Fluorescent labeling complexes with large Stokes shift...

Details Fluorescent labeling complexes with large Stokes shift... Fluorescent labeling complexes with large Stokes shift...

1998-09-11

2002-11-12

Ceperley, Mary E. (Department: 1641)

Chemistry: analytical and immunological testing

Involving producing or treating antigen or hapten

Producing labeled antigens

C435S006120, C435S007200, C435S188000, C436S527000, C436S529000, C436S530000, C436S534000, C436S800000, C530S391300, C530S391500, C530S402000, C530S409000

Reexamination Certificate

active

06479303

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fluorescent labeling complexes, and more particularly to low molecular weight fluorescent complexes with large Stokes shifts.
2. Description of the Invention Background
Fluorescence labeling is an important technology for detecting biological molecules. For example, antibodies can be labeled with fluorescent dyes. The binding of antibodies to their specific target molecules can then be monitored on the basis of a fluorescence signal, which may be detected with a spectrometer, immunofluorescence instrument, flow cytometer, or fluorescence microscope. In a similar way, DNA sequences can be detected with fluorescence detection instruments after the DNA has been “hybridized” with a complementary DNA sequence that has been labeled with a fluorescent dye.
Very bright and water soluble fluorescent labeling reagents are important for sensitive detection of labeled antibodies, DNA probes, ligands, cytokines, drugs, lipids, metabolites and other molecules and compounds of interest. Multiparameter analysis using fluorescent labels with distinctly different emission wavelengths further increase the importance of this technology by providing a powerful tool for correlating multiple antigenic or genetic parameters in individual cells. In epifluorescence microscopy, a continuous light source with different sets of excitation and emission filters are used to excite and detect each fluorescent species. This approach works especially well if the absorption and emission wavelengths of each of the fluorophores are relatively close together (e.g. Stokes shifts of 15-30 nm). Most of the highly fluorescent, low molecular weight fluorochromes like the cyanines and xanthenes have narrow absorption and emission peaks and small Stokes shifts. Up to 5 separate fluorescent labels have been analyzed on the same specimen by microscopy using epifluorescence filter sets as described in DeBiasio, R., Bright, G. R., Ernst, L. A., Waggoner, A. S., Taylor, D. L. “Five-parameter fluorescence imaging: Wound healing of living Swiss 3T3 cells,” Journal of Cell Biology, vol. 105, pp.1613-1622 (1987).
Flow cytometers and confocal microscopes are different from microscopes equipped with separate epifluorescence filter sets, in that they utilize lasers with defined wavelengths for fluorescence excitation. While it is easy to find a single fluorophore that can be efficiently excited at a particular laser wavelength, it is difficult to find additional fluorescent labels with large enough Stokes shifts to provide emission well separated from that of the first fluorophore. The naturally occurring phycobiliproteins are a class of multichromophore fluorescent photosystem proteins that have large wavelength shifts. See, Oi, V. T., Glazer, A. N., Stryer, L. “Fluorescent phycobiliprotein conjugates for analyses of cells and molecules,” Journal of Cell Biology, vol.93, pp.981-986 (1982). These can be covalently coupled to antibodies and have become widely used in flow cytometry for 2 color lymphocyte subset analysis. R-phycoerythrin (R-PE), a photosystem protein containing 34 bilin fluorophores which can be excited at 488 nm with the widely available argon ion laser, has been especially useful. It fluoresces maximally at 575 nm. R-PE and fluorescein can both be excited at 488 nm, but R-PE can readily be discriminated with optical band-pass interference filter sets from the fluorescein signal, which appears at 525 nm. Recently, 3-color immunofluorescence by flow cytometry has become possible through the development of tandem conjugate labeling reagents that contain a reactive cyanine fluorescent dye which is excited at 488 nm and fluoresces at 613 nm, and is sold commercially under the name Cychrome. See, U.S. Pat. No. 4,876,190 and Waggoner, A. S., Ernst, L. A., Chen, C. H., Rechtenwald, D. J., “PE-CY 5; A new fluorescent antibody label for 3-color flow cytometry with a single laser,” Ann. NY Acad. Sci., vol.677, pp.185-193 (1993). With these tandem fluorophores, energy transfer from excited R-PE to the Texas Red or the reactive pentamethine cyanine known as CY5 leads to fluorescence at 620 nm or 670 nm, respectively.
The phycobiliprotein-based labels are very fluorescent and provide excellent signals in 2 and 3-parameter experiments for detection of cell surface antigens. However, these reagents have not been widely utilized for measurement of cytoplasmic antigens or for detection of chromosomal markers by fluorescence in situ hybridization because their large size (MW=210,000 Daltons) limits penetration into dense cell structures.
There is a need for a new class of low molecular weight fluorescent labels that will provide multicolor fluorescence detection using single wavelength excitation. There is a further need for several such flourescenct labels each of which can be excited optimally at a particular laser wavelength but that fluoresce at significantly different wavelengths.
SUMMARY OF THE INVENTION
The present invention provides a low molecular weight fluorescent labeling complex which includes a first, or donor, fluorochrome having first absorption and emission spectra, and a second, or acceptor, fluorochrome having second absorption and emission spectra. At least one of the first or second fluorochromes is a cyanine dye. The wavelength of the emission maximum of the second fluorochrome is longer than the wavelength of the emission maximum of the first fluorochrome, and a portion of the absorption spectrum of the second fluorochrome overlaps a portion of the emission spectrum of the first fluorochrome for transfer of energy absorbed by the first fluorochrome upon excitation with light to the second fluorochrome.
The complex also includes a linker for covalently attaching the fluorochromes to permit resonance energy transfer between the first and the second fluorochromes. The linker may be flexible and in a preferred embodiment, separates the fluorochromes by a distance that provides efficient energy transfer, preferably better than 75%. The linker may be about 2 to 20 bond lengths. A preferred length for the linker is less than 70 Angstroms (7 nm), and more preferably, less than 20 Angstroms (2 nm). In the case of flexible linkers, particularly when the labeling complexes are in solution, the relative orientations of the first and second fluorochromes changes as the linker flexes.
The first fluorochrome preferably has an extinction coefficient greater than 20,000 Liters/mole cm and preferably greater than 50,000 Liters/mole cm and the second fluorochrome has a fluorescence quantum yield greater than or equal to about 0.05. Quantum yield is generally related to a molecule's rigidity or planarity and indicates the molecules propensity to fluoresce, i.e. to give off energy as light, rather than as heat when energy is provided to the molecule. The combined molecular weight of the fluorochromes and the linker is less than about 20,000; Daltons, and preferably in the range of 500 to 10,000 Daltons.
The complex includes a target bonding group capable of forming a covalent bond with a target compound to enable the complex to label the target, such as a carrier material or a biological compound. The target bonding group may be a reactive group for reacting with a functional group on the target compound or molecule. Alternatively, the complex may contain the functional group and the target may contain the reactive constituent. The reactive group is preferably selected from the group consisting of succinimidyl ester, isothiocyanates, dichlorotriazine, isocyanate, iodoacetamide, maleimide, sulfonyl halide, acid halides, alkylimidoester, arylimidoester, substituted hydrazines, substituted hydroxylamines, carbodiimides, and phosphoramidite. The functional group may be selected from the group consisting of amino, sulfhydryl, carboxyl, hydroxyl and carbonyl. The target may be antibody, antigen, protein, enzyme, nucleotide derivatized to contain one of an amino, hydroxyl, sulfhydryl, carboxyl or carbonyl groups, and oxy or deoxy polynucleic

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