Imaging Agents with Improved Pharmacokinetic Profiles

Abstract

The invention relates to compounds suitable for use in an imaging agent said imaging agent showing an improved pharmacokinetic profile.

Description

EXAMPLE 1

Compound 3 was synthesised using a manual nitrogen bubbler apparatus on a 0.05 mmol scale using Fmoc-protected Rink Amide MBHA resin (Novabiochem), Fmoc-3-iodo-Tyr-OH (Novabiochem), Fmoc PEG propionic acid (Polypure AS, Cat 15137-1195) and compound 1. All acid functions were pre-activated prior to amide bond formation using HATU/DIEA as coupling reagents with DMF as solvent. Reaction steps were analysed by Kaiser test. Fmoc-deprotection was carried out using 20% piperidine in DMF treating first for 5 minutes followed by 40 minutes with fresh piperidine solution. The cleavage from the resin was carried out in TFA containing 2.5% H₂O and 2.5% triisopropylsilane for 2 hours. Crude material was purified by preparative HPLC (column Phenomenex Luna C18(2) 10 μm 250×10 mm; solvents A=water/0.1% TFA and B=acetonitrile/0.1% TFA; gradient 20-40% B over 60 min; flow 5.0 ml/min; UV detection at 214 nm) to give 5-10 mg of white solid. Analysis by LC-MS (column Phenomenex Luna C18(2) 3 μm 2.0×50 mm, solvents: A=water/0.1% TFA and B=acetonitrile/0.1% TFA; gradient 10-80% B over 10 min; flow 0.3 ml/min, UV detection at 214 and 254 nm, ESI-MS positive mode) gave peak expected for [MH]+.

EXAMPLE 2

Compound 4 was synthesised using a manual nitrogen bubbler apparatus on a 0.05 mmol scale using Fmoc-protected Rink Amide MBHA resin (Novabiochem), Pmoc-3-iodo-Tyr-OH (Novabiochem), Fmoc-amino-PEG-diglycolic acid (Polypure AS, Cat. 15131-0295) and compound 1. All acid functions were pre-activated prior to amide bond formation using HATU/DIEA as coupling reagents with DMF as solvent. Reaction steps were analysed by Kaiser test. Fmoc-deprotection was carried out using 20% piperidine in DMF treating first for 5 minutes followed by 40 minutes with fresh piperidine solution. The cleavage from the resin was carried out in TFA containing 2.5% H₂O and 2.5% triisopropylsilane for 2 hours. Crude material was purified by preparative HPLC (column Phenomenex Luna C18(2) 10 μm 250×10 mm; solvents A=water/0.1% TFA and B=acetonitrile/0.1% TFA; gradient 20-40% B over 60 min; flow 5.0 ml/min; UV detection at 214 nm) to give 5-10 mg of white solid. Analysis by LC-MS (column Phenomenex Luna C18(2) 3 μm 2.0×50 mm, solvents: A=water/0.1% TFA and B=acetonitrile/0.1% TFA; gradient 10-80% B over 10 min; flow 0.3 ml/min, UV detection at 214 and 254 nm, ESI-MS positive mode) gave peak expected for [MH]+.

EXAMPLE 3

Radiolabelled Compounds 2,3 and 4

The identical set of compounds described in Preparation C, Examples 1 and 2 were synthesised where the 3-iodo-tyrosine residue was exchanged for tyrosine. The tyrosine residue was then labelled as the final step using the general procedure described below:

10 μL 0.1 mM Na¹²⁷I (in 0.01M NaOH, 1×10⁻mol) was added to a vial containing 200 μL 0.2M NH₄OAc buffer (pH 4). This solution was added to the vial containing Na¹²³I (in 0.05M NaOH), which was then transferred to a silanised reaction P15 vial. 5 μL (2.5×10⁻⁸mol) of a freshly prepared peracetic acid solution in water (approx. 5 mM) was added to the reaction vial. 17 μL (5×10⁻⁸ mol) of a 3 mM solution of substrate in MeOH was added to the reaction vial and the solution mixed by pipetting. The compounds were purified by HPLC, solvent A: 0.1% TFA in water and solvent B: 0.1% TFA in MeCN using a Phenomenex Luna 5 μm C18(2) 150×4.6 mm column. The following gradient was applied:

