A first-in-human study of the safety, tolerability, pharmacokinetics and pharmacodynamics of PF-06741086, an anti-tissue factor pathway inhibitor mAb, in healthy volunteers

Essentials Tissue factor pathway inhibitor (TFPI) is an antagonist of FXa and the TF-FVIIa complex. PF-06741086 is an IgG1 monoclonal antibody that targets the Kunitz-2 domain of TFPI. Single doses of PF-06741086 were evaluated in a phase 1 study in healthy volunteers. Data from this study support further investigation of PF-06741086 in individuals with hemophilia.

SUMMARY

Background Tissue factor pathway inhibitor (TFPI) is a protease inhibitor of the tissue factor-activated factor VII complex and activated FX. PF-06741086 is a mAb that targets TFPI to increase clotting activity. Objectives This study was a randomized, double-blind, sponsor-open, placebo-controlled, single intravenous or subcutaneous dose escalation study to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of PF-06741086. Patients/Methods Volunteers who provided written informed consent were assigned to cohorts with escalating dose levels. Safety endpoints included treatment-emergent adverse events (TEAEs), infusion/injection site reactions, vital signs, electrocardiogram, and coagulation and hematology laboratory parameters. Pharmacokinetic (PK) and pharmacodynamic (PD) endpoints included exposures of PF-06741086 in plasma and measures of PF-06741086 pharmacology, respectively. Results Forty-one male volunteers were recruited overall. Thirty-two were dosed with PF-06741086 from 30 mg subcutaneously to 440 mg intravenously. All doses were safe and well tolerated. TEAEs were mild or moderate in severity, laboratory abnormalities were transient, there were no serious adverse events, there were no infusion/injection site reactions, and no dose escalation stopping criteria were met. Plasma exposures of PF-06741086 increased greater than proportionally with dose under the same dosing route. Coagulation pharmacology was demonstrated via total TFPI, dilute prothrombin time, D-dimer, prothrombin fragment 1 + 2 and thrombin generation assay parameters. Conclusions Single doses of PF-06741086 at multiple dose levels were safe and well tolerated in a healthy adult male population. The safety, PK and PD data from this study support progression to a multiple-dose study in hemophilic patients.

Phase 1 dose-escalating study to evaluate the safety, pharmacokinetics, and pharmacodynamics of a recombinant factor Xa variant (FXaI16L )

Essentials FXaI16L is a recombinant zymogen-like variant of activated coagulation factor X (FXa). A phase 1 dose escalation clinical trial of FXaI16L was conducted in healthy adults. FXaI16L was safe and tolerated at doses up to 5 μg/kg; no dose-limiting toxicity was observed. Data support further development of FXaI16L for patients with acute hemorrhagic conditions.

SUMMARY

Background FXaI16L (PF-05230907) is a zymogen-like variant of activated factor X (FXa). It shows enhanced resistance to inactivation by endogenous inhibitors as compared with wild-type FXa, and restores hemostatic activity in non-clinical models of various bleeding conditions. Objectives To evaluate the safety, pharmacokinetics and pharmacodynamics of FXaI16L by performing a phase 1, first-in-human, dose-escalation clinical trial in healthy adult volunteers. Methods Participants were assigned to one of six ascending single-dose cohorts (0.1, 0.3, 1, 2, 3 or 5 μg kg-1 ), each planned to comprise six volunteers treated with FXaI16L and two treated with placebo. Assessments included safety monitoring, pharmacokinetic and pharmacodynamic (PD) analyses, and immunogenicity testing. Results The trial enrolled 49 male volunteers. Administration of a single intravenous bolus dose of FXaI16L was safe and tolerated at all dose levels tested, with no dose-limiting toxicity or serious adverse events. FXaI16L plasma levels appeared to increase dose-proportionally, with a half-life of ~ 4 min. Treatment-related PD changes were observed for activated partial thromboplastin time, thrombin generation assay, thrombin-antithrombin complexes, prothrombin fragment 1 + 2, and D-dimer. One volunteer had a weak and transient non-neutralizing antidrug antibody response, which did not cross-react with native FX or native FXa. Conclusions FXaI16L was safe and tolerated, and showed a pharmacologic effect in healthy adults when administered at doses up to 5 μg kg-1 . The safety profile, pharmacokinetics and pharmacodynamics observed in this clinical trial support the further development of FXaI16L for hemostatic treatment in individuals with acute hemorrhagic conditions.

Using a Systems Pharmacology Model of the Blood Coagulation Network to Predict the Effects of Various Therapies on Biomarkers

A number of therapeutics have been developed or are under development aiming to modulate the coagulation network to treat various diseases. We used a systems model to better understand the effect of modulating various components on blood coagulation. A computational model of the coagulation network was built to match in-house in vitro thrombin generation and activated Partial Thromboplastin Time (aPTT) data with various concentrations of recombinant factor VIIa (FVIIa) or factor Xa added to normal human plasma or factor VIII-deficient plasma. Sensitivity analysis applied to the model revealed that lag time, peak thrombin concentration, area under the curve (AUC) of the thrombin generation profile, and aPTT show different sensitivity to changes in coagulation factors' concentrations and type of plasma used (normal or factor VIII-deficient). We also used the model to explore how variability in concentrations of the proteins in coagulation network can impact the response to FVIIa treatment.

Adenoviral-mediated transfer of human BMP-6 gene accelerates healing in a rabbit ulnar osteotomy model

This study evaluated healing of rabbit bilateral ulnar osteotomies 6 and 8 weeks after surgery in response to percutaneous injection of transgenic adenoviral (Ad) bone morphogenetic protein-6 (BMP-6) vector or green fluorescent protein vector control (Ad-GFP) administered 7 days after surgery compared to untreated osteotomy controls. The amount, composition and biomechanical properties of the healing bone repair tissue were compared among groups and to historical data for intact rabbit ulnae obtained from similar studies at the same institution. Quantitative computed tomography was used to determine area, density and mineral content of the mineralized callus in the harvested ulnae. Maximum torque, torsional stiffness, and energy absorbed to failure were determined at 1.5 degrees /s. Calcified sections of excised ulnae (5 microm) were stained with Goldner's Trichrome and Von Kossa, and evaluated for callus composition, maturity, cortical continuity, and osteotomy bridging. Radiographic assessment of bone formation indicated greater mineralized callus in the ulnae injected with Ad-hBMP-6 as early as 1 week after treatment (2 weeks after surgery) compared to untreated osteotomy ulnae (p < 0.006) and Ad-GFP treated osteotomy ulnae (p < 0.002). Quantitative computed tomography confirmed greater bone area and bone mineral content at the osteotomy at 6 weeks in Ad-BMP-6 treated osteotomy as compared to untreated osteotomy ulnae (p < 0.001) and Ad-GFP treated osteotomy ulnae (p < 0.01). Ad-BMP-6 treated osteotomy ulnae were stronger (p < 0.001 and 0.003) and stiffer (p < 0.004 and 0.003) in torsion at 6 weeks than untreated osteotomy ulnae or Ad-GFP treated osteotomy ulnae, respectively. Maximum torque, torsional stiffness, and energy absorbed to failure were greater in Ad-BMP-6 treated osteotomy ulnae compared to their respective untreated contralateral osteotomy ulnae at 8 weeks [p < 0.03]. Maximum torque and torsional stiffness in the Ad-BMP-6 treated osteotomy ulnae were not different to intact ulnae values at 6 and 8 weeks. These experiments confirm that BMP-6 can be potently osteoinductive in vivo resulting in acceleration of bone repair.

