A cancer treatment 66 million years in the making

The first time a bundle of iridium arrived on this planet, it took out the dinosaurs. Now, a group of Chinese and UK researchers are hoping to use this rare metal to wipe out cancer.

A team from the University of Warwick Department of Chemistry, Coventry, United Kingdom, and Sun Yat-Sen University, Guangzhou, China, has demonstrated that iridium—the world’s second-densest metal—can be used to kill cancer cells by filling them with a deadly version of oxygen that does not harm healthy tissue. The findings are published in the journal Angewandte Chemie.

“The precious metal platinum is already used in more than 50% of cancer chemotherapies,” said Peter Sadler, PhD, professor of chemistry at the University of Warwick. “The potential of other precious metals such as iridium to provide new targeted drugs which attack cancer cells in completely new ways and combat resistance, and which can be used safely with the minimum of side effects is now being explored.”

Iridium, which is in the same family as platinum, was discovered in 1803. The metal is rare on Earth, but is abundant in asteroids. Large amounts of iridium from about 66 million years ago have been discovered in the Earth’s crust, leading to the theory that it came to this planet with an asteroid that helped cause the extinction of the dinosaurs.

In this study, a compound of iridium and organic material was created to target cancerous cells. The compound transfers energy to cancer cells to turn the oxygen inside them into singlet oxygen, a high-energy form of oxygen that kills the cell and leaves healthy tissue unharmed.

The process is triggered by shining visible laser light through the skin onto the cancerous area. The light-reactive coating of the compound is then triggered, and the metal begins to fill the cancer with singlet oxygen.

A model of lung cancer cells was grown in the laboratory to form a tumor-like sphere. After attacking the cells with red laser light, the activated organic-iridium compound penetrated and infused into every layer of the tumor to kill it.

The researchers also directed the treatment at non-cancerous tissue, and it had no effect.

State-of-the-art ultra-high resolution mass spectrometry gave the team unprecedented views of individual proteins within the cancer cells, which allowed them to determine precisely which proteins were attacked by the organic-iridium compound.

“Our innovative approach to tackle cancer involving targeting important cellular proteins can lead to novel drugs with new mechanisms of action. These are urgently needed,” said Pingyu Zhang, PhD, Royal Society Newton International Fellow in Warwick’s Department of Chemistry.

Analysis of the data showed that the iridium compound had damaged the proteins responsible for heat shock stress and glucose metabolism—both known as key molecules in cancer.

“This project is a leap forward in understanding how these new iridium-based anticancer compounds are attacking cancer cells, introducing different mechanisms of action, to get around the resistance issue and tackle cancer from a different angle,” said co-author Cookson Chiu, a postgraduate researcher in Warwick’s Department of Chemistry.

To read more about this study, click here.