SELF-ASSEMBLING FLUORESCENT DIAGNOSTIC AGENTS

Abstract: Components of fluorescent conjugates are supplied separately to an environment and are coupled in the presence of a target organism cell or tissue to obtain a fluorescent conjugate which can be used to detect the target.

Description: SELF-ASSEMBLING FLUORESCENT DIAGNOSTIC AGENTS Technical Field The invention relates to the detection of cells and tissues which are affected with a condition which renders their detection desirable. More specifically, the invention concerns the in situ formation of fluorescent conjugates from separately administered components to detect these targets. Background Art U.S. Patent 4,812,449, issued to the applicant herein and incorporated herein by reference discloses the general approach of providing active materials in the form of component precursors so as to permit self assembly in a target microenviron ent. As described in the above referenced patent, a "target" refers to an organism, tissue, cell, or other biologically responsive material which it is desired to modify. The target will occur in a general environment which may be an j_n vitro or an n vivo environment, and supplies its own "microenvironment". The patent discloses a large number of reaction types which may be employed to form a conjugate jLn situ, including hydrazone formation. As explained in this issued patent, the self-assembly of a conjugate which is intended to interact with the target in situ has a number of advantages, including selectivity provided by the individual components, delay of the effect until the assembly is completed in the microenvironment in which it is intended to take place, enhancement of rate constants and selectivity, and a resulting dosage enhancement as compared to administration of the preformed conjugate. The invention herein represents a particularly advantageous specific embodiment of this general approach—namely, use of a self-assembling conjugate to generate fluorescence for detection of target conditions either jj vivo or ij vitro. In addition, it is possible to enhance the selectivity for target by conjugating one or both of the components of the self-assembling conjugate to a target-specific ligand. Disclosure of the Invention The invention is directed to self-assembling conjugates which emit fluorescence and permit the detection of target organisms, cells or tissues in an in vivo or an jLn vitro environment. The precursors of a highly fluorescent material, which themselves are not fluorescent, or which emit substantially less fluorescence than does the conjugate and/or which limit fluorescence at different wavelengths from conjugate, are supplied to the environment in which the target is contained. Due either to intrinsic factors characteristic. of the components or to modifications thereof which enhance selectivity, the components are selectively combined in situ in the desired target to permit detection through emission of fluorescence. In addition, the conjugates may be cytotoxic. Thus, in one aspect, the invention is directed to a method to detect a target organism, cell or tissue in an in vivo or an in vitro environment which method co prises administering to the environment containing the target, components of a conjugate which will self- assemble in the microenvironment of the target to form a fluorescent conjugate, and detecting the fluorescence emitted. In another aspect-, the invention is directed to compositions, especially pharmaceutical compositions which contain these components. Brief Description of the Drawings Figure 1 shows the structures of illustrative aldehyde K, hydrazine L and conjugate M, which conjugate is highly fluorescent. Figure 2 shows the ability of the conjugate M preformed or formed jln situ to label MCF-7 cells .in vitro. Figure 3 shows an isobologram for inhibition of MCF-7 human breast carcinoma cells using combinations of compounds K and L. Figure 4 shows the effect of compounds K, M, and L on fluorescence emitted by MIA PaCa cells in . vitro. Figure 5 shows an isobologram for inhibition of MIA PaCa cells by various combinations of components K and L. Modes of Carrying Out the Invention The invention is directed to methods to detect target organisms, cells or tissue by emitted fluorescence using fluorescent conjugates which have been formed in situ by two precursor components. In the invention herein, the components are preferably an aldehyde and a hydrazine, neither of which is highly fluorescent, but which, when condensed to form the hydrazone, result in a highly fluorescent conjugate. Preferred aldehydes are polyaromatic aldehydes with a high level of conjugation; a similar description would ' apply to preferred embodiments of the hydrazines. Particularly preferred are the aldehyde and hydrazine shown as structures K and L in Figure 1. The invention method relies in part on the ability of the components of the conjugates to migrate preferentially to the target organism, cell or tissue. Typical suitable targets include those moieties whose detection is of medical interest, such as tumor cells, infectious organisms, diseased tissue, and the like. The homing specificity of the components can be enhanced by coupling the component to a targeting ligand using general coupling methods known in the art, including direct coupling, but preferentially utilizing linker molecules which permit more controlled coupling reactions. Commercially available linkers, such as those from Pierce Chemical Company, Rockford, IL, may be used, for example. The targeting ligand can be, for example, an antibody or an immunoreactive fragment thereof, such as an Fab or Fab' fragment, a receptor ligand wherein the receptor is characteristic of the target cell, organism or tissue, or a substrate for active molecules present in high concentration in the microenvironment of the target. The targeting ligand can be coupled to either the aldehyde or the hydrazine component or to both. Coupling to both greatly enhances the selectivity of the conjugation. In general, the invention method comprises supplying the environment of the target with the two components either simultaneously or, according to the nature of the target, one or the other of the components may be supplied initially followed by the other. When sufficient time has been allotted to permit the components to home to the target, and to conjugate in situ, the fluorescence emitted is detected using standard techniques. The application of the present method permits the use of fluorescence analysis jLn vivo rather than histological staining of fixed tissues. Furthermore, in some instances, as in the example below, the conjugate may also be toxic to the target, and both treatment and monitoring thereof can be simultaneously effected. The following examples are meant to illustrate but not to limit the invention. Example 1 Fluorescent Staining of MCF-7 Cells In Vitro MCF-7 human breast carcinoma cells were cultured under standard conditions and treated with the components K and L shown in Figure 1 at various concentrations of each. K is P-(triphenyl phosphonium methyl) benzaldehyde, L is hydrazinostilbazole; they react to obtain the corresponding hydrazone. Phase contrast photographs and fluorescent micrographs were taken of the cells after treatment, and after washing to remove extracellular agents. As shown in Figure 2, hydrazone of structure M shown in Figure 1 can be formed iri situ by separate provision of K and L precursors either simultaneously or using prior administration K before administration of L. Figure 2A and B show the phase contrast photograph and fluorescent micrograph of MCF-7 cells treated with a saline control. No fluorescence is seen. C, E and G show the phase contrast photographs and D, F and H show fluorescence micrographs of MCF-7 cells which have been treated with reagents L, K or M, respectively, for 24 hours. As shown in Figure 2, panels D and F, neither 11.2 μg/ml L or 16.8 μg/ml of K provided any fluorescence labeling for these cells. In contrast, only 5 2.6 μg/ml of M provided a high contrast micrograph. Figure 2, panels A 1 and B 1 , are the . corresponding results for MCF-7 cells incubated simultaneously for 24 hours with 5.6 μg/ml L and 8.5 μg/ml K. Panel B shows that a fluorescent signal is 10 readily obtained. On the other hand, panels C and D' show that if L is administered before , even in higher amount, no fluorescence is obtained. Administration of 11.2 μg/ml L for 24 hours followed by washing and treatment with 16.8 μg/ml K for 24 hours did not result 15 in fluorescence. Conversely, panels E 1 and F' show that fluorescence was obtained when the protocol of panels C and D 1 was simply reversed. Evidently, the pre- administered aldehyde K was retained by the cells. 20 The combinations of K and L were also cytotoxic for MCF-7 cells i-n vitro. In this case, the compositions of mixtures capable of showing a 50% inhibition of MCF-7 growth over a 48 hour period are plotted. As shown in Figure 3, somewhat over 100 μM L or somewhat over 150 μM 25. of K either taken alone effect this 50% inhibition. On the other hand, combinations of K and L below 50 μM each were able to display this effect. Example 2 30 Detection and Cvtotoxicity for MIA PaCa Cells In protocols similar to those set forth in Example 1, MIA PaCa human pancreatic carcinoma cells were treated with reagent K, L or M or combinations thereof at various concentrations. These results are shown as photomicrographs and fluorescence micrographs in Figure 4. Figures 4A and B show the result for saline control and Figures C/D, E/F, and G/H provide the results using incubation for 24 hours with 11.2 μg/ml of compound L, 16.8 μg/ml of compound K, and 2.6 μg/ml of compound M, respectively. As was the case in Example 1, only incubation with compound M resulted in fluorescence. On the other hand, as shown in Figure 4, panels A'/B 1 , a mixture of 5.6 μg/ml L with 8.4 μg/ml of compound K for 24 hours resulted in excellent fluorescence. Again, pre- administration of compound L, as shown in panels C'/ D '. followed by administration of K, gave no fluorescence, while reversing the procedure gave a successful result in detecting the MIA PaCa cells. Again, apparently, the aldehyde is retained in the cells. The cytotoxicity of this conjugate is shown in Figure 5 with respect to MIA PaCa 2 cells. As shown, either 20 μM L or 55 μM K were able, taken alone, to effect 50% growth inhibition in MIA PaCa cells over a 48 hour period. However, combinations of these components at less than 10 μM concentration of each were able to exhibit a comparable cytotoxic Effect.

