Toxicologic Pathology Forum Opinion Piece: Use of Virtual Control Groups in Nonclinical Toxicity Studies: The Anatomic Pathology Perspective

In the last decade, numerous initiatives have emerged worldwide to reduce the use of animals in drug development, including more recently the introduction of Virtual Control Groups (VCGs) concept for nonclinical toxicity studies. Although replacement of concurrent controls (CCs) by virtual controls (VCs) represents an exciting opportunity, there are associated challenges that will be discussed in this paper with a more specific focus on anatomic pathology. Coordinated efforts will be needed from toxicologists, clinical and anatomic pathologists, and regulators to support approaches that will facilitate a staggered implementation of VCGs in nonclinical toxicity studies. Notably, the authors believe that a validated database for VC animals will need to include histopathology (digital) slides for microscopic assessment. Ultimately, the most important step lies in the validation of the concept by performing VCG and the full control group in parallel for studies of varying duration over a reasonable timespan to confirm there are no differences in outcomes (dual study design). The authors also discuss a hybrid approach, whereby control groups comprised both concurrent and VCs to demonstrate proof-of-concept. Once confidence is established by sponsors and regulators, VCs have the potential to replace some or all CC animals.

Detection of MET mRNA in gastric cancer in situ. Comparison with immunohistochemistry and sandwich immunoassays

Determination of predictive biomarkers by immunohistochemistry (IHC) relies on antibodies with high selectivity. RNA in situ hybridization (RNA ISH) may be used to confirm IHC and may potentially replace it if suitable antibodies are not available or are insufficiently selective to discriminate closely related protein isoforms. We validated RNA ISH as specificity control for IHC and as a potential alternative method for selecting patients for treatment with MET inhibitors. MET, the HGF receptor, is encoded by the MET proto-oncogene that may be activated by mutation or amplification. MET expression and activity were tested in a panel of control cell lines. MET could be detected in formalin fixed paraffin, embedded (FFPE) samples by IHC and RNA ISH, and this was confirmed by sandwich immunoassays of fresh frozen samples. Gastric cancer cell lines with high MET expression and phosphorylation of tyrosine-1349 respond to the MET inhibitor, BAY-853474. High expression and phosphorylation of MET is a predictive biomarker for response to MET inhibitors. We then analyzed MET expression and activity in a matched set of FFPE vs. fresh frozen tumor samples consisting of 20 cases of gastric cancer. Two of 20 clinical samples investigated exhibited high MET expression with RNA ISH and IHC. Both cases were shown by sandwich immunoassays to exhibits strong functional activity. Expression levels and functional activity in these two cases were in a range that predicted response to treatment. Our findings indicate that owing to its high selectivity, RNA ISH can be used to confirm findings obtained by IHC and potentially may replace IHC for certain targets if no suitable antibodies are available. RNA ISH is a valid platform for testing predictive biomarkers for patient selection.

Detection of canine distemper virus nucleoprotein RNA by reverse transcription-PCR using serum, whole blood, and cerebrospinal fluid from dogs with distemper

Reverse transcription-PCR (RT-PCR) was used to detect canine distemper virus (CDV) nucleoprotein (NP) RNA in serum, whole blood, and cerebrospinal fluid (CSF) samples from 38 dogs with clinically suspected distemper. Results were correlated to clinical findings, anti-CDV neutralizing antibody titers, postmortem findings, and demonstration of CDV NP antigen by immunohistochemistry. The specificity of the RT-PCR was ensured by amplification of RNA from various laboratory CDV strains, restriction enzyme digestion, and Southern blot hybridization. In 29 of 38 dogs, CDV infection was confirmed by postmortem examination and immunohistochemistry. The animals displayed the catarrhal, systemic, and nervous forms of distemper. Seventeen samples (serum, whole blood, or CSF) from dogs with distemper were tested with three sets of primers targeted to different regions of the NP gene of the CDV Onderstepoort strain. Expected amplicons were observed in 82, 53, and 41% of the 17 samples, depending upon the primer pair used. With the most sensitive primer pair (primer pair I), CDV NP RNA was detected in 25 of 29 (86%) serum samples and 14 of 16 (88%) whole blood and CSF samples from dogs with distemper but not in body fluids from immunohistochemically negative dogs. Nucleotide sequence analysis of five RT-PCR amplicons from isolates from the field revealed few silent point mutations. These isolates exhibited greater homology to the Rockborn (97 to 99%) than to the Onderstepoort (95 to 96%) CDV strain. In summary, although the sensitivity of the RT-PCR for detection of CDV is strongly influenced by the location of the selected primers, this nucleic acid detection system represents a highly specific and sensitive method for the antemortem diagnosis of distemper in dogs, regardless of the form of distemper, humoral immune response, and viral antigen distribution.

