Safety, Tissue Distribution, and Metabolism of LNA-Containing Antisense Oligonucleotides in Rats.

Antisense oligonucleotides (ASOs) are chemically modified nucleic acids with therapeutic potential, some of which have been approved for marketing. We performed a study in rats to investigate mechanisms of toxicity after administration of 3 tool locked nucleic acid (LNA)-containing ASOs with differing established safety profiles. Four male rats per group were dosed once, 3, or 6 times subcutaneously, with 7 days between dosing, and sacrificed 3 days after the last dose. These ASOs were either unconjugated (naked) or conjugated with N-acetylgalactosamine for hepatocyte-targeted delivery. The main readouts were in-life monitoring, clinical and anatomic pathology, exposure assessment and metabolite identification in liver and kidney by liquid chromatography coupled to tandem mass spectrometry, ASO detection in liver and kidney by immunohistochemistry, in situ hybridization, immune electron microscopy, and matrix-assisted laser desorption/ionization mass spectrometry imaging. The highly toxic compounds showed the greatest amount of metabolites and a low degree of tissue accumulation. This study reveals different patterns of cell death associated with toxicity in liver (apoptosis and necrosis) and kidney (necrosis only) and provides new ultrastructural insights on the tissue accumulation of ASOs. We observed that the immunostimulatory properties of ASOs can be either primary from sequence-dependent properties or secondary to cell necrosis.

Pediatric Safety of Polysorbates in Drug Formulations.

Polysorbates 20 and 80 are the most frequently used excipients in biotherapeutics, the safety data for which have been well documented in adults. The polysorbate content in therapeutic formulations that are administered to children, however, has been less clearly regulated or defined with regard to safety. In pediatric patients, excessive amounts of polysorbate in biotherapeutics have been linked to hypersensitivity and other toxicity-related effects. To determine safe levels of polysorbates for young patients, we have developed the progressive pediatric safety factor (PPSF), an age- and weight-based tool that estimates the amount of parenterally administered polysorbates 20 and 80 in formulations that will avoid excipient-related adverse events. Compared with existing modalities for calculating maximum acceptable doses of excipients for initial clinical trials in pediatrics, the PPSF is far more conservative, thus constituting an added margin of safety for excipient exposure in the most sensitive subpopulations-i.e., neonates and infants. Further, the PPSF may be applied to any relevant excipient, aiding pharmaceutical developers and regulatory authorities in conservatively estimating the safety assessment of a biotherapeutic's formulation, based on excipient levels.

Interspecies Variation of Outer Retina and Choriocapillaris Imaged With Optical Coherence Tomography.

Purpose: The purpose of this study is to assess with spectral-domain optical coherence tomography (OCT) the interspecies variation of outer retinal morphology and identification of choriocapillaris in four research animal species. Methods: Spectralis HRA+OCT images acquired from locations dorsal, central, and ventral to the optic disc in healthy, anesthetized animals were evaluated by two independent readers. First, the number of OCT B-scans on which a choriocapillaris layer could clearly be identified was determined and quantified, and B-scans were correlated with histology. Second, B-scans demonstrating the highest number of discernable individual outer retinal bands (ORBs) were defined as ideal presentation and quantified. Interrater agreement was evaluated. Results: Five-hundred seventy-four B-scans from 96 subjects were evaluated. The choriocapillaris layer was identified in 100.0% of minipig, 70.8% of rabbit, 75.4% of pigmented rat, 77.7% of albino rat, 56.5% of pigmented mouse, and 50.8% of albino mouse OCT scans. The percentage of ideal ORB presentation in B-scans was 11.7% in minipigs, 73.8% in rabbits, and 80.0%, 91.0%, 28.5%, and 62.5% in pigmented rats and mice and albino rats and mice, respectively. The interrater evaluation for both attributes showed substantial to perfect agreement in all species. Conclusions: The choriocapillaris is an easy and valid marker for identification of the outer retinal margin. ORB presentation likely varies due to differences in retinal anatomy and pigmentation between animal species and strains and between anatomic locations. Proper and consistent outer retinal margin and ORB identification are essential for research result reproducibility and translation.

