A novel role for Sema3A in neuroprotection from injury mediated by activated microglia.

Microglia exist under physiological conditions in a resting state but become activated after neuronal injury. Recent studies have highlighted the reciprocal role of neurons in controlling both the number and activity of microglia. In this study, microglia derived from newborn rat cortices were cultured and activated by interferon-gamma (IFNgamma) treatment, then exposed to recombinant Sema3A or conditioned medium derived from stressed embryonic cortical neurons. We found that activation of microglia by IFNgamma induced differential upregulation of the semaphorin receptors Plexin-A1 and Neuropilin-1. This result was confirmed by Northern blotting, reverse transcription-PCR, and Western blotting. Furthermore, recombinant Sema3A induced apoptosis of microglia when added to the in vitro culture, and a similar result was obtained on activated microglia when Sema3A was produced by stressed neurons. Using an in vivo model of microglia activation by striatal injection of lipopolysaccharide demonstrated a corresponding upregulation of Plexin-A1 and Neuropilin-1 in activated microglia and enhanced production of Sema3A by stressed adult neurons. These results suggest a novel semaphorin-mediated mechanism of neuroprotection whereby stressed neurons can protect themselves from further damage by activated microglia.

Preclinical safety testing of biotechnology-derived pharmaceuticals: understanding the issues and addressing the challenges.

The unique and complex nature of biotechnology-derived pharmaceuticals has meant that it is often not possible to follow the conventional safety testing programs used for chemicals, and hence they are evaluated on a case-by-case basis. Nonclinical safety testing programs must be rationally designed with a strong scientific understanding of the product, including its method of manufacture, purity, sequence, structure, species specificity, pharmacological and immunological effects, and intended clinical use. This knowledge, coupled with a firm understanding of the regulatory requirements for particular product types, will ensure that the most sensitive and regulatory-compliant test systems are used to optimize the chances of gaining regulatory approval for clinical testing or marketing authorization in the shortest possible time frame.

In vitro preclinical lead optimisation technologies (PLOTs) in pharmaceutical development.

The explosion of genuine high throughput technologies has allowed large compound libraries to be screened with ever increasing biological specificity, exacerbating the problem of lead candidate selection for subsequent drug development. To avoid creating a bottleneck, compounds identified from the high throughput screens undergo lead optimisation, a medium-throughput screen which allows ranking in terms of their basic absorption, distribution, metabolism, excretion (ADME) and toxicological properties. The historical role of the preclinical scientist in the drug discovery/development continuum has been to perform ADME and toxicology studies, simply to support the regulatory submission of lead candidates. This situation is, however, changing with the development of preclinical lead optimisation technologies (Approaches to High Throughput Toxicity Screening, London, Atterwill et al., 1999) facilitating the selection of leading candidates, thereby bridging the gap between high throughput efficacy screens and traditional safety assessment programmes.