Osteogenic potential of five different recombinant human bone morphogenetic protein adenoviral vectors in the rat

Bone morphogenetic protein (BMP) adenoviral vectors for the induction of osteogenesis are being developed for the treatment of bone pathology. However, it is still unknown which BMP adenoviral vector has the highest potential to stimulate bone formation in vivo. In this study, the osteogenic activities of recombinant human BMP-2, BMP-4, BMP-6, BMP-7, and BMP-9 adenoviruses were compared in vitro, in athymic nude rats, and in Sprague-Dawley rats. In vitro osteogenic activity was assessed by measuring the alkaline phosphatase activity in C2C12 cells transduced by the various BMP vectors. The alkaline phosphatase activity induced by 2 x 10(5) PFU/well of BMP viral vector was 4890 x 10(-12) U/well for ADCMVBMP-9, 302 x 10(-12) U/well for ADCMVBMP-4, 220 x 10(-12) U/well for ADCMVBMP-6, 45 x 10(-12) U/well for ADCMVBMP-2, and 0.43 x 10(-12) U/well for ADCMVBMP-7. The average volume of new bone induced by 10(7) PFU of BMP vector in athymic nude rats was 0.37+/-0.03 cm(3) for ADCMVBMP-2, 0.89+/-0.07 cm(3) for ADCMVBMP-4, 1.02+/-0.07 cm(3) for ADCMVBMP-6, 0.24+/-0.05 cm(3) for ADCMVBMP-7, and 0.63+/-0.07 cm(3) for ADCMVBMP-9. In immunocompetent Sprague-Dawley rats, no bone formation was demonstrated in the ADCMVBMP-2, ADCMVBMP-4, and ADCMVBMP-7 groups. ADCMVBMP-6 at a viral dose of 10(8) PFU induced 0.10+/-0.03 cm(3) of new bone, whereas ADCMVBMP-9 at a lower viral dose of 10(7) PFU induced more bone, with an average volume of 0.29+/-0.01 cm(3).

Engineered human mesenchymal stem cells: a novel platform for skeletal cell mediated gene therapy

BACKGROUND

Human mesenchymal stem cells (hMSCs) are pluripotent cells that can differentiate to various mesenchymal cell types. Recently, a method to isolate hMSCs from bone marrow and expand them in culture was described. Here we report on the use of hMSCs as a platform for gene therapy aimed at bone lesions.

METHODS

Bone marrow derived hMSCs were expanded in culture and infected with recombinant adenoviral vector encoding the osteogenic factor, human BMP-2. The osteogenic potential of genetically engineered hMSCs was assessed in vitro and in vivo.

RESULTS

Genetically engineered hMSCs displayed enhanced proliferation and osteogenic differentiation in culture. In vivo, transplanted genetically engineered hMSCs were able to engraft and form bone and cartilage in ectopic sites, and regenerate bone defects (non-union fractures) in mice radius bone. Importantly, the same results were obtained with hMSCs isolated from a patient suffering from osteoporosis.

CONCLUSIONS

hMSCs represent a novel platform for skeletal gene therapy and the present results suggest that they can be genetically engineered to express desired therapeutic proteins inducing specific differentiation pathways. Moreover, hMSCs obtained from osteoporotic patients can restore their osteogenic activity following human BMP-2 gene transduction, an important finding in the future planning of gene therapy treatment for osteoporosis.

Engineered human mesenchymal stem cells: a novel platform for skeletal cell mediated gene therapy

BACKGROUND

Human mesenchymal stem cells (hMSCs) are pluripotent cells that can differentiate to various mesenchymal cell types. Recently, a method to isolate hMSCs from bone marrow and expand them in culture was described. Here we report on the use of hMSCs as a platform for gene therapy aimed at bone lesions.

METHODS

Bone marrow derived hMSCs were expanded in culture and infected with recombinant adenoviral vector encoding the osteogenic factor, human BMP-2. The osteogenic potential of genetically engineered hMSCs was assessed in vitro and in vivo.

RESULTS

Genetically engineered hMSCs displayed enhanced proliferation and osteogenic differentiation in culture. In vivo, transplanted genetically engineered hMSCs were able to engraft and form bone and cartilage in ectopic sites, and regenerate bone defects (non-union fractures) in mice radius bone. Importantly, the same results were obtained with hMSCs isolated from a patient suffering from osteoporosis.

CONCLUSIONS

hMSCs represent a novel platform for skeletal gene therapy and the present results suggest that they can be genetically engineered to express desired therapeutic proteins inducing specific differentiation pathways. Moreover, hMSCs obtained from osteoporotic patients can restore their osteogenic activity following human BMP-2 gene transduction, an important finding in the future planning of gene therapy treatment for osteoporosis.

A light and electron microscopic study of ectopic tendon and ligament formation induced by bone morphogenetic protein-13 adenoviral gene therapy

OBJECT

Bone morphogenetic proteins (BMPs) are involved in the growth and development of many tissues, but it is their role in skeletal development and their unique ability to induce ectopic and orthotopic osteogenesis that have attracted the greatest interest. Expression of the BMP-13 gene is predominantly localized to hypertrophic chondrocytes in regions of endochondral bone formation during development, as well as in mature articular cartilage in the adult. In addition, the application of BMP-13 on a collagen carrier induces neotendon/neoligament formation when delivered subcutaneously or intramuscularly in rodents. The aim of the present study was to determine the histological and ultrastructural changes that occur after the intramuscular injection of a first-generation BMP-13 adenoviral vector.

METHODS

Athymic nude rats were injected with 3.75 x 10(10) plaque-forming units of adenovirus (Ad)-BMP-13 or Ad-beta-galactosidase in the thigh musculature, and the region was examined using light and electron microscopy at various time points between 2 days and 100 days postinjection. As early as 2 days after injection of Ad-BMP-13, progenitor cells were observed infiltrating between the transduced muscle fibers. These cells subsequently proliferated, differentiated, and secreted large amounts of collagenous extracellular matrix. By 100 days postinjection, the treated tissue displayed the histological and ultrastructural appearance of neotendon/neoligament, which was clearly demarcated from the surrounding muscle. Small foci of bone and fibrocartilage were also seen within the treated tissue. A short-term bromodeoxyuridine study also demonstrated rapid mesenchymal cell proliferation at the Ad-BMP-13 injection site as early as 48 hours postinjection. At all time points, the control AD-beta-gal injection sites were found to contain only normal muscle, without evidence of inflammation or mesenchymal cell proliferation.

