Predicting Cancer Drugs' Impact

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Tracking chemotherapy: The imaging probe provides contrast in x-ray images by targeting tumor blood vessels. The tumor shown on top here is grayer than the one on the bottom. It has accumulated more of the imaging agent because its blood vessels are leakier, and it is therefore likely to accumulate more of the drug doxil too. Both the tumors are in mice. Credit: Radiology

"These probes might be useful for entire classes of drugs," says Caius Radu, a professor of molecular and medical pharmacology at the University of California, Los Angeles, School of Medicine. Given the tremendous potential payoffs for patients, "there will be many [imaging agents] like this," he predicts.

Radu's own lab reported the success of a similar project this week, using a contrast agent visible on positron-emission tomography (PET) scans. The agent enters leukemia cells by the same mechanism as a drug used to treat the disease. Both the drug and the contrast agent enter tumors that express a particular protein, which normal cells do not produce. By tracking the imaging agent's route through the body, the researchers can accurately predict whether the drug will extend the life span of mice with leukemia. His team describes these results in a paper published in the Proceedings of the National Academy of Sciences.

The chemistry of the two imaging agents is fundamentally different, but the philosophy behind them is the same. "We have to stop treating diseases and treat patients," Radu says. Both groups hope that their imaging agents can help doctors pick the right therapy immediately, sparing patients from grueling drugs and the need to wait six months or so for conventional imaging results to show whether their tumor has shrunk.

Tailoring therapy is important, says Daniel Kopans, a professor of radiology at Harvard Medical School. However, he cautions, "don't forget: this is in mice. Certainly many things that work in mice do not work in humans."

Edward Graves, a professor of radiation oncology at Stanford Medical School, is also cautiously optimistic. The two new imaging agents are part of a growing number of probes that track cancer molecules inside the body. But most of these agents remain in preclinical or very early clinical tests. "No one knows how best to interpret this data in a clinical setting," Graves says. "What implications do [these imaging signals] have for cancer progression and therapy?"

Bellamkonda says that a Houston-based startup called Marval Biosciences has agreed to license his group's liposome-imaging technology. In 16 months' time, the company plans to apply to the Food and Drug Administration for permission to test the imaging method in people. The University of California researchers hope to have enough data to move to human studies by the end of the year.