Claims: CLAIMS 1. A method to detect target organisms, cells or tissues in an _in vitro or an ir vivo environment, which method comprises providing said environment with at least two components which may be the same or different; wherein said components become covalently bonded when present in the target organisms, cells or tissues to obtain a conjugate which emits fluorescence; and detecting the fluorescence emitted. 2. The method of claim 1 wherein one of said components is an aldehyde and the other a hydrazine. 3. The method of claim 2 wherein said aldehyde is a phosphonium aldehyde and the hydrazine is an aromatic hydrazine. 4. The method of claim 3 wherein the aldehyde is of the formula K and the hydrazine is of the formula L. 5. The method of claim 1 wherein said target cells are tumor cells or tissue. 6. The method of claim 1 wherein said components are provided to said environment simultaneously. 7. The method of claim 2 wherein said aldehyde component is provided to the environment prior to providing the hydrazine. 8. A pharmaceutical composition containing at least two components which are differentially capable, in the presence of the microenvironment of a target organism, cell or tissue as compared to the surroundings of said organim, cell or tissue to bind covalently to form a conjugate which emits fluorescence. 9. The composition of claim 8 wherein one of said components is an aldehyde and the other a hydrazine. 10. The composition of claim 9 wherein said aldehyde is a phosphonium aldehyde and the hydrazine is an aromatic hydrazine. 11. The composition of claim 10 wherein the aldehyde is of the formula K and the hydrazine is of the formula L. 12. The composition of claim 8 wherein at least one of said components is conjugated to a targeting ligand which is specific for the target cell or tissue. 13. The composition of claim 12 wherein both said components are coupled to targeting ligands specific for said cell or tissue. 14. The composition of claim 12 wherein the targeting ligand is an antibody or fragment thereof.

Inventors: RIDEOUT DARRYL C, RIDEOUT, DARRYL, C.
Applicants: SCRIPPS RESEARCH INST, THE SCRIPPS RESEARCH INSTITUTE
Application year: 1991
Main classification: G01N33
IPC codes: A61K49, C12Q1, G01N33