Inhibition of potentially anti-apoptotic proteins by antisense protein kinase C-alpha (Isis 3521) and antisense bcl-2 (G3139) phosphorothioate oligodeoxynucleotides: relationship to the decreased viability of T24 bladder and PC3 prostate cancer cells.

Isis 3521 and G3139 are 20- and 18-mer phosphorothioate oligonucleotides, respectively, targeted to the protein kinase C (PKC)-alpha and bcl-2 mRNAs. Treatment of T24 bladder and PC3 prostate carcinoma cells with full-length and 3'-truncation mutants of Isis 3521 causes down-regulation of PKC-alpha protein and mRNA. However, at the level of a 15-mer and shorter, down-regulation of mRNA expression is no longer observed. Further, no diminution in cellular viability, as measured by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide assay, in response to increasing concentrations of paclitaxel, can be observed for these shorter oligomers. These observations not only indicate that PKC-alpha protein expression can be down-regulated by both RNase H-dependent and -independent mechanisms but also that down-regulation of PKC-alpha is insufficient by itself to "chemosensitize" cells. G3139, which down-regulates bcl-2 protein and mRNA expression, also down-regulates PKC-alpha protein and mRNA expression but not that of PKC-betaI, -epsilon, or -zeta. However, the down-regulation of PKC-alpha and bcl-2 are not linked. When the carrier Eufectin 5 is employed, only bcl-2 is down-regulated in both T24 and PC3 cells at 50 nM oligonucleotide concentration. At 100 nM, both bcl-2 and PKC-alpha expression are down-regulated, and only at this concentration can "chemosensitization" to paclitaxel and carboplatin be observed. In contrast, the down-regulation of bcl-2 seems to be linked with that of RelA (p65). However, this too is also not sufficient for chemosensitization, even though it leads to the loss of expression of genes under the putative control of nuclear factor-kappaB and to detachment of the cells from plastic surfaces. These results underscore the complexity of the intracellular requirements for the initiation of chemosensitization to anti-neoplastic agents.

Formation of a G-tetrad and higher order structures correlates with biological activity of the RelA (NF-kappaB p65) 'antisense' oligodeoxynucleotide.

We have examined the behavior of the phosphorothioate antisense Rel A (NF-kappaB p65) oligodeoxynucleotide (oligo) and related molecules. Because of the presence of a G-tetrad near its 5'terminus, this molecule is capable of forming tetraplexes and other higher order structures in a temperature and time dependent manner. The G-tetrad in the phosphodiester congener is protected from methylation by dimethylsulfate when the oligomer is 3'-phosphorylated. However, this protection is completely lost when it is 5'phosphorylated, indicating that the formation of at least some higher order structures has been blocked. In addition, we also prevented tetraplex formation by substitution of 7-deazaguanosine (7-DG) for guanosine at several positions within and outside of the tetrad. This substitution retains Watson-Crick base pair hybridization but prevents Hoogsteen base-pair interactions. When murine K-Balb cells were treated with 20microM antisense RelA oligo, complete blockade of nuclear translocation of RelA was observed. However, this effect was virtually entirely abrogated in most cases by 7-DG substitution within the tetrad, but retained when the substitution was made 3' to the tetrad. The AS RelA-induced downregulation of Sp-1 activity behaved similarly after 7-DG substitution. Thus, the parent phosphorothioate AS RelA molecule cannot be a Watson-Crick antisense agent. However, these conclusions cannot be extrapolated to other G-tetrad containing oligomers and each must be evaluated individually.