Étude du mode de liaison de l’antagoniste de CXCR4, TC14012, sur ACKR3 et évaluation de CXCR4 et d’ACKR3 comme marqueurs de survie de la leucémie pédiatrique dans un modèle murin xénogénique

CXCL12 is a non-inflammatory chemokine involved in hematopoietic stem cell homing and retention to specific bone marrow niches. Its signaling is transduce through two 7 transmembrane receptors, CXCR4 and ACKR3. CXCR4 controls migration cues and cellular attachment by a G-protein-dependant signaling pathway. The second receptor, ACKR3, promotes CXCL12 degradation through a G-proteinindependent, arrestin-dependant pathway. The latter leads to the generation and maintenance of a sharp CXCL12 gradient, promoting directional cell migration. Because of its involvement in a range of pathological processes including, but not restricted to, HIV entry and metastatic dissemination of cancers, CXCR4 is an attractive pharmacological target. Over the past two decades, several antagonists targeting it were synthetized. Despite the low sequence homology between CXCR4 and ACKR3, two of these antagonists, AMD3100 and TC14012, were shown to act as agonists on ACKR3. The causes of this reverse effect on CXCR4 and ACKR3 are not known. Thus, in the first article of this thesis, we used ACKR3 substitution mutants and molecular modeling based on the CXCR4 crystal bound to CVX15 (a TC14012 derivative) to determine the binding mode of TC10412 on ACKR3. The cumulative results of functional assays and molecular dynamics simulations allowed the identification of key determinants in the interaction between ACKR3 and TC14012. These results provide essential information for the future development of more specific ligands targeting one of these receptors. B-cell precursor acute lymphoblastic leukemia (B-ALL) is the most common pædiatric neoplasia. While the 5-year event-free survival exceeds 85%, more than 25% of these “cured” children will suffer potentially life-threatening sequelæ due to overtreatment. A more precise stratification strategy of the individual risk of relapse is required to allow an accurate personalised therapy reduction or intensification. It has recently been shown that the survival of patient-derived xenografted (PDX) mice correlates with the individual risk of relapse in children with B-ALL. Thus, in the VI second section of this thesis, we report for the first time a method to identify new risk markers using B-ALL PDX mice model. The model was first validated using known prognostic markers for pædiatric B-ALL (t(12;21), hyperdiploid (HD) and CD20). We then demonstrated that the combined use of markers (CXCR4high ACKR3low, nont( 12;21) and non-HD) predicts with great sensitivity a short survival of PDX mice. The key parameters highlighted in this study will now have to be validated in a prospective or retrospective study. The latter would test the association of our combined parameters with the individual clinical outcome of B-ALL children to validate our PDX results. Our algorithm may eventually lead to a more accurate individual risk stratification of pædiatric B-ALL patients thus guiding personalized therapy adjustment.

Keyphrases: CXCL12, CXCR4, ACKR3, CXCR7, T140, TC14012, CXCR4 inhibitors, PDX mice, Leukemia, Pediatric cancer, Risk stratification