Introduction Medulloblastoma is the most common malignant brain tumour in children. Chemoresistance and treatment toxicity are major problems for this disease. New effective and less toxic therapies are needed.
Short-Interfering-RNA’s (siRNA) are gene silencing molecules which have potential as a new class of cancer therapeutics. siRNA can be designed to inhibit any gene of choice including those which promote tumour growth and chemoresistance and are difficult to target using chemical agents. However, siRNA requires a delivery vehicle to enable it to enter cells and be released into the cytoplasm. The aim of this study was to design and generate nanoparticles which can deliver and release therapeutic siRNA into medulloblastoma cells and silence a gene (polo-like kinase-1, PLK1) which plays a major role in regulating their growth and chemosensitivity.
Material and methods Star-shaped nanoparticles (Star) were synthesised using RAFT polymerisation chemistry. Star size, surface charge and ability to package siRNA were assessed using dynamic light scattering, transmission electron microscopy and gel electrophoresis. Star-siRNA cellular internalisation and gene silencing activity was examined using correlative light electron microscopy, confocal microscopy, qPCR, western blotting and colony formation assay.
Results and discussions Star nanoparticles packaged siRNA with very high efficiency (>90% encapsulation efficiency, n=3) to form uniform nano-complexes (19.1 nm ±0.7) with a near neutral charge (5.8 mV ±0.2). Star-siRNA complexes were stable in human and mouse serum. Star-siRNA was internalised into medulloblastoma cells via endocytosis and siRNA was trafficked to the cytoplasm. Star-siRNA inhibited PLK1 protein expression by 70% (p<0.001, n=3) when compared to control cells (star-non-functional siRNA). Knockdown of PLK1 resulted in G2 cell cycle arrest (p<0.001) and DNA damage. This led to the induction of apoptosis and cell death (p<0.001). Star-PLK1 siRNA also sensitised cells to cisplatin.
Conclusion This is the first study to demonstrate that star nanoparticles can deliver siRNA to medulloblastoma cells. This nanomedicine may be a new therapeutic tool which has potential to revolutionise medulloblastoma treatment and could enhance precision-medicine where it can be used to inhibit the expression of any tumour-promoting gene or cocktail of genes personalised to the genetic profile of a patient’s tumour.
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