CA2051699A1 - 99mtc (iii) myocardial imaging agents that are effective in humans - Google Patents

Abstract

A myocardial imaging agent for humans is a technetium(III) complex ligated in the planar positions by a tetradentate ligand such as (acac)2en and in the axial positions by an ether containing phosphine ligand such as tris(3-methoxy-1-propyl)-phosphine. The agent exhibits extremely rapid blood clearance after injection into a human (as shown in the figures) and has a sufficiently high heart/liver and heart/lung ratios to provide effective myocardial images.

Description

WO90/141~ PCT/US90/01497 99mTc(III) MYOCARDIAL IMAGING AGENTS
THAT ARE EFFECTIVE IN HUMANS
Bac~around of the Invention Several non-invasive methods of imaging body organs have been developed over the past decades.
These procedures are based on the tendency of a body organ to concentrate some detectable chemical.
Particularly useful chemicals are those which emit gamma radiation. Subsequent scanning of the organ with a gamma ray camera provides an image of the organ from which diagnostic information can be obtained.
99mTc (Tc-99m) has been found to be particularly useful in this area because of its half-life and gamma ~ -ray emission.
Over the past several years different Tc-99m compounds have been disclosed for use as positive myocardial imaging agents. These different imaging agents, based on substantially different chemistries, have exhibited varying levels of utility in different ~ . .,.:.
mammals. To effectively image the heart the agent must localize in the heart 2nd at the same time rapidly clear from neighboring organs such as the _ . . .
. . .
. . - . . , :
.
, ~, ' '''' ~ , .

2 0 5 ~ 2- PCI/US90/01497 lungs and in particular the liver. Further, the ima~ing agent must not bind tightly to the blood or else image quality will be poor. An imaging agent which localizes in the heart and at the same time localizes in the liver does not provide a good image of the heart since the apex of the human heart is often obscured bv the liver.
One recent paten~ which discloses Tc-99m myocardial imaging agents is Deutsch et al U.S. Patent No. ~,795,626. This discloses a type of myocardial imaging agent which due to its ligand system is not reducible in vivo. Thus, the disclosed Tc(III) complexes remain in this oxidation state for imaging pùrposes. This has been found somewhat useful in myocardial imaging.
- Unfortunately, the prototypical agent of this class has relatively slow blood clearance and high liver uptake which gives rise to rather low heart/liver ratio. This is reported in the Journal of Nuclear Medicine, 28:1070 1000, 1987. The ligand system acac2en bonded to the four planar coordinations ' t`;~
sites of the technetium and PMe3 (trimethylphosphine) bonded to the axial sites simply did not provide an efficacious myocardial imaging agent in humans.
one commercially acceptable product is Cardiolite sold by DuPont. This is an isonitrile ~
Tc(I) complex. The isonitrile ligands contain alkyl ~ ;

:' - -' . . ,' :' :
' ', '~

WO 90tl4106 - 3 - 2 ~ 5 1 ~ g 9 PCr/US90/01497 ether groups. ~lso, ~iuclear Medicine Communication, 10(4), April, 1989, p.245 reports myocardial imaging agents in which 99m~c is complexed to bidentate phosphorus ligands containing alkyl ether groups.
This brlef abstract reports a heart/liver ratio of 0.75 which is lower than what is required to obtain a good ~yocardial image.
Summarv of the Invention The present invention is premised on the realization that Tc(III) myocardial imaging agents which are not reducible in vivo can be very effective myocardial imaging agents if the ligands contain one or more ether moietes in the ligand system.
More particularly, the present invention is premised on the realization that an effective myo- ~
cardial imaging agent for humans can be prepared by -ligating a tetradentate ligand system to the 4 planar coordination bonding sites of an octahedrally coor-dinated technetium center and bonding ligands con-taining ether moietes to the axial positions of the technetium center. Specifically, the present inven-tion is premised on the realization that a Tc(III) acac2en complex having alkyl ether substituted phos-phine ligands at the axial positions provides a commercially viable heart imaging agent.
The present invention will be further -appreciated in light of the following detailed description and drawing in which:
.

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.... .
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: ~
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- - - - ..

