In detail

Tryptophan and arginine catabolism are important mechanism of peripheral immune tolerance contributing to tumoral immune resistance, and indoleamine 2,3-dioxygenases (IDO and TDO) and arginase (Arg1) inhibition are validated strategy for anticancer drug development.

The implication of IDO in the phenomenon of tumoral immune resistance was the focus of intense research and the enzyme is now recognized as a validated target for anti-cancer therapy. In contrast, the effect of TDO expression on the immune response has only been relatively recently investigated in detail. Indeed, we showed in collaboration with the group of Prof Van den Eynde (DDUV) that TDO was effectively overexpressed by a number of human tumors and that this expression prevented rejection of tumor cells. We designed a novel TDO inhibitor and proved, in a preclinical model, the concept that TDO inhibition promotes tumoral immune rejection. Our recent works (PhD thesis of Séraphin Lacour) led to the discovery of new TDO inhibitors acting at the TDO active site. Interrestingly, because TDO is only active in the tetrameric form, we have also recently started to study the TDO oligomeric interface with the goal to discover potential TDO oligomeric disuptors (PhD thesis of Mrs Caroline Mathieu). 

Arginine (L-Arg) catabolism by Arginase 1 (Arg1) is another mechanism contributing to tumoral immune resistance. In recent works, we have identified novel boronic acids compounds as promising Arginase inhibitors. But because boronic acids are not characterized with adequate PK properties we have recently undertook a new strategy targeting the oligomerization site of Arg1 that is a trimer (PhD thesis of Juhans Dechenne). So far, several mutants of Arg1 were produced as well as truncated and wild-type Arg1. The stability and activity of these Arg1 mutants as well as the effect of peptide disruptors are currently being investigated by biophysical and biochemical methodologies.

Tumor cells are characterized by a remarkable metabolic plasticity allowing them to survive and proliferate in hypoxic and extracellular acidic environments. In tumor cells, this plasticity allows the coexistence and coordination of several metabolic phenotypes, leading to an optimal use or resources. Hypoxic cells use glucose that is metabolized by anaerobic glycolysis. Lactate is secreted and diffuses, and can be subsequently used by oxygenated tumor cells as a preferred energetic source to glucose. The lactate oxidative pathway requires the entrance of lactate in oxidative cells via a process that is mainly facilitated by the Monocarboxylate Transporter MCT1 and the oxidation of lactate to pyruvate by the lactate dehydrogenase B (LDHB). The pyruvate can then fuel the Krebs cycle and NADH uses the malate-aspartate shuttle to directly fuel the mitochondrial respiration chain. The oxidative use of lactate in the oxygenated tumor compartment therefore optimizes the availability of glucose for cells of the hypoxic compartment, thus constituting a unique metabolic cooperation.

Several observations made in collaboration with the team of Pierre Sonveaux (IREC) suggest that LDHB may be a new target in cancer therapy. However, there is currently no selective inhibitor of this enzyme, and the consequences of systemic inhibition of LDHB activity remain largely unknown.

In this project (Postdocs Ferran Nadal-Bufi & Quentin Spillier, and PhD thesis of Chiara Brustenga & Perrine Savoyen), our aim is to develop and validate a peptide inhibitor and a non-peptide inhibitor to selectively inhibit tetramerization of LDHB. Our strategy will involve the use of Protein-Protein Interaction Inhibitor (PPI) identification methods that is, a highly multidisciplinary approach involving molecular modeling studies (identification of "Hot Spots"), biochemical studies (in vitro and in vivo inhibition of LDHB tetramerization, selectivity study) and biophysical studies (nuclear magnetic resonance analysis of ligand-LDHB interaction). To achieve the goal of a selective inhibition of LDHB, we will use an innovative strategy targeting the tetramerization site of LDHB rather than the active site of the enzyme.

So far, our pivotal collaborative works led to (a) the delineation of hot spots at the LDH tetramerization site, (b) the design and synthesis of original (stapled) peptides capable of preventing LDH self-association and/or disrupting a preformed LDH tetramer, and (c) the development of some chemical biology tools to interrogate LDH tetramerization using NMR spectroscopy (STD and WaterLogSy experiments), thermal shift, microscale thermophoresis, and fluorescence spectroscopy experiments.

