Mutants of the factor VII-activating protease and detection...

Details Mutants of the factor VII-activating protease and detection... Mutants of the factor VII-activating protease and detection...

2001-07-26

2004-12-14

Slobodyansky, Elizabeth (Department: 1652)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carbohydrates or derivatives

C536S023500, C435S226000

Reexamination Certificate

active

06831167

ABSTRACT:

The invention relates to mutants of the blood clotting factor VII-activating protease (FSAP), to methods for detecting FSAP and its mutants at the protein level and also RNA/DNA level or in a tissue sample and also to specific antibodies for said detection methods.
The German patent application 199 03 693.4 already discloses a protease which has been isolated from blood plasma and which can activate clotting factor VII. Owing to this first finding, said protease was denoted factor VII-activating protease (FSAP). Detailed studies showed that FSAP is also a potent activator of single-chain plasminogen activators such as prourokinase or single-chain tissue plasminogen activator (sct-PA). Owing to these properties, possible applications of FSAP have been described, for example its application as coagulation-promoting agent based on FVII activation-assisted acceleration of coagulation. FSAP may also be used, alone or in combination with plasminogen activators, for fibrinolysis, for example in the case of thrombotic complications.
As described in the German patent applications 199 03 693.4 and 19926531.3, assays for detecting the protease have been developed which make it possible to quantify both the FSAP antigen content and its activity, for example in the plasma. In this connection, antigen determination is preferably carried out by means of an ELISA assay. As described in the German patent application 19926531.3 FSAP activity can be determined by quantifying the activation of prourokinase to urokinase and reaction of the latter with a chromogenic substrate by subsequently measuring the difference in extinction. Surprisingly, it was found during said activity assay that the FSAP proenzyme isolated from, for example, plasma was activated under the chosen incubation conditions and thus made activation of prourokinase possible. More recent studies have shown that FSAP is converted into the active form by self activation and thus, for example, can activate prourokinase or FVII. This is further supported by the abovementioned incubation conditions, i.e. neutral to alkaline pH, calcium ions and heparin. Moreover, most recent results indicate that prourokinase/urokinase (or single-chain and double-chain tPA) themselves cause or assist activation of single-chain FSAP.
Using the two abovementioned assay systems, i.e. the ELISA and prourokinase activation assay, more than 180 plasmas of healthy blood donors were studied. It was found that 5 to 10% of all samples had a markedly decreased potential of FSAP-effected prourokinase activation compared with a plasma pool (of more than 100 healthy donors) or with the average of the whole test group.
In contrast, average FSAP antigen values were measured in the majority of said donors (with decreased activity). It is assumed therefore that in the blood samples studied one or more FSAP modifications which would lead to reduced or missing activities could be present. The reason for this could be polymorphisms in the population, i.e. one or more mutations in the FSAP structures, which are indicated in a modification of the FSAP amino acid sequence, as was already assumed in the German patent application 199 26 531.3. The activities which are usually 50 to 70% lower than the average value of all donors studied indicate a heterozygous mutation. The resulting phenotype could be a probably equal presence of both FSAPs, namely the wild type FSAP and the mutant variant, in the plasma. Assuming the mutated variant had (almost) completely lost the property to activate prourokinase, then on average about half the activity would be measured. In addition, however, pseudohomozygous manifestations of heterozygous mutations of other proteins have also been described, in which merely the mutated protein which itself, however, had only lost part of the appropriately detected biological property was detectable.
In order to exclude that the deficiency or reduction in unknown potential cofactors is responsible for the detected reduction in FSAP activity, FSAP samples of three donors whose donated samples had repeatedly shown significantly reduced activity were purified. The highly purified proteins likewise showed a markedly reduced activity compared with FSAP purified from the plasma pool. This reduces the possibility of a cofactor influence and increases that of a protein modification in the abovementioned sense. A surprising result was the apparently unreduced potential for activating factor VII. For this reason, mutants of this kind are particularly suitable for the abovementioned application as clotting-promoting agent, as described in the German Patent application 199 03 693.4, since their fibrinolytic potential is apparently limited. Said mutants may be prepared recombinantly or transgenically based on the findings described below of the nucleotide sequence modifications. However, they may, like the corresponding FSAP protein (single-chain or double-chain FSAP), also be isolated directly from natural sources such as blood plasma. The German Patent applications 199 03 693.4, 199 37 219.5 and 199 37 218.7 have already described methods which involve preparation of FSAP, preferably with the aid of immunoabsorption, as is illustrated in detail in the German Patent application 100 36 641.4. However, as far as it is known, the monoclonal antibodies used up until now do not discriminate between FSAP wild type and FSAP mutants. Accordingly, only monoclonal antibodies reacting specifically with the mutants can be used for preparing the mutants. It is possible to obtain the antibodies by immunization with the mutant. It is also possible to use peptides with protein regions corresponding to amino acids 389 to 397 ( . . . SFRVQKIFK . . . ) and/or 534 to 539 ( . . . EKRPGV . . . ) of SEQ ID NO:4 for immunization and for generation of corresponding antibodies according to known methods. In addition, said antibodies are also used to specifically detect said mutants, for example as reagents in detection methods such as ELISA Western Blots, in immunohistology or in fluorescence assisted cell sorting (=FACS).
On the other hand, antibodies specific for FSAP wild type or directed against the corresponding amino acid sequences of the wild type, for example directed against the amino acid sequence 389 to 397 ( . . . SFRVEKIFK . . . ) and/or against the amino sequence 534 to 539 ( . . . GKRPGV . . . ) may be used especially in humanized form as a pharmaceutical for prophylactic or therapeutic inhibition of FSAP activity in order to counteract, for example, hyperfibrinolyses causing bleedings. In addition, it is also possible to use said antibodies for the purification, detection and distinction of wild type FSAP in the above described manner.
The genomic FSAP sequence was identified in the gene bank under accession no. AC 006097 by comparison with the known cDNA sequence (Choi-Miura, Accession No. S 83182) and intron and exon sequences were derived in the process. A total of 12 primer pairs was designed in order to be able to amplify the coding sequences in specific PCR reactions together with a small part of the respective flanking intron sequences.
First, genomic DNA from the blood of 2 subjects with reduced activity and from four subjects with normal prourokinase activity was isolated, amplified using all primer pairs and then the DNA sequence was determined using the PCR primer. The result is shown in Table 1. A total of 4 nucleotide positions in the coding region were polymorphic, i.e. at these positions two bases were detected simultaneously. It can therefore be assumed that these cases are heterozygous, having one wild type and one mutant allele. Two of these (at positions 183 and 957) are third base exchanges which do not result in amino acid exchange. The other two which were found only in the DNA of the subjects with reduced prourokinase activity lead to amino acid exchanges as depicted in Table 1.
TABLE 1
DNA sequence at nucleotide positions*
ProUK
Subject No.
activity
183
957
1177
1601
S83182
T
G
G
G
9689
normal
T/C
G
G
G
9690
normal
T/C
G
G
G
9704
normal
T
G/A
G
G

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