In vivo targeting leukaemic fusion genes with siRNAs

A research team based at Newcastle University working with a co-investigator at the University of Stuttgart aim to develop a non-toxic therapeutic drug to treat a specific type of leukaemia prevalent in children. Leukaemia occurs due to a genetic change (mutation) within the DNA of bone marrow cells. This results in a mutant RNA transcript which produces an improperly functioning protein. The result is failure of the normal control mechanism for cell development and the uncontrolled growth of white blood cells. The current treatment is chemotherapy with highly toxic and non-specific drugs. Chemotherapy can affect all cells in the body leading to side effects ranging from general ill health during treatment but also, often life-threatening long term damage to organs and unfortunatly imparement or even loss of fertility. The proposed novel therapeutic approach comprises a tiny particle which specifically recognises and attaches to leukaemic cells and then delivers a unique genetic component (so-called short interfering RNAs or siRNAs) into the leukaemic cell. This siRNA adds a second degree of specificity as it recognises and binds only to the unique mutant RNA in the leukaemic cells. This prevents production of the mutant protein and so stops the aberant excessive cell division characteristic of the disease. The particle itself is a mix of fats and protein combined with the siRNA, so the therapy is non toxic to normal cells but lethal to leukaemic cells.

Fusion oncogenes and their encoded products provide ideal targets for leukaemia-specific therapeutic strategies because of their exclusive expression in leukaemic cells. However, the majority of these fusion proteins are transcription factors, which are difficult to target with conventional small molecule-based approaches. Using RNA interference (RNAi) with small inhibitory RNA (siRNA), we have demonstrated that several fusion proteins are indispensable for the maintenance of leukaemic growth both in vitro and in vivo. We propose a therapy based on a targeted siRNA delivery system which provides a highly selective approach towards the transformed cells but will not affect healthy haematological cells. We have developed antibody-conjugated nanoparticles which efficiently deliver siRNAs to leukaemic cells subsequently causing a knock-down of the targeted fusion gene. This has been demonstrated as a potential target specific siRNA therapy for Acute Myeloid Leukaemia (AML) in cell culture and murine transplantation models. In the proposed project, we will determine if this Antibody Targeted Nanoparticle (AnTaNa) approach overcomes the problem of delivering sufficient siRNA to be therapeutically effective by assessing the in vivo efficacy, toxicity, pharmacokinetics and -dynamics in murine xenotransplantation models. A specific and efficient antileukaemic effect in these model systems would provide a strong impetus for progressing to clinical studies.