Andrei Sommer and colleagues have used laser light with a wavelength of 670 nm to expand and contract the water naturally contained in cancer cells. When the laser is on, the water expands and when it is switched off, the water retracts almost immediately. This process forces the cells to "suck" in drugs from a surrounding solution.

Most existing chemotherapy techniques rely on cells to take up drugs into their interior by diffusion across the bilayer lipid structure of the cell membrane. However, this type of treatment does not always work because cancer cells sometimes become resistant and simply push the drug molecules back out.

Sommer's team may now have found a way to address this problem. When irradiated with moderately intense (1000 W/m2) red laser light with a wavelength of 670 nm, the density of the nanoscopic water layers naturally confined in biological cells decreases. This instantly expands the volume of the water (since density=mass/volume). The effect is not seen for ordinary, "bulk", water because it hardly absorbs light of this wavelength.

When the laser is then turned off, the water quickly returns to its original high-density state. To compensate for this increase in density, and subsequent decrease in volume, the cells are forced to absorb water, and any other molecules, from their surroundings.

The researchers confirmed the viability of their technique using doxorubicin, methotrexate and epigallocatechin gallate – three commonly used anti-cancer drugs – and a fluorescent dye that they saw being literally sucked into irradiated human cervical cancer cells in one minute. The method would also work for other chemotherapeutics. "It even promises to be instrumental in transporting drugs deep into solid tumours where poor penetration of anticancer drugs imposes a major limitation to drug efficacy," Sommer told

Kurt Naber, former president of the International Society of Chemotherapy, says that the technique, which forces cancer cells to uptake high doses of drugs in a short time, could help to improve treatments for multilocular bladder cancers. Here, pulsed laser light irradiation would be applied to bladder mucosa at the same time as instilling intravesical drugs.

Horst-Dieter Foersterling of Philipps University in Marburg, Germany, adds: "I am really impressed by this new work – it is a breakthrough in understanding how drugs act against cancer cells in the presence of pulsed irradiation with laser light."

The work was reported in the Journal of Controlled Release.