A nelarabine-resistant T-lymphoblastic leukemia CCRF-CEM variant cell line is cross-resistant to the purine nucleoside phosphorylase inhibitor forodesine

BACKGROUND/AIM

Forodesine inhibits purine nucleoside phosphorylase, resulting in an accumulation of intracellular dGTP and consequently cell death. 9-β-D-Arabinofuranosylguanine (ara-G) is an active compound of nelarabine that is intracellularly phosphorylated to a triphosphate form, which inhibits DNA synthesis. Both agents show cytotoxicity toward T-cell malignancies. In the present study, we investigated the cytotoxicity of forodesine in vitro using ara-G-resistant leukemia cells.

MATERIALS AND METHODS

T-Lymphoblastic leukemia cell line CCRF-CEM and ara-G-resistant CEM variant cell line CEM/ara-G that we had previously established were used.

RESULTS

A growth-inhibition assay demonstrated that CEM cells were insensitive to single-agent forodesine treatment. The cells were also insensitive to deoxyguanosine at a maximal concentration of 10 μM. CEM/ara-G cells were 80-fold more resistant to ara-G than were CEM cells, and the mode of sensitivity to forodesine and deoxyguanosine was similar to that of CEM cells. In the presence of 10 μM deoxyguanosine, forodesine effectively inhibited the growth of CEM cells but not that of CEM/ara-G cells. Flow cytometric analyses showed that combination of forodesine and deoxyguanosine induced apoptosis of CEM cells but not of CEM/ara-G cells. The addition of ara-G did not augment the cytotoxicity of the forodesine/deoxyguanosine combination towards CEM cells or CEM/ara-G cells. The combination index revealed antagonism between forodesine and ara-G. The intracellular production of ara-G triphosphate was reduced in the presence of forodesine.

CONCLUSION

Nelarabine-resistant CEM/ara-G cells are insensitive to forodesine.

Synthesis and biological evaluation of 2- and 7-substituted 9-deazaadenosine analogues

A series of 2-halogen and 7-alkyl substituted analogues of 9-deazaadenosine and 2'-deoxy-9-deazaadenosine was synthesized by new efficient methodology involving transformation of corresponding 9-deazaguanosine and 2'-deoxyguanosine, which in turn were synthesized by direct C-glycosylation of 1-benzyl-9-deazaguanine with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose and methyl 2-deoxy-3,5-di-O-(p-toluoyl)-D-ribofuranoside, respectively. Deoxychlorination of C6 and diazotization/chloroor fluoro-dediazoniation of the sugar-protected 9-deazaguanosine, followed by selective ammonolysis at C6 and deprotection of the sugar moiety, gave 2-chloro- and 2-fluoro-9-deazaadenosine (6 and 9). Substitution of the 7-position of the dihalogen-intermediate with alkyl groups, followed by ammonolysis and deprotection, provided 2-chloro-7-alkyl-9-deazaadenosines (13a-e) and 2-fluoro-7-benzyl-9-deazaadenosine (13f). Catalytic hydrogenation of 13a-e gave 7-alkyl-9-deazaadenosines 14a-e. Similarly, 2-chloro-2'-deoxy-9-deazaadenosine (21), 2-chloro-2'-deoxy-7-methyl-9-deazaadenosine (25), 2'-deoxy-9-deazaadenosine (22), and 2'-deoxy-7-methyl-9-deazaadenosine (26) were prepared from sugar-protected 2'-deoxy-9-deazaguanosine. Among these compounds, 7-benzyl-9-deazaadenosine (14b) showed the most potent cytotoxic activity, with IC50 values of 0.07, 0.1, 0.2 and 1.5 microM, while both 7-methyl-9-deazaadenosine (14a) and 2-fluoro-9-deazaadenosine (9) also demonstrated significant cytotoxic activity with IC50 values of 0.4, 0.7, 0.3, and 1.5 microM, and 1.5, 0.9, 0.3, and 5 microM against L 1210 leukemia, P388 leukemia, CCRF-CEM lymphoblastic leukemia, and B16F10 melanoma cells, respectively.

Assessment of the genotoxic potential of nitric oxide-induced guanine lesions by in vitro reactions with Escherichia coli DNA polymerase I

It has been suggested that carcinogenesis associated with chronic inflammation involves DNA damage by nitric oxide (NO) and other reactive species secreted from macrophages and neutrophils. The guanine moiety of DNA reacts with NO, yielding two major deamination products: xanthine (Xan) and oxanine (Oxa). Oxa reacts further with polyamines and DNA binding proteins to form cross-link adducts. In the present study, we characterized the structure of the cross-link adducts of Oxa with spermine (Oxa-Sp). Spectrometric analysis of Oxa-Sp adducts showed that they are ring-opened adducts of Oxa covalently bonded to the terminal amino (major product) and internal imino (minor product) groups of spermine. To assess genotoxic potential, Xan, Oxa, Oxa-Sp and an abasic (AP) site were site specifically incorporated into oligonucleotide templates. These lesions differentially blocked in vitro DNA synthesis catalyzed by DNA polymerase I Klenow fragment (Pol I Kf). The relative efficiency of translesion synthesis was G (1) > Oxa (0.19) > Xan (0.12) > AP (0.088) > Oxa-Sp (0.035). Primer extension assays with a single nucleotide and Pol I Kf revealed that non-mutagenic dCMP was inserted most efficiently opposite Xan and Oxa, with the extent of primer elongation being 65% for Xan and 68% for Oxa. However, mutagenic nucleotides were also inserted. The extent of primer elongation for Xan was 16% with dTMP and 14% with dGMP, whereas that for Oxa was 49% with dTMP. For Oxa-Sp, mutagenic dAMP (13%) was preferentially inserted. Accordingly, when generated in vivo, Xan and Oxa would constitute moderate blocks to DNA synthesis and primarily elicit G:C to A:T transitions when bypassed, whereas Oxa-Sp would strongly block DNA synthesis and elicit G:C to T:A transversions.

