Targeting deoxycytidine kinase improves symptoms in mouse models of multiple sclerosis.

Multiple sclerosis (MS) is an autoimmune disease driven by lymphocyte activation against myelin autoantigens in the central nervous system leading to demyelination and neurodegeneration. The deoxyribonucleoside salvage pathway with the rate-limiting enzyme deoxycytidine kinase (dCK) captures extracellular deoxyribonucleosides for use in intracellular deoxyribonucleotide metabolism. Previous studies have shown that deoxyribonucleoside salvage activity is enriched in lymphocytes and required for early lymphocyte development. However, specific roles for the deoxyribonucleoside salvage pathway and dCK in autoimmune diseases such as MS are unknown. Here we demonstrate that dCK activity is necessary for the development of clinical symptoms in the MOG35-55 and MOG1-125 experimental autoimmune encephalomyelitis (EAE) mouse models of MS. During EAE disease, deoxyribonucleoside salvage activity is elevated in the spleen and lymph nodes. Targeting dCK with the small molecule dCK inhibitor TRE-515 limits disease severity when treatments are started at disease induction or when symptoms first appear. EAE mice treated with TRE-515 have significantly fewer infiltrating leukocytes in the spinal cord, and TRE-515 blocks activation-induced B and T cell proliferation and MOG35-55 -specific T cell expansion without affecting innate immune cells or naïve T and B cell populations. Our results demonstrate that targeting dCK limits symptoms in EAE mice and suggest that dCK activity is required for MOG35-55 -specific lymphocyte activation-induced proliferation.

Signaling Pathways That Drive 18F-FDG Accumulation in Cancer.

18F-FDG measures glucose consumption and is an integral part of cancer management. Most cancer types upregulate their glucose consumption, yielding elevated 18F-FDG PET accumulation in those cancer cells. The biochemical pathway through which 18F-FDG accumulates in cancer cells is well established. However, beyond well-known regulators such as c-Myc, PI3K/PKB, and HIF1α, the proteins and signaling pathways that cancer cells modulate to activate the facilitated glucose transporters and hexokinase enzymes that drive elevated 18F-FDG accumulation are less well understood. Understanding these signaling pathways could yield additional biologic insights from 18F-FDG PET scans and could suggest new uses of 18F-FDG PET in the management of cancer. Work over the past 5 years, building on studies from years prior, has identified new proteins and signaling pathways that drive glucose consumption in cancer. Here, we review these recent studies and discuss current limitations to our understanding of glucose consumption in cancer.

Modelling the antimicrobial pharmacodynamics for bacterial strains with versus without acquired resistance to fluoroquinolones or cephalosporins.

OBJECTIVES: Antimicrobial resistance threatens therapeutic options for human and animal bacterial diseases worldwide. Current antimicrobial treatment regimens were designed against bacterial strains that were fully susceptible to them. To expand the useable lifetime of existing antimicrobial drug classes by modifying treatment regimens, data are needed on the antimicrobial pharmacodynamics (PD) against strains with reduced susceptibility. In this study, we generated and mathematically modelled the PD of the fluoroquinolone ciprofloxacin and the cephalosporin ceftriaxone against non-typhoidal Salmonella enterica subsp. enterica strains with varying levels of acquired resistance. METHODS: We included Salmonella strains across categories of reduced susceptibility to fluoroquinolones or cephalosporins reported to date, including isolates from human infections, food-animal products sold in retail, and food-animal production. We generated PD data for each drug and strain via time-kill assay. Mathematical models were compared in their fit to represent the PD. The best-fit model's parameter values across the strain susceptibility categories were compared. RESULTS: The inhibitory baseline sigmoid Imax (or Emax) model was best fit for the PD of each antimicrobial against a majority of the strains. There were statistically significant differences in the PD parameter values across the strain susceptibility categories for each antimicrobial. CONCLUSION: The results demonstrate predictable multiparameter changes in the PD of these first-line antimicrobials depending on the Salmonella strain's susceptibility phenotype and specific genes conferring reduced susceptibility. The generated PD parameter estimates could be used to optimise treatment regimens against infections by strains with reduced susceptibility.

Mathematical modeling of the 'inoculum effect': six applicable models and the MIC advancement point concept.

Antimicrobial treatment regimens against bacterial pathogens are designed using the drug's minimum inhibitory concentration (MIC) measured at a bacterial density of 5.7 log10(colony-forming units (CFU)/mL) in vitro. However, MIC changes with pathogen density, which varies among infectious diseases and during treatment. Incorporating this into treatment design requires realistic mathematical models of the relationships. We compared the MIC-density relationships for Gram-negative Escherichia coli and non-typhoidal Salmonella enterica subsp. enterica and Gram-positive Staphylococcus aureus and Streptococcus pneumonia (for n = 4 drug-susceptible strains per (sub)species and 1-8 log10(CFU/mL) densities), for antimicrobial classes with bactericidal activity against the (sub)species: ß-lactams (ceftriaxone and oxacillin), fluoroquinolones (ciprofloxacin), aminoglycosides (gentamicin), glycopeptides (vancomycin) and oxazolidinones (linezolid). Fitting six candidate mathematical models to the log2(MIC) vs. log10(CFU/mL) curves did not identify one model best capturing the relationships across the pathogen-antimicrobial combinations. Gompertz and logistic models (rather than a previously proposed Michaelis-Menten model) fitted best most often. Importantly, the bacterial density after which the MIC sharply increases (an MIC advancement-point density) and that density's intra-(sub)species range evidently depended on the antimicrobial mechanism of action. Capturing these dependencies for the disease-pathogen-antimicrobial combination could help determine the MICs for which bacterial densities are most informative for treatment regimen design.

