152. Tumor Inhibition by Using Chitosan:siRNA PDGFR-β in Breast Cancer Model of Rat

Abstract

Platelet-derived-growth factors (PDGFs) may represent a novel target in human cancer because they regulate many cellular processes, including cell proliferation, transformation, apoptosis and angiogenesis. PDGF-D's exert their cellular effects by two receptors PDGFR-α and PDGFR-β. Moreover PDGF ligands and receptors are proto-oncogenes that can be activated by various types of alternatives in cancer cells. Breast cancer is the most common and fatal type of cancer. The PDGF pathway is essential in tumor angiogenesis. It is known that the expression of PDGF receptors is altered and upregulated in breast cancer. Delivery is very important for success in gene therapy. Among the different non-viral gene delivery system, chitosan has very useful properties as a gene carrier. In this study; we investigated the effect of chitosan:siRNA complexes on tumor angiogenesis in breast tumor models of rats. Firstly chitosan:siRNA complexes (1/5-1/20 rate) targeting to PDGFR-β were prepared and characterized in vitro. Transfection efficiency of these nanoplexes in breast cancer cells such MCF-7, MDA-MB-231 and MDA-MB-435 was assayed. In in vitro transfection studies, 54%-65% of PDGFR-β inhibition was measured. Then these chitosan:siRNA complexes were injected intratumorally to tumor bearing Sprague Dawley rats. After tumor reached to constant size, complexes (20/1) were injected (40µg siRNA) and tumor volumes were measured periodically. After sacrification of animals, tissue and blood samples were taken and investigated histologically and immuno-histochemically. Expression levels of PDGFR-β determined by ELISA, mRNA levels were measured by RT-PCR also. Nanoplexes having 207 ± 3.5 nm size and 14.2 mV surface charge were used in this study. Tumor volume of nanoplex treated rats decreased at 92.49% at the end of the experiment (28th day). After free siRNA treatment, however, tumor volume increased very slowly until 21 days (68.1 % of decreasing value) then went up fastly. RT-PCR, Western-blot studies and immuno-histochemical data showed similarity with tumor volume measurements. Similar IFN response with tumor (untreated) was obtained after nanoplex administration. In conclusion, chitosan can be complexed with siRNA targeting PDGFR-β and chitosan:siRNA PDGFR-β nanocomplexes may be useful alternative in the treatment of breast cancer. The receptors of PDGF may be also suitable target in breast cancer.