Doctors typically judge a cancer patient’s response to chemotherapy by using imaging techniques such as CT or MRI to see whether a tumor has changed size. However, it usually takes two to three months of therapy before the response can be determined via these methods. With earlier identification of patients who are not responding to therapy, another treatment could be tried much sooner. The recent increase in the number of available treatments makes early knowledge of how the patient is responding even more important.Researchers at Vanderbilt-Ingram Cancer Center and at Vanderbilt University School of Medicine, both in Nashville, Tenn., recently discovered a peptide that can identify tumors that are responding to chemotherapy. The peptide could hasten determination of which patients are not responding, possibly even within days after treatment has begun. Researchers have identified a peptide that may enable determination of a tumor’s response to treatment within days. Here, the tumor responding (LLC) is easily seen, while the tumor not responding (B16) is now labeled. Reprinted with permission of Nature Medicine.From a panel of billions of peptides, the researchers identified one that specifically binds to tumors responding to therapy. They attached the Cy7 fluorophore to the peptide and injected the construct into tumor-bearing mice that had undergone cancer treatments. Near-infrared images of the mice from a Xenogen small-animal imaging system showed that, within two days of starting treatment, tumors responding to therapy were brighter than nonresponding tumors. This was true for brain, lung, colon, prostate and breast cancers, showing the technique’s potential. The work was published online in Nature Medicine on Feb. 24.To move from animal testing to use in humans, the researchers are adapting the technique for PET imaging, and they expect it to enter clinical trials in about 18 months. If successful, it could help accelerate the early stages of clinical trials for new chemotherapeutic drugs because response could be gauged within days of starting treatment rather than months.