Design, efficient synthesis, and anti-HIV activity of 4'-C-cyano- and 4'-C-ethynyl-2'-deoxy purine nucleosides

Some 4'-C-ethynyl-2'-deoxy purine nucleosides showed the most potent anti-HIV activity among the series of 4'-C-substituted 2'-deoxynucleosides whose 4'-C-substituents were methyl, ethyl, ethynyl and so on. Our hypothesis is that the smaller the substituent at the C-4' position they have, the more acceptable biological activity they show. Thus, 4'-C-cyano-2'-deoxy purine nucleosides, whose substituent is smaller than the ethynyl group, will have more potent antiviral activity. To prove our hypothesis, we planned to develop an efficient synthesis of 4'-C-cyano-2'-deoxy purine nucleosides (4'-CNdNs) and 4'-C-ethynyl-2'-deoxy purine nucleosides (4'-EdNs). Consequently, we succeeded in developing an efficient synthesis of six 2'-deoxy purine nucleosides bearing either a cyano or an ethynyl group at the C-4' position of the sugar moiety from 2'-deoxyadenosine and 2,6-diaminopurine 2'-deoxyriboside. Unfortunately, 4'-C-cyano derivatives showed lower activity against HIV-1, and two 4'-C-ethynyl derivatives suggested high toxicity in vivo.

Synthesis and cytotoxicity of 9-(2-deoxy-2-alkyldithio-β-D-arabinofuranosyl)purine nucleosides which are stable precursors to potential mechanistic probes of ribonucleotide reductases

A series of 2[prime or minute]-thionucleosides, as potential inhibitors of ribonucleotide reductases, has been synthesized. Treatment of the 3[prime or minute],5[prime or minute]-O-TPDS-2[prime or minute]-O-(trifluoromethanesulfonyl)adenosine with potassium thioacetate gave the arabino epimer of 2[prime or minute]-S-acetyl-2[prime or minute]-thioadenosine which was deacetylated to give 9-(3,5-O-TPDS-2-thio-[small beta]-d-arabinofuranosyl)adenine in high yield. Treatment of the latter with diethyl azodicarboxylate-C(3)H(7)SH-THF gave 2[prime or minute]-propyl disulfide which was desilylated to give 9-(2-deoxy-2-propyldithio-[small beta]-d-arabinofuranosyl)adenine. Subsequent tosylation (O5[prime or minute]) and displacement of the tosylate with pyrophosphate afforded the 5[prime or minute]-O-diphosphate in a stable form as propyl mixed-disulfide, which upon treatment with dithiothreitol releases 9-(2-thio-[small beta]-d-arabinofuranosyl)adenine 5[prime or minute]-diphosphate. The arabino 2[prime or minute]-mercapto group might interact with the crucial thiyl radical at cysteine 439 leading to the inhibition of ribonucleotide reductases via formation of a Cys439-2[prime or minute]-mercapto disulfide bridge. The 2,6-diamino-, 2-amino-6-chloro- and 2-amino-6-methoxypurine ribosides were also converted to the corresponding 2[prime or minute]-deoxy-2[prime or minute]-propyldithio-[small beta]-d-arabinofuranosyl nucleosides, which might serve as convenient precursors to the arabino epimer of 2[prime or minute]-thioguanosine. Analogously, 2[prime or minute]-deoxy-2[prime or minute]-propyldithioadenosine was prepared from 9-([small beta]-d-arabinofuranosyl)adenine. The nucleoside disulfides show modest cytotoxicity in a panel of human tumor cell lines.

Phase I clinical trial and pharmacokinetic study of the spicamycin analog KRN5500 administered as a 1-hour intravenous infusion for five consecutive days to patients with refractory solid tumors

PURPOSE

The spicamycin analogue KRN5500 is a nucleoside-like antibiotic with broad spectrum activity against human solid tumor models. It appears to possess a novel mechanism of action directed against the endoplasmic reticulum and Golgi apparatus with effects on protein processing. A Phase I trial was undertaken to determine the maximum tolerated dose (MTD), dose-limiting toxicities, and pharmacokinetic behavior of KRN5500 given as a 1-h i.v. infusion for 5 consecutive days every 3 weeks.

