Potentiation of bleomycin cytotoxicity by high molecular weight polyacrylic acid. II. Involvement of rapid conformational change of polyacrylate

We report that bleomycin (BLM) cytotoxicity is dramatically potentiated in the presence of high molecular weight polyacrylic acid (A119). For potentiation, an appropriate amount of divalent cations such as Ca++, Mg++, or Ba++ was required, in addition to vortex - stirring of the reaction mixture. There was no potentiation when A119 alone was pre-stirred or left standing for several days in the presence of divalent cations prior to use. Taking into account of kinematic viscosity of A119 observed during the treatment, a rapid conformational change of A119 in the presence of divalent cations might be involved in the potentiation mechanism.

Syntheses and studies of metaphase-arresting pyrimidinones

Methods are described for the syntheses of chloromethyl hydroxyalkylphenyl and benzyl ethers, and for the synthesis of bromomethyl phenyl ketone analogs. The hydroxy groups were protected as acetates. The halogenomethyl derivatives have been used for N-alkylation of 5-chloro-2(1H)-pyrimidinone. The acetyl groups in the products were removed by aminolysis or by enzymatic (pig liver esterase) hydrolysis. The hydroxy derivatives are chemically labile because of polymerization reactions. Adduct formation (1:1) with sodium hydrogensulfite improved the stability. The products are specific inhibitors of the cell cycle in the metaphase. In vitro data are given from screening in cultivated Chang liver cells.

DNA-drug recognition and effects on topoisomerase II-mediated cytotoxicity. A three-mode binding model for ellipticine derivatives

Cytotoxic effects and topoisomerase II-mediated DNA breaks induced in vitro by ellipticine derivatives were examined in connection with 1H NMR and circular dichroism (CD) studies on molecular structures and interactions of drugs with DNA. The compounds included four 9-hydroxyellipticine and two 7-hydroxyisoellipticine derivatives. Structure-activity relationships indicated that a change in nitrogen atom position in the pyridinic ring greatly affected drug effects both on topoisomerase II action and cytotoxicity to L1210 cells. The four 9-hydroxyellipticine derivatives yielded bell-shaped curves in in vitro topoisomerase II-mediated DNA break assays, whereas the two 7-hydroxyisoellipticine derivatives demonstrated an almost linear increase at the same concentration (0-10 microM). In both cases, the intensity of cleavage was modulated by the position and the degree of methylation on the pyridinic ring, and results were correlated with cytotoxic activity expressed as the in vitro ID50 values for L1210 leukemia cells. 1H NMR experiments performed on free drug molecules in solution revealed that the two protons (alpha and beta) contiguous to the biologically important hydroxy group were sensitive to changes in electron distribution produced by the distant chemical modifications and methylations of the pyridinic ring. A linear relationship was observed between the differences in chemical shifts of alpha and beta protons (delta delta alpha-beta) versus ID50 values. CD experiments indicated that, at weak ionic strength I = 0.02 and at pH 7, drugs interact with the poly[d(A-T)] duplex according to a "three-mode binding model" which is governed by the drug structure and the drug to DNA ratio. The intercalation mode was related to the induction of topoisomerase II-mediated DNA cleavage, while the external binding mode consecutive to intercalation was related to cleavage suppression. These two modes concerned the good intercalators 9-hydroxyellipticines. The third was found for the weak intercalators 7-hydroxyisoellipticines and was characterized by self-stacked molecules bound "outside" DNA, presumably in the minor groove. Ligands either could be intercalated partially or linked at the edge of bases with a small number of molecules filling intercalation sites, for the second alternative. In addition to having different binding modes, 9-hydroxyellipticines were better inducers of DNA distortions than 7-hydroxyisoellipticines. The incidence of the drug binding modes on DNA-topoisomerase II recognition was discussed in connection with the in vitro cytotoxic activity exhibited by the drugs.

