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Aims: Folate receptors (FRs) mediate cellular uptake of folates in many cancer cells and in folate deficiency heterogeneous nuclear ribonucleoprotein E1 (hnRNP-E1) mediates translational upregulation of FR in cultured cervical [...]

Background: Previously, we determined that heterogeneous nuclear ribonucleoprotein E1 (hnRNP-E1) functions as an intracellular physiologic sensor of folate deficiency. In this model, l-homocysteine, which accumulates intracellularly in proportion to the extent of folate deficiency, covalently binds to and thereby activates homocysteinylated hnRNP-E1 to interact with folate receptor-α mRNA; this high-affinity interaction triggers the translational upregulation of cell surface folate receptors, which enables cells to optimize folate uptake from the external milieu. However, integral to this model is the need for ongoing generation of hnRNP-E1 to replenish homocysteinylated hnRNP-E1 that is degraded. Objective: We searched for an interrelated physiologic mechanism that could also maintain the steady-state concentration of hnRNP-E1 during prolonged folate deficiency. Methods: A novel RNA-protein interaction was functionally characterized by using molecular and biochemical approaches in vitro and in vivo. Results: l-homocysteine triggered a dose-dependent high-affinity interaction between hnRNP-E1 and a 25-nucleotide cis element within the 5'-untranslated region of hnRNP-E1 mRNA; this led to a proportionate increase in these RNA-protein complexes, and translation of hnRNP-E1 both in vitro and within placental cells. Targeted perturbation of this RNA-protein interaction either by specific 25-nucleotide antisense oligonucleotides or mutation within this cis element or by small interfering RNA to hnRNP-E1 mRNA significantly reduced cellular biosynthesis of hnRNP-E1. Conversely, transfection of hnRNP-E1 mutant proteins that mimicked homocysteinylated hnRNP-E1 stimulated both cellular hnRNP-E1 and folate receptor biosynthesis. In addition, ferrous sulfate heptahydrate [iron(II)], which also binds hnRNP-E1, significantly perturbed this l-homocysteine-triggered RNA-protein interaction in a dose-dependent manner. Finally, folate deficiency induced dual upregulation of hnRNP-E1 and folate receptors in cultured human cells and tumor xenografts, and more selectively in various fetal tissues of folate-deficient dams. Conclusions: This novel positive feedback loop amplifies hnRNP-E1 during prolonged folate deficiency and thereby maximizes upregulation of folate receptors in order to restore folate homeostasis toward normalcy in placental cells. It will also functionally impact several other mRNAs of the nutrition-sensitive, folate-responsive posttranscriptional RNA operon that is orchestrated by homocysteinylated hnRNP-E1., (© 2017 American Society for Nutrition.)

We synthesized a series of serum-stable covalently linked drugs derived from 3'-C-methyladenosine (3'-Me-Ado) and valproic acid (VPA), which are ribonucleotide reductase (RR) and histone deacetylase (HDAC) inhibitors, respectively. While the combination of free VPA and 3'-Me-Ado resulted in a clear synergistic apoptotic effect, the conjugates had lost their HDAC inhibitory effect as well as the corresponding apoptotic activity. Two of the analogs, 2',5'-bis-O-valproyl-3'-C-methyladenosine (A160) and 5'-O-valproyl-3'-C-methyladenosine (A167), showed promising cytotoxic activities against human hematological and solid cancer cell lines. A167 was less potent than A160 but had interesting features as an RR inhibitor. It inhibited RR activity by competing with ATP as an allosteric effector and concomitantly reduced the intracellular deoxyribonucleoside triphosphate (dNTP) pools. A167 represents a novel lead compound, which in contrast to previously used RR nucleoside analogs does not require intracellular kinases for its activity and therefore holds promise against drug resistant tumors with downregulated nucleoside kinases., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Most cases of cervical cancer are associated with human papilloma virus (HPV) infection of high risk types. In folate deficiency, heterogeneous nuclear ribonucleoprotein E1 (hnRNP-E1) interferes with HPV16 viral capsid protein synthesis. We aimed to study the importance of 1-carbon metabolism in cervical carcinogenesis by examining serum vitamin B12 (cobalamin), homocysteine, folate levels, and the RNA and protein expression of HPV16 L1, L2, E6, E7, and to correlate them with hnRNP-E1 expression and HPV infection in normals, squamous intraepithelial lesions (SILs), and cervical cancer subjects. Serum cobalamin, folate, and homocysteine were estimated using kits, RNA by real time PCR and proteins by Western blotting. We observed that lower folate and vitamin B12 levels were associated with HPV infection. hnRNP-E1 progressively decreased from normals (100%) to SILs (75%) to cervical cancer (52.6%). The findings show that HPV16 E6 and E7 are overexpresed whereas HPV16 L1 and L2 are downregulated at mRNA and protein levels in cervical cancer as compared to normals and SILs. The results indicate that perhaps the reduced expression of hnRNP-E1 might be involved with the cervical cancer pathogenesis, with folate playing a role in the natural history of HPV infection.

Colorectal cancer cells exhibit limited cytotoxicity towards Tiazofurin, a pro-drug metabolized by cytosolic nicotinamide mononucleotide adenylyltransferase2 (NMNAT2) to thiazole-4-carboxamide adenine dinucleotide, a potent inhibitor of inosine 5'-monophosphate dehydrogenase required for cellular guanylate synthesis. We tested the hypothesis that colorectal cancer cells that exhibit low levels of NMNAT2 and are refractory to Tiazofurin can be rendered sensitive to Tiazofurin by overexpressing NMNAT2. Transfection of hNMNAT2 resulted in a six- and threefold cytoplasmic overexpression in Caco2 and HT29 cell lines correlating with Tiazofurin-induced enhanced cell-kill. Folate receptors expressed on the cell surface of 30-50% colorectal carcinomas were exploited for cellular targeting with Tiazofurin encapsulated in folate-tethered nanoparticles. Our results indicated that in wild-type colorectal cancer cells, free Tiazofurin-induced EC50 cell-kill was 1500-2000 μM, which was reduced to 66-156 μM in hNMNAT2-overexpressed cells treated with Tiazofurin encapsulated in non-targeted nanoparticles. This efficacy was improved threefold by encapsulating Tiazofurin in folate-tethered nanoparticles to obtain an EC(50) cell-kill of 22-59 μM, an equivalent of 100-300 mg m(-2) (one-tenth of the approved dose of Tiazofurin in humans), which will result in minimal toxicity leading to cancer cell-kill. This proof-of-principle study suggests that resistance of colorectal cancer cell-kill to Tiazofurin can be overcome by sequentially overexpressing hNMNAT2 and then facilitating the uptake of Tiazofurin by folate-tethered nanoparticles, which enter cells via folate receptors.

