Rapid development in nanotechnology allows the incorporation of multiple therapeutic agents (e.g. liposomes) into nanoparticle with a size range from 1 to 1000 nm. These nanocarrier systems provide new approaches to treat aggressive malignancy. Nano-based delivery systems hold an advantage over traditional small molecule therapy in that they can deliver drugs preferentially to tumors due to the enhanced permeability and retention (EPR) effect. On one hand, high permeability of the tumor vessels and a lack of functional lymphatic vessels results in the EPR effect, driving nanoparticle extravasation. On the other hand, these phenomena lead to high interstitial fluid pressure (IFP), limiting nanoparticle extravasation. In this study, we have used dynamic-contrast enhanced (DCE) MRI with small (Dotarem, 5 nm) and large (Vistarem, 25 nm) contrast agents (CAs) to examine tumor vessel permeability in SJSA-1 osteosarcoma tumor-bearing rats. An inversion-recovery true fast imaging with steady state precession (TrueFISP) was employed to determine the transfer constant Ktrans in subcutaneous and intra-tibia tumor models. When the tumor cells were injected in both niches within the same animal, Ktrans was significantly lower in intra-tibia tumors with both CAs, and blood vessels significantly less and larger compared to subcutaneous tumors. Moreover, Ktrans negatively correlated with tumor bioluminescence for the intra-tibia model, suggesting that EPR decreased inversely with tumor size, while the opposite was noticed for the subcutaneous tumors. These data demonstrate for the first time that the EPR of tumors with a similar size within the same animal can be influenced by the microenvironment. Moreover, they show that the therapeutic index of a nanotherapeutics may be different if it's determined with either an orthotopic or ectopic model.

Citation Format: Stephane Ferretti, Nicolau Beckmann, laura Holzer, Michael Obrecht, Marjorie Berger, Michael Rugaard Jensen. The tumor microenvironment of preclinical tumor models may have an impact on the therapeutic index of nanotherapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2111.