19 F labelled antibodies and fragments thereof as NMR imaging and spectroscopy agents
This is a continuation-in-part of U.S. application Ser. No. 07/482,879, filed on Feb. 21, 1990, now U.S. Pat. No. 5,236,694. That application is incorporated here by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Nuclear magnetic resonance (NMR) techniques are finding increasing use in medical diagnostics. NMR imaging, or magnetic resonance imaging (MRI) as it is sometimes known, has been found to be useful in the detection of a variety of diseases and disorders. MRI has several advantages over other imaging techniques. For example, unlike computerized tomographic methods, MRI does not employ ionizing radiation, and therefore is believed to be safer. Also, MRI can provide more information about soft tissue than can some other imaging methods. 
     The majority of the NMR techniques developed so far have been based on imaging of hydrogen nuclei. However, other nuclei offer potential advantages with respect to NMR.  19  F in particular is of interest. The fluorine nucleus offers a strong NMR signal magnitude (high gyromagnetic ratio) similar to that of protons. Virtually no imagable fluorine exists naturally in the human body, so no background signal exists; any detectable signal comes only from whatever  19  F has been administered to the subject. 
       19  F is a stable isotope and is naturally abundant, so there is no need for isotopic enrichment. Because its gyromagnetic ratio is about 94% that of hydrogen, existing equipment designed to image protons can be inexpensively adapted for  19  F. 
     As a separate matter, the concept of targeting tissues using antibodies that have been radiolabeled was described years ago (Pressman, D. J. Immunol. 1949, vol. 63, pp 375-388). The advent of hybridoma technology (Kohler, G. and Milstein, C., Nature 1975, vol. 144, pp 873-881) enabled the production of monoclonal antibodies that are homogeneous, each reacting with a single epitope on an antigenic moiety. 
     Since then a number of monoclonal antibodies have been developed and characterized for their ability to recognize surface antigenic markers that are expressed in high levels on tumor cells and at significantly lower levels (100 to 1,000 fold less) on their normal counterparts. Several such antibodies and their fragments have been used as radiolabeled agents in cancer patients and X-ray images have been obtained (for a summary, see Biotechnology 1992, vol. 10, pp 246). Many other monoclonal antibodies and their fragments have been used in preclinical studies to obtain X-ray images of human tumor grafts in mice and cancerous or other lesions in patients. 
     Certain of these monoclonal antibodies target well-characterized cancer antigens such as the carcinoembryonic antigen (CEA), the TAG-72 antigen, high molecular weight milk fat globule mucin antigen (HMFG) and the like. Yet others are characterized with respect to their reactivity patterns for different tumor tissues although the molecular characterization of the reactive antigens is not complete (for example, the NR-Lu 10 antibody described by Paul Abrams and colleagues of NeoRx Corporation, B38.1 antibody described by David Colcher and his collaborators and various other antibodies described in the literature). 
     The use of tools of molecular biology has provided genetically engineered antibodies and their fragments which are either chimeric or humanized wherein the complementary determining regions of, e.g., a mouse monoclonal antibody is grafted into a human antibody molecule (described by Winter and his colleagues from the MRC, England). Yet additional technologies describe the use of combinatorial libraries that express antigen binding fragments encoded by human genetic sequences (described by Richard Lorner and his colleagues). 
     Although  19  F NMR has potential benefits, there is a need for new and improved  19  F-containing agents, such as  19  F-labeled antibodies, which can be used in NMR imaging and spectroscopy techniques. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a  19  F labelled NMR composition which comprises a  19  F-containing sensor moiety and an antibody (or antibody fragment) which reacts specifically with a particular antigen, and which is bound to the  19  F-containing sensor moiety. The amount of  19  F contained by the composition is effective to provide a detectable NMR signal. 
     In preferred embodiments of the invention, the antibody is a monoclonal antibody, and is specific for a human tumor antigen. The  19  F-containing moiety is preferably selected from the group consisting of fluorinated alkyls, fluorinated acetates, fluoroaniline, and fluoroalkyl phosphonates. 
     In another embodiment the composition further comprises a spacer moiety, with the  19  F-containing sensor moiety and antibody being bound to the spacer moiety (as opposed to the  19  F-containing sensor moiety being directly bonded to the antibody). The spacer moiety can be used to isolate the  19  F atoms from the substrate, thereby enhancing the NMR signal produced. The spacer moiety can be, for example, an alkyl hydrocarbon having a chain length of approximately 1-100 carbon atoms and containing an amino group. Alternatively, the spacer moiety can be selected from the group consisting of alkyl, alkoxy, aryl, and alkaryl hydrocarbons which contain an amino group, hydrazine, hydrazide, semicarbazide, and hydroxylamine. The spacer moiety can optionally include one or more  19  F atoms. 
     The present invention also relates to a method of using the above composition, specifically a method of  19  F NMR imaging or spectroscopy (MRI or MRS). The method comprises the steps of: (a) administering to a living mammalian subject, in an amount effective to provide a detectable  19  F NMR signal, a  19  F labelled NMR composition as described above; and (b) detecting the  19  F NMR signal produced thereby by means of  19  F NMR. The signal detected by this method can be used, for example, in tumor imaging. 
     In one aspect, the present invention relates to the attachment of  19  fluorine to antibodies by direct derivatization or by the linking of  19  fluorinated molecular amplifiers as described elsewhere in this application. The resulting  19  fluorinated antibodies are formulated in a pharmaceutically-acceptable, injectable excipient and used in targeted imaging of lesions such as a tumor mass that displays the antigens reactive with the monoclonal antibody. In a typical situation, the hybridoma cell line or a genetically engineered host cell producing the antibody or its antigen binding domain is cultured in a suitable nutrient medium. The antibody or its antigen binding domain is purified from the harvest by using chromatographic, ultrafiltration and other approaches commonly used by one skilled in the art. The purified antibody or an antigen binding fragment (produced either by cleavage of the antibody enzymatically, chemically or otherwise, or directly from a genetically engineered host) is coupled with  19  fluorine using methods described elsewhere in this application. The  19  fluorinated antibody is separated from unreacted  19  fluorine materials by the use of conventional size separation approaches, tested for specific reactivity to the antigenic target and is then ready for injection in a pharmaceutically acceptable dosage ranging from between about 5 mg to about 50 mg per patient. 
     Because the  19  F nucleus is very sensitive to changes in its steric and electronic environment, the composition can be used to sense different tissue parameters and cell properties through  19  F NMR spectroscopy, as well as being used for  19  F MRI. 
     Fluorinated compositions in accordance with the present invention have both diagnostic and prognostic uses, and can serve as physiological probes and cell-function reporters. They can be used not only to delineate tissues at risk and to characterize disease states, but also for monitoring the results of therapy. Specific uses for such compounds include vascular imaging, tumor imaging, and detection of lesions in atherosclerosis, bone metastases, and myocardial infarction. Among the physiologically important parameters that could be sensed are oxygen content, temperature, pH, and the concentration of ions such as Na+, Ca 2+ , and Mg 2+ . 
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     A wide variety of antibodies can be used in the present invention. The following table is a list of some suitable monoclonal antibodies, their tumor or antigen target and source: 
     
