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Hong JS, Waud WR, Levasseur DN, Townes TM, Wen H, McPherson SA, Moore BA, Bebok Z, Allan PW, Secrist JA, Parker WB, Sorscher EJ. Excellent in vivo bystander activity of fludarabine phosphate against human glioma xenografts that express the escherichia coli purine nucleoside phosphorylase gene. Cancer Res 2004; 64:6610-5. [PMID: 15374975 DOI: 10.1158/0008-5472.can-04-0012] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Escherichia coli purine nucleoside phosphorylase (PNP) expressed in tumors converts relatively nontoxic prodrugs into membrane-permeant cytotoxic compounds with high bystander activity. In the present study, we examined tumor regressions resulting from treatment with E. coli PNP and fludarabine phosphate (F-araAMP), a clinically approved compound used in the treatment of hematologic malignancies. We tested bystander killing with an adenoviral construct expressing E. coli PNP and then more formally examined thresholds for the bystander effect, using both MuLv and lentiviral vectoring. Because of the importance of understanding the mechanism of bystander action and the limits to this anticancer strategy, we also evaluated in vivo variables related to the expression of E. coli PNP (level of E. coli PNP activity in tumors, ectopic expression in liver, percentage of tumor cells transduced in situ, and accumulation of active metabolites in tumors). Our results indicate that F-araAMP confers excellent in vivo dose-dependent inhibition of bystander tumor cells, including strong responses in subcutaneous human glioma xenografts when 95 to 97.5% of the tumor mass is composed of bystander cells. These findings define levels of E. coli PNP expression necessary for antitumor activity with F-araAMP and demonstrate new potential for a clinically approved compound in solid tumor therapy.
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Bennett EM, Anand R, Allan PW, Hassan AEA, Hong JS, Levasseur DN, McPherson DT, Parker WB, Secrist JA, Sorscher EJ, Townes TM, Waud WR, Ealick SE. Designer gene therapy using an Escherichia coli purine nucleoside phosphorylase/prodrug system. ACTA ACUST UNITED AC 2004; 10:1173-81. [PMID: 14700625 DOI: 10.1016/j.chembiol.2003.11.008] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Activation of prodrugs by Escherichia coli purine nucleoside phosphorylase (PNP) provides a method for selectively killing tumor cells expressing a transfected PNP gene. This gene therapy approach requires matching a prodrug and a known enzymatic activity present only in tumor cells. The specificity of the method relies on avoiding prodrug cleavage by enzymes already present in the host cells or the intestinal flora. Using crystallographic and computer modeling methods as guides, we have redesigned E. coli PNP to cleave new prodrug substrates more efficiently than does the wild-type enzyme. In particular, the M64V PNP mutant cleaves 9-(6-deoxy-alpha-L-talofuranosyl)-6-methylpurine with a kcat/Km over 100 times greater than for native E. coli PNP. In a xenograft tumor experiment, this compound caused regression of tumors expressing the M64V PNP gene.
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Parker WB, Barrow EW, Allan PW, Shaddix SC, Long MC, Barrow WW, Bansal N, Maddry JA. Metabolism of 2-methyladenosine in Mycobacterium tuberculosis. Tuberculosis (Edinb) 2004; 84:327-36. [PMID: 15207808 DOI: 10.1016/j.tube.2004.02.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2003] [Revised: 02/16/2004] [Accepted: 02/20/2004] [Indexed: 11/24/2022]
Abstract
2-Methyladenosine (methyl-Ado) has selective activity against Mycobacterium tuberculosis (M. tuberculosis). In an effort to better understand its mechanism of action, we have characterized its metabolism in M. tuberculosis cells. The primary intracellular metabolite of methyl-Ado was 2-methyl-adenylate (methyl-AMP). Very little of the methyl-AMP was metabolized further. A M. tuberculosis strain that was resistant to methyl-Ado did not express adenosine kinase and did not convert methyl-Ado to methyl-AMP in intact cells. In contrast to these results, the primary intracellular metabolite of adenosine in M. tuberculosis cells was ATP, which was readily incorporated into RNA. The rate of metabolism of methyl-Ado to methyl-AMP was similar to the rate of metabolism of adenosine to ATP. Treatment of M. tuberculosis with methyl-Ado did not affect intracellular ATP levels. Methyl-Ado and Ado were also cleaved to 2-methyladenine and adenine, respectively, which accumulated in the medium outside the cells. These studies suggested that methyl-AMP was the active metabolite responsible for the cytotoxicity of this agent. Furthermore, because methyl-Ado was poorly metabolized in human cells, these studies indicated that the selective activity of methyl-Ado was due to its selective activation by M. tuberculosis. These studies have identified two enzyme reactions (Ado kinase and Ado cleavage) in M. tuberculosis that could be exploited for the rational design of new and selective anti-M. tuberculosis agents.
