overcome resistance to oncolytic adenovirus in human osteosarcoma cells

Tumor suppressor p53 is a multifunctional transcription factor that regulates diverse cell fates, including apoptosis and autophagy in tumor biology. p53 overexpression enhances the antitumor activity of oncolytic adenoviruses; however, the molecular mechanism of this occurrence remains unclear. We previously developed a tumor-specific replication-competent oncolytic adenovirus, OBP-301, that kills human osteosarcoma cells, but some human osteosarcoma cells were OBP-301-resistant. In this study, we investigated the antitumor activity of a p53-expressing oncolytic adenovirus, OBP-702, and the molecular mechanism of the p53-mediated cell death pathway in OBP-301-resistant human osteosarcoma cells. The cytopathic activity of OBP-702 was examined in OBP-301-sensitive (U2OS and HOS) and OBP-301-resistant (SaOS-2 and MNNG/HOS) human osteosarcoma cells. The molecular mechanism in the OBP-702-mediated induction of two cell death pathways, apoptosis and autophagy, was investigated in OBP-301-resistant osteosarcoma cells. The antitumor effect of OBP-702 was further assessed using an orthotopic OBP-301-resistant MNNG/HOS osteosarcoma xenograft tumor model. OBP-702 suppressed the viability of OBP-301-sensitive and -resistant osteosarcoma cells more efficiently than OBP-301 or a replication-deficient p53-expressing adenovirus (Ad-p53). OBP-702 induced more profound apoptosis and autophagy when compared with OBP-301 or Ad-p53. E1A-mediated miR-93/106b upregulation induced p21 suppression, leading to p53-mediated apoptosis and autophagy in OBP-702-infected cells. p53 overexpression enhanced adenovirus-mediated autophagy through activation of damage-regulated autophagy modulator (DRAM). Moreover, OBP-702 suppressed tumor growth in an orthotopic OBP-301-resistant MNNG/HOS xenograft tumor model. These results suggest that OBP-702-mediated p53 transactivation is a promising antitumor strategy to induce dual apoptotic and autophagic cell death pathways via regulation of miRNA and DRAM in human osteosarcoma cells.

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.

Inhibitory effect of Survivin promoter-regulated oncolytic adenovirus carrying P53 gene against gallbladder cancer

Gene therapy has become an important strategy for treatment of malignancies, but problems remains concerning the low gene transferring efficiency, poor transgene expression and limited targeting specific tumors, which have greatly hampered the clinical application of tumor gene therapy. Gallbladder cancer is characterized by rapid progress, poor prognosis, and aberrantly high expression of Survivin. In the present study, we used a human tumor-specific Survivin promoter-regulated oncolytic adenovirus vector carrying P53 gene, whose anti-cancer effect has been widely confirmed, to construct a wide spectrum, specific, safe, effective gene-viral therapy system, AdSurp-P53. Examining expression of enhanced green fluorecent protein (EGFP), E1A and the target gene P53 in the oncolytic adenovirus system validated that Survivin promoter-regulated oncolytic adenovirus had high proliferation activity and high P53 expression in Survivin-positive gallbladder cancer cells. Our in vitro cytotoxicity experiment demonstrated that AdSurp-P53 possessed a stronger cytotoxic effect against gallbladder cancer cells and hepatic cancer cells. The survival rate of EH-GB1 cells was lower than 40% after infection of AdSurp-P53 at multiplicity of infection (MOI) = 1 pfu/cell, while the rate was higher than 90% after infection of Ad-P53 at the same MOI, demonstrating that AdSurp-P53 has a potent cytotoxicity against EH-GB1 cells. The tumor growth was greatly inhibited in nude mice bearing EH-GB1 xenografts when the total dose of AdSurp-P53 was 1 × 10(9) pfu, and terminal dUTP nick end-labeling (TUNEL) revealed that the apoptotic rate of cancer cells was (33.4 ± 8.4)%. This oncolytic adenovirus system overcomes the long-standing shortcomings of gene therapy: poor transgene expression and targeting of only specific tumors, with its therapeutic effect better than the traditional Ad-P53 therapy regimen already on market; our system might be used for patients with advanced gallbladder cancer and other cancers, who are not sensitive to chemotherapy, radiotherapy, or who lost their chance for surgical treatment.

