Method for Producing High Potency Factor VIII

The present invention is concerned with a more concentrated, and hence more active form of Factor VIII, antihemophilic factor, and with a method for producing it.

It is known that the clotting of human blood is a complicated process, involving a series of reactions mediated by 13 different factors. It also is well known that a cause of hemophilia is the inability of the afflicted individual to synthesize one of these factors, known variously as antihemophilic factor, AHF, AHG or Factor VIII, in amounts sufficient to support adequate clotting. About 40 percent of hemophiliacs have no ability to synthesize Factor VIII, while the others have diminished ability. Dried preparations of Factor VIII concentrate are sold commercially for administration to hemophiliacs for treatment of bleeding or in advance of surgery. The Factor VIII concentrate is obtained from plasma obtained from human donors, through the use of known techniques. At the time of use, the dried concentrate is dissolved is sterile water, and the resulting solution is administered intravenously.

The Factor VIII preparation is not pure Factor VIII. Rather, it is a Factor VIII-enriched fraction obtained from plasma and contains other components. It is highly desirable that the Factor VIII concentrate be as pure as possible, but further improvements in purity through modification of the procedure for isolating Factor VIII from plasma are not practically feasible due to the difficulty of separating plasma components.

In accordance with this invention, Factor VIII having increased purity and potency is obtained from the plasma of donors having elevated levels of Factor VIII obtained by administration to such donor an analog of vasopressin known as 1-deamino-8-D-arginine vasopressin, or dDAVP, which is described in U.S. Pat. No. 3,497,491.

dDAVP is known to be pharmaceutically useful as an anti-diuretic. More recently, however, it has been reported by Mannucci et al in "1-Deamino-8-D-Arginine Vasopressin: A New Pharmacological Approach to the Management of Haemophilia and Von Willebrand's Disease," The Lancet, (i) 869 (1977), that when dDAVP is administered to those hemophiliacs having diminished ability to synthesize Factor VIII, the ability to synthesize Factor VIII can be increased to normal levels.

It has now been discovered in accordance with this invention that the administration of dDAVP to non-hemophiliacs causes them to synthesize amounts of Factor VIII substantially in excess (e.g., of the order of from about 3 to about 10 times) of the normal amount. That is, when dDAVP is administered to a normal human, the concentration of Factor VIII in the plasma increases above normal levels by from about 3 to about 10 times. On the other hand, the increased levels of Factor VIII do not cause an undesirable increase in the rate of clotting in normal humans. Apparently this is due, at least in part, to the fact that the levels of one or more of the other factors involved in clotting are such that the overall clotting reaction cannot proceed at a rate greater than normal, despite the presence of elevated levels of Factor VIII. In addition, it appears that administration of dDAVP to humans also increases the level of plasminogen activator, which is known to inhibit or reduce clotting. The increased levels of plasminogen activator may serve to protect against increased clotting. Regardless of theory, however, it has been shown that dDAVP can be administered to normal humans at levels which cause substantial increases in the circulating level of Factor VIII without significant change in clotting and without significant side-effect other than antidiuresis. This latter effect poses no problem, however, since it is accompanied by inhibition of thirst and there is no danger of voluntary overhydration.

The amount of dDAVP which is effective to increase the circulating level of Factor VIII ordinarily is an amount sufficient to establish a circulating dosage of about 10 to about 50 .mu.g, and preferably from about 10 to about 20 .mu.g, of dDAVP in the subject. This corresponds to about 0.2 .mu.g to about 1 .mu.g, and preferably from about 0.2 to about 0.4 .mu.g of dDAVP per kilogram of body weight. This may be achieved directly by intravenous injection of dDAVP, or it may be achieved indirectly by intranasal administration of dDAVP, i.e., in the form of nose drops. In the latter case, however, the applied dosage of dDAVP per individual should be about ten times the desired circulating dosage. Thus, an intranasal dosage of from about 100 to about 500 .mu.g and preferably from about 100 to about 200 .mu.g (corresponding to from about 2 to about 10, and preferably from about 2 to about 4 .mu.g/kg) is employed.

The dDAVP is administered in solution in a suitable solvent, preferably water. The solution may contain various additives generally known to the art. A preferred medium is physiological saline solution. The solution is preferably acidic, having a pH of from about 3 to about 5, and especially about 4, to stabilize and dDAVP. It is also desirable to include small amounts of bacteriostat, e.g., chlorobutanol, to minimize bacterial contamination in the intranasal preparation.