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Parker WB, Secrist JA, Waud WR. Purine nucleoside antimetabolites in development for the treatment of cancer. CURRENT OPINION IN INVESTIGATIONAL DRUGS (LONDON, ENGLAND : 2000) 2004; 5:592-6. [PMID: 15242246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
Purine nucleoside analogs are an important class of drugs that are used in the treatment of cancer. Five purine analogs have been approved by the FDA (mercaptopurine, thioguanine, fludarabine monophosphate, deoxycoformycin and cladribine) and four compounds are currently being evaluated clinically (clofarabine, immucillin-H, nelarabine and 8-chloroadenosine). In addition, two gene therapy approaches are being evaluated that are based on the selective activation of purine nucleoside analogs (ganciclovir, fludarabine monophosphate and others) in tumor cells. Even though nucleoside analogs have been extensively evaluated over the last 50 years, the development of these new compounds demonstrates that there is still much promise in identifying new anticancer drugs from this class of compounds.
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Curlee KV, Parker WB, Sorscher EJ. Tumor sensitization to purine analogs by E. coli PNP. METHODS IN MOLECULAR MEDICINE 2004; 90:223-45. [PMID: 14657566 DOI: 10.1385/1-59259-429-8:223] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
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Hassan AEA, Parker WB, Allan PW, Montgomery JA, Secrist JA. Selective metalation of 6-methylpurines: synthesis of 6-fluoromethylpurines and related nucleosides. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2003; 22:747-9. [PMID: 14565269 DOI: 10.1081/ncn-120022625] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
A selective metalation at the 6-CH3 over C-8 of 6-methylpurine derivative 6 was observed with softer counter cation (Na+ or K+) of the base, while the harder Li+ showed no selectivity. In the presence of N-fluorobenzenesulfonamide (NFSI), this property was utilized for the synthesis of 6-fluoromethylpurine derivatives 4 and 5 as potential toxins for suicide gene therapy.
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Long MC, Escuyer V, Parker WB. Identification and characterization of a unique adenosine kinase from Mycobacterium tuberculosis. J Bacteriol 2003; 185:6548-55. [PMID: 14594827 PMCID: PMC262096 DOI: 10.1128/jb.185.22.6548-6555.2003] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adenosine kinase (AK) is a purine salvage enzyme that catalyzes the phosphorylation of adenosine to AMP. In Mycobacterium tuberculosis, AK can also catalyze the phosphorylation of the adenosine analog 2-methyladenosine (methyl-Ado), the first step in the metabolism of this compound to an active form. Purification of AK from M. tuberculosis yielded a 35-kDa protein that existed as a dimer in its native form. Adenosine (Ado) was preferred as a substrate at least 30-fold (Km = 0.8 +/- 0.08 microM) over other natural nucleosides, and substrate inhibition was observed when Ado concentrations exceeded 5 micro M. M. tuberculosis and human AKs exhibited different affinities for methyl-Ado, with Km values of 79 and 960 microM, respectively, indicating that differences exist between the substrate binding sites of these enzymes. ATP was a good phosphate donor (Km = 1100 +/- 140 microM); however, the activity levels observed with dGTP and GTP were 4.7 and 2.5 times the levels observed with ATP, respectively. M. tuberculosis AK activity was dependent on Mg2+, and activity was stimulated by potassium, as reflected by a decrease in the Km and an increase in Vmax for both Ado and methyl-Ado. The N-terminal amino acid sequence of the purified enzyme revealed complete identity with Rv2202c, a protein currently classified as a hypothetical sugar kinase. When an AK-deficient strain of M. tuberculosis (SRICK1) was transformed with this gene, it exhibited a 5,000-fold increase in AK activity compared to extracts from the original mutants. These results verified that the protein that we identified as AK was coded for by Rv2202c. AK is not commonly found in bacteria, and to the best of our knowledge, M. tuberculosis AK is the first bacterial AK to be characterized. The enzyme shows greater sequence homology with ribokinase and fructokinase than it does with other AKs. The multiple differences that exist between M. tuberculosis and human AKs may provide the molecular basis for the development of nucleoside analog compounds with selective activity against M. tuberculosis.