Relationship between expression of P-glycoprotein and efficacy of trifluoperazine in multidrug-resistant cells

Tumor cell resistance due to enhanced efflux of drugs with diverse structures and/or mechanisms of action is termed multidrug resistance (MDR), and modulation of the MDR phenotype by calcium blockers or calmodulin inhibitors is suggested to involve P-glycoprotein. In drug-sensitive (S) and 5-fold doxorubicin (DOX)-resistant (R0) L1210 mouse leukemia cells, no obvious differences in mdr mRNA or P-glycoprotein expression or alterations in cellular uptake, retention, or cytotoxicity of vincristine (VCR) were observed. However, in the 10-fold (R1) and 40-fold (R2) DOX-resistant sublines, expression of P-glycoprotein was correlated with the level of resistance (R2 greater than R1). An RNase protection assay revealed that elevated levels of mdr1 and mdr2 mRNA were detected in R1 and R2 cells, with an additional increase in mdr3 mRNA in the R2 subline. Further, in the R1 and R2 sublines, no VCR dose-dependent cytotoxicity was apparent, and cell kill of greater than 40% was not achievable following a 3-hr drug exposure. Cellular uptake and retention of VCR were 2- to 4-fold lower in the R1 and R2 sublines, compared with similarly treated S or R0 cells. Potentiation of VCR cytotoxicity by a noncytotoxic concentration of 5 microM trifluoperazine (TFP) was greater than 2-fold in S and R0 cells and less than 1.3-fold in the R1 and R2 sublines. Modulation of VCR uptake by 5 microM TFP in the S and R0 cells was 2-fold and it was 4- to 7-fold in the R1 and R2 sublines. The presence of 5 microM TFP, by competing for efflux, enhanced VCR retention 1.5-fold in S and R0 cells and 2- to 4-fold in the R1 and R2 sublines. In contrast to these results with VCR, dose-dependent cytotoxicity of DOX was apparent in all the resistant sublines, and modulation of DOX cytotoxicity by 5 microM TFP was dependent on the level of resistance. Cellular accumulation of DOX was 20 and 50% lower in the R1 and R2 sublines, respectively, compared with similarly treated S or R0 cells. Marked increases (greater than 1.5-fold) in cellular accumulation of DOX by TFP were apparent only in the R2 subline. Results suggest that a relationship between overexpression of P-glycoprotein isoforms and their role in affecting cellular drug levels and consequent cytotoxicity in MDR L1210 cells determines resistance to VCR but not DOX.(ABSTRACT TRUNCATED AT 400 WORDS)

Polymer-coated albumin microspheres as carriers for intravascular tumour targeting of cisplatin

We used a poly-lactide-co-glycolide polymer (PLAGA 50:50) to formulate cisplatin (cDDP) into microspheres designed for intravascular administration. Two systems were developed. PLAGA-coated albumin microspheres and microspheres consisting of PLAGA only. PLAGA-coated microspheres displayed a mean diameter of 31.8 +/- 0.9 microns and a payload of 7.5% cDDP (w/w). Solid PLAGA microspheres exhibited a mean diameter of 19.4 +/- 0.6 microns and a payload of 20% cDDP. Release characteristics and in vitro effects on L1210 leukemia and B16 melanoma cell lines were investigated. Both types of microsphere overcame the initial rapid release of cDDP (burst effect), and PLAGA-coated albumin microspheres also showed a lag phase of approximately 30 min before cDDP release began. PLAGA-coated albumin microspheres released most of their payload through diffusion, and the coating eventually cracked after 7 days' incubation in saline supplemented with 0.1% Tween at 37 degrees C, enabling the release of any cDDP remaining. Effects of platinum, pre-released from PLAGA-coated albumin microspheres on the in vitro growth of L1210 cells were comparable with those of standard formulations (dissolved) of cDDP. Material released from non-drug-loaded PLAGA microspheres had no effect on L1210 cell growth, suggesting the absence of cytotoxic compounds in the matrix. The colony-forming ability of B16 cells was also equally inhibited by standard cDDP and pre-released drug. These studies show that formulation of cDDP in PLAGA-based microspheres prevents the rapid burst effect of cDDP seen in previous preparations and offers an improved system of administration for hepatic artery infusion or adjuvant therapy, enabling better clinical handling and the promise of a higher ratio of tumour tissue to normal tissue.

