Antisense oligonucleotides as inhibitors of genes that regulate AP-1: pharmacology and clinical development

Synthesis of new OBAN's and further studies on positioning of the catalytic group

Two new zinc ion dependent oligonucleotide based artificial nucleases (OBAN's) have been synthesized. These consist of 2'-O-methyl modified RNA oligomers conjugated to 5-amino-2,9-dimethylphenanthroline (neocuproine)via a urea linker. OBAN 4 carries the catalytic group on a linker extending from the C-4 of an internal cytosine moiety. OBAN 5 has two neocuproine units attached, each to linkers extending from the C-5 position of uridine moieties, one placed internally and the other at the at the 5'-end of the oligonucleotide. The key step in the synthesis of the OBAN systems is conjugation of the catalytic group to the respective amino linkers of the modified oligonucleotides. This is achieved by first converting the 5-amino-2,9-dimethylphenanthroline to the phenylcarbamate. The reaction of this neocuproine phenylcarbamate with the oligonucleotide carrying one or two primary aliphatic amines in aqueous buffer (at pH 8.5) leads to nearly quantitative formation of the urea-linked conjugates. Both OBAN systems were found to cleave RNA in the bulged out regions formed from the non-complementary part of the target sequences, in the presence of Zn(II) ions. Differences in efficiency between these and previously reported systems are discussed.

Enhanced activity of antisense phosphorothioate oligos against leishmania amastigotes: augmented uptake of oligo, ribonuclease H activation, and efficient target intervention under altered growth conditions

Leishmania, a parasitic protozoan, infects human macrophages, often causing severe morbidity and mortality. The pathogenic form of this parasite, the amastigote, lives inside the acidic phagolysosomes of infected macrophages. In our attempt to develop anti-miniexon phosphorothioate oligodeoxyribonucleotides (S-oligos) as an alternative chemotherapy against Leishmania, we found that intracellular as well as 'axenic' amastigotes were more susceptible to these S-oligos than were the cultured promastigotes. Lower pH (4.5) and elevated temperature (35 degrees) of the medium were among the direct enhancing factors for killing. Addition of the cationic polypeptide poly-l-lysine (PLL) to the growth medium further enhanced the killing effect of the S-oligo at pH 4.5. The enhancement of specific ablation of mRNA expression was directly correlated to the increased leishmanicidal activity of the S-oligo. This was shown by the increased inhibition of luciferase activity expressed in transgenic Leishmania amazonensis promastigotes by anti-miniexon S-oligo or anti-luciferase S-oligo at acidic pHs and in the presence of PLL. The leishmanicidal effects of S-oligos at acidic pH and in the presence of PLL were related to increased uptake of the S-oligos under these conditions. The rate of S-oligo uptake was enhanced up to 15-fold at pH 4.5. The addition of PLL to the assay medium at acidic pH further enhanced the uptake of S-oligo up to 80-fold. RNase H is known to accentuate the antisense action of S-oligos. We found that at an elevated temperature RNase H activity in Leishmania cell extracts increased about 5-fold. Thus, enhanced uptake of S-oligos at the acidic pH of macrophage phagolysosomes and activation of RNase H may explain the efficient killing of the parasite in macrophages, both in tissue culture and in the animal model, by antisense miniexon oligonucleotide/PLL, when targeted directly to the parasite-containing phagolysosomes.

Cisplatin resistance and oncogenes--a review

Cisplatin is among the most widely used broadly active cytotoxic anticancer drugs; however, its clinical efficacy is often limited by primary or the development of secondary resistance. Several mechanisms have been implicated in cisplatin resistance, including reduced drug uptake, increased cellular thiol/folate levels and increased DNA repair. More recently, additional pathways have been characterized indicating that altered expression of oncogenes that subsequently limit the formation of cisplatin-DNA adducts and activate anti-apoptotic pathways may also contribute to the resistance phenotype. Several lines of evidence suggest that expression of ras oncogenes can confer resistance to cisplatin by reducing drug uptake and increasing DNA repair; however, this is not a uniform finding. Tumor cells, in contrast to normal cells, respond to cisplatin exposure with transient gene expression to protect or repair their chromosomes. The c-fos/AP-1 complex, a master switch for turning on other genes in response to DNA-damaging agents, has been shown to play a major role in cisplatin resistance. In addition, AP-2 transcription factors, modulated by protein kinase A, are also implicated in cisplatin resistance by regulating genes encoding for DNA polymerase beta and metallothionines. Furthermore, considerable evidence indicates that mutated p53 plays a significant role in the development of cisplatin resistance since several genes implicated in drug resistance and apoptosis (e.g. mismatch repair, bcl-2, high mobility group proteins, DNA polymerases alpha and beta, PCNA, and insulin-like growth factor) are known to be regulated by the p53 oncoprotein. Improved understanding of molecular factors for the development of cisplatin resistance may allow the prediction of clinical response to cisplatin-based treatment. Furthermore, the identification of oncogenes involved in cisplatin resistance has already led to in vitro approaches which successfully inactivated these genes using ribozymes or antisense oligodeoxynucleotides, thus restoring cisplatin sensitivity. It is conceivable that these strategies, once transferred to a clinical setting, may have the potential to enhance the efficacy of cisplatin against a great variety of malignancies and thus more fully exploit the antineoplastic and curative potential of this drug.

