Roadmap to DILI research in Europe. A proposal from COST action ProEuroDILINet.

In the current article the aims for a constructive way forward in Drug-Induced Liver Injury (DILI) are to highlight the most important priorities in research and clinical science, therefore supporting a more informed, focused, and better funded future for European DILI research. This Roadmap aims to identify key challenges, define a shared vision across all stakeholders for the opportunities to overcome these challenges and propose a high-quality research program to achieve progress on the prediction, prevention, diagnosis and management of this condition and impact on healthcare practice in the field of DILI. This will involve 1. Creation of a database encompassing optimised case report form for prospectively identified DILI cases with well-characterised controls with competing diagnoses, biological samples, and imaging data; 2. Establishing of preclinical models to improve the assessment and prediction of hepatotoxicity in humans to guide future drug safety testing; 3. Emphasis on implementation science and 4. Enhanced collaboration between drug-developers, clinicians and regulatory scientists. This proposed operational framework will advance DILI research and may bring together basic, applied, translational and clinical research in DILI.

Direct positive selection for improved nitroreductase variants using SOS triggering of bacteriophage lambda lytic cycle.

Expression of prodrug-activating enzymes that convert non-toxic substrates to cytotoxic derivatives is a promising strategy for cancer gene therapy. However, their catalytic activity with unnatural, prodrug substrates is often suboptimal. Efforts to improve these enzymes have been limited by the inability to select directly for increased prodrug activation. We have focussed on developing variants of Escherichia coli (E. coli) nitroreductase (NTR) with improved ability to activate the prodrug 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB1954), and describe here a novel, direct, positive selection for improved enzymes that exploits the alternative life cycles of bacteriophage lambda. In lambda lysogens of E. coli, the activation of the prodrug CB1954 by NTR triggers the SOS response to DNA damage, switching integrated lambda prophages into lytic cycle. This provides a direct, positive selection for phages encoding improved NTR variants, as, upon limiting exposure of lysogenized E. coli to CB1954, only those encoding the most active enzyme variants are triggered into lytic cycle, allowing their selective recovery. We exemplify the selection by isolating highly improved 'turbo-NTR' variants from a library of 6.8 x 10(5) clones, conferring up to 50-fold greater sensitivity to CB1954 than the wild type. Carcinoma cells infected with adenovirus expressing T41Q/N71S/F124T-NTR were sensitized to CB1954 concentrations 40- to 80-fold lower than required with WT-NTR.

Virus-directed enzyme prodrug therapy using CB1954.

The virus-directed enzyme prodrug therapy (VDEPT) anti-cancer 'gene therapy' strategy relies on the use of viral vectors for the efficient delivery to tumour cells of a 'suicide gene' encoding an enzyme which converts a non-toxic prodrug to a cytotoxic agent. The prodrug 5-(aziridin-1-yl)-2,4 dinitrobenzamide, CB1954, has been proposed for use in enzyme-prodrug gene therapy systems with the Escherichia coli enzyme nitroreductase (Ntr). Ntr converts CB1954 to 2- and 4-hydroxylamino derivatives, whereupon the non-enzymatic reaction of the 4-hydroxylamino derivative with cellular thio- esters generates a potent cytotoxic bifunctional alkylating agent capable of cross-linking DNA. Ntr delivery has been achieved in vitro using retroviral and adenoviral vectors and confirmed by immunocytochemical demonstration of Ntr expression. The Ntr-expressing cells have been shown to be sensitized to CB1954 by up to 2000-fold. The Ntr-CB1954 system shows effective bystander killing in mixed populations of Ntr-expressing and non-expressing cells treated with CB1954. The efficacy of this enzyme-prodrug approach in model systems compared with other VDEPT approaches demonstrates the feasibility and future promise of this gene therapy strategy.