Michael Simpson

Cellular Models of Aggregation-dependent Template-directed Proteolysis to Characterize Tau Aggregation Inhibitors for Treatment of Alzheimer Disease

Background: Tau aggregation inhibitors could treat Alzheimer disease. Results: Stable reduced forms of leucomethylthioninium (LMTX®) are active in blocking prion-like Tau aggregation in novel cellular models. Conclusion: The intracellular Ki (0.12 μm) is comparable with brain levels required for clinical benefit. Significance: LMTX® could treat Alzheimer disease. Alzheimer disease (AD) is a degenerative tauopathy characterized by aggregation of Tau protein through the repeat domain to form intraneuronal paired helical filaments (PHFs). We report two cell models in which we control the inherent toxicity of the core Tau fragment. These models demonstrate the properties of prion-like recruitment of full-length Tau into an aggregation pathway in which template-directed, endogenous truncation propagates aggregation through the core Tau binding domain. We use these in combination with dissolution of native PHFs to quantify the activity of Tau aggregation inhibitors (TAIs). We report the synthesis of novel stable crystalline leucomethylthioninium salts (LMTX®), which overcome the pharmacokinetic limitations of methylthioninium chloride. LMTX®, as either a dihydromesylate or a dihydrobromide salt, retains TAI activity in vitro and disrupts PHFs isolated from AD brain tissues at 0.16 μm. The Ki value for intracellular TAI activity, which we have been able to determine for the first time, is 0.12 μm. These values are close to the steady state trough brain concentration of methylthioninium ion (0.18 μm) that is required to arrest progression of AD on clinical and imaging end points and the minimum brain concentration (0.13 μm) required to reverse behavioral deficits and pathology in Tau transgenic mice.

One-pot production of 18F-biotin by conjugation with 18F-FDG for pre-targeted imaging: Synthesis and radio-labelling of a PEGylated precursor

The biotin-avidin affinity system is exploited in pre-targeted imaging using avidin-conjugated antibodies. (18)F-FDG is available at all PET centres. (18)F-FDG forms oximes by reaction with oxyamine. Herein we describe the synthesis of oxyamine-funtionalised biotin, its (18)F-labelling by conjugation with (18)F-FDG and confirm its ability to interact with avidin.

Development of 18F-fluorinatable dendrons and their application to cancer cell targeting

18F-fluorine is an ideal imaging PET (positron emission tomography) nuclide due to the low energy of its β+ (positron) and pure β+ decay. PAMAM dendrimers are branched organic molecules with multiple NH2 termini each of which can accommodate the attachment of functionalities. The presence of a thiol group also facilitates the conjugation of a targeting molecule. Here we describe the attachment of boroaryl moieties to the terminal NH2 groups of dendrimers and after cleavage of the bridging thiol group conjugation of the functionalized dendrons (half-dendrimers) to biotin. Incubation of the targeted, boroaryl-functionalized dendrons with 18F-fluoride in acetic acid facilitated their radiolabelling with a labelling efficiency of about 60%. We then demonstrated that the 18F-dendron–biotin bound to HER-2 expressing cellsin vitro pre-targeted with the avidin–trastuzumab conjugate. The cell-associated 18F decreased with increasing dendron size suggesting that the larger dendrons sterically hindered binding of avidin with biotin. This is the first study to demonstrate that dendrimers can be functionalized with 18F-fluorinatable groups and used to target cell surface receptors.

18F -PEG-biotin: Precursor (boroaryl-PEG-biotin) synthesis, 18F -labelling and an in-vitro assessment of its binding with Neutravidin™-trastuzumab pre-treated cells.

UNLABELLED In terms of nuclear decay 18F is the most ideal PET nuclide but its short t(½) precludes its use for directly labelling whole antibodies due to their long blood residence times. Pre-targeted imaging using affinity systems such as Neutravidin™-biotin facilitates the application of short-lived nuclides by their attachment to biotin for imaging cell surface proteins targeted with Neutravidin™-conjugated antibodies. METHODS Boroaryl functionalised biotin was prepared with a PEG linker and radiolabelled by incubation with 18F in acidified aqueous solution. Cells expressing high (SKBr3), medium (MDA-MB-453) and low (MDA-MB-468) levels of HER-2 were pre-incubated with Neutravidin™-conjugated trastuzumab, washed, and then incubated with 18F -PEG-biotin. RESULTS The 18F -fluorination of boroaryl-PEG-biotin was much more efficient than reported for other versions of boroaryl-biotin. The novel 18F -PEG-biotin was demonstrated to bind to HER-2-expressing cells in-vitro pre-incubated with Neutravidin™-conjugated trastuzumab. CONCLUSION Biotin can be functionalised with boroaryl and readily 18F -radiolabelled in aqueous solution and will bind to cells pre-incubated with Neutravidin™-antibody conjugates.

Alzheimer's Disease-like Paired Helical Filament Assembly from Truncated Tau Protein Is Independent of Disulfide Crosslinking

Alzheimers disease is characterized by the self-assembly of tau and amyloid β proteins into oligomers and fibrils. Tau protein assembles into paired helical filaments (PHFs) that constitute the neurofibrillary tangles observed in neuronal cell bodies in individuals with Alzheimers disease. The mechanism of initiation of tau assembly into PHFs is not well understood. Here we report that a truncated 95-amino-acid tau fragment (corresponding to residues 297-391 of full-length tau) assembles into PHF-like fibrils in vitro without the need for other additives to initiate or template the process. Using electron microscopy, circular dichroism and X-ray fiber diffraction, we have characterized the structure of the fibrils formed from truncated tau for the first time. To explore the contribution of disulfide formation to fibril formation, we have compared the assembly of tau(297-391) under reduced and non-reducing conditions and for truncated tau carrying a C322A substitution. We show that disulfide bond formation inhibits filament assembly and that the C322A variant rapidly forms long and highly ordered PHFs.

Diethyl 9,10-endo-ethano-9,10-di­hydro­anthracene-11,11-di­carboxyl­ate

The title compound, C22H22O4, possesses normal geometrical parameters and the dihedral angle between the two benzene ring planes is 57.62 (5)°. The crystal packing is controlled by van der Waals forces and a possible C—H⋯O interaction, the latter resulting in a supramolecular C(6) motif.

Cysteine-Independent Inhibition of Alzheimer's Disease-like Paired Helical Filament Assembly by Leuco-Methylthioninium (LMT)

Alzheimers disease is a tauopathy characterized by pathological fibrillization of tau protein to form the paired helical filaments (PHFs), which constitute neurofibrillary tangles. The methylthioninium (MT) moiety reverses the proteolytic stability of the PHF core and is in clinical development for treatment of Alzheimers disease in a stable reduced form as leuco-MT. It has been hypothesized that MT acts via oxidation of cysteine residues, which is incompatible with activity in the predominantly reducing environment of living cells. We have shown recently that the PHF-core tau unit assembles spontaneously in vitro to form PHF-like filaments. Here we describe studies using circular dichroism, SDS-PAGE, transmission electron microscopy and site-directed mutagenesis to elucidate the mechanism of action of the MT moiety. We show that MT inhibitory activity is optimal in reducing conditions, that the active moiety is the reduced leuco-MT form of the molecule and that its mechanism of action is cysteine independent.