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.

Controlling cardiomyocyte survival.

Gradually the distinction between signalling pathways originally believed to be specific for either hypertrophy, cell cycle control, apoptosis and cell survival are fading. The subtle variations in stimuli to a cell and the microenvironment will determine cell fate. In cardiomyocytes the entrance into the cell cycle is efficiently blocked. Therefore attention has focused on pathways involved in hypertrophy to assess effects in ischaemic models and vice versa. Interventions at different levels have been shown to be cardiomyocyte protective. Various growth factors (including IGF1 and FGF1,2) have shown to prevent or delay cardiomyocyte loss in and ex vivo. Similar results have been reported for downstream interventions in the signalling pathways. Strong effects after MAPK activation have been shown in gene targeted mice. Especially constitutive activation of the ERK proteins prevents ischemic damage of the heart with conservation of left ventricular function. Evidence for a key role of nuclear Akt in preventing apoptosis is accumulating from various genetic and pharmacological sources. Development of techniques to measure the level of cardiomyocyte death depends on further improvements in molecular imaging in mouse and human. In addition to studying cardiomyocyte cell death, it is crucial to measure myocardial function. Whether hypertrophy following ischaemia is adaptive or maladaptive and whether all apoptosis is detrimental will have to be determined by assessment of left ventricular function through invasive and noninvasive methods.