New biomarkers of liver injury are required in the clinic and in preclinical pharmaceutical evaluation. Previous studies demonstrate that two liver-enriched microRNAs (miR-122 and miR-192) are promising biomarkers of acetaminophen-induced acute liver injury (APAP-ALI) in mice. We have examined these molecules, for the first time, in humans with APAP poisoning. Serum miR-122 and miR-192 were substantially higher in APAP-ALI patients, compared to healthy controls (median DDCt [25th, 75th percentile]) (miR-122: 1,265 [491, 4,270] and -192 were substantially higher in APAP-ALI patients than CKD patients (miR-122: P < 0.0001; miR-192: P < 0.0004). miR-122 correlated with peak ALT levels in the APAP-ALI cohort (Pearson R 5 0.46, P 5 0.0005), but not with prothrombin time. miR-122 was also raised alongside peak ALT levels in a group of patients with non-APAP ALI. Day 1 serum miR-122 levels were almost 2-fold higher in APAP-ALI patients who satisfied King's College Criteria (KCC), compared to those who did not satisfy KCC, although this did not reach statistical significance (P 5 0.15). Conclusion: This work provides the first evidence for the potential use of miRNAs as biomarkers of human drug-induced liver injury. (HEPATOLOGY 2011;54:1767-1776 T he development of informative biomarkers of drug-induced liver injury (DILI) remains a primary aim in clinical and preclinical settings. The challenge is to develop biomarkers that are stable, that can be rapidly and accurately quantified in standard hospital laboratories, are minimally invasive, tissue specific, and add true diagnostic/prognostic value to detect and monitor the level of a pathogenic insult to the liver.1 The current battery of available biomarkers to assess liver integrity includes circulating protein markers of hepatocellular injury, such as the aminotransferases, markers of liver functional impairment, such as prothrombin time, markers of blood chemistry, and a number of novel mechanistic biomarkers of tissue injury (e.g., cytokeratin-18 and high-mobility group box-1 protein). 2 Deficiencies discovered with current blood-based biomarkers include the unacceptable frequency of false positives/negatives, poor

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Unprecedented developments in stem cell research herald a new era of hope and expectation for novel therapies. However, they also present a major challenge for regulators since safety assessment criteria, designed for conventional agents, are largely inappropriate for cell-based therapies. This article aims to set out the safety issues pertaining to novel stem cell-derived treatments, to identify knowledge gaps that require further research, and to suggest a roadmap for developing safety assessment criteria. It is essential that regulators, pharmaceutical providers, and safety scientists work together to frame new safety guidelines, based on "acceptable risk," so that patients are adequately protected but the safety "bar" is not set so high that exciting new treatments are lost.

Drug-induced mitochondrial dysfunction has been hypothesized to be an important determining factor in the onset of drug-induced liver injury. It is essential to develop robust screens with which to identify drug-induced mitochondrial toxicity and to dissect its role in hepatotoxicity. In this study we have characterised a mechanistically refined HepG2 model, using a panel of selected hepatotoxicants and non-hepatotoxicants. We have demonstrated that acute metabolic modification, via glucose-deprivation over a 4 h period immediately prior to compound addition, is sufficient to allow the identification of drugs which induce mitochondrial dysfunction, in the absence of cell death over a short exposure (2-8 h) using a plate-based screen to measure cellular ATP content and cytotoxicity. These effects were verified by measuring changes in cellular respiration, via oxygen consumption and extracellular acidification rates. Overall, these studies demonstrate the utility of HepG2 cells for the identification of mitochondrial toxins which act directly on the electron transport chain and that the dual assessment of ATP content alongside cytotoxicity provides an enhanced mechanistic understanding of the causes of toxicity.

Immunomodulatory biologics, which render their therapeutic effects by modulating or harnessing immune responses, have proven their therapeutic utility in several complex conditions including cancer and autoimmune diseases. However, unwanted adverse reactions--including serious infections, malignancy, cytokine release syndrome, anaphylaxis and hypersensitivity as well as immunogenicity--pose a challenge to the development of new (and safer) immunomodulatory biologics. In this article, we assess the safety issues associated with immunomodulatory biologics and discuss the current approaches for predicting and mitigating adverse reactions associated with their use. We also outline how these approaches can inform the development of safer immunomodulatory biologics.