CONCLUSIONS

The results of this study indicate that in the future the use of the BMP-13 gene may have therapeutic utility for the healing of tendon and ligament tears and avulsion injuries.

Engineered human mesenchymal stem cells: a novel platform for skeletal cell mediated gene therapy

BACKGROUND

Human mesenchymal stem cells (hMSCs) are pluripotent cells that can differentiate to various mesenchymal cell types. Recently, a method to isolate hMSCs from bone marrow and expand them in culture was described. Here we report on the use of hMSCs as a platform for gene therapy aimed at bone lesions.

METHODS

Bone marrow derived hMSCs were expanded in culture and infected with recombinant adenoviral vector encoding the osteogenic factor, human BMP-2. The osteogenic potential of genetically engineered hMSCs was assessed in vitro and in vivo.

RESULTS

Genetically engineered hMSCs displayed enhanced proliferation and osteogenic differentiation in culture. In vivo, transplanted genetically engineered hMSCs were able to engraft and form bone and cartilage in ectopic sites, and regenerate bone defects (non-union fractures) in mice radius bone. Importantly, the same results were obtained with hMSCs isolated from a patient suffering from osteoporosis.

CONCLUSIONS

hMSCs represent a novel platform for skeletal gene therapy and the present results suggest that they can be genetically engineered to express desired therapeutic proteins inducing specific differentiation pathways. Moreover, hMSCs obtained from osteoporotic patients can restore their osteogenic activity following human BMP-2 gene transduction, an important finding in the future planning of gene therapy treatment for osteoporosis.

Morphologic analysis of BMP-9 gene therapy-induced osteogenesis

The present study was performed to determine the histological, ultrastructural, and radiographic changes that occur over time at intramuscular BMP-9 gene therapy treatment sites. Several members of the bone morphogenetic protein (BMP) family have the potential to induce osteochondrogenesis when the protein is delivered to rodents, canines, rabbits, and nonhuman primates. Previous studies have also demonstrated that BMP gene therapy utilizing adenoviral vectors can also stimulate orthotopic and heterotopic bone formation in rodents and rabbits. Athymic nude and Sprague-Dawley rats were injected with Ad-BMP-9 or Ad-beta-Gal (3.75 x 10(9) particles) in their thigh musculature and light microscopic, electron microscopic, and computerized tomography analysis was performed 3, 6, 9, 12, 15, 18, 21, and 100 days later. To assess early mesenchymal cell proliferation, a bromodeoxyuridine (BrdU) immunohistochemical analysis was also performed 48, 60, and 72 hr postinjection in athymic nude rats. All animals demonstrated extensive endochondral bone formation at the Ad-BMP-9 treatment sites within 3 weeks. The Sprague-Dawley rats also exhibited a massive, acute inflammatory infiltrate during the first week. Proliferating mesenchymal stem cells were clearly evident as early as 2 days after treatment, which differentiated into small or hypertrophied chondrocytes during the next week. During the third week, the cartilaginous matrix mineralized and formed woven bone, which converted to lamellar bone by 3 months. No evidence of bone formation was demonstrated at the Ad-beta-Gal injection sites in the athymic nude or Sprague-Dawley rats. In addition, no cellular proliferation was seen at the Ad-beta-Gal treatment sites in the athymic nude animals as assessed by light microscopy and BrdU immunohistochemistry. The extensive bone formation induced by Ad-BMP-9 suggests that BMP gene therapy may have potential utility in the treatment of degenerative, rheumatic, or traumatic bone pathology.

Use of bone morphogenetic protein-9 gene therapy to induce spinal arthrodesis in the rodent

OBJECT

Bone morphogenetic proteins (BMPs) have been shown to have significant osteoinductive activity in numerous in vitro and in vivo assay systems, and BMP-2 and BMP-7 are currently being evaluated in human clinical studies. In the spinal region, BMPs have been shown to promote spinal arthrodesis at a higher rate than autologous bone alone. The delivery of BMPs via direct or ex vivo gene therapy techniques is also currently being evaluated and has shown promise in several mammalian models. The present study was designed to evaluate the efficacy of the use of direct, percutaneous BMP-9 adenoviral gene therapy to promote spinal fusion in the rodent.

METHODS

Each animal was injected with 7.5x10(8) pfu of a BMP-9 adenoviral vector in the lumbar paraspinal musculature and allowed to survive 16 weeks. Computerized tomography studies and histological analysis demonstrated massive bone induction at the injection sites, clearly leading to solid spinal arthrodesis, without evidence of pseudarthroses, nerve root compression, or systemic side effects.

CONCLUSIONS

The results of this study strongly support the advancement of BMP gene therapy techniques toward clinical use.

In vivo endochondral bone formation using a bone morphogenetic protein 2 adenoviral vector

Bone morphogenetic proteins (BMPs) are polypeptides that induce ectopic bone formation in standard rat in vivo assay systems. Previous studies have demonstrated the clinical utility of these proteins in spinal fusion, fracture healing, and prosthetic joint stabilization. Gene therapy is also a theoretically attractive technique to express BMPs clinically, since long-term, regulatable gene expression and systemic delivery with tissue-specific expression may be possible in future. This study was performed to determine whether an adenoviral vector containing the BMP-2 gene can be used to express BMP-2 in vitro and promote endochondral bone formation in vivo. In vitro, U87 MG cells transduced per cell with 20 MOI of an adenoviral construct containing the BMP-2 gene under the control of the universal CMV promoter (Ad-BMP-2) showed positive antibody staining for the BMP-2 protein at posttransfection day 2. The synthesis and secretion of active BMP-2 into the conditioned medium of Ad-BMP-2-transduced 293 cells were confirmed by Western blot analysis and the induction of alkaline phosphatase activity in a W-20 stromal cell assay. In vivo, Sprague-Dawley rats and athymic nude rats were injected with Ad-BMP-2 in the thigh musculature and were sacrificed on day 3, 6, 9, 12, 16, 21, 60, and 110 for histological analysis. The Sprague-Dawley rats showed evidence of acute inflammation, without ectopic bone formation, at the injection sites. In the athymic nude rats, BMP-2 gene therapy induced mesenchymal stem cell chemotaxis and proliferation, with subsequent differentiation to chondrocytes. The chondrocytes secreted a cartilaginous matrix, which then mineralized and was replaced by mature bone. This study demonstrates that a BMP-2 adenoviral vector can be utilized to produce BMP-2 by striated muscle cells in athymic nude rats, leading to endochondral bone formation. However, in immunocompetent animals the endochondral response is attenuated, secondary to the massive immune response elicited by the first-generation adenoviral construct.

Percutaneous spinal fusion using bone morphogenetic protein-2 gene therapy

OBJECT

Gene therapy has many potential applications in neurosurgery. One application involves bone morphogenetic protein-2 (BMP-2), a low-molecular-weight glycoprotein that induces bone formation in vivo. Numerous studies have demonstrated that the BMP-2 protein can enhance spinal fusion. This study was undertaken to determine whether direct injection of an adenoviral construct containing the BMP-2 gene can be used for spinal fusion.

