Era of Hope 2011 Investigator Vignette

Title: Ligand-Directed Targeted Molecular Imaging

Investigator: Renata Pasqualini, PhD; MD Anderson Cancer Center

The essential basis of our program is the ability to harvest molecular diversity in a communitory way in a relevant disease setting in order to create probes that can specifically localize to disease tissues with the ultimate goal of developing targeted therapies and imaging agents that are improved compared to what's available today.

We're leveraging technology that we have been involved in for about a decade. It's a very clever approach and is based on the recognition that there's a zip code system in the body. And every organ, every tissue carries marker molecules that are accessible to circulating cells and proteins. When there's a disease process going on within an organ, a tumor for example, there's a second layer of diversity that emerges in the sense that if you can pinpoint the zip codes that are unique to tumors you can then use them for targeted delivery of therapies or imaging agents. And this is really the holy grail of-of drug delivery or imaging; essentially the ability to localize a payload to tumors and not the normal tissues.

So we have a large collection of ligands with different binding capabilities. This collection is injected into a live subject. It could be a mouse, a patient, or any-any animal model that mimics the disease. And then we're able to harvest probes that specifically target breast cancer. Once we have these probes validated we can hook payloads to them and then deliver them to tumors specifically.

Work that's being done with chemotherapies shows that when you do targeted delivery using this system drugs become much more potent and less toxic because they're localized tumors. If you use it to deliver imaging agents you're able to learn a lot in real time without the needle biopsies, how the tumor is progressing, if it's responding to a certain type of therapy, and if it's responding because the expression profile of certain genes is responsible for the therapy efficacy.

Each tumor is different; each patient is different. If you're able to have real-time imaging capabilities in a targeted way, which is what we're trying to accomplish, this really may change the landscape of how breast cancer is treated today.

So once a marker is identified, a ligand towards it is developed and then optimized. We can practice imaging exercises by labeling probes that will light up the tumor upon injection, and we can evaluate that specificity in the whole body scan so that you what see is certain organs light up just because of the contrast accumulation but you do see targeted localization based on these ligand receptor pairs in this mouse that has a tumor and you see substantial targeting here once the probe is injected intravenously.

So once this is validated and can evolve two different modalities of imaging. For example by engineering the ligand into an antibody backbone so essentially we are running a similar experiment but in a different setting to obtain further confirmation that the delivery system does work. So this is an antibody again hooked to a contrast agent and showing beautifully that this particular molecule can be targeted in vivo in a very specific way.

Once this is determined one can hook then a grenade, something that is conjugated to the ligand and once it hits the cell that contains the specific marker we're targeting that cell will die.

So this is showing proof of concept comparing a control in which you have a monolayer of healthy cells that were exposed to the killing moiety alone.

It's a chimeric peptide; one arm has a homing domain that localizes the payloads to the tumor and the other arm is a killing domain.

And the killing moiety if it's not targeted this is not able to internalize and penetrate cells and-and therefore is not able to kill cells. But if you-if we give it a ligand that recognizes a marker that's specific for breast cancer, you have then the killing moiety inside the cell and inducing apoptosis. As you see here, the monolayer is done away with--within minutes depending on the concentrations utilized.

And then ultimately in vivo you can do a beautiful experiment that combines thera-agnostic concepts, which is see and treat and treat and see, so first you evaluate the tumors, you treat them, and then you image them again to see what's going on in terms of regression.

And we were able to show very, very powerful efficacy with this particular targeted therapy. And this is allotted for clinical trial and we have the toxicology package for the FDA in progress.