The Effects of Black Raspberry as a Whole Food-Based Approach on Biomarkers of Oxidative Stress in Buccal Cells and Urine of Smokers

Cigarette smoke is a rich source of free radicals that can promote oxidative stress and carcinogenesis, including head and neck squamous cell carcinoma (HNSCC) development; importantly, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-iso-prostaglandin F2α (8-isoprostane) are biomarkers of oxidative stress. Several mechanisms, including the antioxidant properties of black raspberry (BRB), account for their chemopreventive effects. In the present clinical trial, we tested the hypothesis that BRB administration reduces biomarkers levels of oxidative stress in buccal cells and urine of smokers. One week after enrolling 21 smokers, baseline buccal cells and urine samples were collected before the administration of BRB lozenges for 8 weeks (5/day, 1 gm BRB/lozenge). Buccal cells and urine samples were collected at the middle and the end of BRB administration. The last samples were collected after the BRB cessation (washout period). We analyzed levels of 8-oxodG and 8-isoprostane (LC/MS-MS), urinary cotinine (ELISA), and creatinine (spectrophotometry). BRB significantly reduced the levels of 8-oxodG by 17.08% (P = 0.00079) in buccal cells and 12.44% (P = 0.034) in urine at the middle of BRB administration as compared with baseline; the corresponding values at the end of BRB administration were 16.46% (P = 0.026) in buccal cells and 25.72% (P = 0.202) in urine. BRB had no significant effect on the levels of urinary 8-isoprostane. BRB's capacity to inhibit 8-oxodG formation of smokers' buccal cells and urine is clearly evident and the reduction in 8-oxodG suggests that antioxidant abilities are central to BRB's HNSCC chemopreventive properties.

PREVENTION RELEVANCE

Cigarette smoke contains highly active components namely free radicals that can promote oxidative stress and oral cancer. We found that black raspberry (BRB) inhibited the formation of oxidative stress markers in the oral cavity and urine of smokers suggesting the antioxidant abilities of BRB in preventing oral cancer.

A modified nucleoside O6-methyl-2'-deoxyguanosine-5'-triphosphate exhibits anti-glioblastoma activity in a caspase-independent manner

Resistance to temozolomide (TMZ), the frontline chemotherapeutic agent for glioblastoma (GBM), has emerged as a formidable obstacle, underscoring the imperative to identify alternative therapeutic strategies to improve patient outcomes. In this study, we comprehensively evaluated a novel agent, O6-methyl-2'-deoxyguanosine-5'-triphosphate (O6-methyl-dGTP) for its anti-GBM activity both in vitro and in vivo. Notably, O6-methyl-dGTP exhibited pronounced cytotoxicity against GBM cells, including those resistant to TMZ and overexpressing O6-methylguanine-DNA methyltransferase (MGMT). Mechanistic investigations revealed that O6-methyl-dGTP could be incorporated into genomic DNA, disrupting nucleotide pools balance, and inducing replication stress, resulting in S-phase arrest and DNA damage. The compound exerted its anti-tumor properties through the activation of AIF-mediated apoptosis and the parthanatos pathway. In vivo studies using U251 and Ln229 cell xenografts supported the robust tumor-inhibitory capacity of O6-methyl-dGTP. In an orthotopic transplantation model with U87MG cells, O6-methyl-dGTP showcased marginally superior tumor-suppressive activity compared to TMZ. In summary, our research, for the first time, underscores the potential of O6-methyl-dGTP as an effective candidate against GBM, laying a robust scientific groundwork for its potential clinical adoption in GBM treatment regimens.

Telomere Stress Potentiates STING-Dependent Anti-tumor Immunity

Telomerase is an attractive target for anti-tumor therapy as it is almost universally expressed in cancer cells. Here, we show that treatment with a telomere-targeting drug, 6-thio-2'-deoxyguanosine (6-thio-dG), leads to tumor regression through innate and adaptive immune-dependent responses in syngeneic and humanized mouse models of telomerase-expressing cancers. 6-thio-dG treatment causes telomere-associated DNA damages that are sensed by dendritic cells (DCs) and activates the host cytosolic DNA sensing STING/interferon I pathway, resulting in enhanced cross-priming capacity of DCs and tumor-specific CD8⁺ T cell activation. Moreover, 6-thio-dG overcomes resistance to checkpoint blockade in advanced cancer models. Our results unveil how telomere stress increases innate sensing and adaptive anti-tumor immunity and provide strong rationales for combining telomere-targeting therapy with immunotherapy.

