Dr Holly Holliday

My interests lie in the regulation of stem cells during development and disease. We are currently working on developing microRNA-based therapeutics for the treatment of the childhood cancer neuroblastoma.


MicroRNA-based therapeutics for the treatment of high-risk neuroblastoma

Holly Holliday1,2, Eoin Dodson1,2, Iva Nikolic3, Niantao Deng1,2, Benjamin Elsworth1,2, Kaylene Simpson3,4, Alvin Kamili5,6, Madeleine Wheatley5, Joshua McCarroll5, Glenn Marshall7, Jamie Fletcher5, Alex Swarbrick1,2

1 Garvan Institute of Medical Research, Darlinghurst, NSW, Australia 
2 St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Darlinghurst, NSW, Australia
3 Victorian Centre for Functional Genomics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia 
4 Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, VIC, Australia
5 Children's Cancer Institute, Lowy Cancer Research Centre, University of New South Wales, Kensington, NSW, Australia 
6 School of Women's and Children's Health, University of New South Wales, Kensington, NSW, Australia 
7 Sydney Children's Hospital and Children's Cancer Institute, Kensington, NSW, Australia

Neuroblastoma is the most common extra-cranial solid cancer of childhood. High-risk patients have a 5-year survival rate below 50%. Treatment for these patients involves high-dose multi-layered chemotherapy, which is often not curative and causes severe health impacts later in life. There is therefore an urgent need to find alternative drugs to either replace or significantly improve upon conventional therapy. MicroRNAs (miRNA) are potent regulators of gene expression and are emerging as an exciting new class of therapeutic. However, our understanding of miRNA function in neuroblastoma is fragmented, restricting our ability to capitalise on their therapeutic potential.

We aim to screen and validate miRNAs that sensitise neuroblastoma cells to chemotherapy in vitro. Candidate therapeutic miRNAs will then be used to treat pre-clinical models of high-risk neuroblastoma.

We have performed a functional genomic screen of >1200 miRNA mimics in the Kelly cell line, a model of poor-prognosis disease. This was performed in combination with low doses (IC30) of doxorubicin and vincristine. Selected candidate miRNAs are currently being tested in the pre-clinical COG-N-519 patient-derived xenograft (PDX) model, originating from a patient with high-risk disease after several lines of treatment. Star-POEGMA nanoparticles are being used to deliver candidate miRNAs in combination with chemotherapy. Ongoing work includes mechanistic experiments to assess miRNA uptake and their impact on gene expression, and therapeutic experiments to monitor tumour growth and survival.

Three miRNAs, miR-99b-5p, miR-380-3p and miR-485-3p, had potent synthetic lethal interaction with doxorubicin in vitro. Analysis of a clinical cohort revealed that these miRNAs are putative tumour suppressors as they undergo recurrent copy number loss, and low expression predicts poor outcome. Excitingly, the candidate miRNA miR-99b-5p can be effectively delivered into neuroblastoma PDX tumour cells by nanoparticle injection. RNA-Sequencing analysis of miR-99b-5p-treated tumours revealed a decrease in expression of key neuroblastoma dependency genes MYCN, PHOX2B, HAND1/2, GATA3, ISL1 and EZH2. Importantly, many of these genes encode transcription factors, which are considered to be 'undruggable'. Additionally, gene set enrichment analysis revealed upregulation of neuronal differentiation pathways, suggesting that miR-99b-5p is able to reprogram neuroblastoma cells towards a less aggressive cell fate.

We have identified novel chemosensitising miRNAs in the context of neuroblastoma that can be administered in vivo to drive favourable gene expression changes. We predict that restoring the function of tumour suppressive miRNAs in neuroblastoma patients will increase therapeutic outcome, while reducing the toxicity associated with conventional high-dose chemotherapy.