The concentration of dDAVP in the solution is not narrowly critical, and can range from about 1 .mu.g/ml to 1000 .mu.g/ml or higher, depending upon the intended mode of administration and dosage. In general, solutions intended for intanasal applications will contain higher concentrations of dDAVP than solutions intended to be administered by injection. Thus, solutions for intranasal administration ordinarily will contain from about 100 to about 400 .mu.g dDAVP per milliliter, whereas injectable solutions will contain of the order of about 4 to about 10 .mu.g dDAVP per milliliter.

The increase in Factor VIII levels begins within about 15 minutes after administration of dDAVP, and increased levels persist for at least 4 hours. When the circulating dosage of dDAVP is at least 10 .mu.g, the circulating level of Factor VIII is at least 3 times normal, and may be 10 or more times normal. Thus dDAVP is administered to the donor at least 15 minutes prior to collection, and preferably no more than 2 hours prior to collection.

The blood of the donor is collected in any conventional manner, and is treated by conventional techniques, for example by freeze-drying, to form a dried Factor VIII preparation. Because of the increased concentration of Factor VIII in the blood, the amount of Factor VIII in the dried preparation recovered from a constant volume of blood is correspondingly increased. Furthermore, since the amount of blood constituents other than Factor VIII (and plasminogen activator) is not affected, the proportion of "impurities" in the Factor VIII is reduced.

The following examples are illustrative.

Intravenous infusions of 10 .mu.g of 1-deamino-8-D-arginine vasopressin were given to each of five consenting healthy male volunteers aged 26-40. years. After reclining quietly for 30 minutes, each volunteer was infused through a 15-gauge needle introduced into a vein in one antecubital fossa, and blood samples were taken through a 15-gauge needle introduced into a vein in the other antecubital fossa. A Harvard constant-infusion pump first administered 25 ml of sodium chloride solution (154 mmol/l saline) for 15 minutes, followed by the dDAVP in 50 ml saline for a further 15 minutes. Blood was sampled before, during and after infusion. Patency of the sampling needle was maintained by an infusion of saline at 1 ml/min. Pulse rate was recorded throughout.

Plasma samples which were recovered from the blood samples were immediately frozen and stored at -40.degree. C. All samples from a single infusion were then thawed and assayed together, usually on the same day as the infusion, but never more than seven days later. Factor VIII procoagulant activity (VIII-AHF) was assayed by a modification of the activated partial thromboplastin time using severe hemophilic plasma as the substrate (Hardisty & MacPherson, Trombosis et Diathesis Haemorrhagica, 7, 215 (1962), as modified by Veltkamp, M.D. Thesis, University of Leiden, The Netherlands, "Detection of Carrier States in Hereditary Coagulation Disorders," Publ. Schatteur-Verlag, Stuttgard (1967)). The assays were standardized against freezedried plasma of known Factor VIII content, either the 4th or 6th British standard (obtained from the National Institute for Biological Standards and Control, Holly Hill, Hampstead, London). Some samples were also assayed by the two-stage technique of Biggs et al, British Journal of Haemotology, 1, 20 (1955) using the same Factor VIII standards.

Factor VIII-related antigen (VIII-AGN was assayed by the Laurell method, Scandinavian Journal of Clinical and Laboratory Investigation, 29, Supplement 124, 21 (1972)) using 0.4% antiserum (Behringwerke A.G., Marburg, Germany in 1% agarose, Indubiose, L-Industrie Biologique, Brancaise, Gennevilliers, France)). The buffer used was tris-EDTA-borate pH 8.6 (Aronsonn & Gronwall, Scandinavian Journal of Clinical and Laboratory Investigation, 9, 338 (1957)), diluted five-fold. Results were expressed as a percentage of the antigen level in the same freezedried plasma as was used to standardize the bioassay. Crossed immunoelectrophoresis was carried out by a similar modification of the original technique of Laurell.

The mean Factor VIII-AHF (reported as international units) and the mean Factor VIII-AGN (reported as the percent of standard plasma) responses are summarized in tubular form below, together with data obtained in a similar fashion except that saline was substituted for the dDAVP as a control.

As is evident, the administration of dDAVP to the volunteers resulted in a substantial increase in Factor VIII blood levels.

Employing procedures similar to those described in Example 1, the effect of dDAVP at dosage levels of 5 .mu.g, 10 .mu.g and 20 .mu.g on human volunteers was ascertained, there being an interval of at least one week between administration of each dosage. In addition, the pulse rate (per minute) and arterial blood pressure during infusion (diastolic.+-.0.33 pulse pressure) in torr were measured. The results are summarized in tubular form below.

As is evident, the effect of dDAVP in increasing the circulating levels of Factor VIII increased with increasing dosage. The highest dosage was accompanied by a significant increase in pulse rate, facial flushing and a slight feeling of nasal congestion or drowsiness. Similar symptoms were noted to a minor degree at the lower doses.