SLC43A3 Is a Biomarker of Sensitivity to the Telomeric DNA Damage Mediator 6-Thio-2'-Deoxyguanosine

Cell membrane transporters facilitate the passage of nucleobases and nucleosides for nucleotide synthesis and metabolism, and are important for the delivery of nucleoside analogues used in anticancer drug therapy. Here, we investigated if cell membrane transporters are involved in the cellular uptake of the nucleoside analogue DNA damage mediator 6-thio-2'-deoxyguanosine (6-thio-dG). A large panel of non-small cell lung cancer (NSCLC) cell lines (73 of 77) were sensitive to 6-thio-dG; only four NSCLC lines were resistant to 6-thio-dG. When analyzed by microarray and RNA sequencing, the resistant NSCLC cell lines clustered together, providing a molecular signature for patients that may not respond to 6-thio-dG. Significant downregulation of solute carrier family 43 A3 (SLC43A3), an equilibrative nucleobase transporter, was identified as a candidate in this molecular resistance signature. High levels of SLC43A3 mRNA predicted sensitivity to 6-thio-dG and therefore SLC43A3 could serve as a promising biomarker for 6-thio-dG sensitivity in patients with NSCLC. SIGNIFICANCE: These findings identify a biomarker of resistance to the telomeric DNA damage mediator 6-thio-2'-deoxyguanosine.

Anti-inflammatory effects of 8-hydroxydeoxyguanosine in LPS-induced microglia activation: suppression of STAT3-mediated intercellular adhesion molecule-1 expression

To elucidate the roles of 8-hydroxydeoxyguanosine (oh(8)dG), the nucleoside of 8-hydroxyguanine (oh(8)Gua), we examined the effects of oh(8)dG upon LPS-induced intercellular adhesion molecule-1 (ICAM-1) expression and the underlying mechanisms in brain microglial cells. We found that oh(8)dG reduces LPS-induced reactive oxygen species (ROS) production, STAT3 activation, and ICAM-1 expression. oh(8)dG also suppresses pro-inflammatory cytokines, such as TNF-alpha, IL-6 and IFN-gamma. Overexpression of dominant negative STAT3 completely diminshed STAT3-mediated ICAM-1 transcriptional activity. Chromatin immunoprecipitation studies revealed that oh(8)dG inhibited recruitment of STAT3 to the ICAM-1 promoter, followed by a decrease in ICAM-1 expression. Using mice lacking a functional Toll-like receptor 4 (TLR4), we demonstrated that, while TLR4+/+ microglia were activated by LPS, TLR4-/- microglia exhibited inactivated STAT3 in response to LPS. Evidently, LPS modulates STAT3-dependent ICAM-1 induction through TLR4-mdiated cellular responses. Oh(8)dG apparently plays a role in anti-inflammatory actions via suppression of ICAM-1 gene expression by blockade of the TLR4-STAT3 signal cascade in inflammation-enhanced brain microglia. Therefore, oh(8)dG in the cytosol probably functions as an anti-inflammatory molecule and should be considered as a candidate for development of anti-inflammatory agents.

Enhanced toxicity of purine nucleoside analogs in cells expressing Drosophila melanogaster nucleoside kinase mutants

The multisubstrate deoxyribonucleoside kinase of Drosophila melanogaster (Dm-dNK) is investigated for possible use as a suicide gene in combined gene/chemotherapy of cancer. The enzyme has broader substrate specificity and higher catalytic rate compared to herpes simplex type 1 thymidine kinase and other known dNKs. Although the enzyme has broad substrate specificity, it has a preference for pyrimidine nucleosides and nucleoside analogs. We have evaluated the substrate specificity and kinetic properties of Dm-dNK proteins containing M88R, V84A+M88R or V84A+M88R+A110D mutations in the amino-acid sequence. These engineered enzymes showed a relative increase in phosphorylation of purine nucleoside analogs such as ganciclovir, 9-beta-D-arabinofuranosylguanine and 2',2'-difluorodeoxyguanosine compared to the wild-type enzyme. The mutant enzymes were expressed in an osteosarcoma thymidine kinase-deficient cell line and the sensitivity of the cell line to nucleoside analogs was determined. The cells expressing the M88R mutant enzyme showed the highest increased sensitivity to purine nucleoside analogs with 8- to 80-fold decreased inhibition constant IC(50) compared to untransduced control cells or cells expressing the wild-type nucleoside kinase. In summary, our data show that enzyme engineering can be used to shift the substrate specificity of the Dm-dNK to selectively increase the sensitivity of cells expressing the enzyme to purine nucleoside analogs.

