Inhibition of Colorectal Cancer Cell Proliferation by Regulating Platelet-Derived Growth Factor B Signaling with a DNA Aptamer

BACKGROUND: Overexpression of platelet-derived growth factor-BB (PDGF-BB) is associated with colorectal carcinogenesis. PDGF-BB plays a role in the autocrine growth stimulation of cancer cells. Aptamers are short single-stranded oligonucleotides that can bind to cellular targets with high affinity and specificity and offer the advantage of non-immunogenicity, non-toxicity and high stability. Thus, they receive interest as potential therapeutic agents. METHODS: The endogenous level of PDGF-BB in Caco-2 and SW480, colorectal cancer (CRC) cells, was evaluated using ELISA. The effect of the PDGF-BB aptamer on cell proliferation was investigated in two CRC cell lines and CCD841 CoN, normal colon cells. The effective molar ratio between PDGF-BB and PDGF-BB aptamer was further explored. Cell viability in all experiments was analyzed using MTS assay. Western blotting was performed to examine the alteration of relevant signaling pathways. RESULTS: Caco-2 and SW480 cells endogenously synthesized and secreted PDGF-BB to stimulate their growth. Cells treated with the PDGF-BB aptamer proliferated at a slower rate, but CCD841 CoN did not. Pre-incubation of PDGF-BB with the corresponding aptamer at the molar ratio 1:1 could significantly silence its proliferative effect on CRC cells. Western blot analysis revealed that the phosphorylation level of ERK1/2, a key component in PDGF downstream signaling pathway, was down-regulated by the aptamer, indicating the underlying mechanism of inhibition of CRC cell proliferation. CONCLUSIONS: This study demonstrated that using a DNA aptamer to interfere with the binding of PDGF-BB to its receptor suppressed CRC cell proliferation in part via down-regulation of the Ras/Raf/MEK/ERK signaling pathway. It raised the possibility that the PDGF-BB-specific aptamer could be a promising therapeutic agent for CRC targeted therapy.