A new prototype of
polymer-derived drug delivery system, the
nanoconjugate Polycefin, was tested for its ability to accumulate in
tumors based on enhanced permeability and retention (EPR) effect and receptor mediated endocytosis.
Polycefin was synthesized for targeted delivery of
Morpholino antisense oligonucleotides into certain
tumors. It consists of units that are covalently conjugated with poly(beta-l-
malic acid) (M(w) 50,000, M(w)/M(n) 1.3) highly purified from cultures of myxomycete Physarum polycephalum. The units are active in endosomal uptake, disruption of endosomal membranes,
oligonucleotide release in the cytoplasm, and protection against enzymatic degradation in the vascular system. The
polymer is biodegradable, non-immunogenic and non-toxic.
Polycefin was also coupled with AlexaFluor 680 C2-maleimide
dye for in vivo detection. Nude mice received
subcutaneous injections of MDA-MB 468 human
breast cancer cells into the left posterior mid-dorsum or intracranial
injections of human
glioma cell line U87MG.
Polycefin at concentration of 2.5mg/kg was injected via the tail vein. In vivo fluorescence
tumor imaging was performed at different time points, 0-180 min up to 24h after the
drug injection. The custom-made macro-illumination imaging MISTI system was used to examine the in vivo
drug accumulation in animals bearing human breast and
brain tumors. In
breast tumors the fluorescence signal in large blood vessels and in the
tumor increased rapidly until 60 min and remained in the
tumor at a level 6 times higher than in non-
tumor tissue (180 min) (p<0.003). In
brain tumors drug accumulated selectively in 24h without any detectable signal in non-
tumor areas. The results of live imaging were corroborated histologically by fluorescence microscopic examination of various organs. In addition to
tumors, only kidney and liver showed some fluorescent signal.