Platinum coordination complexes which circumvent cisplatin resistance

In the search for a platinum complex capable of oral administration, the poor bioavailability of established drugs has been circumvented by the discovery of a novel class of platinum (IV) ammine/amine dicarboxylate dichlorides. These compounds, when administered orally to mice carrying the ADJ/PC6 plasmacytoma, exhibit antitumor selectivities far superior to those of cisplatin or carboplatin (given intraperitoneally). Oral activity comparable to that of intraperitoneal cisplatin and carboplatin has also been demonstrated in a panel of human ovarian tumor xenografts. Platinum (IV) ammine/amine dicarboxylates retain cytotoxicity in cultures of L1210/cisplatin and L1210/tetraplatin acquired resistant cells. This property does not translate into a cisplatin-resistant variant of the ADJ/PC6 tumor, in the example of JM221. This result reflects experience with tetraplatin, a drug currently in phase I study, which is comparably ineffective against an ADJ/PC6/cisplatin variant. It is a moot point whether either L1210 or ADJ/PC6/cisplatin-resistant variants are clinically predictive screening models, since this issue must be determined ultimately by clinical study. We have attempted to resolve this dichotomy through the establishment of human ovarian carcinoma lines, both in vitro and in vivo, where there is evidence that response to platinum coordination complexes in the several models reflects that of the donor patient's tumor to platinum-based clinical therapy. The data herein for platinum (IV) ammine/amine dicarboxylates in these models gives encouragement to the notion that these novel compounds may be of value as oral therapeutic agents, whilst also providing an important lead to the discovery and development of a new generation of platinum drugs possessing broad clinical utility.

ICI D1694, an inhibitor of thymidylate synthase for clinical study

The TS inhibitor, ICI D1694, is a highly potent inhibitor of tumour growth in vitro and in vivo. Uptake via the RFC and rapid metabolism to polyglutamate forms appear to be responsible for potency. Antiproliferative toxicity in mice was evident although the dose-limiting renal toxicity experienced with CB3717 was not apparent.

Sesquiterpene quinones as immunomodulating agents

The influence of sesquiterpene quinones and of a sesquiterpene hydroquinone, isolated from the sponge Smenospongia sp. on normal and tumour cells, was investigated. Most showed cytotoxic effects on L1210 leukemia cells. However, their activity on normal cells, such as murine spleen lymphocytes and human peripheral lymphocytes, revealed different behaviours: some of them inhibited, while other enhanced mitogen-stimulated lymphocyte proliferation. These biological studies revealed products modulating immune responses.

Intracellular localization of a chalcogenapyrylium dye probed by spectroscopy and sites of photodamage

Site(s) of intracellular localization of a photosensitizing chalcogenapyrylium dye were assessed using murine leukemia cells in culture. While the dye exhibited substantial dark toxicity, additional damage was elicited by irradiation. The fluorescence emission spectrum of intracellular dye suggests an initial moderately hydrophobic site of localization (dielectric constant approx. 20). This might represent a membrane interface. But longer incubations led to alterations in both fluorescence emission and absorbance spectra, indicative of both dye migration to a more hydrophilic cellular site and dye biotransformations. Dye-induced cytotoxicity, in either light or dark, was associated with mitochondrial, rather than membrane damage.

Effects of brequinar and ciprofloxacin on de novo nucleotide biosynthesis in mouse L1210 leukemia

Exposure of mouse L1210 leukemia cells to 25 microM brequinar for 4 h results in large accumulations of N-carbamyl-L-aspartate and L-dihydroorotate to cellular concentrations of 8.5 mM and 0.8 mM, respectively, while UTP and CTP decrease to 4% of their initial levels; incorporation of [14C]bicarbonate into nucleic acids (DNA and RNA) was decreased to 47%. These data provide direct evidence for inhibition of DHO dehydrogenase by brequinar in growing cells. Exposure of leukemia cells to 200 microM ciprofloxacin for 4 h did not affect de novo pyrimidine nucleotide biosynthesis or the incorporation of [14C]bicarbonate into nucleic acids but resulted in a general decrease in nucleoside triphosphates, with concomitant accumulation of nucleoside mono- and diphosphates (the adenylate energy charge decreased from 0.89 to 0.69), consistent with inhibition of the electron transport chain or uncoupling of oxidative phosphorylation.

Inhibition of primary transcription of vesicular stomatitis virus by prostaglandin A1

Prostaglandin A (PGA) exhibits antiviral activity against RNA and DNA viruses. The effect of PGA1 on vesicular stomatitis virus (VSV) was investigated. When VSV-infected L-1210 cells were kept in the presence of PGA1 the amount of all five viral proteins and their respective mRNAs was dose-dependently decreased. To determine whether the effect was on viral transcription or translation, the temperature-sensitive VSV mutant tsG 41 was employed. This is a good model system for the investigation of primary transcription; at the restrictive temperature of 39 degrees C, tsG 41 is unable to replicate but can transcribe viral mRNA. Mutant mRNA synthesis was strongly inhibited by PGA1 at this temperature, indicating that the major effect is on primary transcription. This conclusion is supported by data demonstrating that in vitro transcription of viral genomic RNA was also inhibited by PGA1.