Assessment of Preclinical Liver and Skeletal Muscle Biomarkers Following Clofibrate Administration in Wistar Rats.

Clofibrate is a known rodent hepatotoxicant classically associated with hepatocellular hypertrophy and increased serum activities of cellular alanine aminotransferase/aspartate aminotransferase (ALT/AST) in the absence of microscopic hepatocellular degeneration. At toxic dose, clofibrate induces liver and skeletal muscle injury. The objective of this study was to assess novel liver and skeletal muscle biomarkers following clofibrate administration in Wistar rats at different dose levels for 7 days. In addition to classical biomarkers, liver injury was assessed by cytokeratin 18 (CK18) cleaved form, high-mobility group box 1, arginase 1 (ARG1), microRNA 122 (miR-122), and glutamate dehydrogenase. Skeletal muscle injury was evaluated with fatty acid binding protein 3 (Fabp3) and myosin light chain 3 (Myl3). Clofibrate-induced hepatocellular hypertrophy and skeletal muscle degeneration (type I rich muscles) were noted microscopically. CK, Fabp3, and Myl3 elevations correlated to myofiber degeneration. Fabp3 and Myl3 outperformed CK for detection of myofiber degeneration of minimal severity. miR-122 and ARG1 results were significantly correlated and indicated the absence of liver toxicity at low doses of clofibrate, despite increased ALT/AST activities. Moreover, combining classical and novel biomarkers (Fabp3, Myl3, ARG1, and miR-122) can be considered a valuable strategy for differentiating increased transaminases due to liver toxicity from skeletal muscle toxicity.

Inhibition of EGF Uptake by Nephrotoxic Antisense Drugs In Vitro and Implications for Preclinical Safety Profiling.

Antisense oligonucleotide (AON) therapeutics offer new avenues to pursue clinically relevant targets inaccessible with other technologies. Advances in improving AON affinity and stability by incorporation of high affinity nucleotides, such as locked nucleic acids (LNA), have sometimes been stifled by safety liabilities related to their accumulation in the kidney tubule. In an attempt to predict and understand the mechanisms of LNA-AON-induced renal tubular toxicity, we established human cell models that recapitulate in vivo behavior of pre-clinically and clinically unfavorable LNA-AON drug candidates. We identified elevation of extracellular epidermal growth factor (EGF) as a robust and sensitive in vitro biomarker of LNA-AON-induced cytotoxicity in human kidney tubule epithelial cells. We report the time-dependent negative regulation of EGF uptake and EGF receptor (EGFR) signaling by toxic but not innocuous LNA-AONs and revealed the importance of EGFR signaling in LNA-AON-mediated decrease in cellular activity. The robust EGF-based in vitro safety profiling of LNA-AON drug candidates presented here, together with a better understanding of the underlying molecular mechanisms, constitutes a significant step toward developing safer antisense therapeutics.

From the Cover: The Minipig is a Suitable Non-Rodent Model in the Safety Assessment of Single Stranded Oligonucleotides.

Non-human primates (NHPs) are currently considered to be the non-rodent species of choice for the preclinical safety assessment of single-stranded oligonucleotide (SSO) drugs. We evaluated minipigs as a potential alternative to NHPs to test the safety of this class of compounds. Four different phosphorothioated locked nucleic acid-based SSOs (3 antisense and 1 anti-miR), all with known safety profiles, were administered to minipigs using similar study designs and read-outs as in earlier NHP studies with the same compounds. The studies included toxicokinetic investigations, in-life monitoring, clinical and anatomic pathology. In the minipig, we demonstrated target engagement by the SSOs where relevant, and a similar toxicokinetic behavior in plasma, kidney, and liver when compared with NHPs. Clinical tolerability was similar between minipig and NHPs. For the first time, we showed similar and dose-dependent effects on the coagulation and complement cascade after intravenous dosing similar to those observed in NHPs. Similar to NHPs, morphological changes were seen in proximal tubular epithelial cells of the kidney, Kupffer cells, hepatocytes, and lymph nodes. Minipigs appeared more sensitive to the high-dose kidney toxicity of most of the selected SSOs than NHPs. No new target organ or off-target toxicities were identified in the minipig. The minipig did not predict the clinical features of human injection site reactions better than the NHPs, but histopathological similarities were observed between minipigs and NHPs. We conclude that there is no impediment, as default, to the use of minipigs as the non-rodent species in SSO candidate non-clinical safety packages.

