Altered DNA topoisomerase II activity in Chinese hamster cells resistant to topoisomerase II inhibitors

Most DNA intercalators and epipodophyllotoxins inhibit mammalian topoisomerase II by trapping the enzyme within DNA cleavage complexes that can be detected in cells as protein-associated DNA strand breaks. We have characterized previously a line of Chinese hamster cells (DC3F/9-OHE cells) the resistance of which to the cytotoxic effect of intercalators and etoposide is associated with a reduced formation of protein-associated DNA strand breaks. In the present study, topoisomerases of these cells were compared to those of the parental sensitive cells (DC3F). NaCl extracts (0.35 M) of isolated DC3F/9-OHE nuclei did not form 4'-(9-acridinylamino)methanesulfon-m-anisidide-induced DNA-protein linking, whereas DC3F nuclear extracts did. In addition, DC3F/9-OHE nuclear extract had an unusually high level of DNA linking activity in the absence of 4'-(9-acridinylamino)methanesulfon-m-anisidide. Topoisomerases II from DC3F/9-OHE and DC3F nuclei appeared similar qualitatively. DC3F/9-OHE nuclear extract had approximately twice less topoisomerase II molecules than did DC3F nuclear extract but similar topoisomerase II activity. Topoisomerase I activities appeared also similar in sensitive and resistant cells. However, part of DC3F/9-OHE topoisomerase I copurified with a DNA linking activity which was not present in DC3F nuclei. This unusual DNA linking activity was not sensitive to the stimulatory effect of 4'-(9-acridinylamino)methanesulfon-m-anisidide.

The tissue localization of m-AMSA and its effect on thymidine incorporation in various tissues in vivo

The distribution of 14C-labelled m-AMSA was studied in rats and pigmented mice using whole body autoradiography. The agent rapidly disappeared from the blood, accumulating in significant amounts in large parenchymal organs, certain endocrine tissues, and the retina of the pigmented mouse eye. The hemopoietic and lymphoid tissues showed a moderate uptake of radioactivity with the highest concentration observed in the thymus. The autoradiograms indicated a rapid excretion of radioactivity via the liver, kidney and the glandular part of the gastric mucosa. The distribution pattern of label from 14C-m-AMSA remained unaffected by pretreatment of animals with high dose (500 mg kg-1 b.w.) of cytosine arabinoside. Injection of unlabelled m-AMSA (7 mg kg-1 b.w.) to growing rats 24 h before sacrifice resulted in a highly significant (P less than 0.001) inhibition of 3H-thymidine incorporation into the DNA of thymus and spleen. A less pronounced reduction was observed in the kidney, adrenal, lung and testes. The thymidine incorporation into the DNA of bone marrow was markedly suppressed when calculated per dry weight, but increased when related to the DNA content, suggesting early regeneration of the remaining cells. In contrast, no significant effects were observed on the DNA synthesis in small intestine and liver.

Morphological transformation and chromosome damage by amsacrine in C3H/10T1/2 clone 8 cells

Morphological transformation, cell survival, chromosomal aberrations and micronuclei were measured in C3H/101/2CL8 cells after 24 h exposure to amsacrine. A weak but dose-related increase in the percentage of dishes containing transformed foci occurred. As previously reported for alkylating agents, this effect was increased by treating 5 days instead of 1 day after plating. There was no evidence for gene mutation at the Na/K ATPase locus, although amsacrine induced micronuclei in a large percentage of cells and chromosomal aberrations, including interchange events and double minute chromosomes, in dividing cells. In would appear that transformation and chromosomal events may be related in amsacrine-treated C3H/10T1/2CL8 cells. The results strongly suggest that amsacrine has carcinogenic potential, possibly related to its chromosome-breaking properties.

