Diatom algae - tiny, unicellular, photosynthesizing algae with a skeleton made of silica - can be used as therapeutic nanoparticles, reports a study in Nature Communications this week.

Anti-cancer chemotherapeutic drugs are often toxic to normal tissues. To minimize the off-target toxicity, the drugs can be hidden inside the antibody-coated nanoparticles. The antibody binds only to molecules found on cancer cells, thus delivering the toxic drug specifically to the target cells. However, the production of such nanoparticles is costly.

Nanoparticle-sized (4-6 micrometres in diameter) diatom algae are naturally enclosed in a porous shell made of silica. In this paper, Nicolas Voelcker and colleagues genetically engineer the algae to produce an antibody-binding protein on the surface of their shells. They then allow the shells to bind to cancer-specific antibodies and also to absorb anticancer drugs. When added to cultured human cells, the newly-created diatom nanoparticles kill 90% of cancer cells, while sparing normal cells. Injecting the nanoparticles into four tumour-bearing mice caused tumour regression.

The algae, which require mostly water and light to grow, can reduce the cost and associated toxic waste of therapeutic nanoparticle manufacturing, raising hopes for more affordable treatments.