Characterization of a re-engineered, mesothelin-targeted Pseudomonas exotoxin fusion protein for lung cancer therapy.

Mesothelin overexpression in lung adenocarcinomas correlates with the presence of activating KRAS mutations and poor prognosis. Hence SS1P, a mesothelin-targeted immunotoxin, could offer valuable treatment options for these patients, but its use in solid tumor therapy is hampered by high immunogenicity and non-specific toxicity. To overcome both obstacles we developed RG7787, a de-immunized cytotoxic fusion protein comprising a humanized SS1 Fab fragment and a truncated, B-cell epitope silenced, 24 kD fragment of Pseudomonas exotoxin A (PE24). Reactivity of RG7787 with sera from immunotoxin-treated patients was >1000 fold reduced. In vitro RG7787 inhibited cell viability of lung cancer cell lines with picomolar potency. The pharmacokinetic properties of RG7787 in rodents were comparable to SS1P, yet it was tolerated up to 10 fold better without causing severe vascular leak syndrome or hepatotoxicity. A pharmacokinetic/pharmacodynamic model developed based on NCI-H596 xenograft studies showed that for RG7787 and SS1P, their in vitro and in vivo potencies closely correlate. At optimal doses of 2-3 mg/kg RG7787 is more efficacious than SS1P. Even large, well established tumors (600 mm(3)) underwent remission during three treatment cycles with RG7787. Also in two patient-derived lung cancer xenograft models, Lu7336 and Lu7187, RG7787 showed anti-tumor efficacy. In monotherapy two treatment cycles were moderately efficacious in the Lu7336 model but showed good anti-tumor activity in the KRAS mutant Lu7187 model (26% and 80% tumor growth inhibition, respectively). Combination of RG7787 with standard chemotherapies further enhanced efficacy in both models achieving near complete eradication of Lu7187 tumors.

Vehicle Systems and Excipients Used in Minipig Drug Development Studies.

Minipigs have been used for dermal drug development studies for decades, and they are currently more frequently considered as the second nonrodent species for pivotal nonclinical studies, in lieu of the dog or nonhuman primate, for compounds delivered via standard systemic routes of administration. Little is known about the tolerability of different excipients in minipigs; sharing knowledge of excipient tolerability and compositions previously used in nonclinical studies may avoid testing of inadequate formulations, thereby contributing to reduced animal usage. This article reviews vehicles employed in the Göttingen(®)minipig based on the combined experience from a number of pharmaceutical companies and contract research organizations. The review includes vehicles tolerated for single or multiple dosing by the Göttingen minipig, some of which are not appropriate for administration to other common nonrodent species (e.g., dogs). By presenting these data for dermal, oral, subcutaneous, and intravenous routes of administration, studies to qualify these vehicles in minipigs can be minimized or avoided. Additionally, investigators may more frequently consider using the minipig in place of higher species if the tolerability of a vehicle in the minipig is known.

Recommendations from a global cross-company data sharing initiative on the incorporation of recovery phase animals in safety assessment studies to support first-in-human clinical trials.

