EP1268858A1

EP1268858A1 - Use of particles which have signal-emitting characteristics and at least one group with an affinity for marked nucleic acids

Info

Publication number: EP1268858A1
Application number: EP01929486A
Authority: EP
Inventors: Andreas Bosio; Alexander Scheffold
Original assignee: Memorec Stoffel Medizinisch-Molekulare Entwicklung GmbH
Current assignee: Memorec Biotec GmbH
Priority date: 2000-03-31
Filing date: 2001-03-31
Publication date: 2003-01-02
Also published as: US20030077636A1; AU2001256244A1; WO2001073117A1; WO2001073117A9; JP2003528625A

Abstract

The invention relates to the use of particles with signal-emitting characteristics and at least one group with an affinity for marked nucleic acids, for detecting marked nucleic acids which are hybridised with nucleic acids that are immobilised on a surface. The invention also relates to supports containing particles which have signal-emitting characteristics and at least one group with an affinity for marked nucleic acids, for detecting marked nucleic acids.

Description

Use of particles which have signaling properties and at least one affinity group for labeled nucleic acids

The present invention relates to the use according to claim 1 and carriers according to claim 8.

The invention relates to a carrier which makes it possible to bind two or more differently labeled nucleic acids, which are hybridized independently of one another with nucleic acids immobilized on a surface, and to make them measurable with the aid of the different signaling molecules built into or carried in the carrier.

Microarrays (solid supports, on the surface of which nucleic acids are immobilized at different addressable positions) are increasingly used for the parallel identification and creation of transcription profiles of polynucleic acids. For hybridization, the nucleic acids to be analyzed are changed so that they can subsequently be identified and quantified (radioactivity, chemiluminescence fluorescence, etc.). The modification can either be a

Molecule that can itself emit a signal (direct labeling) or a molecule that is recognized by a second molecule, which in turn is labeled (indirect labeling). A problem when using the microarrays is the sensitivity with which nucleic acids to be analyzed can be recognized on these supports or limited starting amounts of nucleic acid mixtures to be analyzed which do not permit sensitive detection.

In the prior art, there are two ways to solve this problem. Firstly, attempts are made to amplify the available nucleic acid in different ways before it is hybridized with the microarray (T7 in vitro transcription, (Eberwine et al.) Or PCR, to mention only two methods). Secondly, attempts are made to recognize the already hybridized and chemically modified nucleic acids with the aid of the indirect labeling or in combination with the direct labeling and via a secondary reaction in combination with the recognized site, for example by enzymatic reactions to generate strong signals (keyword sandwich, tyramine, horseradish peroxidase etc.). The disadvantages of this procedure lie in the fact that the enzymatic methods used here often lead to a non-linear amplification, which means that the amount of the different nucleic acids present is amplified differently. However, since the amount of nucleic acid is to be determined using the microarray analysis, the uneven amplification questions the entire analysis. Furthermore, both the enzymatic and the non-enzymatic amplification reactions are often multi-stage reactions and are very complex.

The technical problem on which the invention is based is to avoid the disadvantages mentioned above and to ensure a more precise quantification of nucleic acids.

According to the invention, the problem addressed is solved by using particles selected from the group consisting of liposomes and / or micelles with signaling properties and at least one affinity group for labeled nucleic acids for the detection of labeled nucleic acids which are hybridized with nucleic acid immobilized on a surface.

In an advantageous embodiment of the use according to the invention, the nucleic acids have different labels. In this way, for example, healthy and diseased tissue can be differentiated.

The particles preferably have a particle size of 20 to 4000 nm, preferably 200 to 400 nm. The particles and their production are described in Scheffold A, Miltenyi S, Radbruch A, Magnetofluorescent liposomes for increased sensitivity of immunofluorescence. Immunotechnology 1995; l (2): 127-37.