EXPERIMENTAL DESIGN

Adult patients with refractory solid tumors, good performance status, and normal to near normal renal, hepatic, and hematological function were eligible for the study. At least three patients were evaluated at each dose level, and a modified Fibonacci algorithm was used for dose escalation. The MTD was based on the occurrence of severe toxicity during the first cycle of therapy. The plasma pharmacokinetics of KRN5500 was characterized during the first week of dosing.

RESULTS

Characteristics of the 26 patients entered into the study were as follows: 13 males and 13 females; median age, 54.5 years (range, 40-70 years); and Eastern Cooperative Oncology Group performance status 0-1. A majority had refractory colorectal carcinoma (17 of 26 patients) with at least two prior regimens of therapy. The dose of KRN5500 was escalated from 0.8 to 4.9 mg/m(2)/day in five dose levels, and the MTD was 2.9 mg/m(2)/day. All dose-limiting toxicities were nonhematological and included pulmonary toxicities, hyperglycemia, fatigue, hepatotoxicity, and ataxia, with one fatality due to interstitial pneumonitis. Clinically significant toxicities occurring in multiple patients that were not dose-limiting included nausea/vomiting, diarrhea, fatigue, neurological symptoms, hyperbilirubinemia, hyperglycemia, lymphopenia, and thrombocytopenia. There were no objective responses, although 3 of 17 evaluable patients exhibited disease stabilization for 5-6 cycles. The pharmacokinetics for the first dose of KRN5500 was biexponential and linear across all five dose levels. Mean values of pharmacokinetic parameters were as follows: total plasma clearance, 6.15 +/- 2.37 liters/h/m(2); apparent volume of distribution at steady state, 6.56 +/- 1.98 liters/m(2); biological half-life, 1.29 +/- 0.37 h; and mean residence time, 1.07 +/- 0.31 h. Clearance was significantly lower (P = 0.011) in the eight patients who were at least 65 years old (4.6 +/- 1.6 liters/h/m(2)) as compared with the 18 younger patients (7.1 +/- 2.3 liters/h/m(2)). Peak plasma concentrations of KRN5500 in the cohort receiving the MTD ranged from 350 to 400 ng/ml.

CONCLUSIONS

The MTD of KRN5500, when given as a 1-h i.v. infusion for 5 consecutive days, was 2.9 mg/m(2)/day. The only suggestion of therapeutic activity observed in this study was disease stabilization in three patients with chemorefractory colorectal cancer. Administering KRN5500 as a continuous i.v. infusion with the objective of prolonging systemic exposure to potentially cytotoxic concentrations of the drug should be considered.

Synthesis of 4'-ethynyl-purine nucleosides possessing anti-HIV activity

Searching for more effective anti-HIV agents, we have prepared 4'-ethynyl-purine nucleosides. They were derived in several steps from 4-C-triethylsilylethynyl ribose, which was used as an intermediate in the synthesis of pyrimidine nucleosides. The adenine derivative exhibited significant anti-HIV activity and favorable cytotoxicity profile in vitro.

Incorporation of the anticancer agent KRN5500 into polymeric micelles diminishes the pulmonary toxicity

KRN5500 is a highly active new semi-synthetic water-insoluble anticancer agent. The only mechanism of anticancer activity of KRN5500 described so far is an inhibitory effect on protein synthesis. At the time of writing, a phase I clinical trial is under way at the National Cancer Center Hospital, Tokyo, and at the National Cancer Institute in the USA. Although preclinical data did not indicate lung toxicity, some cases of severe pulmonary disorder were reported in the phase I clinical trials. This study has been conducted to examine whether incorporation of KRN5500 into polymeric micelles (KRN/m) could reduce the toxic effects caused by the current formulation of KRN5500. The in vitro and in vivo antitumor activities of KRN5500 and KRN/m were compared. Pulmonary toxicity of KRN5500 and KRN/m was studied using a bleomycin (BLM)-induced lung injury rat model. In BLM-rats, extensive pulmonary hemorrhage with diapedesis was observed with KRN5500 i.v. bolus injection at the dose of 3 mg/kg, which is equivalent to 21.0 mg/m2 (level 5) of the Japanese phase I trial. However, toxicity was not observed when rats were administered KRN / m at the equivalent dose to KRN5500 in potency. Electron microscopy of the lung treated with KRN5500 showed disruption of the alveolar type II membrane with release of lamellar debris. Furthermore, in vivo, KRN/m showed similar antitumor activity to KRN5500. These results indicate that KRN/m may be useful for reducing the pulmonary toxicity associated with the current formulation of KRN5500, while fully maintaining its antitumor activity.