In collaboration with the team of Olivier Riant (IMCN), we are also developing novel chemical biology tools such as novel peptide stapling methodologies, the synthesis of fluorogenic probes including self-immolative linkers, etc. These innovative tools will be very helpful to interrogate LDH self-association (Phd thesis of Yonghua Tan & François Pierrard).

Ferroptosis, first coined in 2012, is a regulated cell death (RCD) characterized by iron-dependent accumulation of lipid hydroperoxides associated with an insufficient capacity to eliminate these oxidation products. A recent report uncovered acyl-CoA synthetase long-chain 4 (ACSL4) as a critical contributor to ferroptosis execution. Therefore, ACSL4 inhibitors are emerging as attractive anti-ferroptotic agents. The goal of our research program is to develop novel ACSL4 inhibitors to help establish the potential link between ACSL4, ferroptosis and NDDs. On a longer-term perspective, it should constitute a strong basis for the development of first-in-class drugs for the treatment of NDDs.

The present project, led in collaboration of colleagues from the University of Lille, France (Prof. Séverine Ravez and Jamal El Bakali) grounds on important preliminary findings generated in our lab (Postdoc Karine Porte and PhD thesis of Romain Marteau & Darius Mazhari). A screening of the Selective Optimization of Side Activity (SOSA) library against ACSL4 was undertaken by TSA. Typically, this approach starts with the screening of a set of limited and structurally diverse drug-like compounds known to possess good bioavailability and safety in humans. So far, we identified three series of molecules that stabilize the folded state of ACSL4 and we validated these hits in our optimized enzymatic assay. The identified micromolar-range inhibitors of ACSL4 represent original starting points for our lead discovery program.

Inhalation is a convenient and effective route of administration of actives as it offers local treatment; nevertheless, small and lipophilic drugs are rapidly absorbed in the systemic circulation following delivery to the lungs. This translates in peaks in blood concentration of the active with consequent occurrence of systemic side effects.

In line with this, Treprostinil, a prostacyclin analogue used in the treatment of pulmonary arterial hypertension (PAH), is inhaled 4 times a day by patients. The quick absorption, with consequent emergence of systemic side effects, implies that the dose administered must be lowered in order to prevent systemic toxicity. Lower doses, more often administered through the day, partially answer the issue of systemic side effect, but the high frequency of administration represents a significant therapy burden for the patient.

The goal of this project, in collaboration with the team of Rita Vanbever (ADDB) (PhD thesis of Giuditta Leone) is to address these limitations by developing a nanomedicine with polyethylene glycol (PEG). The formation of a prodrug between the polymer and the small molecule will allow a slow release of the active, therefore sustaining Treprostinil residency, release and therapeutic activity within the lungs as well and improving its safety and water solubility.

Sarcomas, neuroblastomas and brain tumors frequently activate an alternative and telomerase-independent mechanism of telomere maintenance, dubbed ALT, based on homologous recombination events between telomeric sequences. Being absent from normal cells, the ALT mechanism offers new interesting perspectives for specific and targeted anticancer therapy. However, “druggable” ALT-specific targets are still awaiting identification.

TSPYL5 is suggested as a possible ALT target candidate. Recent discoveries indicated that TSPYL5 depletion induces ALT+ cell death without impacting normal or telomerase-expressing cells. Cell death results from strong DNA damage activation in response to telomere deprotection due to the proteasomal degradation of POT1 telomeric protein. Our current hypothesis is that, through its competitive binding to USP7 deubiquitinase, TSPYL5 inhibits the recruitment of USP7 to telomeres and the subsequent degradation of POT1.

To give a better understanding this ALT+ mechanism, we will focus, in collaboration with the team of Anabelle Decottignies (DDUV), on the TSPYL5-USP7 complex (PhD thesis of Marine Ancia). Biophysical and biochemical experiments will be undertaken to identify the hot spots of this protein-protein interaction and to discover small molecules capable of disrupting the TSPYL5-USP7 interaction. These pharmacological tools will help establishing the proof-of-concept that TSPYL5-USP7 disruption can exert anticancer activity in ALT+ tumour cells.