Noninvasive Imaging of Drug-Induced Liver Injury with 18F-DFA PET.

Drug-induced liver failure is a significant indication for a liver transplant, and unexpected liver toxicity is a major reason that otherwise effective therapies are removed from the market. Various methods exist for monitoring liver injury but are often inadequate to predict liver failure. New diagnostic tools are needed. Methods: We evaluate in a preclinical model whether 18F-2-deoxy-2-fluoroarabinose (18F-DFA), a PET radiotracer that measures the ribose salvage pathway, can be used to monitor acetaminophen-induced liver injury and failure. Mice treated with vehicle, 100, 300, or 500 mg/kg acetaminophen for 7 or 21 h were imaged with 18F-FDG and 18F-DFA PET. Hepatic radiotracer accumulation was correlated to survival and percentage of nonnecrotic tissue in the liver. Mice treated with acetaminophen and vehicle or N-acetylcysteine were imaged with 18F-DFA PET. 18F-DFA accumulation was evaluated in human hepatocytes engrafted into the mouse liver. Results: We show that hepatic 18F-DFA accumulation is 49%-52% lower in mice treated with high-dose acetaminophen than in mice treated with low-dose acetaminophen or vehicle. Under these same conditions, hepatic 18F-FDG accumulation was unaffected. At 21 h after acetaminophen treatment, hepatic 18F-DFA accumulation can distinguish mice that will succumb to the liver injury from those that will survive it (6.2 vs. 9.7 signal to background, respectively). Hepatic 18F-DFA accumulation in this model provides a tomographic representation of hepatocyte density in the liver, with a R2 between hepatic 18F-DFA accumulation and percentage of nonnecrotic tissue of 0.70. PET imaging with 18F-DFA can be used to distinguish effective from ineffective resolution of acetaminophen-induced liver injury with N-acetylcysteine (15.6 vs. 6.2 signal to background, respectively). Human hepatocytes, in culture or engrafted into a mouse liver, have levels of ribose salvage activity similar to those of mouse hepatocytes. Conclusion: Our findings suggest that PET imaging with 18F-DFA can be used to visualize and quantify drug-induced acute liver injury and may provide information on the progression from liver injury to hepatic failure.

18F-FAC PET Selectively Images Liver-Infiltrating CD4 and CD8 T Cells in a Mouse Model of Autoimmune Hepatitis.

Immune cell-mediated attack on the liver is a defining feature of autoimmune hepatitis and hepatic allograft rejection. Despite an assortment of diagnostic tools, invasive biopsies remain the only method for identifying immune cells in the liver. We evaluated whether PET imaging with radiotracers that quantify immune activation (18F-FDG and 18F-1-(2'-deoxy-2'-fluoro-arabinofuranosyl)cytosine [18F-FAC]) and hepatocyte biology (18F-2-deoxy-2-fluoroarabinose [18F-DFA]) can visualize and quantify liver-infiltrating immune cells and hepatocyte inflammation, respectively, in a preclinical model of autoimmune hepatitis. Methods: Mice treated with concanavalin A (ConA) to induce a model of autoimmune hepatitis or vehicle were imaged with 18F-FDG, 18F-FAC, and 18F-DFA PET. Immunohistochemistry, digital autoradiography, and ex vivo accumulation assays were used to localize areas of altered radiotracer accumulation in the liver. For comparison, mice treated with an adenovirus to induce a viral hepatitis were imaged with 18F-FDG, 18F-FAC, and 18F-DFA PET. 18F-FAC PET was performed on mice treated with ConA and vehicle or with ConA and dexamethasone. Biopsy samples of patients with autoimmune hepatitis were immunostained for deoxycytidine kinase. Results: Hepatic accumulation of 18F-FDG and 18F-FAC was 173% and 61% higher, respectively, and hepatic accumulation of 18F-DFA was 41% lower, in a mouse model of autoimmune hepatitis than in control mice. Increased hepatic 18F-FDG accumulation was localized to infiltrating leukocytes and inflamed sinusoidal endothelial cells, increased hepatic 18F-FAC accumulation was concentrated in infiltrating CD4 and CD8 cells, and decreased hepatic 18F-DFA accumulation was apparent in hepatocytes throughout the liver. In contrast, viral hepatitis increased hepatic 18F-FDG accumulation by 109% and decreased hepatic 18F-DFA accumulation by 20% but had no effect on hepatic 18F-FAC accumulation (nonsignificant 2% decrease). 18F-FAC PET provided a noninvasive biomarker of the efficacy of dexamethasone for treating the autoimmune hepatitis model. Infiltrating leukocytes in liver biopsy samples from patients with autoimmune hepatitis express high levels of deoxycytidine kinase, a rate-limiting enzyme in the accumulation of 18F-FAC. Conclusion: Our data suggest that PET can be used to noninvasively visualize activated leukocytes and inflamed hepatocytes in a mouse model of autoimmune hepatitis.