In vivo stimulation by antitumor drugs of the topoisomerase II induced cleavage sites in c-myc protooncogene

Several antitumor drugs including DNA intercalative and non intercalative agents induce in vitro and in vivo double-stranded DNA breaks by stabilization of a topoisomerase II-DNA complex. In order to locate cleavage sites in an actively transcribed oncogene, N417 cells, originating from a human small cell lung carcinoma and containing 45-50 copies of c-myc oncogene, were treated with mAMSA, 9 hydroxyellipticine and VM 26. The presence of DNA lesions in c-myc was investigated by Southern blot hybridization with a human c-myc probe. In addition to normal bands, DNA patterns of drug treated-cells revealed the presence of new bands most likely corresponding to topoisomerase II-mediated cleavage as these bands were not found in untreated control DNA and in DNA treated with oAMSA, a biologically inactive stereoisomer of mAMSA. Major cleavage sites induced by drugs in the N417 cell c-myc locus were located in the 5' end of the c-myc exon 1 closely to some DNAse I hypersensitive sites which are assumed to reflect an activity of the gene. Therefore our data suggest that TopoII-mediated drug activity correlates with gene activity.

Formation of the thiol adducts of 4'-(9-acridinylamino)methanesulfon-m-anisidide and their binding to deoxyribonucleic acid

We investigated the interactions of 4'-(9-acridinylamino)methanesulfon-m-anisidide (mAMSA) with thiol-containing compounds and the potential binding of the thiolytic adducts to DNA. All thiols tested (glutathione, cysteine, coenzyme A, 2-mercaptoethanol and lactate dehydrogenase) formed adducts with mAMSA as evidenced by changes in the absorption spectrum of mAMSA and induction of fluorescence. Spectral changes induced by the thiols were different, suggesting that each thiol induced specific changes in the electronic structure of the acridine nucleus. Treatment of glutathione with p-chloromercuribenzoate eliminated the absorption spectral changes and induction of fluorescence, indicating that the reduced-thiol group is involved. In high ionic strength buffer, addition of calf thymus DNA induced fluorescence-quenching of both the mAMSA-glutathione and mAMSA-cysteine adducts without spectral shift. Viscometric studies showed that mAMSA and mAMSA-glutathione intercalated into DNA and produced similar increases in the length of linear DNA.

Acute promyelocytic leukemia. M.D. Anderson Hospital experience

Sixty patients with acute promyelocytic leukemia were treated between 1973 and 1984. The overall median survival was 16 months with a five-year survival rate of 31 percent. The complete remission rate was 53 percent and was similar whether they received amsacrine- or anthracycline-based regimens (60 percent versus 51 percent). The median remission duration was 29 months. At five years, 43 percent of patients with responses to treatment had continuous remission and 57 percent were alive. Salvage therapy produced remissions in 53 percent of patients during first relapse, with two long-term survivors after further consolidation with bone marrow transplantation. Early fatal hemorrhage associated with disseminated intravascular coagulopathy during induction therapy occurred in 16 patients (26 percent). Multivariate analysis of the pretreatment patient characteristics significantly associated with an increased risk of fatal hemorrhage identified four that have primary prognostic importance: thrombocytopenia, elevated absolute blast and promyelocyte counts, old age, and anemia. Patients having up to two unfavorable features had a low risk of fatal hemorrhage compared with those who had more than two (5 percent versus 58 percent; p less than 0.0001). Overall, patients who received heparin had a lower incidence of fatal hemorrhage than those who did not (19 percent versus 32 percent). Heparin therapy was not beneficial to those at low risk but was associated with a trend towards decreased hemorrhagic deaths among high-risk patients (45 percent versus 67 percent). Cytogenetic studies demonstrated the characteristic 15;17 translocation in 73 percent of patients with analyzable metaphases, whereas 12 percent had other karyotypic abnormalities. Remission induction was often associated with a gradual atypical morphologic evolution into remission without intermediate hypoplasia with the interim marrows showing a high proportion of blasts. It is concluded that acute promyelocytic leukemia is a unique disease with a high potential for cure. Knowledge of its prognosis using present frontline and salvage therapy, of the factors related to fatal hemorrhage, and of the unusual patient marrow profiles during remission induction may improve the therapeutic approach.

