Matrix-addressable, active electrode arrays for neural stimulation using organic semiconductors-cytotoxicity and pilot experiments in vivo.

Organic field effect transistors can be integrated into micromachined polyimide-based neural stimulation electrode arrays in order to build active switching matrices. With this approach, a matrix of N x M electrode contacts requires only N + M interconnects to a stimulator when active switching elements are used instead of N x M interconnects. In this paper, we demonstrated that pentacene-based organic field effect transistors (OFETs) can be used to drive stimulation currents through neural electrodes in a physiological-like environment. In order to prove the general applicability as an implant material, the cytotoxicity of pentacene was evaluated with respect to potential effects on cell viability. The results of these tests indicate that extracts from pentacene inhibit neither proliferation nor metabolism of the tested mouse fibroblasts. However, some effect on cell spreading was observed when cells were in direct contact to pentacene for 48 h. In pilot experiments it was demonstrated for the very first time that pentacene transistors can be used as switching elements, acting as voltage-controlled current sources, capable of driving currents suitable for electrical stimulation of a peripheral nerve via a tripolar cuff electrode.

[Genotoxic and mutagenic activity of antineoplastic anthracyclines and their aglycones: study in two test-systems]. / Genotoksicheskaia i mutagennaia aktivnost' protivoopukholevykh antratsiklinov i ikh aglikonov: izuchenie v test-sistemakh.

Mutagenic (Ames tests) and genotoxic (SOS chromotest) activities of highly-efficient natural anthracycline monosaccharides possessing antitumor activity-daunorubicin (also known as daunomycin or rubomycin), doxorubicin (adriamycin), and carminomycin-were studied. At the same time, the hypothesis was tested that intercalation of the antibiotic moiety into the helix of cell DNA, which was mediated by the saccharide amino group, played a crucial role in genotoxicity of these anthracyclines. The hydrolysis products of these antibiotics (the corresponding aglycones) and aclacynomycin A (an anthracycline trisaccharide), as well as aclavinone (its derivative aglycone), were studied. All these compounds lacked the saccharide amino group necessary for intercalation. It was found that all anthracycline monosaccharides studied had a strong mutagenic effect on strain TA98 and a moderate effect on strain TA100 of Salmonella typhimurium. Aclacynomycin A was found to have no mutagenic effect on any strain. Lack of the glycoside amino group did not necessarily result in loss of mutagenic activity in the derivative aglycones of anthracycline monosaccharides: they exhibited moderate mutagenic activity in strain TA98 and low but significant activity in strain TA100. The S9 microsomal fraction did not alter the mutagenic activity of either anthracycline monosaccharides or their aglycones; however, it dramatically increased the mutagenic activity of aclavinone: correspondence between positive responses in Ames tests and the SOS chromotest was found. Apparently, the mutagenic activity of the substances studied in bacterial cells was mediated by inducing the SOS-repair process. If the compound contained the amino glycoside moiety, functional and structural precursors of the SOS response were formed via intercalation of the reagents into the DNA duplex; if the substance did not contain this moiety, the precursors were formed via ionic interaction.

Role of daunosamine and hydroxyacetyl side chain in reaction with iron and lipid peroxidation by anthracyclines.

Doxorubicin (Adr), daunorubicin (Dnr), and analogs of Adr modified in daunosamine (4'-epi-Adr and 3'-N-acetyl-Adr) were investigated with respect to their reaction with Fe(III) and analyzed for the ability of the corresponding iron complexes to sustain lipid peroxidation of isolated human platelet membranes. When the proportion of iron [25 microM Fe(III)] to Adr was 1:4, almost 50% of the metal was reduced following 1 hour of anaerobic reaction, while only approximately equal to 14% of the bound iron could be extracted as Fe(II) in the reactions of the Dnr complexes. The reaction of Adr was associated with formation of two main novel anthracyclines. One of the products had lost the C14 atom of the C9 chain and displayed chromatographic features and visible UV light spectra identical to those of authentic 9-dehydroxyacetyl-9-carboxyl-Adr. In complexes of iron and Dnr, no significant anthracycline degradation was observed. Reduction of anthracycline-bound Fe(III) by 4'-epi-Adr (38%) and 3'-N-acetyl-Adr (21.2%) was consistently less than that by Adr. Complexes of the anthracyclines investigated had different abilities to sustain lipid peroxidation, which was blocked (a) by the iron chelators deferoxamine and bathophenanthroline, indicating that Fe(III) and Fe(II) were needed for the reaction, and (b) by ICRF-198, the chelating product that forms intracellularly by hydrolysis of razoxane, which can prevent Adr cardiotoxicity. Peroxidation was not affected by scavengers of reduced oxygen radicals (superoxide dismutase, catalase, and mannitol). The isolated membranes contributed to the reduction of anthracycline-bound Fe(III) and probably represented the main determinant of lipid peroxidation by iron-Dnr. Lipid peroxidation was significantly less for complexes of iron with 4'-epi-Adr or 3'-N-acetyl-Adr than for complexes of iron with Adr. The observed differences may be relevant to the different biologic properties of Adr and its analogs, in particular their different degrees of cardiotoxicity.

