Despite considerable progress, the treatment of acute leukemia continues to be a challenge for a significant majority of patients. Using a well-characterized preclinical mouse model of acute promyelocytic leukemia (APL), we evaluated here the antileukemic efficacy of RT53, an anticancer peptide with potential immunological properties. Our results indicate that RT53 possesses a direct antileukemic effect, even at a late stage. We also demonstrate that a single injection of a vaccine consisting of leukemic blasts exposed to RT53, which induces the hallmarks of immunogenic cell death, was highly effective in preventing leukemia development in both prophylactic and therapeutic settings. The vaccine comprising RT53-treated APL cells generated long-term antileukemic protection and depletion experiments indicated that CD4 + T cells were of crucial importance for vaccine efficacy. Combined, our results provide the rationale for the exploration of RT53-based therapies for the treatment of acute leukemia.
BET inhibitors (BETi) including OTX015 (MK-8628) and JQ1 demonstrated antileukemic activity including NPM1c AML cells. Nevertheless, the biological consequences of BETi in NPM1c AML were not fully investigated. Even if of better prognosis AML patients with NPM1c may relapse and treatment remains difficult. Differentiation-based therapy by all trans retinoic acid (ATRA) combined with arsenic trioxide (ATO) demonstrated activity in NPM1c AML. We found that BETi, similar to ATO + ATRA, induced differentiation and apoptosis which was TP53 independent in the NPM1c cell line OCI-AML3 and primary cells. Furthermore, BETi induced proteasome-dependent degradation of NPM1c. BETi degraded NPM1c in the cytosol while BRD4 is degraded in the nucleus which suggests that restoration of the NPM1/BRD4 equilibrium in the nucleus of NPM1c cells is essential for the efficacy of BETi. While ATO + ATRA had significant biological activity in NPM1c IMS-M2 cell line, those cells were resistant to BETi. Gene profiling revealed that IMS-M2 cells probably resist to BETi by upregulation of LSC pathways independently of the downregulation of a core BET-responsive transcriptional program. ATO + ATRA downregulated a NPM1c specific HOX gene signature while anti-leukemic effects of BETi appear HOX gene independent. Our preclinical results encourage clinical testing of BETi in NPM1c AML patients.
Introduction: The dual-specificity protein kinase, monopolar spindle 1 (Mps1) is one the main kinases of the spindle assembly checkpoint (SAC) critical for accurate segregation of sister chromatids during mitosis. A hallmark of cancer cells is chromosomal instability caused by deregulated cell cycle checkpoints and SAC dysfunction. Mps1 is known to be overexpressed in several solid tumors including triple negative breast cancer. Thus, Mps1 seems to be a promising target and small molecules targeting Mps1 entered clinical trials in solid tumors. ALL originates from malignant transformation of B-and T-lineage lymphoid precursors with a variety of genetic aberrations including chromosome translocations, mutations, and aneuploidies in genes responsible for cell cycle regulation and lymphoid cell development. While outcome is excellent for pediatric patients and younger adults, relapsed and refractory disease still remain a clinical challenge for elder patients. Here, we demonstrate for the first time preclinical efficacy of the small molecule Mps1 inhibitor (Mps1i) S81694 in T- and B- ALL cells including BCR-ABL1+-driven B-ALL. Materials and Methods: Expression of Mps1 was determined by RT-qPCR and WB in JURKAT, RS4-11 and BCR-ABL1+ cells (BV-173 and TOM-1). A small molecule Mps1i (S81694) was tested alone (0 to 1000nM) or in combination with imatinib, dasatinib, nilotinib and ponatinib in BCR-ABL1+ ALL cell lines. Cell viability and IC50 was assessed by MTS assays after exposure to Mps1i for 72h. In combination experiments, compounds were added simultaneously and relative cell numbers were determined at 72h with MTS assays and combination index (CI) values were calculated according to the Bliss model. Induction of apoptosis was evaluated by annexin-V exposure and PI incorporation at 72h with increasing doses of Mps1i. Cell-cycle distribution was determined by cytofluorometric analysis detecting nuclear propidium iodide (PI) intercalation at 48h. Phosphorylation of Mps1 was detected in synchronized (by nocodazole and MG-132) cells by immunofluorescence using an anti phospho-Mps1 antibody detecting Thr33/Ser37 residues. Time-lapse microscopy was used in cell lines in presence or absence of S81694 to determine mitosis duration. Bone marrow (BM) nucleated patient cells were obtained after informed consent and incubated in methylcellulose with cytokines with or without Mps1i for 2 weeks to determine colony growth. Results: Expression of Mps1 could be detected by RT-qPCR and at the protein level by WB in all cell lines (Figure 1A and B ). IC50 after Mps1i exposure alone was 126nM in JURKAT cells, 51nM in RS4-11 cells, 75nM in BV-173 cells and 83nM in TOM-1. Significant apoptosis as detected by phosphatidylserine exposure and PI incorporation in all cell lines with BCR-ABL1+ cell lines BV-173 and TOM-1 cells being the most sensitive (80% and 60% apoptotic cells respectively)(Figure 1C). Upon Mps1i exposure we observed targeted inhibition of Mps1 phosphorylation at Thr33/Ser37 residues indicating the specific on target effect of S81694 by inhibiting Mps1 autophosphorylation (Figure 1D and E). Cell cycle profile was generally lost after treatment with S81694 in all cell lines indicating aberrant 2n/4n distribution due to SAC abrogation (Figure 1F). Furthermore, we demonstrated that S81694 exposure accelerated significantly mitosis in BV-173 cell line from 36 minutes to 19 minutes indicating effective inhibition of SAC function (Figure 1G). Interestingly, S81694 induced significant apoptosis (70%) in the imatinib resistant BV173 cell line bearing the E255K-BCR-ABL1-mutation. Combination of S81694 with TKI imatinib, dasatinib and nilotinib (but not ponatinib) was strongly synergistic in BCR-ABL1+ cells (Figure 1H). Finally, we observed inhibition of colony formation in a patient with BCR-ABL1+ B-ALL after exposure to 100nM and 250nM S81694 (reduction of 85% and 100% respectively)(Figure 1I). Conclusion: Mps1i S81694 yields significant preclinical activity in T-and B-cell ALL including BCR-ABL1+ models. Interestingly S81694 was efficacious in a TKI resistant cell line. Disclosures Kaci: Institut de Recherches Internationales Servier (IRIS): Employment. Garrido:Institut de Recherches Internationales Servier (IRIS): Employment. Burbridge:Institut de Recherches Internationales Servier (IRIS): Employment. Dombret:AGIOS: Honoraria; CELGENE: Consultancy, Honoraria; Institut de Recherches Internationales Servier (IRIS): Research Funding. Braun:Institut de Recherches Internationales Servier (IRIS): Research Funding.
Background: AML is a genetically heterogenous disease with poor prognosis and new treatments are needed. MPS1 is the main kinase of the spindle assembly checkpoint (SAC), critical for segregation of chromatids during mitosis. A hallmark of cancer cells is chromosomal instability caused by deregulated cell cycle checkpoints and SAC dysfunction. MPS1 inhibition has been investigated in several solid tumors but not yet in AML. Here, we demonstrate the efficacy of the small molecule MPS1 inhibitor (MPS1i) S81694 in AML cell lines, primary cells and mouse models. Materials and Methods: Cell viability, cell stress and apoptosis were assessed by MTS assays, DiOC2(3) or annexin-V modifications and PI incorporation after exposure to S81694. Cell-cycle and polyploidy were determined by cytofluorometry and FISH. Phosphorylation of MPS1 was detected in synchronized cells by immunofluorescence detecting phosphorylated Thr33/Ser37 residues. Protein modifications were studied by WB. Time-lapse microscopy was used to determine mitosis duration using cells stained with the SiR-DNA live cell probe. Bone marrow cells from patients were obtained after informed consent and incubated on a MSC feeder or in methylcellulose for colony formation assays. All animal studies were performed in accordance with the animal ethics committee's guidelines. NSG mice were sub-lethally-irradiated and injected with AML-NS8 or AML-PS patient derived xenografts. Mice were treated intravenously with S81694 or with vehicle. Results: IC50 for viability after S81694 exposure alone was <1000nM in a panel of 8 AML cell lines. Three cell lines had IC50 >1000nM: the NPM1cmut cell line OCI-AML3, OCI-AML3-TP53mut and K562. In the most sensitive cell lines, including OCI-AML2, S81694 led to inhibition of MPS1 auto-phosphorylation, induced significant cell stress and apoptosis as detected by mitochondrial membrane potential loss, phosphatidylserine exposure and PI incorporation. In these cell lines, the cell cycle was strongly affected by treatment with S81694 showing aberrant 2n/4n ploidy distribution due to SAC abrogation as well as polyploidy (8n and 16n). S81694 exposure triggered mitotic exit as shown by cyclin B1 downregulation and significantly accelerated mitosis. For treated OCI-AML2 and OCI-AML3 cells we observed induction of gamma-H2AX (ser139), p53 upregulation and downstream caspase-3 and PARP cleavage indicating that S81694 induces p53 dependent apoptosis. Furthermore, MPS1i induced downregulation of anti-apoptotic proteins MCL-1 and BCLXL. Finally, for AML patient derived blast cells cells we observed apoptosis after exposure to S81694 and significant reduction of colony number. In two AML PDX models, intravenous administration of S81694 was shown to improve significantly median survival time, as compared to control, by 28 to 41 days and by 33 to 46 days respectively. Conclusion: The MPS1i S81694 shows significant preclinical activity in vitro and in vivo in AML. Combinations with different drugs active in AML are ongoing. Citation Format: Anna Kaci, Emilie Adicéam, Etienne De Braekeleer, Marine Garrido, Jeannig Berrou, Mélanie Dupont, Hanane Djamai, Virginie Eclache, Baruchel André, Claude Gardin, Hervé Dombret, Mike Burbridge, Thorsten Braun. The MPS1 inhibitor S81694 is active in acute myeloid leukemia (AML) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 608.
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