Occurrence and significance of diastereomers of methotrexate alpha-peptides

The L,L diastereomer of methotrexate-alpha-alanine (L,L-MTX-Ala) was synthesized by reaction of alpha-L-glutamyl-L-alanine di-tert-butyl ester with 4-amino-4-deoxy-10-methylpteroic acid, followed by removal of the blocking groups. It was identified by HPLC (C18 reversed-phase silica gel; acetic acid/CH3OH) as the slower of two closely spaced components in DL,L-MTX-Ala prepared previously by a different route [Kuefner et al. (1989) Biochemistry 28, 2288-2297]. The L,L diastereomer was hydrolyzed by pancreatic carboxypeptidase A (to yield MTX and Ala) twice as rapidly as the DL,L mixture. Analysis of the latter by HPLC established that the slower component was hydrolyzed to MTX and that the unreactive, faster component was D,L-MTX-Ala. DL,L-MTX-Arg was resolved by HPLC (NH4OAc/CH3CN) into two closely spaced components, and the diastereomers were partially separated by chromatography on DEAE-Trisacryl (H2O----2% NH4HCO3). Serum carboxypeptidase N hydrolyzed only the slower HPLC component (to yield MTX and Arg), thereby identifying it as the L,L diastereomer. When tested for cytotoxicity against L1210 cells, L,L-MTX-Arg (ID50 = 1.6 X 10(-8) M) was more effective than the D,L diastereomer (ID50 = 2.2 X 10(-7) M). Treatment of MTX with dicyclohexylcarbodiimide and N-hydroxysuccinimide (NHS), followed by hydrolysis of the NHS ester, led to racemization in the L-glutamate moiety of MTX as shown by the fact that the product was hydrolyzed by carboxypeptidase G2 (at the pteroate-Glu bond) only to the extent of ca. 50% compared to the untreated control. These observations have a broad significance, since coupling agents are employed extensively in the derivatization of MTX for attachment to affinity supports and monoclonal antibodies.

A toxic substance produced by Nocardia otitidiscaviarum isolated from cutaneous nocardiosis

During our studies on toxic substances from clinically isolated Nocarida, a new isolate identified as Nocardia otitidiscaviarum from cutaneous nocardiosis was found to produce a toxic substance called HS-6 that had strong in vitro as well as in vivo toxicity. The mouse intraperitoneal LD50 value was 1.25 mg/kg and the ED50 value for L1210 cultured cells was 0.3 ng/ml. The structure of HS-6 was determined and found to belong to the 16-membered macrocyclic group with a molecular formula of C43H68O12. HS-6 also showed activity against pathogenic fungi such as Cryptococcus neoformans.

A CD study of interactions of ellipticine derivatives with DNA. Relations with the in vitro cytotoxicity

UV-absorption and circular dichroism (CD) experiments showed that ellipticine derivatives may interact with DNA according to 3 possible binding modes depending on their structure and concentration. The first mode concerned intercalation of 1-methyl-9-hydroxyellipticine (1-Me-HE) with its long axis perpendicular to the long axis of base pairs. The same drug was able to bind to external sites (second mode) once the intercalation sites were saturated at high concentration. The third mode illustrated by 1,2-dimethyl-9-hydroxyisoellipticinium (1-Me-isoNMHE), concerned self-stacked molecules interacting at the surface of DNA. Biological significance of these different binding modes was then discussed in connection with in vitro cytotoxic activity of compounds.

Discontinuous DNA synthesis by purified mammalian proteins

Five proteins purified from mouse cells acting together efficiently convert a single-stranded circular DNA template to covalently closed duplex circle by a discontinuous mechanism. DNA polymerase alpha/primase with the assistance of alpha accessory factor covers the single-stranded circle with RNA-primed DNA fragments. Primers are removed by a combination of RNase H-1 and a 5'-exonuclease that was identified by its ability to complete this in vitro system. The 5'-exonuclease is required to remove residual one or two ribonucleotides at the primer/DNA junction that are resistant to RNase H-1. Gap filling is by the DNA polymerase alpha/primase, and DNA ligase I converts the DNA fragments to continuous strand. The concerted action of the five proteins emulates synthesis of the staging strand at the replication fork.

