Development of an Effective Drug Delivery System Using Loaded Platelets

Citation

Male, Roxanne (1993) Development of an Effective Drug Delivery System Using Loaded Platelets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1q2y-nz07. https://resolver.caltech.edu/CaltechTHESIS:01022013-133723062

Abstract

Liposomes have been used to deliver diagnostic and therapeutic drugs with moderate success. Current applications include targeting to tumors (1), where the vasculature is leaky and allows liposome penetration, and Kupffer cells in the liver (2). Reticuloendothelial system (RES) uptake and lack of targeting specificity of the liposomes have been the major problems encountered. Several groups including Allen et al. (3) and Liu et al. (4) have increased the circulation times by attaching polyethylene glycol (PEG) or the ganglioside GM_1 to the liposome surface; the circulation half-lives for disteroylphosphatidylcholine (DSPC):cholesterol:PEG and GM_1 liposomes are 20.0 ± 3.5 and 16.4 ± 3.1 hours, respectively as compared to 6.7 ± 4.5 hours for DSPC:cholesterol (2:1 mole ratio) liposomes (3). In addition, some attempts have been made to target specific areas by the addition of ligands, such as human gamma globulin or aminomannose; however this increased targeting has been largely limited to increased Kupffer cell and RES uptake (5,6). Addition of antibodies to the liposomes increases targeting specificity, but has met with limited success since the liposomes are still prone to RES uptake (7).

Reconstituted Sendai virus envelopes (RSVE) are essentially liposomes with binding and fusogenic glycoproteins on their surface. These vesicles have been used as vehicles for delivering molecules into cells in vitro and for the transfer of membrane proteins into the cells' plasma membranes. Similar to intact viruses, RSVE attach preferentially to cells having the appropriate receptors, usually gangliosides, and fuse with the cellular membranes, thus emptying their contents into the cell cytoplasm. This also results in the implantation of the viral envelope components into the recipient cell plasma membrane.

We have studied the in vitro interactions of small unilamellar vesicles (SUV) and reconstituted Sendai virus (RSVE) with platelets with the objective of developing new drug delivery systems. Specifically, we have examined the kinetics and mechanisms of uptake of SUV, with and without covalently attached proteins, and RSVE. Liposomes that have been studied include: DSPC:cholesterol (2:1 mole ratio) liposomes (control) (8) and aminomannose (Am), human gamma globulin (HgG) and transferrin (Tf) labeled control liposomes (9). From our data we conclude that the mechanisms and kinetics of uptake and subsequent specific localization of the lipid and aqueous components of the liposomes within the cells are dependent on the type of liposome used.

Platelets have the unique ability to target to specific areas in vivo including areas of infection and inflammation, tumors and clots. Therefore we hoped to combine this in vivo targeting ability with the platelets' ability to take up liposomes and RSVE in vitro to create new drug delivery systems to deliver diagnostic and therapeutic reagents. Having a variety of systems from which to choose should offer the ability to optimize drug delivery parameters.

In vitro functional assays, including microaggregation, serotonin release and membrane integrity, conclude that platelet function is not inhibited by liposome uptake (8, 9). However, uptake of intact and reconstituted Sendai virus particles induce platelet aggregation and secretion. In vivo organ distribution studies in Sprague-Dawley rats indicate that circulation times and RES uptake of liposome-loaded rat platelets are identical to control rat platelets (10).

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