Purpose: This pilot trial assesses variability of apoptosis and response 1 day after hepatic intraarterial (IA) benzamide riboside (BR) in rodent hepatomas and its correlation to water apparent diffusion coefficient (ADC) and single-quantum (SQ) and triple-quantum-filtered (TQF) sodium-23 ((23)Na) magnetic resonance (MR) imaging., Materials and Methods: Sprague-Dawley rats (n = 8) were inoculated with 10(6) N1-S1 cells. IA BR (20 mg/kg) was infused after 14 days. Animals were killed 1 day (n = 4) or 21 days (n = 4) after therapy. Imaging was performed 1 day before and after treatment. Volume was assessed over 2 weeks. Percentage apoptosis was counted from terminal deoxynucleotidyl transferase dUTP nick-end labeling-stained slides at 400×magnification. Kruskal-Wallis tests were used to compare apoptosis, and Wilcoxon signed-rank tests were used to compare MR signal intensity (SI)., Results: Apoptosis was marginally greater in tumor than in nontumor (6.7% vs 1.3%; P = .08), varying from 2% to 10%. Before treatment, MR SI was greater in tumor than in nontumor (ADC, 1.18 vs 0.76 [P = .0078]; SQ, 1.20 vs 1.04 [P = .03]; TQF, 0.55 vs 0.34 [P = .03]). After treatment, tumors increased in volume (0.62 vs 0.33; P = .016) variably over 2 weeks. MR SI remained greater in tumor than in nontumor (ADC, 1.20 vs 0.77 [P = .0078]; SQ, 1.76 vs 1.15 [P = .016]; TQF, 0.84 vs 0.49 [P = .03]). SQ and TQF SI increased by 47% (P = .016) and 53% (P = .016) in tumors, whereas ADC did not change., Conclusions: Apoptosis was marginal and varied from 2% to 10%. Water ADC, SQ, and TQF MR imaging distinguished tumor from nontumor. Changes in water ADC and sodium MR imaging correlated to apoptosis and volume in select cases, but additional animals are needed to validate this trend against tumor growth., (Copyright © 2013 SIR. Published by Elsevier Inc. All rights reserved.)

Purpose: Benzamide riboside (BR) induces tumor apoptosis in multiple cell lines and animals. This pilot study compares apoptosis and tumor response in rat hepatomas treated with hepatic arterial BR (IA) or intravenous (IV) BR., Methods: A total of 10(6) N1-S1 cells were placed in the left hepatic lobes of 15 Sprague-Dawley rats. After 2 weeks, BR (20 mg/kg) was infused IA (n=5) or IV (n=5). One animal in each group was excluded for technical factors, which prevented a full dose administration (1 IA and 1 IV). Five rats received saline (3 IA and 2 IV). Animals were killed after 3 weeks. Tumor volumes after IA and IV treatments were analyzed by Wilcoxon rank sum test. The percentage of tumor and normal liver apoptosis was counted by using 10 fields of TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling)-stained slides at 40× magnification. The percentage of apoptosis was compared between IV and IA administrations and with saline sham-treated rats by the Wilcoxon rank sum test., Results: Tumors were smaller after IA treatment, but this did not reach statistical significance (0.14 IA vs. 0.57 IV; P=0.138). There was much variability in percentage of apoptosis and no significant difference between IA and IV BR (44.49 vs. 1.52%; P=0.18); IA BR and saline (44.49 vs. 33.83%; P=0.66); or IV BR and saline (1.52 vs. 193%; P=0.18)., Conclusions: Although differences in tumor volumes did not reach statistical significance, there was a trend toward smaller tumors after IA BR than IV BR in this small pilot study. Comparisons of these treatment methods will require a larger sample size and repeat experimentation.

Although HPV16 transforms infected epithelial tissues to cancer in the presence of several co-factors, there is insufficient molecular evidence that poor nutrition has any such role. Because physiological folate deficiency led to the intracellular homocysteinylation of heterogeneous nuclear ribonucleoprotein E1 (hnRNP-E1) and activated a nutrition-sensitive (homocysteine-responsive) posttranscriptional RNA operon that included interaction with HPV16 L2 mRNA, we investigated the functional consequences of folate deficiency on HPV16 in immortalized HPV16-harboring human (BC-1-Ep/SL) keratinocytes and HPV16-organotypic rafts. Although homocysteinylated hnRNP-E1 interacted with HPV16 L2 mRNA cis-element, it also specifically bound another HPV16 57-nucleotide poly(U)-rich cis-element in the early polyadenylation element (upstream of L2L1 genes) with greater affinity. Together, these interactions led to a profound reduction of both L1 and L2 mRNA and proteins without effects on HPV16 E6 and E7 in vitro, and in cultured keratinocyte monolayers and HPV16-low folate-organotypic rafts developed in physiological low folate medium. In addition, HPV16-low folate-organotypic rafts contained fewer HPV16 viral particles, a similar HPV16 DNA viral load, and a much greater extent of integration of HPV16 DNA into genomic DNA when compared with HPV16-high folate-organotypic rafts. Subcutaneous implantation of 18-day old HPV16-low folate-organotypic rafts into folate-replete immunodeficient mice transformed this benign keratinocyte-derived raft tissue into an aggressive HPV16-induced cancer within 12 weeks. Collectively, these studies establish a likely molecular linkage between poor folate nutrition and HPV16 and predict that nutritional folate and/or vitamin-B(12) deficiency, which are both common worldwide, will alter the natural history of HPV16 infections and also warrant serious consideration as reversible co-factors in oncogenic transformation of HPV16-infected tissues to cancer.

