No abstract

Enhanced permeability and retention (EPR), and the (over-) expression of angiogenesis-related surface receptors are key features of tumor blood vessels. As a consequence, EPR-mediated passive and RGD-and NGR-based active tumor targeting have received considerable attention in the last couple of years. Using several different in vivo and ex vivo optical imaging techniques, we here visualized and quantified the benefit of RGD-and NGR-based vascular vs. EPR-mediated passive tumor targeting. This was done using ~10 nm-sized polymeric nanocarriers, which were either labeled with DY-676 (peptide-modified polymers) or with DY-750 (peptide-free polymers). Upon co-injection into mice bearing both highly leaky CT26 and poorly leaky BxPC3 tumors, it was found that vascular targeting did work, resulting in rapid and efficient early binding to tumor blood vessels, but that over time, passive targeting was significantly more efficient, leading to higher overall levels and to more efficient retention within tumors. Although this situation might be different for larger carrier materials, these insights indicate that caution should be taken not to over-estimate the potential of active over passive tumor targeting. KeywordsNanomedicine; Drug targeting; EPR; RGD; NGR Paralleled by the ever-increasing advances in nanotechnology and chemical engineering, nanomedicine formulations have started to attract significant attention in the last couple of years. Nanomedicines are 1-100(0) nm-sized carrier materials designed to improve the biodistribution and target site accumulation of low-molecular-weight (chemo-) therapeutic agents. By means of both passive and active targeting mechanisms, nanocarrier materials * Corresponding Authors Prof. Dr. Fabian Kiessling; Tel: +49-241-8080116; fkiessling@ukaachen.de Dr. Dr. Twan Lammers; Tel: +49-241-8036681; tlammers@ukaachen.de. Supporting Information Materials and methods describing the synthesis and characterization of the polymeric nanocarriers are provided as supplementary information. This material is available free of charge via the Internet at http://pubs.acs.org. Europe PMC Funders GroupAuthor Manuscript Nano Lett. Author manuscript; available in PMC 2014 March 04. Published in final edited form as:Nano Lett. 2014 February 12; 14(2): 972-981. doi:10.1021/nl404391r. Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts aim to more efficiently deliver drug molecules to pathological sites, while at the same time preventing their accumulation in potentially endangered healthy tissues, thereby beneficially affecting the balance between their efficacy and toxicity 1-4 .Passive drug targeting relies on the hyper-permeable tumor vasculature. Endothelial gaps and improperly aligned vascular endothelium result in leaky blood vessels, which enable the extravasation of carrier materials with sizes of up to several 100's of nm into the tumor interstitium. In addition to this, dysfunctional lymphatic drainage results in the retention of extravasated nanomaterials within tumo...

Multidrug (MDR) resistance is a pathophysiological phenomenon employed by cancer cells which limits the prolonged and effective use of chemotherapeutic agents. MDR is primarily based on the over-expression of drug efflux pumps in the cellular membrane. Prominent examples of such efflux pumps, which belong to the ATP-binding cassette (ABC) superfamily of proteins, are Pgp (P-glycoprotein) and MRP (multidrug resistance-associated protein), nowadays officially known as ABCB1 and ABCC1. Over the years, several strategies have been evaluated to overcome MDR, based not only on the use of low-molecular-weight MDR modulators, but also on the implementation of 1-100(0) nm-sized drug delivery systems. In the present manuscript, after introducing the most important physiological principles of MDR, we summarize prototypic nanomedical strategies to overcome multidrug resistance, including the use of carrier materials with intrinsic anti-MDR properties, the use of nanomedicines to modify the mode of cellular uptake, and the co-formulation of chemotherapeutic drugs together with low-and high-molecularweight MDR inhibitors within a single drug delivery system. While certain challenges still need to be overcome before such constructs and concepts can be widely applied in the clinic, the insights obtained and the progress made strongly suggest that nanomedicine formulations hold significant potential for improving the treatment of multidrug-resistant malignancies.

