The Development of Methods to Account for Physiologic Dynamic Changes and Their Effects on the Pharmacokinetics of Therapeutic Monoclonal Antibodies and other Therapeutics

Physiologic changes in the body can drastically affect the clearance of a medication, and therefore increase the variability in exposure to the medication. Physiologic changes that can have a profound effect on the exposure of a medication can stem from changes CYP enzymes, transport proteins, binding protein expression, organ function, immune reactivity, and health status to name a few; with the focus of this dissertation on the dynamic changes in the ontogeny of MRP2 (an apical liver transport protein) and the dynamic changes caused by an immune response to a therapeutic monoclonal antibody (mAb). Several approaches can be used to limit or capture the changes in the pharmacokinetics of a medication caused by ontogeny and immune reactivity related dynamic changes. Three approaches were investigated in this dissertation: 1) preventing/limiting immunogenicity’s effect on a therapeutic mAb, hence eliminating the increase in clearance and variability, 2) using a pharmacometric PK-ADA modeling approach to model immunology-related dynamic and variable effects on a therapeutic mAb and 3) using a systems pharmacology strategy to model the ontogeny changes in a transport protein (MRP2) and the dynamic effects on its drug substrates. In the preclinical and clinical setting, anti-drug antibodies (ADA) that develop against therapeutic mAbs can influence patient safety and interfere with product efficacy. Thus, my first focus in this dissertation investigates methods to limit/prevent immunogenicity and therefore help to eliminate a source of variability and clearance that can be seen in preclinical and clinical studies. My first study investigates the use of immune suppressants in mitigating ADA responses to a fully-humanized mAb in preclinical animal studies. Three groups of Sprague Dawley rats (n=18) were treated with low (0.01 mg/kg), moderate (50 mg/kg), or high (300 mg/kg) doses of a mAb. Experimental groups also received either methotrexate or tacrolimus/sirolimus immune suppression. Methotrexate significantly lowered the incidence of anti-variable region antibodies at moderate mAb dose (P\u3c0.05), while tacrolimus/sirolimus did likewise at moderate and high doses (P\u3c0.01) of mAb. With the exception of low dose mAb plus methotrexate, all immunosuppressed groups displayed more than a 70-fold decrease in ADA magnitude (P\u3c0.05). This abrogation in ADA response correlated with higher mAb exposure in the circulation by week 4 for the moderate and high dosed mAb groups. This method provides an approach to mitigate preclinical immunogenicity by the use of immunosuppressant modalities. Such preconditioning can support preclinical drug development of human therapeutics that are antigenic to animals but not necessarily to humans. Similar approaches to reduce immunogenicity will likely play an essential role with advances in novel therapeutics like fully human mAbs, recombinant proteins, fusion proteins as well as bispecific- and drug-conjugated antibodies. In some cases there may not be a method to reduce/eliminate immunogenicity and the dynamic changes in the elimination of a therapeutic mAb that result. In a preclinical setting, ADA typically influences both multiple dose toxicity studies, as well as preliminary pharmacokinetic (PK) analysis by leading to an increase in clearance of the therapeutic mAb. This increase in clearance caused by ADA can be highly variable due to each animal’s polyclonal immune response to a therapeutic mAb. My second focus aims to account for ADA and its variable effect on a fully human therapeutic mAb. I used data acquired from our previous study that investigated the use of immunosuppressant therapy in mitigating ADA responses to a mAb in a preclinical Sprague Dawley rat study and incorporated much of the data from that study, which included three mAb dosing groups and three immunomodulation therapies. A pharmacometric PK-ADA modeling approach was used to analyze the data. Our model was able to simultaneously capture the pharmacokinetics of the mAb in the presence and absence of ADA, accounting for an immune reaction’s highly variable effect on a therapeutic mAb concentration-time profile. The pharmacometric PK-ADA methodology used in this study demonstrates a modeling strategy that can be applied to other therapeutic mAbs to assess the immunogenicity of a therapeutic mAb and the dynamic effect immunogenicity has on the pharmacokinetics. This modeling methodology can further be applied to the simulation of therapeutic mAbs in the presence of varying rates, magnitudes and affinities of ADA reactions, aiding in the development of appropriately powered toxicology studies and an accurate pharmacokinetic evaluation of a human therapeutic mAb in a preclinical setting. Transport proteins play an important role in determining the disposition of medications in the human body. The expression of transport proteins in the body is not constant throughout childhood development, which affects the pharmacokinetics of a medication that is a substrate of the transport protein. Multidrug resistance protein 2 (MRP2) represents a major hepatic transporter whose expression is dynamic throughout development. MRP2 plays a vital role in the biliary excretion of various organic anions and cations along with glutathione-, glucuronate-, or sulfate-conjugates of several drug substrates. Our third aim is to evaluate the effect the ontogeny of MRP2 has on the pharmacokinetics of ceftriaxone to better understand how a transport protein contributes to the disposition of its substrates throughout childhood development. In order to accomplish our aim, a systems pharmacology modeling approach was used to understand MRP2’s contribution to the elimination of ceftriaxone and the effect of ontogeny changes on the pharmacokinetics of ceftriaxone in pediatric patients. Data from ex vivo studies, preclinical in vivo studies and clinical studies were used to inform our model. Results from the study demonstrate the contribution of MRP2 to the pharmacokinetics of ceftriaxone. Our model was able to capture ceftriaxone’s pharmacokinetics, and MRP2’s contribution to its clearance, allowing for the prediction of pediatric ceftriaxone concentrations. This modeling strategy can also be used to evaluate ontogeny changes in other biochemical transposition proteins, and the subsequent effect on the pharmacokinetics of other therapeutically used compounds. In summary, our work has successfully provided approaches to limit/prevent dynamic changes caused by immune reactions to a therapeutic mAb, demonstrate a pharmacometric PK-ADA approach that can capture the PK changes and variability caused by ADA formation on a therapeutic mAb and demonstrate a systems pharmacology model approach which accounts for the ontogeny of a transport protein and the resultant PK effects on its substrate through childhood development. The following chapters describe and discuss these novel approaches

