In vivo anti-tumor efficacy of afucosylated anti-CS1 monoclonal antibody produced in glycoengineered Pichia pastoris

Monoclonal antibody (mAb) therapy has been successfully used for the treatment of B-cell lymphomas and is currently extended for the treatment of multiple myeloma (MM). New developments in MM therapeutics have achieved significant survival gains in patients but the disease still remains incurable. Elotuzumab (HuLuc63), an anti-CS1 monoclonal IgG1 antibody, is believed to induce anti-tumor activity and MM cytotoxicity through antibody dependent cellular cytotoxicity (ADCC) and inhibition of MM cell adhesion to bone marrow stromal cells (BMSCs). Modulations of the Fc glycan composition at the N297 site by selective mutations or afucosylation have been explored as strategies to develop bio-better therapeutics with enhanced ADCC activity. Afucosylated therapeutic antibodies with enhanced ADCC activity have been reported to possess greater efficacy in tumor growth inhibition at lower doses when compared to fucosylated therapeutic antibodies. The N-linked glycosylation pathway in Pichia pastoris has been engineered to produce human-like N-linked glycosylation with uniform afucosylated complex type glycans. The purpose of this study was to compare afucosylated anti-CS1 mAb expressed in glycoengineered Pichia pastoris with fucosylated anti-CS1 mAb expressed in mammalian HEK293 cells through in vitro ADCC and in vivo tumor inhibition models. Our results indicate that Fc glycosylation is critical for in vivo efficacy and afucosylated anti-CS1 mAb expressed in glycoengineered Pichia pastoris shows a better in vivo efficacy in tumor regression when compared to fucosylated anti-CS1 mAb expressed in HEK293 cells. Glycoengineered Pichia pastoris could provide an alternative platform for generating homogeneous afucosylated recombinant antibodies where Fc mediated immune effector function is important for efficacy.

Optimization of erythropoietin production with controlled glycosylation-PEGylated erythropoietin produced in glycoengineered Pichia pastoris

Pichia pastoris is a methylotropic yeast that has gained great importance as an organism for protein expression in recent years. Here, we report the expression of recombinant human erythropoietin (rhEPO) in glycoengineered P. pastoris. We show that glycosylation fidelity is maintained in fermentation volumes spanning six orders of magnitude and that the protein can be purified to high homogeneity. In order to increase the half-life of rhEPO, the purified protein was coupled to polyethylene glycol (PEG) and then compared to the currently marketed erythropoiesis stimulating agent, Aranesp(®) (darbepoetin). In in vitro cell proliferation assays the PEGylated protein was slightly, and the non-PEGylated protein was significantly more active than comparator. Pharmacodynamics as well as pharmacokinetic activity of PEGylated rhEPO in animals was comparable to that of Aranesp(®). Taken together, our results show that glycoengineered P. pastoris is a suitable production host for rhEPO, yielding an active biologic that is comparable to those produced in current mammalian host systems.

Selection of Pichia pastoris strains expressing recombinant immunoglobulin G by cell surface labeling

A simple cell labeling method for sorting yeast Pichia pastoris antibody expressing strains is described. A small portion of secreted recombinant antibody retained on the cell surface was labeled with fluorescence detection antibody. The signal intensity of the labeled cell was correlated with the cell's antibody productivity. Using this labeling technique to sort a mixture model induced in the same fermenter where the cells of high producing strain were spiked into a population of a low producing strain at the frequency of 1:100,000, one round of sorting achieved a approximately 5000-fold enrichment of the high producing strain. A variety of P.pastoris strains expressing antibody sorted based on the signal intensity on the cell surface yielded titer improvements by 30% to 300%. Our data demonstrate that Pichia cell surface labeling is a simple, effective and reliable method for sorting Pichia antibody expressing strains for productivity improvement.