METHODS

Twelve athymic nude rats were used in this study. Recombinant, replication-defective type 5 adenovirus with the cytomegalovirus (CMV) promoter and BMP-2 gene (Ad-BMP-2) was used. A second adenovirus constructed with the CMV promoter and beta-galactosidase (beta-gal) gene (Ad-beta-gal) was used as a control. In three groups (four rats each) 7.5 microl of virus (5x10(8) particles/microl) was injected percutaneously and paraspinally at the lumbosacral junction: Group 1 received Ad-BMP-2 bilaterally; Group 2 received Ad-BMP-2 on the right, Ad-beta-gal on the left; and Group 3 received Ad-beta-gal bilaterally. Computerized tomography (CT) scans of the lumbosacral spine were obtained at 3, 5, 8, and 12 weeks. At 12 weeks, the animals were killed and underwent histological inspection. Ectopic bone formation was observed both on three-dimensionally reconstructed CT scans and histological examination in all rats at sites treated with Ad-BMP-2. Histological analysis demonstrated bone at different stages of maturity adjacent to the spinous processes, laminae, and transverse processes.

CONCLUSIONS

Results of this study clearly demonstrated that it is possible to produce in vivo endochondral bone formation by using direct adenoviral construct injection into the paraspinal musculature, which suggests that gene therapy may be useful for spinal fusion in the future.

The factor V B-domain provides two functions to facilitate thrombin cleavage and release of the light chain

Blood coagulation factors V and VIII are homologous proteins that have the domain organization A1-A2-B-A3-C1-C2. Upon thrombin activation, the B-domains of both molecules are released. Previous studies on factor VIII showed that the B-domain was not required for thrombin cleavage or activity. In contrast, deletion of the factor V B-domain (residues 709 to 1545) yielded a molecule with sevenfold reduced procoagulant activity that was not cleaved by thrombin. However, this factor V B-domain deletion molecule was activated by factor Xa, although the fold-activation was 85% that of wild-type factor V. Thrombin cleavage of factor V occurs initially after residue 709 and subsequently after residues 1018 and 1545. The requirement for thrombin cleavage within the B-domain at residue 1018 was evaluated by mutagenesis of Arg1018 to Ile. In the resultant R1018I mutant, the rate of thrombin activation and appearance of maximal cofactor activity was delayed and was consistent with delayed cleavage of the light chain at residue 1545. In contrast, the rate of factor Xa activation in the R1018I mutant was not altered. This finding suggests that thrombin cleavage at 1018 facilitates subsequent thrombin cleavage at 1545. Further mutagenesis was used to study the requirement for sequences within the factor V B-domain for thrombin cleavage at residue 1545. Whereas the factor V deletion molecule removing residues 709 to 1545 was not cleaved by thrombin, a smaller B-domain deletion molecule (residues 709 to 1476) containing an acidic amino acid-rich region (residues 1490 to 1520) was effectively cleaved by thrombin. These results show that residues 1476 to 1545, which contain an acidic amino acid-rich region, were required for thrombin cleavage of the light chain. Introduction of an acidic amino acid-rich region from factor VIII (residues 337 to 372) into the factor V 709 to 1545 deletion also restored thrombin cleavage of the light chain. In contrast, similar replacement with the acidic region from the factor VIII light chain (residues 1649 to 1689) was significantly less effective in promoting thrombin cleavage of the light chain. This finding suggests that the different acidic regions in factors V and VIII are not functionally equivalent in their interaction with thrombin.(ABSTRACT TRUNCATED AT 400 WORDS)

A 110-amino acid region within the A1-domain of coagulation factor VIII inhibits secretion from mammalian cells

Factor VIII is the coagulation factor deficient in the X-chromosome-linked bleeding disorder hemophilia A. Factor VIII is homologous to blood coagulation factor V, both having a domain structure of A1-A2-B-A3-C1-C2. Previous transfection studies demonstrated that factor VIII is 10-fold less efficiently expressed than the homologous coagulation factor, factor V. The inefficient expression correlated with interaction of the factor VIII primary translation product with the protein chaperonin BiP in the lumen of the endoplasmic reticulum. In contrast, factor V was not detected in association with BiP and was secreted efficiently. To determine whether specific amino acid sequences within factor VIII inhibit secretion, we have studied the secretion of factor VIII deletion and factor VIII/factor V chimeric proteins upon transient transfection of COS-1 monkey cells. A chimeric factor VIII protein that contained the A1- and A2-domains of factor V was secreted with a similar efficiency as wild-type factor V, whereas the complementary chimera having the A1- and A2-domains of factor VIII was secreted with low efficiency, similar to wild-type factor VIII. These results suggested that sequences within the A1- and A2-domains were responsible for the low secretion efficiency of factor VIII. Secretion of A1-domain-deleted factor VIII was increased approximately 10-fold compared to wild-type factor VIII or A2-domain-deleted factor VIII. Expression of the factor VIII A1-domain alone did not yield secreted protein, whereas expression of the factor VIII A2-domain alone or the factor V A1-domain or A2-domain alone directed synthesis of secreted protein. Secretion of a hybrid in which the carboxyl-terminal 110 amino acids of the A1-domain were replaced by homologous sequences from the factor V A1-domain was also increased 10-fold compared to wild-type factor VIII, however, the secreted protein was not functional and the heavy and light chains were not associated. These results localize a 110-amino acid region within the A1-domain that inhibits factor VIII secretion. This region is clustered with multiple short peptide sequences that have potential to bind BiP.

Role of the B domain for factor VIII and factor V expression and function

Factor V and factor VIII are homologous cofactors in the blood coagulation cascade that have the domain structure A1-A2-B-A3-C1-C2, of which the B domain has extensively diverged. In transfected COS-1 monkey cells, expression of factor VIII is approximately 10-fold less efficient than that of factor V, primarily because of inefficient protein secretion and, to a lesser extent, reduced mRNA expression. To study the functional significance and effect of the B domain on expression and activity, chimeric cDNAs were constructed in which the B domains of factor V and factor VIII were exchanged. Expression of a factor VIII chimera harboring the B-domain of factor V yielded a fully functional factor VIII molecule that was expressed twofold more efficiently than wild-type factor VIII because of increased mRNA expression. Thus, sequences within the factor VIII B domain were not responsible for the inefficient secretion of factor VIII compared with factor V. Expression of a factor V chimera harboring the B domain of factor VIII was slightly reduced compared with wild-type factor V, although the secreted molecule had significantly reduced procoagulant activity correlating with dissociated heavy and light chains and resistance to thrombin activation. Interestingly, the factor V chimera containing the factor VIII B domain was efficiently activated by Russell's viper venum (RVV). A factor V B domain deletion (residues 710-1545) molecule also exhibited significantly reduced procoagulant activity caused by resistance to thrombin cleavage and activation, although this molecule was activatable by RVV. These results show that, in contrast to factor VIII, thrombin activation of factor V requires sequences within the B domain. In addition, thrombin activation of factor V occurs through a different mechanism than activation by RVV.