Analysis of hemin-induced protection of human hemopoietic cells from the cytotoxic effects of anthracyclines.

Experiments were performed with K562 erythroleukemia cells to further characterize the observation that hemin protects hemopoietic cells from the cytotoxic effects of anthracycline drugs. The present studies demonstrate that this protective effect of hemin applies only to anthracyclines and not to other classes of antineoplastic agents. Hemin interferes with the cellular accumulation of various anthracyclines, as measured by cytofluorography, and prevents binding of anthracyclines to isolated cell nuclei. Exposure of K562 cells to hemin retards the anthracycline-induced arrest of cells at the G2-M interphase of the cell cycle and permits cells to undergo continuing division as demonstrated by clonal growth in plasma clot cultures. Furthermore, hemin decreases the ability of anthracyclines to unwind simian virus 40 supercoiled DNA in vitro. The protective effect of hemin fails to occur if cells have been preincubated with this agent for 72 h before they are exposed to Adriamycin in the absence of hemin. The findings suggest that hemin prevents anthracycline-induced cytotoxicity by acting at several levels. These effects may be mediated by direct interactions of hemin with DNA and perhaps other cellular constituents or by molecular complex formation between hemin and anthracyclines at intracellular sites.

Effects of verapamil on uptake and in vitro toxicity of anthracyclines in human leukemic blast cells.

The effect of a calcium channel blocker, verapamil, on intracellular uptake and cytotoxicity of anthracyclines in vitro was studied on leukemic cells from 32 patients with acute non-lymphoblastic leukemia. Cells were isolated from peripheral blood or bone-marrow and incubated with a concentration of 0.2 mumol/l, 0.5 mumol/l and/or 1.0 mumol/l of doxorubicin or daunorubicin in the absence and presence of verapamil at a concentration of 2 mumol/l and/or 10 mumol/l. Intracellular uptake was determined at the end of the incubations by photofluorometer and the in vitro cytotoxicity was determined after 5 days culturing in liquid medium by dye exclusion according to Weisenthal. Verapamil significantly increased the intracellular uptake of anthracyclines 0.5 mumol/l and 1.0 mumol/l and the cytotoxic effect of anthracyclines 0.2 mumol/l and 0.5 mumol/l and affected doxorubicin and daunorubicin equally. There were no significant differences between the two concentrations of verapamil. Cells from different FAB-groups were equally affected by verapamil. The effect on intracellular uptake was higher in cells from patients who were resistant to therapy compared to those who achieved a complete remission. We conclude that verapamil has an effect on intracellular uptake and cytotoxicity of anthracyclines on tumor cells from patients with acute non-lymphoblastic leukemia. The prognostic and therapeutic relevance of this has to be further evaluated.

Anthracycline-induced DNA breaks and resealing in doxorubicin-resistant murine leukemic P388 cells.

