Combination p53 activation and BCL-xL/BCL-2 inhibition as a therapeutic strategy in high-risk and relapsed acute lymphoblastic leukemia.

Due to the rarity of TP53 mutations in acute lymphoblastic leukemia (ALL), p53 re-activation by antagonism of the p53-MDM2 interaction represents a potential therapeutic strategy for the majority of ALL. Here, we demonstrate the potent antileukemic activity of the MDM2 antagonist idasanutlin in high-risk and relapsed ex vivo coculture models of TP53 wildtype ALL (n = 40). Insufficient clinical responses to monotherapy MDM2 inhibitors in other cancers prompted us to explore optimal drugs for combination therapy. Utilizing high-throughput combination screening of 1971 FDA-approved and clinically advanced compounds, we identified BCL-xL/BCL-2 inhibitor navitoclax as the most promising idasanutlin combination partner. The idasanutlin-navitoclax combination was synergistically lethal to prognostically-poor, primary-derived and primary patient blasts in ex vivo coculture, and reduced leukemia burden in two very high-risk ALL xenograft models at drug concentrations safely attained in patients; in fact, the navitoclax plasma concentrations were equivalent to those attained in contemporary "low-dose" navitoclax clinical trials. We demonstrate a preferential engagement of cell death over G1 cell cycle arrest, mechanistically implicating MCL-1-binding pro-apoptotic sensitizer NOXA. The proposed combination of two clinical-stage compounds independently under clinical evaluation for ALL is of high clinical relevance and warrants consideration for the treatment of patients with high-risk and relapsed ALL.

Targeting WEE1 kinase as a p53-independent therapeutic strategy in high-risk and relapsed acute lymphoblastic leukemia.

BACKGROUND: Outcomes for patients with relapsed acute lymphoblastic leukemia (ALL) are poor and there is a need for novel therapies to improve outcomes. Targeted inhibition of WEE1 with small-molecule inhibitor adavosertib (AZD1775) has emerged as a therapeutic strategy to sensitize cancer cells to DNA-damaging chemotherapeutics, particularly in the context of TP53-mutated tumors. However, WEE1 inhibition as a potential therapeutic strategy for patients with high-risk and relapsed ALL, including those with TP53 mutations, has not been definitively evaluated. METHODS: Anti-leukemic effects of adavosertib were investigated using a relapsed TP53 isogenic cell model system, primary patient, and patient-derived ALL samples (n = 27) in an ex vivo co-culture model system with bone marrow-derived mesenchymal stem cells. Combination effects with drugs currently used for relapsed ALL were quantified by Excess over Bliss analyses. Investigations for alterations of cell cycle and apoptosis as well as related proteins were examined by flow cytometry and Western blot, respectively. RESULTS: Our study demonstrates the potent anti-leukemic activity of the clinically advanced WEE1 inhibitor adavosertib in a large majority (n = 18/27) of high-risk and relapsed ALL specimens at lower than clinically attainable concentrations, independent of TP53 mutation status. We show that treatment with adavosertib results in S-phase disruption even in the absence of DNA-damaging agents and that premature mitotic entry is not a prerequisite for its anti-leukemic effects. We further demonstrate that WEE1 inhibition additively and synergistically enhances the anti-leukemic effects of multiple conventional chemotherapeutics used in the relapsed ALL treatment setting. Particularly, we demonstrate the highly synergistic and cytotoxic combination of adavosertib with the nucleoside analog cytarabine and provide mechanistic insights into the combinational activity, showing preferential engagement of apoptotic cell death over cell cycle arrest. Our findings strongly support in vivo interrogation of adavosertib with cytarabine in xenograft models of relapsed and high-risk ALL. CONCLUSIONS: Together, our data emphasize the functional importance of WEE1 in relapsed ALL cells and show WEE1 as a promising p53-independent therapeutic target for the improved treatment of high-risk and relapsed ALL.

Biallelic TET2 mutations confer sensitivity to 5'-azacitidine in acute myeloid leukemia.

Precision medicine can significantly improve outcomes for patients with cancer, but implementation requires comprehensive characterization of tumor cells to identify therapeutically exploitable vulnerabilities. Here, we describe somatic biallelic TET2 mutations in an elderly patient with acute myeloid leukemia (AML) that was chemoresistant to anthracycline and cytarabine but acutely sensitive to 5'-azacitidine (5'-Aza) hypomethylating monotherapy, resulting in long-term morphological remission. Given the role of TET2 as a regulator of genomic methylation, we hypothesized that mutant TET2 allele dosage affects response to 5'-Aza. Using an isogenic cell model system and an orthotopic mouse xenograft, we demonstrate that biallelic TET2 mutations confer sensitivity to 5'-Aza compared with cells with monoallelic mutations. Our data argue in favor of using hypomethylating agents for chemoresistant disease or as first-line therapy in patients with biallelic TET2-mutated AML and demonstrate the importance of considering mutant allele dosage in the implementation of precision medicine for patients with cancer.

Regulation of CHK1 inhibitor resistance by a c-Rel and USP1 dependent pathway.

Previously, we discovered that deletion of c-Rel in the Eµ-Myc mouse model of lymphoma results in earlier onset of disease, a finding that contrasted with the expected function of this NF-κB subunit in B-cell malignancies. Here we report that Eµ-Myc/cRel-/- cells have an unexpected and major defect in the CHK1 pathway. Total and phospho proteomic analysis revealed that Eµ-Myc/cRel-/- lymphomas highly resemble wild-type (WT) Eµ-Myc lymphomas treated with an acute dose of the CHK1 inhibitor (CHK1i) CCT244747. Further analysis demonstrated that this is a consequence of Eµ-Myc/cRel-/- lymphomas having lost expression of CHK1 protein itself, an effect that also results in resistance to CCT244747 treatment in vivo. Similar down-regulation of CHK1 protein levels was also seen in CHK1i resistant U2OS osteosarcoma and Huh7 hepatocellular carcinoma cells. Further investigation revealed that the deubiquitinase USP1 regulates CHK1 proteolytic degradation and that its down-regulation in our model systems is responsible, at least in part, for these effects. We demonstrate that treating WT Eµ-Myc lymphoma cells with the USP1 inhibitor ML323 was highly effective at reducing tumour burden in vivo. Targeting USP1 activity may thus be an alternative therapeutic strategy in MYC-driven tumours.