We’ve never seen IRDye 800CW cross the BBB. The original paper did not claim this, rather the clearance is simple from the serum. In a study of the dye toxicity recently published in Molecular Imaging and Biology, we found no evidence of the dye in the brain, although it was present in other organs. We don’t believe it’s getting through the BBB, rather the neovascular vessels that form as a function of tumor growth are leaky. We think, although we have not yet verified, that the reason it’s not taken up by the brain, even though it seems to involve GLUT1, may be because it is taken up by an inefficient mechanism. It doesn’t go through the transporter in the normal way. Instead, it’s probably endocytotic uptake which may be more efficient in tumor cells. Jusst some thoughts that we are currently investigating.