An international expert group which includes 30 organisations (pharmaceutical companies, contract research organisations, academic institutions and regulatory bodies) has shared data on the use of recovery animals in the assessment of pharmaceutical safety for early development. These data have been used as an evidence-base to make recommendations on the inclusion of recovery animals in toxicology studies to achieve scientific objectives, while reducing animal use. Recovery animals are used in pharmaceutical development to provide information on the potential for a toxic effect to translate into long-term human risk. They are included on toxicology studies to assess whether effects observed during dosing persist or reverse once treatment ends. The group devised a questionnaire to collect information on the use of recovery animals in general regulatory toxicology studies to support first-in-human studies. Questions focused on study design, the rationale behind inclusion or exclusion and the impact this had on internal and regulatory decisions. Data on 137 compounds (including 53 biologicals and 78 small molecules) from 259 studies showed wide variation in where, when and why recovery animals were included. An analysis of individual study and programme design shows that there are opportunities to reduce the use of recovery animals without impacting drug development.

Genotoxicity testing of peptides: folate deprivation as a marker of exaggerated pharmacology.

The incidence of micronucleated-cells is considered to be a marker of a genotoxic event and can be caused by direct- or indirect-DNA reactive mechanisms. In particular, small increases in the incidence of micronuclei, which are not associated with toxicity in the target tissue or any structurally altering properties of the compound, trigger the suspicion that an indirect mechanism could be at play. In a bone marrow micronucleus test of a synthetic peptide (a dual agonist of the GLP-1 and GIP receptors) that had been integrated into a regulatory 13-week repeat-dose toxicity study in the rat, small increases in the incidence of micronuclei had been observed, together with pronounced reductions in food intake and body weight gain. Because it is well established that folate plays a crucial role in maintaining genomic integrity and pronounced reductions in food intake and body weight gain were observed, folate levels were determined from plasma samples initially collected for toxicokinetic analytics. A dose-dependent decrease in plasma folate levels was evident after 4 weeks of treatment at the mid and high dose levels, persisted until the end of the treatment duration of 13-weeks and returned to baseline levels during the recovery period of 4 weeks. Based on these properties, and the fact that the compound tested (peptide) per se is not expected to reach the nucleus and cause DNA damage, the rationale is supported that the elevated incidence of micronucleated polychromatic erythrocytes is directly linked to the exaggerated pharmacology of the compound resulting in a decreased folate level.

Assessment of the genotoxic potential of azidothymidine in the comet, micronucleus, and Pig-a assay.

The genotoxic potential of azidothymidine (Zidovudine, AZT), chosen as a model compound for nucleotide analogs, was comprehensively assessed in vivo for gene mutation, clastogenicity, and DNA breakage endpoints. Male Wistar rats were treated by oral gavage over 7 days with AZT at dose levels of 2×0 (control), 2×250, 2×500, and 2×1000mg/kg/day with a final single dose given on day 8. DNA damage was then evaluated with the comet assay in liver, stomach, and peripheral blood and with the micronucleus test in bone marrow and peripheral blood (by flow cytometry) in the same animals. After a treatment-free period of upto 42 days, the Pig-a gene mutation assay was performed in peripheral blood of the high-dose animals. In the comet assay as well as the micronucleus test, AZT caused a considerable dose-dependent increase in DNA damage in all tissues evaluated and was highly cytotoxic to bone marrow and peripheral blood cells. These data are well in line with published results. Surprisingly, AZT did not significantly increase the number of Pig-a mutant cells. We speculate that two factors likely contributed to this negative result: a predominance of large deletions caused by AZT, and the relatively low statistical power of the first-generation scoring method used for this study.

A global pharmaceutical company initiative: an evidence-based approach to define the upper limit of body weight loss in short term toxicity studies.

Short term toxicity studies are conducted in animals to provide information on major adverse effects typically at the maximum tolerated dose (MTD). Such studies are important from a scientific and ethical perspective as they are used to make decisions on progression of potential candidate drugs, and to set dose levels for subsequent regulatory studies. The MTD is usually determined by parameters such as clinical signs, reductions in body weight and food consumption. However, these assessments are often subjective and there are no published criteria to guide the selection of an appropriate MTD. Even where an objective measurement exists, such as body weight loss (BWL), there is no agreement on what level constitutes an MTD. A global initiative including 15 companies, led by the National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs), has shared data on BWL in toxicity studies to assess the impact on the animal and the study outcome. Information on 151 studies has been used to develop an alert/warning system for BWL in short term toxicity studies. The data analysis supports BWL limits for short term dosing (up to 7days) of 10% for rat and dog and 6% for non-human primates (NHPs).

