New York, March 3 (IANS): Scientists have developed a nanodevice that can block the genes that make tumours drug resistant and then launch a new chemotherapy attack against the growth.

Chemotherapy often shrinks tumours at first, but as cancer cells become resistant to drug treatment tumours can grow back.

The new nanodevice developed by the Massachusetts Institute Of Technology (MIT) researchers consists of gold nanoparticles embedded in a hydrogel that can be injected or implanted at a tumour site.

"Drug resistance is a huge hurdle in cancer therapy and the reason why chemotherapy, in many cases, is not very effective," said lead author of the paper Joao Conde from MIT.

To overcome this, the researchers created gold nanoparticles coated with strands of DNA complementary to the sequence of MRP1 messenger RNA -- the snippet of genetic material that carries DNA's instructions to the rest of the cell.

These strands of DNA, which the researchers call "nanobeacons", fold back on themselves to form a closed hairpin structure.

However, when the DNA encounters the correct mRNA sequence inside a cancer cell, it unfolds and binds to the mRNA, preventing it from generating more molecules of the MRP1 protein.

As the DNA unfolds, it also releases molecules of 5-fluorouracil that were embedded in the strand. This drug then attacks the tumour cell's DNA, since MRP1 is no longer around to pump it out of the cell.

"When we silence the gene, the cell is no longer resistant to that drug, so we can deliver the drug that now regains its efficacy," Conde explained.

Using the new device to block the gene for multi-drug resistant protein 1 (MRP1) in mice and then deliver the chemotherapy drug 5-fluorouracil, the researchers were able to shrink tumours by 90 percent in two weeks.

The same device can also be used more broadly to disrupt any gene involved in cancer, researchers said.

The findings were published in the Proceedings of the National Academy of Sciences.