Faceted nanoparticles shaped somewhat like cut diamonds not only can deliver drugs to tumor cells but also can ensure that the small molecules stick around long enough to do some good, a research team has found (Sci.  Trans.  Med. ,DOI: 10.1126/scitranslmed.3001713). 

Chemotherapy often fails because cells protect themselves by pumping out foreign substances via transmembrane transporter proteins.  As a result, physicians have to administer cancer therapeutics at high, and sometimes harmful, concentrations for them to be efficacious. 

As shown by fluorescence microscopy, nanodiamonds (green) loaded with doxorubicin (schematic, right) can be taken up by HeLa cells (nuclei are orange), which are typically 20–30 µm in size. 

Credit: Science/AAAS

As shown by fluorescence microscopy, nanodiamonds (green) loaded with doxorubicin (schematic, right) can be taken up by HeLa cells (nuclei are orange), which are typically 20–30 µm in size. 

Credit: Science/AAAS

Nanoparticles—materials that can’t as easily be kicked out of cells and can hold high concentrations of bound molecules—show promise as drug delivery vehicles.  The 2- to 8-nm-diameter carbon-based nanodiamonds, in particular, “have unique electrostatic properties that promote potent binding of drugs” and are ideal for chemotherapy, says Dean Ho, the research team’s leader and a biomedical engineering professor at Northwestern University. 

By binding the cancer agent doxorubicin to nanodiamonds, Ho and his team demonstrated particle-mediated delivery of the drug to both liver and mammary gland tumor cells in mice.  In both cases, seven days after injection, the drug-loaded nanodiamonds killed about three times as many tumor cells as doxorubicin alone.  They also circulated in the blood of the mice 10 times as long as the unbound cancer agent. 

When treated with a high dose (200 µg) of doxorubicin, mice riddled with mammary gland tumors died after 15 days.  But those treated with an equivalent dose of a nanodiamond-doxorubicin complex , which is thought to release the drug slowly over time, had a nearly 100% survival rate over the course of the eight-week study, and their tumors decreased in size by about 50%. 

“What is new and striking” about this work, says Fuyu Tamanoi, a biochemist at the University of California, Los Angeles, is that the nanodiamond-doxorubicin formulation blocks tumor growth in the mice with drug-resistant mammary gland tumors cells. “ This suggests that nanodiamonds can overcome drug resistance,” he says.