[A new drug and current strategy in the treatment of acute non-lymphocytic leukemia in adults]

Among new drugs being studied currently, AMSA and mitoxantrone have shown significant usefulness against acute non-lymphocytic leukemia in adults. Remission induction therapy consisting of daunomycin and cytosine arabinoside has been commonly selected as the first line of treatment and the complete remission rate obtained has exceeded 70%. Postremission therapy consolidation has been judged to be necessary while the clinical roles of maintenance and intensification remain to be clarified and appear to still require an investigational approach.

Proliferation dependence of topoisomerase II mediated drug action

Topoisomerase II mediated DNA scission induced by both a nonintercalating agent [4'-demethylepipodophyllotoxin 4-(4,6-O-ethylidene-beta-D-glucopyranoside) (VP-16)] and an intercalator [4'-(9-acridinylamino) methanesulfon-m-anisidide (m-AMSA)] was studied as a function of proliferation in Chinese hamster ovary (CHO), HeLa, and mouse leukemia L1210 cell lines. Log-phase CHO cells exhibited dose-dependent drug-induced DNA breaks, while plateau cells were found to be resistant to the effects of VP-16 and m-AMSA. Neither decreased viability nor altered drug uptake accounted for the drug resistance of these confluent cells. In contrast to CHO cells, plateau-phase HeLa and L1210 cells remained sensitive to VP-16 and m-AMSA. Recovery of drug sensitivity by plateau-phase CHO cells was found to reach a maximum approximately 18 h after these cells regained exponential growth and was independent of DNA synthesis. DNA strand break frequency correlated with cytotoxicity in CHO cells; log cells demonstrated an inverse log linear relationship between drug dose (or DNA damage) and colony survival, whereas plateau-derived colony survival was virtually unaffected by increasing drug dose. Topoisomerase II activity, whether determined by decatenation of kinetoplast DNA, by cleavage of pBR322 DNA, or by precipitation of the DNA-topoisomerase II complex, was uniformly severalfold greater in log-phase CHO cells compared to plateau-phase cells.

DNA damage by antitumor acridines mediated by mammalian DNA topoisomerase II

Antitumor drugs from many chemical classes have been shown to induce protein-linked DNA breaks in cultured mammalian cells and in vitro in the presence of purified mammalian DNA topoisomerase II. The possibility that mammalian DNA topoisomerase II is an intracellular target which mediates drug-induced DNA breaks is supported by the following studies using 4'-(9-acridinylamino)methane-sulfon-m-anisidide (m-AMSA): (a) a single m-AMSA-dependent DNA cleavage activity copurified with calf thymus DNA topoisomerase II activity at all chromatographic steps of the enzyme purification; (b) m-AMSA-induced DNA cleavage by this purified activity resulted in the covalent attachment of protein to the 5'-ends of the DNA via a tyrosyl phosphate bond. This covalently linked protein has the same reduced molecular weight as purified calf thymus DNA topoisomerase II. The possibility that topoisomerase II-mediated DNA breaks may be responsible for cytotoxicity has also been investigated using a number of m-AMSA-related acridines. The level of topoisomerase II-mediated DNA breaks in vitro strongly correlates with the level of protein-linked DNA breaks in cultured cells and drug-induced cytotoxicity. These results suggest that mammalian DNA topoisomerase II may be a cytotoxic target of antitumor acridines.

Randomized trial of high-dose cytarabine versus amsacrine in acute myelogenous leukemia in relapse: a Leukemia Intergroup Study

Patients with acute myelogenous leukemia in relapse who were ineligible for further anthracycline therapy either because they were judged to be anthracycline resistant or had received the maximum doses were randomized to receive high-dose cytarabine (3 g/m2 every 12 hours for 6 days) or amsacrine (75 mg/m2 daily for 7 days). The response rates in both groups were similar: three of 25 patients given high-dose cytarabine and three of 23 given amsacrine obtained complete remissions.