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Bennett EM, Li C, Allan PW, Parker WB, Ealick SE. Structural basis for substrate specificity of Escherichia coli purine nucleoside phosphorylase. J Biol Chem 2003; 278:47110-8. [PMID: 12937174 DOI: 10.1074/jbc.m304622200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Purine nucleoside phosphorylase catalyzes reversible phosphorolysis of purine nucleosides and 2'-deoxypurine nucleosides to the free base and ribose (or 2'-deoxyribose) 1-phosphate. Whereas the human enzyme is specific for 6-oxopurine ribonucleosides, the Escherichia coli enzyme accepts additional substrates including 6-oxopurine ribonucleosides, 6-aminopurine ribonucleosides, and to a lesser extent purine arabinosides. These differences have been exploited in a potential suicide gene therapy treatment for solid tumors. In an effort to optimize this suicide gene therapy approach, we have determined the three-dimensional structure of the E. coli enzyme in complex with 10 nucleoside analogs and correlated the structures with kinetic measurements and computer modeling. These studies explain the preference of the enzyme for ribose sugars, show increased flexibility for active site residues Asp204 and Arg24, and suggest that interactions involving the 1- and 6-positions of the purine and the 4'- and 5'-positions of the ribose provide the best opportunities to increase prodrug specificity and enzyme efficiency.
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Barrow EW, Westbrook L, Bansal N, Suling WJ, Maddry JA, Parker WB, Barrow WW. Antimycobacterial activity of 2-methyl-adenosine. J Antimicrob Chemother 2003; 52:801-8. [PMID: 14563890 DOI: 10.1093/jac/dkg444] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
OBJECTIVES The aims of this study were to assess the in vitro activity of 2-methyl-adenosine against Mycobacterium tuberculosis and evaluate, and to intracellular efficacy, and to evaluate its effectiveness against M. tuberculosis in a persistent state model and examine its potential mechanism of action. METHODS In vitro activity was determined by means of a colorimetric microdilution broth assay. Intracellular activity was assessed with a Mono Mac 6 human monocytic cell line. A hypoxic shift-down model was used to evaluate the effect of 2-methyl-adenosine on M. tuberculosis in a persistent state. Mechanism-of-action studies were conducted by examining the effect of 2-methyl-adenosine on the uptake of appropriate radiolabelled precursors into respective mycobacterial macromolecular components. RESULTS Studies confirmed the in vitro activity of 2-methyl-adenosine against M. tuberculosis and demonstrated intracellular efficacy against M. tuberculosis within macrophages. 2-Methyl-adenosine was able to significantly affect the viability of M. tuberculosis in a hypoxic shift-down model previously described to simulate the persistent state that results during tuberculosis. Mechanism-of-action studies revealed that the immediate inhibitory effects of 2-methyl-adenosine were associated with protein and DNA synthesis and not RNA synthesis. CONCLUSIONS Results indicate that 2-methyl-adenosine, or similar derivatives, might be effective against M. tuberculosis infections during latency. This information should be helpful in understanding purine metabolism of M. tuberculosis and also the metabolic activity of this important human pathogen in the persistent state.
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Gadi VK, Alexander SD, Waud WR, Allan PW, Parker WB, Sorscher EJ. A long-acting suicide gene toxin, 6-methylpurine, inhibits slow growing tumors after a single administration. J Pharmacol Exp Ther 2003; 304:1280-4. [PMID: 12604707 DOI: 10.1124/jpet.102.044743] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have demonstrated antitumor activity against refractory human glioma and pancreatic tumors with 6-methylpurine (MeP) using either a suicide gene therapy strategy to selectively release 6-methylpurine in tumor cells or direct intratumoral injection of 6-methylpurine itself. A single i.p. injection in mice of the prodrug 9-beta-D-[2-deoxyribofuranosyl]-6-methylpurine (MeP-dR; 134 mg/kg) caused sustained regression lasting over 70 days of D54 (human glioma) tumors transduced with the Escherichia coli purine nucleoside phosphorylase (PNP), and a single intratumoral injection of 6-methylpurine (5-10 mg/kg) elicited prolonged delays of the growth of D54 tumors and CFPAC human pancreatic carcinoma. Because the D54 tumor doubling time is >15 days, the experiments indicate that prodrug activation by E. coli PNP engenders destruction of both dividing and nondividing tumor compartments in vivo and, therefore, address a fundamental barrier that has limited the development of suicide gene strategies in the past. A prolonged retention time of 6-methylpurine metabolites in tumors was noted in vivo (T(1/2) >24 h compared with a serum half-life of <1 h). By high-pressure liquid chromatography, metabolites of [(3)H]MeP-dR were 5- to 6-fold higher in tumors expressing E. coli PNP. These experiments point to new endpoints for monitoring E. coli PNP suicide gene therapy, including intratumoral enzymatic activity, in situ (intratumoral) prodrug conversion, and tumor regressions after direct injection of a suicide gene toxin. The findings also help explain the strong in vivo bystander killing mechanism ascribed by several laboratories to E. coli PNP in the past.