Identification of individual tyrosine sulfation sites within factor VIII required for optimal activity and efficient thrombin cleavage

Factor VIII functions as an essential cofactor in the blood coagulation cascade for the factor IXa-mediated activation of factor X. Factor VIII contains 6 tyrosine residues at positions 346, 718, 719, 723, 1664, and 1680 that are modified by post-translational sulfation. This modification is required for full factor VIII procoagulant activity. We have employed site-directed mutagenesis to identify the individual sulfated tyrosines within factor VIII that influence activity. The molecules were expressed in COS-1 monkey cells by transient transfection, and the resultant proteins were characterized. Metabolic incorporation of [35S]sulfate demonstrated that all 6 tyrosine residues are sulfated in factor VIII. Sulfation at residues 346 and 1664 was required for full activity in a factor VIII clotting assay but did not affect factor VIII activity monitored by a factor Xa generation assay. The Tyr346-->Phe and Tyr1664-->Phe mutants displayed delayed thrombin activation that correlated with delayed cleavage at residues 372 and 1689, respectively. In contrast, these mutants were efficiently activated by factor Xa. A triple Tyr to Phe mutant at residues 718, 719, and 723 displayed both reduced factor VIII clotting activity and factor Xa generation activity. Finally, a Tyr1680-->Phe mutant factor VIII displayed a 5-fold reduced affinity for von Willebrand factor. The results demonstrate that 1) sulfation at tyrosine residues 346 and 1664 increases factor VIII activity by increasing the rate of thrombin activation and cleavage; 2) sulfation at tyrosine residues 718, 719, and 723 increases the intrinsic activity of factor VIIIa; and 3) sulfation at tyrosine residue 1680 increases the affinity for vWF. In addition, the results implicate that thrombin interacts with three distinct sites within factor VIII, two of which are required for proteolytic activation. The results demonstrate that the six sites of tyrosine sulfation modulate factor VIII activity through different mechanisms.

Post-translational requirements for functional factor V and factor VIII secretion in mammalian cells

Coagulation factors V and VIII are homologous glycosylated plasma proteins that provide essential functions for hemostasis. Factor V is secreted as a single chain polypeptide, whereas factor VIII is processed intracellularly to yield a metal-ion-associated heterodimer that is stabilized through interaction with von Willebrand factor. In transfected mammalian cells, factor V is more efficiently secreted than factor VIII. To provide insight into the different secretion efficiencies, we compared the post-translational processing requirements for factor V and factor VIII expressed in mammalian cells. In contrast to factor VIII, factor V was not detected in association with the immunoglobulin-binding protein (BiP), a chaperonin protein of the endoplasmic reticulum (ER). Depletion of intracellular ATP levels by treatment of cells with low concentrations of carbonyl cyanide 3-chlorophenylhydrazone (CCCP), protonophore that uncouples oxidative phosphorylation, inhibited secretion of factor VIII but had no effect on the secretion of factor V. Inhibition of N-linked oligosaccharide addition by treatment with tunicamycin prevented secretion of both factor V and factor VIII, whereas treatment with an inhibitor of complex oligosaccharide addition, deoxymannojirimycin, did not affect secretion, although the specific activities of both factor V and factor VIII were slightly increased. Thus, complex oligosaccharide addition was not required for secretion or functional activity of either factor V or factor VIII. Depletion of intralumenal calcium with the ionophore A23187 did not affect secretion of either factor V or factor VIII. In the presence of A23187, the secreted factor V was fully functional, whereas the factor VIII heavy and light chains were not associated and the secreted molecule was inactive. In addition, A23187 treatment inhibited addition of serine/threonine (O)-linked oligosaccharides to factor V and factor VIII. The differences between factor V and factor VIII were further evaluated by characterization of a single chain mutant factor VIII. The single chain factor VIII was secreted with an efficiency similar to wild-type factor VIII and also required von Willebrand factor for stabilization. In addition, the activity of single chain factor VIII was also inhibited by A23187 treatment, suggesting a unique metal-ion requirement within the secretory pathway for functional factor VIII folding. The differences identified in BiP association, ATP requirements, and metal-ion dependence for effective functional secretion of these two molecules may underlie mechanisms accounting for their different secretion efficiencies.

Posttranslational sulfation of factor V is required for efficient thrombin cleavage and activation and for full procoagulant activity

Factor VIII and factor V function as cofactors in the blood coagulation cascade to accelerate the rate of activation of factor X and prothrombin, respectively. Both cofactors require proteolytic activation by either activated factor X or thrombin for functional activity. Human factor VIII and factor V expressed in mammalian cells are both modified by posttranslational sulfation of tyrosine residues. In the present study, the posttranslational addition of sulfate in factor V expressed in transfected Chinese hamster ovary (CHO) cells was demonstrated by [35S]sulfate incorporation into the thrombin-cleaved 94-kDa heavy chain and the 150-kDa activation peptide. The presence of tyrosine sulfate in recombinant factor V was confirmed by barium hydroxide hydrolysis and two-dimensional thin-layer electrophoresis. The importance of sulfation for factor V secretion and activity was evaluated by characterizing factor V expressed in Chinese hamster ovary cells grown in the presence of sodium chlorate, a potent inhibitor of posttranslational sulfation in intact cells. Increasing concentrations of sodium chlorate inhibited the incorporation of [35S]sulfate into factor V but did not inhibit the synthesis or secretion of factor V. However, the specific activity of factor V secreted in the presence of sodium chlorate was reduced 5-fold. The reduced activity was attributed to (1) slower cleavage and activation by thrombin and (2) a reduced intrinsic activity of factor Va. In contrast, sulfation of factor V did not affect the rate of activation mediated by factor Xa. These results show that sulfation of factor V is required for efficient thrombin activation but not for activation by factor Xa.(ABSTRACT TRUNCATED AT 250 WORDS)

[Results of twenty year follow-up of patients with inoperable prostate cancer (stage C) treated by radiotherapy. Report of a national multicenter study]

This is a report on a National Cooperative study of Radiotherapy for inoperable patients with cancer of the prostate: 372 patients with adenocarcinoma of the prostate, stage C, received radiotherapy from 1967 to 1973, according to a very strict protocol. With minor variations, all patients received the same total dose: 7000 cGy in 47 days or 7500 cGy in 54 days. Mild episodes of hematuria and rectal bleeding were observed in a number of patients: urethral and rectal strictures also resulted in a few cases, but were no life-threatening complications. A total of 177 patients (47%) died from prostatic cancer, mostly bony metastases that may have been present when the patients were first seen; death from prostatic cancer decreased as the years went by. Only 4 patients (1%) were lost to follow-up, only one before ten years, and none had evidence of cancer when last seen. However, 167 (44%) of the 372 patients lived for various periods of times and died without ostensible evidence of prostatic cancer. In addition 24 were still living after 20 years. Thus, more than half of these elderly inoperable patients treated by radiotherapy lived to die of something else.

