Rw. Storrs et al., PARAMAGNETIC POLYMERIZED LIPOSOMES - SYNTHESIS, CHARACTERIZATION, ANDAPPLICATIONS FOR MAGNETIC-RESONANCE-IMAGING, Journal of the American Chemical Society, 117(28), 1995, pp. 7301-7306
Liposomes are biocompatible materials that show promise as vehicles fo
r drug delivery, inhibitors of cell adhesion, and carriers for the int
roduction of genetic material into cells. In this paper, we describe t
he synthesis and characterization of a new class of polymerized liposo
me particles (paramagnetic polymerized liposome (PPL), Figure 1) that
have lanthanide ion chelates as head groups and that can be easily vis
ualized using magnetic resonance imaging (MRI). The R(1) molar relaxiv
ity was found to depend primarily on the linker length (m) and on the
surface metal density and only weakly on particle size. PPLs containin
g 10 mol % of compound 1b (m = 2) and 90 mol % of compound 3 had a R(1
) = 12.2 mM(-1) s(-1), while PPLs with 10 mol % compound 1a (m = 1) an
d 90 mol % of compound 3 had a R(1) = 5.7 mM(-1) s(-1). PPLs with 10 m
ol % of compound 1a and 90 mol % of compound 4 had a R(1) = 8.9 mM(-1)
s(-1), while PPLs with 50 mol % of compound 1a and 50 mol % of compou
nd 4 had a R(1) = 4.3 mM(-1) s(-1). A biotinylated lipid (compound 2)
was also incorporated into the particle without affecting R(1) relaxiv
ities for use as a marker for histochemical studies. We have also for
the first time used atomic force microscopy (AFM) to investigate the s
ize and nature of these particles in an aqueous environment. We feel t
hat these new materials may prove useful for the in vivo investigation
of liposome formulations as vehicles for therapeutic applications and
for evaluating tissue pathology with MRI.