Fatal bleomycin toxicity from a low cumulative dose in a patient with renal insufficiency

A 54-year-old man with advanced non-Hodgkin's lymphoma and chronic renal insufficiency was treated with combination chemotherapy which included bleomycin. Fatal pulmonary toxicity developed after administration of a total bleomycin dose of only 60 U. Transbronchial biopsy and autopsy demonstrated pathologic findings consistent with bleomycin-induced pulmonary fibrosis. High-dose corticosteroid therapy did not appear to alter the clinical course. Extreme caution should be exercised when administering bleomycin to patients with renal insufficiency.

Bleomycin-induced DNA cleavage: studies in vitro and in intact cells

Bleomycin, an important chemotherapeutic agent useful in the treatment of testicular carcinoma, can cause lung parenchymal injury. Prior studies showing that different cell types have different susceptibilities to bleomycin suggest that intracellular conditions for bleomycin-DNA interactions vary. The purpose of the present studies was to test the effects of therapeutic concentrations of bleomycin on DNA in vitro, and then to study the effects of these levels of bleomycin on intracellular DNA. In the absence of ferrous ion (Fe+2), bleomycin caused no DNA strand scission at any concentration tested. The addition of as little as 100 nmol/L Fe+2 resulted in DNA strand scission at concentrations of bleomycin greater than or equal to 10 nmol/L. Glutathione dramatically augmented the DNA strand breakage. With use of a viral minichromosome replicating in cultured cells, bleomycin caused DNA strand scission at levels equivalent to therapeutic serum concentrations. These studies reveal that bleomycin causes dose-dependent DNA damage at therapeutic serum concentrations in vitro and in intact cells. The observation that in vitro DNA damage is dependent on the availability of ferrous ion and is augmented by glutathione suggests that different cells, which may differ in their intracellular levels of Fe+2 and reducing capacity, may vary in their sensitivity to bleomycin-induced DNA strand scission.

Redox cycling of bleomycin-Fe(III) by an NADH-dependent enzyme, and DNA damage in isolated rat liver nuclei

Isolated rat liver nuclei were incubated aerobically with bleomycin (BLM) and FeCl3 in the presence of NADH. An increase in NADH and oxygen consumption was observed accompanied by DNA cleavage as shown by gel electrophoresis. Malondialdehyde (MDA) was also formed, which partly derived from DNA indicating an oxidative cleavage mechanism. BLM and NADH were obligatory to provide these effects, whereas FeCl3 could be omitted, without a complete loss of the activities mentioned above. This was explained by the presence of some iron in the nuclei. NADPH was consumed to a lesser extent compared to NADH and was less effective with respect to O2 consumption and MDA formation. It could be excluded that mitochondrial or microsomal contaminations in nuclear preparations were responsible for the effects observed. The results suggest that the BLM-Fe(III)-complex can be repeatedly reduced (redox cycled) by NADH- (and NADPH-) dependent reductases of liver nuclei to BLM-Fe(II) which is known to form reactive oxygen species and to damage DNA. It is concluded that the enzymatic reduction of a BLM-metal complex in the cell nucleus may be an essential step in the cytotoxic activity of bleomycin.

Microsome-stimulated activation of ferrous bleomycin in the presence of DNA

The inhibition of Fe(II)-bleomycin activation, by a large excess of DNA, is overcome by rat liver microsomes in the presence of NADPH. This release of inhibition, as indicated by increased yields of base propenal from DNA scission, is enhanced by menadione, is inhibited by superoxide dismutase, and is therefore dependent on superoxide anion. Microsomal activation of Fe(II)-bleomycin doubles the stoichiometry of base propenal yield compared to that obtained upon self-activation of the drug; 0.5 mol of base propenal is formed and 0.5 mol of NADPH is oxidized per mol of Fe(II)-bleomycin. In the presence of a large excess of DNA, Cu(II)-bleomycin is not reduced and Fe(III)-bleomycin is neither reduced nor activated by microsomes in cases where activation of Fe(II)-bleomycin is maximal. We suggest that in vivo, electron transport enzymes at or near the nucleus can stimulate the activation of Fe(II)-bleomycin under conditions where self-activation does not readily occur.