Immunopharmacological and antitumor effects of second-generation immunomodulatory oligonucleotides containing synthetic CpR motifs

Bacterial and synthetic DNAs containing CpG dinucleotides in specific sequence contexts (CpG DNA) activate the vertebrate immune system and produce potent Th1 immune responses. Recently, we reported immunomodulatory oligonucleotides (IMOs) containing 3'-3'-attached novel structures (immunomers) and synthetic immunostimulatory CpR (R=2'-deoxy-7-deazguanosine) dinucleotides show potent stimulatory activity with distinct cytokine secretion profiles. In the present study, we evaluated in vivo immunopharmacological and antitumor properties of second-generation immunomodulatory oligonucleotides (IMOs) either alone or in combination with chemotherapeutic agents. Repeated peritumoral administration of IMOs at 1 mg/kg to mice bearing established subcutaneous CT26 colon tumor or B16.F0 melanoma resulted in complete regression or strong inhibition of tumor growth. Direct peritoneal injection of IMOs at 2.5 mg/kg to mice bearing peritoneally implanted ascites CT26 or B16.F0 tumors completely eradicated or inhibited tumor growth. Treatment of mice bearing beta-gal expressing CT26.CL25 tumor with IMOs resulted in a significant tumor-specific CTL responses compared with treatment with a control non-CpG DNA or PBS. These responses correlated with IFN-gamma, but not IL-4 secreted in IMO, treated mice. A 5-fold increase in beta-gal specific IgG2a antibodies was found in mice, significantly increasing the IgG2a/IgG1 ratio. IMOs showed similar antitumor activity in both wt and IL-6 knockout (ko) C57BL/6 mice but failed to elicit activity in IL-12 ko C57BL/6 mice. Tumor-free mice from the IMO treatment group rejected the same tumor cell rechallenge, suggesting an adaptive immune response against these cells. Moreover, naïve mice quickly developed specific antitumor response without IMO treatment following adoptive transfer of splenocytes obtained from tumor free mice from the IMO treated group. Additionally, the co-administration of IMOs with chemotherapeutic agents, docetaxel and doxorubicin, resulted in synergistic antitumor effects in both B16.F0 melanoma and 4T1 breast carcinoma models. These results demonstrate potent antitumor activity of second-generation IMO compounds containing a synthetic CpR stimulatory motif in a broad spectrum of tumor models through induction of strong Th1 immune responses. IMO treatment resulted in the development of tumor-specific memory immune responses. No treatment-related toxicity was observed in mice at the doses and treatment schedules studied.

Multi-log cytotoxicity of carbocyclic 2'-deoxyguanosine in HSV-TK-expressing human tumor cells

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.

Therapeutic potential of a novel synthetic selectin blocker, OJ-R9188, in allergic dermatitis

1. We investigated the ability of a newly synthesized sugar derivative, OJ-R9188, [N-(2-tetradecylhexadecanoyl)-O-(L-alpha-fucofuranosyl)-D-seryl]-L-glutamic acid 1-methylamide 5-L-arginine salt, to block binding of selectins to their ligands in vitro and inhibit the infiltration of leukocytes in vivo. 2. OJ-R9188 prevented the binding of human E-, P- and L-selectin-IgG fusion proteins to immobilized sialyl Lewis(x) (sLe(x))-pentasaccharide glycolipid, with IC(50) values of 4.3, 1.3, and 1.2 microM, respectively. 3. In a mouse model of thioglycollate-induced peritonitis, OJ-R9188 at 10 mg kg(-1), i.v. inhibited neutrophil accumulation in the peritoneal cavity. In the IgE-mediated skin reaction, OJ-R9188 at 3 and 10 mg kg(-1), i.v. significantly inhibited extravasation of neutrophils and eosinophils into the inflammatory sites and at 10 mg kg(-1), i.v. also inhibited infiltration caused by picryl chloride-induced delayed-type hypersensitivity in mice. These results suggest that OJ-R9188 may be a useful selectin blocker, with activity against human and mouse E-, P- and L-selectins in vitro and in vivo, and that blocking selectin-sLe(x) binding is a promising strategy for the treatment of allergic skin diseases.