Structure-activity studies with chiral isomers and with segments of the antimitotic marine peptide dolastatin 10

Eighteen configurational isomers of the antimitotic peptide dolastatin 10 (Bai et al., Biochem Pharmacol 39: 1941-1949, 1990) derived from Dolabella auricularia, together with segments obtained as precursors in its synthesis (Pettit et al., J Am Chem Soc 111: 5463-5465, 1989), were examined as inhibitors of tubulin polymerization and as inhibitors of growth of L1210 murine leukemia cells in culture. Dolastatin 10 consists of four amino acids (in order from the amino terminus: dolavaline, valine, dolaisoleucine, and dolaproine), three unique to D. auricularia, linked to an unusual primary amine (dolaphenine, probably derived from phenylalanine) at what would otherwise be its carboxyl terminus. Dolastatin 10 has nine asymmetric carbon atoms, and available isomers included alternate configurations at five positions (positions 9 and 10 in the dolaproine moiety and positions 18, 19 and 19a in the dolaisoleucine moiety). For tubulin polymerization, only alterations at positions 18 and 19 resulted in loss of inhibitory activity of the isomer. In addition, a tripeptide containing dolavaline, valine and dolaisoleucine with all asymmetric carbons identical configurationally to those in dolastatin 10 was found to be about 30% as effective as dolastatin 10 in inhibiting tubulin polymerization. Cytotoxic effects were much more sensitive to alterations in the dolastatin 10 structure. The only modification which did not lead to reduced cytotoxicity was reversal of configuration at position 19a in the dolaisoleucine moiety. Both this isomer and dolastatin 10 had IC50 values of less than 1 nM. Several other isomers had IC50 values with the L1210 cells in the range of 30-90 nM, but these did not correlate well with their inhibitory effects on tubulin polymerization. The tripeptide effective as an inhibitor of tubulin polymerization had no activity against the L1210 cells.

Mycenon, a new metabolite from a Mycena species TA 87202 (basidiomycetes) as an inhibitor of isocitrate lyase

Mycenon (C11H5Cl3O3), a new inhibitor of isocitrate lyase (EC 4.1.3.1) was isolated from the culture broth of a basidiomycete, Mycena sp. Mycenon is a novel chlorinated benzoquinone derivative which is also active against bacteria and fungi. Malate synthase (EC 4.1.3.2) the second key enzyme of the glyoxylate cycle was not affected by mycenon. Isocitrate lyase preparations from plants, bacteria and fungi were sensitive. The following Ki-values for mycenon have been determined: Ricinus communis, 5.2 microM; Acinetobacter calcoaceticus, 11 microM; Neurospora crassa, 7.4 microM. The structure of mycenon has been determined by a single crystal X-ray analysis.

Structure-activity relationships of elloramycin and tetracenomycin C

The structure-activity relationships of the anthracycline-related antibiotics of the tetracenomycin C/elloramycin-type were investigated by derivatization of elloramycin (1) and elloramycinone (2). During hydrolysis experiments a unique transglycosylation reaction was discovered, converting elloramycin (1) into isoelloramycin (10) by treatment with anhydrous trifluoroacetic acid. Following the proposed structure-activity relationship concept, 8-O-methylelloramycinone (14) was synthesized from elloramycinone (2), and was shown to be the most active derivative according to the proliferation inhibition assay against murine L1210 leukemia cells.