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Someya H, Shaddix SC, Tiwari KN, Secrist JA, Parker WB. Phosphorylation of 4'-thio-beta-D-arabinofuranosylcytosine and its analogs by human deoxycytidine kinase. J Pharmacol Exp Ther 2003; 304:1314-22. [PMID: 12604712 DOI: 10.1124/jpet.102.045435] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
4'-thio-beta-D-arabinofuranosylcytosine (T-araC) exhibits excellent in vivo antitumor activity against a variety of solid tumors despite its structural similarity to beta-D-arabinofuranosylcytosine (araC), an agent which is poorly active against solid tumors in vivo. It is of great interest to elucidate why these compounds show a profound difference in antitumor activity. Because deoxycytidine kinase (dCK) is the critical enzyme in the activation of both compounds, here we report the differences in the substrate characteristics with human dCK between these compounds. The catalytic efficiency (V(max)/K(m)) of araC was 100-fold higher than that of T-araC using either ATP or UTP as the phosphate donor. However, V(max) values of araC and T-araC were similar when UTP was the phosphate donor. Since UTP is believed to be the true phosphate donor for dCK in intact cells, these data indicated that the rates of phosphorylation of these two compounds at high pharmacologically relevant concentrations would be similar. This prediction was confirmed in intact cell experiments, which supported the hypothesis that UTP is the physiological phosphate donor for dCK phosphorylation in cells. The relative lack of importance of phosphate donor to the phosphorylation of T-araC by dCK revealed important insights into the activation of this compound in human cells at pharmacological doses. These studies indicated that replacement of the 4'-oxygen with sulfur significantly reduced the substrate activity of nucleoside analogs with dCK and that the superior activity of T-araC with respect to araC against solid tumors was not due to superior activity with dCK.
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Parker WB, Allan PW, Hassan AEA, Secrist JA, Sorscher EJ, Waud WR. Antitumor activity of 2-fluoro-2'-deoxyadenosine against tumors that express Escherichia coli purine nucleoside phosphorylase. Cancer Gene Ther 2003; 10:23-9. [PMID: 12489025 DOI: 10.1038/sj.cgt.7700520] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2002] [Indexed: 11/09/2022]
Abstract
The selective expression of Escherichia coli purine nucleoside phosphorylase (PNP) in solid tumors has been successfully used to activate two purine nucleoside analogs [9-(2-deoxy-beta-D-ribofuranosyl)-6-methylpurine (MeP-dR) and 9-beta-D-arabinofuranosyl-2-fluoroadenine (F-araA)] resulting in lasting tumor regressions and cures. E. coli PNP also cleaves 2-fluoro-2'-deoxyadenosine (F-dAdo) to 2-F-adenine, which is the toxic purine analog liberated from F-araA that has high bystander activity and is active against nonproliferating tumor cells. As F-dAdo is 3000 times better than F-araA as a substrate for E. coli PNP, we have evaluated its antitumor activity against D54 gliomas that express E. coli PNP and have characterized its in vivo metabolism in order to better understand its mechanism of action with respect to the other two agents. Like MeP-dR and F-araA-5'-monophosphate (F-araAMP, a prodrug of F-araA), treatment of mice bearing D54 tumors that express E. coli PNP with F-dAdo resulted in excellent antitumor activity. Although F-dAdo was as active as MeP-dR and better than F-araAMP, it was not dramatically better than either compound because of its short plasma half-life and the limited activation of F-adenine to toxic metabolites. Regardless, these results indicated that F-dAdo was also an excellent prodrug for use with gene vectors that deliver E. coli PNP to tumor cells.
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Rose JD, Parker WB, Someya H, Shaddix SC, Montgomery JA, Secrist JA. Enhancement of nucleoside cytotoxicity through nucleotide prodrugs. J Med Chem 2002; 45:4505-12. [PMID: 12238929 DOI: 10.1021/jm020107s] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A common reason for the lack of cytotoxicity of certain nucleosides is thought to be their inability to be initially activated to the monophosphate level by a nucleoside kinase or other activating enzyme. In a search for other nucleosides that might be worthwhile anticancer agents, we have begun to examine the utilization of monophosphate prodrugs in order to explore whether any enhanced cytotoxicity might be found for the prodrugs of candidate nucleosides that have little or no cytotoxicity. To that end, 5'-bis(pivaloyloxymethyl) phosphate prodrugs of two weakly cytotoxic compounds, 8-aza-2'-deoxyadenosine (5) and 8-bromo-2'-deoxyadenosine (9), have been prepared. These prodrugs (8 and 12) were examined for their cytotoxicity in CEM cells and were found to possess significantly enhanced cytotoxicity when compared with the corresponding parent nucleosides. Further cell culture experiments were conducted to gain insight into the mechanisms of cytotoxicity of these two prodrugs, and those data are reported.