Antitumor efficacy of SarCNU in a human glioma xenograft model expressing both MGMT and extraneuronal monoamine transporter

Treatment of malignant brain tumors with chloroethylnitrosoureas (CENUs) in addition to surgical resection and radiotherapy remains the foundation of glioma therapy. However, the clinical response to CENUs is at best modest. A novel analogue of nitrosoureas, 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU), as compared to the standard CENU, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), has been demonstrated to have increased anticancer effects both in vitro and in vivo. Unfortunately, many human tumors have been known to be resistant to CENUs since they express DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). In order to assess whether SarCNU has an effect on MGMT positive tumors, we evaluated its antitumor efficacy using an MGMT positive human glioma (SF-767) nude mouse xenograft model. Since SF-767 has high MGMT levels, BCNU treatment (20 mg/kg, Q4D x 3 i.p.) alone did not result in a satisfactory anticancer effect (p > 0.05). As expected, O6-benzylguanine (O6-BG) (100 mg/kg), which was given prior to BCNU treatment, by depleting MGMT activity, significantly enhanced BCNU antitumor efficacy (p < 0.001). Moreover, SarCNU treatment (167 mg/kg, Q4D x 3 i.p.) alone had a better antitumor effect than O6-BG plus BCNU treatment (F = 51.7, p = 0.0004). However, in this xenograft model, O6-BG did not significantly enhance the anticancer efficacy of SarCNU (F = 0.8, p = 0.411). The SF-767 human glioma xenograft is positive for extraneuronal monoamine transporter EMT (EMT) as determined by reverse-transcription polymerase chain reaction (RT-PCR). Our present results suggest that SarCNU is also effective for MGMT positive tumor if they exhibit EMT.

Thresholds of O6-alkylguanine-DNA alkyltransferase which confer significant resistance of human glial tumor xenografts to treatment with 1,3-bis(2-chloroethyl)-1-nitrosourea or temozolomide

Bis-2-chloroethylnitrosourea (BCNU) or temozolomide (TMZ) were tested alone or in combination with the AGT inhibitors O6-benzyl-2'-deoxyguanosine (dBG) or O6-benzylguanine (BG) against human glial tumor xenografts growing s.c. in athymic mice. Four glioblastoma (SWB77, SWB40, SWB39, and D-54) and one anaplastic oligodendroglioma (SWB61) xenografts having O6-alkylguanine-DNA alkyltransferase (AGT) activities of 75, 45, 10, < 10, and 16 fmol/mg protein, respectively, were used. BCNU at 35 mg/m2 was ineffective against these tumors, although 70 mg/m2 (LD10, 75 mg/m2) produced a marked tumor growth delay (T-C) in D54 but had no effect against SWB40 or SWB77. Coadministration of BG or dBG and BCNU necessitated reduction of the BCNU dose to a maximum of 30 and 35 mg/m2, respectively, because of increased toxicity. Optimized treatment with dBG (250 mg/m2) and BCNU (35 mg/m2) resulted in T-Cs of 30, 29, 11, 16, and 14 days for SWB77, SWB40, SWB39, D-54 and SWB61, respectively. These delays were more pronounced than those induced with optimized, isotoxic treatments with BG (180 mg/m2) and BCNU (30 mg/m2). In comparison to BCNU, TMZ was less toxic, with an LD10 of 400 mg/m2. TMZ (300 mg/m2) was more effective than BCNU against SWB77, SWB40, and SWB61, inducing T-Cs of 23, 53, and 56 days, respectively. BG and dBG enhanced the toxicity of TMZ in athymic mice by decreasing the LD10 from 400 to 200 mg/m2. TMZ (180 mg/m2) with either BG (180 mg/m2) or dBG (250 mg/m2) resulted in T-Cs of 31 and 49 days in SWB77, respectively, as compared with 16 days for TMZ (180 mg/m2) alone. In SWB40, the combination of TMZ with dBG, but not with BG, was significantly more effective than the maximum tolerated dose of TMZ (300 mg/m2) alone. The combination of TMZ with AGT inactivators had no benefit, as compared with TMZ alone, against xenografts with marginal AGT activity. In conclusion, at equimolar doses dBG was less toxic than BG in athymic mice when combined with either BCNU or TMZ. In this regard, BCNU or TMZ can be used at higher doses in combination with dBG than with BG. This study further demonstrates that there is a significant benefit of depleting AGT with nonspecific AGT inhibitors prior to treatment with either BCNU or TMZ in tumors having AGT activity >45 fmol/mg protein.