Morphologic and functional effects of gamma secretase inhibition on splenic marginal zone B cells.

The γ-secretase complex is a promising target in Alzheimer's disease because of its role in the amyloidogenic processing of ß-amyloid precursor protein. This enzyme also catalyzes the cleavage of Notch receptor, resulting in the nuclear translocation of intracellular Notch where it modulates gene transcription. Notch signaling is essential in cell fate decisions during embryogenesis, neuronal differentiation, hematopoiesis, and development of T and B cells, including splenic marginal zone (MZ) B cells. This B cell compartment participates in the early phases of the immune response to blood-borne bacteria and viruses. Chronic treatment with the oral γ-secretase inhibitor RO4929097 resulted in dose-dependent decreased cellularity (atrophy) of the MZ of rats and mice. Significant decreases in relative MZ B-cell numbers of RO4929097-treated animals were confirmed by flow cytometry. Numbers of MZ B cells reverted to normal after a sufficient RO4929097-free recovery period. Functional characterization of the immune response in relation to RO4929097-related MZ B cell decrease was assessed in mice vaccinated with inactivated vesicular stomatitis virus (VSV). Compared with the immunosuppressant cyclosporin A, RO4929097 caused only mild and reversible delayed early neutralizing IgM and IgG responses to VSV. Thus, the functional consequence of MZ B cell decrease on host defense is comparatively mild.

A European pharmaceutical company initiative challenging the regulatory requirement for acute toxicity studies in pharmaceutical drug development.

Regulatory guidelines indicate acute toxicity studies in animals are considered necessary for pharmaceuticals intended for human use. This is the only study type where lethality is mentioned as an endpoint. The studies are carried out, usually in rodents, to support marketing of new drugs and to identify the minimum lethal dose. A European initiative including 18 companies has undertaken an evidence-based review of acute toxicity studies and assessed the value of the data generated. Preclinical and clinical information was shared on 74 compounds. The analysis indicated acute toxicity data was not used to (i) terminate drugs from development (ii) support dose selection for repeat dose studies in animals or (iii) to set doses in the first clinical trials in humans. The conclusion of the working group is that acute toxicity studies are not needed prior to first clinical trials in humans. Instead, information can be obtained from other studies, which are performed at more relevant doses for humans and are already an integral part of drug development. The conclusions have been discussed and agreed with representatives of regulatory bodies from the US, Japan and Europe.

An in vitro embryotoxicity assay based on the disturbance of the differentiation of murine embryonic stem cells into endothelial cells. II. Testing of compounds.