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WO90/141~ 2 ~ 9 3 PCT/US90/01497 Brief Descri~tion of the Drawinas Fig. 1 is a graph showing blood clearance f rom a human volunteer during a stress evaluation of a myocardial imaging agent made according to the present invention.
Fig. 2 is a graph showing blood clearance from a human volunteer at rest of a myocardial imaging agent made according to the present invention.
Detailed DescriDtion of the 'nvention The technetium compounds which are useful as myocardial imaging agents in humans are hexadentate technetium complexes which have an overall cationic charge. More specifically, the complexes will be technetium complexes in the +3 oxidation state coor-dinatively bonded to six atoms as shown in Formula 1.

R
.; ,-I
R
Formula 1 "' ' ' ~' - ` . ' '. : '.. : - - ,, . - : ::
.. ,: .,- . ~ .
:: :. . ;
. ' ~

WO ~/141~ 2 ~ 5 1 ~ 9 9 PCT/US90/01497 _, _ R~ and R''' represent ~, hydroxyl, Cl-C5 alkyl, cl-c5 alkyl substituted by hydroxyl, ether, amide, ketone, aldehyde or nitrile group.
R'' represents Cl-C~ alkylene, Cl-C4 alkenyl which may be substituted with hydroxyl, ether, amide, ester, ketone, aldehyde or nitrile group.
The present technetium compound is bonded generally to three ligands, two axial ligands Rl and R2 as in Formula 1 and a tetradentate ligand having the following formula:

~'~ ", .

R~
R~

Formula 2 The preferred tetradentate ligand is N,N'-ethylenebis(acetylacetone iminato) hereinafter referred to as (acac)2en wherein R'' represents methylene and all the R's represent hydrogen and all the R'''s represent methyl. ~lso suitable tetra-dentate ligands include N,N'-ethylenebis(tert-butylacetoacetate iminato) hereinafter referred to as (buac)2en, N,N'-ethylenebis(benzoylacetone iminato) "' .'' 5 ', , ".' ' ~' ' ' ' ' . ' . "" , : , ' .' : ''' '. ' ' ; '. ~'~ ' ' ' ': ' :
:

WO90/14106 2 ~ 5 1 6 9 9 -s- PCT/US90/01497 also referred to as (bzac)2en, N,N~-ethylenebis(3- .
bromoacetyacetone iminato) also referred to as (brac)2en and N,N'-methylethylenebis(acetylacetone iminato) also referred to as (acac)2pn.
Ligands Rl and R2 also referred to as the axial ligands represent the same or different ligands both falling within the following general formula:
,R3 R

Formula 3 -wherein R3 and R4 represent a moiety having the "~;r~
following general formulas 4 and 5: .

-(CH2)x -O- (CH2)y CH3 Formula 4 ; ~ : .

( H2)x Cl - (CH2)2 - O - (CH2)y - CH3 ~
CH3 Formula 5 ;

X = 1-4 .
y = 0-4 Z = 0-4 and wherein R5 can represent .he same moietes repre-sented by R3 and R4 above or ~ay in addition represent ~ ' : , , ' ' ' ' :
- ' - ' ' ':
' :
': , : ::' , ' ':' :
' WO 90/14106 ~7 ~ 2 0 5 1 ~ 9 9 PCr/US90/01497 -OCH3, and Cl-C, alkyl. Such a ligand can be made according to the following example.

Standard procedures are used to convert 22.5 grams of 3-methoxy-1-propylchloride (CH3OCH2CH2CH2Cl) and 4.9 g Mg metal to the corresponding Grignard reagen~ in 110 mL tetrahydrofuran. To the Grignard reagent cooled in a dry ice acetone bath is slowly added 4.6 g of phosphorus t-ichloride in 40 mL of tetrahydrofuran. The reaction mixture is then allowed .""~., ~. :, .
ts warm to room temperature, and is subsequently heated al reflux for 30 min. This reaction mixture is then cooled to lO C, and 70 mL of a saturated aqueous solution of ammonium chloride is added. This hydrolyzed mixture is then filtered, and the aqueous -layer is removed. The organic layer is dried over potassium carbonate and magnesium sulfate, the tetrahydrofuran is removed by distillation, and the desired phosphine product (P(CH2CH2CH20CH3)3 = TMPP) is recovered by vacuum distillation (114-116~C a~ 1.5 mm Hg). This phosphine is converted to the hydro-chloride adduct (P(CH2CH2CH20CH3)3 + HCl = TMPP.HCl) with gaseous HCl (yield = 5.8 g, 70%). 31-P NMR shows a single peak at -29.844 ppm (vs. H3P0~) for the free phosphine, and a doublet at 20.654, 16.406 ppm (vs.
H3P04) for the hydrochloride adduct. FAB-MS (positive - .: . : . .: . : , - , . ~ . -: .. .. . -. . : ,-: , . , - . -::: . . , - - . . . .
- - - . ~. , . ... , , .. :
- , . . .
: .- ~ . , , , ~': ~ -.: . :.

