Over 65 million years ago, an asteroid some 10 km (6 mi) wide crashed into the Earth and wiped out the dinosaurs. Strangely, the legacy of this huge space rock could include a treatment for cancer after scientists from the UK and China demonstrated that iridium – a rare metal delivered to Earth by the asteroid – can be enlisted to kill cancer without harming healthy cells.

Laser-based techniques are emerging as viable treatments for cancer, targeting tumors far more precisely than the shotgun blast of radiation and chemotherapy. In that vein, researchers from the University of Warwick in the UK and Sun Yat-Sen University in China have found that laser light can turn iridium into an effective cancer killer.

First, the team created a compound of iridium and organic materials, and then introduced it into a lung cancer tumor grown in the lab. When red laser light is shone onto it through the skin, the compound is activated, converting the oxygen in the tumor into singlet oxygen, a poisonous form of the element that effectively kills the cancer cells from the inside. With cancer becoming resistant to certain treatments, it's crucial to find new methods such as this.

Further study found that the compound was effective because it had managed to penetrate every layer of the tumor. To identify exactly what was going on during that process, the team used ultra-high resolution mass spectrometry to highlight which proteins in the cancer cells were being targeted. It turns out that the compound had damaged proteins that manage heat shock stress and glucose metabolism, which are known to be crucial molecules for cancer's survival.

Better yet, when the researchers tested the iridium compound on a clump of non-cancerous tissue they found it had no effect, meaning it seems to be a highly targeted treatment that doesn't attack healthy cells.

Iridium is relatively rare on Earth naturally, but scientists have found a spike in the Chicxulub crater, which is often associated with the asteroid impact that wiped out the dinosaurs.

"The precious metal platinum is already used in more than 50 percent of cancer chemotherapies," says Peter Sadler, lead author of the study. "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. It's certainly now time to try to make good medical use of the iridium delivered to us by an asteroid 66 million years ago!"

The research was published in the journal Angewandte Chemie.

Source: University of Warwick

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