Characterization of acquired epipodophyllotoxin resistance in a Chinese hamster ovary cell line: loss of drug-stimulated DNA cleavage activity

Recent evidence indicates that type II DNA topoisomerases mediate epipodophyllotoxin-induced DNA damage and may be intrinsic to the drug's antitumor effects. Using an epipodophyllotoxin-resistant cell line, we have now further defined the relationship between DNA damage and cell death and delineated the significance of certain drug-enzyme interactions. When compared to wild-type cells, the mutant Chinese hamster ovary cell line, VpmR-5, exhibits marked resistance to both the cytotoxic and DNA cleavage activities of etoposide (VP-16). Steady-state concentrations of radiolabeled VP-16 are identical in both cell lines. Catalytic activity in crude nuclear extracts from wild-type and VpmR-5 cells is equal and is equally sensitive to inhibition by VP-16. However, using an assay that specifically measures generation of 5' protein-linked breaks in 32P-labeled 3' DNA, we have found that DNA cleavage activity in nuclear extract from the VpmR-5 line is profoundly resistant to stimulation by VP-16. Further, a somatic cell hybrid line of VpmR-5 cells and drug-sensitive EOT-3 cells exhibits recovery of VP-16 sensitivity in concert with reconstitution of DNA cleavage activity. These data indicate that stimulation of enzyme-mediated DNA cleavage, rather than loss of normal topoisomerase function, is responsible for epipodophyllotoxin-induced cytotoxicity.

Kinetic and equilibrium studies of the interaction of amsacrine and anilino ring-substituted analogues with DNA

The kinetic stability of complexes of the clinical antileukemic drug amsacrine and anilino ring-substituted analogues with DNA has been studied by using the surfactant sequestration technique in a stopped-flow spectrophotometer. In addition, viscometric measurements using covalently closed circular DNA and displacement measurements of DNA-bound ethidium have been performed to evaluate helix unwinding angles and association constants, respectively. Amsacrine and its analogues dissociate from DNA by a complex kinetic pathway which involves at least three discernible transiently bound forms of the drug. Dissociation time constants for amsacrine are found to range from less than 1 to 6 ms in buffer of ionic strength 0.1, and the biomolecular association rate constant is greater than 10(6) M-1 s-1. We find that amsacrine forms one of the weakest intercalation complexes among the compounds studied, as judged by the criteria of kinetic stability, affinity, and chromophore-base pair stacking interactions. Unlike other compounds of this broad class (intercalating chromophores bearing sterically-demanding side chains), addition of the bulky side chain has little effect on the kinetic stability of the drug-DNA complexes, suggesting that the acridinesulfonanilides may intercalate into DNA from the less sterically demanding major groove of the helix. Such a binding geometry would facilitate the formation of the previously proposed ternary complex between amsacrine, DNA, and gene-regulatory enzymes (e.g., topoisomerases and repressors) which are known to bind in the major groove.

Comparison of the pharmacokinetics and protein binding of the anticancer drug, amsacrine and a new analogue, N-5-dimethyl-9-[(2-methoxy-4-methylsulfonylamino)phenyl-amino] -4-acridinecarboxamide in rabbits

Amsacrine (NSC 249 992) is a new anticancer drug which, although effective for the treatment of various disseminated tumors, has shown disappointing activity against most solid tumors. A new analogue, N-5-dimethyl-9-[(2-methoxy-4-methylsulfonylamino)phenylamino] -4-acridine-carboxamide (CI-921, NSC 343 499) has been identified, which might offer a broader clinical antitumor spectrum. This analogue is more lipophilic (0.5 log p units) and is also a considerable weaker base (pKa 6.40) than amsacrine (pKa 7.43). This study compared the pharmacokinetics of total and unbound amsacrine and CI-921 in plasma after equimolar dose infusions (12.7 mumol/kg) in a balanced crossover design in six rabbits. Drug concentrations were determined by high-pressure liquid chromatography and the unbound fraction by equilibrium dialysis. Threefold higher total plasma concentrations were achieved with CI-921 than with amsacrine. However, the unbound fraction was significantly less for CI-921 (0.33% +/- 0.04) than for amsacrine (2.78% +/- 0.53). There was no significant difference between distribution and elimination half-life and mean residence time, but the apparent volume of distribution (means, 121 vs 45 l/kg) and clearance (means, 46.6 vs 16.3 l h-1 kg-1) of unbound CI-921 were threefold greater than the corresponding parameters for unbound amsacrine. We suggest that despite higher binding in plasma, the greater distribution or tissue uptake of CI-921 may be partly responsible for its greater anticancer activity in vivo.

