Antisense oligodeoxynucleotides (ODNs) are designed to bind to and inhibit a 
target mRNA. We used a novel approach for the design of ODNs to the c-myc mRNA 
using protein binding sites as targets for ODN action. Our strategy was to 
identify ODNs that could interfere with the coding region determinant-binding 
protein (CRD-BP), a protein that binds to the CRD region of the c-myc mRNA. 
Using an in vitro gel shift assay, we show that ODN molecules can occlude the 
CRD-BP from the mRNA. The best ODN, CRD-ODN4, was able to inhibit RNA binding of 
the CRD-BP by 75%. This effect was sequence-specific and concentration 
dependent. K562 cells treated with a 2'-O-methyl derivative of CRD-ODN4 showed a 
concentration-dependent decrease in both c-myc mRNA and protein levels, with a 
maximal 65% inhibition of protein expression at 200 nM CRD-ODN4. In contrast, a 
2'-O-methyl ODN derivative targeting the translation initiation codon 
(antimyc-aug) reduced c-myc protein but actually increased mRNA levels, an 
effect resulting at least partly from stabilization of the c-myc mRNA. CRD-ODN4 
treatment did not alter the c-myc mRNA half-life. CRD-ODN4 was more effective in 
inhibiting K562 cell growth than antimyc-aug, reducing cell number by 
approximately 70% after 48 h of exposure to 750 nM. The correlation between ODN 
effects on RNA-protein interactions in vitro and those observed in cells 
supports the hypothesis that CRD-ODN4 inhibits the interaction between the 
CRD-BP and the c-myc mRNA and that disrupting this RNA-protein interaction 
reduces c-myc expression in cells.