Cobalt chelate of bleomycin. I. Physicochemical properties and distribution in tumor bearing mice

Metal complexes of bleomycin: evaluation of [Rh-105]-bleomycin for use in targeted radiotherapy

Bleomycin has been used as a carrier for several radioisotopes; however, its potential for clinical use has been limited either by the in vivo stability of the complexes or the half-life of the isotope used. The chemical, biological, and radiological properties of 105Rhodium appear to make it an ideal choice for targeted radiotherapy. The synthesis and purification of a hereto unreported 105Rhodium-bleomycin (105Rh-BLM) complex is described. The stability of this complex in plasma is sufficient to allow targeted delivery of the radioisotope. 57Cobalt-bleomycin was studied under identical conditions for comparative purposes. The suitability of 105Rh-BLM for targeted therapy, which appears to be limited by the renal clearance of this agent, is discussed.

Distribution of111 in-bleomycin complex in small cell lung cancer cells by autoradiography

The distribution of 111In-bleomycin Complex (111In-BLMC) in small cell lung cancer (SCLC) cells was studied by autoradiography. SCLC cells were exposed to 111In-BLMC and 111Indium chloride (111InCl3) for 1 hour, 3 hours, and 4 hours; washed with fresh medium; and spread on slides. The slides were smeared with NTB2 (NTB3) emulsion by wet or dry-mount technique and exposed 3 to 15 days. 111In-BLMC was found to localize in the cell nucleus and nuclear membrane (78.3%); 111InCl3 located mainly in the cytoplasm (52.3%). This distribution of labeled BLM may explain the mechanism of killing SCLC cells by 111In-BLMC.

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.

Differences between sites of binding to DNA and strand cleavage for complexes of bleomycin with iron or cobalt

The sequence specificity of bleomycin A5 and of its light-activated cobalt complex were compared by examining the relative cleavage of each strand of two DNA fragments by either species. Significant differences between the two metallobleomycins were observed. The iron-bleomycin (Fe-BLM) complex cleaved the DNA molecules preferentially at dinucleotides GpT and GpC, whereas the light-activated cobalt-bleomycin complex (Co-BLM) showed a preference for cutting at the dinucleotide GpA in addition to cleavage at every GpT dinucleotide. Further, new sites of preferential cleavage were noted for Co-BLM in regions of the DNA where enhanced reaction with DNAaseI can be observed in the presence of the antibiotic. No differences in the cutting behaviour of the Fe-BLM were evident upon irradiation of the reaction mixture. A reduction in the relative efficiency of cutting at GpC sequences by Co-BLM is responsible for the previously observed diminution of double-strand breaks under conditions of photoactivated cleavage. The results are discussed in terms of the likely production of highly reactive, diffusible cutting elements in the light activated reaction which cause cleavage of the DNA in regions where the antibiotic is not bound.

Killing of human lung cancer cells using a new [111In]bleomycin complex [111In]BLMC

The ability of a [111In]bleomycin complex [( 111In]BLMC) to kill five cell lines of human lung cancer (small cell lung cancer) was investigated. Cells were exposed to either 0.9% NaCl, [111In]Cl3, BLM, [111In]BLMC, nonradioactive InCl3, or In-BLMC for 60 minutes, plated in soft agarose, and assessed for colony formation. [111In]BLMC (40-200 microCi carried by 15-25 micrograms BLM/ml) was more cytotoxic than BLM (15-25 micrograms BLM/ml) by a factor of 1.6-5.3 for five cell lines. The percent survival of N417 cells was 28.4 for [111In]BLMC (40 microCi/15 micrograms BLM/ml) and 54.3 for BLM (15 micrograms/ml); 1.9 for [111In]BLMC (200 microCi/25 micrograms BLM/ml), and 10.0 for BLM (25 micrograms/ml). 111InCl3 (200 microCi/ml) and nonradioactive InCl3 failed to inhibit colony formation. The new [111In]BLMC may be useful for therapy of some lung cancer patients.

