Chemical, biochemical, and cellular properties of copper and iron bleomycins

Bleomycin-mediated pulmonary toxicity: evidence for a p53-mediated response

Bleomycin damages DNA and causes lung injury and fibrosis. To determine whether bleomycin is associated with the appearance of DNA damage-inducible proteins, C3H mice received either 0.4 mg bleomycin or normal saline intratracheally and were killed 1 to 14 d later. The lungs were examined for expression of p53, p21(WAF1/PiCl), and proliferating cell nuclear antigen (PCNA) using immunohistochemistry and Western blotting. p53-positive cells first appeared at 5 d after treatment and peaked at 7 d; PCNA-positive cells appeared at 1 d after treatment and peaked at 7 d; and p21-positive cells appeared at 5 d and peaked at 9 d. Western blot analysis confirmed that bleomycin upregulated the DNA damage-inducible proteins in a similar fashion. This is the first evidence that bleomycin causes a p53-dependent response associated with acute injury in the lung.

EPR spin trapping of free radicals produced by bleomycin and ascorbate

In the presence of ascorbate, bleomycin (BLM) is converted to a redox-inactive form that is incapable of inducing DNA strand scission. We have employed EPR spin trapping with 5,5-dimethylpyrroline-1-oxide (DMPO) to examine free radical production during this process. The introduction of ascorbate to an Fe(III)BLM-DMPO system results in the formation of three EPR observable free radicals. One of these radicals is the resonance-stabilized ascorbate free radical (aH = 1.8 G) that is not spin trapped by DMPO; the other two are the result of DMPO spin trapping. These radicals appear to be two carbon-centered radicals, DMPO/.CR1, (aN1 = 15.75 G, aH1 = 22.30 G, aN/aH = 0.706) and DMPO/.CR2 (aN2 = 15.20 G, aH2 = 19.20 G, aN/aH = 0.79). Although it is not possible to identify the exact structures of the carbon-centered radicals that are spin trapped, the hyperfine splittings, as well as the aN/aH values, are characteristic of the presence of electron-withdrawing groups, such as the oxygen atom when attached to the carbon atom. In fact, these parameters are characteristic of DMPO spin trapping results obtained when sugars are subjected to oxidative insult from HO.. Thus, these BLM-ascorbate produced radicals may well be derived from the sugar moiety of BLM.

Spin-trapping studies of the oxidation-reduction reactions of iron bleomycin in the presence of thiols and buffer

The reaction of ferrous bleomycin with dioxygen is reexamined to clarify whether radical species derived from molecular oxygen are generated. Detection of low levels of spin-trapped oxyradicals confirm the production of OH during this reaction when bleomycin is present in excess, but not when iron and drug concentrations are equal. In phosphate buffer, hydroxyl radicals continue to be spin trapped for at least 15 min after Fe(II)bleomycin has been oxidized to Fe(III)bleomycin. In HEPES buffer, detection of a HEPES radical in the absence of spin trap over the same period independently supports the conclusion that reactive radicals are present after the initial oxidation of Fe(II)bleomycin is complete. When glutathione is included in the aerobic reaction mixture, thiyl radical species are spin trapped. The reaction of Fe(III)bleomycin with cysteine produces thiyl radical without spin-trapped hydroxyl radical.

Historical aspects of glutathione and cancer chemotherapy

This presentation sets in historical context the impact of glutathione and its metabolism upon the efficacy of several anticancer drugs. The basic biochemistry of the tripeptide is reviewed briefly, highlighting its role in oxido-reduction and in the gamma-glutamyl cycle. The ability of selective modulators of glutathione metabolism, such as buthionine sulfoximine, as adjuncts to chemotherapy is also discussed.