Oxygen radical formation and DNA damage due to enzymatic reduction of bleomycin-Fe(III)

Aerobic incubations of bleomycin, FeCl3, DNA, NADPH, and isolated liver microsomal NADPH-cytochrome P-450 reductase resulted in NADPH and oxygen consumption and malondialdehyde formation, indicating that the deoxyribose moiety of DNA was split. All parameters measured depended on the active enzyme, bleomycin and FeCl3. In the absence of oxygen malondialdehyde formation was very low. When bleomycin, FeCl3 and the reductase were incubated with methional ethene (ethylene) was formed, suggesting that during the enzyme-catalyzed redox cycle of bleomycin-Fe(III/II) hydroxyl radicals were formed. Ethene formation also depended on oxygen, NADPH, the enzyme, bleomycin, and FeCl3. During aerobic incubations of bleomycin, FeCl3, NADPH, and isolated liver nuclei oxygen and NADPH were consumed and malondialdehyde was formed. Oxygen and NADPH consumption and malondialdehyde formation depended on bleomycin and FeCl3. In the absence of oxygen malondialdehyde was not formed. These results indicate that nuclear NADPH-cytochrome P-450 reductase redox cycles the bleomycin-Fe(III/II) complex and that the reduced complex activates oxygen, whereby hydroxyl radicals are formed which damage the deoxyribose of nuclear DNA.

Sequence-selective binding of phleomycin to DNA

The binding of phleomycin and bleomycin to DNA has been investigated by studying their effects on cleavage by DNAase I and micrococcal nuclease. In the presence of cobalt, cleavage of DNA by the antibiotics is suppressed, yet they still provide protection from nuclease attack in regions surrounding the drug cleavage sites. We conclude that cleavage by phleomycin occurs at bonds around which the antibiotic is already selectively bound.

ESR studies on the active intermediate in the enzymatic reduction of the Fe-bleomycin complex

The spin trapping method was applied to elucidate the active intermediate during the enzymatic reduction of Fe(III)-bleomycin in the presence of NADPH-cytochrome P-450 reductase and O2. Although the hydroxyl adducts to spin traps were observed, the adduct formation was not inhibited by catalase nor by SOD. Furthermore, in Tris-HCl buffer, no Tris adduct to the spin trap was observed. The results lead to the conclusion that there is no participation of free OH radical in the reactive intermediate in this reduction system. Effect of phosphate buffer on the reactivity of Fe(II)-bleomycin and spin state of Fe(III)-bleomycin were discussed.

Development of acute lung injury after the combination of intravenous bleomycin and exposure to hyperoxia in rats

Pulmonary toxicity is an important adverse effect of bleomycin treatment. Very little is known of the mechanisms underlying the development of lung injury, especially after intravenous administration, or how it can be modulated. In this study acute lung injury induced by bleomycin has been examined in rats by assessment of alveolar lavage cell profiles, histological examination, and measurement of the total pulmonary extravascular albumin space. Intratracheal instillation of bleomycin 1.5 mg resulted in a severe pneumonitis with influx of inflammatory cells into the alveoli as assessed by alveolar lavage, oedema of the alveolar walls, and up to an eight fold increase in the total pulmonary extravascular albumin space, maximal at 72 hours. Intravenous bleomycin 0.15-5 mg produced no detectable injury when assessed in these ways. Exposure to hyperoxia (40-90%) after intravenous bleomycin, however, induced lung injury similar to that produced by intratracheal bleomycin. A much more severe injury followed administration of intravenous bleomycin after an exposure to hyperoxia, which itself resulted in lung injury; but lung injury was still detectable after bleomycin when the exposure to hyperoxia was insufficient to induce changes in control animals. Lung injury was not observed when the exposure to hyperoxia preceded bleomycin treatment. These results indicate the importance of oxygen in the pathways leading to acute lung injury following intravenous bleomycin. We conclude that exposure to oxygen might induce lung injury during and after bleomycin treatment, and suggest that in these circumstances oxygen therapy should be kept to a minimum.