The embryonic stem cell test (EST) developed by Spielmann et al. [Spielmann, H., Pohl, I., Doering, B., Liebsch, M., Moldenhauer, F., 1997. The embryonic stem cell test, an in vitro embryotoxicity test using two permanent mouse cell lines: 3T3 fibroblasts and embryonic stem cells. In Vitro. Toxicol. 10, 119-127] is currently the most promising in vitro assay to predict the embryotoxic potential of compounds. In this assay the disturbance of the differentiation of embryonic stem (ES) cells into contracting cardiomyocytes by test compounds as well as the direct cytotoxicity of the test compounds on ES cells and 3T3 fibroblasts is analyzed. On the basis of these results and by applying a biostatistical prediction model (PM) [Genschow, E., Scholz, G., Brown, N., Piersma, A., Brady, M., Clemann, N., Huuskonen, H., Paillard, F., Bremer, S., Becker, K., Spielmann, H., 2000. Development of prediction models for three in vitro embryotoxicity tests in an ECVAM validation study. In Vitr. Mol. Toxicol. 13, 51-66; Genschow, E., Spielmann, H., Scholz, G., Pohl, I., Seiler, A., Clemann, N., Bremer, S., Becker, K., 2004. Validation of the embryonic stem cell test in the international ECVAM validation study on three in vitro embryotoxicity tests. Altern. Lab. Anim. 32, 209-244; Genschow, E., Spielmann, H., Scholz, G., Seiler, A., Brown, N., Piersma, A., Brady, M., Clemann, N., Huuskonen, H., Paillard, F., Bremer, S., Becker, K., 2002. The ECVAM international validation study on in vitro embryotoxicity tests: results of the definitive phase and evaluation of prediction models. European Centre for the Validation of Alternative Methods. Altern. Lab. Anim. 30, 151-176] test compounds can be classified as non-embryotoxic, weakly or strongly embryotoxic. In order to introduce a further endpoint into the EST, the disturbance of vasculogenesis and/or angiogenesis, a protocol to differentiate ES cells into endothelial cells, was established in the accompanying paper. PECAM-1 and VE-Cadherin gene expressions, quantified by real-time TaqMan PCR, were shown to be appropriate molecular markers for the differentiation of ES cells into endothelial cells. In the present study, the disturbance of the differentiation of ES cells into endothelial cells (i.e. the reduction in the expression of PECAM-1 and VE-Cadherin) by six test compounds with known embryotoxic potential was investigated: all-trans-retinoic acid (RA) and 5-fluorouracil (5-FU) are strongly embryotoxic, diphenylhydantoin (DPH) and valproic acid (Val) are weakly embryotoxic and saccharin (Sacch) and penicillin G (Pen G) are non-embryotoxic. In a first step the concentration of the test compound resulting in a 50% inhibition of PECAM-1 and VE-Cadherin gene expression and the concentration leading to a 50% decrease in the viability of ES cells and 3T3 fibroblasts were determined. In a second step and in a first attempt to assess the predictive potential of the newly developed test system the concentration values obtained were applied in the PM of the established EST to classify the selected test compounds. All six test compounds were correctly classified (i.e. the data obtained in vitro correlated with their known embryotoxic potential in vivo). Taken together it can be concluded that the disturbance of the differentiation of murine ES cells into endothelial cells represents a very promising new endpoint in a broadened EST with PECAM-1 and VE-Cadherin as specific differentiation marker genes.

An in vitro embryotoxicity assay based on the disturbance of the differentiation of murine embryonic stem cells into endothelial cells. I: Establishment of the differentiation protocol.

The aim of the present study was to establish an experimental protocol to differentiate murine embryonic stem (ES) cells into endothelial cells in vitro. The spinner flask technique as well as the hanging drop method were used to generate so-called embryoid bodies (EBs). In order to find out the optimal differentiation environment, EBs were cultured under various experimental conditions for up to 14 days. The influence of basic fibroblast growth factor (bFGF) alone, vascular endothelial growth factor (VEGF) alone, bFGF and VEGF together and a cocktail consisting of bFGF, VEGF, interleukin-6 (IL-6) and erythropoietin (Epo) on the induction of differentiation of ES cells into endothelial cells was studied. Different concentrations of growth factors and times of treatment were applied. Endothelial cells were characterized by analyzing the expression of platelet-endothelial cell adhesion molecule (PECAM-1), the endothelial-specific vascular endothelial cadherin (VE-Cadherin), the angiopoietin receptor Tie-2, VEGF receptors 1 and 2 (Flt-1 and Flk-1, respectively) and the soluble form of Flt-1 (sFlt) at the mRNA level. PECAM-1 and VE-Cadherin were also studied at the protein level. The data clearly showed that EBs generated by the hanging drop method, followed by their transfer into suspension culture on day 3 of differentiation and their subsequent plating on day 5 is the best of the studied methods to differentiate ES cells into endothelial cells. Addition of VEGF alone or a cocktail consisting of VEGF, bFGF, IL-6 and Epo resulted in the strongest gene expression levels of the above mentioned endothelial cell markers in the differentiated ES cells.