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Shewach DS, Murphy PJ, Robinson BW, Vuletich J, Boucher PD, Blobaum AL, Zerbe L, Secrist JA, Parker WB. Multi-log cytotoxicity of carbocyclic 2'-deoxyguanosine in HSV-TK-expressing human tumor cells. Hum Gene Ther 2002; 13:543-51. [PMID: 11874632 DOI: 10.1089/10430340252809838] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ganciclovir (GCV) is widely used as a prodrug for selective activation in tumor cells expressing herpes simplex virus thymidine kinase (HSV-TK) because of its ability to induce multi-log cytotoxicity to HSV-TK-expressing as well as nonexpressing bystander cells. We now report that another substrate for HSV-TK, D-carbocyclic 2'-deoxyguanosine (CdG), induces multi-log cytotoxicity in HSV-TK-expressing and bystander cells at concentrations <or=3 microM. We have compared the cytotoxicity and cell cycle effects of CdG to that observed with GCV in two human tumor cell lines. The results demonstrated that cytotoxicity of CdG was similar to that of GCV in both U251 glioblastoma and SW620 colon carcinoma cells that stably expressed HSV-TK. In addition, CdG induced a potent bystander effect in both cell types in co-cultures consisting of HSV-TK-expressing and nonexpressing bystander (lacZ-expressing) cells at ratios of 50:50 or 10:90. Selectivity for HSV-TK-expressing compared to lacZ-expressing cells was similar for CdG and GCV in the U251 cells, however CdG was less selective than GCV in the SW620 cell lines. Despite their ability to induce multi-log cytotoxicity at similar concentrations, CdG and GCV exhibited differential effects on cell cycle progression. Cells incubated with 1 microM CdG for 24 hr accumulated in S-phase and G(2)/M after drug washout, and the majority of cells died prior to cell division. This contrasts with the delayed effects of 1 microM GCV that were not evident until after cell division when cells attempted S-phase for the second time. Thus, CdG is a potent cytotoxic agent that merits further investigation to determine whether it will be therapeutically effective in enzyme-prodrug therapy with HSV-TK.
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Chen CK, Barrow EW, Allan PW, Bansal N, Maddry JA, Suling WJ, Barrow WW, Parker WB. The metabolism of 2-methyladenosine in Mycobacterium smegmatis. MICROBIOLOGY (READING, ENGLAND) 2002; 148:289-295. [PMID: 11782521 DOI: 10.1099/00221287-148-1-289] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
2-Methyladenosine (methyl-ado) has demonstrated selective activity against Mycobacterium tuberculosis, which indicates that differences in the substrate preferences between mycobacterial and human purine metabolic enzymes can be exploited to develop novel drugs for the treatment of mycobacterial diseases. Therefore, in an effort to better understand the reasons for the anti-mycobacterial activity of methyl-ado, its metabolism has been characterized in Mycobacterium smegmatis. In a wild-type strain, methyl-ado was phosphorylated by adenosine kinase to methyl-AMP, which was further converted to methyl-ATP and incorporated into RNA. In contrast, a mutant strain of M. smegmatis was isolated that was resistant to methyl-ado, deficient in adenosine kinase activity and was not able to generate methyl-ado metabolites in cells treated with methyl-ado. These results indicated that phosphorylated metabolites of methyl-ado were responsible for the cytotoxic activity of this compound. Methyl-ado was not a substrate for either adenosine deaminase or purine-nucleoside phosphorylase from M. smegmatis. Treatment of M. smegmatis with methyl-ado resulted in the inhibition of ATP synthesis, which indicated that a metabolite of methyl-ado inhibited one of the enzymes involved in de novo purine synthesis. These studies demonstrated the importance of adenosine kinase in the activation of methyl-ado to toxic metabolites in M. smegmatis.
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Parker WB, Shaddix SC, Rose LM, Waud WR, Shewach DS, Tiwari KN, Secrist JA. Metabolism of 4'-thio-beta-D-arabinofuranosylcytosine in CEM cells. Biochem Pharmacol 2000; 60:1925-32. [PMID: 11108809 DOI: 10.1016/s0006-2952(00)00520-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Because of the excellent in vivo activity of 4'-thio-beta-D-arabinofuranosylcytosine (T-araC) against a variety of human solid tumors, we have studied its metabolism in CEM cells to determine how the biochemical pharmacology of this compound differs from that of beta-D-arabinofuranosylcytosine (araC). Although there were many quantitative differences in the metabolism of T-araC and araC, the basic mechanism of action of T-araC was similar to that of araC: it was phosphorylated to T-araC-5'-triphosphate (T-araCTP) and inhibited DNA synthesis. The major differences between these two compounds were: (i) T-araC was phosphorylated to active metabolites at 1% the rate of araC; (ii) T-araCTP was 10- to 20-fold more potent as an inhibitor of DNA synthesis than was the 5'-triphosphate of araC (araCTP); (iii) the half-life of T-araCTP was twice that of araCTP; (iv) the catalytic efficiency of T-araC with cytidine deaminase was 10% that of araC; and (v) the 5'-monophosphate of araC was a better substrate for deoxycytidine 5'-monophosphate deaminase than was the 5'-monophosphate of T-araC. Of these differences in the metabolism of these two compounds, we propose that the prolonged retention of T-araCTP is a major factor contributing to the activity of T-araC against solid tumors. The data in this study represent another example of how relatively small structural changes in nucleoside analogs can profoundly affect the biochemical activity.