A comparison of bone strain measurements at anatomically relevant sites using surface gauges versus strain gauged bone staples

Instrumented bone staples were first introduced as an alternative to surface-mounted strain gauges for use in human in vivo bone strain measurements because their fixation to bone is secure and requires not only minimally invasive surgery. Bench-top bone bending models have shown that the output from strain gauged bone staples compares favorably to that of traditional mounted gauges. However their within- and across-subject performance at sites typically instrumented in vivo has never been examined. This study used seven human cadaver lower extremities with an age range of 23-81 years old and a dynamic gait simulator to examine and compare axial strains in the mid tibial diaphysis and on the dorsal surface of the second metatarsal as measured simultaneously with strain gauged bone staples and with traditional surface-mounted gauges. Rosette configurations were used at the tibial site for deriving principal compression and tension, and shear strains. Axial outputs from the two gauge types demonstrated strong linear relationships for the tibia (r(2)=0.78-0.94) and the second metatarsal (r(2)=0.96-0.99), but coefficients (slopes) for the relationship were variable (range 7-20), across subjects and across sites. The apparent low reliability of strain gauged staples may be explained by the fact that both strain gauged staples and surface strain gauges are inexact to some degree, do not measure strains from exactly the same areas and strain gauged staples reflect surface strains as well as deformations within the cortex. There were no relationships for the principal tibia compression, tension or shear strain measurements derived from the two rosette gauge types, reflecting the very different anatomical areas measured by each of the constructs in this study. Strain gauged bone staples may be most useful in comparing relative axial intra-subject differences between activities, but inter-subject variability may require larger sample sizes to detect differences between populations.

Acute Effects of Moderate Intensity Resistance Exercise on Bone Cell Activity

Resistance exercise has positive effects on bone mass, but little is known about the mechanisms by which this occurs. The purpose of this study was to determine if a single bout of moderate intensity resistance exercise alters biochemical markers of bone cell activity. Indices of bone turnover were measured in nine healthy, untrained men (21.9 +/- 1.2 yrs old), before and following a single 45 minute session of resistance exercise, and during a control trial. A cross-over design was used so that all participants performed both trials in random order. Blood samples were collected immediately before, immediately after, and at 1, 8, 24, and 48 hours post exercise and analyzed for bone-specific alkaline phosphatase (BAP), type I collagen propeptide (PICP), and type I collagen N-telopeptide (sNTX). Urine from the second morning void was collected over four days (day before, day of, and two days following exercise) and analyzed for type I collagen N-telopeptide (uNTX). Exercise resulted in a significant increase (p < 0.05) in the ratio of biochemical markers of bone formation to bone resorption eight hours post exercise, largely due to a decrease in sNTX. Markers return to baseline within 24 hrs. These data suggest that moderate intensity resistance training acutely reduces bone resorption, leading to a favorable change in overall bone turnover, for at least 8 hours post exercise in untrained young men. Further work is needed to determine if long-term benefits to bone strength follow with persistent training.

Metatarsal strains are sufficient to cause fatigue fracture during cyclic overloading

Human in vivo tibial strains during vigorous walking have not been found to exceed 1200 microstrains. These values are below those found in ex vivo studies (>3000 microstrains) to cause cortical bone fatigue failure, suggesting that an intermediate bone remodeling response may be associated with tibial stress fractures. Metatarsal stress fractures, however, often develop before there is time for such a response to occur. Simultaneous in vivo axial strains were measured at the mid diaphysis of the second metatarsal and the tibia in two subjects. Peak axial metatarsal compression strains and strain rates were significantly higher than those of the tibia during treadmill walking and jogging both barefoot and with running shoes and during simple calisthenics. During barefoot treadmill walking metatarsal compression strains were greater than 2500 microstrains. During one- and two-leg vertical jumps and broad jumping, both metatarsal compression and tension strains were >3000 microstrains. Compression and tension strains in the metatarsus unlike those of the tibia may be sufficiently high even during moderate exertional activities to cause fatigue failure of bone secondary to the number of loading cycles without an intermediate bone remodeling response.

Structural, material, and anatomic characteristics of the collateral ligaments of the canine cubital joint

OBJECTIVE

To document gross and microscopic anatomic features of the collateral ligaments of the canine cubital joint and to determine their structural and material properties.

ANIMALS

37 canine cadavers.

PROCEDURE

After measurement of ligament dimensions, the bone-collateral ligament-bone specimens were loaded in tension until failure, using a materials testing machine. Data from the load-displacement curves were used to determine the structural and material properties of the ligaments. Gross anatomic features were studied during dissection of the specimens from the medial collateral ligament (MCL) and lateral collateral ligament (LCL), which then were saved for microscopic examination.