,. . . . . - .. - .. , - . .. . ..... -, Wo ~/141~ PCT/US90/01497 2 0 ~ 9 -a -ion mode) shows a parent peak at ~51 amu for the hydrochloride adduct.
The ligated technetium complex shown in Formula l is manufactured in a two step process. A
99m-pertechnetate solution ls obtained from a 99-Mo generator. This method of obtaining 99mTc is well known to those skilled in the ar. and is disclosed for example in Deutsch et al U.S. Pat. No. 4,489,054 incorporated herein by reference. This is also disclosed in Glavan et al U.s. Pat. No. 4,374,821 also incorporated herein by reference. This pertechnetate can be diluted to the desired radioactive concentration of lO-lO0 mCi/mL with normal saline.
The 99mTco4 (pertechnetale) in which Tc has an oxidation state of +7 is reduced to a technetium +5 complex having a formula 99mTcVO(L)+. This is formed by heating 99mTcO4 in the presence of the ~ ~;
tetradentate ligand and a reducing agent such as stannous chloride or sodium borohydride. In the second step the 99mTc~OL complex is further reduced Ir by treating it with the axial ligand of Formula 3 at slightly elevated temperatures, i.e., heating the 99mTc(V) complex in the presence of the ligand. A
chemical reducing agent such as borohydride salts, stannous ion salts or hyposulfite salts can also be added.

' ~ ' , `' ' ' : ` .
.

i.

WO 90/14106 2 0 S 1 ~ 9 9 PCrtUS90/01497 The preparation of the Tc~V) complex is further described in Examples 2 and 3 wherein the ligand is (acac)2en.

Preparation of 99m~cVO(acac)2en in Ethanol Pertechnetate is purified according to the method disclosed in U.S. Patent ~,7~8,672. A C18 Sep-pak cartridge was rinsed with 5 mL ethanol and then 3 mL of 0.01M tetrabutylammonium bromide in water. A desired amount of 99m~cO4 in saline was combined with 1 ~L of 0.lM te-raDutylammonium bromide, mixed well, and passed slowly through the C18 Sep-pak.
The Sep-pak was washed with 10 mL water, 10 mL air were passed through, and the activity eluted with 1-2 mL ethanol.
A solution of 17 mg H2acac2en in 0.25 mL is combined with 1 mL of the above tetrabutylammonium 99m-pertechnetate solùtion and the resulting solution is deaereated for 15 minutes. ~hen 20 microliters of lM KOH and 10 microliters of a freshly prepared solution of 30 mg SnC12 in 20 mL ethanol are added.
The mixture is incubated at 90 C for 15 minutes.
EXAMPLr 3 Preparation of 99mTcO2(acac)2en+ in Water 17 mg of H2acac2en ~-as dissolved in 0.1 mL
of ethanol. Then 0.1 ~L of ~9mTc04 and 0.9 mL of water wes added and the mixtu-e de~reated for 15 -.

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, , : , , .' ' ' ' : ' 1 .

