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

BACKGROUND: Gold 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. RESULTS: RALA/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. CONCLUSIONS: This 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.

Exploiting the anticancer effects of a nitrogen bisphosphonate nanomedicine for glioblastoma multiforme.

Glioblastoma multiforme (GBM) is an incurable aggressive brain cancer in which current treatment strategies have demonstrated limited survival benefit. In recent years, nitrogen-containing bisphosphonates (N-BPs) have demonstrated direct anticancer effects in a number of tumour types including GBM. In this study, a nano-formulation with the RALA peptide was used to complex the N-BP, alendronate (ALN) into nanoparticles (NPs) < 200 nm for optimal endocytic uptake. Fluorescently labelled AlexaFluor®647 Risedronate was used as a fluorescent analogue to visualise the intracellular delivery of N-BPs in both LN229 and T98G GBM cells. RALA NPs were effectively taken up by GBM where a dose-dependent response was evidenced with potentiation factors of 14.96 and 13.4 relative to ALN alone after 72 h in LN229 and T98G cells, respectively. Furthermore, RALA/ALN NPs at the IC50, significantly decreased colony formation, induced apoptosis and slowed spheroid growth in vitro. In addition, H-Ras membrane localisation was significantly reduced in the RALA/ALN groups compared to ALN or controls, indicative of prenylation inhibition. The RALA/ALN NPs were lyophilised to enhance stability without compromising the physiochemical properties necessary for functionality, highlighting the suitability of the NPs for scale-up and in vivo application. Collectively, these data show the significant potential of RALA/ALN NPs as novel therapeutics in the treatment of GBM.

Cell-Penetrating Peptides as a Tool for the Cellular Uptake of a Genetically Modified Nitroreductase for use in Directed Enzyme Prodrug Therapy.

Directed enzyme prodrug therapy (DEPT) involves the delivery of a prodrug-activating enzyme to a solid tumour site, followed by the subsequent activation of an administered prodrug. One of the most studied enzyme-prodrug combinations is the nitroreductase from Escherichia coli (NfnB) with the prodrug CB1954 [5-(aziridin-1-yl)-2,4-dinitro-benzamide]. One of the major issues faced by DEPT is the ability to successfully internalize the enzyme into the target cells. NfnB has previously been genetically modified to contain cysteine residues (NfnB-Cys) which bind to gold nanoparticles for a novel DEPT therapy called magnetic nanoparticle directed enzyme prodrug therapy (MNDEPT). One cellular internalisation method is the use of cell-penetrating peptides (CPPs), which aid cellular internalization of cargo. Here the cell-penetrating peptides: HR9 and Pep-1 were tested for their ability to conjugate with NfnB-Cys. The conjugates were further tested for their potential use in MNDEPT, as well as conjugating with the delivery vector intended for use in MNDEPT and tested for the vectors capability to penetrate into cells.

Enhanced nanoparticle delivery exploiting tumour-responsive formulations.

Nanoparticles can be used as drug carriers, contrast agents and radiosensitisers for the treatment of cancer. Nanoparticles can either passively accumulate within tumour sites, or be conjugated with targeting ligands to actively enable tumour deposition. With respect to passive accumulation, particles < 150 nm accumulate with higher efficiency within the tumour microenvironment, a consequence of the enhanced permeability and retention effect. Despite these favourable properties, clinical translation of nano-therapeutics is inhibited due to poor in vivo stability, biodistribution and target cell internalisation. Nano-therapeutics can be modified to exploit features of the tumour microenvironment such as elevated hypoxia, increased pH and a compromised extracellular matrix. This is in contrast to cytotoxic chemotherapies which generally do not exploit the characteristic pathological features of the tumour microenvironment, and as such are prone to debilitating systemic toxicities. This review examines strategies for tumour microenvironment targeting to improve nanoparticle delivery, with particular focus on the delivery of nucleic acids and gold nanoparticles. Evidence for key research areas and future technologies are presented and critically evaluated. Among the most promising technologies are the development of next-generation cell penetrating peptides and the incorporation of micro-environment responsive stealth molecules.