         ______________________________________                                    
Designation                                                               
         Target       Source                                              
______________________________________                                    
B72.3; CC49                                                               
         Ovary, Colon Schlom, J. et al.; NCI, USA                         
         (TAG-72)                                                         
SM-3;    Breast       Taylor, J. et al.; ICRF, UK                         
HMFG 1   (mucins, milk fat                                                
         globule)                                                         
OVB-3    Ovary        Pastan, I. et al.; NCI, USA                         
B38.1    Lung, Colon, Colcher, D. et al.; NCI, USA                        
         Breast, Prostate                                                 
ING-1    same as B38.1                                                    
                      Robinson, R. et al.; XOMA                           
(chimeric)            Corp., USA                                          
NR-Lu10  Lung, Colon  Abrams, P. et al.; NeoRx                            
                      Corp., USA                                          
PR-1-A3; Lung         Bodmar, W. et al.; ICRF, UK                         
UJ 13A                                                                    
7E11-C5  Prostate     Gilman, S. et al.; Cytogen                          
                      Corp., USA                                          
Mab 170  Lung, Colon, Suresh, M. et al.; Biomira,                         
         Breast, Cervix                                                   
                      Inc., Canada                                        
         (adeno-                                                          
         carcinomas)                                                      
Mab 174  Lung,        Suresh, M. et al.; Biomira,                         
         Head/Neck,   Inc., Canada                                        
         Cervix (squamous                                                 
         carcinomas)                                                      
Mab, B80 Prostate     Suresh, M. et al.; Biomira                          
                      Inc., Canada                                        
Mab B43  Ovary        Suresh, M. et al.; Biomira,                         
                      Inc., Canada                                        
791T36   Colon        Baldwin, R. et al.; Xoma                            
                      Corp., USA                                          
XMME-1   Melanoma     Scannon, P. et al.; Xoma                            
                      Corp., USA                                          
R24      Melanoma     Old, L. et al.; Memorial                            
                      Sloan Kettering, USA                                
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     Among the suitable  19  F-containing sensor moieties are simple fluorinated alkyls such as CH 2  F, CHF 2 , CF 3 , fluorinated acetates such as COCH 2  F, COCHF 2 , and COCF 3 , as well as fluoroaniline (useful for sensing pH), fluorinated pyrophosphate analogs such as fluoroalkyl phosphonates, fluorinated polyamines, fluorinated porphyryns and their metal complexes, fluorinated histochemicals, and fluorinated biotin or avidin. 
     Methods of fluorination in accordance with the present invention can suitably be by one of the following methods. 
     The hydroxyl groups of a polymer can be replaced by  19  F atoms, using chemical, enzymatic, or a combination of chemical and enzymatic methods. Partial hydroxyl replacement can be accomplished by using diethylaminosulfur trifluoride (DAST) as a fluorinating agent. 
     Alternatively, CHO groups on the polymer can be replaced by  19  F using DAST. 
     As another option polymeric hydroxyl groups can be esterified, for example: 
     
