Cross-resistance of novobiocin-resistant BHK cell line to topoisomerase II inhibitors

A novobiocin-resistant BHK cell line, designated as NovrA2, was found to exhibit cross-resistance to other topoisomerase II inhibitors such as 4'-dimethylepipodophyllotoxin-4-(4,6-O-ethylidine-beta-D-glu copyranoside) (VP-16), adriamycin, and 4'-(9-acridinyl-amino)methanesulfon-m-anisidide (m-AMSA), and also to different types of drugs such as vinblastine and arabinocytidine. Nalidixic acid-resistant cells (A2Nalr) of the NovrA2 cell line were phenotypically reverted to novobiocin sensitivity like wild-type cells and were also partially reverted to sensitivity to VP-16 and adriamycin, but not to vinblastine and arabinocytidine. When VP-16 was added to cell culture, the drug-induced DNA strand breaks were much fewer in NovrA2 cells than in BHK cells. This reduced level of strand breaks in NovrA2 cells was not due to reduced drug uptake, because the two cell lines accumulated similar levels of radiolabeled VP-16. VP-16 also induced fewer DNA breaks in isolated nuclei of NovrA2 cells than in those of BHK cells. There was no significant difference in the VP-16-induced DNA cleavage activities of partially purified topoisomerase II from BHK and Novr cells. These results show that the resistance of NovrA2 cells to various drugs is not acquired by a defense mechanism related to membrane permeability and suggest that the resistance of the NovrA2 cells to topoisomerase II inhibitors might be due in part to alteration in a topoisomerase II associated factor(s).

Resistance of human leukemic and normal lymphocytes to drug-induced DNA cleavage and low levels of DNA topoisomerase II

Adriamycin, amsacrine, and etoposide produce protein-associated DNA breaks in numerous cell types. However, in vitro exposure to Adriamycin (0.1-50.0 micrograms/ml) resulted in no detectable DNA cleavage in lymphocytes from patients with B-cell chronic lymphocytic leukemia (CLL) or in either B- or T-lymphocytes from normal donors. In contrast, DNA cleavage was observed in T-cells from CLL patients. Exposure to amsacrine or etoposide caused at least 50-fold less DNA cleavage in CLL and normal lymphocytes as compared to L1210 cells. These findings cannot be accounted for by differences in drug uptake. An attempt was made to explain the relative resistance of human lymphocytes to drug-induced DNA cleavage. DNA topoisomerase II, an intracellular target of tested drugs, was assayed in CLL and normal human blood lymphocytes by immunoblotting. The enzyme was detected neither in unfractionated lymphocytes nor in the enriched B- and T-cells from 28 untreated patients with CLL (Stage 0-IV) and from seven normal donors. Exponentially growing L1210 cells had approximately 7 x 10(5) enzyme copies per cell, suggesting a 100-fold higher content than that of CLL or normal lymphocytes. There were, however, detectable levels of DNA topoisomerase II in cells obtained from patients with diffuse histiocytic, nodular poorly differentiated and nodular mixed lymphomas, in Burkitt's lymphoma, acute lymphoblastic leukemia and CLL with prolymphocytic transformation. DNA topoisomerase I, a potential target for anticancer chemotherapy, was detectable in CLL and normal lymphocytes, as well as in cells of other malignancies tested. The above results may offer an explanation for the ineffectiveness of Adriamycin in the treatment of CLL. It could be suggested that low levels of DNA topoisomerase II contribute to drug resistance operating in human malignancies with a large compartment of nonproliferating cells.

Reduced DNA topoisomerase II activity and drug-stimulated DNA cleavage in 9-hydroxyellipticine resistant cells

We have isolated a Chinese hamster lung cell line resistant to 9-hydroxyellipticine (DC-3F/9-OH-E) which is also cross-resistant to topoisomerase II inhibitors such as amsacrine and etoposide. In this work we have studied quantitatively both DNA topoisomerase II activity by decatenation of kinetoplast DNA and drug-stimulated DNA cleavage of pBR 322. DNA topoisomerase II activity of DC-3F/9-OH-E nuclear extract was reduced by 3.5-fold as compared to that from DC-3F (sensitive parent) nuclear extract. We also found that DC-3F/9-OH-E nuclear extracts have a reduced capacity to induce in vitro topoisomerase II-mediated DNA cleavage upon stimulation by etoposide and amsacrine (7- and 10-fold respectively). Besides, mixing nuclear extracts from both sensitive and resistant cells indicates that either the enzyme in resistant cells is modified or a modulating factor is associated to it. Our results suggest that the resistance of the DC-3F/9-OH-E cell line to topoisomerase II inhibitors might be due to both a reduced amount of the enzyme and its reduced ability to form the cleavable complex in the presence of drugs.