Application of a new approach for the quantitation of drug synergism to the combination of cis-diamminedichloroplatinum and 1-beta-D-arabinofuranosylcytosine

This report describes the application of a new approach, the universal response surface approach, to the quantitative assessment of drug interaction, i.e., the determination of synergism, antagonism, additivity, potentiation, inhibition, and coalitive action. The specific drug combination and experimental growth system for this introductory application was that of 1-beta-D-arabinofuranosylcytosine (ara-C) and cisplatin with simultaneous drug exposure (1, 3, 6, 12, or 48 h) against L1210 leukemia in vitro. To quantitate the type and degree of drug interaction, a model was fitted using nonlinear regression to the data from each separate experiment, and parameters were estimated (K. C. Syracuse and W. R. Greco, Proc. Biopharm. Sect. Am. Stat. Assoc., 127-132, 1986). The parameters included the maximum cell density over background in absence of drug, the background cell density in presence of infinite drug, the 50% inhibitory concentrations and concentration-effect slopes for each drug, and a synergism-antagonism parameter, alpha. A positive alpha indicates synergism, a negative alpha, antagonism, and a zero alpha, additivity. Maximal synergy was found with a 3-h exposure of ara-C + cisplatin, with alpha = 3.08 +/- 0.96 (SE) and 2.44 +/- 0.70 in two separate experiments. Four different graphic representations of the raw data and fitted curves provide visual indications of goodness of fit of the estimated dose-response surface to the data and visual indications of the intensity of drug interaction. The universal response surface approach is mathematically consistent with the traditional isobologram approach but is more objective, is more quantitative, and is more easily automated. Although specifically developed for in vitro cancer chemotherapy applications, the universal response surface approach should prove to be useful in the fields of pharmacology, toxicology, epidemiology, and biomedical science in general.

5-Hexyl-2'-deoxyuridine blocks the cytotoxic effects of 5-fluorodeoxyuridine or deoxyadenosine in leukemia L1210 cells in culture

Antitumor agents which block the de novo synthesis of nucleotides can be circumvented by the presence of salvage pathways for the reutilization of nucleobases and nucleosides. Studies have been carried out which show that 5-hexyl-2'-deoxyuridine (HdUrd) effectively blocks the cytotoxic effects of deoxyadenosine and fluorodeoxyuridine in L1210 cells. Although HdUrd (500 microM) had essentially no effect on the growth of L1210 cells in culture, the total uptake of [14C]cytidine into these cells was inhibited 99% by this concentration of HdUrd. The inhibitory effects of fluorodeoxyuridine (FdUrd) and deoxyadenosine could be completely prevented by the presence of HdUrd (200 microM). The growth inhibitory effects of fluorouracil were not prevented by HdUrd. Dipyridamole prevented the inhibition of L1210 cell growth by FdUrd but not by deoxyadenosine or fluorouracil. 5-Isopropyl-, 5-pentyl-, and 5-octyldeoxyuridine were not effective in preventing the cytotoxic effects of deoxyadenosine. The data suggest that HdUrd might be useful in blocking the salvage of nucleosides, thereby potentiating the effects of inhibitors of de novo nucleotide synthesis.

Structure-activity relationships of antineoplastic agents in multidrug resistance

Clinical resistance to many antineoplastic agents is a major cause of treatment failure. The well-documented phenomenon addressed as multidrug resistance (MDR) allows cells to withstand exposure to lethal doses of drugs with dissimilar chemical structures, modes of action, and physicochemical properties. In one of the earliest studies on MDR, Biedler and Riehm in an attempt to explain the cross-resistance profile of actinomycin D resistant Chinese hamster cells suggested that molecular weight was an important determinant. Our statistical analysis of their data validates their claim and indeed strongly demonstrates that cross resistance is enhanced by the increased size and hydrophobicity of the antitumor agent. Our preliminary studies with methotrexate-resistant L1210 cells indicates that cross resistance is increased in the case of moderate-sized, hydrophilic drugs. These two studies and others suggest that current chemotherapy regimens may be improved by treating resistant cells with antineoplastic agents displaying physicochemical characteristics opposite to that of the original inducing agent.

Synthesis, antiproliferative, and antiviral activity of certain 4-substituted and 4,5-disubstituted 7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3-d]pyrimidines