Radiation doses from 51Cr-bleomycin

Extensive studies were made of long-term whole-body retention, plasma concentration, urinary excretion and organ retention of 51Cr in rats after intravenous injection of 51Cr-bleomycin. A similar but less extensive investigation was performed on rabbits, and whole-body retention, plasma concentration and urinary excretion was also followed in patients given 51Cr-bleomycin for diagnostic purposes. From an analysis of the collected information it followed that integrated whole-body and organ retention, corrected for radioactive decay, is similar in man and rabbit, and higher by a factor of about 2 in the rat. Doses to organs and whole body in man were calculated using the MIRD methodology and assuming conservatively that the kinetic data derived in rats are applicable to man. The organ and whole-body MIRD doses after 51Cr-bleomycin administration are comparable to those after 67Ga-citrate and the effective dose equivalent from a diagnostic amount of 740 MBq of the 51Cr complex amounts to about 6 mSv. However, the subcellular distribution in the liver of 51Cr, administered in the form of 51Cr-bleomycin, indicated a significant enrichment of 51Cr in the nuclei and in the DNA over mean concentrations in the liver cells. Also, the quality factor for Auger electrons, emitted by 51Cr, when assessed on the basis of the Q vs. LET relationship, as proposed by ICRP, was substantially higher than unity. Doses calculated for cell nuclei and the DNA in the liver cells were higher than the cell-averaged values by a factor 2.5 and 5, respectively, and the corresponding dose equivalents by a factor of 9 and 24. The effective dose equivalent, estimated on the basis of dose equivalents to cell nuclei and the DNA, amounted to 33 and 83 mSv per examination (740 MBq of 51Cr-bleomycin), respectively.

Subcutaneous infusion of bleomycin--a practical alternative to intravenous infusion

The phase specificity and short half-life of bleomycin make it likely that it would be more effective when administered by continuous infusion. This is supported by studies using cell lines, as well as by animal studies and clinical experience in humans. This study was conducted to compare the pharmacokinetics of intravenous (IV) and subcutaneous infusions of bleomycin. The serum concentrations of bleomycin were measured using a sensitive and specific radioimmunoassay. The results demonstrate similar plasma concentrations and area under the curve for both routes. The subcutaneous infusions were well tolerated, without local discomfort or excoriation. Subcutaneous infusion of bleomycin may thus offer a practical alternative to IV infusions and can be administered to patients who are ambulatory and out of hospital.

The nature of thiol-compounds which trap cuprous ion reductively liberated from bleomycin-Cu(II) in cells

Bleomycin-Cu(II) [BLM-Cu(II)], which does not cause DNA strand breaks in vitro, exhibits antitumor activity in vivo. The copper in BLM-Cu(II) is reductively removed in vivo, and the liberated Cu(I) is trapped by intracellular thiol-proteins, thus yielding metal-free BLM. The bioactive species of BLM appears to be the iron-complex. For characterization of the thiol-proteins, thiol-compounds such as dithiothreitol (DTT), cysteine, metallothionein (MT) and alcohol dehydrogenase (ADH) were examined for their ability to trap Cu(I) liberated from BLM-Cu(II). BLM-Cu(II) was incubated at 37 degrees C with the thiol-compounds anaerobically for 1 hour followed by aerobic incubation for 10 minutes. Under these conditions DTT converted BLM-Cu(II) to metal-free BLM, but cysteine did not. However, in the presence of MT, cysteine gave metal-free BLM. The Cu(I) liberated from BLM-Cu(II) by cysteine was trapped by MT with accompanying liberation of Zn(II) and Cd(II) from MT. A part of the liberated Zn(II) formed the complex with the metal-free BLM. Metal-free BLM was also formed from BLM-Cu(II) by combined treatment with cysteine and ADH. BLM-Cu(II) was aerobically incubated with cytosol of MT-induced rat liver at 37 degrees C for 1 hour, and the mixture was analyzed with Sephadex G-75 column chromatography. The amount of copper in the MT fraction was increased concomitant with decrease of the Zn(II) and Cd(II). These results suggest that MT, ADH and other thiol-compounds, which have polythiol ligands, act as Cu(I)-trapping agents to yield metal-free BLM in cells.

Ascorbic acid oxidation and DNA scission catalyzed by iron and copper chelates

The asorbic acid (AH-) auto-oxidation rates catalyzed by copper chelates of 1,10-phenanthroline (OP) or by iron chelates of bleomycin (BLM) are only slightly higher than the oxidation rates catalyzed by the metal ions. AH- oxidation in the presence of DNA is accompanied by degradation of the DNA. The rates of DNA scission by the metal chelates are markedly higher than the rates induced by the free metal ions. AH- oxidation is slowed down in the presence of DNA which forms ternary complexes with the chelates. The ternary complexes react slowly with AH- but induce DNA double strand breaks more efficiently than the free metal chelates. With OP, DNA is degraded by the reaction of the ternary complex, DNA-(OP)2Cu(I), with H2O2. AH- oxidation in the presence of DNA was biphasic, showing a marked rate increase after DNA was cleaved. We suggest that this sigmoidal pattern of the oxidation curves reflects the low initial oxidative activity of the ternary complexes, accelerating as DNA is degraded. Using O2- produced by pulse radiolysis as a reductant, we found that AH- oxidation with (OP)2Cu(II) induced more DNA double strand breaks per single strand break than bipyridine-copper. The site specific DNA damaging reactions indicated by these results are relevant to the mechanism of cytotoxic activities of bleomycin and similar antibiotics or cytotoxic agents.