Characterization of wild-type and Ser53 mutant eukaryotic initiation factor 4E overexpression in mammalian cells

Eukaryotic translation initiation factor 4E (eIF-4E) is one component of the m7G-cap-binding protein complex eIF-4F and is required for cap-dependent translation initiation. The phosphorylation state of eIF-4E correlates with increased activity and a major phosphorylation site resides at serine 53. To further evaluate the role of eIF-4E phosphorylation, eIF-4E wild-type and two Ser53 mutants, Ser53Ala and Ser53Asp, were expressed at high level, representing almost 2% of the total cell protein, by transient transfection of COS-1 monkey cells. 32PO4 metabolic labeling of transfected cells demonstrated both Ser53 mutants were phosphorylated at an alternate serine residue. [35S]Methionine pulse-labeling demonstrated that the wild-type and both Ser53 mutants were equally incorporated into the eIF-4F complex. The effect of wild-type and Ser53 mutant overexpression on cap-dependent translation initiation and internal translation initiation was monitored by cotransfection with an expression vector encoding a dicistronic mRNA for which the 5' cistron is translated in a cap-dependent manner, and the 3' cistron is translated by internal ribosome binding. Unexpectedly, overexpression of the wild-type or either mutant did not affect the efficiency of either cap-dependent or internal initiation. These results demonstrate that phosphorylation of eIF-4E at residue 53 is not required for interaction with p220 and suggest that Ser53 phosphorylation may not be required for cap-dependent translation initiation in this system.

Biochemical, immunological, and in vivo functional characterization of B-domain-deleted factor VIII

Coagulation factor VIII (FVIII) is a cofactor in the intrinsic pathway of blood coagulation for which deficiency results in the bleeding disorder hemophilia A. FVIII contains a domain structure of A1-A2-B-A3-C1-C2 of which the B domain is dispensable for procoagulant activity in vitro. In this report, we compare the properties of B-domain-deleted FVIII (residues 760 through 1639, designated LA-VIII) to wildtype recombinant FVIII. In transfected Chinese hamster ovary (CHO) cells, LA-VIII was expressed at a 10- to 20-fold greater level compared with wildtype FVIII. The specific activity of purified LA-VIII was indistinguishable from wild-type recombinant FVIII and both exhibited similar thrombin activation coefficients. Wildtype recombinant-derived FVIII and LA-VIII also displayed similar timecourses of thrombin activation and heavy chain cleavage. However, compared with wildtype recombinant-derived FVIII, the light chain of LA-VIII was cleaved fivefold more rapidly by thrombin. Addition of purified von Willebrand factor (vWF) did not alter the kinetics of thrombin cleavage or activation of either wildtype recombinant-derived FVIII or LA-VIII. The immunogenicity of LA-VIII was compared with wildtype FVIII in a novel model of neonatal tolerance induction in mice. The results did not detect any immunologic differences between wildtype FVIII and LA-VIII, suggesting that LA-VIII does not contain significant new epitopes that are absent in wildtype FVIII. LA-VIII was tolerated well on infusion into FVIII-deficient dogs and was able to correct the cuticle bleeding time similar to wildtype recombinant factor VIII. In vivo, LA-VIII was bound to canine vWF and exhibited a half-life similar to wildtype recombinant FVIII. These studies support that B-domain-deleted FVIII may be efficacious in treatment of hemophilia A in humans.

Twenty years follow-up of patients with inoperable cancer of the prostate (stage C) treated by radiotherapy: report of a national cooperative study

PURPOSE

To evaluate the longevity and curability of patients with inoperable, Stage C, carcinomas of the prostate by means of external pelvic irradiation.

METHODS AND MATERIALS

372 patients, averaging 61 years of age, with histologically proven adenocarcinoma of the prostate, Stage C, received radiotherapy as part of a National Research Study, from 1967 to 1973. Treatments were administered in accordance with a strict protocol. Portals of entry were optional but it was required that the total dose received at the center of the prostate should be no less than 7000 cGy in no less than 47 days or 7500 cGy in 54 days.

RESULTS

245 of the 372 patients survived 5 years without evidence of recurrence of metastases; 142 were living after 10 years, 64 after 15 years, and 24 after 20 years. A total of 167 patients (44%) survived for years and died from intercurrent diseases without evidence of prostatic cancer. A total of 177 patients (47%) died of prostatic cancer in decreasing proportions in the years after treatment. Mild episodes of hematuria and of rectal bleeding were recorded in a number of patients; urethral and rectal strictured occurred following cystitis and proctitis but no life-threatening complications occurred.

CONCLUSIONS

Adequately fractionated external pelvic irradiation can eradicate inoperable intrapelvic prostatic cancer. A simple statement of survival would disregard the fact that these elderly patients may be cured of cancer and yet may die of intercurrent diseases proper of their age. Also, it may be expected that a number of patients with Stage C may have unsuspected subclinical bone metastases when first seen and that death from metastases is not necessarily a reflection on the effectiveness of the regional treatment.

Identification and functional importance of tyrosine sulfate residues within recombinant factor VIII

Sulfated tyrosine residues within recombinant human factor VIII were identified by [35S]sulfate biosynthetic labeling of Chinese hamster ovary cells which express human recombinant factor VIII. Alkaline hydrolysis of purified [35S]sulfate-labeled factor VIII showed that greater than 95% of the [35S]sulfate was incorporated into tyrosine. [3H]Tyrosine and [35S]sulfate double labeling was used to quantify the presence of 6 mol of tyrosine sulfate per mole of factor VIII. Amino acid sequence analysis of thrombin and tryptic peptides isolated from [35S]sulfate-labeled factor VIII demonstrated tyrosine sulfate at residue 346 in the factor VIII heavy chain and at residues 1664 and 1680 in the factor VIII light chain. In addition, the carboxyl-terminal half of the A2 domain contained three tyrosine sulfate residues, likely at positions 718, 719, and 723. Interestingly, all sites of tyrosine sulfation border thrombin cleavage sites. The functional importance of tyrosine sulfation was examined by treatment of cells expressing factor VIII with sodium chlorate, a potent inhibitor of tyrosine sulfation. Increasing concentrations of sodium chlorate inhibited sulfate incorporation into factor VIII without affecting its synthesis and/or secretion. However, factor VIII secreted in the presence of sodium chlorate exhibited a 5-fold reduction in procoagulant activity, although the protein was susceptible to thrombin cleavage. These results suggest that tyrosine sulfation is required for full factor VIII activity and may affect the interaction of factor VIII with other components of the coagulation cascade.