RESULTS

Failure load and stiffness values for the LCL were significantly (P < 0.05) greater than those for the MCL. The LCL had obvious cranial and caudal components that attached to the radius and ulna, respectively. The MCL also had cranial and caudal components; however, the cranial component was indistinct, appearing only as a slight thickening of the joint capsule. The caudal component was more prominent; as it extended distad, it had minor attachments to the interosseous and annular ligaments and attached principally on the caudolateral surface of the proximal portion of the radius. The caudal component did not have substantial attachment to the ulna in any of the specimens studied. Both ligaments were composed of closely packed, parallel fascicles of dense collagen, with scant amounts of fibrocartilage and no detectable elastin.

CONCLUSIONS

Gross anatomic features of the collateral ligaments of the canine cubital joint indicate that they provide principal structural support to the joint; microscopic anatomic features are typical of other ligaments. The LCL is stronger and stiffer than the MCL; however, their material properties are similar.

CLINICAL RELEVANCE

Knowledge of the sites of attachment of collateral ligament components is essential for surgeons undertaking repair or reconstruction of these structures.

The effects of irradiation dose on the stiffness of cartilage grafts

Various centers report irradiated cartilage graft absorption rates that differ quite widely. We postulated that a major factor governing this phenomenon might be irradiation dose. Irradiation produces collagen cross-binding and increased resistance to absorption of such material when implanted. Since cross-binding produces stiffening of collagen, cartilage grafts were exposed to increasing doses of irradiation and their elastic modulus was measured. The postulate was that increasing radiation doses will produce grafts of increasing stiffness. Sternal cartilage, harvested from horses, was cut into blocks of a standard size and irradiated to 4, 6, 8, and 10 megarads. The elastic modulus of each specimen and matched control were measured on an Instron flexural testing machine (Instron Corp, Canton, MA). Irradiation at all four doses reduced the elastic modulus of the cartilage grafts, with the lowest dose producing a reduction of 50% and the highest dose one of 90%. High-dose irradiation appears to lessen greatly the stiffness of cartilage grafts and may be responsible for increasing absorption of grafts in centers in which high doses are used.

Effect of maturation and aging on material and ultrasonographic properties of equine superficial digital flexor tendon

Results of studies in human beings and other species have indicated that aging significantly influences the strength, modulus of elasticity, and energy storage ability of tendon. We wanted to determine the effects of aging on the material and ultrasonographic properties of equine superficial digital flexor (SDF) tendon. Ultrasonographic measurements of left forelimb SDF tendon cross-sectional area and mean echogenicity were made in 23 standing horses ranging in age from 2 to 23 years. All horses had not been in work for a minimum of 6 months prior to the study. After euthanasia, left forelimb bone-muscle-tendon-bone specimens were mounted in a materials testing system. The SDF tendon was cyclically loaded sinusoidally 100 times at 0.5 Hz from 1.5 to 5.0% strain, then was submitted to 10-minute creep-and-stress relaxation tests. Modulus of elasticity, load at 3% strain, and creep-and-stress relaxation were determined for each specimen. A significant positive correlation was found between elastic modulus and age. Correlation was not found between age and SDF tendon cross-sectional area or mean echogenicity. When 2-year-old horses were compared with older horses, the latter had tendons with a significantly (P = 0.007) greater modulus of elasticity. The authors conclude that increasing age through maturity is associated with a corresponding increase in equine SDF tendon elastic modulus.