Topoisomerase-II-mediated lesions in nascent DNA: comparison of the effects of epipodophyllotoxin derivatives, VM-26 and VP-16, and 9-anilinoacridine derivatives, m-AMSA and o-AMSA

This study compares the effects of the epipodophyllotoxin derivatives, VM-26 and VP-16, and the 9-anilinoacridine derivatives, m-AMSA and o-AMSA, on nascent and mature DNA. Two types of lesion which are putatively mediated by topoisomerase II, DNA-protein crosslinks and DNA double-strand breaks, were analyzed in drug-treated nuclei from 3H/14C labelled L1210 cells. Potassium/dodecyl sulfate precipitation assay was used to assess DNA-protein crosslinks in mature and nascent (1 min old) DNA. Both epipodophyllotoxins and m-AMSA showed a strong preference for nascent DNA. DNA double-strand cleavage induced by VM-26 and m-AMSA also showed a preference for nascent DNA as indicated by neutral elution technique. Sedimentation on neutral sucrose gradients revealed that these drugs generated highly degraded fragments (under 30 S) in nascent DNA substantially faster than in mature DNA. Lesions in nascent DNA were diminished substantially by the omission of ATP or the addition of novobiocin. The ability to induce lesions in nascent DNA correlates with cytotoxic potency of the agents studied. The results suggest that replicating DNA may constitute a preferential target for antitopoisomerase II drugs.

DNA-binding and DNA-cleaving properties of a synthetic model AGAGLU related to the antitumour drugs AMSA and bleomycin

We have previously described two synthetic models gathering a simplified model of the complexing part of Bleomycin (Blm) and the intercalating moiety of m-AMSA. These molecules, namely AGGA and AGAMGA, do not seem able to cleave DNA as Blm does. The present work is devoted to the study of a new derivative, AGAGLU, which includes in its structure a judiciously chosen connector between the two parts of the molecule. This compound, the chelating and DNA-binding properties of which are described here, has been shown to induce single-strand breakage of duplex DNA in a high level.

Energetics and stereochemistry of DNA complexation with the antitumor AT specific intercalators tilorone and m-AMSA

Computations by the SIBFA method on the intercalative interaction energies of tilorone and m-AMSA with B-DNA representative oligonucleotides account for the specificity of these antitumor drugs for AT sites and minor groove intercalation. In tilorone this specificity is due to the strong preference of the side chains for the minor groove, which overcomes the preference of the chromophore for a GC intercalation site. In m-AMSA the specificity is due to the combined preference of both the chromophore and the anilino side chain for AT intercalation site and minor groove, respectively. o-AMSA is shown to manifest a similar (although significantly less pronounced specificity) as m-AMSA but a higher affinity for DNA. A comparison of the energetics and stereochemistry of intercalative binding to DNA of m-AMSA (AT minor groove specific) and 9-aminoacridine-4-carboxamide (GC major groove specific), which possess the same chromophore and differ only by the nature and position of the side chains, shows the possibility of important variations in the intercalative behaviour of chromophoric drugs as a function of the substituent groups attached to them.

Effects of antileukemia agents on nuclear matrix-bound DNA replication in CCRF-CEM leukemia cells

The effects of various antileukemic agents on DNA replication associated with the nuclear matrix were investigated in CCRF-CEM leukemia cells. Residual nuclear matrices were prepared by sequential treatment of nuclei with 1.5 M NaCl, DNase I, and Triton X-100 and contained 1-5, 10, and 37% of the total nuclear DNA, protein, and phospholipid, respectively. In control cells pulse-labeled for 45 s with [3H]thymidine, the specific activity of nascent DNA was four-fold greater in the nuclear matrix fraction relative to the specific activity of the high salt-soluble (nonmatrix) DNA fraction. Pulse-labeling and reconstitution experiments indicated that this enrichment of newly replicated DNA on the nuclear matrix did not result from aggregation of nascent DNA with the matrix. A 2-h incubation of tumor cells with either 0.1 microM teniposide (VM-26), 0.2 microM VM-26, or 0.5 microM amsacrine (m-AMSA) reduced the relative specific activity of nascent DNA on the nuclear matrix by 59, 61, and 54%, respectively, compared to control cells. In contrast hydroxyurea and cytosine arabinoside, at concentrations that markedly inhibited total nuclear DNA synthesis, did not decrease the relative specific activity of newly replicated DNA on the matrix. The results provide evidence that the antiproliferative effects of the DNA topoisomerase II inhibitors, VM-26 and m-AMSA, are localized on the nuclear matrix of CCRF-CEM leukemia cells.

