Multifunctional and water-soluble superparamagnetic iron oxide (SPIO) nanocarriers were developed for targeted drug delivery and positron emission tomography/magnetic resonance imaging (PET/MRI) dual-modality imaging of tumors with integrin αvβ3 expression. An anticancer drug was conjugated onto the PEGylated SPIO nanocarriers via pH-sensitive bonds. Tumor targeting ligands, cyclo(Arg-Gly-Asp-D-Phe-Cys) (c(RGDfC)) peptides, and PET 64Cu chelators, macrocyclic 1,4,7-triazacyclononane-N, N′, N″-triacetic acid (NOTA), were conjugated onto the distal ends of the PEG arms. The effectiveness of the SPIO nanocarriers as an MRI contrast agent was evaluated via an in vitro r2 MRI relaxivity measurement. cRGD-conjugated SPIO nanocarriers exhibited a higher level of cellular uptake than cRGD-free ones in vitro. Moreover, cRGD-conjugated SPIO nanocarriers showed a much higher level of tumor accumulation than cRGD-free ones according to noninvasive and quantitative PET imaging, and ex vivo biodistribution studies. Thus, these SPIO nanocarriers demonstrated promising properties for combined targeted anticancer drug delivery and PET/MRI dual-modality imaging of tumors. Keywords: superparamagnetic iron oxide; drug delivery; Positron Emission Tomography (PET); Magnetic Resonance Imaging (MRI); nanomedicine

A multifunctional stable and pH-responsive polymer vesicle nanocarrier system was developed for combined tumor-targeted delivery of an anticancer drug and superparamagnetic iron oxide (SPIO) nanoparticles (NPs). These multifunctional polymer vesicles were formed by heterofunctional amphiphilic triblock copolymers, that is, R (folate (FA) or methoxy)-poly(ethylene glycol)(M(w):5000)-poly(glutamate hydrozone doxorubicin)-poly(ethylene glycol) (M(w):2000)-acrylate (i.e., R (FA or methoxy)-PEG(114)-P(Glu-Hyd-DOX)-PEG(46)-acrylate). The amphiphilic triblock copolymers can self-assemble into stable vesicles in aqueous solution. It was found that the long PEG segments were mostly segregated into the outer hydrophilic PEG layers of the vesicles, thereby providing active tumor targeting via FA, while the short PEG segments were mostly segregated into the inner hydrophilic PEG layer of the vesicles, thereby making it possible to cross-link the inner PEG layer via the acrylate groups for enhanced in vivo stability. The therapeutic drug, DOX, was conjugated onto the polyglutamate segment, which formed the hydrophobic membrane of the vesicles using a pH-sensitive hydrazone bond to achieve pH-responsive drug release, while the hydrophilic SPIO NPs were encapsulated into the aqueous core of the stable vesicles, allowing for ultrasensitive magnetic resonance imaging (MRI) detection. The SPIO/DOX-loaded vesicles demonstrated a much higher r(2) relaxivity value than Feridex, a commercially available SPIO-based T(2) contrast agent, which was attributed to the high SPIO NPs loading level and the SPIO clustering effect in the aqueous core of the vesicles. Results from flow cytometry and confocal laser scanning microscopy (CLSM) analysis showed that FA-conjugated vesicles exhibited higher cellular uptake than FA-free vesicles which also led to higher cytotoxicity. Thus, these tumor-targeting multifunctional SPIO/DOX-loaded vesicles will provide excellent in vivo stability, pH-controlled drug release, as well as enhanced MRI contrast, thereby making targeted cancer therapy and diagnosis possible.

IMPORTANCEThe accumulation of aggregated β-amyloid and tau proteins into plaques and tangles is a central feature of Alzheimer disease (AD). While plaque and tangle accumulation likely contributes to neuron and synapse loss, disease-related changes to oligodendrocytes and myelin are also suspected of playing a role in development of AD dementia. Still, to our knowledge, little is known about AD-related myelin changes, and even when present, they are often regarded as secondary to concomitant arteriosclerosis or related to aging. OBJECTIVE To assess associations between hallmark AD pathology and novel quantitative neuroimaging markers while being sensitive to white matter myelin content.DESIGN, SETTING, AND PARTICIPANTS Magnetic resonance imaging was performed at an academic research neuroimaging center on a cohort of 71 cognitively asymptomatic adults enriched for AD risk. Lumbar punctures were performed and assayed for cerebrospinal fluid (CSF) biomarkers of AD pathology, including β-amyloid 42 , total tau protein, phosphorylated tau 181, and soluble amyloid precursor protein. We measured whole-brain longitudinal and transverse relaxation rates as well as the myelin water fraction from each of these individuals.MAIN OUTCOMES AND MEASURES Automated brain mapping algorithms and statistical models were used to evaluate the relationships between age, CSF biomarkers of AD pathology, and quantitative magnetic resonance imaging relaxometry measures, including the longitudinal and transverse relaxation rates and the myelin water fraction. RESULTSThe mean (SD) age for the 19 male participants and 52 female participants in the study was 61.6 (6.4) years. Widespread age-related changes to myelin were observed across the brain, particularly in late myelinating brain regions such as frontal white matter and the genu of the corpus callosum. Quantitative relaxometry measures were negatively associated with levels of CSF biomarkers across brain white matter and in areas preferentially affected in AD. Furthermore, significant age-by-biomarker interactions were observed between myelin water fraction and phosphorylated tau 181/β-amyloid 42, suggesting that phosphorylated tau 181/β-amyloid 42 levels modulate age-related changes in myelin water fraction.CONCLUSIONS AND RELEVANCE These findings suggest amyloid pathologies significantly influence white matter and that these abnormalities may signify an early feature of the disease process. We expect that clarifying the nature of myelin damage in preclinical AD may be informative on the disease's course and lead to new markers of efficacy for prevention and treatment trials.

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