Dynamic analysis of a magnetic bearing system with flux control

Using measured values of two-dimensional forces in a magnetic actuator, equations of motion for an active magnetic bearing are presented. The presence of geometric coupling between coordinate directions causes the equations of motion to be nonlinear. Two methods are used to examine the unbalance response of the system: simulation by direct integration in time; and determination of approximate steady state solutions by harmonic balance. For relatively large values of the derivative control coefficient, the system behaves in an essentially linear manner, but for lower values of this parameter, or for higher values of the coupling coefficient, the response shows a split of amplitudes in the two principal directions. This bifurcation is sensitive to initial conditions. The harmonic balance solution shows that the separation of amplitudes actually corresponds to a change in stability of multiple coexisting solutions

Governance and Performance of National Government-Constituencies Development Funds in Kenya

The main objective of the study was to establish the relationship between governance and performance of National GovernmentConstituencies Development Funds (NG-CDFs) in Kenya. A census survey was carried out on all the 290 NG-CDFs performance in Kenya. A positivistic research philosophy and a descriptive cross-sectional survey design were used. Data was collected using structured and unstructured questionnaire. Secondary data was easily accessible from the National Treasury, Kenya National Bureau of Statistics, the General Auditor’s reports and NG-CDF website and was collected for the period 2014 to 2018. Simple regression analysis was used to test the hypotheses at 95 percent confidence level. The results of the study were established and compared to various theories anchoring the study and conceptual, contextual and empirical evidence. It was established that there is a statistically significant relationship between governance and NG-CDFs performance in Kenya. The study benefits policy makers such that the NG-CDF board should ensure that all NG-CDFs have homogeneous governance practices that ensure enhanced performance. Managerial practitioners especially in NG-CDF may consider strengthening governance to enhance performance and use Data Envelopment Analysis (DEA) technique to measure performance in NG-CDFs

Distributions and abundances of Pacific sardine (Sardinops sagax) and other pelagic fishes in the California Current Ecosystem during spring 2006, 2008, and 2010, estimated from acoustic–trawl surveys