A2 domain of human recombinant-derived factor VIII is required for procoagulant activity but not for thrombin cleavage

Thrombin treatment of the coagulation factor VIII results in a rapid activation of procoagulant activity with a subsequent first order decay. The structural requirements for thrombin-activated factor VIII were characterized using recombinant-derived human factor VIII and site-directed DNA-mediated mutagenesis. Thrombin-activated human recombinant-derived factor VIII was isolated in an active form by passage over Mono-S fast protein liquid chromatography. The peak fractions had a specific activity of 60,000 U/mg. The subunit composition in the peak fraction contained the 50-Kd A1 domain from the heavy chain, the 73-Kd light chain fragment, and trace amounts of the 43-Kd A2 domain. The requirement of domain A2 for functional activity was shown in several ways. First, the addition of an inhibitory monoclonal antibody that recognizes domain A2 destroyed factor VIIIa activity. Second, addition of a Mono-S FPLC fraction that contained the A2 domain polypeptide back to the peak activity fraction increased activity of the factor VIIIa by 22-fold. The maximum specific activity achieved was 180,000 U/mg. Finally, expression of an A2 domain deletion mutant did not yield procoagulant activity, although the mutant was effectively secreted from the cell, exhibited appropriate heavy and light chain association, and was susceptible to thrombin cleavage. Cotransfection of this A2 domain deletion mutant with an A2 domain expression vector yielded a secreted complex and restored procoagulant activity in the conditioned medium. This result shows that the A2 domain can fold and assemble with A2-deleted factor VIII to yield a functional molecule. We conclude that the A2 domain is required for functional factor VIIIa activity and loss of activity in activated factor VIII may result from dissociation of A2 from the thrombin-activated heterotrimer.

The role of von Willebrand factor multimers and propeptide cleavage in binding and stabilization of factor VIII

von Willebrand factor (vWF) is a multimeric glycoprotein that promotes platelet aggregation and stabilizes coagulation factor VIII in the plasma. vWF is also required for the stable accumulation of recombinant factor VIII secreted from cells in a heterologous expression system. In this report, we show that vWF can promote the in vitro reconstitution of factor VIII activity from dissociated heavy and light chains of factor VIII, suggesting that vWF may act to promote stable assembly of factor VIII subunits at the site of secretion. The structural requirements for vWF propeptide cleavage and for vWF multimerization in its binding and stabilization of factor VIII was examined using specifically altered recombinant vWF. The mutant vWF molecules were also assayed for their function in ristocetin-induced platelet agglutination mediated through the platelet receptor GPIb. Deletion of the vWF propeptide produced a dimeric vWF molecule that failed to mediate platelet agglutination, suggesting that multimerization is required for vWF to attain functional GPIb binding. This mature dimeric form of vWF, however, was fully capable of binding to and supporting stable secretion of factor VIII. A vWF mutant with an altered propeptide cleavage site formed large multimers of uncleaved pro-vWF that functioned in platelet agglutination. However, this noncleavage mutant neither bound to or supported stable accumulation of factor VIII. Analysis of the vWF propeptide, expressed independently, demonstrated that it could not bind factor VIII or stabilize its secretion. These results show that the dimeric mature vWF subunit is sufficient to bind and stabilize factor VIII and that the presence of uncleaved vWF propeptide inhibits both factor VIII binding and stabilization.

The effect of plasma von Willebrand factor on the binding of human factor VIII to thrombin-activated human platelets

The binding of 35S-labeled recombinant human Factor VIII to activated human platelets was studied in the presence and absence of exogenous plasma von Willebrand factor. In the absence of added von Willebrand Factor, platelets bound 210 molecules of Factor VIII/platelet when the unbound Factor VIII concentration was 2.0 nM (Kd = 2.9 nM). As the von Willebrand factor concentration was increased, the number of Factor VIII molecules bound/platelet decreased to 10 molecules of Factor VIII bound/platelet at 24 micrograms/ml of added vWF. Addition of an anti-vWF monoclonal antibody that inhibits the vWF-Factor VIII interaction attenuated the ability of vWF to inhibit binding of Factor VIII to platelets. In contrast, addition of a control anti-vWF antibody that does not block the vWF-Factor VIII interaction did not affect the ability of vWF to inhibit Factor VIII binding to platelets. From the vWF concentration dependence of inhibition of Factor VIII-platelet binding, a dissociation constant for the Factor VIII-vWF interaction was calculated (Kd = 0.44 nM). To further elucidate the role that vWF may play in preventing the interaction of Factor VIII with platelets, the platelet binding properties of a Factor VIII deletion mutant (90-73) which lacks the primary vWF-binding site was studied. The binding of this mutant was unaffected by added exogenous vWF. These observations demonstrate that Factor VIII can interact with platelets in a manner independent of vWF but that excess vWF in plasma can effectively compete with platelets for the binding of Factor VIII. In addition, since cleavage of Factor VIII by thrombin separates a vWF-binding domain from Factor VIIIa, we propose that activation of Factor VIII by thrombin may elicit release of activated Factor VIII from vWF and thereby make it fully available for platelet binding.

Cloning and expression in COS-1 cells of a full-length cDNA encoding human coagulation factor X

A 1.5-kb cDNA (FX) encoding full-length human coagulation factor X was isolated from a human fetal liver cDNA library. The identity of the insert in a selected phage lambda clone was confirmed to be FX by nucleotide (nt) sequence analysis and restriction mapping. This FX cDNA clone contained 1467 bp of coding sequence, no 5'-untranslated sequence, a short 3'-untranslated sequence of 10 nt and a poly(A) tail at the 3'-end. The FX cDNA was inserted into a mammalian expression vector and transfected into COS-1 monkey kidney cells. Media from transfected cells showed evidence of factor X antigen and, following addition of Russel's viper venom factor X activator, enhanced amidolytic activity toward a synthetic peptide rho-nitroanilide substrate. Immunoprecipitation with an anti-factor X monoclonal antibody of [35S]methionine-labeled cell-conditioned media showed evidence of polypeptides of 74, 55, and 17 kDa, as determined by SDS-PAGE followed by autoradiography. Together, these results indicate that an active factor X can be successfully expressed in a recombinant DNA expression system. This approach will allow the systematic structure/function investigation of this important blood-clotting enzyme.

Radiation oncology: postgraduate medical education in the United States, 1988

The fourteenth survey of postgraduate medical education in radiation oncology in the United States was conducted in the first three months of 1988. It revealed stability in the number of approved programs, positions offered, and physicians in training compared with 1986. The proportion of trainees who were U.S. citizens by birth rose to an all-time high of 88%, and the proportion of foreign medical graduates decreased to 9%. The proportion of women in residency has remained unchanged (24%) over the past 6 years. At present, approximately 150 physicians complete residency and enter practice each year, one-third of whom commence in an academic setting. A high proportion of recent graduates of approved programs successfully completes the examinations and becomes certified by the American Board of Radiology.