The role of nucleoside analogues in the treatment of chronic lymphocytic leukemia-lessons learned from prospective randomized trials

The newer purine nucleoside analogues (PNA), fludarabine (FAMP) and cladribine (2-chlorodeoxyadenosine, 2-CdA) have been synthesized recently and introduced into the treatment of chronic lymphocytic leukemia (CLL). The results of large phase II studies indicate that FAMP and 2-CdA are similarly active in CLL. Unfortunately, no prospective randomized study comparing the results of the treatment of CLL patients with FAMP and 2-CdA has been published so far. Significantly higher overall response (OR) and complete remission (CR) in patients treated initially with PNA than with chlorambucil or cyclophosphamide based combination regimens has been recently confirmed in five prospective multicentre randomized trials. These studies have also shown longer response duration in patients treated with PNA than with conventional chemotherapy. Overall survival progression free and events free survival were similar in patients treated with PNA and with chlorambucil or other alkylating agent based regimens. However, the majority of randomized trials were designed as cross over studies and most patients, treated with conventional chemotherapy were given PNA when refractory or in early relapse, which may influence the survival time. The results of a randomized study have shown a higher incidence of neutropenia and infections in patients treated with PNA than with chlorambucil. However. the frequency of autoimmune hemolytic anemia, pure red cell aplasia, secondary neoplasms and Richter's syndrome seems to be similar in patients treated with PNA and standard alkylating agents based chemotherapy. In conclusion, alkylating agents still have an important place in the routine management of the majority of CLL patients. They are in general safe, given on an out patients basis and significantly cheaper than PNA. PNA should be routinely used as second line treatment, and possibly as first line therapy in younger patients, who are candidates for potentially curative treatment such as stem cell transplantation and/or monoclonal antibodies.

KRN5500, a novel antitumor agent, induces apoptosis or cell differentiation in HL-60 cells

BACKGROUND

KRN5500, a derivative of spicamycin, shows antitumor activity against a variety of tumor cell lines. However, the mechanism of cytotoxic action has remained unclear.

METHODS

The viability of HL-60 human leukemic cells treated with KRN5500 was studied by the dye exclusion assay. Induction of apoptosis and effects on the cell cycle were investigated by flow cytometry: We measured cellular DNA content after extraction of fragmented DNA, and apoptosis-induced DNA strand breaks. Cell morphology was observed by light microscopy. DNA strand breaks at a nucleosomal unit were analyzed by electrophoresis.

RESULTS

Our data demonstrated that KRN5500 caused inhibition of cell growth, and that apoptosis was the mode of cell death. G(1) phase cells were more susceptible to KRN5500 induced apoptosis. In addition, KRN5500 induced cell differentiation at lower concentration.

CONCLUSIONS

It is anticipated that KRN5500 will be used clinically as an anti-leukemic agent. Its mechanism of antitumor action is to induce apoptosis or cell differentiation.

Synthesis and anti-HIV and anti-HBV activities of 2'-fluoro-2', 3'-unsaturated L-nucleosides

The synthesis of L-nucleoside analogues containing 2'-vinylic fluoride was accomplished by direct condensation method, and their anti-HIV and anti-HBV activities were evaluated in vitro. The key intermediate 8, the sugar moiety of our target compounds, was prepared from 1,2-O-isopropylidene-L-glyceraldehyde via (R)-2-fluorobutenolide intermediate 5 in five steps. Coupling of the acetate 8 with the appropriate heterocycles (silylated uracil, thymine, N4-benzoylcytosine, N4-benzoyl-5-fluorocytosine, 6-chloropurine, and 6-chloro-2-fluoropurine) in the presence of Lewis acid afforded a series of 2'-fluorinated L-nucleoside analogues (15-18, 23-26, 36-45). The newly synthesized compounds were evaluated for their antiviral activities against HIV-1 in human peripheral blood mononuclear (PBM) cells and HBV in 2.2.15 cells. Cytosine 23, 5-fluorocytosine 25, and adenine 36 derivatives exhibited moderate to potent anti-HIV (EC50 0.51, 0.17, and 1.5 microM, respectively) and anti-HBV (EC50 0.18, 0.225, and 1.7 microM, respectively) activities without significant cytotoxicity up to 100 microM in human PBM, Vero, CEM, and HepG2 cells.

Reduction of the side effects of an antitumor agent, KRN5500, by incorporation of the drug into polymeric micelles

For intravenous (i.v.) injection of a water-insoluble antitumor drug, KRN5500, we have successfully incorporated KRN5500 into polymeric micelles. In the present study, in vitro and in vivo anti-tumor activity against several human tumor cell lines and toxicity in mice of polymeric micelles incorporating KRN5500 (KRN/m) were evaluated in comparison with those of the prototype KRN5500. KRN/m was found to express similar antitumor activity to KRN5500 in the in vitro and in vivo systems. However, the vascular damage and liver focal necrosis observed with KRN5500 i.v. injection were not seen when KRN/m was administered i.v. Therefore, we expect that KRN/m will be superior to KRN5500 for clinical use and that the methodology of polymeric micelle drug carrier systems can be applied to other water-insoluble drugs.