A new 111In-bleomycin complex for combined radiotherapy and chemotherapy

Six days after tumor transplantation three daily intraperitoneal doses of 0.9% NaCl, bleomycin (BLM), or a new 111In-bleomycin complex (BLMC, 15 microCi/g body weight) were administered to glioma-bearing mice. After therapy, tumors in mice treated with 111In-BLMC were smaller than those treated with BLM. Sixteen days after the first injection tumor size for 111In-BLMC-treated mice was 560 (240-1,030) mm3, 1,980 (1,400-3,290) mm3 for BLM (P less than 0.025), and 4,830 (2,580-9,180) mm3 for NaCl (0.1 less than P less than 0.2). Thirteen days after tumor transplantation glioma-bearing mice received single intratumor injection of 0.9% NaCl, BLM, or 111In-BLMC (1.5 mCi, carried by 0.5 mg BLM/g tumor weight). The average tumor size for 111In-BLMC was smaller than that for BLM by a factor of 2.5-3.7. Host weights for these two groups were similar, and morphologic abnormalities were not found in kidney or liver.

Use of 111In-bleomycin for combining radiotherapy and chemotherapy on glioma-bearing mice

Mice bearing transplanted glioma received 0.9% NaCl, 0.1 mg of BLM, or 200-250 microCi of 111In-BLM (0.1 mg BLM) daily for 5 days intraperitoneally. After therapy, tumor sizes were in the order NaCl greater than BLM greater than 111In-BLM. On the 11th day after the first injection, tumor size (mm3) in the 111In-BLM group was 1,220; in the BLM group, it was 2,310 (P less than .025). After intratumor injection of a total dose of 0.1 mg of BLM/gm tumor weight, or of 1 mCi/gm tumor weight of 111In-BLM (carried by 0.1 mg of BLM/gm tumor weight), the tumor size decreased in the 111In-BLM group more than in the BLM group. On the 5th day after the 2nd dose therapy, the tumor size in the 111In-BLM group was 2,020; in the BLM group it was 4,220 (P less than .05). Host weights for these two groups were similar. The necrotic area in the tumor was much greater in the 111In-BLM group than in the BLM group. These results suggest the use for radiotherapy and chemotherapy.

A new tumor imaging agent--111In-bleomycin complex. Comparison with 67Ga-citrate and 57Co-bleomycin in tumor-bearing animals

We have found a new 111In-bleomycin complex (BLMC), which has high affinity to tumor, does not bind to transferrin and is stable in vivo. Distribution in animals bearing glioma, hepatoma, or mammary adenocarcinoma at 48 hours showed: the ratios of tumor to blood, brain, heart, lung, liver, pancreas, stomach, and femur were 1.4-22.4 times as high for 111In-BLMC as for 67Ga-citrate. In mammary adenocarcinoma, 111In-BLMC bound more to viable and 57Co-Bleomycin (BLM) more to necrotic tumor. In viable tumor, the concentration of 111In-BLMC was similar to that of 57Co-BLM. The ratios of tumor to stomach and pancreas were higher, to blood, brain, muscle, heart, and femur were lower for 111In-BLMC than those for 57Co-BLM. The ratios of tumor to lung, liver, spleen, skin, and kidney were similar for the two compounds. Tumors were imaged more distinctly with the new 111In-BLMC and 57Co-BLM than with 67Ga-citrate. 111In-BLMC is promising for tumor imaging.

Radioiodinated bleomycin: stoichiometry of iodination and structural characterization by 1H-nuclear magnetic resonance

Bleomycin was iodinated by reaction with iodine monochloride (ICl). A direct relationship was found to exist between the average number of iodine atoms bound per molecule of bleomycin and the ICl: bleomycin molar ratio. Characterization by 1H-NMR analysis denoted that mono, di-, tri- and tetraiodobleomycin are formed when the reacting molar ratios, respectively, are 2:1, 4:1, 6.8:1 and 8.5:1 or greater. The sites of iodination of the bleomycin molecule have been identified to be the imidazole ring which iodinates first, followed by the bithiazole ring system which iodinates last.

A new 111In-bleomycin complex for tumor imaging: preparation, stability, and distribution in glioma-bearing mice

A new 111In-bleomycin complex (111In-BLMC) is here reported. Its radiochemical purity was 99% by thin-layer chromatography (TLC) (Rf 0.65) and in 5% agarose gel electrophoresis in 0.02 M NaHCO3 it migrated toward the anode. Autoradiographs of TLC and gel electrophoresis plates showed no change on storage for 3 weeks. Urine and plasma from untreated or glioma-bearing mice after injection of 111In-BLMC were analyzed by TLC and gel electrophoresis. Results indicated stability in vivo, nonbinding to transferrin, affinity to viable tumor, and excretion faster than 111In-BLM-B2, 111In-BLM, or 57Co-BLM. Tissue distributions 24 hr after injection of radiopharmaceutical showed activity ratios of tumor to blood, muscle, and brain of 13.1, 12.4, and 81.6, respectively, which were significantly higher than those for previously prepared 111In-BLM-B2 or 111In-BLM (except for brain, 0.05 less than P less than 0.1). The new 111In-BLM complex may be useful in clinical imaging and for combining radionuclide radiotherapy and chemotherapy.

