Antimetabolites: molecular design and mode of action

Comparison of the anticancer properties of a novel valproic acid prodrug to leading histone deacetylase inhibitors

The HDAC inhibitory activity of valproic acid (VPA) has led to on-going evaluation of it as an anticancer agent. The histone deacetylase (HDAC) inhibitor AN446, a prodrug of VPA, releases the acid upon metabolic degradation. AN446 is >60-fold more potent than VPA in killing cancer cells in vitro. Herein, we compare the activities of AN446, as an anticancer agent, to those of representative types from each of the four major classes of HDAC inhibitors (HDACIs): vorinostat, romidepsin, entinostat, and VPA. AN446 exhibited the greatest selectivity and HDAC inhibitory activity against cancer cells. In glioblastoma cells only AN446, and in MDA-MB-231 cells only AN446 and VPA interacted in synergy with doxorubicin (Dox). AN446 was superior to the studied HDACIs in inducing DNA-damage in cancer cells, while in normal astrocytes and cardiomyoblasts AN446 was the least toxic. AN446 was the only HDACI tested that exhibited selective HDAC inhibitory activity that was high in cancer cells and low in noncancerous cells. This discriminating inhibition correlated with the toxicity of the HDACIs, suggesting that their effects could be attributed to HDAC inhibition. In cardiomyoblasts, the HDACIs tested, except for AN446, hampered DNA repair by reducing the level of Rad 51. VPA and AN446 were the most effective HDACIs in inhibiting in vitro migration and invasion. The advantages of AN446 shown here, position it as a potentially improved HDACI for treatment of glioblastoma and triple negative breast cancer.

Structure-activity relationships and mode of action of 5-mercapto-substituted oligo- and polynucleotides as antitemplates inhibiting replication of human immunodeficiency virus type 1

Introduction of a reactive 5-mercapto group into some of the cytosine and/or uracil bases of various oligo- and polynucleotides by partial thiolation resulted in several potent inhibitors of the replication of human immunodeficiency virus type 1 (HIV-1) in primary human lymphocytes. These compounds exhibited little if any toxicity against uninfected peripheral blood mononuclear cells and showed 15 to 75 times higher antitemplate activity against a p66/p51 HIV-1 recombinant reverse transcriptase (RT) than against the DNA polymerase alpha from human lymphocytes. In contrast, the unthiolated oligo- and polynucleotides are void of antitemplate activity, and their apparent inhibitory effect on HIV-1 closely paralleled their toxicity for the cells. Partially thiolated poly(dC) (MPdC) was the most potent of all the compounds tested against HIV-1 in peripheral blood mononuclear cells (50% effective concentration, 1.8 micrograms/ml or 0.019 microM), while showing low cytotoxicity (greater than 100 micrograms/ml). The corresponding unmodified poly(dC) showed no anti-HIV-1 activity at 50 micrograms/ml but had pronounced cytotoxicity. MPdC was also a potent inhibitor of HIV-1 RT (50% inhibitory concentration, 0.30 micrograms/ml). The inhibitory activities of thiolated homooligo(dCs) against both HIV-1 replication and HIV-1 RT increased with increasing chain length. The heterooligonucleotides included in this study were designed as structural analogs of portions of the natural primer of HIV-1 RT, i.e., tRNA(3Lys). An 18-mer analog of the 3' terminus, complementary (antisense) to the primer-binding site of the HIV-1 genome, was attached to an oligo(dC) tail and 5-thiolated; this increased its activity and decreased its toxicity. This compound will serve as a new lead in the development of more effective antitemplates against HIV-1.

Synthesis and properties of poly 5-methylthiouridylic acid

In an effort to search for good methods for the enzymatic synthesis of polynucleotide analogs with antitemplate activity, 5-methylthiouridine-5'-diphosphate (ms5UDP) has been synthesized and investigated as a substrate for polynucleotide phosphorylase. While ms5UDP was polymerized at a very low rate to give a 6% yield of polynucleotides by the polynucleotide phosphorylase of Micrococcus luteus, it was utilized more efficiently by the corresponding enzyme of Escherichia coli resulting in a 15% yield of poly (5-methylthiouridylic) acid. Results of the co-polymerization of ms5UDP and UDP revealed that the ratio of 5-methylthiouridylate to uridylate residues in the polynucleotide product was lower than the ratio of ms5UDP to UDP in the substrate mixture. The 5-methylthio group conferred only minute changes on the conformation of the modified polyuridylic acid, and the complexes formed between poly-(5-methylthiouridylic) acid and poly(adenylic) acid possessed slightly higher Tm values than did the unmodified counterparts. Poly(5-methylthiouridylic) acid was a potent inhibitor of calf thymus DNA polymerase alpha.

Enzymatic synthesis of polyuridylic acid containing modified bases

5'Mercaptouridine-5'-diphosphate (hs5UDP) has been synthesized and investigated as a substrate of the polynucleotide phosphorylase of Micrococcus luteus. While hs5UDP is not utilized alone, it can be copolymerized with UDP; however, unusually for this enzyme, the ratio of 5'mercaptouridylate vs. uridylate residues in the polynucleotide product (MPU) is always lower than the ratio of hs5UDP v. UDP in the substrate mixture. Furthermore, hs5UDP decreases the rate of the enzymic polymerization reaction. The MPU product forms two-stranded and three-stranded complexes with poly(A). The circular dichroic spectra of these complexes are similar to those formed between poly(U) and poly(A), but their melting profiles indicate somewhat lower stability. The physicochemical and biochemical properties of the enzymic product are qualitatively similar to those of MPU prepared by chemical modification; both are potent inhibitors of a DNA-dependent RNA polymerase.