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.

Regulation of PAI-1 concentration in platelets by systemic administration of antisense oligonucleotides to rats

In this report we tested the effect of oligodeoxyribonucleotides antisense to PAI-1 mRNA administered into rats on PAI-1 concentration in platelets. Low doses of the antisense oligonucleotide (MPO-16R) reduced PAI-1 activity, both in rat blood plasma and platelet lysates by 20.5% and 28.7%, respectively. There was no change in platelet count after treatment with MPO-16R but treated platelets showed lower aggregability as compared with controls (37 +/- 13% and 54 +/- 12%, respectively). In an experimental model of rat arterial thrombosis, low doses of MPO-16R caused a significant delay in the occlusion time (31.8%). These data further support for the role of PAI-1 as a major determinant of arterial thrombolysis resistance and for the first time demonstrate the possibility of reduction of platelet PAI-1 concentration by antisense approach.

Effect of P-chirality of internucleotide bonds on B-Z conversion of stereodefined self-complementary phosphorothioate oligonucleotides of the [PS]-d(CG)4 and [PS]-d(GC)4 series

Diastereomerically pure, partially modified (in selected positions) or fully modified phosphorothioate oligomers of the [PS]-d(CG)(4) and [PS]-d(GC)(4) series were investigated with respect to their ability to adopt the left-handed conformation at high sodium chloride concentration. NaCl induces the B-Z transition of [All-S(P)R(P)-PS]-d(CG)(4) with a midpoint of transition at ca. 2 M, which is approximately 1 M less than for unmodified d(CG)(4). Also, [All-R(P)S(P)-PS]-d(GC)(4) at 5 M NaCl converts to the Z form to the extent of ca. 55%, while the unmodified d(GC)(4) counterpart does not convert at all. This enhanced ability of stereodefined phosphorothioate oligomers to adopt the Z conformation is discussed in terms of already known structural factors (hydrogen bonding and water bridges) facilitating the B-Z transition, identified for unmodified d(CG)(n) oligonucleotides. By CD spectroscopy, the [All-S(P)-PS]-d(CG)(4) oligomer at a NaCl concentration higher than 0.01 M adopts a unique conformation as assessed from the presence of an additional negative band centered at 282 nm.

Effect of P-chirality of oligo(deoxyribonucleoside phosphorothioate)s on the activity of terminal deoxyribonucleotidyl transferase

Phosphorothioate analogues of oligonucleotides (PS-oligos) of predetermined chirality at the phosphorus atom at each internucleotide linkage have been used as primers for terminal deoxyribonucleotidyl transferase (TdT, EC 2.7.7.31). The enzyme catalyzes efficient elongation of PS primers in which all phosphorothioate internucleotide linkages are uniformly of the [R(P)] configuration, while the presence of the linkage(s) of the [S(P)] configuration significantly decreases or completely inhibits the primer extension. Our results indicate that for the elongation of phosphorothioate oligomers the most important is the internucleotide bond located between the second and the third nucleoside from the 3'-end. The presence of [S(P)] linkage at this position strongly reduces the enzyme activity while the [R(P)] bond allows for effective elongation of the primer. The activity of the enzyme is also influenced by base composition and sequence of phosphorothioate primer as well as the dNTP used for elongation process.

Stereodependent inhibition of plasminogen activator inhibitor type 1 by phosphorothioate oligonucleotides: proof of sequence specificity in cell culture and in vivo rat experiments

Hexadecadeoxyribonucleotides complementary to a fragment of human PAI-1 mRNA located upstream of the start codon and their phosphorothioate analogs were studied in cultured HUVECs as sequence-dependent inhibitors of PAI-1 expression. The activity of the random mixture of diastereomers of phosphorothioate hexadecanucleotide PS-16H has been compared with that of isosequential, stereoregular [All-Sp] and [All-Rp] isomers. The highest inhibitory effect on PAI-1 synthesis was observed with the [All-Sp] diastereomer. Stereorandom phosphorothioate oligonucleotide PS-16R complementary to the same region of rat PAI-1 mRNA, when injected into tail vein of rats, substantially decreased the level of PAI-1 in blood plasma.