The signaling property is caused in particular by electromagnetic radiation, in particular fluorescence, radioactivity, luminescence, phosphorescence, electromagnetic resonance. The affinity group is preferably an antibody or an antibody fragment. The affinity grouping can be directed against any kind of low molecular haptens such as Alexa Fluor 488; Amino-3-deoxydigoxigenin hemisuccinamide; biotin; BODIPY; Cascade Blue; Cy2; CY3; CY5; dansyl; DNP (dinitrophenol); DIG (digoxigenin); Alexa Fluor 488; 5 (6) - SFX; fluorescein; Lucifer yellow iodoacetamide; Marina Blue; Oregon Green 488; 5 (6) -TAMRA; PE (phycoerythrin); Rhodamine Red; Texas Red. The nucleic acids must then be labeled with the corresponding haptens.

The invention also relates to supports with a surface on which nucleic acids are immobilized which are hybridized with labeled nucleic acids, particles which have signaling properties and at least one affinity group for the labeled nucleic acids, after which the first affinity group is bound to the labeled nucleic acids.

The particles for the carrier according to the invention for the highly sensitive immunofluorescence detection of hybridized nucleic acids preferably consist of magnetofluorescent liposomes which contain several thousand fluorescent molecules and colloidal magnetic particles.

The liposomes are preferably composed of 40 to 50 mol%, in particular 45 mol% of phosphatidylcholine, 5 to 15 mol%, in particular 10 mol% of phosphatidylglycerol, 2 to 10 mol%, in particular 5 mol% of phosphatidylethanolamine and 35 to 45 mol%, in particular 40 mol% cholesterol.

When using water-soluble fluorophores (e.g. carboxyfluorescein), the liposomes contain a 1 to 100 mM solution of the fluorescent dye depending on the solubility and the fluorescence behavior of the respective fluorophore, which solution is obtained by immersing the liposomes in a correspondingly concentrated fluorophore solution and diffusing the fluorophore into the liposomes be preserved. When water-insoluble fluorophores are used, the liposomes contain the corresponding fluorophore in a molar ratio of 1: 100 to 1: 1000 depending on the solubility and the fluorescence behavior of the respective fluorophore. The fluorophore-containing liposomes are obtained by the fact that during the production of the liposomes Depending on the solubility and the fluorescence behavior of the fluorophore, the corresponding fluorophore is added in a molar ratio of 1: 100 to 1: 1000 based on the number of moles of the lipids.

The liposomes contain superparamagnetic microparticles with a diameter of 50 to 100 nm. These are obtained by immersing the liposomes in a solution of superparamagnetic microparticles, the absorption of which at 500 nm is 500 nm (optical density, OD ₄₅₀ ).

A striking difference between liposomes (particles with a pseudo-fluid, biphasic surface) and all other microparticles is that due to the fluidic properties, an affinity grouping on the surface of the liposomes can move freely. This is of crucial importance for the affinity or avidity (total bond strength between two molecules or particles, which is influenced by several binding regions), because:

A) For theoretical, steric and manufacturing reasons, only a finite number of affinity groups can be introduced on the surface of a particle.

B) The density of the affinity groups applied must be selected very precisely, since if the density is too high a mutual repulsion and hindrance can be expected, but if the loading density is too low the probability of binding to the target molecule is greatly reduced.

The binding strength between rigid, spherical particles (microspheres) with a diameter of 20 to 4000 nm, and a relatively rigid tube with a diameter of approx. 2 nm (double-stranded DNA) is therefore decisive for steric reasons through the binding of a single one Affinity group determined. The bond strength between fluidic, spherical particles (liposomes and micelles) with a diameter of 20 to 4000 nm, and a relatively rigid tube with a diameter of approx. 2 nm (double-stranded DNA) is most likely determined by more than one affinity group. This can be explained as follows: After a target molecule has been bound by a first affinity group of a liposome, further affinity groups of the same liposome can develop in the course of the constant lateral diffusion (approx. 10 ^"6 - 10 ^{" 7} m per s) - as they do for lipid bilayers is known - migrate to an adjacent target molecule and form a second bond.