Antisense oligonucleotides with different backbones. Modification of splicing pathways and efficacy of uptake

A novel, positive read-out assay that quantifies only sequence-specific nuclear activity of antisense oligonucleotides was used to evaluate morpholino and 2'-O-methyl sugar-phosphate oligonucleotides. The assay is based on modification of the splicing pathway of human beta-globin pre-mRNA. In addition, scrape-loading of cells with oligonucleotides allows the separate assessment of intracellular antisense activity of the oligonucleotides and their ability to penetrate the cell membrane barrier. The results show that, with scrape-loading, the morpholino oligonucleotides were approximately 3-fold more effective in their intrinsic antisense activity than alternating phosphodiester/phosphorothioate 2'-O-methyl-oligoribonucleotides and 6-9- and almost 200-fold more effective than the exclusively phosphorothioate and phosphodiester derivatives, respectively. The morpholino oligonucleotides were over 20-fold more effective than the phosphorothioate 2'-O-methyl-oligoribonucleotides in free uptake from the culture media. The antisense activity of the morpholino oligonucleotides was detectable not only in monolayer HeLa cells but also in suspension K562 cells. Time course experiments suggest that both the free uptake and efflux of morpholino oligonucleotides are slow.

Pharmacology of antisense oligonucleotide inhibitors of protein expression

The dramatic increase in recent years of both the amount and rate of accumulation of novel genomic sequence information has generated enormous opportunities for the development of new classes of drugs. For these opportunities to be fully capitalized upon, investigators must choose molecular targets for drug development that are likely to yield attractive therapeutic profiles. This will require rapid and effective determination of gene functions in multiple cellular settings. The development of antisense oligonucleotides as specific inhibitors of gene expression should allow such determination of gene function. In addition, the antisense oligonucleotides themselves will likely prove useful as drugs. In this review, we discuss some of the issues surrounding the use of antisense oligonucleotides as research tools to help elucidate gene function, and highlight some of the approaches that can be taken to generate and use effective antisense reagents.

The Jun kinase 2 isoform is preferentially required for epidermal growth factor-induced transformation of human A549 lung carcinoma cells

We have previously found that epidermal growth factor (EGF) mediates growth through the Jun N-terminal kinase/stress-activated kinase (JNK/SAPK) pathway in A549 human lung carcinoma cells. As observed here, EGF treatment also greatly enhances the tumorigenicity of A549 cells, suggesting an important role for JNK in cancer cell growth (F. Bost, R. McKay, N. Dean, and D. Mercola, J. Biol. Chem. 272:33422-33429, 1997). Several isoforms families of JNK, JNK1, JNK2, and JNK3, have been isolated; they arise from alternative splicing of three different genes and have distinct substrate binding properties. Here we have used specific phosphorothioate oligonucleotides targeted against the two major isoforms, JNK1 and JNK2, to discriminate their roles in EGF-induced transformation. Multiple antisense sequences have been screened, and two high-affinity and specific candidates have been identified. Antisense JNK1 eliminated steady-state mRNA and JNK1 protein expression with a 50% effective concentration (EC50) of <0.1 microM but did not alter JNK2 mRNA or protein levels. Conversely, antisense JNK2 specifically eliminated JNK2 steady-state mRNA and protein expression with an EC50 of 0.1 microM. Antisense JNK1 and antisense JNK2 inhibited by 40 and 70%, respectively, EGF-induced total JNK activity, whereas sense and scrambled-sequence control oligonucleotides had no effect. The elimination of mRNA, protein, and JNK activities lasted 48 and 72 h following a single Lipofectin treatment with antisense JNK1 and JNK2, respectively, indicating sufficient duration for examining the impact of specific elimination on the phenotype. Direct proliferation assays demonstrated that antisense JNK2 inhibited EGF-induced doubling of growth as well as the combination of active antisense oligonucleotides did. EGF treatment also induced colony formation in soft agar. This effect was completely inhibited by antisense JNK2 and combined-antisense treatment but not altered by antisense JNK1 alone. These results show that EGF doubles the proliferation (growth in soft agar as well as tumorigenicity in athymic mice) of A549 lung carcinoma cells and that the JNK2 isoform but not JNK1 is utilized for mediating the effects of EGF. This study represents the first demonstration of a cellular phenotype regulated by a JNK isoform family, JNK2.