Dominating interleukin-10 mRNA expression induction in cerebrospinal fluid cells of dogs with natural canine distemper virus induced demyelinating and non-demyelinating CNS lesions

Canine distemper virus (CDV) infection in dogs is commonly associated with demyelinating leukoencephalitis (DL). Although the mechanism of primary demyelination in distemper remains undetermined recent studies showed a direct virus-induced cytolysis in early non-inflammatory and immune-mediated mechanisms in inflammatory lesions. To further investigate the pathogenesis of this morbillivirus-induced demyelination the expression of a variety of cytokine mRNA species (interleukin (IL)-1beta, IL-2, IL-6, IL-10, IL-12, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta1, and interferon (IFN)-gamma in cerebrospinal fluid cells of 12 dogs with CDV encephalitis was investigated employing reverse transcription-polymerase chain reaction (RT-PCR) and these findings were correlated to the type of CNS lesions. Neuropathology revealed the whole spectrum of distemper DL lesions from acute to chronic alterations, however, most plaques lacked active demyelination. Three control animals were devoid of any cytokine expression, whereas in distemper animals IL-10 transcripts were found in nine dogs with acute and chronic lesions. IL-6, TNF, and TGF mRNA was found in six, four, and three animals, respectively. IL-12 and IFN-gamma, suggestive of a TH1-like dominated immune response, were detected only in one animal with chronic lesions. Summarized, TNF and IL-6, associated with disease exacerbation, and IL-10 and TGF, indicative of remission, were often observed simultaneously in distemper DL and could not be assigned to a specific disease stage. However IL-10 mRNA remained the most frequently detected cytokine indicating a stage of inactivity in most animals investigated.

Cytokine mRNA expression in whole blood samples from dogs with natural canine distemper virus infection

Cytokines are soluble polypeptides with many physiological functions and a special role during infection and inflammation. Little is known about cytokine regulation in naturally occurring viral diseases of animals. Especially the role of cytokines in the development and progression of lesions in canine distemper virus (CDV) infection in dogs is largely unknown. Whole blood samples from 14 dogs with CDV infection and three dogs suffering from non-distemper diseases were examined for mRNA of pro-inflammatory cytokines such as interleukin-1beta (IL-1), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-12 (IL-12), tumor necrosis factor-alpha (TNF), interferon-gamma (IFN), and the anti-inflammatory transforming growth factor-beta1 (TGF) using reverse transcription polymerase chain reaction (RT-PCR). Blood samples from the three dogs that showed no clinical abnormalities during a pre-vaccination physical examination served as control. CDV infection was confirmed by post-mortem immunohistochemistry for CDV nucleoprotein. The degree of immunoreactivity and the number of virus antigen positive organs were expressed as antigen index. IFN transcripts were not identified in any dog and IL-8 transcripts were present in RNA isolates from all 20 dogs. None of the other cytokines was detected in control animals. IL-1 and IL-6 were each found in one non-distemper dog and TGF transcripts were amplified in two dogs with non-distemper disease. The following transcripts were found in variable numbers in distemper dogs: IL-1 (7/14 dogs), IL-6 (3/14 dogs), IL-12 (3/14 dogs), TNF (8/14 dogs), and TGF (10/14 dogs) with multiple cytokines in ten dogs. No cytokine transcripts were detected in three distemper dogs. There was no obvious correlation between cytokine mRNA expression and respiratory and gastrointestinal tract diseases. In the CNS, demyelination was frequently associated with IL-1, IL-12, TNF and TGF mRNA expression in the blood. IL-6 transcripts were found only in animals with early CNS lesions and TGF was the only detectable cytokine in an animal with chronic demyelination. Lack of detectable cytokine transcripts in whole blood samples was associated with a high antigen index and viremia, indicating that an overwhelming virus infection may suppress cytokine production, possibly due to paralysis of the immune system. Simultaneous occurrence of pro- and anti-inflammatory cytokines in whole blood preparation from most of the dogs with distemper, indicated a complex most likely disease stage dependent orchestrated cytokine expression.