An antigen (target molecule) is bound in a first approximation by one of the two binding sites of an antibody in a reversible bimolecular reaction. The affinity constant for most antibodies is K = 10 ⁵ to 10 ¹¹ L / mol. The simple bimolecular reaction can only be used for the reaction between an antigen with an epitope and homogeneous antibodies. If there are two identical epitopes on the antigen at such a distance that the two binding sites of one antibody or two contiguous antibodies (e.g. IgM or the liposomes equipped with the antibodies described here) contain the same or two adjacent, contiguous antigen molecules (labeled, double-stranded DNA) the reaction is no longer bimolecular, so that complicated equations have to be used for the kinetics of immune complex formation. If the two antibody binding sites can react, the second binding site, for example, is bound to the epitope much more quickly than the first (entropic effect) because the antigen molecule is already very close to the antibody, so that the apparent affinity (avidity) is usually at least that is increased 10 ⁴ times.

The increased affinity (avidity) leads to an increased and more specific binding, which explains the higher sensitivity and specificity of the liposomes, ie particles that have a biphasic fluidic surface, compared to other spherical particles. Antibodies, for example anti-DNP, anti-DIG etc., are added to the amino groups of the amino acids in the with succinimidyl-4- (N-maleimidomethyl) cyclohexane-1-carboxylate via thiol groups, which can be exposed by reagents reducing SS groups Liposomes conjugated to phosphatidyl ethanolamines. Typical reduction conditions are set with dithiothreitol.

The RNAs to be examined are transcribed into the corresponding cDNA using a conventional RT reaction. Here derivatized nucleotides such as DNP-dCTP, DIG-CTP etc. are added, which are incorporated into the resulting cDNA. Using differently derivatized nucleotides, different cDNAs can be labeled differently in independent reactions. These differently labeled total cDNAs, e.g. healthy and diseased tissue are placed on a microarray for hybridization. After hybridization has been carried out, the derivatized and hybridized cDNAs can be recognized with the aid of the antibodies directed against them, which are conjugated to the liposomes, and can be identified and quantified by measuring the different fluorescences. Thus, several thousand fluorescent molecules can be used in one step for a correspondingly high sensitivity of the analysis without enzymatic amplification.

The invention is illustrated by the following examples.

Example 1)

Liposomes for signal enhancement

Approx. 300 bp long cDNA fragments were generated with the incorporation of biotin-dUTP or digoxigenin-dUTP by means of PCR ("EC20 biotin" or "EC20 digoxigenin") were dropped twice onto a coated slide (300 pg) and bound covalently ( see PCT / EP 99/04014). On these "EC20Bio_EC20Dig-Arrays" each spot contained a mixture of both cDNA fragments in the ratio EC20 biotin: EC20 digoxigenin of 1000: 1; 200: 1; 40: 1; 8: 1; 1: 1; 1: 8; 1:40; 1: 200; 1: 1000. In addition, two negative controls were dropped: 1) spotting buffer 2) herring sperm DNA. The arrays were washed for 15 min in TNT buffer at RT, blocked for 30 min with TNB buffer at RT and then simultaneously for 1 h with Cy3 and Cy5-labeled liposomes (antiBio-Cy3 or antiDig-Cy5 liposomes) or with Cy3-labeled streptavidin ( Strept Cy3) stained at RT with shaking (150 rpm) in a total volume of 50 μl. For this purpose, the liposomes were washed beforehand with a 10-fold volume of PBS and centrifuged for 20 min at 4 ° C. and 13000 rpm.