Human thiopurine methyltransferase pharmacogenetics. Kindred with a terminal exon splice junction mutation that results in loss of activity

Thiopurine methyltransferase (TPMT) catalyzes S-methylation of thiopurine drugs such as 6-mercaptopurine. Large variations in levels of TPMT activity in human tissue can result from a common genetic polymorphism with a series of alleles for low activity. This polymorphism is an important factor responsible for large individual variations in thiopurine toxicity and therapeutic efficacy. We now report a new variant allele, TPMT*4, that contains a G--> A transition that disrupts the intron/exon acceptor splice junction at the final 3' nucleotide of intron 9, the terminal intron of the TPMT gene. This new allele cosegregated within an extended kindred with reduced TPMT activity. We attempted to determine the mechanism(s) by which the presence of TPMT*4 might result in low enzyme activity. Although very few mature transcripts derived from allele TPMT*4 were detected, the mutation did lead to generation of at least two aberrant mRNA species. The first resulted from use of a novel splice site located one nucleotide 3' downstream from the original splice junction. That mRNA species contained a single nucleotide deletion and a frameshift within exon 10, the terminal exon of the gene. The second novel mRNA species resulted from activation of a cryptic splice site located within intron 9, leading to inclusion of 330 nucleotides of intron sequence. That sequence contained a premature translation termination codon. TPMT*4 is the first reported allele for low TPMT activity as a result of a mutation within an intron. These observations also provide insight into mechanisms of mRNA processing after disruption of a terminal exon splice junction.

In vivo gene therapy of cancer with E. coli purine nucleoside phosphorylase

We have developed a new strategy for the gene therapy of cancer based on the activation of purine nucleoside analogs by transduced E. coli purine nucleoside phosphorylase (PNP, E.C. 2.4.2.1). The approach is designed to generate antimetabolites intracellularly that would be too toxic for systemic administration. To determine whether this strategy could be used to kill tumor cells without host toxicity, nude mice bearing human malignant D54MG glioma tumors expressing E. coli PNP (D54-PNP) were treated with either 6-methylpurine-2'-deoxyriboside (MeP-dR) or arabinofuranosyl-2-fluoroadenine monophosphate (F-araAMP, fludarabine, a precursor of F-araA). Both prodrugs exhibited significant antitumor activity against established D54-PNP tumors at doses that produced no discernible systemic toxicity. Significantly, MeP-dR was curative against this slow growing solid tumor after only 3 doses. The antitumor effects showed a dose dependence on both the amount of prodrug given and the level of E. coli PNP expression within tumor xenografts. These results indicated that a strategy using E. coli PNP to create highly toxic, membrane permeant compounds that kill both replicating and nonreplicating cells is feasible in vivo, further supporting development of this cancer gene therapy approach.

Antiproliferative activity in vitro and in vivo of the spicamycin analogue KRN5500 with altered glycoprotein expression in vitro

The spicamycin analogue KRN5500 (NSC 650426; SPA) is derived from Streptomyces alanosinicus. The unique structure contains a purine, an aminoheptose sugar, glycine, and a tetradecadiene fatty acid. SPA potently inhibits the growth of certain human tumor cell lines in vitro (IC50 for growth <100 nM) and displays marked activity in vivo in Colo 205 colon carcinoma xenografts. Selective inhibition of labeled precursor incorporation was not evident at 1 or 4 h of exposure to the drug, but at 8 h, [3H] leucine incorporation was inhibited by approximately 40% at or below the IC50 for cell growth. Because of the structural similarity of SPA to inhibitors of glycoprotein processing, we examined the effect of SPA on indicators of glycoprotein synthesis and processing in HL60TB promyelocytic leukemia and Colo 205 colon carcinoma cells. Brief periods of exposure ( approximately 30 min) to SPA at the IC50 for growth increased incorporation of [3H]mannose. When examined by Western blotting after prolonged (40-48 h) incubation with lectins that target mannose-containing carbohydrates, Galanthus nivalis agglutinin and concanavalin A, a qualitative change in the pattern of mannose-containing glycoproteins was observed in HL60TB cells. Significant changes in the pattern of surface glycoprotein expression in intact cells were demonstrated by flow cytometry using fluorescence-labeled lectins. An increase in the number of cells binding G. nivalis agglutinin (indicating terminal mannose) was noted, but a decrease in the amount of lectin bound per cell was noted for wheat germ agglutinin (detecting sialic acid and terminal beta-N-acetyl glucosamine residues). Electron microscopy revealed loss of microvilli, and the Golgi apparatus appeared inflated. Our findings, therefore, raise the possibility that cells exposed to SPA have altered glycoprotein processing after exposure to low concentrations of drug, prior to the occurrence of overt cytotoxicity. These effects are consistent with a prominent early effect of SPA on the enzymatic machinery or organelles important for proper glycoprotein processing and emphasize the novelty of this agent's likely mechanism of action.

In vitro cytotoxicity of a novel antitumor antibiotic, spicamycin derivative, in human lung cancer cell lines

