Identification of Peptide 3, the first BSCI, and other peptide analogs
MCP-1 is just one chemokine in a large family which today has almost 50 members. It signals predominantly through CCR2 which is just one of more than 20 chemokine receptors. All the available evidence suggested that different chemokines could substitute for one another (functional redundancy) at least partially, and that highly specific chemokine inhibitors might therefore have little effect in vivo. Our approach, therefore, was to design broad-spectrum chemokine inhibitors which affected multiple chemokine signalling pathways simultaineously, but left other cytokine signals untouched. Although there was widespread skepticism that such molecules would be highly toxic once we had found them (on the basis that chemokines occupy a central nexus in the control of the immune system that disruption of many of them simulatenously must be damaging), nevertheless we persevered because such a conclusion could only be drawn once molecules with the appropriate properties had been identified and tested.
The approach we followed was to align the sequences of chemokines from different species and look for regions of sequence conservation. We then synthesised peptides which replicated the sequence of these islands of conservation and tested them for their ability to block leukocyte migration induced by chemokines, but not by other cytokines such as TGF-beta or fMLP. The first two peptides failed to show much inhibitory activity, but the third sequence, termed Peptide 3, completely inhibited leukocyte migration induced with any of five different chemokines tested but did not affect signals from other cytokines. The properties of this peptide were first described by us in 1999 (Biochem J 340:803). Peptide 3 was the original member of a class of Chemokine Inhibitory Peptides or Chemotides.
Peptide 3 had exactly the properties we were looking for in so far as it inhibited chemokine function but left other cytokines untouched. But, being a peptide, it had a number of limitations: it was not very potent, requiring concentrations of approximately 10µM to block chemokine function in vitro, and perhaps more importantly, it was not ideal for use in vivo.
Once a biological function has been ascribed to a peptide, there are range of approaches which can be adopted to make molecules which have better pharmacokinetic properties in vivo but which retain the biological function. One of the most theoretically attractive approaches in the retroinverso approach which had worked well for Jameson et al (Nature 368:744), although more often than not it fails to be useful in practice. In simple terms the peptide sequence is turned upside down and inside out which changes the orientation of the backbone peptide bond structures but leaves the spatial orientation of the functional side chains relatively unchanged. We synthesised a cyclic derivative of the retroinverso sequence of peptide 3, which was termed NR58-3.14.3 and showed that this molecule not only retained the functional properties of Peptide 3, but was actually considerably more potent. NR58-3.14.3 blocks chemokine-induced migration at 5nM (a concentration 2,000 fold lower than for the parental Peptide 3 sequence). The properties of this analog were first published in 2001 (Immunology 103:244).
In 1998, Cambridge University signed an agreement with NeoRx Corporation (Seattle, USA) to further develop NR58-3.14.3 as a potential anti-inflammatory drug. Over a three year period, scientists at NeoRx worked in co-operation with the Inflammation Research and Therapy lab to demonstrate that NR58-3.14.3 not only had anti-inflammatory properties in a range of disease models, but that it was apparently free of either acute or chronic toxic side effects.
The number of disease models where NR58-3.14.3 has been shown to be effective is increasing all the time. Our first demonstration was the inhibition of bacterial endotoxin-induced inflammation in the skin (Immunology 103:244). Since then, it has been shown to be effective in asthma, atherosclerosis, stroke (J Cereb Blood Flow Met 21:683) and bronchiolitis obliterans syndrome (Ann Thorac Surg 75:1118). A range of collaborations have been established with academic laboratories both in the USA and Europe to investigate further the properties of NR58-3.14.3 in various diseases and publications from these studies are currently under consideration by a number of journals.
At the end of 2000, NeoRx focussed their operations on their core oncology technologies and elected to return the rights to NR58-3.14.3 to Cambridge University. With a substantial package of data supporting the broad anti-inflammatory function of these novel compounds, together with some indication that they were devoid of side-effects, enabled us to secure agreement with the Ipsen pharmaceutical group who took a licence to the BSCI technology in 2001. Scientists in the Beaufour-Ipsen group have been working closely with us throughout 2002 examining ways to improve further on the NR58-3.14.3 structure producing hundreds of new analogs many of which promise to have superior properties in vivo. The next big hurdle will be initiation of human clinical trials to discover whether Chemotides can fulfill their potential as novel anti-inflammatory drugs of great promise.