Semen was recently shown to contain amyloid fibrils formed from a self-assembling peptide fragment of the protein prostatic acid phosphatase. These amyloid fibrils, termed semen-derived enhancer of virus infection, or SEVI, have been shown to strongly enhance HIV infectivity and may play an important role in sexual transmission of HIV, making them a potential microbicide target. One novel approach to target these fibrils is the use of small molecules known to intercalate into the structure of amyloid fibrils, such as derivatives of thioflavin-T. Here, we show that the amyloid-binding small molecule BTA-EG6 (the hexa(ethylene glycol) derivative of benzothiazole aniline) is able to bind SEVI fibrils and effectively inhibit both SEVI-mediated and semen-mediated enhancement of HIV infection. BTA-EG6 also blocks the interactions of SEVI with HIV-1 virions and HIV-1 target cells but does not cause any inflammation or toxicity to cervical epithelial cells. These results suggest that an amyloid-binding small molecule may have utility as a microbicide, or microbicidal supplement, for HIV-1.

A new family of fluorescent markers containing an Amino Naphthalenyl-2-Cyano-Acrylate (ANCA) motif has been synthesized and evaluated for its capability to associate with aggregated β-amyloid (Aβ) peptides. These fluorescent probes contain a nitrogen donor group that is connected via a naphthalene unit to an electron acceptor motif containing Water Solubilizing Groups (WSG). Chemical modifications were introduced to explore their effect on the capability of the ANCA-based probes to fluorescently label aggregated Aβ peptides. All synthesized probes bind to aggregated Aβ fibrils with low micromolar affinity and fluorescently stain amyloid deposits in human brain tissue from patients with Alzheimer’s disease. We found that structural modifications of the WSG site do not affect considerably the binding affinity. However, changes of the nitrogen donor group alter significantly the binding affinity of these probes. Also, increasing the hydrophilicity of the donor group leads to improved contrast between the Aβ deposits and the surrounding tissue in histological staining experiments.

Alzheimer's disease (AD) is characterized by a progressive loss of cognitive function and constitutes the most common and fatal neurodegenerative disorder.[1] Genetic and clinical evidence supports the hypothesis that accumulation of amyloid deposits in the brain plays an important role in the pathology of the disease. This event is associated with perturbations of biological functions in the surrounding tissue leading to neuronal cell death, thus contributing to the disease process. The deposits are comprised primarily of amyloid (Aβ) peptides, a 39-43 amino acid sequence that self aggregates into a fibrillar β-pleated sheet motif. While the exact three-dimensional structure of the aggregated Aβ peptides is not known, a model structure that sustains the property of aggregation has been proposed. [2] This creates opportunities for in vivo imaging of amyloid deposits that can not only help evaluate the time course and evolution of the disease, but can also allow the timely monitoring of therapeutic treatments. [3] Keywords amyloid peptides; fluorescent probes; imaging agents; molecular rotors Historically, Congo Red (CR) and Thioflavin T (ThT) have provided the starting point for the visualization of amyloid plaques and are still commonly employed in post mortem histological analyses (Figure 1).[4] However, due to their charge these probes are unsuitable for in vivo applications. [5] To address this issue, several laboratories developed probes with noncharged, lipophilic (log P = 0.1-3.5) and low-molecular weight chemical structures (MW <650) that facilitate crossing of the blood-brain barrier.[6] Further functionalization of these compounds with radionuclides led to a new generation of in vivo diagnostic reagents (Figure 1) that target plaques and related structures for imaging with positron emission tomography (PET) and single-photon emission computed tomography (SPECT Figure 1 reveals that the majority of these probes contain an electrondonor unit in conjugation with an electron acceptor (D-π-A motif). This motif is a typical feature in molecular rotors, a family of fluorescent probes known to form twisted intramolecular charge-transfer (TICT) complexes in the excited state producing a fluorescence quantum yield that is dependent on the surrounding environment.[11] Following photoexcitation, this motif has the unique ability to relax either via fluorescence emission or via an internal nonradiative molecular rotation. This internal rotation occurs around the σ-bonds that connect the electron-rich π-system with the donor and acceptor groups, and can be modified by altering the chemical structure and microenvironment of the probe.[12] Hindrance of the internal molecular rotation of the probe by increasing the surrounding media rigidity, or by reducing the available free volume needed for relaxation, leads to a decrease in the nonradiative decay rate and consequently an increase in fluorescence. In contrast, relaxation proceeds mainly via nonradiative pathways in environments of low viscosity or of hi...

This paper evaluates the use of oligovalent amyloid-binding molecules as potential agents that can reduce the enhancement of HIV-1 infection in cells by SEVI fibrils. These naturally occurring amyloid fibrils found in semen have been implicated as mediators that can facilitate the attachment and internalization of HIV-1 virions to immune cells. Molecules that are capable of reducing the role of SEVI in HIV-1 infection may, therefore, represent a novel strategy to reduce the rate of sexual transmission of HIV-1 in humans. Here, we evaluated a set of synthetic, oligovalent derivatives of BTA (a known amyloid-binding molecule) for their capability to bind cooperatively to aggregated amyloid peptides and to neutralize the effects of SEVI in HIV-1 infection. We demonstrate that these BTA derivatives exhibit a general trend of increased binding to aggregated amyloids as a function of increasing valence number of the oligomer. Importantly, we find that oligomers of BTA show improved capability to reduce SEVI-mediated infection of HIV-1 in cells compared to a BTA monomer, with the pentamer exhibiting a 65-fold improvement in efficacy compared to a previously reported monomeric BTA derivative. These results, thus, support the use of amyloid-targeting molecules as potential supplements for microbicides to curb the spread of HIV-1 through sexual contact.

The tetra(ethylene glycol) derivative of benzothiazole aniline, BTA-EG 4 , is a novel amyloid-binding small molecule that can penetrate the blood-brain barrier and protect cells from A␤-induced toxicity. However, the effects of A␤-targeting molecules on other cellular processes, including those that modulate synaptic plasticity, remain unknown. We report here that BTA-EG 4 decreases A␤ levels, alters cell surface expression of amyloid precursor protein (APP), and improves memory in wild-type mice. Interestingly, the BTA-EG 4 -mediated behavioral improvement is not correlated with LTP, but with increased spinogenesis. The higher dendritic spine density reflects an increase in the number of functional synapses as determined by increased miniature EPSC (mEPSC) frequency without changes in presynaptic parameters or postsynaptic mEPSC amplitude. Additionally, BTA-EG 4 requires APP to regulate dendritic spine density through a Ras signaling-dependent mechanism. Thus, BTA-EG 4 may provide broad therapeutic benefits for improving neuronal and cognitive function, and may have implications in neurodegenerative disease therapy.