Doctoral Dissertations

Date of Award

3-1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major Professor

Leaf Huang

Committee Members

Stephen Kennel, Kenneth Monty, Ernesto Freire

Abstract

A novel target-sensitive inimunoliposome system was designed, characterized and demonstrated to be both an efficient site-specific drug delivery system and a basic immune detection tool. As the name implies, these liposomes exposing immunoglobulin G (IgG) antibody on their surface, could selectively attach to target antigen, self-destabilize, and release aqueous contents in a site-specific manner. This unique characteristic of the target sensitive design was derived from the ability of membrane acylated IgG to stabilize phosphatidylethanolamine (PE) in a bilayer. Antibody-stabilized PE immunoliposomes were rapidly destabilized upon binding to multivalent antigen expressing targets while monovalent, soluble antigen failed to cause liposome destabilization, indicating the necessity of multivalent binding for destabilization. In addition to the requirement of multivalent antigen on targets, kinetic and ultrastructural studies of interactions between liposomes and herpes simplex virus (HSV) virions indicated that HSV-induced destabilization of PE-immunoliposomes involved liposomevirus fusion intermediates which collapsed after increasing in size to finally allow PE to assume its original non-bilayer form, hexagonal HII phase. Freeze-fracture electron microscopy further demonstrated the reversion of PE to a HII phase. Using target-sensitive immunoliposomes bearing anti-HSV-glycoprotein D, with peroxidase as an encapsulated enzyme marker, we quantitated HSV in test samples by detecting peroxidase enzymatic activity expression due to HSV-induced liposome destabilization. Evaluation of the HSV target-sensitive immunoliposome-based immunoassay (ILA) on clinical samples showed that the ILA was equally sensitive to the currently employed virus plaque assay. In comparison, a commercial enzyme-linked-immunosorbent assay for HSV antigen was less sensitive. Site-specific release of liposome contents from target-sensitive immunoliposomes was implemented for use as an anti-viral drug-delivery system to suppress HSV replication. Results showed that encapsulation of nucleoside analogs in target-sensitive immunoliposomes not only decreased the nonspecific cytotoxicity, but also enhanced the potency of the antiviral drug. This target-sensitive immunoliposome design should be applicable in site-specific drug delivery, to improve existing immune detection systems, and as an approach to treat the foci of infections or neoplasms.

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