Unravelling biological heterogeneity in neoplastic myeloproliferative stem cells

One of the key challenges in cancer biology is to better understand why patients with the same subtype of cancer show remarkably different responses to treatment. One emerging explanation for this observation is that not all cells within a specific cancer behave in the same way. This partly reflects variability in the types of DNA damage or mutation(s) carried within each cell but might also be related to the type of cell which carries the mutation(s) as only some cancer cells, known as cancer stem cells (CSCs), are able to propagate disease relapse in patients. Our ability to understand the biology underlieing this variability is limited as most methods of analysing cancer cells involve pooling large populations of cancer cells, often many millions of cells, and thus the variability within individual cells is lost. This is important as the cancer cell which ultimately cause relapse following treatment may in some cases only account for a small proportion of cancer cells at diagnosis; akin to "finding a needle in a haystack". One approach that can be used to overcome this is to analyse single cancer cells. Whilst single cell analysis is not a new approach, previous methods have been limited by issues of sensitivity and technical variation making it difficult to understand which of the findings are "real" and which simply reflect "noise" in the testing process. An exciting new technology, introduced to the WIMM by AJM, allows analysis of single cancer cells, thus overcoming the above limitations. This technology will allow both mutation testing and analysis of the expression of genes all from the same cell, thus allowing presence of specific mutations to be correlated with the biology of single cells and also, most importantly, outcome of the patient. During this fellowship, AJM will develop and apply single cell analysis to a particular form of blood cancer known as myeloproliferative neoplams (MPN). Chronic myeloid leukaemia (CML) is a type of MPN which can now be highly effectively treated with a drug called imatinib. Whilst imatinib induces remissions in almost all patients with CML, the disease remains detectable in the large majority of patients due to the presence of imatinib resistant CML-CSCs. As these CML-CSCs are "hidden" amongst the normal bone marrow stem cells, single cell analysis is required to distinguish CML-CSCs form their normal counterparts in order to understand how these CSCs might be more effectively treated. A similar strategy will be used to investigate high-risk MPN patients receiving novel JAK2 inhibitor treatment, an exciting new treatment for patients with certain types of MPN. Whilst JAK2 inhibitor treatment induces symptomatic improvement in patients, it is also clear that MPN-CSCs are largely unaffected by the treatment and single cell analysis of MPN-CSCs will help to understand the reasons for this. Importantly, whilst these studies are specific to MPNs, as this is the area of clinical medicine in which AJM specialises, the findings of these studies will also be more broadly applicable across cancer biology. In order to understand how different types of cells respond to the acquisition of specific cancer causing mutations, a complementary approach is required. AJM will develop a number of model systems allowing the selective targeting of combinations of different MPN causing mutations to different types of bone marrow stem cells. It is possible, for example, that the same mutation may behave very differently depending on the cell type which originally acquires the mutation, thus influencing influence the resulting disease type, even though the mutation might remain the same. Through application of these state of the art cell and molecular biology techniques in humans and model systems, these studies will provide a substantial contribution to the understanding of MPN-CSCs and the findings will highlight the clinical applicability of single cell technology across cancer biology.