In vivo modulation of the stem cell programme of cancer stem cells in childhood acute lymphoblastic leukaemia

Lead Research Organisation: Newcastle University
Department Name: Northern Institute for Cancer Research


A number of cancers are thought to be maintained by a rare population of stem cells which are able to evade current therapies. These cancer stem cells are able to divide an infinite number of times, as well as being able to develop into each of the different cells within a tumour. This means that if they are not completely removed by initial treatment, they are able to initiate relapse of the cancer. Unlike many tumours, we have shown that in childhood acute lymphoblastic leukaemia, cancer cells at different stages of development are able to behave as stem cells. The aim of this fellowship is to investigate the genetic programme which allows these leukaemic cells to cause relapse.
The gene PIWIL2 is known to be important in testicular stem cells, which form sperm. PIWIL2 has also been found in a number of cancers, including childhood leukaemia. By both preventing and forcing leukaemic cells to make PIWIL2, we can assess the effects of this gene on those cellsā€˜ ability to cause disease relapse. We will look at the genetic pathways associated with PIWIL2 to identify additional important genes which may, in future, provide targets against which new drugs can be developed.

Technical Summary

Cancer stem cells demonstrate the core stem cell properties of self-renewal and differentiation into all cells of the tumour tissue. Activation of a genetic stem cell programme may allow them to express, in addition to these core properties, protective mechanisms such as drug resistance and DNA repair pathways. In some malignancies, including acute myeloid leukaemia, cancer stem cells are found only in a single, defined, cell population. However, we have shown that in childhood acute lymphoblastic leukaemia, cells at multiple stages of immunophenotypic maturation display stem cell behaviour.
The aim of this fellowship is to assess the importance of the germline stem cell protein PIWIL2 to the cancer stem cell programme in childhood acute lymphoblastic leukaemia. Physiologically PIWIL2 is expressed primarily in testes where it functions via a distinct pathway of RNA interference. However, PIWIL2 has also been demonstrated in a number of malignancies, including both solid tumours and acute lymphoblastic leukaemias.
The functional importance of PIWIL2 in primary leukaemic blasts will be assessed by RNA knockdown and complementary over-expression studies. Initially, in vitro work will optimise this established technique for PIWIL2 in the childhood acute lymphoblastic leukaemia cell line, SEM. Subsequent work will develop a stable lentiviral transduction system to allow conditional modulation of PIWIL2 expression. Optimisation of this system for use in primary bone marrow blasts, taken at diagnosis from children with acute lymphoblastic leukaemia, will form the primary goal of this fellowship, followed by serial transplantation in a NOD/scid mouse model. Serial leukaemic engraftment will provide the most sensitive and specific measure of malignant stem cell activity in modulated blasts and will be accompanied by assessment of morphologic and immunophenotypic stability and confirmatory cytogenetic analysis. Finally, assessment of the self-renewal and differentiation potential of modulated blasts will be compared with their expression profiles to identify pathways related to the stem cell function of PIWIL2.
The opportunity that this fellowship offers is to investigate for the first time the programme underlying the biology of the cancer stem cell programme in childhood acute lymphoblastic leukaemia. Through understanding of the elements of this programme and the pathways with which they interact, it is hoped that subsequent work will identify suitable targets for development of novel therapeutics. Expression of PIWIL2 across a range of solid and haematological malignancies, in both children and adults, suggests that it is possible such a drug may have applications outside paediatric haemato-oncology.


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