Identification of the active species in deoxyribonucleic acid breakage induced by 4'-(9-acridinylamino)methanesulfon-m-anisidide and copper

Cyclic voltammetry and UV/VIS spectrometry studies show that 4'-(9-acridinylamino)methanesulfon-m-anisidide (mAMSA) can be oxidized electrochemically to N1-methylsulfonyl-N4-(9-acridinyl)-3-methoxy-2,5-cyclohexadiene-1,4-d iimine (mAQDI) in Tris buffer, pH 7.5. The formal potential of this 2-electron process, as determined by spectroelectrochemical techniques, was 0.141 V versus saturated calomel electrode. Voltammetric data also indicate that an electron transfer reaction between mAMSA and Cu(II) was thermodynamically favored. Two lines of evidence suggest that mAQDI and Cu(I) are the active species in DNA breakage: (1) mAQDI, in the presence of Cu(I), induced both single- and double-strand DNA breakage of the superhelical pDPT275 form I DNA. mAQDI or Cu(I), when used alone, was less effective. (2) The DNA-breaking activity of an mAMSA-Cu(II) mixture was kinetically correlated with the production of both Cu(I) and mAQDI. Thin-layer chromatographic studies showed that mAMSA was oxidized to mAQDI which, in turn, was hydrolyzed. The end product was identified as 9-aminoacridine. When DNA breakage activity was measured as a function of reaction time, a biphasic response was observed. Maximal DNA-breaking activity was obtained upon mixing mAMSA and Cu(II) for 2-4 hr, depending on the concentrations of mAMSA and Cu(II), and was followed by a subsequent decrease in breakage. The decrease appears to be due to the decrease in Cu(I) production and the hydrolysis of mAQDI. These results substantiate the proposed mechanism that DNA breakage induced by mAMSA-Cu(II) involves a rate-limiting electron transfer step to form mAQDI and Cu(I), which are the active species for DNA breakages.

Cross-resistance to intercalating agents in an epipodophyllotoxin-resistant Chinese hamster ovary cell line: evidence for a common intracellular target

Several intercalating agents, as well as the epipodophyllotoxins, appear to effect DNA damage through their interaction with type II DNA topoisomerases. However, the relationship of this phenomenon to anti-tumor activity remains unproven. Our studies with an epipodophyllotoxin-resistant cell line not only provide additional evidence that the enzyme is a multidrug target but also serve to implicate it as a mediator of cytotoxic effect. When compared to wild-type cells, the epipodophyllotoxin-resistant Chinese hamster ovary cell line, VpmR-5, exhibits cross-resistance to both the cytotoxic and DNA cleavage activities of 4',9-acridinylaminomethanesulfon-m-anisidide, mitoxantrone, and Adriamycin. Steady-state concentrations of radiolabeled-4',9-acridinylaminomethanesulfon-m-anisidide and daunomycin are identical in both cell lines. Sharp plateaus in the VpmR-5 dose-response curves for Adriamycin-induced DNA strand breaks and cytotoxicity appear to be related to interference with type II topoisomerase-mediated cleavage of DNA at high concentrations of the intercalator. These data support a direct role for DNA strand scission in cell death and also suggest that multidrug resistance may be acquired by a qualitative change in type II topoisomerase that alters interaction of drug with the enzyme or enzyme-DNA complex.

Acute myocardial necrosis during administration of amsacrine

The authors report a case of focal myocardial necrosis, presenting clinically as an acute myocardial infarction during the administration of the antineoplastic drug, amsacrine, in a patient without coronary artery disease. In addition to the recognized arrhythmic complications, the authors emphasize myocardial necrosis as a possible further manifestation of amsacrine-related cardiotoxicity.