Energy-dependent drug efflux is believed to be a major factor in cellular resistance to doxorubicin (DOX). However, recent studies have shown that decreased retention alone cannot account for anthracycline resistance, and possibly other factors, such as drug metabolism, free radical scavengers, and altered DNA damage/repair, may be involved. We have measured DOX-induced DNA damage and its repair in P388 cells sensitive (P388/S) and resistant (P388/R) to DOX. Our studies show 2- to 5-fold less DNA damage, measured as protein-associated single-strand DNA breaks, in P388/R cells when compared to similarly treated P388/S cells. The repair of DNA in whole cells, expressed as percent DNA rejoined, was complete in 4 hr in P388/R, whereas no repair was seen in P388/S cells until 20 hr. No difference in repair of DNA lesions was observed when nuclei were used in repair experiments. The absence of repair in sensitive whole cells may be due to high retention or slow drug efflux. Increase of cellular DOX retention by exposure of cells to trifluoperazine (TFP) or verapamil (VPL) did not result in the increase of DNA damage in P388/R cells. DOX analogs, N-trifluoroacetyladriamycin-14-valerate (AD 32), 4'-O-tetrahydropyranyladriamycin (THP-adriamycin), and N-benzyladriamycin-14-valerate (AD 198), induced 2- to 4-fold more DNA damage than DOX in resistant cells. There was no difference in the poly(ADP-ribose) synthesis of P388/S and P388/R cells exposed to DOX or AD 32. Since ADP-ribose polymer synthesis is associated with free radical-induced DNA damage and is indicative of DNA repair by an excision-repair mechanism, data from these studies suggest that DNA breaks in anthracycline-exposed cells may not be due to free radical production but rather to other mechanisms, such as inhibition of DNA topoisomerase II activity. The present studies, in addition to emphasizing the role of DNA damage in resistance, also underscore the relative importance of DNA topoisomerase II function in anthracycline cytotoxicity.

[Action of the antitumor antibiotic aclarubicin on the blood system and bone marrow hematopoiesis in an experiment]. / Deistvie protivoopukholevogo antibiotika aklarubitsina na sistemu krovi i kostnomozgovoe krovetvorenie v éksperimente.

The effect of various doses of antitumor antibiotic aclarubicin on the peripheral blood system and medullary hemopoiesis was studied on Wistar rats. It was shown that intraperitoneal administration of the drug in doses of 0.08, 0.33 and 1.2 mg/kg daily for 6 months did not induce any significant changes in the blood count of the animals. The dose of 1.2 mg/kg which is almost 2.5 times higher than the maximum course dose of aclarubicin for patients induced a decrease in the hemoglobin count recorded within the whole observation period. A single administration of aclarubicin in LD50 equal to 17.4 mg/kg resulted in marked suppression of hemopoiesis. The drug had the most prolonged suppressive effect on the bone marrow myeloid body. Depression of erythropoiesis was short-term.

Preliminary evaluation of treatment and selection conditions which affect expression of anthracycline mutagenicity in Salmonella typhimurium and a diploid human lymphoblast cell line.

Mutagenic potency in the Ames Salmonella test is an important endpoint that can be influenced by biological and technical factors. The ranking of mutagenic activity of a series of anthracyclines was measured using different conditions of exposure and mutation selection. A 20 min preincubation treatment version of the Ames test using a 0.2-2.0 microgram/ml (0.36-3.60 nM/ml) dose range of each of the anthracyclines Adriamycin, Daunomycin, Carminomycin, 4'-O-methyldoxorubicin and 4-demethoxydoxorubicin confirmed the order of mutagenic potency seen with the same compounds under direct plating conditions. Preincubation results also confirm direct-plating results by showing the greater sensitivity of selection to His+ reversion over 8-azaguanine resistance to anthracycline mutagenicity. However, the order of mutagenic potency was changed by lengthening the preincubation treatment time to 2 h or reducing the population density of the treated cell inoculum by ten fold. These results suggest that certain treatment conditions enable the treated cells to diminish the phenotypic expression of anthracycline mutagenicity. For comparative purposes, daunomycin and Adriamycin mutagenicity in response to 0.1-0.2 nM/ml and 0.1-0.3 nM/ml dose ranges, respectively, were assessed in a human cell culture system with 6-thioguanine and 5-trifluorothymidine forward mutation selection. A daunomycin dose of 0.1 nM/ml generated approximately 25-fold and 20-fold increases in mutant fraction with 6-thioguanine and 5-trifluorothymidine selections, respectively. Equivalent dosing with Adriamycin generated approximately a 4-fold increase in mutant fraction with 6-thioguanine selection and little or no increase with 5-trifluothymidine selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Function of the anthracycline amino group in cellular transport and cytotoxicity.

