Next generation leukemia diagnostics and therapy through p53 isoform analysis

Acute myeloid leukemia (AML) is an aggressive cancer of the white blood cells, originating in the bone marrow, causing leukemic cells to replace production of normal blood cells. Acute leukemia is traditionally treated with chemotherapy, and in younger fit patients the therapy is consolidated by stem cell transplantation. However, not all patient groups respond well to transplantation. Patients above 70 years of age have a poor prognosis, with a 2-year survival rate of below 20%. Notably, leukemia therapy has not changed substantially during the last 15 years. The main problem is that current therapy does not sufficiently distinguish between different patients, and within a single patient the therapy does not sufficiently distinguish between different pools of cancer cells occurring in each patient. These cancer cell subsets are characterized by differing activity of certain genes and their product proteins that have important functions for normal behavior of blood cells: in our project we are focusing on one such important protein called p53. As of now clinical researchers do not have a complete overview over the function and regulation of such genes and proteins, and they do not yet have reliable tools for predicting whether a patient will respond well to available/offered chemotherapeutic drugs. One of these proteins, which we believe is important in development and progression of leukemia, is the p53 protein. p53 is a transcription factor, crucial in the protection of DNA and cell integrity. The TP53 gene is mutated in over 50% of cancers, especially in solid tumors. However, in leukemia p53 is rarely mutated, but its function is rather disturbed by dysregulation. The genetic information coding p53 protein in humans is the origin of 12 separate protein variants, also called protein isoforms, due to alternative transcription initiation and differential splicing of its pre-mRNA. These protein isoforms are differently expressed in different tissues throughout the human body. Others and we have reported these isoforms to be aberrantly expressed in various cancers. The p53 isoforms have distinct functions, both alone and in orchestra with the other isoforms. We have previously reported p53 isoform expression in AML, and that certain p53 expression profiles correlate with response to treatment. In this project we have studied the p53 isoform expression map in in different cancer clones to study if this varies between patients. We have analyzed p53 isoform expression on both protein and mRNA levels, by novel and well-established methodologies. Further, we have performed functional studies of p53 isoforms with the aim to find the optimal treatment plan based on p53 isoform expression as a diagnostic indicator. This holds great potential for possibility in predicting therapy responses in individual patient.

Prosjektet har en tilnærming som grunnforskning til funksjon av p53 isoformer. Betydningen av p53 isoformer trenger mer modning, og likeledes trenger vi nye verktøy.

Acute myeloid leukemia (AML) is an aggressive bone marrow cancer with median age of 70 years and overall survival below 20%. Since 2017 novel targeted therapies have been approved and will change the therapeutic reallity for upto 50% of the patients. At least three of the new molecules in development is targeting wild type or mutated p53 protein. TP53 is encoding the p53 protein, and p53 is a stress sensor and guardian of genomic damage in cells. In general, approximately 50% of all cancers comprise mutated TP53. However, TP53 is only mutated in about 10% of AML. Patients with mutated TP53 have poor prognosis compared to wild type TP53 AML, a poor prognostic marker shared among all hematopoietic malignancies. We have previously shown than p53 protein is rapidly stabilized in AML hours after start of chemotherapy (Anensen et al. 2006), and the gene expression is dominated by p53 induced genes at least up to 24 hours (Øyan et al. 2009). is However ...... Therapy of acute myeloid leukemia (AML) has not changed substantially the last 15 years, and patients above 70 years of age have median survival of only 2-3 months while patients 18-65 years of age in general not exceed three years survival of 50%. p53 is rigorously regulated through pre-mRNA splicing, extensive posttranslational protein modifications directing complex formation, subcellular localization and protein stabilization. We hypothesize that isoform specific degradation of p53 splicing isoforms beta and gamma represent a new regulatory mechanism that are druggable through novel sophisticated p53-targeted therapy. Modulation of the p53 isoforms in AML patients will be analysed early after induction chemotherapy through analysis of signal networks. Results from these studies will be employed for enhancement of therapy through resolution of chemoresistance. Validation of p53 protein isoform distribution in prognostication of AML and functional validation of isoform expression in chemoresistance will be performed in murine models of AML including patient derived xenografts and bone marrow transplanted TP53 knock-out. Identification of multiple AML subclones based on profiling of phosphorylation-based signalling will be extended into analyses of subclone specific p53 isoforms and posttranslational modifications. Together, this project will build biological evidence of p53 as therapy target as well as biomarker in prognostication and in monitoring of targeted therapy response in aggressive blood cancer.