An αv-RGD Integrin Inhibitor Toolbox: Drug Discovery Insight, Challenges and Opportunities.

There is a requirement for efficacious and safe medicines to treat diseases with high unmet need. The resurgence in αv-RGD integrin inhibitor drug discovery is poised to contribute to this requirement. However, drug discovery in the αv integrin space is notoriously difficult due to the receptors being structurally very similar as well as the polar zwitterionic nature of the pharmacophore. This Review aims to guide drug discovery research in this field through an αv inhibitor toolbox, consisting of small molecules and antibodies. Small-molecule αv tool compounds with extended profiles in αvß1, 3, 5, 6 and 8 cell adhesion assays, with key physicochemical properties, have been collated to assist in the selection of the right tool for the right experiment. This should also facilitate an understanding of partial selectivity profiles of compounds generated in different assays across research institutions. Prospects for further αv integrin research and the critical importance of target validation are discussed, where increased knowledge of the selectivity for individual RGD αv integrins is key. Insights into the design of small-molecule RGD chemotypes for topical or oral administration are provided and clinical findings on advanced molecules are examined.

Solid phase synthesis of peptides containing backbone-fluorinated amino acids.

Backbone-fluorinated amino acids exhibit unique conformational behaviour, and have potential utility as components of bioactive shape-controlled peptides. However, methods for the elaboration of backbone-fluorinated amino acids have thus far been limited to solution phase peptide coupling reactions. In this paper, protocols are developed that allow the successful manipulation of backbone-fluorinated amino acids using Fmoc-strategy solid phase peptide synthesis. To exemplify this strategy, several fluorinated RGD peptide analogues were synthesised in moderate to good overall yields.

A phenotypic screening approach in cord blood-derived mast cells to identify anti-inflammatory compounds.

Mast cells are unique hematopoietic cells that are richly distributed in the skin and mucosal surfaces of the respiratory and gastrointestinal tract. They play a key role in allergic inflammation by releasing a cocktail of granular constituents, including histamine, serine proteases, and various eicosanoids and cytokines. As such, a number of drugs target either inhibition of mast cell degranulation or the products of degranulation. To identify potential novel drugs and mechanisms in mast cell biology, assays were developed to identify inhibitors of mast cell degranulation and activation in a phenotypic screen. Due to the challenges associated with obtaining primary mast cells, cord blood-derived mononuclear cells were reproducibly differentiated to mast cells and assays developed to monitor tryptase release and prostaglandin D2 generation. The tryptase assay was particularly sensitive, requiring only 500 cells per data point, which permitted a set of approximately 12,000 compounds to be screened robustly and cost-effectively. Active compounds were tested for concomitant inhibition of prostaglandin D2 generation. This study demonstrates the robustness and effectiveness of this approach in the identification of potential novel compounds and mechanisms targeting mast cell-driven inflammation, to enable innovative drug discovery efforts to be prosecuted.

The integrin alphavbeta3 is a receptor for the latency-associated peptides of transforming growth factors beta1 and beta3.

The integrins alpha(v)beta(1), alpha(v)beta(5), alpha(v)beta(6) and alpha(v)beta(8) have all recently been shown to interact with the RGD motif of the latency-associated peptide (LAPbeta(1)) of transforming growth factor beta(1) (TGFbeta(1)), with binding to alpha(v)beta(6) and alpha(v)beta(8) leading to TGFbeta(1) activation. Previously it has been suggested that the remaining alpha(v) integrin, alpha(v)beta(3,) does not interact with LAPbeta(1). However, here we show clearly that alpha(v)beta(3) does indeed interact with the LAPbeta(1) RGD motif. This interaction is similar to other alpha(v)beta(3) ligands in terms of the cations required for adhesion, the concentrations of LAPbeta(1) required for binding and the ability of a small-molecule inhibitor of alpha(v)beta(3), SB223245, to block the interaction. Using glutathione S-transferase fusion proteins we have mapped a minimal integrin-binding loop in LAPbeta(1) and then used this approach to probe the integrin-binding properties of the equivalent loops in LAPbeta(2) and LAPbeta(3). We show that the RGD motif of LAPbeta(3) also interacts with alpha(v)beta(3), in addition to alpha(v)beta(6), alpha(v)beta(1) and alpha(v)beta(5), whereas the corresponding loop in LAPbeta(2) does not interact with these integrins. These observations therefore correct a previously reported inaccuracy in the literature. Furthermore, they are important as they link alpha(v)beta(3) and TGFbeta, which may have implications in cancer and a number of inflammatory and fibrotic diseases where expression of both proteins has been documented.