Resonance Raman Studies of HOO−Co(III)Bleomycin and Co(III)Bleomycin:  Identification of Two Important Vibrational Modes, ν(Co−OOH) and ν(O−OH)

Abstract

Bleomycin is an antitumor agent whose cytotoxicity is dependent on its ability to bind DNA in the nucleus and effect double-stranded DNA cleavage, which is difficult for the cell to repair. In order for this DNA cleavage to occur, bleomycin must, through a series of reactions, form a low-spin Fe(III) complex, the putative "activated" form of the drug, HOO-Fe(III)bleomycin. The relative strengths of the bonds in the Fe(III)-OOH linkage have not been determined due to the weakness of the hydroperoxo-to-iron(III) charge-transfer transition. The much more stable HOO-Co(III)bleomycin has often been studied as a structural analogue of HOO-Fe(III)bleomycin, and hence, an understanding of the relative bond strengths in the Co-OOH linkage may serve to enhance our understanding of the analogous Fe-OOH linkage. In this report, we present resonance Raman data that identify two important vibrational modes in the Co-OOH linkage, the stretching modes, nu(Co-OOH) and nu(O-OH). Both of these vibrational modes were found to be unperturbed by complexation of the drug with calf thymus DNA. Advantage was also taken of the isostructural realtionship between Fe-bleomycin and Co-bleomycin to analyze and assign the high-frequency modes for HOO-Co(III)bleomycin and Co(III)bleomycin (A(2) and B(2)). These data could be useful for future studies of photoactivated Co-bleomycin and Co-bleomycin analogues in an attempt to characterize oxygen-independent DNA damage pathways.

Resonance Raman spectroscopic studies of hydroperoxo derivatives of cobalt-substituted myoglobin

“…As has been well documented in many earlier studies comparing the M-O-O fragments of the parent dioxygen adducts of heme proteins and model compounds, the ν(Co-O) is typically observed to occur at frequencies that are 30–50 cm −1 lower than the corresponding ν(Fe-O) modes [12,39,45–48]. The newly acquired data presented here for the hydroperoxo derivative of CoMb are entirely consistent with this trend, documenting a 34 cm −1 lower frequency for the ν(Co-O) mode compared with the 617 cm −1 value observed for the native protein; it is also noted that similar differences in ν(M-O) have been observed [46] and calculated [49, 50] in comparing the hydroperoxo forms of cobalt (545 cm −1 ) and iron (575 cm −1 , calculated) bleomycins. A comparison of corresponding ν(O-O) modes is strictly not possible, given the fact that these are not resonance enhanced for the native systems; the relatively scarce data available for the parent dioxygen adducts, obtained mainly from IR difference spectroscopy, generally show that this mode is reflective of a bound superoxide formulation and is about 7–10 cm −1 lower for the native systems than for the cobalt-substituted analogues [47,48].…”

Resonance Raman Detection of the Hydroperoxo Intermediate in the Cytochrome P450 Enzymatic Cycle

“…However, as can be seen in traces G−J, upon subtraction of the overlapping heme macrocycle modes, the 16 O/ 18 O difference features attributable to such a fragment are clearly evident; that is, the 40 cm -1 shift indicated by the positive and negative components shown in trace G is entirely consistent with that expected for the ν(O−O) mode of an Fe−O−O fragment of a peroxo/hydroperoxo formulation. [21][22][23][24] However, bands observed near this frequency region, which also exhibit comparable 16 O/ 18 O shifts, have also been observed for Fe(IV) O fragments in Compound I and Compound II derivatives of various heme proteins, and without additional experimental data, there might NOT THE PUBLISHED VERSION; this is the author's final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation at the bottom of the page.…”

“…However, as can be seen in traces G−J, upon subtraction of the overlapping heme macrocycle modes, the 16 O/ 18 O difference features attributable to such a fragment are clearly evident; that is, the 40 cm -1 shift indicated by the positive and negative components shown in trace G is entirely consistent with that expected for the ν(O−O) mode of an Fe−O−O fragment of a peroxo/hydroperoxo formulation. [21][22][23][24] However, bands observed near this frequency region, which also exhibit comparable 16 …”

“…[11][12][13] A conclusive set of experiments is realized, however, by employing the scrambled isotopomeric mixture mentioned earlier; that is, the 1:2:1 mixture of ( 16 O2: 16 [21][22][23][24] As is shown in Supporting Information (Figure S3), the lowfrequency spectra also exhibit new 16 O/ 18 O isotopic-sensitive bands at 559/532 cm -1 that are most reasonably assigned to the ν(Fe−O) modes of an Fe−OOH(D) fragment, based on a 3 cm -1 shift in D2O and comparisons with other such species. 14,15 Thus, the present results indicate that the ν(Fe−O) bond is stronger for the hydroperoxo species relative to the nonreduced oxy complex, based on a shift of 13 cm -1 to higher frequency.…”

Synthetic analogue approach to metallobleomycins: syntheses, structure and properties of mononuclear and tetranuclear gallium(III) complexes of a ligand that resembles the metal-binding site of bleomycin

“…Most of the efforts, however, have been devoted to the determination of the solution structure of MBLMs using spectroscopic methods [i.e., NMR, EPR (electron paramagnetic resonance)] [16][17][18][19][20][21][22][23][24], theoretical calculations [25][26][27] or both [28]. In a very recent report, Petering and coworkers [29] presented resonance Raman data that identified two important vibrational modes in the HOO-Co(III)BLM linkage, the stretching modes m(Co-OOH) and m(O-OH). Advantage was also taken of the isostructural relationship between Fe(III)BLM and Co(III)BLM to analyze and assign the high-frequency modes for HOO-Co(III)BLM and Co(III)BLM (A 2 and B 2 ).…”