Second Generation Antisense Oligonucleotides—Inhibition of PKC-α andc-rafKinase Expression by Chimeric Oligonucleotides Incorporating 6″-Substituted Carbocyclic Nucleosides and 2″-O-Ethylene Glycol Substituted Ribonucleosides

6′-substituted carbocyclic deoxyribonucleosides and 2′-O-ethylene glycol substituted ribonucleosides have been evaluated as building blocks for antisense oligonucleotides. Within the former class 6′-hydroxy substituted building blocks in combination with internucleoside phosphorothioate linkages have the potential to enhance antisense activity. 2′-O-ethylene glycol substituted ribonucleosides generally allow for the construction of potent antisense oligonucleotides with reduced phosphorothioate content, but differences exist in their effects on biological activity in cell culture in spite of virtually identical effects on RNA-binding affinity. Activity enhancement was most pronounced for a 2′-O-methoxyethyl substituent.