Mechanism of resistance of non-cycling mammalian cells to 4'-[9-acridinylamino]methanesulphon-m-anisidide: role of DNA topoisomerase II in log- and plateau-phase CHO cells

CHO-AA8 cells were used as a model system to study the role of DNA topoisomerase II in the resistance of non-cycling cells to amsacrine. Plateau-phase AA8 cells have previously been shown to be resistant to amsacrine and to contain fewer DNA breaks than log-phase cells after drug treatment (Robbie, M.A., Baguley, B.C., Denny, W.A., Gavin, J.R. and Wilson, W.R. (1988) Cancer Res., in press). The phage P4-unknotting activity of nuclear extracts decreased 2-fold when AA8 cells entered into the non-cycling state, but there was no difference in sensitivity to amsacrine between log- and plateau-phase nuclear extracts. Drug stimulation of protein-DNA complex formation was similar in whole cells, isolated nuclei and nuclear extracts from either log- or plateau-phase cells. However, stimulation of complex formation in cells, nuclei or nuclear extracts was approx. 4-fold lower in plateau-phase than in log-phase. The data presented suggested that drug-enzyme interaction was altered in plateau-phase cells.

Comparison of the mutagenicity of amsacrine with that of a new clinical analogue, CI-921

The mutagenicity of CI-921, the 4-methyl-5-(N-methyl)carboxamide derivative of the clinical antileukaemia agent, amsacrine, has been assessed using both bacterial and mammalian cells. CI-921 is distinguished from amsacrine in its high activity against some experimental tumours and is currently undergoing phase I clinical trial. Like 9-aminoacridine and amsacrine, CI-921 is mutagenic to the Salmonella typhimurium frameshift tester strain TA1537, but shows no sign of inducing base pair changes in strain TA100. In Chinese hamster cell culture, however, it differs from 9-aminoacridine in causing extensive chromosomal aberrations and an increase in mutations at the hypoxanthine-guanine phosphoribosyltransferase locus. It induces the formation of tightly packed and multilayered colonies in treated cultures of C3H/10T1/2 cells, but its action differs from that of benzo[a]pyrene, which induces type III fibroblastic multilayered colonies. Side-by-side comparison of the mutagenic properties of CI-921 and amsacrine showed no substantial differences at similar toxicity, suggesting that the increased lipophilicity and DNA-binding affinity of CI-921, which are thought to contribute to its increased antitumour activity, do not concomitantly increase the efficiency of in vitro mutagenesis or cell transformation.

Sister chromatid exchanges, chromosomal aberrations, and cytotoxicity produced by antitumor topoisomerase II inhibitors in sensitive (DC3F) and resistant (DC3F/9-OHE) Chinese hamster cells

4'-(9-Acridinylamino)methanesulfon-m-anisidide, etoposide, and 2-methyl-9-hydroxyellipticinium are antitumor topoisomerase II (topo II) inhibitors. The relationship between drug-induced sister chromatid exchanges (SCEs) or chromosomal aberrations and cytotoxicity was investigated in Chinese hamster cells sensitive (DC3F) and resistant (DC3F/9-OHE) to topo II inhibitors. Thirty-min drug treatments produced SCEs and chromosomal aberrations in sensitive (DC3F) cells, 4'-(9-acridinylamino)methanesulfon-m-anisidide being more potent than etoposide or 2-methyl-9-hydroxyellipticinium at equimolar concentrations. Comparable treatments of resistant (DC3F/9-OHE) cells did not produce chromosomal damage. The cytotoxicity of 4'-(9-Acridinylamino)-methanesulfon-m-anisidide was also greater than that of etoposide or 2-methyl-9-hydroxyellipticinium in DC3F cells, and no cytotoxicity was observed in DC3F/9-OHE at drug concentrations that produced more than two logs of cell kill in DC3F cells. A plot of cytotoxicity versus SCEs showed a good correlation between the two parameters. Therefore, short treatments of mammalian cells with topo II inhibitors produce reversible topo II-mediated DNA breaks which are associated with chromosomal aberrations and SCEs whose number correlates with cytotoxicity. In addition, topo II mutant DC3F/9-OHE cells were more sensitive than DC3F cells to the chromosomal, DNA cross-linking and cytotoxic effects of mitomycin C and were equally sensitive to the cytotoxic effect of camptothecin.