The role of redox-active metals in the mechanism of action of bleomycin

Belomycin is a glycopeptide antibiotic routinely used to treat human cancer. It is commonly thought to exert its biological effects as a metallodrug, which oxidatively damages DNA. This review systematically examines the properties of bleomycin which contribute to its reaction with DNA in vitro and may be important in the breakage of DNA in cells. Because strand cleavage results from the reductive activation of dioxygen by metallobleomycins, the mechanism of this process is given primary attention. Current understanding of the structures of the coordination sites of various metallobleomycins, their thermodynamic stabilities, their propensity to form adduct species, and their properties in ligand substitution reactions provide a foundation for consideration of the chemistry of dioxygen activation as well as a basis for thinking about the metal-speciation of bleomycin in biological systems. Oxidation-reduction pathways of iron-bleomycin, copper-bleomycin, and other metal-bleomycin species with O2 are then examined, including information on photochemical activation. With this background, structural and thermodynamic features of the binding interactions of DNA with bleomycin, its metal complexes, and adducts of metallobleomycins are reviewed. Then, the DNA cleavage reaction involving iron-bleomycin is scrutinized on the basis of the preceding discussion. Particular emphasis is placed on the constraints which the presence of DNA places on the mechanism of dioxygen activation. Similarly, the reactions of other metalloforms of bleomycin with DNA are reviewed. The last topic is an analysis of current understanding of the relationship of bleomycin-induced cellular DNA damage to the model developed above, which has evolved on the basis of chemical experimentation. Consideration is given to the question of the importance of DNA strand breakage caused by bleomycin for the mechanism of cytotoxic activity of the drug.

The roles of intracellular glutathione in antineoplastic chemotherapy

Glutathione is a sulfhydryl containing tripeptide that participates in detoxification of xenobiotic compounds, including the alkylating agents melphalan, cyclophosphamide, and BCNU. The role of glutathione in the detoxification of these compounds, both in terms of initial tumor response, and drug-induced resistance to these alkylating agents is examined. Since glutathione disulfide and glutathione are a pivotal redox pair, the modulation of intracellular glutathione levels is shown to change the cytotoxicity of drugs dependent on the redox cycle, such as adriamycin and bleomycin, as well as the oxygen dependent drug neocarzinostatin. Areas of further research are discussed.

Alteration of bleomycin cytotoxicity by glutathione depletion or elevation

In part, some of the cytotoxicity of bleomycin may be lessened or enhanced by modulation of glutathione (GSH) concentrations. Enhancement of bleomycin cytotoxicity was observed when GSH levels were low and protection was observed when GSH levels were elevated. Since H2O2 is one of the reactive species produced by bleomycin catalyzed oxygen activation, we studied the effects of H2O2 exposure after GSH depletion. H2O2, like bleomycin, shows enhanced cytotoxicity in GSH depleted cells. It has been proposed that bleomycin cytotoxicity requires reducing equivalents from non-protein bound thiols (such as GSH) to activate the bleomycin-metal complex, which in turn reacts with oxygen to generate free radicals and peroxides. Our data suggest that either GSH is not required to cycle reducing equivalents to the oxidized bleomycin-metal complex, or the low levels of depleted GSH attained (less than 5% of control) were still sufficient to effect reduction. Further, our data shows that GSH in fact provides a means of protection and detoxification from the cytotoxic effects of bleomycin. Our data suggest that caution should be exercised clinically when one uses drugs that modulate GSH because there may be either enhancement of normal tissue toxicity or decreases in tumor targeted cytotoxicity resulting from bleomycin treatment.

Interactions among iron(II) bleomycin, Lewis bases, and DNA

The interaction of sulfur-containing ligands with complexes of Fe(II) bleomycin [Fe(II)Blm] was investigated by comparing DNA strand-scission activity with the structural characteristics of the complex. The bithiazole ring of excess Blm can form intermolecular complexes with Fe(II)Blm and with NO-Fe(II)Blm, and the bithiazole groups of CO-Fe(II)Blm interact with the metal center. This binding can be reversed by glutathione, CO-Fe(II)Blm binds to poly(dA-dT) . poly(dA-dT) via its bithiazole group to change the environment of the Fe2+ ion. Glutathione binds to the CO-Fe(II)Blm-poly(dA-dT) . poly(dA-dT) complex under conditions in which it stimulates DNA strand scission by Fe(II)Blm.