         polymer-OH+C.sub.2 F.sub.5 COOCOC.sub.2 F.sub.5 →polymer-OCOCF.sub.2 CF.sub.3 
    
     
         polymer-OH+ClCOC.sub.2 F.sub.5 →polymer-OCOCF.sub.2 CF.sub.3 
    
     
         polymer-OH+CF.sub.3 COOCOCF.sub.3 →polymer-OCOCF.sub.3 
    
     
         polymer-OH+ClCOCF.sub.3 →polymer-O-COCF.sub.3 
    
     Also, hydroxyl groups could be oxidized using reagents such as periodate, and then coupled to the amino groups of  19  F-labelled compounds, then reduced with reagents such as NaBH 4 . 
     Polymer hydroxyl groups could be activated by cyanogen bromide and then coupled to a fluorinated amine, yielding an iminocarbonic acid ester. 
     Polymer hydroxyl groups, such as in a dextran polymer, can be utilized to form 3-bromo-2-hydroxyl propyl dextrans, which can be transformed into epoxide derivatives. The epoxide derivative is highly reactive and in alkaline solution at room temperature can be coupled with substances containing nucleophilic groups like alkyl and aryl primary amines, hydroxyl groups, and thiol groups. For example: 
     
         dextran(OH).sub.3 +3-bromo-2-hydroxyl propyl epoxide→3-bromo-2-hydroxy propyl dextran 
    
     
         Rxn with NaOH→dextran with epoxide 
    
     
         Rxn with RAH→dextran-OCH.sub.2 CHOHCH.sub.2 AR 
    
     A=0, S, NH 
     R=organic fluorine-containing moiety 
     Fluorinated amines can be attached to polysaccharides. For instance, carboxymethyl-cellulose can be esterified to produce the methyl ester which, on treatment with hydrazine hydrate, forms hydrazide. The hydrazide on diazotization with Hcl and NaNO 2  forms a reactive azide. The azide in alkaline solution will react rapidly with amines to form the covalently bonded product polymer-CONHR, where R is a fluorinated aliphatic or aromatic amine. 
     