Distribution and stability of [111In]bleomycin and its fractions in tumor-bearing mice

The tissue distributions in glioma-bearing mice given injections of [111In]bleomycin (BLM) indicated that tumor concentrations and ratios of tumor to blood, muscle and brain for [111In]BLM-B2 and -A2 were higher than those for unfractionated [111In]BLM. Autoradiographs of electrophoretic gels of urine containing [111In]BLM or one of its fractions differed from those containing 111InCl3. [111In]BLM and its fractions (A2 and B2) were found to be stable in vivo. The fractions may be more useful in the clinic than [111In]BLM.

Stability of 111In-bleomycin in vivo--properties compared with 57Co-bleomycin

111Indium-bleomycin (111In-BLM) and 57Co-bleomycin (57Co-BLM) were prepared and their distributions were compared in the tissues, blood, and urine in tumor-bearing and in untreated mice and rats. Autoradiographs of electrophoresis gels showed that patterns for urine from untreated and tumor-bearing animals, collected 1-3 h or 48 h after injection of 111In-BLM were similar to those for in vitro mixtures of urine and 111In-BLM, but differed from the patterns obtained with 111InCl3 under in vivo or in vitro conditions. In rats bearing mammary adenocarcinoma, 48 h after administration of the radiopharmaceutical, the activity ratio of tumor to eleven different tissues was 1.2-4.6 times higher for injected 111In-BLM than for 111InCl3 (P less than or equal to 0.001 or P less than or equal to 0.05). Imaging with a gamma camera depicted tumors in mice more distinctly with 111In-BLM than with 111InCl3. These findings were interpreted as reflecting the stability of 111In-BLM in vivo. The tumor concentration (%dose/g) was higher for the viable area than for the necrotic area for 111In-BLM, but the reverse was true for 57Co-BLM.

Identification of a key structural feature of cobalt(III)-bleomycins: an exogenous ligand (e.g. hydroperoxide) bound to cobalt

A series of cobalt(III) complexes of the anticancer antibiotic bleomycin has been prepared. Mass spectrometry and enzymatic analysis show that the green cobalt-bleomycin complex contains a hydroperoxide (-OOH) group bound to cobalt with unusual stability. Under appropriate conditions, cobalt-bleomycins containing other monodentate ligands to cobalt can be formed; fast-atom bombardment mass spectra of such complexes show peaks for cobalt-bleomycin at the expected mass, and also peaks for the intact complexes at the required higher mass.

Labeled bleomycin as a tumor localizing agent III. Selectivity of tumor tissue uptake of the different forms of [57Co] bleomycin A2 and B2

The cell uptake of the different forms (I and II) of [57Co]bleomycin A2 and B2 was studied in a Rhabdomyosarcoma cell culture. The results show that the uptake of form I appears to be significantly higher than the uptake of form II. The evidence presented indicates that form I is formed in vivo as well as in vitro from form II by biotransformation. Transferrin stimulates the uptake of Co-bleomycin B2 form I only. As a result of trypsin treatment, it is suggested that form II binds only on the outer cell membrane and is not able to pass this membrane.

[Concentrations of cytostatic drugs in organs and tumors: comparison after intravenous and intratumoral injection (author's transl)]

The cytostatic drugs Chlorambucil and Bleomycin were labeled with 131I and with 57Co, respectively: Ruthenocenealdehyde-(N-methyl-N-beta-chlorethyl)-hydrazone and Ruthenocene-3-phenyl-prop.1-en-3-one were labeled with the gamma emitter 103Ru. In tumor-bearing mice the elimination and organ distribution of these radioactive substances were tested after intravenous (i.v.) and intratumoral (i.t.) injection of the drugs. The organ load showed lower values after i.t. than after i.v. application, while the radioactivity concentrations in the tumor were considerably increased after i.t. injection. The integrals of the concentration-time curves showed 10--80 times higher concentrations in the tumor after i.t. compared to i.v. injection of the drugs.