By Rideeta Raquib ’19

Gene regulation induced by light has potential for noninvasive control over the function of target cells. One such method involves the delivery of photothermal heaters and heat shock protein (HSP) promoter-driven protein expression vectors into the cells and then illuminating them to activate the cells. HSP promoters are controlled by heat shock factor, which is a transcription factor in the cytosol that remains dormant in an undisturbed environment. When HSF is exposed to cellular stress, it is activated. This induces the expression of downstream HSPs, which are necessary for defense mechanisms. Heat and light are plausible examples of sources of stress that can activate defense. Exposure to these sources is an approach that can be utilized to control protein expression.

A laser wavelength in the near-infrared (NIR) region (650–900 nm) for therapy may reduce the invasiveness of the photoactivation of HSP promoters. A study conducted by a research team in Kyoto University illustrated that gold nanorods (AuNRs) functionalized with two specific lipids can undergo transfection efficiently and photoactivation or light activation of HSP promoter. Transfection refers to the insertion of genetic material, such as DNA or RNA into cells.

The first step of the study involved treating AuNRs with oleate or polystyrene sulfonate (PSS). This was followed by treatment with cationic dispersants, including 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Dispersants are used to disperse insoluble particles into a medium and in this case, enabled the AuNRs to suspend better in solution and interact with cells more effectively. Gel electrophoresis was utilized to analyze the plasmid DNA or pDNA-binding capacity. The transfection efficiency was evaluated using HEK293T cells and HeLa cells. It was found that only DOTAP-AuNRs and polyethyleneimine PEI-treated AuNRs (PEI-AuNRs) showed significant transfection abilities in both HEK293T cells and HeLa cells. The infiltration of the AuNRs into the cells will enable it to heat up and provide the stress for the defense mechanism to occur.

Overall, this study developed a method for the surface modification of AuNRs with oleate and DOTAP, enabling simultaneous transfection of plasmid DNAs and heat-generating AuNRs highly efficiency. This paves way for further research regarding the delivery and photoactivation of DOTAP-AuNRs in tumor tissues in vivo.

References:

1. Hirotaka Nakatsuji, Kelly Kawabata Galbraith, Junko Kurisu, Hiroshi Imahori, Tatsuya Murakami, Mineko Kengaku. Surface chemistry for cytosolic gene delivery and photothermal transgene expression by gold nanorods. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-04912-1
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