Rare palladium metal provides new cancer therapies

Image credit: Yen Chew
Figure 1. Diagram showing how inactive prodrugs can be activated specifically in cancer cells by delivering artificial exosomes with palladium to the cancer site. 

A rare metal used widely in different industries such as electronics and dentistry, could play an important role in future cancer therapies.

A team of researchers at the University of Edinburgh and the Universidad de Zaragoza in Spain have successfully hijacked exosomes – the cellular postal service – as Trojan horses to deliver tiny amounts of palladium into cancer cells. 

The team extracted cancer-derived exosomes from lung cancer cells, and carefully grew nano-sized sheets of palladium inside the exosomes without damaging the membrane and its targeting properties.

So what are exosomes exactly? Cells transport biological material between each other, such as proteins, lipids and genetic material. They do this by using bubble-like carriers called exosomes which are released and taken up by cells,  acting as a molecular shuttle system, depositing its content from one cell to another. Exosomes play a fundamental role in the communication between cancer cells. A lot of research carried out in recent years has shown that this complex communication network can be exploited as a drug delivery service. Only a limited amount of drug, however, can be loaded into an exosome at a time. The team of researchers from the University of Edinburgh and the Universidad de Zaragoza, found an alternative way to amplify the production of drugs only in cancer cells, allowing local treatment.

The team experimented on a new method by loading minute amounts of catalyst palladium – a rare metal mainly used in catalytic converters to detoxify exhaust gas – into exosomes and delivering them directly to the cancer site. The team extracted cancer-derived exosomes from lung cancer cells, and carefully grew nano-sized sheets of palladium inside the exosomes without damaging the membrane and its targeting properties. The cancer-derived exosomes have unique proteins on the membrane that act as a disguise, tricking cancer cells to take up the artificial palladium-loaded exosomes (Figure 1).

When the exosomes reach the cancer site, the metal catalyst chemically activates a chemotherapy prodrug into an active drug while accelerating its production in cancer cells due to its catalytic activity. This would leave healthy cells unaffected, reducing the side effects of chemotherapy without compromising the treatment.This concept still has far to go, and is something that has to be validated in the future. 

By proving the concept, this successful proof-of-concept study has given the researchers a patent which gives them exclusive rights to trial palladium-based therapies in medicine. The study was published in the Nature Catalysis journal and was funded by the Engineering and Physical Sciences Research Council and the European Research Council. 

The paper can be found at https://www.nature.com/articles/s41929-019-0333-4

Written by Yen Chew and edited by Tara Wagner-Gamble

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