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Gadi VK, Alexander SD, Kudlow JE, Allan P, Parker WB, Sorscher EJ. In vivo sensitization of ovarian tumors to chemotherapy by expression of E. coli purine nucleoside phosphorylase in a small fraction of cells. Gene Ther 2000; 7:1738-43. [PMID: 11083495 DOI: 10.1038/sj.gt.3301286] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This report examines a major barrier to suicide gene therapy in cancer and other diseases: namely, bystander cell killing. Existing vectors for in vivo gene delivery are inefficient and often transduce or transfect less than 1% of target cells. The E. coli PNP gene brings about cellular necrosis under conditions when 1 in 100 to 1 in 1000 cells express the gene product in vitro. In vivo bystander killing at or near this magnitude has not been reported previously. In the present experiments, transfection of cells with the E. coli PNP gene controlled by a SV40 promoter resulted in 30 nmol 6-methyl purine deoxyriboside (MeP-dR) converted per milligram tumor cell extract per hour (or conversion units (CU)). This level of expression led to elimination of entire populations of tumor cells in vitro after treatment with MeP-dR. Much earlier killing was observed using a tat transactivated E. coli PNP vector (approximately seven-fold higher activity, 230 CU). In vivo effects on tumor growth were next examined. Human ovarian tumors transfected with E. coli PNP were excised 5 days after i.p. implantation from the peritoneal cavities of mice in order to determine both E. coli PNP enzymatic activity and the fraction of cells expressing the gene. PNP activity at 5 days after gene transfer was approximately 170 CU and was expressed in approximately 0.1% of the tumor cells as judged by in situ hybridization. The expression of E. coli PNP at this level produced a 30% increase in life span (P < 0.001) and 49% reduction in tumor size (P < 0.005) after MeP-dR treatment, as compared with control tumors. Our observations lead to the conclusion that pronounced bystander killing by E. coli PNP is conferred in vivo, and that vectors capable of transgene expression in as few as one in 1000 cells can produce substantial antitumor effects if expression on a per cell basis is very high.
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Tiwari KN, Shortnacy-Fowler AT, Cappellacci L, Waud WR, Parker WB, Montgomery JA, Secrist JA. Synthesis and structure activity relationships of 5-substituted-4'-thio-beta-D-arabinofuranosylcytosines. NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS 2000; 19:2005-17. [PMID: 11200287 DOI: 10.1080/15257770008045474] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Four 5-substituted (chloro, fluoro, bromo, methyl) 1-(4-thio-beta-D-arabinofuranosyl)cytosines and their alpha anomers were synthesized by a facile route in high yields. All of these nucleosides were evaluated for cytotoxicity against a panel of human tumor cell lines in vitro. Only 5-fluoro-1-(4-thio-beta-D-arabinofuranosyl)cytosine was found to be highly cytotoxic in all the cell lines and was further evaluated in vivo.
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Tendian SW, Parker WB. Interaction of deoxyguanosine nucleotide analogs with human telomerase. Mol Pharmacol 2000; 57:695-9. [PMID: 10727514 DOI: 10.1124/mol.57.4.695] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To maintain the telomeres at the ends of the chromosomes, telomerase in human cells adds a repeating sequence of nucleotides (TTAGGG) to the 3'-end of each chromosome using an RNA component of the enzyme as the template for DNA synthesis. Because of the selective expression of this enzyme in cancer cells, we have evaluated the interaction of human telomerase with several deoxyguanosine nucleotides of clinical importance. 2',3'-dideoxyguanosine 5'-triphosphate, 6-thio-2'-deoxyguanosine 5'-triphosphate (T-dGTP), carbovir 5'-triphosphate, and D-carbocyclic-2'-deoxyguanosine 5'-triphosphate (D-CdG-TP) inhibited telomerase activity by 50% when these analogs were present at only 2 to 9 times the dGTP concentration. The L-enantiomer of CdG-TP was far less inhibitory, thereby demonstrating the stereoselectivity of telomerase for nucleotide substrates. T-dGTP was incorporated into the DNA by telomerase in the absence of dGTP, but unlike dGTP there was little extension of the DNA chain after its incorporation. These results indicate that the metabolites of three clinically useful agents (6-mercaptopurine, 6-thioguanine, and Abacavir) can inhibit human telomerase activity, and it is possible that the effect of these nucleotides on telomerase activity or telomere function could contribute to the mechanism of action of these agents.
