Implanted drug delivery devices are usually no good after they’ve released their contents. But a noninvasive refilling method could extend their lifetime, according to David J. Mooney and coworkers at Harvard University. The researchers have shown they can replenish hydrogel-based drug delivery depots in mice multiple times via intravenous injections (Proc. Natl. Acad. Sci. USA 2014, DOI: 10.1073/pnas.1413027111). The drug-laden hydrogels are made of DNA-labeled calcium alginate. To refill depleted depots, the Harvard team injects drug-conjugated alginate strands labeled with DNA that is complementary to the DNA in the hydrogel. The complementary DNA allows the circulating alginate to home in on the hydrogels, where it binds to resupply the drug. The researchers demonstrated the refilling method using the drug doxorubicin to treat mice with breast cancer tumors. After initially injecting loaded hydrogel depots into tumors, they refilled the depots four times at one-week intervals. Refilling the hydrogels was more effective at slowing tumor growth than administering doxorubicin on its own, Mooney and coworkers say.