One way to inhibit a tumor’s growth is to choke off its blood supply. The trick is to create a clot that specifically blocks flow to the tumor without harming other parts of the body. To accomplish this, a research team led by Dr. Erkki Ruoslahti, distinguished professor at Sanford-Burnham, coated nanoparticles with two different homing signals that specifically direct them to proteins on tumor blood vessels. One signal was generated by a string of just five amino acids (the molecular subunits that make up a protein), while the other consisted of six amino acids. These two types of targeted nanoparticles worked cooperatively to induce blood clots, and an elongated version of these particles, called “nanoworms,” did an even better job of it. As the nanoworms induced clotting, more and more binding sites appeared, attracting more nanoworms and further enhancing the blockage.

In a study published June 29, 2010 in the journal Blood, the researchers used the targeted nanoworms to treat a mouse model of human prostate cancer. The nanoworms triggered widespread clotting in the prostate tumor vessels, but left normal tissues alone. As a result, the cancer cells starved and the tumors shrank.

“The nanoparticle combination we used gives a dramatic reduction in tumor growth, and there is no drug involved,” explained Dr. Ruoslahti. “Next, we’ll add a drug to one or both of the nanoparticles to further boost the efficacy, hopefully to a point where we can cure the mice of their tumors.”