Eradication of human medulloblastoma tumor xenografts with a combination of O6-benzyl-2'-deoxyguanosine and 1,3-bis(2-chloroethyl)1-nitrosourea

O6-Benzyl-2'-deoxyguanosine (dBG), a water-soluble inhibitor of O6-methylguanine-DNA methyltransferase (MGMT), potentiates the efficacy of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) against MGMT-positive, BCNU-resistant Daoy human medulloblastoma tumor xenografts in athymic mice (S. C. Schold et al., Cancer Res., 56: 2076-2081, 1996). Such potentiation was comparable to that observed for O6-benzylguanine, the prototype MGMT inhibitor that is currently undergoing clinical trials. In this study, we optimized the therapeutic effect of the dBG and BCNU combination against brain tumor xenografts without inducing substantial toxicity in the host by adjusting the doses of both compounds. dBG was escalated from 133 mg/m2 to 200 and 300 mg/m2, whereas corresponding doses of BCNU were reduced from 25 mg/m2 to 17 and 11 mg/m2, respectively. The growth delays of 30.2, 38.4, and 22.3 days, respectively, observed for the above regimens suggest that the optimal drug combination is not achieved with maximum doses of dBG. In fact, the highest doses of dBG (300 mg/m2) contributed to more frequent BCNU-related toxicities, despite the reduced BCNU dosage, and a reduction of the therapeutic effect. Toxicity was related to the depletion of MGMT activity in the gut of host mice and was manifested by edema, inflammation, and hemorrhage in the bowel wall by subsequent BCNU administration. With additional dosage adjustments, we found that tumor suppression of >90 days without toxicity was observed at 200 mg/m2 dBG and 23 mg/m2 BCNU. At these doses, tumors were eradicated (regressed to an undetectable size for >90 days) in 8 of 12 animals. Thus, dBG is the first of the MGMT inhibitors to show a curative effect in combination with BCNU against a human central nervous system tumor xenograft in athymic mice.

Efficacy of the carbocyclic 2'-deoxyguanosine nucleoside BMS-200475 in the woodchuck model of hepatitis B virus infection

Daily oral treatment with the cyclopentyl 2'-deoxyguanosine nucleoside BMS-200475 at doses ranging from 0.02 to 0.5 mg/kg of body weight for 1 to 3 months effectively reduced the level of woodchuck hepatitis virus (WHV) viremia in chronically infected woodchucks as measured by reductions in serum WHV DNA levels and endogenous hepadnaviral polymerase activity. Within 4 weeks of daily therapy with 0.5 or 0.1 mg of BMS-200475 per kg, endogenous viral polymerase levels in serum were reduced about 1,000-fold compared to pretreatment levels. Serum WHV DNA levels determined by a dot blot hybridization technique were comparably decreased in these treated animals. In the 3-month study, the sera of animals that had undetectable levels of WHV DNA by the dot blot technique were further analyzed by a highly sensitive semiquantitative PCR assay. The results indicate that BMS-200475 therapy reduced mean WHV titers by 10(7)- to 10(8)-fold, down to levels as low as 10(2) to 10(3) virions/ml of serum. Southern blot hybridization analysis of liver biopsy samples taken from animals during and after BMS-200475 treatment showed remarkable reductions in the levels of WHV DNA replicative intermediates and in the levels of covalently closed circular viral DNA. WHV viremia in BMS-200475-treated WHV carriers eventually returned to pretreatment levels after therapy was stopped. These results indicate that BMS-200475 should be evaluated in clinical trials for the therapy of chronic human hepatitis B virus infections.

Phosphorylation of anticancer nucleoside analogs by human mitochondrial deoxyguanosine kinase

The kinetic properties of recombinant human mitochondrial deoxyguanosine kinase (dGK, EC 2.7.1.113) for 2'-deoxyguanosine and the clinically important nucleoside analogs 2-chloro-2'-deoxyadenosine (CdA), 9-beta-D-arabinofuranosylguanine (araG) and 2',2',-difluorodeoxyguanosine (dFdG) were determined. The Michaelis-Menten kinetic parameters, comparing ATP and UTP as phosphate donors, demonstrated a marked increase in phosphorylation efficiency (VmaxKm) with UTP in comparison with ATP for both CdA and araG. The difluoro analog dFdG was an efficient substrate for recombinant dGK with an apparent Km of 16 microM with ATP as phosphate donor. We compared the kinetic properties of dGK with those of the related enzyme deoxycytidine kinase (dCK, EC 2.7.1.74). Although the purines 2'-deoxyguanosine (dGuo) and 2'-deoxyadenosine are substrates for both dGK and dCK, only CdA among the purine nucleoside analogs tested was an efficient substrate for both dCK and dGK. In competition with dGuo, the most efficient analog for phosphorylation by dGK was araG, as indicated by a lower Ki value than for CdA and dFdG. Of the purine analogs tested as substrates for dCK, only CdA could compete with 2'-deoxycytidine (dCyd). No inhibition of dCK-mediated dCyd phosphorylation was found by either araG or dFdG. In crude cell extract of HeLa and Capan 2 cells, the major CdA phosphorylation was contributed by dCK, while most araG phosphorylation was a result of dGK activity. Our study with pure recombinant enzymes confirms that dGK is mainly responsible for araG and dFdG phosphorylation, whereas dCK is the most important enzyme for activation of CdA and 2',2'-difluorodeoxycytidine (dFdC).