         CMCOOH+CH.sub.3 OH+NH.sub.2 NH.sub.→CMCOHNNH.sub.2 
    
     
         Rxn with NaNO.sub.2 +HCl→CMCON.sub.3 
    
     
         Rxn with RNH.sub.2 →CMCONHR 
    
     Aminodextrans can be fluorinated using S-ethyl thiol trifluoroacetate (SETFA) as a fluorinating agent. Acylation of available amino groups can be accomplished by using an excess of SETFA as the acylating reagent. 
     Alternatively, amino groups can be acylated using acid fluorides (anhydrides). 
     
         D-NH.sub.2 +(CF.sub.3 CF.sub.2 CO).sub.2 O→D-NHCOCF.sub.2 CF.sub.3 
    
     
         D-NH.sub.2 +ClCO-AR→D-NHCO-AR 
    
     
         AR=aromatic ring containing F 
    
     
         D-NH.sub.2 +ClCO-AR-LF.sub.3 →D-NHCO-AR-LF.sub.3 
    
     AR=aromatic ring 
     L=alkyl chain 
     Other possible reactions include acylation using fluorinated propionic anhydride, succinic anhydride (for example--trifluoroacetamido succinic anhydride) reactions with fluorinated phenyl isothiocyanate, and reactions with fluorinated alkyl isothiocyanate. 
     Where antibodies or fragments thereof are used, the sensor moieties can be selectively attached to sites not directly involved in antibody-antigen binding, thereby allowing the antibody to retain its immunoreactivity. Possible sites for attachment include carbohydrate groups, amino groups, sulfhydryl groups, or combinations thereof. 
     The following specific examples illustrate the preparation of compounds in accordance with the present invention. 
     N-Trifluoroacetamide D-Glucose 
     Glucosamine in anhydrous methanol was treated with s-ethyl thiol trifluoroacetate (SETFA) as described by Wolform and Conigliaro, Carbohydrate Research, 11, 63 (1969). A suspension of 2-amino-deoxy-D-glucose hydrochloride (10 g) in 50 ml anhydrous methanol was treated with an equivalent amount of sodium methoxide in methanol (1.06 g of Na in 10 ml methanol). The mixture was stirred (magnetic stirrer) till a clear solution was obtained. NaCl precipitate remained at the bottom. To this, SETFA (10 g) was added. The reaction mixture was stirred at room temperature for 24 hrs. The solution was evaporated to a solid residue and the residue was extracted with hot acetone. Ether was added to the cooled acetone extract and the mixture was refrigerated overnight. The white crystalline compound was recrystallized from a mixture of acetone-ether to obtain shiny crystals. 
     
         ______________________________________                                    
Results                                                                   
Yield: 8.2 g. MP: 193-195° C.                                      
Analysis                                                                  
           Element:                                                       
             C      H          N    F                                     
______________________________________                                    
Calculated:  34.92  4.40       5.09 20.72                                 
Found:       36.89  4.75       4.92 20.75                                 
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     The product was soluble in water. Elemental analysis data were in agreement with the calculated values. 
     Proton and F-19 NMR data confirmed the formation of N-trifluoroacetamido-D-glucose. ##STR1## 
     Trifluoroacetyl-DL-Lysine 
     Trifluoroacetyl-DL-lysine was obtained by treating DL-lysine monohydrochloride with s-ethyl thiol trifluoro acetate (SETFA) in basic solution, as described in Schallenberg and Calvin, JACS 77, 2779 (1955). ##STR2## 
     SETFA (4.0 ml) was added to DL-lysine monohydrochloride 3.6 g (20 mmol), dissolved in 20 ml of 1N NaOH. The heterogeneous mixture was stirred for 6 hours at room temperature and cooled for 1 hour in an ice cold water bath. 
     The solid that separated was filtered and washed with cold water. It was recrystallized from ethanol. 
     Results 
     Yield: 0.8 g (16%) (Loss of product due to washing with cold water). 
     MP: 262°-263° C. 
     H-1 NMR: 3.82 δ CH; J=1.5, 1.7, 1.96, 3.41 (Solvent D 2  O). 
     F-19 NMR: Sharp signal (solvent D 2  O). 
     