W090/14106 ~ 5 i ~ ~ ~ PCT/US90/01497 ~inutes wlth scrubbed argon. ~o ~icroliters of lM ~H
and the reducing agent were added next. The best results were obtained with 2-20 microliters of a solution of 0.l mmole (l~mg) stannous chloride in 20 mL H2O.
The mixture was heated for 15 minutes at 90tC and cooled to room temperature. The reaction was moni~ored by HPLC on a PRP-l column in 90% MeOH/0.0lM
Na phosphate and 0.0l M Na heptanesulfonate (pH 7.0) at a flow rate of l mL/min. The Tc(V)O(acac2en) cation elutes at ~.0-4.2 min. (As in all cases the positive charge of the cation is offset by a biologically acceptable anion such as chloride, as is well known.) According to the present invention a myo-cardial imaging agent is prepared by reducing the 99mTc(V) complex as prepared in Examples 2 and 3 to a 99mTc(III) complex. To accomplish this, the 99m~c(V) complex is combined with an ether substituted phos-phine ligand such as P(CH2CH2CH20CH3)3. A solution of the ligand is introduced, at ambient or elevated temperature. This acts to reduce the 99mTc(V) complex to a 99mTc(III) complex. The Tc(III) complex can then be purified on cationic exchange resin or a reversed phase Cl8 Sep-Pak. The 99mTc(III) complex will have the structure of Formula l.

.. : . . : , .. ..

~, : , , . ; ~ . .

.

W090/14106 2 0 ~ 1 ~ 9 9 PCT/US90/0149~

This is further described in Examples 4 and 5.

0.3 mL of O.lM aqueous T~PP.HCl solution from Example 1 is added to the 99mTc(V) preparation from Example 2 and the mixture incubated for 15 minutes at 70'C.
The preparation is diluted with 20 mL
deareated water (filtering may be needed to re~ove precipitated ligand) and loaded on a C18 Sep-pak which was prewashed with 5 mL ETOH and 20 mL H20. ~he car-tridge is rinsed with 20 mL H20 and then twice with 2 mL 80% ethanol-water. The compound is eluted in 1-2 mL 80% ethanol-saline.

O.3 mL of a O.lM TMPP.HCl solution from Example 1 was added to the 99mTc(V) preparation from Example 3 and incubated at 70 C for 15 minutes. This is then ready for use.
To demonstrate the effectiveness of the myocardial imaging agent formed using the method of Example 4 about 13 millicuries of 99mTc activity was injected into a human volunteer under stress (having exercised until the volunteer's heart rate was approx-imately 80% of maximum predicted by the patient's age and physical condition). ~lood samples were then taken immediately after injection and for intervals up .. .

! - .

~.. ` ' ' ' ' ' , '' :

WO90/14106 ~ PCT/US~/01497 to 60 minutes thereafter. The blood clearance data are shown in Fig. l. Likewise the same test was conducted on a human volunteer at rest and the data are shown in Fig. 2.
This demonstrates extremely quick and effective blood clearance which enables obtaining a clear useful myocardial image as soon as 5-l0 minutes after injection. In fact, due to the effective blood clearance as well as the high heart/liver ratio very clear myocardial images, including computer assisted tomographic images, were obtained of these volunteers, making this a commercially acceptable positive myo-cardial imaging agent.
All the 99mTc(III) complexes describ~d above are administered intravenously as radiopharmaceuticals in a radioactive dose of from 0.0l mCi/ml to l0 mCi/ml most preferably 2 mCi/ml-SmCi/ml. The administration dose for humans is usually in the range 10-30 mCi.
Imaging of the heart can be carried out by scanning techniques after waiting an appropriate period of time to permit blood clearance of the radiopharmaceutical. For example, time dependent scintiscans of the chest region of a patient can be used. A computer interfaced 16 crystal, Ohio Nuclear Spectrometer can be used for .hese scans. The com-plexes of the present invention can also be used in single photon emission computed tomography as , . ~ . , ~. ~ ' ' , .

