Novel mycophenolic adenine bis(phosphonate)s as potent anticancer agents and inducers of cells differentiation

Inhibitors of the IMPDH enzyme as potential anti-bovine viral diarrhoea virus agents

Ribavirin and mycophenolic acid (MPA) are known inhibitors of the IMPDH enzyme (E.C. 1.1.1.205). This enzyme catalyzes the conversion of inosine monophosphate to xanthine monophosphate, leading eventually to a decrease in the intracellular level of GTP and dGTP. The antiviral effect against bovine viral diarrhoea virus (BVDV) of 15 analogues related to MPA was determined. MDBK cells were infected with the cytopathic strain of BVDV in presence or absence of test compounds. Viral RNA was extracted from the cell supernatant fluids and quantified by RT-PCR. Ribavirin showed a potent antiviral effect against BVDV with 90% effective concentration (EC90) of 4 microM. MPA along with several analogues, including both its corresponding aldehyde and alcohol, and modifications in the length of the side chain (C2- and C4-derivatives) were tested. We have identified previously unreported IMPDH inhibitors that have potent anti-BVDV activity, namely: C6-MPAlc (5), C6-MPA-Me (7), C4-MPAlc (8), C4-MPA (10) and C2-MAD (20). Most of these compounds inhibited the IMPDH enzyme in the nanomolar range (4-800 nM) in cell-free assays. Some compounds, such as mizoribine, which is a potent inhibitor of IMPDH in vitro (enzyme 50% inhibitory concentration IC50=4 nM), had no detectable anti-BVDV activity up to 100 microM. The compounds were essentially non-toxic to a confluent monolayer of MDBK cells. However, in exponentially growing cells, they showed minimal toxicity at 100 microM over a 24 h period, but the toxicity was more pronounced after 3 days [50% cytotoxic concentration (CC50) value ranged from 5 to 30 microM].

Cytotoxicity and cellular differentiation activity of methylenebis(phosphonate) analogs of tiazofurin and mycophenolic acid adenine dinucleotide in human cancer cell lines

Mycophenolic acid (MPA) is a fungally-derived inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH). MPA binds IMPDH at the nicotinamide sub-site of the NAD cofactor binding domain leaving the adenosine sub-site empty. In order to improve the binding affinity we synthesized MPA analogs by linking adenosine 5'-methylenebis(phosphonate) with mycophenolic alcohols containing 2-, 4-, and 6-carbon atoms in their aliphatic side chain. Adenine dinucleotide analogs of tiazofurin, selenazofurin and benzamide riboside were synthesized as P1, P2-disubstituted pyrophosphates. Cytotoxicity of each analog was examined in human colon adenocarcinoma HT-29 and erythroleukemia K562 cells, and induction of differentiation in K562 cells by these agents was determined. Mycophenolic acid is currently used as an immunosuppressant but its anticancer action is limited by inactivation due to rapid glucuronidation. The new analogs show resistance to metabolism to inactive species and exhibit enhanced cytotoxicity in tumor cell lines, and therefore could be useful as anticancer agents.

Novel mycophenolic adenine bis(phosphonate) analogues as potential differentiation agents against human leukemia

Novel mycophenolic adenine dinucleotide (MAD) analogues have been prepared as potential inhibitors of inosine monophosphate dehydrogenase (IMPDH). MAD analogues resemble nicotinamide adenine dinucleotide binding at the cofactor binding domain of IMPDH; however, they cannot participate in hydride transfer and therefore inhibit the enzyme. The methylenebis(phosphonate) analogues C2-MAD and C4-MAD were obtained by coupling 2',3'-O-isopropylideneadenosine 5'-methylenebis(phosphonate) (22) with mycophenolic alcohols 20 and 21 in the presence of diisopropylcarbodiimide followed by deprotection. C2-MAD was also prepared by coupling of mycophenolic methylenebis(phosphonate) derivative 30 with 2',3'-O-isopropylideneadenosine. Compound 30 was conveniently synthesized by the treatment of benzyl-protected mycophenolic alcohol 27 with a commercially available methylenebis(phosphonic dichloride) under Yoshikawa's reaction conditions. C2-MAD and C4-MAD were found to inhibit the growth of K562 cells (IC(50) = 0.7 microM and IC(50) = 0.1 microM, respectively) as potently as mycophenolic acid (IC(50) = 0.3 microM). In addition, C2-MAD and C4-MAD triggered vigorous differentiation of K562 cells an order of magnitude more potently than tiazofurin, and MAD analogues were resistant to glucuronidation in vitro. These results show that C2-MAD and C4-MAD may be of therapeutic interest in the treatment of human leukemias.