Inhibiting Chromatin Assembly by Targeting Histone Chaperones – CHAPINHIB

ASF1 protein has no catalytic activity that could be targeted by small chemical molecules. Its main function is to assemble and disassemble histones. Thus to inhibit its activity, we tried to prevent its interaction with histones by the action of high affinity competitive peptides for ASF1 (in the nanomolar range). Starting from a first peptide capable of binding ASF1 with a modest affinity (micromolar), we sought to improve its inhibitory properties by optimizing not only its affinity for the target, but also its selectivity and bioavailability in cellulo. To achieve these goals, we developed an interdisciplinary approach, combining rational design, directed evolution, structural biophysical approaches, and analyses of the effects of peptides on model cell lines, then models of breast tumor in mice.

We have designed peptides with affinity in the nanomolar range for ASF1 that are able to dissociate its binding with histones in vitro and in cells with high specificity. These peptides exhibit antiproliferative activity in tumor cell lines and in a breast cancer model in mice. However, these peptides are rapidly degraded in the cells and in the plasma. The first tracks explored to stabilize their structure while maintaining their activity have been successfully carried out. This work led to the deposit of an international patent, and numerous articles and journal publications in international journals with high impact factor

The Chapinhib project has led to the development of an original method for peptide design inhibiting protein-protein interactions. The inhibition of the ASF1-Histone interaction is a difficult case, the success of this design pushes the limits of the approach, and will have applications for other complexes of therapeutic interest in the future. The benefits of this project are thus in the field of both fundamental and applied research.

The Chapinhib project led to numerous developments in the teams involved, and publication of articles in international and national journals, or oral communications (including 34 articles in peer-reviewed journals, 3 book chapters, 21 oral communications etc...). A patent has been filed and a second is being drafted. Several multi-partner articles that describe the methods developed for the design of ASF1 inhibitory peptides, as well as the performance of the obtained peptides, and their potentials for inhibiting the proliferation of cancer cells are under revision or in the process of being written.

Histone chaperones ensure the proper provision, deposition and placement of histones onto DNA, and therefore play a key role directly impacting genome function and integrity. Anti-silencing function 1 (Asf1) is a highly conserved histone chaperone that escorts histones H3-H4 and contributes to their deposition onto DNA to form nucleosomes. The recent discovery involving Asf1B in tumor cell proliferation - among the two Asf1 paralogs that exist in mammals (termed Asf1A and Asf1B in human) - already proved that Asf1B can serve as a prognostic marker for breast cancer. These findings raise the possibility of developing promising anti-cancer drugs by designing compounds targeting Asf1 activity. At this point in time, we have already developed a first generation compound that inhibits the Asf1-histone interaction. We can deliver it efficiently into cells where it impedes proliferation by blocking cell cycle progression and induces cell death in tumorigenic cell lines. Based on this ground work, the CHAPINHIB project aims to further develop highly potent and selective peptide-based compounds to inhibit Asf1 activity and to demonstrate their therapeutic potential in cultured cells and in animal models. The project will benefit from the complementary expertise of partners from distinct scientific backgrounds, providing a necessary interdisciplinary approach to carry out the proposed work. This project should advance not only the design and use of peptide-based compounds to target Asf1 protein-protein interactions with the ultimate goal to apply this knowledge to fight cancer, but will also provide unique tools to improve our basic knowledge concerning histone usage and general paradigms to interfere with any protein interactions.