Traditional chemotherapy kills cells and so if a tumor shrinks, you know the drugs are effective. But new therapies may not kill cells. Instead, they may stop cancer cells from replicating or might cut off their food supply and it may be months into treatment before a tumor shrinks.
“When we give a patient one of these targeted therapies, the patient still has a tumor but the tumor is hibernating. We need to know if the tumor will stay quiet,” says Natalie Serkova, PhD, investigator at the University of Colorado Cancer Center and associate professor at the University of Colorado School of Medicine.
Serkova’s recent article in the journal Drug Resistance Updates describes new imaging techniques that look creatively at tumor biology to discover immediately, rather than in months, if a tumor is responding to treatment.
For example, “If you’re working with anti-angiogenic drugs [ones that stop the formation of new blood vessels needed to feed tumor tissues], then MRI scans can tell you how fast a contrast agent is being delivered to the tumor site, and from that we can imply how angiogenesis is affected,” Serkova says.
Less of this blood-delivered dye showing up in tumor tissue implies fewer new blood vessels in the tumor, which eventually (but not immediately!) will lead to the tumor’s death. MRI can show this taking effect sooner rather than later.
Or take the new class of cancer drugs known as signal transduction inhibitors, which exploit a difference between healthy and cancerous cells to cut off cancer cells’ ability to trap the sugars they need, eventually starving them. “In this case, we can use an imaging technique called Positron Emission Tomography (PET),” says Serkova. In this technique radioactive glucose is introduced into the body and then researchers can watch a tumor’s ability to take up this glucose. If the tumor site doesn’t light up with radioactive glucose, doctors can be sure the drug is having its intended effect — plugging cancer cells’ insulin-receptor pathway.
This glucose PET imaging technique was recently studied in preclinical and clinical trials at the CU Cancer Center, with results forthcoming in the journal Clinical Cancer Research.
“Everybody’s talking about personalized medicine,” says Serkova. “But if you have two patients with the same disease, even if they have pretty similar genetic profiles, you can never be sure a particular patient will respond to a drug. These imaging techniques are the best way to learn quickly if a therapy is effective.”