Evidence that hepatocyte turnover is required for rapid clearance of duck hepatitis B virus during antiviral therapy of chronically infected ducks

Duck hepatitis B virus (DHBV) DNA synthesis in congenitally infected ducks is inhibited by 2'-deoxycarbocyclic guanosine (2'-CDG). Three months of therapy reduces the number of infected hepatocytes at least 10-fold (W.S. Mason, J. Cullen, J. Saputelli, T.-T. Wu, C. Liu, W.T. London, E. Lustbader, P. Schaffer, A.P. O'Connell, I. Fourel, C.E. Aldrich, and A.R. Jilbert, Hepatology 19:393-411, 1994). The present study was performed to determine the kinetics of disappearance of infected hepatocytes and to evaluate the role of hepatocyte turnover in this process. Essentially all hepatocytes were infected before drug therapy. Oral treatment with 2'-CDG resulted in a prompt reduction in the number of infected hepatocytes. After 2 weeks, only 30 to 50% appeared to still be infected, and less than 10% were detectably infected after 5 weeks of therapy. To assess the possible role of hepatocyte turnover in these changes, 5-bromo-2'-deoxyuridine (BUdR) was administered 8 h before liver biopsy to label host DNA in hepatocytes passing through S phase, and stained nuclei were detected in tissue sections by using an antibody reactive to BUdR. The extent of nuclear labeling after 5 weeks was the same as that before therapy (ca. 1%). However, biopsies taken after 2 weeks of therapy showed a ca. 10-fold elevation in the number of nuclei labeled with BUdR. This result suggested that a rapid clearance of infected hepatocytes by 2'-CDG was caused not just by the inhibition of viral replication but also by an acceleration of the rate of hepatocyte turnover. To test this possibility further, antiviral therapy was carried out with another strong inhibitor of DHBV DNA synthesis, 5-fluoro-2',3'-dideoxy-3'-thiacytidine (524W), which did not accelerate hepatocyte turnover in ducks. 524W administration led to a strong inhibition of virus production but to a slower rate of decline in the number of infected hepatocytes, so that ca. 50% (and perhaps more) were still infected after 3 months of therapy. In addition, histopathologic evaluation of 2'-CDG-treated ducks revealed liver injury, especially at the start of therapy. No liver damage was observed during 524W therapy. These results imply that clearance of infected hepatocytes from the liver is correlated with hepatocyte turnover. Thus, in the absence of immune clearance or other sources for the accelerated elimination of infected hepatocytes, inhibitors of virus replication would have to be administered for a long period to substantially reduce the burden of infected hepatocytes in the liver.

Improvement in allograft survival of islets of Langerhans by pretreatment with deoxyguanosine

In vitro pretreatment of isolated islets of Langerhans prior to transplantation with deoxyguanosine (dGuo) was found to be effective in improving the survival in fully allogeneic diabetic rats (Wistar----PVG). Post transplant immunosuppression was not used. Islets pretreated with various concentrations of dGuo, 1, 1.35, 1.5 and 2 microM dGuo per islet showed a graft survival of 9, 36, 9 and 14% respectively.

Fluorocarbocyclic nucleosides: synthesis and antiviral activity of 2'- and 6'-fluorocarbocyclic 2'-deoxy guanosines

A series of four isomeric 2'- and 6'-fluorocarbocyclic guanosine analogues have been prepared and evaluated as potential anti-herpes agents. The racemic 2' beta-fluoro isomer 2-amino-1,9-dihydro- 9-[(1 alpha, 2 alpha, 3 beta, 4 alpha)-2-fluoro-3-hydroxy-4- (hydroxymethyl)cyclopentyl]-6H-purin-6-one (11a, C-AFG) and its 2' alpha-fluoro epimer 11b plus the chiral 6' beta-fluoro isomer 2-amino-1,9-dihydro-9-[[1S-(1 alpha, 2 alpha, 3 alpha, 4 beta)]- 2-fluoro-4-hydroxy-3-(hydroxymethyl)cyclopentyl]-6H-purine-6-one (11c) and its 6' alpha-fluoro epimer 11d were prepared from their respective fluoro amino diol hydrochlorides (6a,d). For comparison, the furanosyl compound 9-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)guanine (17, AFG) was prepared by coupling 2-amino-6-chloropurine with 2-deoxy-2-fluoro-3,5-di-O-benzoyl-alpha- D-arabinofuranosyl bromide followed by base hydrolysis. The 6' alpha-fluoro derivative 11d exhibited comparable activity to that of acyclovir (ACV) against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in vitro but was greater than 30-fold more active than ACV against HSV-1 and HSV-2 in vivo in the mouse systemic model. The 2' beta-fluoro derivative (11a, C-AFG) was extremely potent in vitro against HSV-1 and HSV-2 (ID50 0.006 and 0.05 micrograms/mL) and in vivo it was greater than 2 orders of magnitude more potent than ACV against HSV-1 and 70-fold more potent against HSV-2. The 2' alpha-fluoro 11b and 6' beta-fluoro 11c isomers were much less active.