The mechanism underlying the sensing of varying degrees of physiological folate deficiency, prior to adaptive optimization of cellular folate uptake through the translational up-regulation of folate receptors (FR) is unclear. Because homocysteine, which accumulates intracellularly during folate deficiency, stimulated interactions between heterogeneous nuclear ribonucleoprotein E1 (hnRNP-E1) and an 18-base FR-α mRNA cis-element that led to increased FR biosynthesis and net up-regulation of FR at cell surfaces, hnRNP-E1 was a plausible candidate sensor of folate deficiency. Accordingly, using purified components, we evaluated the physiological basis whereby L-homocysteine triggered these RNA-protein interactions to stimulate FR biosynthesis. L-homocysteine induced a concentration-dependent increase in RNA-protein binding affinity throughout the range of physiological folate deficiency, which correlated with a proportionate increase in translation of FR in vitro and in cultured human cells. Targeted reduction of newly synthesized hnRNP-E1 proteins by siRNA to hnRNP-E1 mRNA reduced both constitutive and L-homocysteine-induced rates of FR biosynthesis. Furthermore, L-homocysteine covalently bound hnRNP-E1 via multiple protein-cysteine-S-S-homocysteine mixed disulfide bonds within K-homology domains known to interact with mRNA. These data suggest that a concentration-dependent, sequential disruption of critical cysteine-S-S-cysteine bonds by covalently bound L-homocysteine progressively unmasks an underlying RNA-binding pocket in hnRNP-E1 to optimize interaction with FR-α mRNA cis-element preparatory to FR up-regulation. Collectively, such data incriminate hnRNP-E1 as a physiologically relevant, sensitive, cellular sensor of folate deficiency. Because diverse mammalian and viral mRNAs also interact with this RNA-binding domain with functional consequences to their protein expression, homocysteinylated hnRNP-E1 also appears well positioned to orchestrate a novel, nutrition-sensitive (homocysteine-responsive), posttranscriptional RNA operon in folate-deficient cells.

Nicotinamide adenine dinucleotide (NAD+) is synthesized by the action of nicotinamide mononucleotide adenylyltransferase (NMNAT) from NMN and ATP. The mouse homolog of NMNAT-2 (mmNMNAT-2) was cloned, expressed, and subsequently identified using MALDI-TOF in conjunction with the ProFound database. Circular dichroism analyses of recombinant mmNMNAT-2 showed α helical and β sheet secondary structures, consistent with the known structure of the human isoform. Competition experiments using mouse pancreatic tissue lysates with recombinant mmNMNAT-2 demonstrated that the activity of the expressed protein was similar to the human isoform. Immunohistochemistry of mouse embryonic tissues with hNMNAT-2 also showed a tissue- and cellular-specific expression of this isoform. Therefore, our studies demonstrate for the first time the clear biological evidence for the existence of a mouse isoform of hNMNAT-2. These studies may help in future investigations aimed at understanding the regulation of this gene and its pathway, and in turn, will spur the development of novel therapies for diseases such as cancer and diabetes since mice are the most frequently used experimental system for in vivo studies.

Aim: To monitor the effects of the apoptotic agent benzamide riboside (BR) on tumor volume and water apparent diffusion coefficient (ADC) in rat hepatocellular carcinoma (HCC)., Materials and Methods: Water ADC of the tumors and nearby liver tissue was measured using diffusion-weighted 1H MRI (DWI). The two groups of BR-treated animals, which differed in their sensitivity to the treatment, were identified as responsive (RBR) and non-responsive (NRBR)., Results: Tumor growth in the RBR group was arrested and the mean tumor volume in this group was 1/6th and 1/16th compared to that of the NRBR group on days 7 and 14 after treatment, respectively. Water ADC of HCC was higher than in nearby normal liver tissue. Before BR treatment, the mean water ADC was significantly higher in the RBR group compared to the NRBR group. BR therapy did not change the water ADC value regardless of tumor sensitivity., Conclusion: Although the water ADC did not change after chemotherapy by BR, DWI has great potential for detecting and predicting response to chemotherapy in HCC.

A series of N6-aminopurine-9-β-D-ribonucleosides and ribose-modified 3'-C-methyl analogues substituted at N6-position with a small group like hydroxy, methoxy or amino group or at C2(N6) position have been synthesized and tested against a panel of human leukemia and carcinoma cell lines. N6-Hydrazino-9-β-D-ribofuranosyl-purine (5) displayed the best antiproliferative activity in the low micromolar or submicromolar range against all tested tumor cell lines. The activity of this nucleoside is related in part to ribonucleotide reductase inhibition. C2-modification or 3'-C-methylation in N6-substituted adenosine analogues leads to a decrease or loss in activity., (Copyright © 2011 Elsevier Masson SAS. All rights reserved.)

