Musings on "Cornell Dots" clinical trial and radioactive iodine

Schematic representation of a Cornell Dot, with several molecules of dye encapsulated in the center (Image (c) Cornell University)

Cornell researchers' efforts at tagging tumors has been approved by the US Food and Drug Administration for a clinical trial in humans.

"Cornell Dots" are silica spheres less than 8 nanometers in diameter that enclose several dye molecules and attach to tumor cells.  The glass-like shell is chemically inert and coated with polyethylene glycol to avoid being treated as a foreign substance by the body.  Organic molecules that bind to tumor surfaces are attached to the shell so the dots stick to tumors and flouresce much more brightly than unencapsulated dyes.

This can show the extent of a tumor’s blood vessels, cell death, treatment response and invasive or metastatic spread to lymph nodes and distant organs.  In the new clinical trials, the dots will be labeled with radioactive iodine so they're visible in PET scans and can show how many attach to tumors and where else in the body they go.

The dots will hopefully stay in the body (and attached to the tumor) during surgery, thus providing a useful visual for the surgeon.  They also may be useful for delivering radioactivity or drugs to tumors.  Other potential applications include biological imaging, optical computing, sensors and microarrays such as DNA chips.

But what about the radioactive iodine?  Is this going to be particularly relevant to the clinical trial which has five melanoma patients as subjects?

Now, to treat chronic lymphocytic leukemia (CLL), monoclonal antibodies that bind to particular structures on leukemic cells can be used to deliver payloads of radioactive iodine to the tumor cells.  The radioactive iodine-antibody combination is a drug called Bexxar.  The antibody identifies the targeted cell for destruction by the immune system, but also zaps it with radiation just to be sure.

The Cornell Dots trial seems to use radioactive iodine as a label. But given that the trial involves skin cancer patients, could the radioactive iodine not actually be used to kill the melanoma cell in the same way that Bexxar attacks CLL cells with radiation?

If the organic molecule on the dots' shells is able to identify and attach to melanoma cells, whether or not it singles out the cells for immune destruction, it seems that this clinical trial could shed new light on a possible radioimmunotherapy treatment.



Ow, Hooiswing et al., Bright and Stable Core-Shell Fluorescent Silica Nanoparticles.  Nano Letters Vol. 5, No. 1., 113-117, 2005.

http://www.newswise.com/articles/view/572923/?sc=dwhr&xy=10005433