Formulating RALA/Au nanocomplexes to enhance nanoparticle internalisation efficiency, sensitising prostate tumour models to radiation treatment

Lindsey A Bennie,Christopher Emmerson,Jie Feng,Jonathan A Coulter,Wendy B Hyland,Kyle B Matchett,Helen O Mccarthy

doi:10.1186/s12951-021-01019-8

Abstract

BackgroundGold nanoparticles (AuNP) are effective radiosensitisers, however, successful clinical translation has been impeded by short systemic circulation times and poor internalisation efficiency. This work examines the potential of RALA, a short amphipathic peptide, to enhance the uptake efficiency of negatively charged AuNPs in tumour cells, detailing the subsequent impact of AuNP internalisation on tumour cell radiation sensitivity.ResultsRALA/Au nanoparticles were formed by optimising the ratio of RALA to citrate capped AuNPs, with assembly occurring through electrostatic interactions. Physical nanoparticle characteristics were determined by UV–vis spectroscopy and dynamic light scattering. Nano-complexes successfully formed at w:w ratios > 20:1 (20 µg RALA:1 µg AuNP) yielding positively charged nanoparticles, sized < 110 nm with PDI values < 0.52. ICP-MS demonstrated that RALA enhanced AuNP internalisation by more than threefold in both PC-3 and DU145 prostate cancer cell models, without causing significant toxicity. Importantly, all RALA-AuNP formulations significantly increased prostate cancer cell radiosensitivity. This effect was greatest using the 25:1 RALA-AuNP formulation, producing a dose enhancement effect (DEF) of 1.54 in PC3 cells. Using clinical radiation energies (6 MV) RALA-AuNP also significantly augmented radiation sensitivity. Mechanistic studies support RALA-AuNP nuclear accumulation resulting in increased DNA damage yields.ConclusionsThis is the first study to demonstrate meaningful radiosensitisation using low microgram AuNP treatment concentrations. This effect was achieved using RALA, providing functional evidence to support our previous imaging study indicating RALA-AuNP nuclear accumulation.Graphic abstract

Highlights

Gold nanoparticles (AuNP) are effective radiosensitisers, successful clinical translation has been impeded by short systemic circulation times and poor internalisation efficiency
RALA effectively complexes with negatively charged citrate-AuNPs (− 27 mV ± 11.3) forming sub-110 nm particles at w:w ratios of 20 μg RALA:1 μg AuNP or above (Fig. 1A)
A positive surface charge promotes electrostatic repulsion of the condensed nanoparticles, preventing agglomeration, an adverse effect observed at w:w ratios of 15:1 or below

Summary

Introduction

Gold nanoparticles (AuNP) are effective radiosensitisers, successful clinical translation has been impeded by short systemic circulation times and poor internalisation efficiency. High-Z nanomaterials such as gadolinium (Z = 64), and gold (Z = 79) are proven radiosensitisers, but commercial development leading to widespread use in clinical practice has been hampered by issues that include short systemic circulation, endosomal entrapment and poor target cell uptake [6]. Hydrophilic arginine (R) residues are spatially segregated within its alpha-helical structure, residing on one face of the peptide, with hydrophobic leucine (L) residues located on the other. This confirmation was purposely designed to enhance cell membrane interactions.

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