.
, WO go/l4l06 2 ~ 9 9 PCT/US90/01497 descrlbed in Bever et al, Diagnostic Nuclear Medicine, Volume l, No . 2, page lO ~summer of 1984).
The present invention is particularly suitable for use in a kit preparation. The kit preparation would consist of two sterile, pyrogen free vials, the first vial containing an effective ligand havinq the structure shown in Formula l in combination with an effective reducing agent in this case the tin chloride. This would be a lyophilized composition.
The second vial would contain a protected salt of the phosphine ligand shown in Formula 3. Typically, this would be the phosphine salt bonded to HCl, H25O4, iron(II), copper(I) or zinc(II). The acid salts are preferred. The kit would be used by injecting the purified 99m-pertechnetate obtained from a molybdenum generator into the first vial. This is heated as per Example 3. Saline is added to the second vial to dissolve the protected ligand. This saline solution is then added to the first vial which is heated to effec~ convers1on to Tc(III). The contents of the first vial can be directly injected into the patient without further purification.
The 99mTc(III) complexes of the present invention provide a radiopharmaceutical uniquely adapted for use in myocardial imaging of humans.
These radiopharmaceuticals neither hang up in the ,: , ' :.

WO90/141~ ~ V~ 14- PCT/US90/01497 blood system nor the liver and yet bind to the hear for long periods of time ( Sh) to provide useful positive human heart lmages.
Accordingly having described our invention, we claim:

: . . ' - ,' ,, ~ . ' ~ ' ' ' ' ', .

Claims (12)

1. A myocardial imaging agent having the following general formula:

wherein R' and R''' represents H, hydroxyl, C1-C5 alkyl, C1-C5 alkyl substituted by hydroxyl, ether, amide, ketone, aldehyde or nitrile groups and R'' represents C1-C4 alkylene, C1-C4 alkylene which may be substituted with hydroxyl, ether, amide, ketone, aldehyde or nitrile groups; and wherein R1 and R2 represent the same or different phosphine ligand wherein said ligand has the following general formula:

wherein R4 and R5 represent a moiety selected from the following -(CH2)x -O- (CH2)y - CH3 wherein X = 1-4, Y = 0-4 and Z = 0-4 and wherein R3 is a moiety selected from the moieties represented by R4 or R5 and -OCH3, C1-C5 alkyl.

2. The composition claimed in claim 1 wherein R'' represents methylene and R' represents hydrogen and R''' represents CH3.

3. The complex claimed in claim 1 wherein R1 and R2 represent P(CH2CH2CH2OCH3)3.

4. A myocardial imaging agent comprising [99mTc(III)(acac2en)(P(CH2CH2CH2OCH3)3)2]+.

5. The method of imaging the heart of a human comprising:
intravenously applying an effective amount of the complex claimed in claim 1 into said human and detecting radiation emitted from said complex which localizes in the heart of said human.

6. The method of imaging the heart of a human comprising:
intravenously applying an effective amount of the complex claimed in claim 2 into said human and detecting radiation emitted from said complex which localizes in the heart of said human.

7. The method of imaging the heart of a huma.
comprising:
intravenously applying an effective amount of the complex claimed in claim 3 into said human and detecting radiation emitted from said complex which localizes in the heart of said human.

8. The method of imaging the heart of a human comprising:
intravenously applying an effective amount of the complex claimed in claim 4 into said human and detecting radiation emitted from said complex which localizes in the heart of said human.

9. A kit for preparing a technetium 99m myo-cardial imaging agent, said kit comprising:
a first and second vial, said first vial containing a lyophilized pyrogen free sterile mixture of an effective reducing agent and a ligand having the following general formula:

wherein R' and R''' represent H, hydroxyl, C1-C5 alkyl, C1-C5 alkyl substituted by hydroxyl, ether, amide, ketone, aldehyde or nitrile groups and R'' represents C1-C4 alkylene, C1-C4 alkylene which may be substituted with hydroxyl ether amide ketone aldehyde or nitrile groups and wherein said second vial contains a lyophilized, pyrogen free, sterile protected salt of a phosphine ligand, said phosphine ligand having the following general formula:

wherein R4 and R5 represent the same or different group -(CH2)x -O- (CH2)y - CH3 wherein X = 1-4, Y = 0-4 and Z = 0-4 and wherein R3 represents the same ligands represented by R4 or R5 or may represent: -OCH3, -C1-C5 alkyl.

10. The kit claimed in claim 9 wherein said first ligand is H2acac2en.

11. The kit claimed in claim 9 wherein said effective reducing agent is tin chloride.

12. The kit claimed in claim 9 wherein said phosphine ligand comprises P(CH2CH2CH2OCH3)3.