Spicamycin (SPM), produced by Streptomyces alanosinicus, induces potent differentiation in a human leukemia cell line, HL60. One of the derivatives of SPM (SPM-D), KRN5500, has a wide range of antitumor activity against human cancer cell lines. We examined the cytotoxicity of SPM-D in small and non-small cell lung cancer cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and colony assays. SPM-D was active against a wide range of lung cancer cell lines. All three cisplatin (CDDP)-resistant cell lines established in our laboratory (PC-9/CDDP, PC-14/CDDP, and H69/CDDP) showed collateral sensitivity to SPM-D with relative resistance values of 0.43, 0.34, and 0.32, respectively. Intracellular SPM-D in PC-14/CDDP was 35% higher than that for PC-14 suggesting that intracellular accumulation can explain the collateral sensitivity to SPM-D at least in PC-14/CDDP. On the other hand, in PC-9/CDDP cells, no increase of intracellular SPM-D accumulation was observed, but the conversion ratio of a metabolite (the amino nucleoside moiety of spicamycin binding with glycine, SAN-G) from SPM-D evaluated by TLC was higher as compared with that of parental PC-9 cells (45.5% versus 37%; PC-9/CDDP versus PC-9). The increased intracellular metabolism of SPM-D could explain the mechanism of collateral sensitivity in PC-9/CDDP cisplatin-resistant cell lines. To elucidate the determinant of the SPM-D-induced cytotoxicity, we established SPM-D-resistant cell lines, PC-9/SPM-D, PC-14/SPM-D, and H69/SPM-D, by exposing cells to stepwise increases in SPM-D concentration. The relative resistances of these sublines were more than 5000, 46.6, and 37.8 times those of the parental cell lines, respectively. The intracellular concentration of the active metabolite, SAN-G, was found to be decreased in the SPM-D-resistant sublines. This result indicates that the intracellular metabolism of SPM-D to SAN-G is one of the determinants of cellular sensitivity to SPM-D in these SPM-D-resistant cell lines. In conclusion, both drug accumulation and metabolism may contribute to the sensitivity/resistance to SPM-D and both may merit investigation.

Adenosine, deoxyadenosine, and deoxyguanosine induce DNA cleavage in mouse thymocytes

When thymocytes were cultured with adenosine, deoxyadenosine, or deoxyguanosine at 1 mM for 24 h, DNA cleavage at internucleosomal sites with multiples of approximately 180 bp was induced, followed by lactate dehydrogenase release into the medium. In the presence of coformycin, an adenosine deaminase inhibitor, or formycin B, a purine nucleoside phosphorylase inhibitor, DNA cleavage was induced by these nucleosides at concentrations of less than 50 microM. Other purine and pyrimidine ribo- and deoxyribonucleosides did not induce DNA cleavage or LDH release. Because thymocyte nuclei contain a Ca2+,Mg2+-dependent endonuclease, which preferentially cuts DNA in its linker regions, DNA fragmentation induced by the three purine nucleosides was suggested to occur through increased activity of the endonuclease. The DNA cleavage induced by the nucleosides required protein phosphorylation and synthesis, inasmuch as it was inhibited by an inhibitor of protein kinases, H-7, and by an inhibitor of protein synthesis, cycloheximide. The inhibition of DNA cleavage was accompanied by a reduction in lactate dehydrogenase release, suggesting a causal relationship between DNA cleavage and cell death. The DNA cleavage and subsequent cell lysis might be related to the selective thymocyte deletion observed in patients with adenosine deaminase or purine nucleoside phosphorylase deficiency.

Treatment of schistosomiasis by purine nucleoside analogues in combination with nucleoside transport inhibitors

In contrast to their effects on mammalian cells, the nucleoside transport inhibitors nitrobenzylthioinosine 5'-monophosphate (NBMPR-P) dilazep, benzylacyclouridine (BAU), and to a lesser extent, dipyridamole have no significant effect on the in vitro uptake of adenosine analogues by Schistosoma mansoni [el Kouni and Cha, Biochem. Pharmac. 36, 1099 (1987)]. Coadministration of either NMBPR-P or dilazep with potentially lethal doses of tubercidin (7-deazaadenosine), nebularine or 9-deazaadenosine protected mice from the toxicity of these adenosine analogues. Dipyridamole caused partial protection, whereas BAU did not protect the animals from this toxicity. Toyocamycin caused delayed mortality (after 16 weeks) which could not be prevented by coadministration of NBMPR-P. In S. mansoni infected mice, treated with the combination of NBMPR-P and 9-deazaadenosine was not effective against the parasite. On the other hand, the combinations of NBMPR-P or dilazep with either tubercidin or nebularine were highly toxic to the parasite but not the host. Combination therapy caused a marked reduction in the number of pairing of worms. Effectiveness of combination therapy could also be noted by a drastic decrease in the number of eggs in the liver and small intestine. All eggs found were dead, indicating a direct effect on ovigenesis. Although dipyridamole was less effective than NBMPR-P or dilazep in protecting the host from the toxicity of tubercidin or nebularine, the combinations with dipyridamole produced similar significant therapeutic effects in animals that survived. Mice receiving the combination of tubercidin (or nebularine) plus NBMPR-P or dilazep, as well as those that survived the combination with dipyridamole, appeared healthy and were found to have normal size livers and spleens. These results suggest that highly selective toxicity against schistosomes can be achieved by coadministration of various nucleoside transport inhibitors with adenosine analogues.

Comparative studies to determine the efficiency of 6 methylpurine deoxyriboside to detect cell culture mycoplasmas

Studies were performed to compare three methods to detect mycoplasmal infection of cell cultures. The methods included microbiological assay by inoculation into broth and onto agar with anaerobic incubation, fluorescent DNA staining by Hoechst 33258, and mycoplasmal mediated cytotoxicity by 6 methylpurine deoxyriboside (6MPDR). Fluorescent DNA staining and 6MPDR assays were performed in an indicator cell culture system. A total of 2589 cell cultures were assayed. Mycoplasmas were detected in 174, an incidence of 6.7%. Species isolated were: Acholeplasma laidlawii, Mycoplasma orale, M. arginini, M. hyorhinis, M. fermentans, M. pirum, and M. pneumoniae. In separate studies, 6MPDR also detected infection with Spiroplasma mirum when this organism was deliberately inoculated into cell cultures. The efficiencies of microbiological testing, fluorescent DNA assays, and 6MPDR were 43.1, 98.8, and 97.1%, respectively.