Using a number of derivatives of doxorubicin (Adriamycin) and daunomycin, we have examined how substitution of the anthracycline amine affected net cellular accumulation and cytotoxic potency in HL-60 leukemia cells. Octanol/buffer partitioning demonstrated that each of the derivatives had an amino group titratable between pH 5 and 8, with the exception of derivatives containing a cyanomorpholino-substituted amine, which had a significantly lower pKa value. The steady state cellular drug levels for the Adriamycin and daunomycin series decreased in the following order: N,N-dimethyl-greater than morpholino-greater than parent greater than cyanomorpholino-. Thus, the net cellular accumulation of an anthracycline was found to be influenced by the basicity of the amino group; drugs with a non-basic amino group exhibited reduced uptake. Soft agar clonogenic assays showed the following order of cytotoxicity for both series: cyanomorpholino-much greater than parent greater than morpholino-approximately equal to N,N-dimethyl-. The data demonstrate an inverse correlation between uptake and potency; thus, differences in net cellular accumulation do not account for the order of anthracycline potency.

A possible role for membrane lipid peroxidation in anthracycline nephrotoxicity.

Adriamycin causes both glomerular and tubular lesions in kidney, which can be severe enough to progress to irreversible renal failure. This drug-caused nephrotoxicity may result from the metabolic reductive activation of Adriamycin to a semiquinone free radical intermediate by oxidoreductive enzymes such as NADPH-cytochrome P-450 reductase and NADH-dehydrogenase. The drug semiquinone, in turn, autoxidizes and efficiently generates highly reactive and toxic oxyradicals. We report here that the reductive activation of Adriamycin markedly enhanced both NADPH- and NADH-dependent kidney microsomal membrane lipid peroxidation, measured as malonaldehyde by the thiobarbituric acid method. Adriamycin-enhanced kidney microsomal lipid peroxidation was diminished by the inclusion of the oxyradical scavengers, superoxide dismutase and 1,3-dimethylurea, and by the chelating agents, EDTA and diethylenetriamine-pentaacetic acid (DETPAC), implicating an obligatory role for reactive oxygen species and metal ions in the peroxidation mechanism. Furthermore, the inclusion of exogenous ferric and ferrous iron salts more than doubled Adriamycin-stimulated peroxidation. Lipid peroxidation was prevented by the sulfhydryl-reacting agent, p-chloromercuribenzenesulfonic acid, by omitting NAD(P)H, or by heat-inactivating the kidney microsomes, indicating the requirement for active pyridine-nucleotide linked enzymes. Several analogs of Adriamycin as well as mitomycin C, drugs which are capable of oxidation-reduction cycling, greatly increased NADPH-dependent kidney microsomal peroxidation. Carminomycin and 4-demethoxydaunorubicin were noteworthy in this respect because they were three to four times as potent as Adriamycin. In isolated kidney mitochondria, Adriamycin promoted a 12-fold increase in NADH-supported (NADH-dehydrogenase-dependent) peroxidation. These observations clearly indicate that anthracyclines enhance oxyradical-mediated membrane lipid peroxidation in vitro, and suggest that peroxidation-caused damage to kidney endoplasmic reticulum and mitochondrial membranes in vivo could contribute to the development of anthracycline-caused nephrotoxicity.

Single-strand DNA breaks induced by chromophore-modified anthracyclines in P388 leukemia cells.

Single-strand DNA breaks induced by chromophore-modified anthracyclines related to doxorubicin (including 11-deoxydaunorubicin, 4-demethoxydaunorubicin, 4-demethoxy-11-deoxy-4'-epi-daunorubicin, 4-demethyl-6-O-methyldoxorubicin) in cultured P388 leukemia cells were determined by the filter alkaline elution method. The tested analogues differed markedly in their cytotoxic potency. In the range of cytotoxic concentrations, 11-deoxydaunorubicin produced single-strand DNA break frequency of the same order of magnitude as that produced by doxorubicin, while other derivatives caused much more marked damage on DNA than doxorubicin. Since DNA breaks were found to be protein associated, the type of DNA damage produced by all tested derivatives presumably resulted by action of DNA topoisomerases II, as proposed for doxorubicin and other intercalating agents. Although the "potent" (with respect to DNA damage) derivatives, except 4-demethyl-6-O-methyldoxorubicin, showed an increased cellular drug accumulation as compared to doxorubicin, this did not account for the marked differences in ability to damage DNA. 4-Demethyl-6-O-methyldoxorubicin was the most efficient derivative, producing DNA breaks in a lower range of cellular drug content. A striking biphasic dose-response curve was observed for the 4-demethoxy derivatives, suggesting a complex mechanism of interaction among drug, DNA, and enzyme. A lack of correlation was noted among DNA binding affinity, induction of strand breaks, and cytotoxic activity of these chromophore-modified derivatives. From these observations, it is suggested that multiple actions of anthracyclines at the DNA level are responsible for their cytotoxic activity, which is not simply related to inhibition of a specific DNA-dependent enzyme and/or function.

