PF163 TARGETING LYSOSOMES AS A POTENTIAL THERAPEUTIC APPROACH FOR T‐CELL ACUTE LYMPHOBLASTIC LEUKAEMIA (2019)

Background: Tcell acute lymphoblastic leukaemia (T–ALL) is an immature lymphoid tumour characterized by the diffuse infiltration of the bone marrow by malignant lymphoblasts expressing immature T‐cell markers. T–ALL results from a multistep transformation process in which accumulating genetic alterations coordinately disrupt key oncogenic, tumour suppressor and developmental pathways responsible for the normal control of cell growth, proliferation, survival and differentiation during thymocyte development. T‐ALL represents about 15% of paediatric and 25% of adult cases of ALL. The actual treatment for T‐ALL typically consists of a remission‐induction phase, a consolidation phase, and continuation therapy to eliminate residual disease. Recently (Sachlos et al. 2012), dopamine receptor was identified as a possible target for cancer stem cells, validated in acute myeloid leukemia (AML) and breast cancer. We then hypothesized that based on biological similarities between AML and T‐ALL and the existence of leukemic stem cells in both neoplasms, dopamine receptors may constitute a therapeutic target also in T‐ALL Aims: The main objective of the study was to validate dopamine receptors as a therapeutic target in T‐ALL. Methods: Dopamine receptor modulators were selected in concordance with the affinity for the dopamine receptor (1‐5). To study the antileukaemic effect of selected drugs, cell viability assays were performed in 3 human T‐ALL cell lines, 1 T‐ALL‐patient‐derived xenograft (PDX), 4 healthy‐donor buffy coats and 5 umbilical cord blood samples. In vivo studies were performed with conditioned adult NOD.Cg‐ Prkdc scid Il2rg tm1Wjl /SzJ (NSG) mice xenotransplanted with T‐ALL PDX or cord blood cells treated with dopamine receptor antagonists for 18 h and engraftment levels were determined after 3 or 8 week respectively. The effect on lysosomes and autophagy was determined using the lysotracker and CytoID stainings by flow cytometry and fluorescence microscopy. Results: Among all subtype‐specific dopamine receptor modulators, only antagonists specific for dopamine receptor type 4 (DR4) (L741‐742, Nemonapride, RBI 257) significantly reduced cell viability in T‐ALL cells in the low microMolar range, while no effect on healthy cells was observed. In vivo studies further confirmed the differential antileukaemic effect, as the treatment with L741‐742 significantly reduced leukaemic engraftment, while sparing normal haematopoiesis. T‐ALL cell lines lacked the expression of DR4 on the surface; thus, we searched for an alternative mechanism of action. Our data demonstrated that these drugs produced an expansion of the lysosomal compartment and consequently the failure of the cell recycling system, this induced an overactivation of autophagy and the disruption of cell homestasis, eventually leading to cell death. These 3 antileukaemic DR4 antagonists shared cationic amphiphilic properties, known to induce tropism towards lysosomes, thus providing an explanation for early drug‐induced events, which could ultimately activate the autophagy‐dependent cell death program. Summary/Conclusion: A group of DR4 antagonists selectively eliminates T‐ALL cells, targeting the lysosomal compartment in a dopamine receptor‐independent manner. This organelle disruption leads to the activation of the autophagy‐dependent cell death program. Interestingly, these drugs have little effects in healthy blood cells. Therefore, our results support the further preclinical development of these drugs as potential treatments for T‐ALL.