         ______________________________________                                    
Elemental Analysis:                                                       
           C    H          N      F                                       
______________________________________                                    
Found:       39.87  5.45       11.61                                      
                                    23.52                                 
Calculated:  39.67  5.41       11.57                                      
                                    23.55                                 
______________________________________                                    
 
    
     Aminodextrans 
     Aminodextrans (molecular weight: 10k, 40k, and 70k) were obtained from Molecular Probes, Inc., Portland, Oreg. 
     
         ______________________________________                                    
Molecular Size                                                            
            Number of amino groups per molecule                           
______________________________________                                    
10k         6.8                                                           
40k         13                                                            
70k         30                                                            
______________________________________                                    
 
    
     Aminodextran molecule was reacted with s-ethyl thioltrifluoracetate (SETFA) in a formamide and pyridine mixture to yield a product in which the amino groups of the aminodextrans were modified with trifluoracetyl moiety, as described in Goldberg and Anfinsen, Biochem., 1, 401 (1962). 
     
         Dextran-NH.sub.2 +CF.sub.3 COSC.sub.2 H.sub.5 →Dextran-NHCOCF.sub.3 +C.sub.2 H.sub.5 SH↑ 
    
     The general synthesis procedure was as follows: Aminodextran was dissolved in formamide and pyridine (2:1  v/v). S-ethylthioltrifluoroacetate (SETFA) was added slowly with stirring. The mixture was stirred overnight. The desired product was precipitated with cold ethanol and further purified by dialysis against water, and the powdered product obtained by lyophilization. 
     As a specific example, aminodextran 70k (0.6 g) was dissolved in 10 ml formamide by stirring for 2-3 hours. Pyridine 5 ml was added, and stirring continued until the homogeneous solution was obtained. The pH was approximately 7 by paper. S-ethylthioltrifluoroacetate 3 ml was added dropwise for a period of 30 minutes with vigorous stirring. This reagent is immiscible with the above solvent system. However, it forms small droplets and slowly undergoes reaction which could be seen by the fall in pH values and homogeneity of the solution. The mixture was stirred overnight and poured on chilled (-12° C.) absolute ethanol (150 ml) with vigorous stirring. The white precipitate obtained was held at -12° C. for an additional 4 hours with stirring. The precipitated product was centrifuged and washed with ethyl alcohol. The product was dissolved in distilled water and dialyzed against distilled water for 24 hours with 6 changes using 1000 ml of water each time. The dialyzed solution was centrifuged and the clear solution was lyophilized to obtain a white silky solid. 
     Yield: 0.56 g 
     TLC Matrix: silica gel 60A, MK6F, Whatman 
     Solvent: Pyridine/acetic/acid water (9:1:90, v/v/v) 
     Detection: 50% H 2  SO 4   
     R f  of starting material: 0.41 
     R f  of final product: 0.74 
     Proton NMR spectra: Typical polymeric appearance 
     F-19 NMR spectra: Single (Fluorine) sharp signal 
     
         ______________________________________                                    
Elemental Analysis                                                        
           C    H          N      F                                       
______________________________________                                    
Calculated*: 43.87  5.94       1.11 2.88                                  
Found:       40.65  5.78       0.62 2.26                                  
______________________________________                                    
 *percentages of elements calculated by assuming the molecular weight of  
 dextran to be 70k.                                                       
 
    
     Results 
     Trifluoroacetylated aminodextran 10K and 40K: 
     10K: TLC analysis: 
     Solvent system: pyridine/acetic acid/H 2  O (9:1:90) 
     R f  of starting material: 0.5 
     R f  of final product: 0.84 
     NMR spectra analysis: 
     Proton spectra: Typical polymeric compounds (D 2  O) 
     F-19 spectra: Single fluorine, sharp signal (D 2  O) 
     