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Parker WB, Shaddix SC, Rose LM, Pham PT, Hua M, Vince R. Metabolism of O6-propyl and N6-propyl-carbovir in CEM cells. NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS 2000; 19:795-804. [PMID: 10960036 DOI: 10.1080/15257770008035025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The metabolism of O6-propyl-carbovir and N6-propyl-carbovir, two selective inhibitors of HIV replication, has been evaluated in CEM cells. Both compounds were phosphorylated in intact cells to carbovir-5'-triphosphate. The metabolism of these two agents was inhibited by deoxycoformycin and mycophenolic acid, but not erythro-9-(2-hydroxy-3-nonyl)adenine. No evidence of the 5'-triphosphate of either compound was detected in CEM cells.
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Tiwari KN, Shortnacy-Fowler AT, Cappellacci L, Parker WB, Waud WR, Montgomery JA, Secrist JA. Synthesis of 4'-thio-beta-D-arabinofuranosylcytosine (4'-thio-ara-C) and comparison of its anticancer activity with that of ara-C. NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS 2000; 19:329-40. [PMID: 10772718 DOI: 10.1080/15257770008033012] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
4'-thio-beta-D-arabinofuranosylcytosine was synthesized by a facile route in high yields. It was evaluated for antitumor activity against a panel of human tumors, both in vitro and in vivo.
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Secrist JA, Parker WB, Allan PW, Bennett LL, Waud WR, Truss JW, Fowler AT, Montgomery JA, Ealick SE, Wells AH, Gillespie GY, Gadi VK, Sorscher EJ. Gene therapy of cancer: activation of nucleoside prodrugs with E. coli purine nucleoside phosphorylase. NUCLEOSIDES & NUCLEOTIDES 1999; 18:745-57. [PMID: 10432677 DOI: 10.1080/15257779908041562] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
During the last few years, many gene therapy strategies have been developed for various disease targets. The development of anticancer gene therapy strategies to selectively generate cytotoxic nucleoside or nucleotide analogs is an attractive goal. One such approach involves the delivery of herpes simplex virus thymidine kinase followed by the acyclic nucleoside analog ganciclovir. We have developed another gene therapy methodology for the treatment of cancer that has several significant attributes. Specifically, our approach involves the delivery of E. coli purine nucleoside phosphorylase, followed by treatment with a relatively non-toxic nucleoside prodrug that is cleaved by the enzyme to a toxic compound. This presentation describes the concept, details our search for suitable prodrugs, and summarizes the current biological data.
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Parker WB, Shaddix SC, Rose LM, Shewach DS, Hertel LW, Secrist JA, Montgomery JA, Bennett LL. Comparison of the mechanism of cytotoxicity of 2-chloro-9-(2-deoxy-2- fluoro-beta-D-arabinofuranosyl)adenine, 2-chloro-9-(2-deoxy-2-fluoro- beta-D-ribofuranosyl)adenine, and 2-chloro-9-(2-deoxy-2,2-difluoro- beta-D-ribofuranosyl)adenine in CEM cells. Mol Pharmacol 1999; 55:515-20. [PMID: 10051535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023] Open
Abstract
In an effort to understand biochemical features that are important to the selective antitumor activity of 2-chloro-9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)adenine [Cl-F( upward arrow)-dAdo], we evaluated the biochemical pharmacology of three structurally similar compounds that have quite different antitumor activities. Cl-F( upward arrow)-dAdo was 50-fold more potent as an inhibitor of CEM cell growth than were either 2-chloro-9-(2-deoxy-2-fluoro-beta-D-ribofuranosyl)adenine [Cl-F( downward arrow)-dAdo] or 2-chloro-9-(2-deoxy-2, 2-difluoro-beta-D-ribofuranosyl)adenine [Cl-diF( upward arrow downward arrow)-dAdo]. The compounds were similar as substrates of deoxycytidine kinase. Similar amounts of their respective triphosphates accumulated in CEM cells, and the rate of disappearance of these metabolites was also similar. Cl-F( upward arrow)-dAdo was 10- to 30-fold more potent in its ability to inhibit the incorporation of cytidine into deoxycytidine nucleotides than either Cl-F( downward arrow)-dAdo or Cl-diF( upward arrow downward arrow)-dAdo, respectively, which indicated that ribonucleotide reductase was differentially inhibited by these three compounds. Thus, the differences in the cytotoxicity of these agents toward CEM cells were not related to quantitative differences in the phosphorylation of these agents to active forms but can mostly be accounted for by differences in the inhibition of ribonucleotide reductase activity. Furthermore, the inhibition of RNA and protein synthesis by Cl-F( downward arrow)-dAdo and Cl-diF( upward arrow downward arrow)-dAdo at concentrations similar to those required for the inhibition of DNA synthesis can help explain the poor antitumor selectivity of these two agents because all cells require RNA and protein synthesis.