Ultrasonography as a method to determine tendon cross-sectional area

Ultrasonographic cross sectional area (CSA) measurements of equine superficial digital flexor (SDF) tendon were obtained to determine the feasibility of ultrasonography for CSA measurement of tendon in vivo and in vitro. Ultrasonographic measurements were compared with a more traditional CSA measurement method, ink-blot analysis. In addition, values for ultrasonographic SDF tendon mean echogenicity were obtained in vivo and in vitro. The left forelimb SDF tendons of 23 horses were evaluated ultrasonographically. Cross sectional images were acquired at 4-cm intervals distal to the base of the accessory carpal bone (DACB) to the level of the proximal sesamoid bones while horses were standing squarely. After euthanasia, the left forelimbs were mounted in a materials testing system (MTS) and loaded under tension to standing load. Ultrasonographic images were again acquired at the same locations. The ultrasonographic images were digitized, and values for ultrasonographic CSA and mean echogenicity were obtained for each level. immediately after mechanical testing, a 1-cm-thick transverse section of SDF tendon at 12 cm DACB was removed. Three ink blots were prepared from each end of the removed tendon section and digitized. The 6 CSA values were averaged to generate a value for morphologic CSA for each SDF tendon at 12 cm DACB. Standing ultrasonographic tendon CSA at 12 cm DACB was consistently smallest (mean +/- SD CSA 86 +/- 11 mm2), followed by MTS ultrasonographic CSA (mean, 95 +/- 12 mm), with ink-blot morphologic CSA being largest (mean, 99 +/- 15 mm2). Comparison of standing and MTS ultrasonographic CSA values at 12 cm DACB revealed a strong positive linear correlation between methods (R2 = 0.74, P = 0.001). Comparison of ink blot CSA at 12 cm DACB with standing and MTS ultrasonographic CSA revealed strong positive linear correlations (R2 = 0.64, P = 0.001 and R2 = 0.72, P = 0.001, respectively). For ultrasonographic mean echogenicity, standing values insignificantly exceeded MTS values at each level. The authors conclude that ultrasonography is a useful technique for the noninvasive assessment of SDF tendon CSA that can be applied in vivo and in vitro.

Anterior cruciate ligament allograft transplantation in dogs

The biomechanical and clinical performance of bone-ligament-bone anterior cruciate ligament (ACL) allografts was studied in eight dogs. Allografts were collected from skeletally mature, healthy dogs using aseptic technique, and stored at -70 degrees for three to five weeks before implantation. The allografts were size-matched to the recipient dogs using ACL length and then rigidly fixed in position with interference screws and Kirschner wires. Three dogs regained a normal gait, and their grafts sustained breaking loads that were 25%, 41%, and 59% of controls. Partial or complete graft failure occurred in the other five dogs at some point in the study. Four had intraligamentous rupture and one had an avulsion fracture of the femoral attachment site. Joint-fluid cytology was normal in all eight dogs. Histologic examination showed persistent lymphoplasmacytic infiltrate. Eventually the allograft cores were incorporated in the host bed. Hyperplasia and fibrosis of the synovial membrane were diffuse and persisted as focal accumulations of mononuclear inflammatory cells.

Interlocking femoral components for revision arthroplasty with allografts

The use of interlocking screws has been advocated to fix major proximal femoral allografts to femoral prostheses. This study examines the effect of interlocking screws on strength of the component. Model femoral components were tested in axial compression. Drilling one hole diagonally (lateral to medial), drilling one hole anterior to posterior, or drilling one diagonal hole plus one anterior-to-posterior hole did not significantly decrease failure load compared to controls with no holes. However, two diagonal holes or horizontal, medial-to-lateral holes were weaker. Four cases have been done with proximal femoral allografts fixed to porous-coated femoral components with proximal and distal interlocking screws. Initial results in these cases are good.

Replacement of the anterior cruciate ligament. A comparison of autografts and allografts in dogs

To compare the efficacy of allograft versus autograft replacement of the anterior cruciate ligament, 15 dogs had the ligament cut and replaced 1 month later: 11 dogs received a frozen bone-ligament-bone allograft cruciate ligament, while 4 dogs received a standard autogenous replacement with iliotibial band. Three of 11 allograft dogs developed postoperative infections and were removed from the study; and two of the remaining eight allograft ligaments were absent at autopsy. All the autograft ligaments were present. From serial clinical and radiographic examinations, there were no differences observed in the two groups. Autopsy studies at 4 months, however, showed an increased inflammatory, pannus-like reaction about the origins and insertions of the six allograft ligaments as compared with the four autografts. The ligament hydroxyproline uptake was lower in the allograft group, averaging 60 percent of the contralateral unoperated on control versus equal to the control in the autograft group. The tensile strength of the allografts reached only 17 percent of the control value versus 41 percent for the autografts. Lymphocytotoxicity testing at 1 month revealed a donor-specific antibody response in 4 of 8 allograft dogs; however, no histologic evidence of immune response was observed in the ligaments. The synovial fluid leukocyte count was elevated in the allograft group at 4 months. The increased synovial leukocyte counts and joint cartilage erosion, the decreased strength and metabolic activity of the grafts, and the evidence of an immune response in the allograft dogs do not support implantation of cadaver cruciate ligaments clinically at this time.

