Ph.D Thesis


Ph.D StudentTomer Bronshtein
SubjectCo-Receptor Conjugated Liposomes: A Novel Drug-Delivery
System to HIV-Infected Cells
DepartmentDepartment of Biotechnology and Food Engineering
Supervisors Full Professors Machluf Marcelle
Professor Pollack Shimon


Abstract

Anti-retroviral-therapies against HIV/AIDS focus on inhibiting viral growth and may slow AIDS, but not cure the disease. Here we describe an approach to treat HIV as a cellular pathology by targeting cell derived liposomes and synthetic liposomes at HIV-infected cells. Cell-derived-liposomes (CDLs) were prepared from the cytoplasmatic membranes of cells expressing CCR5, the human receptor for gp120, that is found on the surface of virions and HIV-infected cells. Synthetic liposomes were constructed by conjugating CCR5 with liposomes prepared from synthetic lipids. ENV-expressing model cell-lines were engineered to mimic the membranal interactions of HIV-infected cells and to serve as targets for the liposomes. All constructed liposomes were found to express native and correctly oriented CCR5 and were shown to specifically target HIV-infected model cells to varying extent. CDLs and synthetic nano-liposomes exhibited unilamellar morphology and were found to be of 100-200 nm in diameter. The specific targeting and cytotoxicity of the CDLs towards gp120-expressing cells was found to be the highest of all liposomal constructs. EDTA was selected as a liposomal encapsulate and was shown to cause considerable cytotoxic effect when introduced into the cell cytoplasm. Finally, CDLs containing EDTA caused over 60% reduction in the viability of gp120-expressing cells compared to no effect on control cells. Taking the results all together, we can conclude that CCR5-conjugated cell derived liposomes can specifically bind, fuse and deliver their content into gp120-expressing cells. Moreover, the bio-chemical properties of EDTA make it an ideal encapsulate for a liposomal system. The intra-cellular toxic effect of EDTA ensures it will act only upon introduction into the cell cytoplasm via the liposomal mechanism of membrane fusion. Moreover, targeted liposomes containing EDTA can significantly reduce the viability of model HIV-infected cells while spearing "healthy" control cells. Hence, this system can be used as a drug-delivery system to HIV-infected cells. All in all, the specific targeting and cytotoxic effect of CCR5-conjugated CDLs towards gp120-expressing HIV model cells suggests a potential new therapeutic approach.