About the Project
Approximately 30 years ago, Poly ADP Ribose Polymerase (PARP) activity was shown to play a critical role in the processes of DNA repair in nucleated cells. PARP1 and PARP2, which function as homo- and as hetero-dimers, are two essential components of base excision repair. Although, PARP1 provides the majority of PARP activity in the cell, as many as 17 proteins have now been identified to share homology to the catalytic domain of PARP1. Amongst the more characterized are PARP5 (Tankyrase1) and PARP6 (Tankyrase2) known to be involved in telomere maintenance and are essential for resolving sister telomeres during mitosis. In the main, the function and cellular compartment of PARP family members are unknown. However, the PARPs have been shown to regulate transcription and cell signalling and thus play key roles in a number of biological processes such as cell differentiation, inflammation and stem cell function.
In addition, to discovering the DNA repair activity of PARP, those seminal researchers postulated that inhibition of PARP activity could provide a potential, novel modality for cancer therapy. However, it wasn’t until 2005 that the major breakthrough was achieved when it was realized that the inhibition of PARP activity and a BRCA deficiency seen in familial breast and ovarian cancers in combination of would be lethal. Now with significant single agent anti-tumour responses coupled with a wide therapeutic index have been influential in moving PARP inhibitors to the clinical arena. There are currently over 60 clinical trials in progress in which PARP inhibitors are being tested in a very wide range of malignancies, including breast and ovarian cancers.
To fully realize the potential of PARP inhibitors, the multifunctional and ubiquitous nature of PARP activity requires investigation and is the basis for this project.
1. 17 proteins have been determined to have PARP activity and the specificity of PARP inhibitors to PARP1 is essential in reducing non-PARP1 related side-effects. The inhibitory effects of PARP inhibitors on individual PARPS such as the tankyrases (PARP 5 and 6) would be studied using specific RNA interference experiments to disrupt tankyrase expression and to investigate subsequent telomere maintenance properties. Moreover, the potential difference in expression levels of PARP isoforms in normal versus cancer cells has the potential to affect the therapeutic window and the efficacy of PARP inhibition. RNA interference and expression analysis of various PARPs would be performed to validate PARP inhibitor specificity and expression of PARP isoforms in normal versus cancer cells.
2. Little is also known of the long term inhibition of PARP1 in terms of its effects on bone marrow function and differentiation. PARP1 has been previously shown to modulate stem cell function. As leukaemia is a disorder of haematopoietic progenitors associated with increased bone marrow apoptosis and peripheral cytopenia, the therapeutic benefit of PARP inhibition in leukaemia requires further investigation. In vitro long term culture of haematopoietic stem cells and progenitors with PARP inhibitors are required to determine the effects on haematopoietic stem cell function and differentiation. As PARP is also associated with differentiation of cardiac, lymphocyte and muscle cells, how the administration of PARP inhibitors affects the relative differentiation of leukaemic versus normal cells further exemplifying the need for further insight into long term inhibition of PARP activity. Gene expression profiling will be used to study PARP inhibitor dependent changes in cellular differentiation.
3. Numerous studies reported the role of PARP1 in the inflammatory response by acting as a co-activator of NF-B to regulate pro-inflammatory genes. PARP1 has also shown to be required for immunoglobulin class switching in B cells. Moreover, Inhibition of PARP1 abrogates lymphocyte production and cytokine induction, whilst PARP1 deficiency has been shown to promote differentiation and expansion of T-regs (CD4+, CD25+, and FOXP3+). Disruption of immune function is likely to significantly affect the efficacy of response to PARP inhibitor therapy. We will employ immunological analysis to study the effect of PARP inhibitor on immune function.
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