Cofactor-type inhibitors of inosine monophosphate dehydrogenase (IMPDH) that target the nicotinamide adenine dinucleotide (NAD) binding domain of the enzyme are modular in nature. They interact with the three sub-sites of the cofactor binding domain; the nicotinamide monophosphate (NMN) binding sub-site (N sub-site), the adenosine monophosphate (AMP) binding sub-site (A sub-site), and the pyrophosphate binding sub-site (P sub-site or P-groove). Mycophenolic acid (MPA) shows high affinity to the N sub-site of human IMPDH mimicking NMN binding. We found that the attachment of adenosine to the MPA through variety of linkers afforded numerous mycophenolic adenine dinucleotide (MAD) analogues that inhibit the two isoforms of the human enzyme in low nanomolar to low micromolar range. An analogue 4, in which 2-ethyladenosine is attached to the mycophenolic alcohol moiety through the difluoromethylenebis(phosphonate) linker, was found to be a potent inhibitor of hIMPDH1 (K(i)=5 nM), and one of the most potent, sub-micromolar inhibitor of leukemia K562 cells proliferation (IC(50)=0.45 μM). Compound 4 was as potent as Gleevec (IC(50)=0.56 μM) heralded as a 'magic bullet' against chronic myelogenous leukemia (CML). MAD analogues 7 and 8 containing an extended ethylenebis(phosphonate) linkage showed low nanomolar inhibition of IMPDH and low micromolar inhibition of K562 cells proliferation. Some novel MAD analogues described herein containing linkers of different length and geometry were found to inhibit IMPDH with K(i)'s lower than 100 nM. Thus, such linkers can be used for connection of other molecular fragments with high affinity to the N- and A-sub-site of IMPDH., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Nicotinamide mononucleotide adenylyltransferease (NMNAT), a rate-limiting enzyme present in all organisms, reversibly catalyzes the important step in the biosynthesis of NAD from ATP and NMN. NAD and NADP are used reversibly in anabolic and catabolic reactions. NAD is necessary for cell survival in oxidative stress and DNA damage. Based on their localization, three different NMNAT's have been recognized, NMNAT-1 (homohexamer) in the nucleus (chromosome 1 p32-35), NMNAT-2 (homodimer) in the cytoplasm (chromosome 1q25) and NMNAT-3 (homotetramer) in the mitochondria. NMNAT also catalyzes the metabolic conversion of potent antitumor prodrugs like tiazofurin and benzamide riboside to their active forms which are analogs of NAD. NAD synthase-NMNAT acts as a chaperone to protect against neurodegeneration, injury-induced axonal degeneration and also correlates with DNA synthesis during cell cycle. Since its activity is rather low in tumor cells it can be exploited as a source for therapeutic targeting. Steps involved in NAD synthesis are being utilized as targets for chemoprevention, radiosensitization and therapy of wide range of diseases, such as cancer, multiple sclerosis, neurodegeneration and Huntington's disease.

Small molecules that act on multiple biological targets have been proposed to combat the drug resistance commonly observed for cancer chemotherapy. By combining the structural features of known inhibitors of inosine monophosphate dehydrogense (IMPDH) and histone deacetylase (HDAC), dual inhibitors of IMPDH and HDAC based on the scaffold of cinnamic hydroxamic acid (CHA) have been designed, synthesized, and evaluated in biological assays. Key features, including the linker length, linker functionality, substitution position, and interacting groups, have been explored. Their individual contribution to the inhibitory activities against human IMPDH1 and IMPDH2 as well as HDAC has been assessed., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Benzamide riboside (BR) is a novel anticancer agent exhibiting potent cytotoxic activity in malignant cell lines. However, the mechanism of induction of apoptosis is not clear. The purpose of this study was to elucidate the apoptotic signaling induced by BR on different human cancer cell lines. Our results revealed that BR at a dose of 50 microM induces apoptosis in SiHa, Hep2, and Ca Ski cells as studied by morphology and flow cytometry. A downregulation of anti-apoptotic proteins Bcl-2 and Bcl-xL was observed, whereas the expression level of the pro-apoptotic protein Bax remained unaffected. An upregulation of p53 was observed while no change was seen on the level of apoptosis inducing factor (AIF). A significant increase in caspase-3 and -9 activities was seen, which was accompanied by PARP cleavage. Release of cytochrome c from the mitochondria to the cytosol was also observed. Taken together, the findings suggest that BR induces apoptosis in SiHa, Hep2, and Ca Ski cells via the intrinsic mitochondrial pathway.

Background: AMP-dependent protein kinase (AMPK) and peroxisome proliferator-activated receptor (PPAR) alpha facilitate fatty acid oxidation. We have shown that treatment of hepatoma cells with ethanol or feeding ethanol-containing diets to mice inhibited both PPARalpha and AMPK activity. Importantly, WY-14,643 reversed the development of fatty liver in alcohol-fed mice. Whether WY-14,643, a PPARalpha agonist, has any effects on AMPK is not known. The aim of this study was to investigate the effect of WY-14,643 on AMPK activity., Methods: The effect of WY-14,643 on AMPK phosphorylation and activity were examined in rat hepatoma cells (H4IIEC3). The effect of WY-14,643 on upstream kinases of AMPK, PKC-zeta/LKB1, intracellular AMP:ATP ratio, oxidative stress, and AMPK gene expression were studied., Results: Treatment of the H4IIEC3 cells with WY-14,643 for 24h led to 60% increase in the phosphorylation of AMPK. The effect of WY-14,643 on AMPK phosphorylation is PKC-zeta/LKB1 independent. WY-14,643 did not alter the levels of intracellular AMP:ATP ratio and it did not increase the levels of reactive oxygen species at 24-h of treatment. WY-14,643-induced AMPK alpha subunit expression by 2- to 2.5-fold, but there was no change in AMPKalpha subunit protein at 24h. The effect of WY-14,643 on AMPK phosphorylation did not altered by the presence of an NADPH oxidase inhibitor., Conclusions: WY-14,643 induced AMPKalpha subunit phosphorylation and the activity of the enzyme. This was associated with induction of AMPKalpha1 and alpha2 mRNA, but the mechanism for this activation is uncertain.

The present study was undertaken to assess the technical feasibility of transfemoral hepatic artery catheterization in rats and to describe the imaging techniques that can be used on tumors in rats. A total of 106 N1-S1 cells were inoculated into the left lobes of 74 rats. In 17, transfemoral angiography was attempted. Tumor volumes for 2 weeks before angiography were measured with magnetic resonance imaging in 40 animals. Tumors grew in 63 animals. Angiography was successful in 16 rats. Mean tumor volumes were 0.13 mL and 0.9 mL after 1 and 2 weeks, respectively. In conclusion, transfemoral hepatic artery catheterization is feasible in this animal model.

