Oligodeoxynucleotides induce brain inflammation in rats when infused intracerebroventricularly

Considerations in the Preclinical Assessment of the Safety of Antisense Oligonucleotides

The nucleic acid therapeutics field has made tremendous progress in the past decades. Continuous advances in chemistry and design have led to many successful clinical applications, eliciting even more interest from researchers including both academic groups and drug development companies. Many preclinical studies in the field focus on improving the delivery of antisense oligonucleotide drugs (ONDs) and/or assessing their efficacy in target tissues, often neglecting the evaluation of toxicity, at least in early phases of development. A series of consensus recommendations regarding regulatory considerations and expectations have been generated by the Oligonucleotide Safety Working Group and the Japanese Research Working Group for the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use S6 and Related Issues (WGS6) in several white papers. However, safety aspects should also be kept in sight in earlier phases while screening and designing OND to avoid subsequent failure in the development phase. Experts and members of the network "DARTER," a COST Action funded by the Cooperation in Science and Technology of the EU, have utilized their collective experience working with OND, as well as their insights into OND-mediated toxicities, to generate a series of consensus recommendations to assess OND toxicity in early stages of preclinical research. In the past few years, several publications have described predictive assays, which can be used to assess OND-mediated toxicity in vitro or ex vivo to filter out potential toxic candidates before moving to in vivo phases of preclinical development, that is, animal toxicity studies. These assays also have the potential to provide translational insight since they allow a safety evaluation in human in vitro systems. Yet, small preliminary in vivo studies should also be considered to complement this early assessment. In this study, we summarize the state of the art and provide guidelines and recommendations on the different tests available for these early stage preclinical assessments.

Intracerebroventricular Administration of a 2'-O-Methyl Phosphorothioate Antisense Oligonucleotide Results in Activation of the Innate Immune System in Mouse Brain

Antisense oligonucleotides (AONs) are versatile molecules that can be used to modulate gene expression by binding to RNA. The therapeutic potential of AONs appears particularly high in the central nervous system, due to excellent distribution and uptake in brain cells, as well as good tolerability in clinical trials thus far. Nonetheless, immune stimulation in response to AON treatment in the brain remains a concern. For this reason we performed RNA sequencing analysis of brain tissue from mice treated intracerebroventricularly with phosphorothioate, 2′-O-methyl modified AONs. A significant upregulation of immune system associated genes was observed in brains of AON treated mice, with the striatum showing largest transcriptional changes. Strongest upregulation was seen for the antiviral enzyme 2′-5′-oligoadenylate synthase-like protein 2 (Oasl2) and Bone marrow stromal antigen 2 (Bst2). Histological analysis confirmed activation of microglia and astrocytes in striatum. The upregulation of immune system associated genes was detectable for at least 2 months after the last AON administration, consistent with a continuous immune response to the AON.

Antisense inhibition at the beta-secretase-site of beta-amyloid precursor protein reduces cerebral amyloid and acetyl cholinesterase activity in Tg2576

Misprocessing of beta-amyloid precursor protein (APP) leading to the formation of elevated quantities of beta-amyloid peptide (Abeta), derived by a cleavage at the beta-secretase site (N-671/673aa) and by a cleavage at the gamma-secretase site (C-711/713aa) of APP, is considered a key event in the pathogenesis of Alzheimer disease (AD). Point mutations near the beta-secretase site in the human gene for APP, such as in the Swedish mutation-KM670/671NL, lead to a form of dominantly inherited AD. These mutations are known to promote beta-site cleavage and to increase levels of Abeta. Abeta has been shown previously to increase acetyl cholinesterase (AChE) activity in vitro. We wished to test whether translational blocking of APP-mRNA at the mutated beta-site by antisense (AS) oligodeoxynucleotides (ODNs) directed to the mutated site will reduce cerebral amyloid in the Swedish transgenic mouse model (Tg2576). Mice were injected i.c.v. with AS-ODNs directed at the mutated beta-site (AS-beta site) or with AS-ODNs directed at the normal gamma-site (AS-gamma site) of human APP-mRNA, and compared with procedural controls that received i.c.v. injections of sense ODNs at the beta-site (S-beta site), sense ODNs at the gamma-site (S-gamma site) or mismatched ODNs, and with untreated littermates (Lt) and untreated transgenic mice (Tgs). ODNs were injected into the 3rd ventricle once a week for 4 weeks. Brains were processed for enzyme-linked immunosorbent assay analysis of beta- and gamma-cleaved soluble Abeta40 (sAbeta40), beta- and gamma-cleaved soluble Abeta42 (sAbeta42) and alpha-cleaved soluble beta-amyloid precursor protein (sAPPalpha). The physiological relevance of AS ODNs was tested by evaluating the cerebral distribution of AChE before and after the treatment. AChE was found increased about fivefold in Tg cortex as compared with control brain. Results show that compared with untreated and procedural controls, AS-beta increased cerebral levels of sAPPalpha by 43% and reduced sAbeta40/42 by approximately 39%; while simultaneously reducing the cortical density of AChE by approximately fourfold in the treated Tg animals, almost to the level found in the control brain (all values P<0.0001, analysis of variance, unpaired two-tailed Student's t-test), while AS-gamma did not have any effect. These results indicate that AS directed to the mutated beta-site may be an effective approach to treat familial AD.