The abundances and distributions of coastal pelagic fish species in the California Current Ecosystem from San Diego to southern Vancouver Island, were estimated from combined acoustic and trawl surveys conducted in the spring of 2006, 2008, and 2010. Pacific sardine (Sardinops sagax), jack mackerel (Trachurus symmetricus), and Pacific mackerel (Scomber japonicus) were the dominant coastal pelagic fish species, in that order. Northern anchovy (Engraulis mordax) and Pacific herring (Clupea pallasii) were sampled only sporadically and therefore estimates for these species were unreliable. The estimates of sardine biomass compared well with those of the annual assessments and confirmed a declining trajectory of the “northern stock” since 2006. During the sampling period, the biomass of jack mackerel was stable or increasing, and that of Pacific mackerel was low and variable. The uncertainties in these estimates are mostly the result of spatial patchiness which increased from sardine to mackerels to anchovy and herring. Future surveys of coastal pelagic fish species in the California Current Ecosystem should benefit from adaptive sampling based on modeled habitat; increased echosounder and trawl sampling, particularly for the most patchy and nearshore species; and directed-trawl sampling for improved species identification and estimations of their acoustic target stre

Investigation of Spiral Bevel Gear Condition Indicator Validation via AC-29-2C Using Fielded Rotorcraft HUMS Data

This report presents the analysis of gear condition indicator data collected on a helicopter when damage occurred in spiral bevel gears. The purpose of the data analysis was to use existing in-service helicopter HUMS flight data from faulted spiral bevel gears as a Case Study, to better understand the differences between HUMS data response in a helicopter and a component test rig, the NASA Glenn Spiral Bevel Gear Fatigue Rig. The reason spiral bevel gear sets were chosen to demonstrate differences in response between both systems was the availability of the helicopter data and the availability of a test rig that was capable of testing spiral bevel gear sets to failure. The objective of the analysis presented in this paper was to re-process helicopter HUMS data with the same analysis techniques applied to the spiral bevel rig test data. The damage modes experienced in the field were mapped to the failure modes created in the test rig. A total of forty helicopters were evaluated. Twenty helicopters, or tails, experienced damage to the spiral bevel gears in the nose gearbox. Vibration based gear condition indicators data was available before and after replacement. The other twenty tails had no known anomalies in the nose gearbox within the time frame of the datasets. These twenty tails were considered the baseline dataset. The HUMS gear condition indicators evaluated included gear condition indicators (CI) Figure of Merit 4 (FM4), Root Mean Square (RMS) or Diagnostic Algorithm 1 (DA1) and +/- 3 Sideband Index (SI3). Three additional condition indicators, not currently calculated on-board, were calculated from the archived data. These three indicators were +/- 1 Sideband Index (SI1), the DA1 of the difference signal (DiffDA1) and the peak-to-peak of the difference signal (DP2P). Results found the CI DP2P, not currently available in the on-board HUMS, performed the best, responding to varying levels of damage on thirteen of the fourteen helicopters evaluated. Two additional CIs also not in the on-board system, DiffDA1and SI1, also performed well responding to twelve and ten of the fourteen helicopters evaluated respectively. Of the three CIs currently available in the MSPU, DA1, FM4 and SI3, SI3, responded to eight, DA1 responded to six and FM4 responded to four of the fourteen helicopters evaluated. FM4, the poorest performing CI, was not as responsive to damage as the other five CIs. Conversely, when compared to the other two, it was the only CI that responded to damage on two helicopters. CI response could not be correlated to specific failure modes due to limited pictures and subjective descriptions found within the TDA. Flight regime did affect CI response to some gear faults. Due to the range of operating conditions for each regime, more studies are required to determine their sensitivity to regimes

Data Fusion Tool for Spiral Bevel Gear Condition Indicator Data

Tests were performed on two spiral bevel gear sets in the NASA Glenn Spiral Bevel Gear Fatigue Test Rig to simulate the fielded failures of spiral bevel gears installed in a helicopter. Gear sets were tested until damage initiated and progressed on two or more gear or pinion teeth. During testing, gear health monitoring data was collected with two different health monitoring systems. Operational parameters were measured with a third data acquisition system. Tooth damage progression was documented with photographs taken at inspection intervals throughout the test. A software tool was developed for fusing the operational data and the vibration based gear condition indicator (CI) data collected from the two health monitoring systems. Results of this study illustrate the benefits of combining the data from all three systems to indicate progression of damage for spiral bevel gears. The tool also enabled evaluation of the effectiveness of each CI with respect to operational conditions and fault mode