Estrogen-induced potentiation of DNA damage and cytotoxicity in human breast cancer cells treated with topoisomerase II-interactive antitumor drugs

Hormone stimulation of responsive neoplasms is a potential strategy for improving the target selectivity of cancer chemotherapy. Using an alkaline DNA-unwinding technique to detect drug-induced DNA strand breakage, we have shown that estrogen stimulation of T-47D human breast cancer cells enhances induction of DNA cleavage by etoposide (VP-16), 4',9-acridinylaminomethanesulfon-m-anisidide (m-AMSA), mitoxantrone, and doxorubicin, drugs known to interact with the DNA-modifying enzyme topoisomerase II. No enhancement of DNA cleavage or cytotoxicity was seen in estrogen-treated cells exposed to X-rays or bleomycin. Novobiocin (an inhibitor of topoisomerase II) markedly antagonized the enhancing effect of estrogen on VP-16-induced DNA cleavage, while neutral nucleoid sedimentation detected less than 10% of such strand breaks revealed in estrogen-treated cells by alkaline unwinding. Estrogen did not affect DNA repair of lesions induced by X-rays, VP-16, or ultraviolet radiation. Enhancement of DNA cleavage was accompanied by a corresponding enhancement of cytotoxicity in cells treated with VP-16 or m-AMSA, but only minimal enhancement of cytotoxicity was seen following treatment with mitoxantrone or doxorubicin. Estrogen-treated and control cells treated with VP-16 and m-AMSA sustained similar levels of DNA cleavage for equivalent levels of cytotoxicity. These findings suggest that estrogen potentiates the cytotoxicity of VP-16 and m-AMSA by enhancing topoisomerase II-mediated DNA damage but that such "damage" does not contribute significantly to cytotoxicity induced by mitoxantrone or doxorubicin. Estrogen stimulation of receptor-positive breast cancer may prove to be a clinically relevant strategy for improving the selectivity and cytotoxicity of some, but not all, topoisomerase II-interactive drugs.

Mechanism of resistance of noncycling mammalian cells to 4'-(9-acridinylamino)methanesulfon-m-anisidide: comparison of uptake, metabolism, and DNA breakage in log- and plateau-phase Chinese hamster fibroblast cell cultures

Resistance of noncycling cells to amsacrine (m-AMSA) has been widely reported and may limit the activity of this drug against solid tumors. The biochemical mechanism(s) for this resistance have been investigated using spontaneously transformed Chinese hamster fibroblasts (AA8 cells, a subline of Chinese hamster ovary-cells) in log- and plateau-phase spinner cultures. In early plateau phase most cells entered a growth-arrested state with a G1-G0 DNA content and showed a marked decrease in sensitivity to cytotoxicity induced by a 1-h exposure to m-AMSA or to its solid tumor-active analogue, CI-921. Studies with radiolabeled m-AMSA established that similar levels of drug were accumulated by log- and plateau-phase cells and that there was no significant drug metabolism in either of these cultures after 1 h. However, marked differences in sensitivity to m-AMSA-induced DNA breakage were observed using a fluorescence assay for DNA unwinding (Kanter P.M., and Schwartz, H.S., Mol. Pharmacol., 22: 145-151, 1982). Changes in sensitivity to DNA breakage occurred in parallel with changes in sensitivity to m-AMSA-induced cell killing. DNA breaks disappeared rapidly after drug removal (half-time approximately 4 min), suggesting that these lesions were probably mediated by DNA topoisomerase II. Resistance to m-AMSA may therefore be associated with changes in topoisomerase II activity in noncycling cells.

