Chemistry: analytical and immunological testing – Biospecific ligand binding assay
Reexamination Certificate
2000-05-15
2004-01-20
Sisson, Bradley L. (Department: 1634)
Chemistry: analytical and immunological testing
Biospecific ligand binding assay
C514S002600, C530S350000, C530S399000
Reexamination Certificate
active
06680207
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to tagged molecules (distinguishable from untagged, but otherwise identical, molecules), methods of preparing tagged molecules, nucleic acid sequences and constructs encoding tagged molcules, and a method of distinguishing between tagged and untagged (but otherwise identical) molecules.
In particular, the present invention relates to a method of tagging a protein with a therapeutically acceptable tag which enables detection of the tagged protein administered exogenously to humans, bovines or other animals where the same (but untagged) protein is produced endogenously, and a method of detecting and differentiating the tagged protein over the endogenous protein. In particular, the method is suitable for application to human growth hormone (hGH), to enable differential detection of exogenously administered hGH in humans, for example, to determine whether hGH is being administered unlawfully for its performance enhancing effects.
BACKGROUND OF THE INVENTION
Previously, the usual method of differentiating exogenously administered protein from the endogenous one has been to tag the exogenous protein with radioactive labels. Because of the hazards of radioactivity, radioactively tagged proteins are administered to patients over short periods of time in controlled conditions and under medical supervision. Further, radioactive labels are not therapeutically acceptable since they are intrusive to the biological system in which such tagged proteins are administered. Other tagging methods tend to alter the biological function of the protein molecule and therefore are no longer suitable for therapeutic use. Such prior art tagging methods are therefore limited to controlled research uses and do not have widespread cost effective commercial applications.
Some amino acids, for example tryptophan (W) and tyrosine (Y) in particular, are natural fluorophores, which fluoresce when appropriately stimulated. This fluorescence can be detected and measured with standard prior art fluorescence detection techniques. Proteins which contain such fluorophores in their amino acid sequence may also fluoresce when appropriately stimulated. The level of fluorescence can be crudely related to the number of fluorophores in the protein. The fluorescent yield of any fluorophore is sensitive to its local environment such that, for example, there may be a difference between its fluorescence in an aqueous and a hydrophobic environment. Waldman et al (1987 Biochem. Biophys. Acta 931, 66-71; 1988 Biochem. Biophys Res. Comm. 150 (2), 752-759), Corinne (1991 Biochemistry 30, 1028-1036) and others have exploited this property to perform in vitro laboratory studies on conformational and structural changes of lactate dehydrogenase when, for example, substrate binding occurs. Waldman and Corrine have mutated lactate dehydrogenase to incorporate tryptophan residues at the substrate binding site. This technique is restricted to use as a research tool for conformational and structural studies of proteins in vitro, since often the full biological activity or structural conformation of the native protein is lost. Thus, such modified proteins are no longer suitable for therapeutic purposes and there is no disclosure or suggestion of pharmaceutical compositions comprising the mutated protein. Moreover, there is no disclosure or suggestion in the prior art that such mutations could form the basis for a method of distinguishing the altered compound from the naturally occurring compound.
WO 94/10200 discloses and is concerned with amino acid substitutions in somatotropin (i.e. Growth Hormone) which provide increased conformational and chemical stability.
There is no suggestion in WO 94/10200 that modifications can be made to Growth Hormone for the purpose of distinguishing between endogenous Growth Hormone present in a subject and exogenous Growth Hormone administered to the subject. A number of amino acid substitutions in somatotropin are disclosed or suggested in WO 94/10200 which, because of the natural fluorophore activity of the amino acid residues tryptophan and tyrosine (discussed above), result in a somatotropin molecule having an altered fluorescence activity relative to the wild type, unsubstituted molecule Such substitutions include the following:
G40→Y (i.e. glycine substituted by tyrosine at residue number 40); F52→Y: W86→F, Y, L, I or V; F103→Y; 1137→Y;
A reliable method for differentiating and detecting exogenously administered hGH is particularly desirable when attempting to monitor the pharmacokinetics and/or pharmacodynamics of hGH, or to detect its unlawful administration by athletes and others who illicitly use hGH for improving their performance. Presently, standard detection methods (e.g. HPLC, ELISA), are used for measuring the total amount of hGH in an athletes' blood or urine samples, and by subtracting the expected levels referenced to the general population, estimations of elevated hGH levels can be made. However, as levels vary considerably between individuals, and exogenous levels fall rapidly with time, this is a very crude measurement. In addition, as the performance enhancing effects last much longer than the detectable transient elevated levels of hGH in these samples, unless samples are taken shortly after administration the technique does not give indisputable proof that exogenous hGH has or has not been used.
The present invention seeks to alleviate the above mentioned problems by tagging or modifying a protein (such as hGH) with a therapeutically acceptable tag which can be detected simply and can be differentiated from the endogenous protein present in a sample of cells, blood, urine or other body fluid. The invention has little or no effect on the biological activity of the protein, such that the modified protein can be administered therapeutically in the same manner as the unmodified protein. Thus, the modified or tagged protein can be safely prescribed by physicians for existing or new therapeutic purposes, and also economically manufactured commercially at substantially the same cost as the untagged protein.
A further advantage of the present invention is that although levels of the exogenous protein may drop rapidly after administration, the specificity for the tagged protein and high sensitivity of the detection method allow detection long after the exogenous protein has been administered. Thus, an abuser cannot claim abnormally elevated production of the endogenous protein, and unlawful use of the tagged protein can be detected. Additionally, the present invention allows the pharmacokinetics and/or pharmacodynamics of the tagged exogenous protein to be detected and monitored.
Therefore, it is an object of the present invention to provide a method for tagging proteins which method enables detection of the exogenous tagged protein over any endogenous polypeptide which may be present in a sample (e.g. such as blood or urine) taken from, for example, a human subject (e.g. an athlete) or other mammalian subject (e.g. domesticated farm livestock).
It is another object of the present invention to provide a modified polypeptide molecule, such as hGH tagged in a manner which is therapeutically acceptable. Further, the tagging method of the present invention enables the biological activity per se of a protein to remain substantially unaltered such that the therapeutic efficacy is maintained and the protein can be administered in a manner identical to or similar with the unmodified protein.
A further specific object of the present invention is to provide a modified hGH molecule substituted with tryptophans at strategic positions in the native hGH sequence.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides a method of detecting the presence in a sample of a polypeptide exogenously administered to a mammalian subject from whom the sample is obtained, and distinguishing between such an exogenously administered polypeptide and a naturally-occurring endogenous polypeptide present in the sample; the method compris
Atkinson Anthony
Murphy Jonathan P.
Generic Biologicals Limited
Pillsbury & Winthrop LLP
Sisson Bradley L.
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