<strong>Platforms for Molecular Mechanisms and Improvement in Subcutaneous Injection of Biotherapeutics</strong>

Biotherapeutics, such as monoclonal antibodies (mAbs), represent a primary mechanism for treatment of human disease, and there has been a steady increase in Food and Drug Administration approvals since the first one in 1982. Subcutaneous (SC) injection of protein-based therapeutics is a convenient and clinically established drug delivery method that increases the convenience and reduces cost compared to other delivery methods. However, progress is needed to optimize bioavailability via this route. This dissertation describes the methods for evaluation of mass transport of high molecular weight proteins, such as mAbs, following SC injection using in vitro and ex vivo modeling developed to describe the factors relevant for optimal distribution prior to uptake into systemic circulation. The first chapter describes a novel collagen and hyaluronic acid (HA) based hydrogel for investigation of macromolecule transport based on the physiochemical properties of the diffusing molecule and the tissue matrix. This initial study demonstrated that, in collagen alone, collagen combined with HA, and HA alone, the molecules demonstrated different transport paradigms dependent primarily on molecule size, matrix viscosity, and electrostatic charge, respectively. This showed that the local tissue heterogeneity and therapeutic properties could be determining factors for molecule transport and bioavailability. The second, third, and fourth chapters describe two novel platforms for the investigation of injection plume formation in SC tissue utilizing three-dimensional X-ray tomography. Injection plume analysis has been studied comprehensively in the context of insulin transport using co-injection of radiopaque dyes to track the protein distribution. However high molecular weight therapeutics have vastly different physiochemical properties than insulin and are injected under different rates, concentrations, volumes, and viscosities due to dosing considerations. To address the gap mAb distribution, we first developed a novel protein conjugated to an x-ray contrast agent to directly track injection plume formation and investigated the effects of injection rate and tissue location through injections into ex vivo porcine tissue, described in chapters three and four. Ex vivo tissue analysis showed that the rate did not influence the distribution, however, plume volume was lower in porcine belly compared to neck tissue. Whereas porcine tissue is an excellent model to represent the structural features of human injection, the large heterogeneity between animal subjects and collected samples is a disadvantage. Therefore, the fourth chapter describes the fabrication of a gelatin hydrogel-based injection platform representing the dermal and subcutaneous tissue layers for controlled injection plume analysis. In summary, all three models represent useful platforms for the assessment of macromolecular mass transport, pharmaceutical autoinjector performance, as well as the potential impact of tissue properties and intersubject heterogeneity on plume formation. Overall, the findings in these studies might better inform drug designers and clinicians on how to most optimally engineer an injection to deliver the most efficient patient outcomes through better dosing and increased cost savings.