Time  % B
0.0   30
20.0  70
20.20 100
23.20 100
23.70 30
30.0  30

EXAMPLE 4

Biodistribution of Radiolabelled Compounds 2, 3 and 4

Radiolabelled compounds 2-4 comprise 127I as an imageable moiety and residue X

as a non-peptidic vector moiety that is an inhibitor for matrix metalloproteinase. Compounds 2 and 3 do not comprise PEG moieties according to the invention and serve as comparison compounds.

Biodistribution studies were carried out in a Lewis Lung mouse Carcinoma model as described in Bae et al, Drugs Exp Clin Res, 2003; 29 (1): 15-23.

Following tail vein injection of the compounds, e the excretion profile was monitored at 5, 30, 60 and 120 minutes. The results are displayed in Table 1.

TABLE 1
Compound	% ID/g liver	% ID/g kidney
2	71	7
3	61	20
4	20	70

From the biodistribution results in table 1 it is apparent, that the presence of a PEG containing moiety that comprises 2 to 50 ethylene glycol units in compound 4—i.e. a compound according to claim 1, remarkably improves the biodistribution of the compound in comparison to compounds 2 and 3; the compound is preferably excreted via the renal system.

Claims

1. A compound suitable for use as an imaging agent said compound consists of i) a PEG containing moiety having a molecular weight of less than 3000 Da and comprising 2 to 50 ethylene glycol units;ii) an imageable moiety; andiii) a non-peptidic vector moiety with the proviso that the non-peptidic vector moiety (iii) is not a non-peptidic vector moiety having affinity for the Angiotensin II receptor.

2. A compound according to claim 1 wherein the PEG containing moiety (i) is a straight chain PEG containing moiety comprising two or more ethylene glycol units or a dendrimeric PEG containing moiety comprising more than one PEG unit, wherein a PEG unit is a unit comprising at least two ethylene glycol units.

3. A compound according to claim 1 wherein the PEG containing moiety (i) is a straight chain PEG containing moiety comprising one or more PEG units.

4. A compound according to claim 1 wherein the PEG containing moiety (i) forms a linker between the imageable moiety (ii) and the non-peptidic vector moiety (iii).

5. A compound according to claim 1 wherein the PEG containing moiety has a molecular weight of less than 2000 Da, preferably a molecular weight of from 600 to 1000 Da.

6. A compound according to claim 1 wherein the PEG containing moiety comprises 10 to 30 ethylene glycol units, preferably 2 to 6 ethylene glycol units.

7. A compound according to claim 1 wherein the imageable moiety (ii) is an imageable moiety selected from the group of consisting of imageable moieties useful in radio imaging, imageable moieties useful in SPECT imaging, imageable moieties useful in PET imaging, imageable moieties useful in MR imaging and imageable moieties useful in optical imaging.

8. A compound according to claim 1 wherein the imageable moiety (ii) comprises a radionuclide, a paramagnetic metal ion or a chromophore.

9. A compound according to claim 1 wherein the non-peptidic vector moiety (iii) is a small organic molecule, preferably a small organic molecule of less than 1000 Da.

10. A compound according to claim 1 for use as an imaging agent.

11. An imaging agent comprising the compound according to claim 1 and one or more pharmaceutically acceptable adjuvants, excipients or diluents.

12. Imaging agent according to claim 11 for use in enhancing image contrast in in vivo imaging of the human or non-human animal body.

13. A method of generating contrast enhanced images of a human or non-human animal body, wherein an imaging agent according to claim 11 is used to achieve said contrast enhancement.