A new Fragment-based Approach for inhibition of hk3 and matriptase, two up-regulated serine proteases implicated in tumor progression – FragSPIN

Our medicinal chemistry approach is based on recent literature that has addressed the suitability of small molecules to produce valuable lead compounds. This strategy named «Fragment-based lead discovery and assembly«, in which leads are built progressively by growing or combining small molecules, offers potential advantages compared to traditional lead-discovery processes. The direct involvement of the target in the screening selection and evolution of drug candidates can accelerate the discovery process by bypassing the traditionally iterative cycles of synthesis and screening.

In a fundamental point of view, the direct involvement of an enzyme for the selection and the evolution of a drug candidate by combining small fragments is a relatively unexplored option that is of a great value to accelerate medicinal chemistry programs. However, development of new irreversible chemistries that allow fragment selection and linking may offer some opportunities to achieve the discovery of enzyme inhibitors. For that reason, this academic research program present a real interest and could lead to international oral communications and writing reports in some peer-reviewed research proceeding and publications.

In the field of cancer and tumor progression new series of hKs and TTSPs reversible inhibitors are of great importance. Therefore, identified hit compounds will be patent and will be used as a starting point for a classical medicinal chemistry program, i.e. chemical modifications, in order to improve the biological and physiochemical properties to gain drug candidates. At this stage, new academic and/or industrial partners will be of a great value for in-vivo evaluation of their activities on ovarian, breast and prostate cancers.

No scientific production in 2011_2012

Serine proteases are ubiquitous, being found in diverse biological processes, including blood coagulation, inflammation and tissue remodeling. It is essential that their expression and activation are tightly controlled so that the integrity of the organism can be maintained. Evidence accumulating over the past decade has revealed that alteration of extracellular and transmembrane protease activity play a key role in tumor progression and metastasis: proteases act as processing enzymes that carry out highly selective cleavage of specific substrates and influence cell behaviour, survival and death. The current dogma asserts that a pericellular cascade initiated by the serine protease system of urokinase plasminogen activator (uPA), uPA receptor (uPAR) and plasminogen, which results in the activation of latent matrix metalloproteinases, is mainly responsible for extracellular proteolysis in cancer. It is recognized that up-regulation of uPA is a feature of malignancy and is correlated with tumor progression and metastasis and the inhibition of its activity leads to a reduction in the invasive and metastatic capacity of many tumors. However, this proteolytic network is becoming increasingly complex and many other players have been implicated in modulating the tumour microenvironment, including the tissue-kallikrein family of serine protease and some type II transmembrane serine proteases (TTSPs). Numerous experimental results indicate that hK expression and proteolytic activity are dysregulated in tumours, mainly adenocarcinomas and are often associated with patient prognosis. As example, hK1, hK2 and hK3 might stimulate the growth and survival of tumour cells, by degrading insulin-like growth factor binding proteins (IGFBP2, 3, 4 and 5), thereby liberating the mitogenic growth factor insulin-like growth factor 1 (IGF1), which binds to its cell-surface receptor and induces cell proliferation and prevents apoptosis. hK2 and hK4 also activate the uPA–uPAR system, particularly in malignant prostate cancers, leading to release and/or activation of latent growth factors from the extracellular matrix (ECM). hKs could directly stimulate tumour-cell growth through protease-activated receptors (PARs). Through similar ways, TTSPs play a key role during tumor progression since their extracellular proteolytic domains are able to activate pro-uPA and uPARs, as well growth factors. These enzymes are also involved in the degradation of the extracellular matrix. As example, matriptase, a TTSPs up-regulated in diverse epithelial tumors, including breast, ovarian and prostate cancers contribute substantially to these processes.
In view of the key feature of serine proteases in tumor progression and metastasis, there has been considerable interest to develop some selective synthetic inhibitors. In the last decades, structural design based on peptidomimetic backbone has been one of the most promising approaches to give highly potent inhibitors. However, optimization of peptidomimetic leads produced compounds exhibiting extremely poor pharmacokinetic properties. In the following project, we propose a new general "fragment-based" approach that could be applied to diverse serine proteases, especially hK and TTSPs. The aim is to use the enzyme target to select two fragments and connect them: formally the enzyme is used to choose the best fragments from a set of small molecules and to connect them in order to synthesize its own ligand. This approach depends on the simultaneous binding of the two types of fragments, decorated with complementary reactive groups, to adjacent sites of the protein: their co-localization is then likely to accelerate the reaction that connects them. Therefore, this will limit compound synthesis to those with affinity for the target. We propose to apply this strategy to the development of original non-peptidic inhibitors of the two serine proteases hk3 and Matriptase, which play key roles in prostate cancer.