Expression of recombinant human adenovirus-p53 gene delivered into rabbit VX2 tumors by interventional methods

AIM: To investigate the expression of recombinant human adenovirus-p53 gene (rAd-p53, 1×10¹² VP) delivered into rabbit VX2 tumors by interventional methods.

METHODS: Thirty New Zealand rabbits were used to establish an animal model of hepatocarcinoma by implantation of the VX2 tumors into the liver. Eleven days after implantation, magnetic resonance imaging (MRI) and computed tomography (CT) scans were performed. Successful implantation was achieved in 27 rabbits. These rabbits were randomly divided into three groups: A, B and C. Groups A and B were infused through the hepatic artery with rAd-p53 (5 × 10⁶ VP) alone and rAd-p53 (5 × 10⁶ VP) plus lipiodol ultra fluid (0.5 mL), respectively, while group C was injected with rAd-p53 (5 × 10⁶ VP) into tumors by surgery. All model rabbits underwent digital subtraction angiography (DSA) during operation. The expression of P53, Bax and Bcl-2 proteins in tumor and peritumoral tissue was detected by immunohistochemistry at 24 and 72 hours and on 6 days after the operation.

RESULTS: MRI and CT scans showed that successful implantation was achieved in 27 rabbits, and the success rate was 95%. Immunohistochemical analysis indicated that P53, Bax and Bcl-2 proteins were expressed in all the three groups. The expression levels of P53 and Bax reached the peak at 72 hours. The expression levels of P53 and Bax in group C at 72 hours were significantly higher than those in groups A and B (P53: 70.3% ± 3.4% vs 62.4% ± 3.2% and 65.4% ± 2.1%; Bax: 43.7% ± 2.1% vs 35.7% ± 1.3% and 37.6% ± 2.4%, respectively; all P < 0.05). In contrast, the expression level of Bcl-2 in group C at 72 hours was significantly lower than those in groups A and B (12.0% ± 2.6% vs 18.0% ± 4.3% and 16.2% ± 3.1%, respectively; both P < 0.05).

CONCLUSION: P53 protein is expressed in rabbit VX2 tumors in a time-dependent manner. The expression level of P53 protein depends on the delivery methods used. The highest expression of P53 protein is achieved by intratumoral injection, followed by infusion of rAd-p53 plus lipiodol ultra fluid and rAd-p53 alone through the hepatic artery.

A novel triple-regulated oncolytic adenovirus carrying PDCD5 gene exerts potent antitumor efficacy on common human leukemic cell lines

PDCD5 (programmed cell death 5) accelerates apoptosis of certain tumor cells and the replication-defective Ad-PDCD5 may be a promising agent for enhancing chemosensitivity. In this study, a triple-regulated conditionally replicating adenoviruses (CRAd) carrying PDCD5 gene expression cassette, SG611-PDCD5, was engineered. In SG611-PDCD5, the E1a gene with a deletion of 24 nucleotides within CR2 region is controlled under the human telomerase reverse transcriptase (hTERT) promoter, the E1b gene expression is directed by the hypoxia response element (HRE), whereas the PDCD5 gene is controlled by the cytomegalovirus promoter. The tumor-selective replication of this virus and its antitumor efficacy were characterized in several leukemic cell lines in vitro and in xenograft models of human leukemic cell line in nude mice. It was found by RQ-RT-PCR assay that SG611-PDCD5 expressed PDCD5 efficiently in leukemic cells. In K562 tumor xenograft models, SG611-PDCD5 displayed a tumor killing capacity. At a dose of 1 x 10(9) plaque-forming units, SG611-PDCD5 alone could completely inhibit the tumor growth and more effective than replication-defective Ad-PDCD5. Histopathologic examination revealed that SG611-PDCD5 administration resulted in leukemic cell apoptosis. We concluded that the triple-regulated SG611-PDCD5, as a more potent and safer antitumor therapeutic, could provide a new strategy for leukemia biotherapy.