2-Chloroadenosine: a selective lethal effect to mouse macrophages and its mechanism

In our studies on the effects of purine compounds on immune responses in vitro, we found that 2-chloroadenosine (2-Cl Ado) exhibited a potent lethal effect on a viability of mouse adherent cells derived from the peritoneal cavity. The lethal effect was specific for adherent peritoneal cells (PC) (macrophages) and was prevented by exogenous addition of adenosine (Ado) or coformycin, a potent inhibitor of adenosine deaminase. A rapid decrease of intracellular ATP content (26% of control) in adherent PC was observed soon after 1 hr exposure to 2-Cl Ado (0.1 mM), and this decrease of ATP was comparable with that of monoiodoacetate (MIA, 0.1 mM)- or NaN3 (5 mM)-treated adherent PC. The ATP decrease by 2-Cl Ado was restored to 88 or 90% of control value by 1 hr addition of Ado or coformycin, respectively. Polymorphonuclear cells and lymphocytes to which 2-Cl Ado did not exhibit the lethal effect did not cause a significant ATP decrease of the cells. Therefore, the data suggested that the reason for the lethal effect on adherent PC treated with 2-Cl Ado could be attributed to a rapid decrease of ATP content at an early time. We assume that 2-Cl Ado competes with intracellular Ado in macrophages and then causes the adenosine starvation resulting in the ATP decrease.

Carbocyclic analogues of xylofuranosylpurine nucleosides. Synthesis and antitumor activity

(+/-)-4 alpha-Amino-2 alpha,3 beta-dihydroxy-1 alpha-cyclopentanemethanol (6), the carbocyclic analogue of xylofuranosylamine, was synthesized from the previously reported 4 alpha-acetamido-2 alpha,3 alpha-epoxycyclopentane-1 alpha-methanol. Amine 6 was converted to (+/-)-4 alpha-[(5-amino-6-chloro-4-pyrimidinyl)amino]-2 alpha,3 beta-dihydroxy-1 alpha-cyclopentanemethanol (7) by condensation with 5-amino-4,6-dichloropyrimidine. From 7, the carbocyclic analogues of xylofuranosyladenine and xylofuranosyl-8-azaadenine were prepared. In contrast to 9-beta-D-xylofuranosyladenine and its 8-aza analogue, the corresponding carbocyclic nucleosides were resistant to deamination by adenosine deaminase. The carbocyclic 8-aza derivative 10 exhibited significant in vivo antitumor activity which varied according to treatment schedule.

S-adenosylhomocysteine hydrolase inactivation and purine toxicity in cultured human T- and B-lymphoblasts

Accumulation of intracellular deoxyadenosine triphosphate and inactivation of the enzyme S-adenosylhomocysteine hydrolase by deoxyadenosine have been suggested as molecular mechanisms for lymphoid toxicity of inherited or acquired deficiency of adenosine deaminase. The relative roles of these two deoxyadenosine-mediated effects for lymphotoxicity have been explored by employing mutant human T- and B-lymphoblasts deficient in either adenosine kinase, deoxycytidine kinase, or both. At low concentrations (less than 25 mumol/L) of deoxyadenosine or ara-adenine, deoxycytidine kinase deficiency decreases growth sensitivity of human T-lymphoblasts to deoxyadenosine approximately fourfold, and to ara-adenine approximately twofold. Loss of both activities completely eliminates deoxyadenosine phosphorylation and cellular dATP accumulation, and decreases deoxyadenosine growth sensitivity approximately 200-fold and ara-adenine sensitivity approximately 80-fold. The inactivation by deoxyadenosine of intracellular S-adenosylhomocysteine hydrolase activity of human adenosine deaminase-deficient B-lymphoblasts and wild-type or deoxycytidine kinase-deficient T-lymphoblasts is comparable, despite the differing toxicity of this compound for these cell lines. Adenosine kinase deficiency in T-lymphoblasts results in resistance to 2'-deoxyadenosine--but not ara-adenine--associated inactivation of S-adenosylhomocysteine hydrolase, and this compound produces comparable degrees of inactivation of S-adenosylhomocysteine hydrolase in both the wild-type and double mutant cells, despite markedly different growth sensitivity. For B-lymphoblasts, 2'-deoxyadenosine together with adenosine produces comparable growth inhibition of wild-type and adenosine kinase-deficient cells, and this inhibition is more marked than with adenosine alone, but is independent of S-adenosylhomocysteine hydrolase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and antiviral evaluation of carbocyclic analogues of ribofuranosides of 2-amino-6-substituted-purines and of 2-amino-6-substituted-8-azapurines