Replacement of the anterior cruciate ligament with a bone-ligament-bone anterior cruciate ligament allograft in dogs

Acute replacement of the canine anterior cruciate ligament (ACL) with a frozen, bone-ligament-bone anterior cruciate ligament preparation was studied using biochemical, immunologic, and biomechanical testing methods. Nine dogs were used for the study, six dogs received allografts and three received autografts. No tissue antigen matching was performed. All nine dogs were killed nine months after surgery. Necropsy examination revealed that the ACL was not present in three joints (one autograft, two allografts). The two autograft and four allograft ligaments available for mechanical testing sustained mean maximum loads that were 10% and 14%, respectively, of the mean maximum loads sustained by the contralateral ACL. Autoradiography indicated that cellular activity was more pronounced in the autograft specimens. Hydroxyproline uptake was 200% and 45% of normal in the autograft and allograft ligaments, respectively. Both autograft and allograft specimens were producing Type I collagen at the time of killing. Antidonor dog leukocyte antigen (DLA) antibody was detected in the synovial fluid taken at the time of killing from six of six dogs that received allografts and in zero of three dogs that received autografts.

Effects of ovariectomy in beagle dogs

Beagle dogs 3-7 years old were ovariectomized (n = 9) or sham operated (n = 6) and followed for 48 weeks with measurements of body weight, tibial shaft bone mineral content (BMC), and serum biochemistry. Following killing, measurements were made of bone strength and histomorphometry. Ovariectomy (OX) significantly reduced serum estrone and estradiol concentrations and their variability from month to month. There was a transient decrease in cortical BMC of the OX dogs during the first 12 postoperative weeks but no difference between the groups after 48 weeks. Serum osteocalcin was elevated, but there was little effect on serum alkaline phosphatase, Ca, P, or calcitonin. OX increased the number of tetracycline-labeled osteons in cortical bone but reduced the percent trabecular surface labeled with tetracycline. OX produced no significant changes in the composition of the bones or loss of cortical area, but a statistically significant 15% trabecular bone loss occurred in the spine. However, bone strength had not been significantly affected at the time of sacrifice.

The calcar bone graft

A canine model was developed to investigate the use of an autogeneic iliac bone graft to treat the calcar deficiency commonly found at the time of revision surgery for femoral component loosening. Five large male mixed-breed dogs had bilateral total hip arthroplasty staged at three-month intervals, and were sacrificed at six months. Prior to cementing the femoral component, an experimental calcar defect was made, and a bicortical iliac bone graft was fashioned to fill the defect. Serial roentgenograms showed the grafts had united with no resorption. Technetium-99 bone scans showed more uptake at three months than at six months in the graft region. Disulfine blue injection indicated all grafts were perfused at both three and six months. Thin section histology, fluorochromes, and microradiographs confirmed graft viability in all dogs. Semiquantitative grading of the fluorochromes indicated new bone deposition in 20%-50% of each graft at three months and 50%-80% at six months. Although the calcar bone graft was uniformly successful in this canine study, the clinical application of this technique should be evaluated by long-term results in humans.

In vivo versus in vitro polymerization of acrylic bone cement: effect on material properties

Flexural strength and molecular weight of polymethylmethacrylate bone cement were determined for cement polymerized in vivo in a canine total hip replacement and cement from the same batch polymerized in vitro. Both in vivo and in vitro samples showed a slight increase in flexural strength and modulus at 2 weeks, followed by a nearly equivalent decline at 8 weeks. In vitro and in vivo samples exhibit a comparable stress to failure, but the in vivo samples show a significantly increased strain and decreased modulus. Cement from the proximal region of the prosthesis has significantly decreased flexural strength, lower modulus, and lower molecular weight than cement from the distal region and plug, suggesting that failures in the proximal region of a prosthesis may be due to inferior physical and mechanical properties of the bone cement in that region.