In vivo modelling of mutation order and oncogene addiction in myeloproliferative neoplasms

Aims

To develop a novel myeloproliferative neoplasm (MPN) in vivo model allowing conditional and reversible expression of the JAK2V617F mutation in order to address the following questions:
1.What is the impact of order of acquisition of cooperating somatic mutations on disease phenotype?
2.Following the development of overt disease, is the phenotype fully reversible following genetic correction of the mutation?

Background and project overview

It has also long been recognized that tumours evolve through serial acquisition of somatic driver mutations through an often highly complex process of genetic diversification and clonal selection. However, the precise mechanisms by which mutated genes interact to generate overt neoplastic disease remain largely unclear. Myeloproliferative neoplasms (MPNs) are incurable clonal diseases characterised by frequent presence of the activating JAK2V617F mutation which often occurs together with other collaborating mutations, most frequently inactivating mutations of the epigenetic regulators TET2 or DNMT3A. Thus, MPNs are an excellent tractable disease model to better understand how different genetic lesions cooperate during development of neoplastic disease.

In MPNs, cooperating mutations are acquired in a stepwise manner, and recent evidence arising from analysis of MPN patient samples has raised the possibility that the order of acquisition of these mutations can have a profound impact on the resulting disease phenotype. Furthermore, advances in molecularly targeted therapy and genome editing techniques present new opportunities to target the JAK2 mutation in patients. However, clinical experience with JAK2 inhibitors has been disappointing due to their failure to fully reverse the disease phenotype in patients, raising the possibility that the mutation might cause irreversible damage to the stem cell that acquires it. However, an alternative explanation is that JAK2 inhibitor treatments currently fail to effectively inhibit JAK2 signalling.

In order to address these issues, we have developed a novel mouse model that will allow conditional activation of the JAK2V617F mutation either in isolation, or before/after collaborating mutation of TET2 or DNMT3A (all models already available). Further, this model will also allow subsequent deletion of the JAK2V617F mutation in order to determine the reversibility of the resulting disease. Beyond simply reversing the disease phenotype, one additional possibility is that MPN stem cells become “addicted” to oncogenic JAK2V617F signalling and will therefore be selectively eradicated when the mutation is removed.

This project will involve deep characterisation of the phenotype associated with this novel JAK2V617F mouse model using a combination of state of the art stem cell assays and molecular techniques, including single cell analysis. Disease mechanisms will be further explored using cutting edge genome editing approaches in order to modify candidate target genes. This project provides an opportunity to address some fundamental questions in cancer biology with the potential to have a high impact on the field.