Carbocyclic analogues of ribofuranosides of 2-amino-6-substituted-purines and of 2-amino-6-substituted-8- azapurines were prepared from the 2-amino-6-chloropurine ribofuranoside analogue (2) and the 2-amino-6-chloro-8- azapurine ribofuranoside analogue (9), respectively. Analogues of purine ribofuranosides with the chloro, amino, methylamino, or methylthio group at position 6, the thioguanosine analogue, and the previously reported guanosine analogue were evaluated in vitro against herpes simplex virus, type 1 (HSV-1). 8- Azapurine ribofuranoside analogues with the chloro, amino, or methylthio group at position 6 and the previously reported 8- azaguanosine analogue were also evaluated against HSV-1. The carbocyclic analogue (6) of 2,6-diaminopurine ribofuranoside is highly active against HSV-1 and, also, against vaccinia virus. The 2-amino-6-chloropurine, 2-amino-6-(methylamino)purine, and the 2,6-diamino-8- azapurine derivatives also demonstrated significant activity against HSV-1.

Protection of mice against lethal dosages of nebularine by nitrobenzylthioinosine, an inhibitor of nucleoside transport

In the presence of nitrobenzylthioinosine (NBMPR) a potent inhibitor of nucleoside transport, Roswell Park Memorial Institute 6410 cells proliferating in culture were protected from otherwise inhibitory concentrations of 9-beta-D-ribofuranosylpurine (nebularine); cellular uptake of nebularine was greatly reduced under these circumstances. Initial rates of nebularine uptake by Roswell Park Memorial Institute 6410 cells were inhibited by NBMPR, indicating that the latter interfered with nebularine transport. NBMPR protected mice against potentially lethal treatment regimens with nebularine, 4-amino-7-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine (tubercidin) or 4-amino-5-cyano-7-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine (toyocamycin); protection resulted when NBMPR was administered i.p. in advance of or simultaneously with nebularine, but not when NBMPR followed nebularine by 1 hr. Both NBMPR and its 5'-monophosphate protected mice against nebularine lethality when administered s.c.

Teratogenicity of adenine arabinoside (Ara-A)

The potentially teratogenic effect of antiviral drugs, particularly when given systemically, prompted the evaluation of the teratogenic effect of Ara-A when given systemically in doses significantly higher than those used clinically. Under the conditions of this study, neither teratogenic nor embryocidal effects of Ara-A were observed.

Toxicity of adenine arabinoside in humans

Six forms of reversible adverse reactions to adenine arabinoside (vidarabine) were observed in a two-year period among 42 patients (19 of whom had lymphomas, leukemias, or other malignancies) who were treated for complicated infections with varicella-zoster or herpes simplex virus. Six patients received placebo. Ten patients received 10 mg of adenine arabinoside/kg per day; three received 15 mg/kg; 22 received 20 mg/kg; and one received 30 mg/kg. Patients were treated (by continuous intravenous injection) for an average of seven days. Toxic effects were nausea and vomiting, weight loss, weakness (often with impaired ambulation), megaloblastosis in erythroid series in bone marrow, tremors five to seven days after the start of therapy (including tremors in one patient with abnormal electroencephalograms that were consistent with toxic-metabolic encephalopathy), and thrombophlebitis at the intravenous site. Side effects clearly predominated in patients who received 20 mg/kg per day. Therefore, treatment with 10 mg/kg per day appears preferable until the relation of toxicity to dosage level can be clarified.

Two approaches that increase the activity of analogs of adenine nucleosides in animal cells

Deamination of many analogs of adenine nucleosides results in the loss of their chemotherapeutic efficacy. Two approaches have been used in this study to overcome this problem. First, some adenine nucleotides, which are resistant to mammalian adenosine deaminase, are more toxic to animal cells than are the respective nucleosides. For toxic to animal cells than are the respective nucleosides. For example, 9-beta-D-arabinofuranosyladenine 5'-phosphate, a molecule that penetrates the cell without degradation, has a more sustained toxicity against mouse fibroblasts (L-cells) than does 9-beta-D-arabinofuranosyladenine (ara-A). Furthermore, L-cells treated with 2',3'-dideoxyadenosine 5'-phosphate are extensively killed after 48 hr, whereas 2',3'-dideoxyadenosine is almost nontoxic to L-cells. Specific inhibition of adenosine deaminase by nontoxic concentrations of erythro-9-(2-hydroxy-3-nonyl)adenine greatly potentiates the biological activity of both ara-A and 3'-deoxyadenosine (cordycepin). Simultaneous administration of cytostatic concentrations of ara-A and the inhibitor of adenosine deaminase to L-cells killed greater than 99.9 percent of cells in 36 hr. A similar concentration of ara-A plus the deaminase inhibitor also markedly extended the mean survival of mice bearing Ehrlich ascites carcinoma as compared to ara-A alone. A cytostatic concentration of cordycepin 1 x 10-4 M), administered in the presence of deaminase inhibitor, killed greater than 99.9 percent of cultured L-cells in only 8 hr. During the latter incubation, accumulation of uridine in acid-insoluble material reached a maximum after 30 min, and incorporation of thymidine into acid-insoluble material was almost totally arrested after 2 hr.