The colored arrays were then washed with TNT buffer with shaking for 20 min and with 0.06 x SSC for 2 min. The arrays were measured with a laser scanning device (ScanArray 3000, General Scanning, Inc.) and the signal intensities were calculated (Imagene 2.0, Biodiscovery, Inc.), see FIGS. 1 and 2. In the summary figure (overlay) represents the green color bound anti-Dig-Cy5 liposomes, while the red color represents antiBiotin-Cy3 liposomes. I can see that a) the staining of the cDNA fragments is specific, b) the mixing ratios of the applied cDNA fragments are detectable and c) the signal intensity of the antiBio Cy3 liposomes is greater than that of Strep Cy3.

Example 2) In this experiment it was to be determined whether the staining using liposomes produced a signal amplification in comparison to the conventional direct incorporation of fluorescence-labeled nucleotides.

For this purpose, cDNA arrays with 18 different cDNAs (300 pg) were produced, with each cDNA being applied 8 times in total (four identical quadrants, each with 2 spots). The cDNAs applied are summarized in Table 1. The order of the cDNAs in the respective quadrants is from bottom right to top left, so that, for example, cDNA No. 1 "EC7" can be found in the bottom right corner of the respective quadrant. For the investigation, RNA was extracted from murine spleen and liver. The mRNA was isolated from this. In each case 1 μg, 0.1 μg and 0.01 μg of the mRNA was reverse transcribed with the incorporation of a) fluorescence-labeled nucleotides (Cy3-dCTP for spleen and Cy5-dCTP for Liver) and b) biotinylated (spleen) and digoxigenated dUTP (liver) rewritten in cDNA. The conventionally labeled Cy3 and Cy5 cDNAs were hybridized together on an array. It can be seen from FIG. 3 that the intensity of the signals decreases with decreasing output quantity, so that with 0.01 μg output quantity, hardly any signals can be recognized. The biotin or digoxigenin-labeled samples were also hybridized together on arrays and then labeled as in Example 1 with antiBio-Cy3 or antiDig-Cy5 liposomes. It can be seen here that the signal intensity also decreases with decreasing output quantity, but that all signals can still be recognized even at 0.01 μg. This shows that liposome labeling is much more sensitive than conventional direct labeling.

The signal quotients of the individual arrays are summarized in a bar diagram in FIG. It can be seen here that the signal quotients are comparable for both methods, with the exception that with the standard method the yellow bars (0.01 μg starting quantity) are no longer available for some genes, since the absolute signal intensity of the underlying signals is too low. Table 2 summarizes the signal quotients again in a table. The number of detectable genes is also shown here. "Detectable genes" are those whose signal intensity in at least one of the two fluorescence channels is at least 2 times higher than the corresponding signal intensity of the mean value of the negative controls (herring sperm DNA and salt). This again shows that liposome labeling is more sensitive than conventional direct labeling.

Claims

claims

1. Use of particles selected from the group consisting of liposomes and / or micelles with signaling properties and at least one affinity group for labeled nucleic acids for the detection of labeled nucleic acids which are hybridized with nucleic acids immobilized on a surface.

2. Use according to claim 1, wherein the particles carry different affinity groups and / or have different signaling properties.

3. Use according to one of claims 1 or 2, wherein the particles have a particle size of 20 to 4000 nm.

4. Use according to one of claims 1 to 3, wherein the signaling property is based on electromagnetic radiation, in particular fluorescence, radioactivity, luminescence, phosphorescence, electromagnetic resonance, or combinations thereof.

5. Use according to one of claims 1 to 4, wherein the affinity grouping is an antibody or antibody fragment.

6. Use according to one of claims 1 to 5, wherein the affinity grouping is directed against low-molecular haptens.

7. Use according to any one of claims 1 to 6, wherein the nucleic acids are labeled with low molecular weight haptens.

8. Carriers with a surface on which nucleic acids are immobilized which are hybridized with labeled nucleic acids, particles which have signaling properties and at least one affinity group for the labeled nucleic acids, after which the first affinity group is bound to the labeled nucleic acids.

9. A carrier according to claim 8, wherein the particles carry different affinity groups and / or have different signaling properties.