AMP-activated protein kinase (AMPK) responds to oxidative stress. Previous work has shown that ethanol treatment of cultured hepatoma cells and of mice inhibited the activity of AMPK and reduced the amount of AMPK protein. Ethanol generates oxidative stress in the liver. Since AMPK is activated by reactive oxygen species, it seems paradoxical that ethanol would inhibit AMPK in the hepatoma cells. In an attempt to understand the mechanism whereby ethanol inhibits AMPK, we studied the effect of ethanol on AMPK activation by exogenous hydrogen peroxide. The effects of ethanol, hydrogen peroxide, and inhibitors of protein phosphatase 2A (PP2A) [either okadaic acid or PP2A small interference RNA (siRNA)] on AMPK phosphorylation and activity were examined in rat hepatoma cells (H4IIEC3) and HeLa cells. In H4IIEC3 cells, hydrogen peroxide (H(2)O(2), 1 mM) transiently increased the level of phospho-AMPK to 1.5-fold over control (P < 0.05). Similar findings were observed in HeLa cells, which do not express the upstream AMPK kinase, LKB1. H(2)O(2) markedly increased the phosphorylation of LKB1 in H4IIEC3 cells. Ethanol significantly inhibited the phosphorylation of PKC-zeta, LKB1, and AMPK caused by exposure to H(2)O(2). This inhibitory effect of ethanol required its metabolism. More importantly, the inhibitory effects of ethanol on H(2)O(2)-induced AMPK phosphorylation were attenuated by the presence of the PP2A inhibitor, okadaic acid, or PP2A siRNA. The inhibitory effect of ethanol on AMPK phosphorylation is exerted through the inhibition of PKC-zeta and LKB1 phosphorylation and the activation of PP2A.

Mycophenolic acid (MPA), a clinically used immunosuppressant, is extensively metabolized into an inactive C7-glucuronide and removed from circulation. To circumvent the metabolic liability imposed by the C7-hydroxyl group, we have designed a series of hybrid MPA analogs based on the pharmacophores present in MPA and new generations of inosine monophosphate dehydrogenase (IMPDH) inhibitors. The synthesis of MPA analogs has been accomplished by an allylic substitution of a common lactone. Biological evaluations of these analogs and a preliminary structure-activity relationship (SAR) are presented.

A series of cycloalkyl, bicycloalkyl, aryl, and heteroaryl N (6)-substituted derivatives of the antitumor agent 3'- C-methyladenosine (3'-Me-Ado), an inhibitor of the alpha Rnr1 subunit of mammalian ribonucleotide reductase (RR), were synthesized. The cytotoxicity of these compounds was evaluated against a panel of human leukemia and carcinoma cell lines and compared to that of some corresponding N (6)-substituted adenosine analogues. N (6)-cycloalkyl-3'- C-methylribonucleosides 2- 7 and N (6)-phenyl analogue 8 were found to inhibit the proliferation of K562 leukemia cells. N (6)-(+/-)- endo-2-norbornyl-3'- C-methyladenosine ( 7) was found to be the most cytotoxic compound, with GI 50 values slightly higher than that of 3'-Me-Ado against K562 and carcinoma cell lines and 2.7 fold higher cytotoxicity against human promyelocytic leukemia HL-60 cells. The SAR study confirms that an unsubstituted N (6)-amino group is essential for optimal cytotoxicity of 3'-Me-Ado against both K562 and carcinoma cell lines. Computational studies, carried out on the eukaryotic alpha subunit (Rnr1) of RR from Saccharomyces cerevisiae were performed to rationalize the observed structure-activity relationships.

Mycophenolic acid (MPA), an inhibitor of IMP-dehydrogenase (IMPDH), is used worldwide in transplantation. Recently, numerous studies showed its importance in cancer treatment. Consequently, MPA entered clinical trials in advanced multiple myeloma patients. Suberoylanilide hydroxamic acid (SAHA), a potent differentiation agent acting through inhibition of histone deacetylases (HDACs), was recently approved for treatment of cutaneous T cell lymphoma. We report herein the synthesis of dual inhibitors of IMPDH and HDACs. We found that mycophenolic hydroxamic acid (9, MAHA) inhibits both IMPDH (Ki=30 nM) and HDAC (IC50=5.0 microM). A modification of SAHA with groups known to interact with IMPDH afforded a SAHA analogue 14, which inhibits IMPDH (Ki=1.7 microM) and HDAC (IC50=0.06 microM). Both MAHA (IC50=4.8 microM) and SAHA analogue 14 (IC50=7.7 microM) were more potent than parent compounds as antiproliferation agents. They were also significantly more potent as differentiation inducers.

Novel tiazofurin adenine dinucleotide (TAD) analogues 25-33 containing a substituent at C2 of the adenine ring have been synthesized as inhibitors of the two isoforms of human IMP-dehydrogenase. The 2-ethyl TAD analogue 33 [Ki = 1 nM (type I), Ki = 14 nM (type II)] was found to be the most potent. It did not inhibit three other cellular dehydrogenases up to 50 microM. Mycophenolic adenine bis(phosphonate)s containing a 2-phenyl (37) or 2-ethyl group (38), were prepared as metabolically stable compounds, both nanomolar inhibitors. Compound 38 [Ki = 16 nM (type I), Ki = 38 nM (type II)] inhibited proliferation of leukemic K562 cells (IC50 = 1.1 microM) more potently than tiazofurin (IC50 = 12.4 microM) or mycophenolic acid (IC50 = 7.7 microM).

A methylenebis(sulfonamide) linked NAD analogue has been designed to circumvent the metabolically unstable, ionic nature of the natural pyrophosphate linkage. This NAD analogue is assembled through two Mitsunobu reactions of a methylenebis(sulfonamide) linker with two protected nucleosides. A 2,4-dimethoxybenzyl group is used as a sulfonamide protective group, which allows facile removal under mildly acidic conditions. This NAD analogue inhibits IMPDH at low micromolar concentration.

An efficient five step synthesis of benzamide riboside (BR) amenable for a large scale synthesis has been developed. It allows for extensive pre-clinical studies of BR as a potential anticancer agent.

Novel methylenephosphophosphonate analogues of mycophenolic adenine dinucleotide (MAD) have been prepared as potential inhibitors of IMP dehydrogenase. A coupling of the mycophenolic (hydroxymethyl)phosphonate 6 with the phosphitylated adenosine analogue 11 followed by oxidation and deprotection afforded the phosphophosphonate 8. A similar coupling between adenosine (hydroxymethyl)phosphonate 10 and phosphitylated mycophenolic alcohol 5 gave the corresponding phosphophosphonate 13. Both 8 and 13 (Ki = 20-87 nM) were found to be the most potent cofactor type inhibitors of IMP dehydrogenase.

