Technetium-99m labeled peptides for imaging

Details Technetium-99m labeled peptides for imaging Technetium-99m labeled peptides for imaging

1995-02-09

2000-07-11

Dees, Jose G.

Drug, bio-affecting and body treating compositions

Radionuclide or intended radionuclide containing; adjuvant...

In an organic compound

530300, 424 111, 424 91, 534 14, A61K 5100, A61M 3614

Patent

active

06086849&

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to radiodiagnostic reagents and peptides, and methods for producing labeled radiodiagnostic agents. Specifically, the invention relates to peptides, methods and kits for making such peptides, and methods for using such peptides to image sites in a mammalian body labeled with technetium-99m (Tc-99m) via a radiolabel-binding moiety which forms a neutral complex with Tc-99m.
2. Description of the Prior Art
In the field of nuclear medicine, certain pathological conditions are localized, or their extent is assessed, by detecting the distribution of small quantities of internally-administered radioactively labeled tracer compounds (called radiotracers or radiopharmaceuticals). Methods for detecting these radiopharmaceuticals are known generally as imaging or radioimaging methods.
In radioimaging, the radiolabel is a gamma-radiation emitting radionuclide and the radiotracer is located using a gamma-radiation detecting camera (this process is often referred to as gamma scintigraphy). The imaged site is detectable because the radiotracer is chosen either to localize at a pathological site (termed positive contrast) or, alternatively, the radiotracer is chosen specifically not to localize at such pathological sites (termed negative contrast).
A number of factors must be considered for optimal radioimaging in humans. To maximize the efficiency of detection, a radionuclide that emits gamma energy in the 100 to 200 keV range is preferred. To minimize the absorbed radiation dose to the patient, the physical half-life of the radionuclide should be as short as the imaging procedure will allow. To allow for examinations to be performed on any day and at any time of the day, it is advantageous to have a source of the radionuclide always available at the clinical site.
A variety of radionuclides are known to be useful for radioimaging, including .sup.67 Ga, .sup.99m Tc (Tc-99m), .sup.111 In, .sup.123 I, .sup.125 I, .sup.169 Yb, or .sup.186 Re. Tc-99m is a preferred radionuclide because it emits gamma radiation at 140 keV, it has a physical half-life of 6 hours, and it is readily available on-site using a molybdenum-99/technetium-99m generator.
The sensitivity of imaging methods using radioactively-labeled peptides is much higher than other radiopharmaceuticals known in the art, since the specific binding of the radioactive peptide concentrates the radioactive signal over the area of interest. Small synthetic peptides that bind specifically to targets of interest may be advantageously used as the basis for radiotracers. This is because: 1. they may be synthesized chemically (as opposed to requiring their production in a biological system such as bacteria or mammalian cells, or their isolation from a biologically-derived substance such as a fragment of a protein); 2. they are small, hence non-target bound radiotracer is rapidly eliminated from the body, thereby reducing background (non-target) radioactivity and allowing good definition of the target; and 3. small peptides may be readily manipulated chemically to optimize their affinity for a particular binding site.
Small readily synthesized labeled peptide molecules are preferred as routinely-used radiopharmaceuticals. There is clearly a need for small synthetic labeled peptides that can be directly injected into a patient and will image pathological sites by localizing at such sites. Tc-99m labeled small synthetic peptides offer clear advantages as radiotracers for gamma scintigraphy, due to the properties of Tc-99m as a radionuclide for imaging and the utility of specific-binding small synthetic peptides as radiotracer molecules.
Radiolabeled peptides have been reported in the prior art.
Ege et al., U.S. Pat. No. 4,832,940 teach radiolabeled peptides for imaging localized T-lymphocytes.
Olexa et al., 1982, European Patent Application No. 823017009 disclose a pharmaceutically acceptable radiolabeled peptide selected from Fragment E.sub.1 isolated from cross-linked fibrin, Fragment E.sub.2 isolated

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