Magnetite (Fe 3 O 4 ) nanoparticles with uniform sizes of 10, 20, and 31 nm were prepared by thermal decomposition of Fe(III) oleate or mandelate in a high-boiling point solvent (>320 °C). To render the particles with hydrophilic and antifouling properties, their surface was coated with a PEG-containing bisphosphonate anchoring group. The PEGylated particles were characterized by a range of physicochemical methods, including dynamic light scattering, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and magnetization measurements. As the particle size increased from 10 to 31 nm, the amount of PEG coating decreased from 28.5 to 9 wt.%. The PEG formed a dense brush-like shell on the particle surface, which prevented particles from aggregating in water and PBS (pH 7.4) and maximized the circulation time in vivo . Magnetic resonance relaxometry confirmed that the PEG-modified Fe 3 O 4 nanoparticles had high relaxivity, which increased with increasing particle size. In the in vivo experiments in a mouse model, the particles provided visible contrast enhancement in the magnetic resonance images. Almost 70% of administrated 20-nm magnetic nanoparticles still circulated in the blood stream after four hours; however, their retention in the tumor was rather low, which was likely due to the antifouling properties of PEG.

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The lack of cellular and tissue specificities in conventional chemotherapies along with the generation of a complex tumor microenvironment (TME) limits the dosage of active agents that reaches tumor sites, thereby resulting in ineffective responses and side effects. Therefore, the development of selective TMEresponsive nanomedicines is of due relevance toward successful chemotherapies, albeit challenging. In this framework, we have synthesized novel, ready-to-use ROSresponsive amphiphilic block copolymers (BCs) with two different spacer chemistry designs to connect a hydrophobic boronic ester-based ROS sensor to the polymer backbone. Hydrodynamic flow focusing nanoprecipitation microfluidics (MF) was used in the preparation of well-defined ROS-responsive PSs; these were further characterized by a combination of techniques [ 1 H NMR, dynamic light scattering (DLS), static light scattering (SLS), transmission electron microscopy (TEM), and cryogenic TEM (cryo-TEM)]. The reaction with hydrogen peroxide releases an amphiphilic phenol or a hydrophilic carboxylic acid, which affects polymersome (PS) stability and cargo release. Therefore, the importance of the spacer chemistry in BC deprotection and PS stability and cargo release is herein highlighted. We have also evaluated the impact of spacer chemistry on the PS-specific release of the chemotherapeutic drug doxorubicin (DOX) into tumors in vitro and in vivo. We demonstrate that by spacer chemistry design one can enhance the efficacy of DOX treatments (decrease in tumor growth and prolonged animal survival) in mice bearing EL4 T cell lymphoma. Side effects (weight loss and cardiotoxicity) were also reduced compared to free DOX administration, highlighting the potential of the well-defined ROS-responsive PSs as TMEselective nanomedicines. The PSs could also find applications in other environments with high ROS levels, such as chronic inflammations, aging, diabetes, cardiovascular diseases, and obesity.

Transgenic mice expressing green fluorescent protein (GFP) are useful in transplantation experiments. When we used ubiquitin-GFP (UBC-GFP) transgenic mice to study the availability of niches for transplanted hematopoietic stem and progenitor cells, the results were strikingly different from the corresponding experiments that used congenic mice polymorphic in the CD45 antigen. Analysis of these unexpected results revealed that the hematopoiesis of UBC-GFP mice was outcompeted by the hematopoiesis of wild-type (WT) mice. Importantly, UBC-GFP mice engrafted the transplanted bone marrow of WT mice without conditioning. There was a significant bias toward lymphopoiesis in the WT branch of chimeric UBC-GFP/WT hematopoiesis. A fraction of immature Sca-1 cells in the spleen of UBC-GFP mice expressed GFP at a very high level. The chimeric hematopoiesis was stable in the long term and also after transplantation to secondary recipient mice. The article thus identifies a specific defect in the hematopoiesis of UBC-GFP transgenic mice that compromises the lymphoid-primed hematopoietic stem cells in the bone marrow and spleen. Stem Cells 2018;36:1237-1248.

Regeneration of severely damaged adult tissues is currently only partially understood. Hematopoietic tissue provides a unique opportunity to study tissue regeneration due to its well established steady-state structure and function, easy accessibility, well established research methods, and the well-defined embryonic, fetal, and adult stages of development. Embryonic/fetal liver hematopoiesis and adult hematopoiesis recovering from damage share the need to expand populations of progenitors and stem cells in parallel with increasing production of mature blood cells. In the present study, we analyzed adult hematopoiesis in mice subjected to a submyeloablative dose (6 Gy) of gamma radiation and targeted the period of regeneration characterized by massive production of mature blood cells along with ongoing expansion of immature hematopoietic cells. We uncovered significantly expanded populations of developmentally advanced erythroid and myeloid progenitors with significantly altered immunophenotype. Their population expansion does not require erythropoietin stimulation but requires the SCF/c-Kit receptor signaling. Regenerating hematopoiesis significantly differs from the expanding hematopoiesis in the fetal liver but we find some similarities between the regenerating hematopoiesis and the early embryonic definitive hematopoiesis. These are in (1) the concomitant population expansion of myeloid progenitors and increasing production of myeloid blood cells (2) performing these tasks despite the severely reduced transplantation capacity of the hematopoietic tissues, and (3) the expression of CD16/32 in most progenitors. Our data thus provide a novel insight into tissue regeneration by suggesting that cells other than stem cells and multipotent progenitors can be of fundamental importance for the rapid recovery of tissue function.