Lipid-based microbubbles for enhanced delivery of anti PD-l1

Thesis

Despite major advances in cancer immunotherapies, their clinical use in cancer patients has reached an inflection point due to variable efficacy and systemic toxicities. A major development was the discovery of checkpoint blockade inhibition – referring to the use of antibodies that block immune-inhibitory pathways. While checkpoint inhibitors can be highly effective for cancer treatment, these bulky molecules do not distribute uniformly or broadly in solid tumours, where high interstitial pressure and abnormal vasculature impedes the normal physiological interstitial perfusion from blood stream to the tumour.

This inhomogeneous distribution may limit the efficacy of immunotherapy relying on antibodies that act primarily on the tumour. Ultrasound-induced cavitation, a physical phenomenon in which bubbles expand and violently collapse, can improve the extravasation of drugs into tumour from the blood stream. It has been recently shown that cavitation seeded by microbubbles can improve the efficacy of co-injected checkpoint inhibitors. This thesis aims to investigate whether further improvements in therapeutic response can be achieved by conjugating immunotherapeutic drugs, i.e. anti PD-L1, onto microbubbles via chemical conjugation or physical methods. However, clinical translation requires an accurate characterisation method for antibody loading, as well as the establishment of point-of-care manufacturing processes for antibody conjugation.

This thesis presents the development of a novel two-dimensional, single-bubble flow cytometry method for accurately detecting and quantifying antibody loading on microbubbles without the need for purification or fluorescent labelling. This method is further extended to enable absolute quantification of antibody on non-fluorescently labelled microbubbles, providing a robust quality control suitable for both research and point-of-care manufacturing. In addition, to advance the clinical applicability of antibody-conjugated microbubbles, a maleimide-thiol conjugation strategy was optimised as an alternative to traditional biotin-streptavidin methods, thereby optimising their application in targeted biomedical therapies, specifically for immunotherapy. The drug delivery strategy was further tested in vivo to investigate efficacy and immune response of anti PD-L1-conjugated microbubbles.

Authors: Rivera, J

• DOI: 10.5287/ora-9enegdxxz
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: drug delivery; immunotherapy; ultrasound; microbubbles
• Subjects: Drug delivery systems; Cancer--Immunotherapy; Biomedical engineering; Microbubbles