Exploiting genomic instability in Acute Myeloid Leukemia: when TP53 fails.

Acute myeloid leukemia (AML) is a myeloid neoplasm with a heterogenic genomic background and a poor prognosis. The main aims of this thesis are to deepen the pathogenic mechanism of genomic instability (1) and drug-resistance (2) p53-related, in order to identify new targets and biomarker of response through genomic and in vitro approaches. (1) A peculiar mechanism of genomic instability is chromothripsis, a one-step genome-shattering catastrophe resulting from disruption of one or few chromosomes in multiple fragments and consequent random rejoining and repair. Chromothripsis was detected with a custom algorithm in 26/395 patients. Patients harboring chromothripsis had a poor overall survival, higher age (p = .002), ELN2107 high risk (HR), lower white blood cell count, TP53 loss and/or mutations while FLT3 and NPM1 mutations were mutually exclusive with chromothripsis. Chromothripsis-positive patients presented the hallmarks of chromosome instability [TP53 alteration, 5q deletion, a higher mean of copy number alteration, complex karyotype, alterations in DNA repair and cell cycle]. CBA and FISH showed that chromothripsis was associated with marker, derivative and ring chromosomes. (2) PPM1D is a promising oncogene coding for “Wild type p53-Inducible Phosphatase 1” (WIP1) which negatively regulates p53 and several proteins involved in the DNA damage response. A recent study has demonstrated that PPM1D inhibition by GSK2830371 reverses chemotherapy resistance to Cytarabine. The aim of this work is to investigate whether the inhibition of WIP1 by GSK2830371 could increase the sensitivity to MDM2 inhibitor Nutlin-3a to obtain a novel therapeutic strategy for AML patients restoring p53 activity. Our study showed that in vitro pharmacological inhibition of WIP1 by GSK2830371 potentiates the sensitivity to Nutlin-3a, a MDM2 inhibitor, in AML cells by stabilizing the activity of p53 by activating apoptosis and other p53-downstream genes and pathways, as confirmed by gene expression profile and western blot analyses of treated AML cells.