The sodium salts of 4-chloro- and several 4-chloro-5-substituted-7H-pyrrolo[2,3-d]pyrimidines were treated with [1,3-bis(benzyloxy)-2-propoxy]methyl chloride (6) to provide the corresponding 4-chloro- and 4-chloro-5-substituted-7-[[1,3-bis(benzyloxy)-2-propoxy]methyl]pyrrolo [2,3-d]pyrimidines (7-11). Debenzylation with boron trichloride at -78 degrees C furnished 4-chloro- and several 4-chloro-5-substituted-7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3- d]pyrimidines (12.16). Subsequent amination of 12-16 yielded the 4-amino-5-substituted-7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3- d]pyrimidines (17-21). Treatment of 14 with methylamine and 13 and 14 with ethylamine yielded the 4-(alkylamino)-5-halo-7-[(1,3-dihydroxy-2- propoxy)methyl]pyrrolo[2,3-d]pyrimidines (22-24). Treatment of 12-15 with hydroxylamine in refluxing 2-propanol yielded the 5-substituted-4-(hydroxyamino)-7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrol o [2,3-d]pyrimidines (25-28). Treatment of compound 12 with Pd/C under a hydrogen atmosphere has furnished the nebularine analogue 31. The antiproliferative activity of compounds 17-28 and 31 was studied using L1210 cells in vitro. The 4-amino- and 4-(hydroxyamino)-5-halogenated derivatives (compounds 18-20, 26-28) inhibited cell growth. Although the effect of compounds 18-20 and 27 on final growth rate was pronounced (IC50 = 2.3, 0.7, 2.8, and 3.7 microM, respectively), cells underwent at least one doubling before cell division stopped. The remaining compounds were less cytotoxic, with IC50's greater than 30 microM for 21, 23, 26, and 28, whereas no inhibition of L1210 cell growth was observed with compounds 17, 22, 24, 25, and 31 at 100 microM. The antiviral activity of these compounds also was tested. Compounds 18-20 and 26-28 were active against human cytomegalovirus and herpes simplex type 1. The 4-amino derivatives (18-20) were more active than the 4-hydroxyamino derivatives (26-28), the 4-amino-5-bromo and 4-amino-5-iodo derivatives produced more than five log reductions in virus titer at concentrations of 10-100 microM. Although some cytotoxicity was observed at these concentrations, compound 19 was active against murine cytomegalovirus in vivo. At 5.6 mg/kg, 14/15 animals survived compared to 10/15 treated with 5.6 mg/kg of ganciclovir or 1/15 treated with placebo.

Derivatives of saquayamycins A and B. Regio- and diastereoselective addition of alcohols to the L-aculose moiety

In continuation of our structure-activity investigations on angucycline antibiotics we prepared derivatives of saquayamycins A (1) and B (4) by regio- and diastereoselective nucleophilic addition of different alcohols to the L-aculose moiety. Reversible protection of the 4'-hydroxy group in 1 by silylation allowed a derivatization at both L-aculose moieties without cyclization towards cinerulose B. The in vitro cytotoxic activity remained almost unchanged after variation at the L-aculose moieties whereas a change in the aglycone structure led to a total loss of the biological activity.

DNA breaks and repair in the mouse leukemia L1210 cells exposed to three different types of interstrand DNA cross-linkers

DNA breaks and repair in mouse leukemia L1210 cells treated with 3 different types of cross-linkers, mitomycin C (MMC), 1-(4-amino-2-methyl-5-pyrimidinyl)-methyl-3-(2-chloroethyl)-3-nitroso ure a hydrochloride (ACNU) and SN-07 (a macromolecular antibiotic), were studied. Measured in D37 values, MMC gave the highest number of cross-links per lethal 'hit' directly after the 1-h treatment in the alkaline elution assay, followed by ACNU and SN-07. A good dose-response increase in induced interstrand DNA cross-linking frequency was observed in cells treated with 2.5-10 micrograms/ml MMC and with 10-100 micrograms/ml ACNU for 1 h with and without 24-h post-incubation. After 6-h post-incubation, the highest frequency of cross-linking was observed in cells treated with 2.5 micrograms/ml MMC and 30 micrograms/ml ACNU, while cross-link production continued in the cells treated with SN-07 for 12-h post-incubation. No significant increase in DNA breaks was observed in cells treated with MMC throughout 24-h post-incubation. The highest frequency of single-strand DNA breaks in cells treated with ACNU was observed immediately after the treatment and they disappeared after 6-h post-incubation. After 24-h post-incubation, a marked enhancement of the DNA breaks was observed in cells treated with SN-07 and the cells contained double-strand DNA breaks also. RNA synthesis was not affected in the cells treated with 10 micrograms/ml MMC and slightly inhibited to 70% of control in those treated with 100 micrograms/ml ACNU, while DNA synthesis in both cells was significantly inhibited after 24-h post-incubation. By contrast, both RNA and DNA synthesis were completely inhibited in cells treated with 8.0 micrograms/ml SN-07.