QuatCy-I2 and MHI-I2 in Photodynamic Therapy.

MHI-I2 (1) and QuatCy-I2 (2) were compared in terms of properties important for early-stage photodynamic therapy preclinical candidates. Thus, experiments were performed to monitor dark cytotoxicities, light/dark cytotoxicity ratios, selectivity of localization in tumors over other organs, and clearance from the plasma.

Minimizing solvent waste in catalytic reactions in highly recyclable hydrocarbon solvents.

This paper describes chemistry using organocatalysts in hydrocarbon solvents that minimizes solvent waste by using inexpensive, non-volatile, relatively inflammable, and easily recyclable poly(α-olefin)s (PAOs) as hydrocarbon solvents. These studies show that when substrates have limited solubility in PAO solvents, this issue can be addressed by adding a small amount of a cosolvent. Kinetic studies were also carried out and show that reactions carried out in PAOs are kinetically comparable to reactions in conventional non-recyclable hydrocarbon solvents. A range of strategies that separate and isolate products from reactions in PAOs using a polyisobutylene (PIB)-supported DMAP catalyst have been studied using four different catalytic reactions. In the most general procedure, the PAO phase containing a PIB-bound catalyst is separated from products by low energy liquid/liquid gravity separation. This can be accomplished using a minimal amount of a polar solvent. In another example, the product's low solubility leads to it precipitating during the reaction. In this case, a simple filtration recycles the PAO and a PIB-bound DMAP catalyst. We have demonstrated that the PAO phase containing a PIB bound DMAP catalyst can be recycled for at least 10 cycles without loss of activity. Our studies further showed that leaching of the PAO phase into polar solvents was orders of magnitude less than conventional hydrocarbon solvents such as heptane. The result is that the overall solvent waste generation is lower than for the same reaction carried out in conventional solvents.

Protein labelling and albumin binding characteristics of the near-IR Cy7 fluorophore, QuatCy.

Free cysteine residues react with QuatCy 1, by simply mixing the protein and dye in aqueous buffer at 37 °C. Another dye, MHI-148, can be used for a similar labelling protocol, but QuatCy reacts faster with all proteins studied, except albumin; it emerges here that this is because MHI-148 instantly forms of a non-covalent complex with albumin, but QuatCy does not. Labelling with QuatCy has advantages insofar as it is over five times brighter, and much more photostable, than MHI-148, and combination labelling with this dye pair will allow multiplexing in the near-IR region.

QuatCy: A Heptamethine Cyanine Modification With Improved Characteristics.

A major restriction on optical imaging techniques is the range of available fluorophores that are compatible with aqueous media without aggregation, absorb light above 750 nm with high extinction coefficients, fluoresce with relatively high quantum yields, and resist photodecomposition. Indocyanine green (ICG or A in this paper) is an important example of a fluorophore that fits this description. Other dyes that are becoming increasingly prevalent are select heptamethine cyanine dyes (Cy7) which feature a cyclohexyl framework to rigidify the conjugated alkenes, and meso-chlorine substitution; MHI-148 (B) is one example. Methods: Research described here was initiated to uncover the consequences of a simple isoelectronic substitution to MHI-148 that replaces a cyclohexyl methylene with a dialkyl ammonium fragment. Solubility experiments were carried out in aqueous and cell culture media, photophysical properties including fluorescence quantum yields, brightness and stability were measured. Moreover, in vivo pharmacokinetics, distribution and tumor seeking properties were also explored. Results: Modification to incorporate dialkyl ammonium fragment leads to a brighter, more photostable fluorophore, with a decreased tendency to aggregation, complementary solubility characteristics, and a lower cytotoxicity. Conclusion: All the above-mentioned parameters are favorable for many anticipated applications of the new dye we now call quaternary cyanine-7 or QuatCy.

Optimized Heptamethine Cyanines for Photodynamic Therapy.

Over 10 near-IR fluorescent sensitizers were prepared to explore their properties relevant to potential applications in photodynamic therapy (PDT). Key properties of these compounds are that they can be excited around 800 nm, (i) are hydrophilic, (ii) generate singlet oxygen with acceptable quantum yields, and (iii) are imported into cancer cells via the organic anion transporter proteins (OATPs). (This is crucial to tumor localization.) The N-substituents of these cyanines were varied to adjust their charges and polarities and to accommodate conjugation to other entities (e.g., biomolecules or fragments to expand their theranostic modalities). Thus, it was possible to optimize their photocytotoxicities without compromising their other desirable characteristics for PDT. Overall, sensitizers like this have superior characteristics relative to clinically approved sensitizers for PDT insofar as they can be excited at greater depths in tissue.

Near-infrared aza-BODIPY fluorescent probe for selective Cu2+ detection and its potential in living cell imaging.

A near-infrared (NIR) fluorescent sensor 1 composed of an aza-boron-dipyrromethene (aza-BODIPY) core covalently bound to two di-2-picolylamine moieties was conceived for Cu2+ detection in aqueous solutions. Spectroscopic properties and binding abilities with several metal ions were investigated in phosphate buffered saline (pH 7.4): acetonitrile (95 : 5 v/v) with Triton X-100 via fluorometric titrations. The fluorescence of sensor 1 was quenched selectively by cupric ions in the presence of alkali- and transition-metal-ions. A detection limit of 13 ppb was measured for this system, and this is significantly lower than permissible levels of Cu2+ in drinking water according to the guidelines described by the U.S. Environmental Protection Agency (EPA) and by the World Health Organization (WHO). Application of the sensor in detecting Cu2+ in HepG2 cells was demonstrated.

Oligoethylene glycol-substituted aza-BODIPY dyes as red emitting ER-probes.

This study features aza-BODIPY (BF2-chelated azadipyrromethene) dyes with two aromatic substituents linked by oligoethylene glycol fragments to increase hydrophilicity of aza-BODIPY for applications in intracellular imaging. To prepare these, two chalcones were attached α,ω onto oligoethylene glycol fragments, then reacted with nitromethane anion. Conjugate addition products from this reaction were then subjected to typical conditions for synthesis of aza-BODIPY dyes (NH4OAc, (n)BuOH, 120 °C); formation of boracycles in this reaction was concomitant with creation of macrocycles containing the oligoethylene glycol fragments. Similar dyes with acyclic oligoelythene glycol substituents in the same position were used to compare the efficiencies of the intra- and inter-molecular aza-BODIPY forming reactions, and the characteristics of the products. All the fluors with oligoethylene glycol fragments, i.e. cyclic or acyclic, localized in the endoplasmic reticulum of a fibroblast cell line (WEHI-13VAR), the human pancreatic cancer cell line (PANC-1, rough ER predominates) and human liver cancer cell line (HepG2, smooth ER prevalent). These fluors are potentially useful for near IR (λmax emis at 730 nm) ER staining probes.