Purpose: Benzamide riboside (BR) causes apoptosis in multiple tumor cell lines by its inhibition of guanylate biosynthesis. The purpose of this study was to determine the feasibility of the use of BR as a therapeutic agent for hepatic artery infusional cancer therapy in a rabbit VX2 papilloma tumor model., Materials and Methods: VX2 tumor was implanted into the left lobe of the liver of each of 14 New Zealand White rabbits and allowed to grow for 19 days +/- 3. The proper hepatic artery was selected with a 3-F catheter via right femoral cutdown. The animals were treated with one infusion of 0.9% saline solution (n = 2), 1 mg/kg BR (n = 4), 5 mg/kg BR (n = 4), or 10 mg/kg BR (n = 4). One animal treated with 5 mg/kg BR did not develop tumor. Livers were explanted after 24 hours and sectioned through the tumor. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining was performed on the slides and they were imaged at a magnification of 40 to detect apoptotic cells. Four random fields were obtained from each slide and the percentage of apoptotic cells was calculated by dividing the number of TUNEL-positive cells by the total number of cells. Sections of liver not involved with tumor were seen in five animals: two that received 1 mg/kg BR, one that received 5 mg/kg, and two that received 10 mg/kg., Results: The mean tumor apoptosis rates were 1.3% with saline solution treatment, 44.8% with 1 mg/kg BR, 52.7% with 5 mg/kg BR, and 70.7% with 10 mg/kg BR. The mean tumor apoptosis in treated animals was significantly greater than in control animals (P = .003) and mean tumor apoptosis was significantly greater with 10 mg/kg BR than with 1 mg/kg BR (P = .03). There were no apoptotic cells in normal liver treated with 1 mg/kg BR or 10 mg/kg BR. The animal that received 5 mg/kg BR exhibited 10.5% apoptotic cells in the field examined (eight of 76 cells). In the animal treated with 5 mg/kg BR but in which tumor did not grow, only one of 76 cells (0.65%) was apoptotic in the area of the injection scar., Conclusion: BR induces apoptosis in VX2 tumor in the rabbit model with minimal apoptosis in normal liver.

A series of adenosine derivatives substituted at the 1'-, 2'-, or 3'-position of the ribose ring with a methyl group was synthesized and evaluated for antitumor activity. From this study 3'-C-methyladenosine (3'-Me-Ado) emerged as the most active compound, showing activity against human myelogenous leukemia K562, multidrug resistant human leukemia K562IU, human promyelocytic leukemia HL-60, human colon carcinoma HT-29, and human breast carcinoma MCF-7 cell lines with IC(50) values ranging from 11 to 38 muM. Structure-activity relationship studies showed that the structure of 3'-Me-Ado is crucial for the activity. Substitution of a hydrogen atom of the N(6)-amino group with a small alkyl or cycloalkyl group, the introduction of a chlorine atom in the 2-position of the purine ring, or the moving of the methyl group from the 3'-position to other ribose positions brought about a decrease or loss of antitumor activity. The antiproliferative activity of 3'-Me-Ado appears to be related to its ability to deplete both intracellular purine and pyrimidine deoxynucleotides through ribonucleotide reductase inhibition.

Thiazole-4-carboxamide adenine dinucleotide (TAD) analogues T-2'-MeAD (1) and T-3'-MeAD (2) containing, respectively, a methyl group at the ribose 2'-C-, and 3'-C-position of the adenosine moiety, were prepared as potential selective human inosine monophosphate dehydrogenase (IMPDH) type II inhibitors. The synthesis of heterodinucleotides was carried out by CDI-catalyzed coupling reaction of unprotected 2'-C-methyl- or 3'-C-methyl-adenosine 5'-monophosphate with 2',3'-O-isopropylidene-tiazofurin 5'-monophosphate, and then deisopropylidenation. Biological evaluation of dinucleotides 1 and 2 as inhibitors of recombinant human IMPDH type I and type II resulted in a good activity. Inhibition of both isoenzymes by T-2'-MeAD and T-3'-MeAD was noncompetitive with respect to NAD substrate. Binding of T-3'-MeAD was comparable to that of parent compound TAD, while T-2'-MeAD proved to be a weaker inhibitor. However, no significant difference was found in inhibition of the IMPDH isoenzymes. T-2'-MeAD and T-3'-MeAD were found to inhibit the growth of K562 cells (IC(50) 30.7 and 65.0muM, respectively).

Background: Homocysteine, which increases in folate deficiency, can upregulate folate receptors (FR) at the translational level by increasing the interaction between a short cis-element in the 5'-untranslated region of FR-alpha mRNA and heterogeneous nuclear ribonucleoprotein-E1 (hnRNP-E1). Perturbation of this RNA-protein interaction on GD8.5 induces neural tube defects and neurocristopathies in mice. FR upregulation can also reduce cell proliferation independently of folate deficiency in some human cells. Accordingly, we tested the hypothesis that sustained murine maternal folate deficiency would negatively impact pregnancy outcomes, upregulate FR, and selectively reduce fetal cell proliferation., Methods: Dams were fed chow with various levels of folic acid added for eight weeks before and throughout pregnancy. Following sacrifice on GD17, dams were compared for folate and homocysteine status as well as pregnancy outcomes. Fetuses from some groups were evaluated by specific biochemical, molecular, and immunohistochemical studies for FR, hnRNP-E1, and apoptosis., Results: When compared to dams fed a folate-replete diet, those dams on a folate-depleted diet developed reduced red cell folates and hyperhomocysteinemia and an inverse dose-dependent upregulation of FR and hnRNP-E1 on GD17 without alterations in cell number in the majority of tissues. However, FR overexpression was accompanied by a significant reduction in the net number of cells in the midgut, lung, pons, tongue, and olfactory epithelium, and with premature differentiation in dorsal root ganglion cells and dysplasia of taste buds. By contrast, in the brain, spinal cord, diaphragm, and primordium of follicles of vibrissae, there was less FR expression, which accompanied a net reduction in number of cells and architectural anomalies. Subtle "immunohistochemical footprints" of apoptosis on GD17 fetuses corresponded with net cell loss in the lung and olfactory epithelium. Upregulation of FR could be explained by a homocysteine-induced RNA-protein interaction in folate-depleted fetuses that led to a proportionate increase in murine FR biosynthesis., Conclusions: Maternal folate deficiency results in selective upregulation of FR and hnRNP-E1 associated with multiple aberrations in fetal tissues that include increased cell loss, architectural anomalies, and premature differentiation. The potential significance of these findings to explain the wide spectrum of folate-responsive birth defects in humans is discussed.

