MRI Molecular imaging with albumin nanoparticles: achievements and challenges.

Molecular imaging comprises an important tool in understanding biological processes and allows early detection of tumors and of small metastasis. However, until now detection of malignant cells hidden behind intact blood-tissue barriers still presents an almost invincible hurdle in nanomedicine. This is true for essentially true for all solid tumors. Since each organ maintains its own unique blood-tissue barrier and only one of these barriers (the blood-brain barrier) is partly understood, work should focus on solid tumors for which good models are available in vitro and in situ. A major challenge lies in the fact that tumors in the early stages do not yet release factors which increase the permeability of the blood-vessel-walls. The present state of the art in tumor therapy (Abraxane®) exploits such leaky blood-vessels in addition to the existing hypotension inside the tumor: this allows drugs to be taken up by the so-called “enhanced permeability and retention” effect (EPR-effect) [1]. At present one big challenge in nanomedicine is therefore the creation of particles which can cross tissue-barriers and which are directed by viable targeting groups, leading ideally to a 100% accumulation in the targeted destination. This would allow us to detect and treat in-situ tumors without causing severe side effects, thus increasing patient compliance and health. Interrelated to these research areas, the identification of suitable biomarkers and amplification of MR signals present further major challenges in targeted Molecular Imaging. This paper reports our iterative developmental studies in rats.