Laser-controlled bubbles bring a new approach to gene therapy

Marie Freebody, marie.freebody@photonics.com

Ferrying genetic materials into cells is no easy task. It involves punching tiny holes into living cells without damaging or killing the cell itself or the surrounding tissue. Now, scientists at Georgia Institute of Technology have found a way to use a laser in conjunction with nanoparticles to pierce cells more efficiently and in a controlled manner.

Researchers have been trying for decades to drive DNA and RNA into cells more effectively, using electric fields and ultrasound, along with various other methods, to open cell membranes. However, such methods have generally suffered from safety concerns or low efficiency.

“Our approach is a little different: it’s not a biological one, it’s not a chemical one, it’s a physical one,” explained Mark Prausnitz, a professor in the school of chemical and biomolecular engineering at the institute. “The approach that we’ve taken uses a laser in combination with a carbon nanoparticle to generate forces on the cell that open the cell membrane. This allows molecules to enter in a way that doesn’t kill the cell and we believe doesn’t damage the cell, either.”

A field of human prostate cancer cells is shown after exposure to laser-activated carbon nanoparticles. The many green cells have taken up a model therapeutic compound, calcein, while the few red-stained cells are dead. Each green or red spot is a single cell. Photos courtesy of Prerona Chakravarty.

Many kinds of diseases can be treated by introducing molecules into cells and altering intracellular processes. The primary applications in mind for Prausnitz and colleagues are in treating cancer as well as carrying out DNA vaccination.

In the approach, carbon nanoparticles are activated by bursts of laser light, which trigger tiny blasts that open holes in cell membranes just long enough to admit therapeutic agents contained in the surrounding fluid. By adjusting laser exposure, the researchers successfully administered molecules to 90 percent of targeted cells – while keeping more than 90 percent of the cells alive.

The research was sponsored by the National Institutes of Health and the Institute of Paper Science and Technology at Georgia Institute of Technology and was reported in the August 2010 issue of Nature Nanotechnology.

Pulses from an 800-nm femtosecond laser were used to heat the carbon nanoparticles, which measured approximately 25 nm in diameter. Each carbon nanoparticle reacts with the surrounding water to produce hydrogen and carbon monoxide gas in the form of a bubble. Keeping the laser switched on causes the bubble to continue to grow. Once the laser is switched off, the bubble collapses, triggering a shock wave that perforates the protective membrane of the cell, allowing the therapeutic agents to enter.

This field of human prostate cancer cells has been exposed to laser-activated carbon nanoparticles. The cell membranes have been stained red for better visualization. Each red circle is a single cell.

“It is the heat from the laser that is used to provide energy to drive the chemical reaction, which generates bubbles around many, if not all, of the carbon particles,” Prausnitz said. “We found that we could control the bubble formation, growth and collapse with the laser nanoparticle interaction in a better way than using ultrasound to generate bubbles.”

The researchers demonstrated that they could get the small molecule calcein, the bovine serum albumin protein and plasmid DNA through the cell membranes of human prostate cancer cells and rat gliosarcoma cells using this technique.

Although the study is still in its early stages and much work remains to be done before the approach can be tested in clinical trials, Prausnitz is optimistic for the future.

“If we can understand mechanistically what’s going on and ultimately how the laser and the nanoparticle affect the cell, we can control the process better and optimize it more effectively,” he said. “But we are pressing on to deliver molecules into cells within the tissue of live animals, and we’ll carry that forward with our target applications in cancer and DNA vaccination.”