DNA-synthesis and tumor growth inhibitions by AGGA, a bleomycin-amsacrine hybrid derivative

AGGA, [[(amino-2-ethyl)-2-aminomethyl]-2-pyridine-6-carboxylhistidyl-ami no-4- butyrylglycylamino]-4-phenyl-1-amino-9-acridine is a synthetic model gathering the simplified metal-chelating part of bleomycin and the intercalating moiety of amsacrine. This molecule was found to possess the metal-complexing and intercalative properties of both antitumor parent drugs. On the basis of results obtained on L1210 and HeLa S3 cells growth inhibition studies and labeled thymidine assay, AGGA clearly indicates a cytostatic activity. On the other hand, the oxygenated free radicals produced in the presence of iron and oxygen do not seem to be able to cleave DNA as BLM does. This lack of cytotoxicity is analyzed in terms of fundamental differences between BLM and AGGA-DNA complexes.

Effect of polyamine depletion by alpha-difluoromethylornithine or (2R,5R)-6-heptyne-2,5-diamine on drug-induced topoisomerase II-mediated DNA cleavage and cytotoxicity in human and murine leukemia cells

The effects of alpha-difluoromethylornithine (DFMO), an ornithine analogue which is an ornithine decarboxylase inhibitor, on the actions of the topoisomerase II-reactive agents 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) and etoposide (VP-16) were investigated in 2 murine L1210 leukemia lines and 2 human HL-60 leukemia lines. One of the human lines was resistant to the cytotoxic and DNA cleaving effects of m-AMSA (HL-60/AMSA). In all 4 lines, alpha-DFMO depleted cellular putrescine and spermidine to nondetectable levels. VP-16-induced DNA cleavage (quantified using alkaline elution) was decreased in all lines following alpha-DFMO treatment. The m-AMSA-induced DNA cleavage was decreased in one of the L1210 lines and in the HL-60 line sensitive to m-AMSA; m-AMSA-induced DNA cleavage was increased in the other L1210 line. The low frequency of m-AMSA-induced DNA cleavage produced in HL-60/AMSA was unaffected by alpha-DFMO treatment. Alterations in drug-mediated DNA effects induced by alpha-DFMO could not be uniformly explained by alpha-DFMO-induced alterations in m-AMSA or VP-16 cellular uptake, as indicated by direct measurements of cell-associated drug or results of DNA cleavage assays in nuclei isolated from alpha-DFMO-treated cells. Exogenous putrescine prevented the effects of alpha-DFMO on drug-induced DNA cleavage, substantiating polyamine depletion as the cause of the altered frequency of DNA cleavage. Cytotoxicity assays in 2 of the lines demonstrated that drug-induced reductions in colony-forming ability paralleled drug-induced DNA cleavage. (2R,5R)-6-heptyne-2,5-diamine, a putrescine analogue which is also an ornithine decarboxylase inhibitor, was also used to deplete polyamine levels in HL-60. (2R,5R)-6-heptyne-2,5-diamine was more potent than alpha-DFMO and produced effects on m-AMSA- and VP-16-induced DNA cleavage and cytotoxicity identical to those produced by alpha-DFMO.

Effect of 1-beta-D-arabinofuranosylcytosine (ara-C) on nuclear topoisomerase II activity and on the DNA cleavage and cytotoxicity produced by 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) and etoposide in m-AMSA-sensitive and -resistant human leukemia cells

The ability of a noncytotoxic dose of ara-C to modulate the amount of 4'-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA)- or etoposide-induced topoisomerase II-mediated DNA cleavage and cytotoxicity was examined in m-AMSA-sensitive and -resistant HL-60 human leukemia cells. Ara-C pretreatment (0.1 microM x 48 hr) sensitized m-AMSA-sensitive cells to the cytotoxicity and DNA cleavage produced by both m-AMSA and etoposide. The actions of m-AMSA in the m-AMSA-resistant cells were affected minimally by ara-C. By contrast, ara-C enhanced etoposide-induced DNA cleavage and, to an even greater extent, etoposide-induced cytotoxicity in m-AMSA-resistant cells. These cells were only minimally cross-resistant to etoposide. Ara-C did not affect the cellular uptake of m-AMSA or etoposide, the amount of 0.35 M NaCl-extractable nuclear topoisomerase II activity from either cell line, or the ability of this enzyme activity to covalently bind to DNA in the presence of the drugs, m-AMSA- and etoposide-induced DNA cleavage is thought to result from drug-induced stabilization of a topoisomerase II-DNA complex. The ability of ara-C to modulate this effect and associated cytotoxicity appears to be mediated by the effects of ara-C on cellular targets other than topoisomerase II but which are important to topoisomerase II-mediated events, such as protein-associated DNA cleavage. A good candidate for such a target may be cellular chromatin.

