Fe- and Co-bleomycins bound to site specific and nonspecific DNA decamers: comparative binding and reactivity of their metal centers.

Co- and Fe-bleomycins (Blms) have been reacted with DNAa, d(GGAAGCTTCC)2, containing a specific site for cleavage, and DNAb, d(GGAAATTTCC)2, a closely related nonspecific 10-mer, to survey whether features of structure and reactivity of these adducts vary systematically as a function of the base sequence of the DNA oligomer. The ESR spectrum of NO-Fe(II)BlmDNAa is rhombically perturbed in comparison with that of NO-Fe(II)BlmDNAb, which is nearly identical to the spectrum of NO-Fe(II)Blm. The ESR spectrum of Fe(III)BlmDNAa in phosphate buffer is low-spin; that of Fe(III)BlmDNAb is high-spin as seen with Fe(III)Blm alone. According to absorbance spectroscopy, O2-Fe(II)BlmDNAa is stabilized in comparison with the DNAb adduct. Similar stabilization of O2-Co(II)Blm bound to DNAa but not to DNAb was also observed by ESR spectroscopy. HO2(-)-Co(III)Blm A2 binds in slow exchange on the NMR time scale to DNAa at its 5'-G-pyrimidine-3' site of cleavage. In contrast, fluorescence and NMR spectroscopy demonstrate that most of HO2(-)-Co(III)Blm A2 binds stoichiometrically in fast exchange to DNAb. The reactions of Fe(III)BlmDNAa and Fe(III)BlmDNAb with ascorbate and O2 reveal that the latter becomes activated and cleaves its 10-mer, producing base propenals, at a faster initial rate. Thus, in two series of metallobleomycins, (A) NO-Fe(II)Blm, O2-Fe(II)Blm, Fe(III)Blm in phosphate buffer, and HO2(-)-Fe(III)Blm and (B) O2-Co(II)Blm and HO2(-)-Co(III)Blm, the metal domain of each species interacts differently with DNA depending upon its base sequence.

Different conformations and site selectivity of HO-2-Co(III)-bleomycin A2 and Co (III)-bleomycin A2 bound to DNA oligomers.

Conformational properties of HO2(-)-Co(III)-bleomycin A2 (Form I) and Co(III)-bleomycin (Form II) bound to DNA oligomers offering either principal cleavage site for the drug, d(GGAAGCTTCC)2 or d(AAACGTIT)2, have been studied by NMR methods. Form I binds in slow exchange to these oligomers. It retains most of its solution nuclear Overhauser effects (NOEs) upon binding to either oligomer. Pyrimidinyl methyl protons from the metal domain of the drug make an NOE connection with a G5 2-amino proton on DNA. The bithiazole intercalates between base pairs involving either C6 and T7 or T6 and T7 of the two DNA molecules, according to NOE connections between the bithiazole protons and protons from these bases and changes in the positions of their chemical shifts. Form II also retains most of its solution NOEs upon association with the first oligomer. However, in contrast to Form I it binds to DNA in fast exchange on the NMR time scale over the temperature range of 5-35 degrees C and does not break the degeneracy of the DNA proton chemical shifts. No intermolecular NOEs between Form II and the 10-mer have been detected. Likewise, the major perturbation in chemical shift of the histidine H2 and guanine G5 protons seen in Form I-DNA adducts is absent in Form II-DNA. The association constant of Form II with d(GGAAGCTTCC)2 in 20 mM HEPES buffer at pH 7.4 and 25 degrees C is 1.7 x 10(5) M(-1), and 1.0 mol of Form II bind per mol of 10-mer.

Distant metastases from head and neck squamous cell carcinomas.

Distant metastases (DMs) occurred in 83 (11.4%) of 727 retrospectively studied head and neck cancer patients. Primary tumor location and initial treatment did not influence DM development; larger primaries (P < .04) or more extensive neck disease (P < .007) more often caused DMs. Initial diagnosis to DMs averaged 11.7 months (range, 0 to 60 months), with 84% diagnosed within 24 months. With the exception of laryngeal primaries, no facet of tumor, host, or initial treatment influenced where or how rapidly DMs developed. Lung was the most common DM site (83.4%), then bone (31.1%) and liver (6.0%). Survival with DMs averaged 4.3 months (range, 1 day to 2.7 years); 86.7% died within 1 year. This report yields the following conclusions: 1. Initial tumor size and neck disease are the only predictors of DMs. 2. DMs usually occur within 2 years of the initial diagnosis. 3. Lung is the most common DM site, making chest x-ray the most effective DM screen. 4. Survival with DMs is usually less than a year.

Reaction of DNA-bound ferrous bleomycin with dioxygen: activation versus stabilization of dioxygen.

The properties of binding of dioxygen to ferrous bleomycin [Fe(II)Blm] in the presence of DNA have been examined. Dioxygen reacts rapidly with Fe(II)Blm.DNA, forming an adduct that is increasingly stable to oxidation-reduction as the ratio of base pairs to drug becomes larger. This species has a spectrum similar to that reported for a proposed dioxygenated intermediate in the solution reaction of Fe(II)Blm with O2. It contains Fe(II) as measured with bathophenanthroline disulfonate (BPS) and O2 according to direct observation of stoichiometric release of O2 upon chelation of Fe(II) by BPS. The dioxygenated form O2-Fe(II)Blm.DNA, is highly stable; bound O2 dissociates upon purging with N2 with a rate constant of 0.16 min-1. Although Fe(II)Blm or Fe(II)Blm.DNA reacts almost completely with BPS within the time of mixing, O2-Fe(II) Blm.DNA reacts much slower in a process that is first order in Fe(II) and in BPS at constant DNA concentration. The rate is inversely related to DNA concentration reaching a limiting value at 50-100 base pairs per drug molecule. The kinetics of oxidation of Fe(II)Blm bound to DNA by O2 are biphasic and depend on the base pair to drug ratio. After formation of O2-Fe(II)Blm.DNA, another reaction occurs in which O2 is released, which is second order in dioxygen donor, and in which the second-order rate constant declines with increasing base pairs to FeBlm ratio. The rate of this second-order process accelerates at higher ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)