Liver nuclear NADPH-cytochrome P-450 reductase may be involved in redox cycling of bleomycin-Fe(III), oxy radical formation and DNA damage

When NADPH-cytochrome P-450 reductase isolated from rat liver microsomes was aerobically incubated with bleomycin, FeCl3, NADPH and DNA parallel NADPH and oxygen were consumed and malondialdehyde was formed. A similar parallelism of NADPH- and oxygen-consumption and malondialdehyde formation was observed when cell nuclei isolated from rat liver were incubated under the same conditions. The formation of malondialdehyde which was identified by HPLC and which was most likely released from oxidative cleavage of deoxyribose of nuclear DNA required oxygen, bleomycin, FeCl3 and NADPH. This indicates that a nuclear NADPH-enzyme, presumably NADPH-cytochrome P-450 reductase, is able to redox cycle a bleomycin-iron-complex which in the reduced form can activate oxygen to a DNA-damaging reactive species. The data suggest that the activity of this enzyme in the cell nucleus could play an important role in the cytotoxicity of bleomycin in tumor cells.

Oxidation-reduction reactions of iron bleomycin in the absence and presence of DNA

Using the pulse radiolysis technique, we have demonstrated that bleomycin-Fe(III) is stoichiometrically reduced by CO2- to bleomycin-Fe(II) with a rate of (1.9 +/- 0.2) x 10(8) M-1s-1. In the presence of calf thymus DNA, the reduction proceeds through free bleomycin-Fe(III) and the binding constant of bleomycin-Fe(III) to DNA has been determined to be (3.8 +/- 0.5) x 10(4) M-1. It has also been demonstrated that in the absence of DNA O2- reacts with bleomycin-Fe(III) to yield bleomycin-Fe(II)O2, which is in rapid equilibrium with molecular oxygen, and decomposes at room temperature with a rate of (700 +/- 200) s-1. The resulting product of the decomposition reaction is Fe(III) which is bound to a modified bleomycin molecule. We have demonstrated that during the reaction of bleomycin-Fe(II) with O2, modification or self-destruction of the drug occurs, while in the presence of DNA no destruction occurs, possibly because the reaction causes degradation of DNA.

DNA strand scission by activated bleomycin group antibiotics

The bleomycins (BLMs) are a structurally related group of antitumor antibiotics used clinically for the treatment of certain malignancies. The mechanism of action of the BLM is believed to involve DNA strand scission, a process that requires O2 and an appropriate metal ion; the therapeutically relevant metal is probably iron or copper. DNA strand scission by activated Fe X BLM involves oxygenation C-4' of deoxyribose and leads to two sets of products. One set results from scission of the C-3'--C-4' bond of deoxyribose, with concomitant cleavage of the DNA chain. The other set of products consists of free bases and an alkali-labile lesion, the latter of which leads to DNA chain cleavage on subsequent treatment with base. The structures of all of these degradation products have now been established by direct comparison with authentic synthetic samples. Also studied was the activation of BLM with (mono)oxygen surrogates such as iodosobenzene. The chemistry of the activated BLM so formed was remarkably similar to that of activated cytochrome P-450 and structurally related metalloporphyrins, which suggests a mechanistic analogy between the two. Remarkably, both Fe X BLM and Cu X BLM were also shown to be activated by NADPH cytochrome P-450 reductase in a transformation that was dependent on metal ion, O2 and NADPH.

Pharmacokinetics, subcellular distribution, and covalent binding of [3H]bleomycin in hamsters after intratracheal administration