Comparison of the effects of treatment with the polyamine analogue N1,N8 bis(ethyl)spermidine (BESpd) or difluoromethylornithine (DFMO) on the Topoisomerase II mediated formation of 4'-(9-acridinylamino) methanesulfon-m-anisidide (m-AMSA) induced cleavable complex in the human lung carcinoma line NCI H157

The positively charged polyamines putrescine, spermidine, and spermine are thought to be important in the maintenance of chromosomal structure. Polyamine depletion by the ornithine decarboxylase inhibitor, 2-difluoromethyl-ornithine (DFMO) is known to alter the effect of several DNA active agents, presumably resulting from the altered conformation of the polyamine depleted DNA. Here we compare the polyamine depletion effects of DFMO and the spermidine analogue N1,N8 bis(ethyl)spermidine (BESpd) on the formation of Topoisomerase II mediated, 4'-(9-acridinylamino) methanesulfon-m-anisidide (m-AMSA) induced cleavable complex formation in human large cell undifferentiated lung carcinoma NCI H157 cells. This human cell line responds in the normal cytostatic manner to DFMO, whereas it responds in an unusual cytotoxic manner to treatment with BESpd. Here we report that neither DFMO nor BESpd alone affects the formation of cleavable complex. However, both compounds significantly enhance the m-AMSA induced formation of cleavable complex, each by approximately 1.6 fold. These results indicate that both DFMO and BESpd lead to a similar depletion of nuclear polyamines. Additionally, although BESpd closely resembles the natural polyamine spermidine, it appears that it cannot substitute for Spd at the level of DNA.

Role of DNA intercalation in the inhibition of purified mouse leukemia (L1210) DNA topoisomerase II by 9-aminoacridines

An attempt was made to analyze the mechanism by which 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) inhibits mammalian DNA topoisomerase II. The effects of various 9-aminoacridine derivatives differing by their DNA affinities and DNA sequence selectivity of binding were compared in the presence of purified mouse leukemia L1210 DNA topoisomerase II. No correlation was found between DNA unwinding and topoisomerase II inhibition. 9-Aminoacridine was inactive as a topoisomerase II inhibitor and o-AMSA was only weakly active. The location of L1210 topoisomerase II mediated DNA breaks produced in the absence or presence of 9-aminoacridines were studied in [32P]-end-labeled pBR 322 DNA. All 9-aminoacridines, even those differing by their DNA sequence selectivity of binding, produced similar DNA cleavage patterns. Most drug-induced topoisomerase II mediated DNA breaks appeared at sites that were already cleaved by the enzyme in the absence of drug. The present results suggest that 9-aminoacridines inhibit L1210 DNA topoisomerase II by interacting at or near enzyme-DNA complexes by some unknown DNA effect or by direct protein interaction.

A comparison of adriamycin and mAMSA. II. Studies with V79 and human tumour multicellular spheroids

Multicellular spheroids were used to compare the two chemotherapeutic agents adriamycin (ADM) and 4'[(9-acridinyl)-amino] methanesulphon-m-anisidide (mAMSA). Chinese hamster cells, V79 379A, a human small cell lung carcinoma, designated ME/MAR, and a human melanoma xenograft, HX117, were grown as spheroids (200 or 400 micron in diameter) and treated with either drug for 1 h, at 37 degrees C, in air. Cytotoxicity was assayed using both cell survival and growth delay. Both drugs were highly toxic towards V79 but showed less activity toward the human tumour single cell suspensions; ADM was more effective towards HX117 and ME/MAR than mAMSA. When grown as spheroids, the cells developed marked resistance to both drugs. In all cases, cytotoxicity was drug dose and spheroid size dependent. The response of HX117 spheroids to both drugs was similar. In contrast, ADM was more effective toward 200 micron diameter ME/MAR spheroids, and mAMSA showed greater activity than ADM against V79 spheroids. Both endpoints gave qualitatively equivalent results, and a comparison of the two showed relatively long growth delays for a given level of cell kill, for both drugs and with all three cell lines. The greater cytotoxicity of ADM toward ME/MAR spheroids is consistent with the clinical finding that ADM has a use in the treatment of small cell carcinoma of the lung, while mAMSA has not demonstrated any activity in the treatment of lung cancer.