Benzamide riboside (BR) and tiazofurin (TR) are converted to analogs of NAD that inhibit IMP dehydrogenase (IMPDH), resulting in cellular depletion of GTP and dGTP and inhibition of proliferation. The current work was undertaken to identify the human nucleoside transporters involved in cellular uptake of BR and TR and to evaluate their role in cytotoxicity. Transportability was examined in Xenopus laevis oocytes and Saccharomyces cerevisiae that produced individual recombinant human concentrative nucleoside transporter (CNT) and equilibrative nucleoside transporter (ENT) types (hENT1, hENT2, hCNT1, hCNT2, or hCNT3). TR was a better permeant than BR with a rank order of transportability in oocytes of hCNT3 >> hENT1 > hENT2 > hCNT2 >> hCNT1. The concentration dependence of inhibition of [(3)H]uridine transport in S. cerevisiae by TR exhibited lower K(i) values than BR: hCNT3 (5.4 versus 226 microM), hENT2 (16 versus 271 microM), hENT1 (57 versus 168 microM), and hCNT1 (221 versus 220 microM). In cytotoxicity experiments, BR was more cytotoxic than TR to cells that were either nucleoside transport-defective or -competent, and transport-competent cells were more sensitive to both drugs. Exposure to nitrobenzylmercaptopurine ribonucleoside conferred resistance to BR and TR cytotoxicity to hENT1-containing CEM cells, thereby demonstrating the importance of transport capacity for manifestation of cytoxicity. A breast cancer cell line with mutant p53 exhibited 9-fold higher sensitivity to BR than the otherwise similar cell line with wild-type p53, suggesting that cells with mutant p53 may be potential targets for IMPDH inhibitors. Further studies are warranted to determine whether this finding can be generalized to other cell types.

Cell membrane-associated folate receptors are selectively overexpressed in certain human tumors. The high affinity of folic acid for folate receptors provides a unique opportunity to use folic acid as a targeting ligand to deliver chemotherapeutic agents to cancer cells. Folate-tethered liposomes bearing pteroyl-gamma-glutamate-cysteine-polyethylene glycol (PEG)-distearoylphosphatidylethanolamine (DSPE) as the targeting component are under investigation as mediators of drug and gene delivery to cancer cells that overexpress folate receptors. Pteroyl-gamma-glutamate-cysteine synthesis is one of the crucial starting steps in the preparation of pteroyl-gamma-glutamate-cysteine-PEG-DSPE. However, published methods for the synthesis of pteroyl-gamma-glutamate-cysteine provide low yields and are not easily reproducible. Therefore, we developed a modified synthetic method for the removal of the N(10)-trifluoroacetyl group after cleavage/deprotection that is reliable, is easily reproducible, and has high yield (38%) compared with an unreliable yield of 3-20% with the earlier methods. Folate-tethered liposomes containing calcein or doxorubicin were prepared using pteroyl-gamma-glutamate-cysteine-PEG-DSPE as the targeting component along with nontargeted liposomes with PEG-DSPE. The results of the uptake of calcein and cytotoxicity of doxorubicin in human cervical cancer HeLa-IU(1) cells and human colon cancer Caco-2 cells demonstrated that folate-tethered liposomes were efficient in selective delivery to cancer cells overexpressing folate receptors. The improvement in yield of the targeting component can significantly facilitate "scale up" of folate receptor-mediated liposomal cancer therapy to the preclinical and clinical levels of investigations.

Benzamide riboside (BR) is a novel anticancer agent exhibiting pronounced activity against several human tumor cell lines via the inhibition of inosine 5'-monophosphate dehydrogenase (IMPDH), thereby restricting the biosynthesis of guanylates. Although it has been demonstrated that BR inhibits IMPDH and induces apoptosis, however, not much attention has been directed to the mechanism of apoptosis induction by this compound. The purpose of the present investigation was to investigate the mechanism of cytotoxicity induced by BR in human lung cancer cells. Non-small cell lung cancer [NSCLC] is the most prevalent type of lung cancer especially in India, and displays resistance to anticancer treatment. The results reveal that BR at a dose of 50 microM induces apoptosis in NSCLC H520 cells. This was ascertained by alteration in cellular morphology, TUNEL assay and flow cytometry. While Bax protein level was unaffected there was down regulation of anti-apoptotic Bcl-2 protein and up regulation of p53 as observed by Western blotting. Induction of apoptosis was accompanied by significant increase in caspase-3 activity. BR is a potent growth inhibitory pro-drug rationally synthesized to mimic NAD and inhibits PARP at high concentrations when assayed in permeabilized leukemic cells. Our observations showed that increased caspase-3 activity was accompanied by PARP cleavage. We also observed release of cytochrome c from mitochondria to the cytosol whereas no change was seen in the levels of apoptosis inducing factor (AIF). These findings indicate that BR induces apoptosis in H520 cells via the intrinsic mitochondrial pathway.

IMP dehydrogenase, the key enzyme in de novo synthesis of purine nucleotides, is an important therapeutic target. Three inhibitors of IMP dehydrogenase reached the market; ribavirin (Rebetol) a broad-spectrum antiviral agent, which in combination with interferon-alpha is now used for treatment of hepatitis C virus infections, mizoribine (Bredinin) and mycophenolic mofetil (CellCept) have been introduced as immunosuppressants. Numerous novel inhibitors are under development. This review describes recent progress in the development of new drugs based on inhibition of IMP dehydrogenase.

