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Abstract No.: MoP-199
Session: Metal Ions in Biology
Presentation date: Mon, Aug 28, 2006
Presentation time: 09:50 – 11:20

Electrospray Ionization Mass Spectrometry of Metallated Bleomycin Cations

Janna Anichina1,2, Diethard K. Bohme1,2

1 York University, Toronto, Canada
2 Centre for Research in Mass Spectrometry at York University, Toronto, Canada

Correspondence address: Janna Anichina, York University, Chemistry, 4700 Keele Street, Toronto, M3J 1P3 Canada.

Keywords: Complex; Drug; Electrospray Ionization (ESI); Metals.

Novel aspect: The relative gas phase stabilities of Bleomycin A2 complexes with five transition metal dications were investigated utilizing ESI MS. Also, for the first time the intrinsic stabilities of Fe(III)BLMA2 trication and its peroxide were measured.

 

Bleomycin (BLM), a family of glycopeptide antibiotics isolated from the culture medium of the fungus Streptomyces verticillus, is currently used in the treatment of certain types of cancer, such as head, neck and testicular cancer.1 Similar to many other natural products, Bleomycin contains several analogues, with BLM A2 and B2 being the most abundant (70 and 25 % respectively). The drug antitumor activity is thought to relate to its ability to bind and cleave single and double-stranded DNA in the presence of certain metal cations, particularly doubly or triply charged iron. The active short-lived intermediate, “Activated Bleomycin”, that is believed to cleave DNA is formed in vivo and in vitro when iron Bleomycin reacts with an oxidant (molecular oxygen in vivo and O2/hydrogen peroxide in vitro). Spectroscopic and chemical data indicate that “Activated Bleomycin” actually is a hydroperoxy complex of

In the research presented here we monitored different doubly-charged metallated Bleomycin A2 cations generated from their water/methanol solutions using electrospray ionization mass spectrometry (ESI-MS). The hydroperoxicomplex of iron(III) Bleomycin A2 cation was also observed when hydrogen peroxide was added to a Fe(III)BLM solution. The experiments were performed with a MDS SCIEX API 2000 mass spectrometer.

The intrinsic stability of the metallated Bleomycin A2 dications was probed via Collision Induced Dissociation (CID) with nitrogen used as the collision gas. Six different transition metal ions were investigated (Mn(II), Fe(II) and (III), Co(II), Ni(II), Cu(II)). The CID results indicate that the primary dissociation pathway for all studied dications as well as triply charged iron Bleomycin A2 species is the loss of the terminal dimethylsulfonium group. The onset energies for the loss of this terminal group were relatively low and in the range from 8.8 to 14.0 V in the laboratory frame. Also, the results of tandem MS experiments performed with the “Activated Bleomycin” dication ([HOO-FeBLM]2+) show that the primary dissociation pathway of the latter involves the loss of a hydroxyl radical with the simultaneous formation of high-valent ferryl dication [BLMFe=O]2+ whose further dissociation occurs via three main channels: the loss of a water molecule, the loss of dimethylsulfonium group and the loss of molecular hydrogen.

1. J. S. Lazo, B. A. Chabner, in Cancer Chemotherapy and Biotherapy: Principles and Practice, Eds. B. A. Chabner, D. L. Longo: Lippinkott-raven: Philadelphia, PA, (1996).