Antisense strategy in malignant brain tumours treatment.

Malignant glioma, the most common human brain cancer, is almost uniformly fatal. Median survival is less than one year. The principal strategies of gene therapy for treatment of gliomas, including antisense approach, have been proposed comming from 1990s [1, 2, 3, 4]. The antisense oligonucleotides become the important tool of anti-cancer approach [5, 6]. The "discovery" of antisense approach was done by the groupes of R.M. Harland and of F. Jacob [7, 8]; the untranscribed DNA strand, that has been regarded only as a stabilizer and a protector of genetic material, was shown to reveal transcription activity [9]. It has also been widely proven that a lot of genes present an open reading frame on its antisense strand. Open reading frame on the antisense strand has been found in all genomes studied, both in prokaryotes and eukaryotes [10]. Different molecular pathways altered in cancer were exploited as potential the antisense strand has been found in all genomes studied , both in prokaryotes and eukaryotes [10]. On the basis of mechanism of action, two classes of antisense oligonucleotide can be discerned: (a) the RNase H-dependent oligonucleotides, which induce the degradation of mRNA; and (b) the steric-blocker oligonu-cleotides, which physically prevent or inhibit the progression of splicing or the translational machinery. The majority of the antisense drugs investigated in the clinic functions via an RNase H-dependent mechanism [5]. In prokaryotes and eukaryotes genetic information is supported by double-stranded DNA in which only one strand (sense strand) is usually transcribed to messenger RNA. The second strand is called the antisense strand because its sequence of nucleotides is the complement of message sense. This observation gave the origin to many antisense (as well as nonsense) approaches based on antisense RNA or antisense oligonucleotides, both targeting genes involved in pathological cellular processes. The antisense RNA is delivered to the cells either by a plasmid vector (dsDNA) encoding an antisense RNA or by a single sequence of nucleotides is the complement of message sense). The antisense RNA sequence is then produced by intracellular transcription of plasmid vector and is able to hybridize to the mRNA with subsequent translation blockade. Once hybridiza-tion occurs, the duplex RNA-RNA (DNA) stimulates ribonuclease H, the enzyme involved in DNA replication [11]. The first antisense oligonucleotide used in clinical pharmacolo-gy was as anti-cytomegalovirus therapy (VitraveneTM) [12]. The antisense strategy was then largely used in order to analyze gene expression and intron splicing. …