In vitro and in vivo potentiating the cytotoxic effect of radiation on human U251 gliomas by the c-Met antisense oligodeoxynucleotides

C-Met, a receptor tyrosine kinase, and its ligand, hepatocyte growth factor (HGF), are critical in cellular proliferation, motility, and invasion, and are known to be overexpressed in gliomas, which are related to the repair of damaged DNA. In this study, we investigated both in vitro and in vivo whether inhibition of the c-Met gene by antisense oligonucleotides (ODNs) enhances the cytotoxic effect of radiation on human U251 gliomas. A volume of 100 nM of c-Met antisense ODNs inhibited the level of mRNA by more than 95% and reduced the protein expression by about 70%. Treatment of human U251 glioma cells with 100 nM of c-Met antisense ODNs significantly enhanced the radiation-induced cell kill compared to control cells, and cells treated with nonsense ODNs. When the glioma cells were implanted in the cisterna magna of nude mice followed by treatment with c-Met antisense ODNs, the survival time of the nude mice was markedly prolonged compared to that of the untreated group (P < 0.001, logrank test). In addition, the combination of antisense ODNs and irradiation extended the survival time of the glioma-bearing nude mice much longer than could be achieved with radiation alone (P < 0.0001, logrank test). These results suggest that inhibition of c-Met can be expected to serve as a novel potentiator for radiation therapy in human U251 gliomas.

Intratumoral infusion of interleukin-1β and interferon-γ induces tumor invasion with macrophages and lymphocytes in a rat glioma model

Malignant gliomas are hard to treat successfully. Like other treatments immune therapy fails presumably due to low concentration of immune modifiers within the tumor. However, convection-enhanced delivery (CED) may overcome this problem. So, we analyzed the effect of intratumoral delivery of interleukin (IL)-1beta and interferon (IFN)-gamma by CED on tumor immune cell invasion in a rat glioma model. Tumors were implanted into the left caudate nucleus and tumor growth was demonstrated by MRI. Afterwards intratumoral infusion of IL-1beta or IFN-gamma was started for 48 h. Then animals were sacrificed and the number of tumor infiltrating CD4+ and CD8+ lymphocytes as well as macrophages was analyzed by immunohistochemistry. Our results demonstrate that intratumoral cytokine infusion using CED leads to a strong tumor invasion with macrophages and lymphocytes suggesting a tumor specific immune response.

Deletion of guanine nucleotide binding protein alpha z subunit in mice induces a gene dose dependent tolerance to morphine

The mechanism underlying the development of tolerance to morphine is still incompletely understood. Morphine binds to opioid receptors, which in turn activates downstream second messenger cascades through heterotrimeric guanine nucleotide binding proteins (G proteins). In this paper, we show that G(z), a member of the inhibitory G protein family, plays an important role in mediating the analgesic and lethality effects of morphine after tolerance development. We blocked signaling through the G(z) second messenger cascade by genetic ablation of the alpha subunit of the G protein in mice. The Galpha(z) knockout mouse develops significantly increased tolerance to morphine, which depends on Galpha(z) gene dosage. Further experiments demonstrate that the enhanced morphine tolerance is not caused by pharmacokinetic and behavioural learning mechanisms. The results suggest that G(z) signaling pathways are involved in transducing the analgesic and lethality effects of morphine following chronic morphine treatment.