Quantitative structure-activity relationship study on amsacrine derivatives

Various biological activities of amsacrine derivatives were analyzed in relation to various physico-chemical parameters. The in vitro activity parameters like DNA-binding and cell inhibition constants were found to have significant correlations but with varying physico-chemical parameters. DNA-binding constants were found to be the function of van der Waals volume and the cell inhibition constant to be the function of the hydrophobic parameter. But the in vivo antitumor activity parameters like optimal dose administered intraperitoneally in mice injected with P388 leukemia cells and the percentage increase in life span of treated animals over that of control animals were not found to be related with any property of the molecules.

Cytotoxic action and cell cycle effects of ALGA, a peptidic derivative of the antileukemic drug amsacrine

4'-(9-acridinylamino) methanesulfon-m-anisidide (amsacrine or AMSA), an antitumor drug which has been tested in clinical trials, is known to bind to DNA by the intercalation of its 9-amino acridine moiety between DNA base pairs. Like AMSA, a peptidic derivative of 4-(9-acridinylamino) aniline, 4-(9-acridinylamino)-N-(lysylglycyl) aniline (ALGA) binds to DNA by intercalation and its affinity for the target was found to be higher than the parent drug. The antitumor effect of AMSA and ALGA has been monitored by drug exposure assays on EMT 6 cells. AMSA showed a slightly higher cytotoxic activity. The cell cycle effects of both drugs were studied using flow cytofluorimetry; an accumulation of cells in the S phase followed by a cycle arrest in the G2 phase, characteristic of intercalating drugs, was observed.

Electron transfer-oxy radical mechanism for anti-cancer agents: 9-anilinoacridines

A possible mode of action involving electron transfer is advanced for the 9-anilinoacridines. The mechanism entails formation of toxic oxy radicals which destroy the neoplasm. Cyclic voltammetry was performed on iminium type ions derived by protonation of the acridines. Reductions were generally reversible with potentials of about -0.60 V. Involvement of quinoidal metabolites is also a possibility. The relationship of electrochemical behavior to structure and physiological activity is addressed.

Amsacrine analogues with extended chromophores: DNA binding and anti-tumour activity

A series of phenanthroline analogues of the 9-anilinoacridine anti-leukaemic drug amsacrine were prepared and evaluated, with the aim of providing more weakly-basic derivatives which retained high levels of DNA binding. All the phenanthroline derivatives were stronger DNA-binding ligands than the corresponding acridine compounds, and the 1,7- and 1,8-phenanthrolines were weaker bases by 2 pKa units. The 1,10-phenanthroline derivative showed superior in vivo activity against the P388 leukaemia and the Lewis lung solid tumour than the corresponding acridine derivative amsacrine, but the other phenanthroline compounds did not have improved activity.

Cell cycle stage dependent variations in drug-induced topoisomerase II mediated DNA cleavage and cytotoxicity

The DNA cleavage produced by 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) in mammalian cells is putatively mediated by topoisomerase II. We found that in synchronized HeLa cells the frequency of such cleavage was 4-15-fold greater in mitosis than in S while the DNA of G1 and G2 cells exhibited an intermediate susceptibility to cleavage. The hypersensitivity of mitotic DNA to m-AMSA-induced cleavage was acquired relatively abruptly in late G2 and was lost similarly abruptly in early G1. The susceptibility of mitotic cells to m-AMSA-induced DNA cleavage was not clearly paralleled by an increase in topoisomerase II activity (decatenation of kinetoplast DNA) in 350 mM NaCl extracts from mitotic cells compared to similar extracts from cells in G1, S, or G2. Furthermore, equal amounts of decatenating activity from cells in mitosis and S produced equal amounts of m-AMSA-induced cleavage of simian virus 40 (SV40) DNA; i.e., the interaction between m-AMSA and extractable enzyme was similar in mitosis and S. The DNA of mitotic cells was also hypersensitive to cleavage by 4'-demethylepipodophyllotoxin 4-(4,6-O-ethylidene-beta-D-glucopyranoside) (etoposide), a drug that produces topoisomerase II mediated DNA cleavage without binding to DNA. Thus, alterations in the drug-chromatin interaction during the cell cycle seem an unlikely explanation for results in whole cells. Cell cycle stage dependent fluctuations in m-AMSA-induced DNA cleavage may result from fluctuations in the structure of chromatin per se that occur during the cell cycle.(ABSTRACT TRUNCATED AT 250 WORDS)