␤-Lactam antibiotics provide the cornerstone of treatment and reduce the rate of decline in lung function in patients with cystic fibrosis, but their use is limited by a high frequency of delayedtype allergic reactions. The objective of this study was to use cloned T-cells expressing a single T-cell receptor from five piperacillin-hypersensitive patients to characterize both the cellular pathophysiology of the reaction and antigen specificity to define the mechanism of activation of T-cells by piperacillin. More than 400 piperacillin-responsive CD4ϩ, CD4ϩCD8ϩ, or CD8ϩ T-cell clones were generated from lymphocyte transformation test and ELIspot-positive patients. The T-cell response (proliferation, T helper 2 cytokine secretion, and cytotoxicity) to piperacillin was concentration-dependent and highly specific. Enzyme-linked immunosorbent assay, gel electrophoresis, and mass spectrometry revealed that piperacillin bound exclusively to albumin in T-cell culture. Irreversible piperacillin binding at Lys 190, 195, 199, 432, and 541 on albumin and the stimulation of T-cells depended on incubation time. A synthetic piperacillin albumin conjugate stimulated T-cell receptors via a major histocompatibility complex-and processing-dependent pathway. Flucloxacillin competes for the same Lys residues on albumin as piperacillin, but the resulting conjugate does not stimulate T-cells, indicating that binding of the ␤-lactam hapten in peptide conjugates confers structural specificity on the activation of the T-cell receptors expressed on drug-specific clones. Collectively, these data describe the cellular processes that underlie the structural specificity of piperacillin antigen binding in hypersensitive patients with cystic fibrosis.

Covalent binding to proteins to form neoantigens is thought to be central to the pathogenesis of penicillin hypersensitivity reactions. We have undertaken detailed mass spectrometric studies to define the mechanism and protein chemistry of hapten formation from benzylpenicillin (BP) and its rearrangement product, benzylpenicillenic acid (PA). Mass spectrometric analysis of human serum albumin exposed to BP and PA in vitro revealed that at low concentrations (drug protein molar ratio 0.001:1) and during short time incubations BP and PA selectively target different residues, Lys199 and Lys525, respectively. Molecular modeling showed that the selectivity was a function of noncovalent interaction before covalent modification. With increased exposure to higher concentrations of BP and PA, multiple epitopes were detected on albumin, demonstrating that the multiplicity of hapten formation is a function of time and concentration. More importantly, we have demonstrated direct evidence that PA is a hapten accounting for the diastereoisomeric BP antigen formation in albumin isolated from the blood of patients receiving penicillin. Furthermore, PA was found to be more potent than BP with respect to stimulation of T cells from patients with penicillin hypersensitivity, illustrating the functional relevance of diastereoisomeric hapten formation.

Covalent modification of protein by drugs may disrupt self-tolerance leading to lymphocyte activation. Determination of the threshold required for this process has not hitherto been possible. We have therefore performed quantitative mass spectrometric analyses to define the epitopes formed in tolerant and hypersensitive patients taking the β-lactam antibiotic piperacillin and the threshold required for T-cell activation. A hydrolysed piperacillin hapten was detected on 4 Lys residues of HSA isolated from tolerant patients. The level of modified Lys541 ranged from 2.6-4.8%. Analysis of plasma from hypersensitive patients revealed the same pattern and levels of modification 1-10 days after commencement of therapy. Piperacillin-responsive skin-homing CD4+ clones expressing an array of Vβ receptors were activated in a dose, time and processingdependent manner; analysis of incubation medium revealed that 2.6% of Lys541 in HSA was modified when T-cells were activated. Piperacillin-HSA conjugates that had levels and epitopes identical to those detected in patients were shown to selectively stimulate additional CD4+ clones, which expressed a more restricted Vβ repertoire. To conclude, the levels of piperacillin-HSA modification that activated T-cells are equivalent to the ones formed in hypersensitive and tolerant patients, which indicates that threshold levels of drug antigen are formed in all patients. Thus, the propensity to develop hypersensitivity is dependent on other factors such as on the presence of Tcells within an individual's repertoire that can be activated with the β-lactam hapten and/or an imbalance in immune regulation.