2,6-Diaminopurinedeoxyriboside as a prodrug of deoxyguanosine in L1210 cells

The mode of action of the antiproliferative nucleoside analogue 2,6-diaminopurinedeoxyriboside (DAPdR) has been characterized in cultured L1210 cells. A marked concentration-dependent decrease in DNA synthesis and ribonucleotide reductase activity occurred in L1210 cells exposed to 0.05 to 1.0 mM DAPdR. Concomitantly, dGTP levels increased as much as 1100-fold as compared to untreated controls. Adenosine deaminase efficiently catalyzed DAPdR conversion to deoxyguanosine in vitro. In a comparative study, DAPdR and deoxyguanosine gave similar results. A 50% inhibition of cell growth during a 72-h incubation was achieved with 0.14 mM DAPdR or 0.26 mM deoxyguanosine. Deoxycytidine rescued the L1210 cells from DAPdR and deoxyguanosine toxicity to the same extent. DAPdR and deoxyguanosine counteracted the toxic effects of mycophenolic acid with the same efficiency. While DAPdR was not metabolized to its 5'-triphosphate, 2,6-diaminopurine was converted to 2,6-diaminopurineriboside 5'-triphosphate in L1210 cells; accordingly 50% inhibition of cell growth occurred at 0.015 mM 2,6-diaminopurine. Combinations of DAPdR with erythro-9-(2-hydroxy-3-nonyl)adenine or deoxycoformycin resulted in antagonism instead of an expected synergism. These data suggest that DAPdR exerts its toxicity on L1210 cells as a prodrug of deoxyguanosine.

Phase II trials of hexamethylmelamine, dianhydrogalactitol, razoxane, and beta-2'-deoxythioguanosine as single agents against advanced measurable tumors of the pancreas. Gastrointestinal Tumor Study Group

Phase II trials of several single agents demonstrated only minimal objective response rates in patients with pancreatic carcinoma and measurable tumors: hexamethylmelamine (7%; four responses among 55 patients); dianhydrogalactitol (2.5%; one response among 40 patients); razoxane (7%; two responses among 29 patients); and beta-2'-deoxythioguanosine (6%; two responses among 32 patients). Among patients with a good performance status (0-2) and no prior chemotherapy, response rates were 8% for hexamethylmelamine (two responses among 26 patients); 8% for dianhydrogalactitol (one response among 13 patients); 8% for razoxane (one response among 12 patients); and 10% for beta-2'-deoxythioguanosine (two responses among 20 patients). None of these agents given by the methods of this study offers substantive benefit to the patient with advanced pancreatic cancer.

PLDR inhibitors: their biological and clinical implications

Effects of various nucleoside analogues on X-ray-induced-PLD recovery (PLDR) were examined in plateau phase Chinese hamster HA-1 cells. Among the chemicals tested, 3'-dA (3'-deoxyadenosine) and ara-A (9-beta-D-arabinofuranosyladenine) were most potent inhibitors of PLDR at their slightly toxic doses. N6-butyryl-3'-dA and 3'-dG (3'-deoxyguanosine) were the most effective in suppressing PLDR at non-toxic doses. A specific inhibitor of DNA polymerase beta, 2', 3'-ddT (dideoxythymidine) was intermediately effective. However, possibly due to the lower intracellular incorporation or phosphorylation, 3'-deoxy-pyrimidine analogues and formycin B were less or non-effective. The enhancement of antitumor effect of cyclophosphamide by ara-A and 3'-dG was observed in SCC VII tumors in vivo. The involvement of DSB (or chromosome aberration) and SSB as well as base damage or crosslinks in PLD is suggested, since recently they have been shown not to be rejoined when treated with various agents such as hyperthermia and ara-A.