Nanomedicines are submicrometer-sized carrier materials designed to improve the biodistribution of i.v. administered (chemo-) therapeutic agents. In recent years, ever more efforts in the nanomedicine field have employed optical imaging (OI) techniques to monitor biodistribution and target site accumulation. Thus far, however, the longitudinal assessment of nanomedicine biodistribution using OI has been impossible, due to limited light penetration (in case of 2D fluorescence reflectance imaging; FRI), and to the inability to accurately allocate fluorescent signals to non-superficial organs (in case of 3D fluorescence molecular tomography; FMT). Using a combination of high-resolution micro-computed tomography (μCT) and FMT, we have here set out to establish a hybrid imaging protocol for non-invasively visualizing and quantifying the accumulation of near-infrared fluorophore-labeled nanomedicines in tissues other than superficial tumors. To this end, HPMA-based polymeric drug carriers were labeled with Dy750, their biodistribution and tumor accumulation were analyzed using FMT, and the resulting data sets were fused with anatomical μCT data sets in which several different physiologically relevant organs were pre-segmented. The robustness of 3D organ segmentation was validated, and the results obtained using 3D CT-FMT were compared to those obtained upon standard 3D FMT and 2D FRI. Our findings convincingly demonstrate that combining anatomical μCT with molecular FMT facilitates the non-invasive assessment of nanomedicine biodistribution. KeywordsNanomedicine; Drug targeting; Biodistribution; FMT; FRI; CT Nanomedicines aim to deliver drugs and imaging agents more efficiently and more specifically to pathological sites. A significant amount of evidence has been obtained over the years exemplifying the superiority of nanomedicine formulations over free drugs, both at the preclinical and at the clinical level. [1][2][3][4][5] Prototypic examples of nanomedicine formulations are liposomes, polymers, micelles and nanoparticles. These submicrometersized carrier materials are designed to modulate the pharmacokinetics and the biodistribution of conjugated or entrapped (chemo-) therapeutic drugs. Upon intravenous (i.v.)

Aim: Fluorescence-mediated tomography (FMT) holds potential for accelerating diagnostic and theranostic drug development. However, for proper quantitative fluorescence reconstruction, knowledge on optical scattering and absorption, which are highly heterogeneous in different (mouse) tissues, is required. We here describe methods to assess these parameters using co-registered micro Computed Tomography (µCT) data and nonlinear whole-animal absorption reconstruction, and evaluate their importance for assessment of the biodistribution and target site accumulation of fluorophore-labeled drug delivery systems.Methods: Besides phantoms with varying degrees of absorption, mice bearing A431 tumors were imaged 15 min and 48 h after i.v. injection of a fluorophore-labeled polymeric drug carrier (pHPMA-Dy750) using µCT-FMT. The outer shape of mice and a scattering map were derived using automated segmentation of the µCT data. Furthermore, a 3D absorption map was reconstructed from the trans-illumination data. We determined the absorption of five interactively segmented regions (heart, liver, kidney, muscle, tumor). Since blood is the main near-infrared absorber in vivo, the absorption was also estimated from the relative blood volume (rBV), determined by contrast-enhanced µCT. We compared the reconstructed absorption with the rBV-based values and analyzed the effect of using the absorption map on the fluorescence reconstruction.Results: Phantom experiments demonstrated that absorption reconstruction is possible and necessary for quantitative fluorescence reconstruction. In vivo, the reconstructed absorption showed high values in strongly blood-perfused organs such as the heart, liver and kidney. The absorption values correlated strongly with the rBV-based absorption values, confirming the accuracy of the absorption reconstruction. Usage of homogenous absorption instead of the reconstructed absorption map resulted in reduced values in the heart, liver and kidney, by factors of 3.5, 2.1 and 1.4, respectively. For muscle and subcutaneous tumors, which have a much lower rBV and absorption, absorption reconstruction was less important.Conclusion: Quantitative whole-animal absorption reconstruction is possible and can be validated in vivo using the rBV. Usage of an absorption map is important when quantitatively assessing the biodistribution of fluorescently labeled drugs and drug delivery systems, to avoid a systematic underestimation of fluorescence in strongly absorbing organs, such as the heart, liver and kidney.