NMNAT (nicotinamide 5'-mononucleotide adenylyltransferase; EC 2.7.7.1) catalyses the transfer of the adenylyl group from ATP to NMN to form NAD. We have cloned a novel human NMNAT cDNA, designated hNMNAT-2, from human brain. The cDNA contains a 924 bp open reading frame that encodes a 307 amino acid peptide that was expressed as a histidine-patch-containing thioredoxin fusion protein. Expressed hNMNAT-2 shared only 35% amino acid sequence homology with the human NMNAT enzyme (hNMNAT-1), but possessed enzymic activity comparable with hNMNAT-1. Using human genomic databases, hNMNAT-2 was localized to chromosome 1q25 within a 171 kb gene, whereas hNMNAT-1 is on chromosome 1p32-35. Northern blot analysis revealed highly restricted expression of hNMNAT-2 to brain, heart and muscle tissues, which contrasts with the wide tissue expression of hNMNAT-1; different regions of the brain exhibited differential expression of hNMNAT-2. Substitution mutations of either of two invariant residues, His-24 or Trp-92, abolished enzyme activity. Anti-peptide antibody to a unique epitope within hNMNAT-2 was produced, and immunohistochemical analysis of sections of normal adult human pancreas revealed that hNMNAT-2 protein was markedly expressed in the islets of Langerhans. However, the pancreatic exocrine cells exhibited weak expression of hNMNAT-2 protein. Sections of pancreas from insulinoma patients showed strong expression of hNMNAT-2 protein in the insulin-producing tumour cells, whereas acinar cells exhibited relatively low expression of hNMNAT-2 protein. These data suggest that the unique tissue-expression patterns of hNMNAT-2 reflect distinct functions for the isoforms in the regulation of NAD metabolism.

Cellular acquisition of folate is mediated by folate receptors (FRs) in many malignant and normal human cells. Although FRs are upregulated in folate deficiency and downregulated following folate repletion, the mechanistic basis for this relationship is unclear. Previously we demonstrated that interaction of an 18-base cis-element in the 5'-untranslated region of FR mRNA and a cystolic trans-factor (heterogeneous nuclear ribonucleoprotein E1 [hnRNP E1]) is critical for FR synthesis. However, the molecular mechanisms controlling this interaction, especially within the context of FR regulation and folate status, have remained obscure. Human cervical carcinoma cells exhibited progressively increasing upregulation of FRs after shifting of folate-replete cells to low-folate media, without a proportionate rise in FR mRNA or rise in hnRNP E1. Translational FR upregulation was accompanied by a progressive accumulation of the metabolite homocysteine within cultured cells, which stimulated interaction of the FR mRNA cis-element and hnRNP E1 as well as FR biosynthesis in a dose-dependent manner. Abrupt reversal of folate deficiency also led to a rapid parallel reduction in homocysteine and FR biosynthesis to levels observed in folate-replete cells. Collectively, these results suggest that homocysteine is the key modulator of translational upregulation of FRs and establishes the linkage between perturbed folate metabolism and coordinated upregulation of FRs.

Synthesis and biological activities of cyclosaligenyl-tiazofurin monophosphate (CycloSal-TRMP), a new tiazofurin pronucleotide, are reported. CycloSal-TRMP proved to be active in vitro against human myelogenous leukemia K562 cell line and as A1 adenosine receptor agonist.

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.

Benzamide riboside (BR) is a nucleoside prodrug that is phosphorylated to its 5'-monophosphate (BRMP) and then converted to its active metabolite, BAD (benzamide adenine dinucleotide), an analogue of NAD by the action of NMN adenylyltransferase (NMNAT). BAD is a potent, reversible, and noncompetitive inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH) resulting in depletion of guanylates (GTP and dGTP). IMPDH inhibitors such as BR induce differentiation and apoptosis as a consequence of GTP depletion. Tiazofurin (TR) and selenazofurin (SR) require similar metabolism by NMNAT. NMNAT is the rate-limiting step in the synthesis of NAD and NAD analogues. BR- and TR-sensitive leukemic cells contain high NMNAT activity, whereas resistant clones have greatly downregulated NMNAT activity (<0.1% of wild type). Perhaps the applicability of BR and analogues could be enhanced if combined with NMNAT gene expression in BR-resistant leukemic blasts. NAD has important regulatory role in repair of DNA damage and cell growth since it is a substrate for poly(ADP-ribose) polymerase (PARP). PARP appears to direct short-patch base excision repair and induce p53 upregulation leading to apoptosis. BR inhibits PARP at high concentrations when assayed in permeabilized leukemic cells. Several other IMPDH inhibitors (TR, mycophenolic acid, and ribavirin) exhibit similar PARP inhibitory activity. Although this inhibition was reversible, it was not prevented by the addition of guanosine, GTP, or its nonhydrolyzable analog gamma-S-GTP. Therefore, it can be concluded that IMPDH inhibitors directly inhibit PARP. Presumably, the shared IMP-NAD active site of IMPDH has a similar architecture to the NAD-binding pocket of PARP.

Benzamide is a well known inhibitor of poly(ADP-ribose)polymerase, an enzyme involved in DNA repair. However, benzamide exhibited neuotoxicity in animals and hence, in the hope of overcoming this problem, benzamide riboside (BR) was synthesized. Our mechanism of action studies on BR suggested that the agent was being metabolized to its 5'-monophosphate and then to its NAD analogue (BAD, benzamide adenine dinucleotide) that inhibits Inosine 5'-monophosphate dehydrogenase (IMPDH). IMPDH is the rate-limiting enzyme of the branched purine nucleotide synthetic pathway that provides guanylates including GTP and dGTP. There are two isoforms of IMPDH, type I that is constitutively present in all cells, and type II that is inducible and is present in highly proliferating cells such as cancer. Ongoing studies with BR analogues suggest that they are more selective in inhibiting IMPDH type II. Our studies have characterized the metabolites of BR, especially its NAD analogue, BAD, by synthesizing this active metabolite by enzymatic means, and identifying its structure by NMR and mass spectrometry. We have partially purified IMPDH from tumor cells and have examined the kinetics of inhibition of IMPDH by BAD. We have also compared biochemical and cytotoxic activities of BR with tiazofurin and selenazofurin, that share similar mechanisms of action with BR. Our studies demonstrated that 2-3-fold more BAD is formed compared to TAD and SAD, the active metabolites of tiazofurin and selenazofurin, respectively. BR has demonstrated potent cytotoxic activity in a diverse group of human tumor cells, specifically more active in sarcomas and CNS neoplasms compared to tiazofurin or selenazofurin. Future in vivo animal studies should set a stage for determining its effectiveness in clinical Phase I studies.