Phase I and II agents in cancer therapy: I. Anthracyclines and related compounds.

Anthracycline antibiotics remain among the most potent anticancer drugs, but their efficacy is limited by the development of a dose-dependent irreversible cardiomyopathy and by the emergence of clones of tumor cells resistant to the effects of the drug. Modifications of the basic anthracycline structure have resulted in molecules that may share the activity of the parent compound, with amelioration of some toxicities, absence of cross-resistance, or activity against tumors insensitive to the parent drug. Epirubicin has a unique metabolic pathway, glucuronidation, that may result in more rapid plasma clearance and reduced toxicity as compared with doxorubicin. Epirubicin has demonstrated comparable activity to doxorubicin in breast cancer, with possibly reduced toxicity. Idarubicin is of interest because of its cytotoxic activity when given orally. Idarubicin has prolonged retention in the plasma and has equal cytotoxic activity to the parent compound. Idarubicin has demonstrated activity against acute leukemia and breast cancer; in the latter tumor category, some doxorubicin-resistant tumors have responded. Esorubicin is of interest because of its nearly absent cardiac toxicity. This agent has some activity against solid tumors and is currently being clinically tested. Aclacinomycin A is an anthracycline in which a trisaccharide is substituted for the aminosugar. Aclacinomycin A and the related compound marcellomycin are of interest as both cytotoxic and differentiating agents. Menogaril is an anthracycline with the aminosugar on the D ring; it does not exhibit cross-resistance with doxorubicin or cardiotoxicity. Mitoxantrone is a compound that is related to the anthracyclines but has a different mechanism of action. This agent has significant activity against acute leukemia and breast cancer and is currently being compared with doxorubicin. Amsacrine is another compound related to the anthracyclines that possesses major activity against acute leukemias. Minor modifications of the anthracycline molecule have had major impact on the biologic activity of these drugs. New anthracycline analogues with up to 100 times the potency of currently available anthracyclines are being developed for clinical testing, and these complex molecules retain a nearly unlimited potential for structural modification.

[Effect of anthracycline antibiotics on the morphology of the mouse small intestine]. / Vliianie antratsiklinovykh antibiotikov na morfologiiu tonkoi kishki myshei.

The effect of daunomycin, carminomycin and doxorubicin on the small intestine was studied on mice morphologically and histologically. The toxic action of these antibiotics in maximum tolerance doses was estimated comparatively. It was shown that the anthracycline antibiotics induced hemodynamic disorders, suppression of the crypt epithelium proliferating activity, dystrophic and destructive lesions in the epithelial cells, a decrease in the number of the cells in the crypts and on the villi and development of a large number of pathological mytoses in the small intestine. Recovery of the population count of the small intestine epithelium was associated with an increase in the mytotic activity of the crypts. It was observed by the 7th day after administration of daunomycin or carminomycin, and by the 15th day after administration of doxorubicin. Comparative estimation of the toxic action of the anthracycline antibiotics on the small intestine by such parameters as the percentage of the pathological mytoses and the number of the cells in the crypts and on the villi indicated that the toxic action of doxorubicin was more pronounced as compared to that of carminomycin or daunomycin.

Anthracyclines cardiotoxicity: antagonism by sulmazole, a new cardiotonic agent.

In attempts to alleviate or prevent anthracyclines toxicity, we have recently reported that amrinone markedly reduced the negative inotropic effect of adriamycin in isolated guinea pig atria, in normodynamic or hypodynamic conditions (medium with reduced calcium content). Previous experiments on isolated guinea pig atria showed that the negative inotropic action of anthracyclic compounds was enhanced in hypodynamic conditions. The present study reports the effects of 4-epiadriamycin on spontaneously beating guinea pig atria, in normo- or hypodynamic conditions. 4-Epiadriamycin (100 micrograms/ml) exerts a negative inotropic and chronotropic effect which matches that of adriamycin. The negative effects of the two antitumoral drugs are antagonized by sulmazole, a benzimidazole derivative with cardiotonic activity. In contrast to cardiac glycosides, the new compounds (amrinone, sulmazole, and derivatives) could be experimented in an attempt to antagonize the toxicity of anthracyclic compounds.

