Influence of method of systemic administration of adenovirus on virus-mediated toxicity: focus on mortality, virus distribution, and drug metabolism

Oncolytic adenovirus as pancreatic cancer-targeted therapy: Where do we go from here?

Pancreatic cancer remains one of the deadliest cancers with extremely high mortality rate, and the number of cases is expected to steadily increase with time. Pancreatic cancer is refractory to conventional cancer treatment options, like chemotherapy and radiotherapy, and commercialized immunotherapeutics, owing to its immunosuppressive and desmoplastic phenotype. Due to these reasons, development of an innovative treatment option that can overcome these challenges posed by the pancreatic tumor microenvironment (TME) is in an urgent need. The present review aims to summarize the evolution of oncolytic adenovirus (oAd) engineering and usage as therapeutics (either monotherapy or combination therapy) over the last decade to overcome these hurdles to instigate a potent antitumor effect against desmoplastic and immunosuppressive pancreatic cancer.

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.

Optimized adenovirus-antibody complexes stimulate strong cellular and humoral immune responses against an encoded antigen in naive mice and those with preexisting immunity

The immune response to recombinant adenoviruses is the most significant impediment to their clinical use for immunization. We test the hypothesis that specific virus-antibody combinations dictate the type of immune response generated against the adenovirus and its transgene cassette under certain physiological conditions while minimizing vector-induced toxicity. In vitro and in vivo assays were used to characterize the transduction efficiency, the T and B cell responses to the encoded transgene, and the toxicity of 1 × 10(11) adenovirus particles mixed with different concentrations of neutralizing antibodies. Complexes formed at concentrations of 500 to 0.05 times the 50% neutralizing dose (ND(50)) elicited strong virus- and transgene-specific T cell responses. The 0.05-ND(50) formulation elicited measurable anti-transgene antibodies that were similar to those of virus alone (P = 0.07). This preparation also elicited very strong transgene-specific memory T cell responses (28.6 ± 5.2% proliferation versus 7.7 ± 1.4% for virus alone). Preexisting immunity significantly reduced all responses elicited by these formulations. Although lower concentrations (0.005 and 0.0005 ND(50)) of antibody did not improve cellular and humoral responses in naïve animals, they did promote strong cellular (0.005 ND(50)) and humoral (0.0005 ND(50)) responses in mice with preexisting immunity. Some virus-antibody complexes may improve the potency of adenovirus-based vaccines in naïve individuals, while others can sway the immune response in those with preexisting immunity. Additional studies with these and other virus-antibody ratios may be useful to predict and model the type of immune responses generated against a transgene in those with different levels of exposure to adenovirus.

Organ-specific shifts in mtDNA heteroplasmy following systemic delivery of a mitochondria-targeted restriction endonuclease

Most pathogenic mtDNA mutations are heteroplasmic and there is a clear correlation between high levels of mutated mtDNA in a tissue and pathology. We have found that in vivo double strand breaks (DSB) in mtDNA lead to digestion of cleaved mtDNA and replication of residual mtDNA. Therefore, if DSB could be targeted to mutations in mtDNA, mutant genomes could be eliminated and the wild-type mtDNA would repopulate the cells. This can be achieved by using mitochondria-targeted restriction endonucleases as a means to degrade specific mtDNA haplotypes in heteroplasmic cells or tissues. In the present work we investigated the potential of systemic delivery of mitochondria-targeted restriction endonucleases to reduce the proportion of mutant mtDNA in specific tissues. Using the asymptomatic NZB/BALB mtDNA heteroplasmic mouse as a model, we found that a mitochondria-targeted ApaLI (that cleaves BALB mtDNA at a single site and does not cleave NZB mtDNA) increased the proportion of NZB mtDNA in target tissues. This was observed in heart, using a cardiotropic adeno-associated virus type-6 (AAV6) and in liver, using the hepatotropic adenovirus type-5 (Ad5). No mtDNA depletion or loss of cytochrome c oxidase activity was observed in any of these tissues. These results demonstrate the potential of systemic delivery of viral vectors to specific organs for the therapeutic application of mitochondria-targeted restriction enzymes in mtDNA disorders.

Induction of shock after intravenous injection of adenovirus vectors: a critical role for platelet-activating factor

Innate immune responses are a major barrier to safe systemic gene therapy with adenovirus (Ad) vectors. We show that intravenous (IV) injection of rats with Ad5 vectors causes a novel rapid shock reaction that involves hypotension, hemoconcentration, tissue edema, and vasocongestion, with notable pathology in the pancreas and the gastrointestinal system. We show for the first time that this reaction is dependent on platelet-activating factor (PAF), a lipid signaling molecule that is a known shock inducer. Ad upregulated PAF within 5 minutes in vivo, and antagonists of the PAF receptor were able to prevent Ad-induced shock. Ad upregulated PAF via the reticuloendothelial system (RES), because splenectomy or depletion of phagocytes blocked the ability of Ad to induce both PAF and shock. Rats were considerably more sensitive to Ad-induced shock than were mice, but PAF mediated shock in both species. Other Ad-induced innate immune responses such as cytokine induction and thrombocytopenia were not mediated by PAF. In summary, systemic IV injection of Ad stimulates the RES to upregulate PAF within a matter of minutes, which results in shock. The identification of this novel pathway suggests strategies to improve the safety of systemic gene therapy with Ad vectors.

Drug-virus interaction: effect of administration of recombinant adenoviruses on the pharmacokinetics of docetaxel in a rat model

Modern cancer therapy combines recombinant viruses with traditional chemotherapeutic agents that are metabolized by hepatic cytochrome P450 3A4 (CYP3A4). A single dose of recombinant adenovirus (Ad) expressing beta-galactosidase (AdlacZ) significantly alters CYP3A2, the correlate of CYP3A4, in rats for 14 days. Recombinant adenovirus expressing human p53 (Adp53) also suppresses CYP3A2. Plasma clearance of docetaxel (DTX) in animals given AdlacZ (3.38 ± 0.22 L/h/kg) was significantly lower than that of those given DTX alone (6.41 ± 1.10 L/h/kg, p≤0.05). Area under the plasma concentration-time curve of DTX in rats given AdlacZ (2,987.37 ± 197.97 ng/ml/h) was significantly greater than those given drug alone (1,666.59 ± 317.04 ng/ml/h, p≤0.05). Both viruses prolonged DTX half-life (t_1/2). Ad infection may cause significant variability in the pharmacokinetics and pharmacodynamics of anti-cancer agents and should be considered when designing therapeutic regimens for patients with viral infection and those enrolled in clinical trials employing recombinant viruses.