For instance, treating individual monocyte-derived dendritic cells using the NBD peptide arrested the cells within an immature condition despite stimulation with LPS (Tas (see Table 2) is an effective approach to the treatment of inflammatory diseases in which bone resorption plays a substantial pathological role (Dai have also recently been identified (Gotoh em et al /em ., 2010). protein substrates out-with this cascade. Consequently, close consideration of how these individual complexes transduce extracellular signals and more importantly what impact small molecule inhibitors of the IKKs have on functional outcomes are demanded. A number of adenosine triphosphate (ATP)-competitive IKK-selective inhibitors have been developed but have demonstrated a lack of activity against IKK. A number of these chemicals have also exhibited detrimental outcomes such as cellular toxicity and immuno-suppression. The impact of small molecule inhibitors of IKK catalytic activity will therefore be reappraised, examining the advantages and potential disadvantages to this type of intervention strategy in the treatment of diseases such as arthritis, intestinal inflammation and cancer. Furthermore, we will outline some emerging strategies, particularly the disruption of proteinCprotein interactions within the IKK complex, as an alternative route towards the development of novel pharmacological agents. Whether these alternatives may negate the limitations of ATP-competitive molecules and potentially avoid the issues of toxicity will be discussed. in animal models of disease. In short, full characterization of mechanism of action related to potency effect of cell-permeable peptides targeting the NBD Open in a separate window Aside from HTS strategies with synthetic small molecules, it is also well recognized that natural products may represent a route towards novel pharmacological agents that target the IKKs. For example, wedelolactone [Figure 2, (11)] has been suggested to act as an irreversible inhibitor of both IKK and IKK (Kobori (Asamitsu (Andreakos (Tak (Tysnes, 2010). This feature is relevant in colorectal, pancreatic and lung cancers (Charalambous using cell-permeable peptides have also shown effective inhibition of NF-B signalling. For example, treating human monocyte-derived dendritic cells with the NBD peptide arrested the cells in an immature state despite stimulation with LPS (Tas (see Table 2) is an effective approach to the treatment of inflammatory diseases in which bone resorption plays a substantial pathological role (Dai have also recently been identified (Gotoh em et al /em ., 2010). The chemical structure of these disruptors remains undisclosed, and as such, it is unknown whether these compounds represent low-molecular-weight entities or are peptide-based. The progression of any peptide-based disruptors of proteinCprotein interactions into drug-like molecules brings the significant challenges of in-building the appropriate pharmacology and desired drug-like characteristics. This will likely require the development of peptidomimetics into small drug-like molecules that work as efficiently, if not better, than the original peptide. One technique that is Zapalog proving to be a popular tool in the development of this approach is virtual screening of proteins. For example, the structural determination of human Mdm2 bound to a 15 residue peptide of p53 has led to the development of a number of small non-peptidic inhibitors (Shangary and Wang, 2009). Structure-based drug design has also been used to improve the druggability of a small molecule directed at the interaction between B-cell leukaemia 2 (Bcl2)/Bcl-xl (van Montfort and Workman, 2009). A similar strategy could therefore be applied to the interactions between the IKKs within the IKKs complex, relevant to both the canonical and non-canonical axes. Summary and future perspectives Within the NF-B field and in the study of the IKKs, there remain the key challenges of understanding fully the functional roles of the individual kinase isoforms. This has in part driven the quest for IKK-selective inhibitors and has been based Zapalog primarily on the development of ATP-competitive agents that are more easily identified in HTS. Unfortunately, ATP mimetics have a number of limitations (Garber, 2006). Despite being of low molecular weight, being orally bioavailable and able to inhibit target proteins, they can still hit other kinases to generate off-target/side effects (Garber, 2006). In the SCC3B cancer setting, for example, it has also been observed that the strategy of using ATP-competitive inhibitors may be flawed as tumours, and kinases within them, develop mutations in the ATP-binding pocket that interferes with drug binding, negates its effects and leads to resistance; whether this is relevant to the IKKs across a number of pathophysiological settings remains to be determined. To avoid these issues, alternative strategies to targeting aberrant kinase activity are now emerging as the kinase field embarks on identifying agents that bind to, and inhibit, kinases in novel ways. Substrate-competitive inhibitors particularly are now being developed to this end (e.g. Bogoyevitch and Arthur, Zapalog 2008; Licht-Murava em et al /em ., 2011) and are providing promising leads. In time, this approach will likely be applied to the IKKs. So, to date, despite the limitations of ATP-competitive molecules, significant advances have been made in developing inhibitors of the IKKs, particularly those that target and inhibit the intrinsic catalytic activity of IKK (see Section The development of novel small molecule inhibitors of the IKKs). This has been achieved again through the pursuit of HTS; however, these strategies have not delivered parallel inhibitors of IKK. The synthesis and optimization of highly selective inhibitors of IKK remains one of the key challenges.