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Parker WB, Allan PW, Shaddix SC, Rose LM, Speegle HF, Gillespie GY, Bennett LL. Metabolism and metabolic actions of 6-methylpurine and 2-fluoroadenine in human cells. Biochem Pharmacol 1998; 55:1673-81. [PMID: 9634004 DOI: 10.1016/s0006-2952(98)00034-3] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Activation of purine nucleoside analogs by Escherichia coli purine nucleoside phosphorylase (PNP) is being evaluated as a suicide gene therapy strategy for the treatment of cancer. Because the mechanisms of action of two toxic purine bases, 6-methylpurine (MeP) and 2-fluoroadenine (F-Ade), that are generated by this approach are poorly understood, mechanistic studies were initiated to learn how these compounds differ from agents that are being used currently. The concentration of F-Ade, MeP, or 5-fluorouracil required to inhibit CEM cell growth by 50% after a 4-hr incubation was 0.15, 9, or 120 microM, respectively. F-Ade and MeP were also toxic to quiescent MRC-5, CEM, and Balb 3T3 cells. Treatment of CEM, MRC-5, or Balb 3T3 cells with either F-Ade or MeP resulted in the inhibition of protein, RNA, and DNA syntheses. CEM cells converted F-Ade and MeP to F-ATP and MeP-ribonucleoside triphosphate (MeP-R-TP), respectively. The half-life for disappearance of HeP-ribonucleoside triphosphate from CEM cells was approximately 48 hr, whereas the half-lives of F-ATP and ATP were approximately 5 hr. Both MeP and F-Ade were incorporated into the RNA and DNA of CEM cells. These studies indicated that the mechanisms of action of F-Ade and MeP were quite different from those of other anticancer agents, and suggested that the generation of these agents in tumor cells by E. coli PNP could result in significant advantages over those generated by either herpes simplex virus thymidine kinase or E. coli cytosine deaminase. These advantages include a novel mechanism of action resulting in toxicity to nonproliferating and proliferating tumor cells and the high potency of these agents during short-term treatment.
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Bennett LL, Allan PW, Arnett G, Shealy YF, Shewach DS, Mason WS, Fourel I, Parker WB. Metabolism in human cells of the D and L enantiomers of the carbocyclic analog of 2'-deoxyguanosine: substrate activity with deoxycytidine kinase, mitochondrial deoxyguanosine kinase, and 5'-nucleotidase. Antimicrob Agents Chemother 1998; 42:1045-51. [PMID: 9593124 PMCID: PMC105742 DOI: 10.1128/aac.42.5.1045] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The carbocyclic analog of 2'-deoxyguanosine (CdG) has broad-spectrum antiviral activity. Because of recent observations with other nucleoside analogs that biological activity may be associated the L enantiomer rather than, as expected, with the D enantiomer, we have studied the metabolism of both enantiomers of CdG to identify the enzymes responsible for the phosphorylation of CdG in noninfected and virally infected human and duck cells. We have examined the enantiomers as substrates for each of the cellular enzymes known to catalyze phosphorylation of deoxyguanosine. Both enantiomers of CdG were substrates for deoxycytidine kinase (EC 2.7.1.74) from MOLT-4 cells, 5'-nucleotidase (EC 3.1.3.5) from HEp-2 cells, and mitochondrial deoxyguanosine kinase (EC 2.7.1.113) from human platelets and CEM cells. For both deoxycytidine kinase and mitochondrial deoxyguanosine kinase, the L enantiomer was the better substrate. Even though the D enantiomer was the preferred substrate with 5'-nucleotidase, the rate of phosphorylation of the L enantiomer was substantial. The phosphorylation of D-CdG in MRC-5 cells was greatly stimulated by infection with human cytomegalovirus. The fact that the phosphorylation of D-CdG was stimulated by mycophenolic acid and was not affected by deoxycytidine suggested that 5'-nucleotidase was the enzyme primarily responsible for its metabolism in virally infected cells. D-CdG was extensively phosphorylated in duck hepatocytes, and its phosphorylation was not affected by infection with duck hepatitis B virus. These results are of importance in understanding the mode of action of D-CdG and related analogs and in the design of new biologically active analogs.
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