         ______________________________________                                    
Elemental analysis:                                                       
           C    H          N      F                                       
______________________________________                                    
Found:       40.01  5.65       0.83 2.50                                  
Calculated*: 43.56  5.81       1.39 4.13                                  
______________________________________                                    
 *percentages of elements calculated by assuming the molecular weight of  
 dextran to be 10K.                                                       
 
    
     40K: TLC analysis: 
     Solvent system: pyridine/acetic acid/H 2  O (9:1:90) 
     R f  of starting material: 0.48 
     R f  of final product: 0.76 
     NMR spectra analysis: 
     Proton spectra: Typical polymeric (D 2  O) 
     F-19 spectra: Single fluorine, sharp signal 
     
         ______________________________________                                    
Elemental analysis:                                                       
           C    H          N      F                                       
______________________________________                                    
Found:       40.82  5.97       0.61 1.58                                  
Calculated*: 43.92  5.98       0.99 2.35                                  
______________________________________                                    
 *percentages of elements by assuming the molecular weight of dextran to b
 40K.                                                                     
 
    
     Trifluoroacetylation of Poly-L-Lysine 
     General Procedure: 
     Trifluoroacetylation of poly-L-lysine is carried out with S-ethyl thioltrifluoroacetate in dimethylformamide, as described in Levy and Paselk, Biochem. Biophys. Acta, 310, 398-405 (1973). The amino groups of poly-L-lysine are modified with the trifluoroacetyl moiety. 
     Poly-L-lysine.HBr (molecular weight 8,800) was reacted with S-ethyl-thioltrifluoroacetate in dimethylformamide. Poly-L-lysine.HBr (100 mg, 11.36 μmoles) was dissolved in 20 ml of DMF with stirring, for 30 minutes when an almost clear solution was obtained. Triethylamine (TEA) 50 μl was added (appearance of precipitate noted) and the stirring continued for 15 minutes. S-ethylthioltrifluoroacetate (SETFA 51.737 mg, 327.17 μmoles), dissolved in 1 ml of DMF, was added dropwise to the reaction mixture with constant stirring for 15 minutes. The pH was adjusted after each addition of SETFA. A clear solution obtained at the end, was stirred for another 90 minutes and then poured onto chilled absolute ether. The solution was decanted. The precipitate was centrifuged and then dissolved in 15-20 ml water and dialyzed against distilled water at 41° C. for 48 hours. The shiny powdery product was obtained by lyophilization of the dialyzed solution. 
     Results 
     Yield: 20 mgs 
     F-19 NMR spectra: A sharp single fluorine signal (D 2  O) 
     Trifluoroacetamido-succinylated Poly-L-Lysine: Poly-L-Lysine (50 mg, 5.68 μMol) in 20 ml phosphate buffer (pH=7.24) was reacted with (120 mg) trifluoroacetamidosuccinic anhydride for 30 minutes. General procedure for preparation of succinylated Poly-L-Lysine is described by W. B. Stason, M. Vallotton and E. Haber; Biochem. Biophys. Acta. 133:582-584 (1967). The product was purified by exhaustive dialysis against d. water and lyophilized to obtain white solid. 
     One way of producing a stronger signal from trifluoroacetylated aminodextrans would be to trifluoroacetylate the hydroxyl groups instead of the amino groups, which will dramatically increase the number of available sites, and therefore increase the concentration of  19  F in the molecule. The in vivo NMR signal can also be optimized by using spacer moieties to separate the  19  F from the substrate. 
     In the NMR methods of the present invention, the  19  F-labelled compound is administered to a living subject, preferably parenterally or orally. They can suitably be administered in a formulation containing one or more of the  19  F-labelled compounds and a pharmaceutically acceptable diluent or carrier. 
     The preceding description is intended to illustrate specific embodiments of the present invention, not to provide an exhaustive description of all possible embodiments of the invention. Persons skilled in this field will recognize that modifications could be made to the preceding examples which would still be within the scope of the present invention.