Lactosome is a core-shell type polymeric micelle of ca. 35 nm in diameter, which is consisted from poly(L-lactic acid)-block-poly(sarcosine) (PLLA-block-poly(Sar)) amphiphilic polydepsipeptide. Lactosome shows good blood circulation behavior and accumulates highly at transplanted tumor region by the enhanced permeation and retention (EPR) effect. Therefore, utilization of Lactosome as nano-carrier for drug and/or imaging agent delivery has been expected.In order to evaluate biodistribution of molecular assemblies, radioisotope (RI) labeling method is often utilized. Core-shell type micelle has potential to encapsulate hydrophobic compound in its hydrophobic core, and therefore RI-labeled micelle was prepared by mixing hydrophobic RI-labeled compound. Biodistribution of Lactosome has been discussed by using 125I-labeled Lactosome, which was prepared from the mixture of hydrophobic 125I-labeled PLLA and the amphiphile.However, different from low molecular weight compounds, not only decomposition of the micelle, but also degradation of the amphiphilic polymer are occurred in parallel, which make it difficult to clear in vivo dynamics of Lactosome. Biodistribution of 125I is expected to be well-correlated with dynamics of Lactosome when 125I-labeled PLLA was stably encapsulated into Lactosome, but is strongly reflected hydrophobic PLLA character after Lactosome decomposition. We newly synthesized 3H-labeled PLLA-block-poly(Sar) as Lactosome constituent. 3H-labeled Lactosome was prepared from the amphiphile, and time courses of 3H biodistribution up to 48 h from the administration were evaluated. In this study, effect of RI modification methods on their biodistribution is discussed.

Biodistribution of self-assembled nanoparticulate, �Lactosome� by different two radioisotope modification methods

246th National Meeting (2013)

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