Pharmacokinetics, subcellular distribution (SCD), and covalent binding of a single dose of 1 microCi of [S-methyl-3H]bleomycin ([3H]-BLM]) in combination with one unit of unlabeled bleomycin were studied in hamsters following intratracheal (IT) injection. The radioactivity decreased from the lung biexponentially with time. The apparent half-time of absorption for the alpha-phase was 1.1 and 17.9 hr for the beta-phase. The plasma disappearance curve of [3H]BLM fits to a two-compartmental model with the apparent half-life removal for the alpha-phase being 1.6 hr and for the beta-phase 116.9 hr. The radioactivity was detected in all studied tissues. The radioactivity from spleen, testicle, liver, fat, RBC, brain, adrenal, and kidney manifested only the alpha-phase of the disappearance curve, while the beta-phase was complicated by redistribution processes. Of the eight tissues, the spleen had the shortest (2.0 hr) and kidney the longest (12.1 hr), and the remaining tissues had half-lives which ranged from 4 to 10 hr. The SCD study revealed that 85 to 95% of the total radioactivity in the lung and liver homogenate was associated with the soluble fraction (SF) at 30 min after treatment, thereafter, the radioactivity from both tissues gradually decreased to 60% of the total at 24 hr. The SF of the lung homogenate had the highest specific radioactivity (SRA) of any of the fractions during the period between 0.5 and 6 hr. The SRA, however, decreased biexponentially and attained a value similar to that of the mitochondrial and microsomal fractions at 12 and 24 hr after treatment. In the case of liver, the SF had the highest, the nuclear the lowest, and mitochondrial and microsomal fractions the same level of SRA at 30 min. Thereafter, the SRA of all fractions were increased with time. A significant amount of radioactivity from [3H]BLM was covalently bound to lung, liver, and plasma proteins. The SF of the lung contained an increasing amount of radioactivity covalently bound after 1.5 hr of [3H]BLM injection and nearly all radioactivity measured in the plasma was covalently bound. It was concluded from the findings of this study that the presence of a major portion of [3H]BLM in the SF of the lung and its covalent linkage with the proteins of this fraction might initiate the complex sequence of events at the metabolic level necessary for the pneumotoxicity.

Delivery of antifibroblast agents as adjuncts to filtration surgery. Part I--Periocular clearance of cobalt-57 bleomycin in experimental drug delivery: pilot study in the rabbit

Antitumor and antifibroblast agents show promise as adjuncts after glaucoma filtration surgery in reducing postoperative scarring and failure. We used nuclear imaging in rabbits to investigate periocular clearance of one such agent (57Co-bleomycin). Sub-Tenon injection was compared to other delivery techniques. Our results showed that a collagen sponge and a silastic disc implant with a microhole prolonged drug delivery when compared to sub-Tenon injection alone or injection with a viscosity enhancing agent (0.5% sodium hyaluronate). We theorize that if an antifibroblast agent can be delivered in small and sustained amounts after filtration surgery, this may prolong bleb longevity and avoid unnecessary drug toxicity.

Properties of the initial reaction of bleomycin and several of its metal complexes with Ehrlich cells

Characteristics of the reaction of bleomycin-A2 (BLM) and several of its metal complexes with Ehrlich cells in culture are described. Short incubation of BLM and Fe(III)-, Cu-, Zn-, and CdBLM with Ehrlich cells effectively inhibits cell proliferation. There is a sharp break at 30 min in the dependence of cytotoxicity upon time of exposure of cells to these forms of the drug. Qualitatively, the same curve can be generated by sequential additions of CoCl2 to cells during their first hour of incubation with BLM or Fe(III)BLM. The cobalt salt has less effect on CuBLM. The kinetics of initiation of the effect are directly correlated with the rapid kinetics of uptake of [3H]BLM by cells. Measurements of the initial rate of association of drug with cells as a function of extracellular BLM concentration suggest that a binding step is involved, for the rate of association approaches a maximal velocity at large concentrations of BLM. Uptake leads to both specific and nonspecific binding of tritium label; however, very little BLM gets into these cells. The internal concentration is estimated to be less than that in the external medium. BLM and its Fe(III) and copper complexes are taken up by Ehrlich cells to the same general extent after 60 min incubation; the cellular uptake of CoBLM is 25-50 times higher. Even the distributions of Fe(III)-, Cu-, and metal-free BLM within cytosol are comparable. A fraction binds to macromolecules; the rest appears unbound in low molecular weight fractions. The binding of [3H]BLM to cells cannot be reversed by incubation of labeled cells in drug-free medium or in media containing large concentrations of cold BLM.

Calmodulin: a potential target for cancer chemotherapeutic agents

Calmodulin is a ubiquitous, calcium-binding protein that is responsible for many of the intracellular actions of calcium. Recent evidence suggests that calmodulin may regulate cellular proliferation and that its function may be altered in malignancy. The discovery that drugs such as phenothiazines antagonize the action of calmodulin led to the study of these antagonists against tumor cells. It is now appreciated that calmodulin antagonists are cytotoxic, can restore the sensitivity of resistant cells to drugs such as doxorubicin and vincristine, and can augment the cytotoxicity of bleomycin. This report addresses the possibility of developing new forms of chemotherapeutic agents that work by disrupting the function of this intriguing molecule.