  Chemically functionalized single-walled carbon nanotubes (SWNTs) have shown
promise in tumor targeted accumulation in mice and exhibit biocompatibility,
excretion and little toxicity. Here, we demonstrate in-vivo SWNT drug delivery
for tumor suppression in mice. We conjugate paclitaxel (PTX), a widely used
cancer chemotherapy drug to branched polyethylene-glycol (PEG) chains on SWNTs
via a cleavable ester bond to obtain a water soluble SWNT-paclitaxel conjugate
(SWNT-PTX). SWNT-PTX affords higher efficacy in suppressing tumor growth than
clinical Taxol in a murine 4T1 breast-cancer model, owing to prolonged blood
circulation and 10-fold higher tumor PTX uptake by SWNT delivery likely through
enhanced permeability and retention (EPR). Drug molecules carried into the
reticuloendothelial system are released from SWNTs and excreted via biliary
pathway without causing obvious toxic effects to normal organs. Thus, nanotube
drug delivery is promising for high treatment efficacy and minimum side effects
for future cancer therapy with low drug doses.
