700-nm Zwitterionic Near-Infrared Fluorophores for Dual-Channel Image-Guided Surgery.

PURPOSE: The purpose of this study was to develop a family of 700-nm zwitterionic pentamethine indocyanine near-infrared fluorophores that would permit dual-channel image-guided surgery. PROCEDURES: Three complementary synthetic schemes were used to produce novel zwitterionic chemical structures. Physicochemical, optical, biodistribution, and clearance properties were compared to Cy5.5, a conventional pentamethine indocyanine now used for biomedical imaging. RESULTS: ZW700-1a, ZW700-1b, and ZW700-1c were synthesized, purified, and analyzed extensively in vitro and in vivo. All molecules had extinction coefficients ≥199,000 M(-1) cm(-1), emission ≥660 nm, and stability ≥99 % after 24 h in warm serum. In mice, rats, and pigs, ≥80 % of the injected dose was completely eliminated from the body via renal clearance within 4 h. Either alone or conjugated to a tumor targeting ligand, ZW700-1a permitted dual-channel, high SBR, and simultaneous imaging with 800-nm NIR fluorophores using the FLARE® imaging system. CONCLUSIONS: Novel 700-nm zwitterionic NIR fluorophores enable dual-NIR image-guided surgery.

Hydroxylated near-infrared BODIPY fluorophores as intracellular pH sensors.

In this study, a series of new, highly sensitive BF2-chelated tetraarylazadipyrromethane dyes are synthesized and analyzed to be suitable as on/off photo-induced electron transfer modulated fluorescent sensors for determination of intracellular pH. The ethanolic solutions of the new indicators feature absorption maxima in the range of 696-700 nm and a fluorescence emission maximum at 720 nm. Molar absorptivity and fluorescence quantum yield data were determined for the studied set of aza-BODIPY indicators. These indicators have high molar absorption coefficients of ∼80,000 M(-1) cm(-1) and quantum yields (up to 18%). Corresponding pKa values of indicators are determined from absorbance and fluorescence measurements and range from 9.1 to 10.8, depending on the selective positioning of electron-donating functionalities. The excellent photostability of the aza-BODIPY indicators makes them particularly suitable for long duration measurements. The in vitro cellular staining of living tissues in PC3 cells based on the isosbestic point at pH 7.8 and pH 9.3 has been employed which shows an increase in fluorescence intensity at 800 nm with increase in pH for certain compounds and fluorescence intensity decreases at 700 nm. Therefore, the new indicators are suitable for exploitation and adaptation in a diverse range of analytical applications.

Labeling lysine acetyltransferase substrates with engineered enzymes and functionalized cofactor surrogates.

Elucidating biological and pathological functions of protein lysine acetyltransferases (KATs) greatly depends on the knowledge of the dynamic and spatial localization of their enzymatic targets in the cellular proteome. We report the design and application of chemical probes for facile labeling and detection of substrates of the three major human KAT enzymes. In this approach, we create engineered KATs in junction with synthetic Ac-CoA surrogates to effectively label KAT substrates even in the presence of competitive nascent cofactor acetyl-CoA. The functionalized and transferable acyl moiety of the Ac-CoA analogs further allowed the labeled substrates to be probed with alkynyl or azido-tagged fluorescent reporters by the copper-catalyzed azide-alkyne cycloaddition. The synthetic cofactors, in combination with either native or rationally engineered KAT enzymes, provide a versatile chemical biology strategy to label and profile cellular targets of KATs at the proteomic level.

The fluorescence-based acetylation assay using thiol-sensitive probes.

Lysine acetyltransferases (KATs) catalyze the acetylation of specific lysine residues in histone and nonhistone proteins. The enzymatic activities of KATs are involved in a broad spectrum of cellular processes. Thus far, the reaction of KAT catalysis has been studied by various bioanalytical methods such as radioisotopic labeling, spectrophotometric and fluorometric measurements, and antibody-dependent immunosorbent assays. In particular, the fluorescent method has the advantage of simplicity for implementation, fast assay speed, fine signal to noise ratio, and superior sensitivity. We describe here the technical protocols of using thiol-sensitive fluorogenic probes for the fluorescent analysis of enzymatic activities of KATs, with males on the first (MOF) as an exemplary KAT enzyme. 7-Diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM) is selected as the KAT probe owing to its fast reaction kinetics with coenzyme A (CoA) and excellent fluorogenicity upon thiol conjugation. The fluorescence-based acetylation assay is well suited for both kinetic characterization of KAT catalysis and KAT inhibitor investigation.

Comparative studies of thiol-sensitive fluorogenic probes for HAT assays.

Histone acetyltransferases (HATs) catalyze the acetylation of specific lysine residues in histone and nonhistone proteins. Recent studies showed that acetylation is widely distributed among cellular proteins, suggestive of diverse functions of HATs in cellular pathways. Nevertheless, currently available assays for HAT activity study are still quite limited. Here, we evaluated a series of thiol-sensitive fluorogenic compounds for the detection of the enzymatic activities of different HAT proteins. Upon conjugation to the thiol group of HSCoA, these molecules gain enhanced quantum yields and strong fluorescence, permitting facile quantitation of HAT activities. We investigated and compared the assay performances of these fluorogenic compounds for their capability as HAT activity reporters, including kinetics of reaction with HSCoA, influence on HAT activity, and fluorescence amplification factors. Our data suggest that CPM and coumarin maleic acid ester are excellent HAT probes owing to their fast reaction kinetics and dramatic fluorescence enhancement during the HAT reaction. Further, the microtiter plate measurements show that this fluorescent approach is robust and well suited for adaption to high-throughput screening of small molecule inhibitors of HATs, highlighting the value of this assay strategy in new drug discovery.

6-alkylsalicylates are selective Tip60 inhibitors and target the acetyl-CoA binding site.

Histone acetyltransferases are important enzymes that regulate various cellular functions, such as epigenetic control of DNA transcription. Development of HAT inhibitors with high selectivity and potency will provide powerful mechanistic tools for the elucidation of the biological functions of HATs and may also have pharmacological value for potential new therapies. In this work, analogs of the known HAT inhibitor anacardic acid were synthesized and evaluated for inhibition of HAT activity. Biochemical assays revealed novel anacardic acid analogs that inhibited the human recombinant enzyme Tip60 selectively compared to PCAF and p300. Enzyme kinetics studies demonstrated that inhibition of Tip60 by one such novel anacardic acid derive, 20, was essentially competitive with Ac-CoA and non-competitive with the histone substrate. In addition, these HAT inhibitors effectively inhibited acetyltransferase activity of nuclear extracts on the histone H3 and H4 at micromolar concentrations.