Biological assessment of triazine dendrimer: Toxicological profiles, solution behavior, biodistribution, drug release and efficacy in a PEGylated, paclitaxel construct

The physicochemical characteristics, in vitro properties, and in vivo toxicity and efficacy of a third generation triazine dendrimer bearing approximately nine 2 kDa polyethylene glycol chains and twelve ester linked paclitaxel groups are reported. The hydrodynamic diameter of the neutral construct varies slightly with aqueous solvent ranging from 15.6 to 19.4 nm. Mass spectrometry and light scattering suggest radically different molecular weights with the former ∼40 kDa mass consistent with expectation, and the latter 400 kDa mass consistent with a decameric structure and the observed hydrodynamic radii. HPLC can be used to assess purity as well as paclitaxel release, which is insignificant in organic solvents or aqueous solutions at neutral and low pH. Paclitaxel release occurs in vitro in human, rat, and mouse plasma and is nonlinear, ranging from 7 to 20% cumulative release over a 48 h incubation period. The construct is 2-'3 orders of magnitude less toxic than Taxol by weight in human hepatocarcinoma (Hep G2), porcine renal proximal tubule (LLC-PK1), and human colon carcinoma (LS174T) cells, but shows similar cytotoxicity to Abraxane in LS174T cells. Both Taxol and the construct appear to induce caspase 3-dependent apoptosis. The construct shows a low level of endotoxin, is not hemolytic and does not induce platelet aggregation in vitro, but does appear to reduce collagen-induced platelet aggregation in vitro. Furthermore, the dendrimer formulation slightly activates the complement system in vitro due most likely to the presence of trace amounts (<1%) of free paclitaxel. An animal study provided insight into the maximum tolerated dose (MTD) wherein 10, 25, 50, and 100 mg of paclitaxel/kg of construct or Abraxane were administered once per week for three consecutive weeks to non tumor bearing athymic nude mice. The construct showed in vivo toxicity comparable to that of Abraxane. Both formulations were found to be nontoxic at the administered doses, and the dendrimer had an acute MTD greater than the highest dose administered. In a prostate tumor model (PC-3-h-luc), efficacy was observed over 70 days with an arrest of tumor growth and lack of luciferase activity observed in the twice treated cohort.