ABSTRACT
Peptide nucleic acid (PNA) and locked nucleic acid (LNA) oligomers bind to complementary sequences with extremely high affinity. This high-affinity binding supports the hypothesis that they have advantages for targeting cellular nucleic acids and provide a better route for the development of oligonucleotide-based antiproliferative drugs. This article reviews the properties of PNA and LNA oligomers and describes the challenges that confront their application to cancer therapy.
Subject(s)
Nucleic Acids/therapeutic use , Peptide Nucleic Acids/therapeutic use , Animals , Humans , Nucleic Acids/metabolism , Nucleic Acids/pharmacology , Oligonucleotides, Antisense/therapeutic use , Peptide Nucleic Acids/metabolism , Peptide Nucleic Acids/pharmacology , Ribonuclease H/metabolism , Telomerase/antagonists & inhibitorsABSTRACT
2'-O-(2-methoxyethyl) (2'-MOE) RNA possesses favorable pharmocokinetic properties that make it a promising option for the design of oligonucleotide drugs. Telomerase is a ribonucleoprotein that is up-regulated in many types of cancer, but its potential as a target for chemotherapy awaits the development of potent and selective inhibitors. Here we report inhibition of human telomerase by 2'-MOE RNA oligomers that are complementary to the RNA template region. Fully complementary oligomers inhibited telomerase in a cell extract with IC(50) values of 5-10 nM at 37 degrees C. IC(50) values for mismatch-containing oligomers varied with length and phosphorothioate substitution. After introduction into DU 145 prostate cancer cells inhibition of telomerase activity persisted for up to 7 days, equivalent to six population doublings. Inside cells discrimination between complementary and mismatch-containing oligomers increased over time. Our results reveal two oligomers as especially promising candidates for initiation of in vivo preclinical trials and emphasize that conclusions regarding oligonucleotide efficacy and specificity in cell extracts do not necessarily offer accurate predictions of activity inside cells.
Subject(s)
Enzyme Inhibitors/metabolism , Oligonucleotides/chemistry , Oligonucleotides/metabolism , RNA, Antisense/chemistry , RNA, Antisense/metabolism , Telomerase/antagonists & inhibitors , Animals , Base Pair Mismatch/genetics , Base Pairing , Base Sequence , DNA, Recombinant/chemistry , DNA, Recombinant/genetics , DNA, Recombinant/metabolism , Enzyme Inhibitors/chemistry , Genetic Engineering , Humans , Inhibitory Concentration 50 , Mice , Mice, Nude , Neoplasm Transplantation , Oligonucleotides/genetics , Oligoribonucleotides , RNA/chemistry , RNA/genetics , RNA/metabolism , RNA, Antisense/genetics , Substrate Specificity , Telomerase/genetics , Telomerase/metabolism , Time Factors , Transfection , Tumor Cells, CulturedABSTRACT
Acylfulvenes are a potent class of antitumor agents derived from illudin S, a fungal sesquiterpene. Illudin S possesses antitumor activity but has a poor therapeutic index. Acylfulvene is 100-fold less toxic against human lung adenocarcinoma cells than illudin S, but inhibits tumor growth in human xenografts, opposite to illudin S. An analog of acylfulvene, MGI 114 (hydroxymethylacylfulvene), shows much greater efficacy, producing complete tumor regression in xenograft models. MGI 114 is currently in phase II clinical trials. Cytotoxicity of MGI 114, like that of illudin S, is believed to involve both chemical reaction and enzymatic reduction. Enzymatic reduction by a cytosolic NADPH-dependent enzyme (from rat liver) produced an aromatic metabolite similar to that formed from illudin S. However, the reaction occurred more slowly. In addition, four new metabolites were isolated, two hydroxylated derivatives and two in which the primary allylic hydroxyl was replaced by hydride. All retained the reactive centers of the parent MGI 114.
Subject(s)
Antineoplastic Agents/metabolism , Cytosol/metabolism , Liver/metabolism , Sesquiterpenes/metabolism , Animals , Antineoplastic Agents/toxicity , Biotransformation , Coloring Agents , DNA/metabolism , Humans , In Vitro Techniques , Magnetic Resonance Spectroscopy , Mass Spectrometry , Protein Binding , Rats , Sesquiterpenes/toxicity , Trypan Blue , Tumor Cells, CulturedABSTRACT
Illudins are novel compounds from which a potent class of antitumor agents, called acylfulvenes, have been synthesized. The model illudin, illudin S, has marked in vitro and in vivo toxicity but displays a poor therapeutic index. The toxicity of illudin S is believed to involve a combination of enzymatic reduction and chemical reaction. Enzymatic reduction by a cytosolic NADPH-dependent enzyme produces an aromatic metabolite, as does reaction with thiols. Acylfulvene is formed from illudin S by reverse Prins reaction. Acylfulvene is 100-fold less toxic in vitro and in vivo than illudin S but possesses marked antitumor efficacy in vivo, thus displaying opposite properties from illudin S. For this reason we investigated the in vitro metabolism of acylfulvene. Incubation of acylfulvene with NADPH and rat liver cytosol yielded two metabolites. One metabolite, the aromatic product, is similar to that obtained with illudin S in this in vitro system and was anticipated. The other metabolite, the hydroxylated product, was not expected and no corresponding metabolite for illudin S could be detected. The production of this hydroxylated metabolite from acylfulvene may explain, in part, the increased antitumor activity of novel acylfulvenes as compared with the illudins.