Protein kinase C phosphorylates topoisomerase II: topoisomerase activation and its possible role in phorbol ester-induced differentiation of HL-60 cells

DNA topoisomerase II from Drosophila was phosphorylated effectively by protein kinase C. With a Km of about 100 nM, the reaction was rapid, occurring at 4 degrees C as well as at 30 degrees C and requiring as little as 0.6 ng of the protein kinase per 170 ng of topoisomerase. About 0.85 mol of phosphate could be incorporated per mol of topoisomerase II, with phosphoserine as the only phospho amino acid produced. The reaction was dependent on Ca2+ and phosphatidylserine and was stimulated by phorbol esters. Calmodulin-dependent protein kinase II, but not cyclic AMP-dependent protein kinase, was also able to phosphorylate the topoisomerase. Phosphorylation of topoisomerase II by protein kinase C resulted in appreciable activation of the topoisomerase, suggesting that it may represent a possible target for the regulation of nuclear events by protein kinase C. This possibility is supported by the finding that the phorbol ester-induced differentiation of HL-60 cells was blocked by the topoisomerase II inhibitors novobiocin and 4'-(9-acridinylamino)methanesulfon-m-anisidide(m-AMSA), but not by the inactive analog o-AMSA.

Efficacy and clinical cross-resistance of a new combination therapy (AMSA/VP16) in previously treated patients with acute nonlymphocytic leukemia

We investigated the tolerance, efficacy, and clinical cross-resistance of a new combination chemotherapy in 38 patients with previously treated acute myeloblastic leukemia (AML). It consisted of 120 mg2/d 4'(9-acridinylamino) methanesulfon-m-Anisidide (m-AMSA) in a one-hour infusion and 80 mg/m2/d etoposide (VP-16) in a 24-hour infusion, both administered for 5 days. The first 27 patients also received vinblastine, 6 mg/m2 on day 8, but this therapy was discontinued because of intestinal complications. Thirteen of 23 patients (56%) at first or subsequent relapse and five of 15 patients (33%) who were primarily resistant to an anthracycline/cytarabine combination achieved a complete response (CR) (hemoglobin level not taken into account) with a median CR duration of 5 months and 2 months, respectively. The response rate was as high as 63% for patients at first or second relapse whether the remission was maintained or not. The median times to recovery of normal bone marrow cellularity, of blood granulocyte counts greater than 500/microL, and of platelets greater than 20,000/microL were 34, 27, and 22 days, respectively. Marked but reversible gastrointestinal toxicity was observed in 24% of the patients, and two patients died of infection during induction. The one-hour AMSA/continuous VP-16 combination is effective for patients with relapsing AML and shows no cross-resistance in a proportion of patients refractory to the standard anthracycline-cytarabine combination.

Salvage treatment of unfavorable non-Hodgkin's lymphoma with cisplatin, amsacrine, and mitoguazone: a Southwest Oncology Group Pilot Study

We tested the combination of cisplatin, amsacrine, and mitoguazone as salvage treatment for patients with advanced unfavorable non-Hodgkin's lymphomas. An objective response rate of 43% was noted in 30 evaluable patients, but all responses were partial and the median duration of response was only 2 months. Toxicity included life-threatening and fatal leukopenia and severe gastrointestinal intolerance. We conclude that this combination chemotherapy regimen is not a valuable salvage treatment for patients with non-Hodgkin's lymphoma.

Reduced formation of protein-associated DNA strand breaks in Chinese hamster cells resistant to topoisomerase II inhibitors

