Editors' ChoiceNanotechnology

Carbon Nanotubes Are Picky Hitchhikers

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Science Translational Medicine  30 Apr 2014:
Vol. 6, Issue 234, pp. 234ec77
DOI: 10.1126/scitranslmed.3009258

When tumors develop, they surround themselves with the types of immune cells that normally gather near injuries to promote healing. In particular, inflammatory (Ly6Chigh) monocytes are attracted to tumors, where they differentiate into macrophages that promote cancer progression and metastasis. Because these Ly6Chigh monocytes naturally traffic to cancerous tissue, some think that they would be the perfect drug delivery vehicles. In a recent paper, Smith and colleagues describe progress in this area using single-walled carbon nanotubes (SWNTs).

SWNTs—long, thin tubules built out of carbon hexagons—accumulate in tumors after injection. The authors hypothesized that in addition to passive uptake from the circulation, nanotubes are also actively ferried into tumors via immune cells. To test this concept, they used intravital microscopy to track injected SWNTs in real time in mice. They observed that circulating immune cells take up SWNTs within seconds of injection and actively carry their nanotube payload into tumor tissue. Injected nanotubes were taken up almost exclusively by Ly6Chigh monocytes. Other circulating white blood cells, including phagocytic cells, absorbed only negligible amounts of SWNTs. Although the mechanism behind this selectivity of SWNTs for inflammatory monocytes is unclear, the finding by Smith et al. provides a means to quickly generate cellular delivery vehicles, in which therapeutic or imaging SWNTs hitchhike their way into otherwise inaccessible tumor regions. This approach has the distinct advantage that as opposed to adoptive cell therapy, the immune cells can be made active without first isolating them from the patient. This SWNT technology also holds promise for treating other conditions in which inflammatory monocytes play a major role, including cardiovascular and autoimmune diseases.

B. R. Smith et al., Selective uptake of single-walled carbon nanotubes by circulating monocytes for enhanced tumour delivery. Nat. Nanotechnol., published online 13 April 2014 (10.1038/nnano.2014.62). [Abstract]

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