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Abstract. Gene delivery vectors based on adeno-associated virus (AAV) are highly promising due to several desirable features of this parent virus, including a lack of pathogenicity, efficient infection of dividing and non-dividing cells, and sustained maintenance of the viral genome. However, several problems should be addressed to enhance the utility of AAV vectors, particularly those based on AAV2, the best characterized AAV serotype. First, altering viral tropism would be advantageous for broadening its utility in various tissue or cell types. In response to this need, vector pseudotyping, mosaic capsids, and targeting ligand insertion into the capsid have shown promise for altering AAV specificity. In addition, library selection and directed evolution have recently emerged as promising approaches to modulate AAV tropism despite limited knowledge of viral structure-function relationships. Second, preexisting immunity to AAV must be addressed for successful clinical application of AAV vectors. BShielding^polymers, site-directed mutagenesis, and alternative AAV serotypes have shown success in avoiding immune neutralization. Furthermore, directed evolution of the AAV capsid is a high throughput approach that has yielded vectors with substantial resistance to neutralizing antibodies. Molecular engineering and directed evolution of AAV vectors therefore offer promise for generating Fdesigner_ gene delivery vectors with enhanced properties.

Growing evidence suggests that on-pathway amyloid-β (Aβ) oligomers are primary neurotoxic species and have a direct correlation with the onset of Alzheimer's disease (AD). One promising therapeutic strategy to block AD progression is to reduce the levels of these neurotoxic Aβ species using small molecules. While several compounds have been shown to modulate Aβ aggregation, compounds with such activity combined with safety and high blood-brain barrier (BBB) permeability have yet to be reported. Brilliant Blue G (BBG) is a close structural analogue of a U.S. Food and Drug Administration (FDA)-approved food dye and has recently garnered prominent attention as a potential drug to treat spinal cord injury due to its neuroprotective effects along with BBB permeability and high degree of safety. In this work, we demonstrate that BBG is an effective Aβ aggregation modulator, which reduces Aβ-associated cytotoxicity in a dose-dependent manner by promoting the formation of off-pathway, nontoxic aggregates. Comparative studies of BBG and three structural analogues, Brilliant Blue R (BBR), Brilliant Blue FCF (BBF), and Fast Green FCF (FGF), revealed that BBG is most effective, BBR is moderately effective, and BBF and FGF are least effective in modulating Aβ aggregation and cytotoxicity. Therefore, the two additional methyl groups of BBG and other structural differences between the congeners are important in the interaction of BBG with Aβ leading to formation of nontoxic Aβ aggregates. Our findings support the hypothesis that generating nontoxic aggregates using small molecule modulators is an effective strategy for reducing Aβ cytotoxicity. Furthermore, key structural features of BBG identified through structure-function studies can open new avenues into therapeutic design for combating AD.

Gene delivery to, and gene targeting in, stem cells would be a highly enabling technology for basic science and biomedical application. Adeno-associated viral (AAV) vectors have demonstrated the capacity for efficient delivery to numerous cells, but their application to stem cells has been limited by low transduction efficiency. Due to their considerable advantages, however, engineering AAV delivery systems to enhance gene delivery to stem cells may have an impact in stem cell biology and therapy. Therefore, using several diverse AAV capsid libraries-including randomly mutagenized, DNA shuffled, and random peptide insertion variants-we applied directed evolution to create a "designer" AAV vector with enhanced delivery efficiency for neural stem cells (NSCs). A novel AAV variant, carrying an insertion of a selected peptide sequence on the surface of the threefold spike within the heparin-binding site, emerged from this evolution. Importantly, this evolved AAV variant mediated efficient gene delivery to rat, mouse, and human NSCs, as well as efficient gene targeting within adult NSCs, and it is thus promising for applications ranging from basic stem cell biology to clinical translation.