DNA intercalating drugs and the epipodophyllotoxins etoposide and teniposide interfere with the action of mammalian DNA topoisomerase II by trapping an intermediate complex of the enzyme covalently linked to the 5'-termini of DNA breaks. This effect can be observed in intact cells by alkaline elution measurement of protein-associated DNA strand breaks. To assess the cytotoxic role of this effect, we have studied a subline of DC3F Chinese hamster lung cells selected for resistance to the intercalating agent 9-hydroxyellipticine. This subline (DC3F/9-OHE) was cross-resistant to other intercalators as well as to etoposide. Resistance to Adriamycin was associated with reduced uptake. However, resistance to 4'-(9-acridinylamino)methanesulfon-m-aniside and 2-methyl-9-hydroxyellipticinium was observed in the absence of changes in drug uptake, suggesting a second mode of resistance. DC3F/9-OHE cells formed fewer protein-associated DNA strand breaks in response to 4'-(9-acridinylamino)methanesulfon-m-aniside, 2-methyl-9-hydroxyellipticinium, or etoposide than did the sensitive parental cells. The same was true for isolated nuclei from these cells, which is consistent with a mode of resistance unrelated to drug uptake through the plasma membrane. These data suggest that resistance to DNA topoisomerase II inhibitors exhibited by DC3F/9-OHE cells is due in part to a modification of topoisomerase II activity.

The production of topoisomerase II-mediated DNA cleavage in human leukemia cells predicts their susceptibility to 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA)

Protein-associated DNA cleavage is produced in mammalian cells treated with active antileukemic DNA intercalating agents such as 4'(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). We have examined the ability of m-AMSA to produce DNA cleavage in 3 human myeloid leukemic cell lines with different sensitivities to the cytotoxic actions of m-AMSA to see if the magnitude of DNA cleavage correlated with the degree of m-AMSA sensitivity. DNA alkaline elution was used to quantify DNA cleavage. The amount of m-AMSA-induced DNA cleavage in the two lines sensitive to m-AMSA was 1-2 orders of magnitude greater than that in an m-AMSA-resistant leukemic line. The m-AMSA resistant line had been developed by prolonged exposure of one of the sensitive lines to m-AMSA. This finding was not secondary to a decreased uptake of m-AMSA in the resistant cell line. m-AMSA treatment of the nuclei isolated from the three lines produced DNA cleavage frequencies comparable to the cleavage frequencies produced by m-AMSA treatment of the whole cells from which the nuclei were isolated. The DNA cleaving ability stimulated by m-AMSA is thought to be mediated by drug-induced effects on topoisomerase II, a nuclear enzyme that mediates alterations in DNA conformation. Alterations in the manner in which this enzyme interacts with antineoplastic agents may explain the emergence of resistant cells following initially successful chemotherapy.

Potentiation of sister chromatid exchange by 3-aminobenzamide is not modulated by topoisomerases or proteases

Poly(ADP-ribose) is synthesized in response to DNA strand breaks and covalently modifies numerous intracellular proteins. We have proposed that this modification regulates, i.e., inhibits, the activity of these enzymes, e.g., topoisomerases and proteases, which could otherwise cause additional DNA damage or alterations in chromatin structure. Inhibition of poly(ADP-ribose) polymerase by 3-amino-benzamide (3AB) in cells exposed to DNA-damaging agents would, according to this proposal, eliminate the regulatory role of ADP-ribosylation. When Chinese hamster ovary cells are cultured with methyl methanesulfonate (MMS) and 3AB, a synergistic increase in sister chromatid exchange frequency is observed. We investigated the regulatory role of poly(ADP-ribose) polymerase to see if topoisomerases or proteases are involved in this synergistic increase. Cells were exposed to MMS or the intercalating agent 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA), 3AB, and either the topoisomerase inhibitor novobiocin or the protease inhibitor antipain. Neither novobiocin nor antipain affected the synergistic response of MMS and 3AB or the additive response of m-AMSA and 3AB. These results suggest that topoisomerases or proteases do not account for the effect of 3AB on sister chromatid exchange frequency after DNA damage.

Chemotherapy in metastatic melanoma: phase II studies of amsacrine, mitoxantrone and bisantrene

In a phase II study 20 patients with measurable metastatic melanoma were treated with amsacrine 120 mg/m2 every 3 weeks. No objective responses were observed. In a separate study 29 patients received mitoxantrone 12-14 mg/m2 every 3-4 weeks. One objective partial response was seen. The drug was well tolerated. Seventeen patients were treated with bisantrene 135-200 mg/m2 weekly. No objective responses were observed. Phlebitis was the major non-hematologic toxicity of bisantrene. These agents are not recommended for treatment of malignant melanoma.