The endomyocardial biopsy.

Endomyocardial biopsy (EMB) provides a safe, simple method of gathering unique information. Although the role of EMB continues to evolve rapidly, present consensus includes the following indications, based on the ability of EMB to provide diagnoses unobtainable by other means: assessment of early rejection following cardiac transplantation; determination of myocarditis as etiology of clinically obscure cardiac dysfunction; quantification of chemotherapeutic (especially anthracycline) cardiotoxicity; and distinction between constrictive and restrictive heart disease. Each of these indications carries major therapeutic as well as prognostic implications. Methods of processing EMB are presented, complications listed, artifacts described, findings and uses illustrated, and suggestions for future development addressed briefly.

Acute lymphoblastic leukemia in very young children. Diagnostic and therapeutic aspects of 43 cases.

Between 1974 and 1982, 43 children less than 2 years of age were treated in the hematology department of Hospital Saint-Louis for acute lymphoblastic leukemia (ALL). Of the patients who presented before 18 months of age, 80% had a WBC greater than 100,000 microliter and/or a great tumor bulk. As a result of our experience, treatment regimens have been changed here from conventional chemotherapy to a very intensive program with a heavy induction (vincristine, daunorubicin, cyclophosphamide, prednisone, and L-asparaginase) and monthly reinductions with the same drugs plus ArA-C, without maintenance. Prophylaxis included CNS irradiation (16-24 Gy) after 12 months of age, plus intrathecal methotrexate. Complete remission (CR) occurred in 78% before 18 months and in 100% between 18 and 24 months of age at diagnosis. In this report the probability of a prolonged CR (33% at 2 years) was the same before and after 12 months of age. However, younger patients were more intensively treated. The prognosis for children less than 1 year of age who received very intensive chemotherapy has greatly improved, with a significantly higher probability of long CR (p less than 0.02). Presently, 10 of 43 children are in CR 27 months to 8 years after diagnosis. Of 18 patients aged less than 1 year at diagnosis, four are in CR. No relapse occurred after 23 months. None of these patients presented with important sequellae, with the exception of one child who suffered from severe bacterial meningitis. An aggressive chemotherapy program is indicated in patients less than 2 years of age. The feasibility of this mode of treatment in young patients is possible only with the help of specific supportive care.

Effects of excision repair and plasmid pKM101 on mutagenic and cytotoxic potencies of anthracycline derivatives in test strains of Salmonella typhimurium.

The effects of excision repair and presence of plasmid pKM101 on the mutagenicities and cytotoxicities of the anthracycline derivatives Adriamycin, daunomycin, carminomycin, and 4-demethoxydoxorubicin were examined in strains of Salmonella typhimurium. Plasmid pKM101 has been shown to mediate inducible error-prone repair in S. typhimurium. While the test compounds were shown to produce a range of mutational responses in excision repair defective (uvrB-), pKM101-bearing strains of different his- backgrounds, proficiency in excision repair generally resulted in the elimination of mutagenic responses in all such strains except those that contain the hisG428 site. In the absence of pKM101, only hisD3052 uvrB- strain TA1538 was shown to be sensitive to anthracycline mutagenicity. A suspension (preincubation) test as well as a direct plating test showed that while proficiency in either excision repair (uvr+) or plasmid pKM101 error-prone repair afforded cellular protection against anthracycline cytotoxicity, plasmid-free uvrB- strains were most sensitive to anthracycline cytotoxicity.

Genetic and physiological modulation of anthracycline-induced mutagenesis in Salmonella typhimurium.

The genotoxic properties of adriamycin and daunomycin, anthracycline antibiotics effective in the treatment of a wide variety of malignancies, were examined in the Salmonella/Ames reverse-mutation test. A novel time- and temperature-dependent phenomenon that potentiates the mutagenicity of these compounds, termed mutational enhancement, is described. The results of congeneric and chemical attenuation studies imply that anthracycline-induced free radicals contribute substantively to the mutagenic potentials of adriamycin and daunomycin. These studies show that adriamycin and daunomycin are not simple intercalative compounds. Rather, anthracycline-induced mutagenesis entails at least two separate but intimately related steps, namely, intercalation within discrete base sequences and the free-radical-mediated events that ensue. Implications of the nonrandom and site-specific action of the anthracyclines are discussed.