Synthesis of hypoxanthine, guanine, and 6-thiopurine nucleosides of 6-deoxy-D-allofuranose

Hypoxanthine, guanine, and 6-thiopurine nucleosides of 6-deoxy-D-allofuranose have been prepared as potential antitumor agents. Thus, reaction of 6-deoxy-beta-D-allofuranosyl bromide (1) with the trimethylsilyl derivatives of hypoxanthine and guanine afforded mixtures of the 9- and the 7-substituted bases, which were separated and deblocked with ammonia to give 9-(6'-deoxy-beta-D-allofuranosyl)hypoxanthine (6), 7-(6'-deoxy-beta-D-allofuranosyl)hypoxanthine (7), 9-(6'-deoxy-beta-D-allofuranosyl)guanine (8), and 7-(6'-deoxy-beta-D-allofuranosyl)guanine (9). The two nucleosides with the purine joined at the N-9 position, namely, 6 and 8, are easily distinguished from the other two nucleosides (7 and 9), having N-7 junctions, by their NMR spectra. Reaction of 1 with the trimethylsilyl derivative of 6-chloropurine afforded 10, which upon treatment with thiourea and deblocking gave 9-(6'-deoxy-beta-D-allofuranosyl)-6-thiopurine (12). The hypoxanthine and guanine nucleosides showed no inhibition of mouse leukemia L1210 when tested in vivo, but the thiopurine nucleoside 12 showed strong inhibition of growth of L1210 both in vivo and in vitro. Compound 7 strongly inhibited purine nucleoside phosphorylase (KI = 8.8 X 10(-5) M), while compounds 8, 9, 6, and 12 were inactive.

Selective toxicity of deoxyguanosine and arabinosyl guanine for T-leukemic cells

Deoxyguanosine is selectively cytotoxic to leukemic cells from patients with T-acute lymphoblastic leukemia (T-ALL), whereas all other leukemic cell types were significantly less sensitive. Arabinosylguanine, a deoxyguanosine analog resistant to cleavage by purine nucleoside phosphorylase, is a more potent inhibitor of DNA synthesis in T-leukemic cells than deoxyguanosine and retains a selective cytotoxic activity for T-leukemic cells. Deoxyguanosine and arabinosylguanine are phosphorylated to deoxyGTP and arabinosylGTP, respectively, by T cells but not by other cell types. The phosphorylation and the cytotoxicity of arabinosylguanine are prevented by deoxycytidine. The selectivity of arabinosylguanine for malignant T cells, the exquisite sensitivity of these cells to the drug, and the failure of PNP to cleave the nucleoside indicate its potential in the treatment of T-ALL.

Combinational chemotherapy of L1210 and L1210/ARA-C leukemia with 5-AZA-2'-deoxycytidine and beta-2'-deoxythioguanosine

The in vitro and in vivo antineoplastic activity of 5-AZA-2'-deoxycytidine (5-AZA-CdR) and beta-2'-deoxythioguanosine (TGdR) on L1210 and L1210/ARA-C (resistant to cytosine arabinoside) leukemic cells was investigated. 5-AZA-CdR was a very potent cytotoxic agent against the L1210 leukemia cells. This analogue was inactive against L1210/ARA-C leukemic cells because these cells lack deoxycytidine kinase, the enzyme that converts 5-AZA-CdR to its active nucleotide form. TGdR was a potent cytotoxic agent to both L1210 and L1210/ARA-C leukemic cells. In mice which were injected simultaneously with both L1210 and L1210/ARA-C leukemic cells, the drug combination of 5-AZA-CdR plus TGdR had a very potent antineoplastic activity and produced long-term survivors. Either agent alone did not produce any long-term survivors in the mice with L1210 and L1210/ARA-C leukemia. This experimental model indicates that 5-AZA-CdR plus TGdR is an interesting drug combination for the treatment of leukemia with drug-resistant cells.

Pharmacology and toxicology of alpha-2'-deoxythioguanosine in cancer patients

alpha-2'-Deoxythioguanosine (alpha-TGdR) was administered as a single dose to 13 cancer patients in 18 experiments at dose levels of 150--1500 mg/m2 and as a daily dose to 22 patients in 42 experiments at dose levels of 100--4000 mg/m2/day X 5 days. No significant toxicity was observed. Blood levels and rates of excretion were determined with radiosulfur-labeled alpha-TGdR. Approximately 80% of the dose was excreted in the urine in 24 hours, initially as unchanged alpha-TGdR and increasingly as metabolites. Metabolites appear to be nucleosides and do not include 6-thioguanine, 6-thioxanthine, or 6-thiouric acid to any measurable extent. Small amounts of the alpha-TGdR in blood samples were bound to albumin and to erythrocyte membranes. Blood plasma levels of alpha-TGdR at the highest doses were in the range of 200--300 micrometer, declining in 24 hours to 67--124 micrometer.