Scientists at UC Santa Barbara in the US have designed a nanoparticle that is spherical in shape, silver in composition and is encased in a shell coated with a peptide that enables it to target tumour cells. The shell is also etchable so that those nanoparticles that do not hit their target can be broken down and eliminated. The research findings appear in the journal Nature Materials.
The core of the nanoparticle employs a phenomenon called plasmonics, in which nanostructured metals such as gold and silver resonate in light and concentrate the electromagnetic field near the surface. In this way, fluorescent dyes are enhanced, appearing roughly ten times brighter than their natural state when no metal is present. When the core is etched, the enhancement goes away and the particle becomes dim.
UCSB’s Ruoslahti Research Laboratory also developed a simple etching technique using biocompatible chemicals to disassemble and remove the silver nanoparticles outside living cells. This method leaves only the intact nanoparticles for imaging or quantification, thus revealing which cells have been targeted and how much each cell internalised.
'The disassembly is an interesting concept for creating drugs that respond to a certain stimulus,' said Gary Braun, a postdoctoral associate in the Ruoslahti Lab in the Department of Molecular, Cellular and Developmental Biology (MCDB) and at Sanford-Burnham Medical Research Institute.
'It also minimises the off-target toxicity by breaking down the excess nanoparticles so they can then be cleared through the kidneys.'
These new nanoparticles have some remarkable properties that have already proven useful as a tool in our work that relates to targeted drug delivery into tumours
This method for removing nanoparticles unable to penetrate target cells is said to be unique. 'By focusing on the nanoparticles that actually got into cells, we can then understand which cells were targeted and study the tissue transport pathways in more detail,' Braun said.
Some drugs are able to pass through the cell membrane on their own, but many drugs, especially RNA and DNA genetic drugs, are charged molecules that are blocked by the membrane. These drugs must be taken in through endocytosis, the process by which cells absorb molecules by engulfing them.
'This typically requires a nanoparticle carrier to protect the drug and carry it into the cell,' Braun said. 'And that’s what we measured: the internalisation of a carrier via endocytosis.'
Because the nanoparticle has a core shell structure, the researchers can vary its exterior coating and compare the efficiency of tumour targeting and internalisation. Switching out the surface agent enables the targeting of different diseases — or organisms in the case of bacteria — through the use of different target receptors. According to Braun, this should turn into a way to optimise drug delivery where the core is a drug-containing vehicle.
Erkki Ruoslahti. Photo credit: Spencer Bruttig
'These new nanoparticles have some remarkable properties that have already proven useful as a tool in our work that relates to targeted drug delivery into tumours,' added Erkki Ruoslahti, adjunct distinguished professor in UCSB’s Centre for Nanomedicine and MCDB department and at Sanford-Burnham Medical Research Institute.
'They also have potential applications in combating infections. Dangerous infections caused by bacteria that are resistant to all antibiotics are getting more common, and new approaches to deal with this problem are desperately needed. Silver is a locally used antibacterial agent and our targeting technology may make it possible to use silver nanoparticles in treating infections anywhere in the body.'
