Orthotopic RG-2 malignant glioma tumor tissue Gd concentration curves over 2 hours upon 1 minute bolus intravenous infusion of Gd-DTPA dendrimer generations at dose of 0.09 mmol Gd/kg bw and infusion of Gd-DTPA dendrimer-linker-Rhodamine dendrimer generations at dose of 0.06 mmol Gd/kg body weight (bw). RG-2 glioma tumor tissue concentration curves are weighted with respect to total tumor volume (large anterior and small posterior contralateral) with error bars representing standard deviation (s.d.) and shown once every five minutes for clarity. Tumor N per group: Gd-G1 (n = 10), Gd-G2 (n = 12), Gd-G3 (n = 12), lowly conjugated (LC) Gd-G4 (n = 8), standard (Std) Gd-G4 (n = 12), Gd-G5 (n = 12), Gd-G6 (n = 10), Gd-G7 (n = 10) and Gd-G8 (n = 12); Gd-G5-linker-Rhodamine (n = 10) and Gd-G8-linker-Rhodamine (n = 4). Of note, Normal brain tissue curves concentration curves for Gd-G1 and Gd-G5 dendrimer groups are shown of 9 mm3 brain volumes, which reflect intravascular blood concentration of Gd-dendrimer Gd in the absence of any extra-vascular extravasation of the respective Gd-dendrimer generations (other Gd-dendrimer generations not shown for clarity). Based on the tumor tissue extravasation concentration curves of the non-cationotoxic Gd-dendrimers (non-Rhodamine functionalized), the upper limit of pore size of the blood-tumor barrier is between the size of the Gd-G7 dendrimers (~11 nm) and that of the Gd-G8 dendrimers (~13 nm). Of note, Gd-G5 dendrimer-linker-Rhodamine and Gd-G8 dendrimer-linker-Rhodamine tumor tissue concentration curves accumulate over time in tumor tissue at 2/3rd the dose of the non-Rhodamine Gd-dendrimers, the Gd-G5 dendrimer-linker-Rhodamine dendrimer to a significant extent, which is due to cationic toxicity of the blood-tumor barrier, which is also the case of the Gd-G8 dendrimer-linker-Rhodamine (Curve not shown: The cationotoxic extravasation across the normal blood brain-barrier and accumulation in normal brain tissue, which reflects cationic toxicity to the normal healthy blood–brain barrier) Adapted from references [3,8,28]. A) Gd-G1, B) Gd-G2, C) Gd-G3, D) LC Gd-G4, E) Std Gd-G4, F) Gd-G5, G) Gd-G6, H) Gd-G7, I) Gd-G8.