The binding of 35S-labeled recombinant factor VIII to activated and unactivated human platelets

Recombinant-derived human Factor VIII was labeled intrinsically with [35S]methionine, and its binding to washed human platelets was studied. Binding measurements were performed by incubating Factor VIII and platelets for 15 min at room temperature in Tyrode's solution supplemented with Ca2+ (5.0 mM), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (5.0 mM), 0.50% bovine serum albumin, and the Factor Xa and thrombin inhibitors 5-dimethylaminonaphthalene-1-sulfonylglutamylglycinylarginyl chloromethyl ketone and 5-dimethylaminonaphthalene-1-sulfonyl-arginine-N-(3-ethyl-1, 5-pentanediyl)amide. Separation of free from bound Factor VIII was accomplished by centrifugation through oil, and nonspecific binding was determined with excess unlabeled Factor VIII. Binding was saturable, reversible, and stimulated 20-fold after platelet activation with thrombin. Furthermore, binding was specific in that bound labeled Factor VIII could be displaced by excess unlabeled Factor VIII, but not by Factor V. Scatchard analysis indicated a single class of binding sites with Kd = 2.9 nM and 450 sites/activated platelet. The time course of displacement indicated a t1/2 of bound Factor VIII of approximately 5 min. When platelets were incubated in Ca2+, both the heavy and light chains of Factor VIII were bound, whereas exposure to EDTA resulted in the binding of the light chain only. These results demonstrate the specific reversible binding of Factor VIII to human platelets, likely mediated through the light chain.

Proteolytic requirements for thrombin activation of anti-hemophilic factor (factor VIII)

Factor VIII functions in the intrinsic pathway of coagulation as the cofactor for factor IXa proteolytic activation of factor X. Proteolytic cleavage is required for activation and may be responsible for inactivation of cofactor activity. To identify which of the multiple cleavages are required for activation and inactivation of factor VIII, site-directed DNA-mediated mutagenesis of the factor VIII cDNA was performed and the altered forms of factor VIII were expressed in COS-1 monkey cells and characterized. Conversion of arginine residues to isoleucine residues at the aminoterminal side of the cleavage sites at positions 740, 1648, and 1721 resulted in cleavage resistance at the modified site with no alteration in the in vitro procoagulant activity and the susceptibility to thrombin activation. Similar modification of the thrombin cleavage sites at either position 372 or position 1689 resulted in molecules with residual factor VIII activity but resistant to thrombin cleavage at the modified site and not susceptible to thrombin activation. Modification of the arginine to either an isoleucine or a lysine at residue 336, the site postulated for proteolytic inactivation by activated protein C, resulted in a factor VIII molecule with increased procoagulant activity. This increased activity may result from greater resistance to proteolytic inactivation. A model for the activation and inactivation of factor VIII is proposed.

The propeptide of von Willebrand factor independently mediates the assembly of von Willebrand multimers

The biosynthesis of von Willebrand Factor (vWF) by vascular endothelial cells involves a complex series of processing steps that includes proteolytic cleavage of a 741-residue propeptide and the assembly of disulfide-linked multimers. Using a model system in which experimentally altered vWF cDNAs are expressed in COS-1 cells, we have shown that the vWF propeptide contains determinants that govern the assembly of vWF multimers. Furthermore, the role of the propeptide (in the assembly process) does not require it to be a contiguous part of the pro-vWF primary structure, since independently expressed propeptide was shown to promote the assembly of mature vWF subunits into multimers. Pulse-chase experiments indicated that the independently expressed propeptide formed a transient association with the mature vWF subunit inside the cell. Thus, it appears that the vWF propeptide segment can act in "trans" to direct the assembly of disulfide-linked vWF multimers.

Postgraduate training in radiation oncology in the United States, 1986

The thirteenth survey of training in Radiation Oncology in the United States, conducted in the first half of 1986, revealed a reduction in the number of approved programs, but little change in the number of positions offered. For the first time, every program had trainees, and every available training position was filled. The proportion of foreign exchange students in training fell from 52% 20 years ago, to 12% a decade later, to less than 1% at present. The proportion of foreign medical graduates fell from 29% in 1984 to 18% at present. The proportion of women in residency remained unchanged from 1982 and 1984. Approximately 150 physicians can be expected to complete training and enter the practice of radiation oncology each year for at least the next 4 years.

Complete cDNA and derived amino acid sequence of human factor V

cDNA clones encoding human factor V have been isolated from an oligo(dT)-primed human fetal liver cDNA library prepared with vector Charon 21A. The cDNA sequence of factor V from three overlapping clones includes a 6672-base-pair (bp) coding region, a 90-bp 5' untranslated region, and a 163-bp 3' untranslated region within which is a poly(A) tail. The deduced amino acid sequence consists of 2224 amino acids inclusive of a 28-amino acid leader peptide. Direct comparison with human factor VIII reveals considerable homology between proteins in amino acid sequence and domain structure: a triplicated A domain and duplicated C domain show approximately equal to 40% identity with the corresponding domains in factor VIII. As in factor VIII, the A domains of factor V share approximately 40% amino acid-sequence homology with the three highly conserved domains in ceruloplasmin. The B domain of factor V contains 35 tandem and approximately 9 additional semiconserved repeats of nine amino acids of the form Asp-Leu-Ser-Gln-Thr-Thr/Asn-Leu-Ser-Pro and 2 additional semiconserved repeats of 17 amino acids. Factor V contains 37 potential N-linked glycosylation sites, 25 of which are in the B domain, and a total of 19 cysteine residues.

A large region (approximately equal to 95 kDa) of human factor VIII is dispensable for in vitro procoagulant activity

Factor VIII (antihemophilic factor) is a high molecular weight plasma glycoprotein that participates in the blood clotting cascade. The recent cloning and sequence analysis of the cDNA encoding human factor VIII revealed an obvious domain structure for the protein, which can be represented as A1-A2-B-A3-C1-C2. We now report the DNA sequence analysis of porcine exons encoding the entire B domain and part of the A2 and A3 domains. We found an unusually high degree of porcine-human amino acid sequence divergence in the B region compared with the limited sequence available for other regions of the porcine factor VIII molecule. In addition to sequence divergence, there are numerous gaps in the porcine B domain totalling over 200 amino acids. Recombinant DNA techniques were used to effect the removal of large segments of DNA encoding the B domain from the full-length human factor VIII cDNA. These constructs directed the synthesis of biologically active factor VIII when introduced into mammalian cells despite the deletion of up to 38% of the factor VIII molecule.

Training in therapeutic radiology in the United States, 1984

The 1984 survey of training programs in Therapeutic Radiology in the United States revealed little change in the number of training programs and the number of residency positions offered. However, there has been a striking increase in the number of residents in training since the survey of 1982. The numbers of residents training in the PG-II and PG-III years are more than 50% greater than any previous survey. The proportion of foreign medical graduates is smaller than reported in 1982, but the proportion of women in residency is unchanged.

Molecular cloning of a cDNA encoding human antihaemophilic factor

A complete copy of the mRNA sequences encoding human coagulation factor VIII:C has been cloned and expressed. The DNA sequence predicts a single chain precursor of 2,351 amino acids with a relative molecular mass (Mr) 267,039. The protein has an obvious domain structure, contains sequence repeats and is structurally related to factor V and ceruloplasmin.